publicationDate stringlengths 10 10 | abstract stringlengths 0 37.3k | title stringlengths 1 5.74k | doi stringlengths 11 47 ⌀ |
|---|---|---|---|
2014-01-01 | The first step for performing a dynamic analysis is to set up the equations of motions. We start with Newton’s second law, which is followed by the virtual work principle (D’Alembert’s principle), Hamilton’s principles, and Lagrange’s equations. We shall also see the important role of energy in the study of dynamic analysis. It is noted that each of the formulations basically represents the same dynamic equilibrium but in a unique form of expression. | Governing Equation of Motions | 10.1007/978-3-642-37003-8_2 |
2014-01-01 | A parameterized modal analysis is proposed to evaluate power system small-signal stability and a simulation procedure using DIgSILENT programming language (DPL) is presented for this purpose. Modal analysis, or small-signal stability analysis, refers to the ability of a system to withstand small perturbations around an equilibrium point without reaching instability or displaying sustained oscillations. This is an important problem in real systems as sustained oscillations may cause mechanical failures in generating units and make the system vulnerable to the point of losing stability. In order to define the most critical scenario, the standard approach employed by the industry is to consider the system at its maximum loading. This chapter proposes that critical scenarios should be further sought as in even lighter loading conditions, low-frequency oscillations may dangerously appear. Using DPL, the system modal analysis is parameterized in order to search for critical operating points. To validate the importance of employing a parameterized modal analysis, a real case is studied: the Northern Chile Interconnected System. The obtained results applying parameterized modal analysis show that the system in a real operation only requires minor deviations from the programmed operating points to incur in dangerous low-frequency oscillations. These results validate the importance of searching for critical scenarios and DPL scripting is used to program the steps of the proposed analysis. The scripts and applications presented in this chapter set the basis for additional development to identify critical scenarios for modal analysis in other real systems. | Parameterized Modal Analysis Using DIgSILENT Programming Language | 10.1007/978-3-319-12958-7_10 |
2014-01-01 | In this chapter, the supplemental passive energy dissipation devices, metallic or hysteretic dampers, frictional, viscoelastic and viscous (linear and non-linear) dampers, developed and studied over the years, are briefly described. For each type of device, the physical, mechanical and technological aspects are analysed by describing the construction, hysteretic behavior, physical models, advantages, and disadvantages. Then, the more appropriate mathematical laws to model their dynamic behavior, with particular reference to the viscous and viscoelastic, are described. Finally, a comparison between all the different types of device is reviewed and the main recommendations, reported in the international codes with specific reference to the viscous and viscoelastic, are explained. | Passive Energy Dissipation Devices | 10.1007/978-3-319-02615-2_2 |
2014-01-01 | This chapter addresses the seismic performance of Tuned Mass Dampers (TMDs). In the design of a TMD, two types of uncertainty are relevant: the stochastic excitation modeling the earthquake, and the inherent uncertainty of internal parameters of the damping device and the subsoil. Modeling the excitation by a continuous-time stochastic process the structure-damper system can be described by a linear system of stochastic differential equations. The response is a stochastic process depending on the uncertain parameters of the damping device and the subsoil. These uncertainties are modeled by random sets, i.e., interval-valued random variables. A framework is presented here that admits the combination of these two types of uncertainty leading to a set-valued stochastic process, which is interpreted as containing the true system response. The approach is applied to show how the efficiency of TMDs can be realistically assessed in the presence of uncertainty. The main focus of this paper is on non-stationary models for the excitation based on colored noise multiplied by a prescribed intensity function. | Seismic Performance of Tuned Mass Dampers with Uncertain Parameters | 10.1007/978-3-319-05933-4_3 |
2014-01-01 | The main aim of this paper is to focus on dynamics of the electromechanical system flexibly coupled with a baseplate and damped by an impact element. The model is constructed with three degrees of freedom in the mechanical oscillating part, two translational and one rotational. The system movement is described by three mutually coupled second-order ordinary differential equations. Here, the most important nonlinearities are: stiffness of the support spring elements and internal impacts. As it is shown in the main results, the impact damping device attenuates vibrations of the rotor frame in a wide range of the excitation frequency and the system is showing periodic and chaotic behavior. | Dynamics and Efficiency of an Impact Damper | 10.1007/978-3-319-07401-6_35 |
2014-01-01 | This paper presents performance analysis of a controllable electro-rheological (ER) damper for a passenger vehicle with different tire pressure. In order to achieve this research goal, an ER damper, which satisfies design specifications for a mid-sized passenger vehicle, is designed and manufactured. After experimentally evaluating the field-dependent characteristics of the manufactured ER damper, the quarter-vehicle suspension system consisting of sprung mass, spring, tire and the ER damper is constructed in order to investigate the ride comfort with different tire pressure. After deriving the equations of the motion for the proposed quarter-vehicle ER suspension system, vertical tire stiffness with respect to different tire pressure is experimentally identified. Ride comfort characteristics such as vertical acceleration RMS (root mean square) of sprung mass are evaluated under bump road conditions using a quarter-vehicle test facility. | Performance Analysis of Passenger Vehicle Featuring ER Damper with Different Tire Pressure | 10.1007/978-3-319-13966-1_39 |
2014-01-01 | Running turbines are exposed to high mechanical load. Due to gas excitations the structure can vibrate with high oscillation amplitudes which can damage the turbine blades. Mistuning can additionally lead to high local stresses which must be taken into account in the turbine design process. Introducing damping due to friction in the interface of shrouded turbines can be used to decrease this oscillation amplitudes. The computation of full turbine finite-element models with nonlinear coupling forces causes high computational costs. As a consequence, Component Mode Synthesis methods are used to reduce the number of DOFs of each blade substructure. Mistuning of the blades can now be applied in modal space. Coupling of the mistuned substructures is done by nonlinear interface forces which have to be included in the substructuring formulation. The resulting reduced and mistuned system with nonlinear coupling forces is solved with a Harmonic Balance Method such that the effect of mistuning and interface damping can be studied very efficiently. | Consideration of Interface Damping in Shrouded Mistuned Turbine Blades | 10.1007/978-3-319-04501-6_9 |
2014-01-01 | The development and application of heuristic optimization algorithms have gained a renewed interest due to the limitations of classical optimization tools for tackling several hard-to-solve problems in different engineering fields. Due to the complex nature of power system dynamics, electrical engineering optimization problems usually present a discontinuous multimodal and non-convex landscape that necessarily has to be handled by heuristic optimization algorithms. While most of the pioneer heuristic optimization approaches, such as genetic algorithms , particle swarm optimization , and differential evolution , are undergoing different types of modifications and extensions in order to improve their performance, great focus is also being put into the development of new approaches aiming at conceptual simplicity, easy adaptability for a variety of optimization-based applications, and outstanding performance. The mean–variance mapping optimization (MVMO) is a recent contribution to the family of evolutionary optimization algorithms. Its novel search mechanism performs within a normalized range of the search space for all optimization variables and follows a single parent–offspring pair approach. Besides, MVMO is characterized by a continuously updated knowledge archive storing the n-best solutions achieved so far, from which a special mapping function, which accounts for the mean and variance of the optimization variables, is applied for mutation operation. In this way, the algorithm proceeds by projecting randomly selected variables onto the corresponding mapping function that guides the solution toward the best set achieved so far. Despite the orientation on the best solution, the algorithm keeps on searching globally. This chapter addresses key aspects concerning the implementation of MVMO by using DIgSILENT programming language (DPL). An exemplary application on the coordinated tuning of power system supplementary damping controllers is presented and discussed in order to highlight the feasibility and effectiveness of structuring MVMO-based applications in DIgSILENT PowerFactory environment. | Mean–Variance Mapping Optimization Algorithm for Power System Applications in DIgSILENT PowerFactory | 10.1007/978-3-319-12958-7_12 |
2014-01-01 | The design of modern day offshore wind turbines (OWTs) relies on numerical models, which are used for simulating the dynamic behavior in different operational and environmental conditions. From these results one can estimate ultimate and fatigue loads, which are needed for determining the design life of the turbines. The dynamic behavior, and thus the lifetime, of the turbines are influenced for a large part by its structural properties, such as the natural frequencies and damping ratios. Hence, it is important to obtain accurate estimates of these modal properties. For this purpose Operational Modal Analysis (OMA) techniques are used to estimate the modal domain of the OWT. As, for instance, the loads in the structure and the damping ratios are inversely related, higher damping values will results in lower loads, and hence in more optimized and less costly support structures. In this paper the data-driven Stochastic Subspace Identification (SSI) method is used to evaluate the modal domain of the OWT by using output-only measurements obtained from an installed 3.6 MW offshore wind turbine. In order to better satisfy the OMA assumptions of having a Linear Time-Invariant (LTI) system and white noise uncorrelated input, the analyses are performed in case of idling turbines, thereby avoiding the effect of rotational harmonic components, changing system properties due to yawing and pitching actions, as well as strong aerodynamic nonlinearities. In this paper we focuss on the first four global eigenfrequencies that were found and the associated damping ratios. Even though a sensor mix of several strain gauges and a single bi-directional accelerometer are available, the best results were obtained by only using the accelerometer on the nacelle. | Identifying Structural Parameters of an Idling Offshore Wind Turbine Using Operational Modal Analysis | 10.1007/978-3-319-04546-7_31 |
2014-01-01 | The affinity propagation clustering is a new clustering algorithm. The volatility is introduced to measure the degree of the numerical oscillations. The research focuses on two main parameters of affinity propagation: preference and damping factor, and considers their relation with the numerical oscillating and volatility, and we find that the volatility can be reduced by increasing the damping factor or preference, which provides the basis for eliminating the numerical oscillating. | Research on Parameters of Affinity Propagation Clustering | 10.1007/978-94-007-7262-5_72 |
2014-01-01 | Seismic evaluation plays an important role in performance based seismic engineering (PBSE). The modal system is the basis of structural dynamics, which is closely associated with PBSE. This paper shows that the modal system is not necessary to be a single-degree-of-freedom oscillator. Actually, a modal system with three degrees of freedom is even more suitable for representing a single vibration mode of two-way asymmetrical buildings Asymmetrical buildings Asymmetrical buildings Asymmetrical buildings Asymmetrical buildings . The proposed three-degree-of-freedom modal system has many advantages of seismic evaluation for inelastic or non-proportionally damped asymmetrical buildings Asymmetrical buildings Asymmetrical buildings Asymmetrical buildings Asymmetrical buildings . Furthermore, from the proposed modal system, a novel tuned mass damper has been developed for the modal control of asymmetrical buildings Asymmetrical buildings Asymmetrical buildings Asymmetrical buildings Asymmetrical buildings . The study results show that the novel tuned mass damper is effective in reducing two translational and one rotational displacements simultaneously. | Theory and Applications of the 3-DOF Modal System for PBSE of Asymmetrical Buildings | 10.1007/978-94-017-8875-5_18 |
2014-01-01 | The jointed structures are widely spread but their behaviour is quite hard to model and to simulate. The talk deals with a decomposition in linear and non-linear substructures that allows to make the simulations easier. The authors show that the modal subspace is not optimal to reduce the order of the model. Another choice of reduction subspace is shown to be more optimal as it requires less state-variables and leads to a better correlation with Full Order Models. Finally, the authors show how it is possible to characterize experimentally the joints by loading them in the reduction subspace and to integrate an experimental model in the reduce order simulations of the structure. | Model Reduction and Lumped Models for Jointed Structures | 10.1007/978-3-319-04501-6_26 |
2014-01-01 | Because of its minor environmental impact, electricity generation using wind power is getting remarkable. The further growth of the wind industry depends on technological solutions to the challenges in production and construction of the turbines. Wind turbine tower vibrations, which limit power generation efficiency and cause fatigue problems with high maintenance costs, count as one of the main structural difficulties in the wind energy sector. To mitigate tower vibrations auxiliary measures are necessary. The effectiveness of tuned mass damper is verified by means of a numeric study on a 5 MW onshore reference wind turbine. Hereby, also seismic-induced vibrations and soil–structure interaction are considered. Acquired results show that tuned mass damper can effectively reduce resonant tower vibrations and improve the fatigue life of wind turbines. This chapter is also concerned with tuned liquid column damper and a semiactive application of it. Due to its geometric versatility and low prime costs, tuned liquid column dampers are a good alternative to other damping measures, in particular for slender structures like wind turbines. | Vibration Mitigation of Wind Turbine Towers with Tuned Mass Dampers | 10.1007/978-3-319-08413-8_12 |
2014-01-01 | In this paper, we employ non–sampling techniques based on the generalized polynomial chaos (gPC) expansions to numerical simulation of damped vibration problems including random material and damping parameters. A general stochastic finite element method (SFEM) formulation is presented for damped linear structural vibration. Uncertainty involved in stiffness and damping matrices are represented by the gPC expansions. A hybrid SFEM and the gPC expansion is implemented to generate samples of the parameters for the FEM deterministic code from which the gPC expansions of natural frequencies and damping ratios are calculated. For that, experimental modal data are used to evaluate the coefficient of proportional uncertain damping matrix. The model is validated using experimental modal data for samples of composite plates. | Stochastic FEM to Structural Vibration with Parametric Uncertainty | 10.1007/978-3-319-06331-7_20 |
2014-01-01 | In this chapter, the principal elements of the dynamic response of linear undamped and damped single and multi degrees-of-freedom systems are described in time domain both in terms of the relative motions of the mass and in state space form. In a first stage, the analysis of the dynamic response of linear simple-degree-of-freedom systems in the time domain is described by defining the main dynamic characteristics of the undamped system and, then, evaluating the damped natural frequency of the system and response factor. The modal strain energy method is described to evaluate the damping ratio of the SDOF system equipped with viscous and viscoelastic devices. As for linear multi-degrees-of-freedom systems the decoupling procedure for modal analysis and the proportional damping model are described. Even for these systems the effect of damping, assumed to be proportional, on the natural frequencies is evaluated and the modal strain energy method with regard to viscous and viscoelastic devices is illustrated. Then, the concept of the state of a system, the definition of the state space and its properties are discussed. Finally, with reference to both single-degree-of-freedom that multi-degrees-of-freedom systems the representation of their dynamic response in state space is illustrated. | Dynamic Response of Systems Equipped with Viscous and Viscoelastic Dampers | 10.1007/978-3-319-02615-2_3 |
2014-01-01 | This chapter introduces active and semi-active control systems. We first describe the fundamental differences between active and passive systems. Then, the importance of feedback, computational requirements, and system modelling for active control are discussed. This material is followed by an introductory example involving dynamic feedback control. We also present several active and semi-active device technologies, as well as advanced mitigation schemes including smart materials and hybrid systems. | Applications of Active Control | 10.1007/978-3-319-06281-5_7 |
2014-01-01 | On structures two types of humans may be present. (1) Active humans and (2) passive humans (sitting or standing on the structure). The active humans can excite the structure and cause structural vibrations. The mass of the passive humans will interact with the structure and basically it changes the structural system (modal characteristics and structural vibration levels). The paper addresses this subject and explores the implications of having passive humans present on the structure. | Interaction Between Humans and Structures | 10.1007/978-3-319-04546-7_15 |
2014-01-01 | The Laboratory of Building Physics (LFC) has been developed an important research about air drying technologies applied to buildings treatment. In the last years it was validated and experimentally analysed the operating principle of a technique called “Wall Base Ventilation System” initially developed for the treatment of rising damp problems in historical and ancient building walls, consisting in use the air circulation in the base of the walls of buildings with high thickness and heterogeneity in its constitution, with a relative humidity far off saturation. The first experimental and numerical studies established allowed to value the viability of the proposed system, so it was also developed a designing methodology. Rising Damp coming from the ground by capillarity, rises through porous materials, is one of the main degradation causes of historical and ancient buildings, essentially, of its thick walls with heterogeneous composition where the traditionally techniques era sometimes ineffective or too expensive and that was the reason why it was decided to developed a new way to control it. In this work it is proposed to present two completely different applications of the “Wall Base Ventilation System” technique developed in the LFC: the relative humidity control in crawl spaces where, for a Portuguese building, it is presented the problem, the prediction of mould growth, moisture balance in the crawl space, some numerical simulations and the proposed intervention methodology and for the rising damp in walls where it is presented the problem, an experimental study and the system implementation and optimization. | Air Drying Technologies Applied to Buildings Treatment | 10.1007/978-3-319-04531-3_1 |
2014-01-01 | A semi-active (SA) control system based on the use of smart magnetorheological (MR) dampers to control the structural response of a wind turbine is proposed herein. The innovative approach is based on the implementation and use of a variable-properties base restraint. This is able to modify in real time its mechanical properties according to the instantaneous decision of a given control logic, the latter addressed to control one or more structural response parameters. The smart base restraint is thought to be a combination of a smooth hinge, elastic springs, large-scale adjustable MR dampers, and a control algorithm that instantaneously commands the latter during the motion, making them to modulate the reactive force as needed to achieve the performance goals. The design and operation of such a system are shown with reference to a case study consisting of an almost 100 m tall wind turbine, realized in a 1/20 scale model at the Denmark Technical University (DTU). Shaking table tests have been performed under the action of two different types of wind loads and by using two purposely written control logics, highlighting the high effectiveness of the proposed SA control technique and encouraging to further investigate in such direction. | A Semi-active Control System for Wind Turbines | 10.1007/978-3-319-08413-8_13 |
2014-01-01 | This paper presents experimental testing and evaluation of a prototype magnetorheological (MR) damper. An MR device fills the gap between purely passive and fully active control systems as it offers a reliability of passive systems, and yet it maintains the versatility and adaptability of the fully active devices. The MR devices are categorized as one of the semi-active control systems. Fast response, few moving parts, and low power requirements are one of the major factors that have generated special interest in MR devices. MR dampers are being used for control of vibrations in automobiles, for minimizing damage to civil engineering structures due to seismic motions, etc. In this paper, the basic theory behind the MR dampers and experimental testing is carried out, and its use in vibration control is also studied. For this purpose, an MR damper is fabricated in-house and tested in the newly setup laboratory of the department using an electrodynamic vibration shaker and associated data acquisition system. Its performance is then studied in the form of damping force, etc. | Experimental Testing and Evaluation of a Prototype Magnetorheological Damper | 10.1007/978-81-322-1859-3_9 |
2014-01-01 | Improving ride quality is a paramount concern for road cyclists who are subjected to road induced vibrations during long rides. It has been hypothesized that adding structural damping to the bicycle can decrease the vibration levels transmitted to the cyclist. The human body is most sensitive to vibrations in the frequency range of 0–60 Hz, and the amount of damping added by the cyclist when riding the bicycle is very large. This could potentially reduce the net benefit of small improvements provided by structural damping. This paper reveals the effects of structural damping modifications on the modal parameters of a bicycle frame and on the amount of vibrations transmitted to the cyclist due to road surface excitation. A bicycle frame originally designed with damping gel inserts was tested in three different configurations: (1) with its damping gel inserts, (2) with its damping gel inserts and additional damping material wrapped around the frame’s tubing and (3) without its damping gel inserts. Three different metrics were used to assess the damping material effect on vibrations transmitted to the cyclist at the hands and buttocks: acceleration, transmitted force and power absorbed by the cyclist. This paper shows that in all configurations and measurements, added damping did not reduce the vibrations transmitted to the cyclist. | Effect of Structural Damping on Vibrations Transmitted to Road Cyclists | 10.1007/978-3-319-04753-9_29 |
2014-01-01 | This paper deals with semi-active vibration reduction by means of piezo-actuators shunted to time-variant impedances. Particularly, attention is focused on the Synchronized Switch Damping on Inductance technique applied to single mode control in presence of a random disturbance. Drawbacks of the mentioned method are evidenced, showing that sometimes it can fail. Therefore, an alternative method (which actually is an evolution of SSDI) is proposed and its effectiveness is proved numerically through a model. Such a model is validated experimentally within the paper. | SSDI Technique Evolution to Improve Attenuation Performances with Random Disturbances | 10.1007/978-1-4614-6585-0_10 |
2014-01-01 | Sea vessels are exposed to a complex vibration environment, influenced by the sea as well as by operational conditions. Particularly, the hydrodynamic load effects are difficult to estimate analytically. Experimental results are therefore important to verify the analytical models. In the present paper preliminary results from a full-scale modal test of a Ro-Lo vessel carried out for three different operating conditions are presented. Since little full-scale modal testing seems to have been conducted on vessels in operation, the experimental setup together with preliminary modal parameters extracted from the measurements are presented. This preliminary study is focusing on investigating the data with respect to operational conditions and shows a significant variation of the modal damping of the vessel in operation, with approximately 400 %, 200 % and 400 % difference in the first three global vertical bending modes, respectively. | Modal Test Results of a Ship Under Operational Conditions | 10.1007/978-3-319-04774-4_20 |
2014-01-01 | The characterization of torsional vibrations in rotating machinery is of major importance to ensure reliability. Excessive torsional vibrations can cause wear and even breakdown. At a constant operating speed, risks are generally diminished by avoiding coincidence with torsional natural frequencies. This becomes virtually impossible when there are multiple exciting frequencies occurring in reciprocating engines, variable frequency driven motors or systems that exhibit harmonics. A viable prediction of the vibration amplitudes is the calculation of the forced response provided that there is an accurate knowledge of the system parameters. Modeling of torsional inertias and stiffnesses is generally straightforward, whereas vibration amplitudes or amplification factors highly depend on damping. However, damping is difficult to model especially when being nonlinear. In this research, a method based on the systems eigensolutions is used to reconstruct the physical damping matrix of an experimental setup exhibiting torsional vibration. This experimentally identified matrix provides information of both the spatial distribution of the damping and the reliability of the proposed damping model. The results are compared with a mathematical linear model. A correct interpretation of the results indicates where extra damping should be added. | Torsional Damping Identification in Rotating Machinery | 10.1007/978-3-319-04753-9_13 |
2014-01-01 | The elevated specific strength of fiber reinforced plastics (FRP) is the prominent drive for their ever-growing applications. Their inadequate vibrational damping properties prevent them from replacing conventional metal alloys for certain structural applications. In this study we attempt to utilize a low temperature hydrothermal synthesis to grow ZnO nanorods on the surface of woven carbon fibers and implement the resulting hybridized fibers in an epoxy matrix composite. X-ray diffraction and scanning electron microscopy are carried out to study the morphology of the surface-grown nanorods and their adhesion to the substrate carbon fibers. Two-layered hybrid composite laminas are tested for their structural damping properties using dynamic mechanical analysis (DMA). It is observed that the ZnO nanorods can enhance the damping figure of merit of the composites by 40 % without a major delineation in the storage modulus. The enhanced damping performance can be attributed to the additional surfaces manifested by the presence of the ZnO nanorods and, consequently, augmenting the sliding and frictional mechanisms. Furthermore, ZnO as piezoelectric material has the energy scavenging advantages over other 1D nanostructures which ultimately constitutes the fabricated hybrid composites as a multifunctional structural material for energy harvesting applications. | Superior Damping of Hybrid Carbon Fiber Composites Grafted by ZnO Nanorods | 10.1007/978-1-4614-6585-0_18 |
2014-01-01 | The main problem of torsion balance measurements is the long damping time however it is possible to significantly reduce the observation time by modern technology. The damping curve can be precisely determined by CCD sensors as well as computerized data collection and evaluation. The first part of this curve makes it possible at least theoretically to estimate the final position of the arm at rest. A finite element solution of a fluid dynamics model based on Navier–Stokes equations is presented here to solve the problem. | Reducing the Measurement Time of the Torsion Balance | 10.1007/978-3-642-37222-3_45 |
2014-01-01 | Modal correlation of test and analytical data is an important step in system identification and model updating. The Frequency Response Assurance Criterion (FRAC) is one of the metrics that can be used to quantify the strength of correlation between the test and analytical degrees of freedom (DOF). To calculate FRAC for test and analytical data, frequency response functions (FRF) are required. Techniques to synthesize FRFs from finite element models are discussed in this paper. Methods to represent damping in analytical models are also presented. These techniques were applied to synthesize FRFs from a finite element model of a rectangular steel plate structure. Comparing the synthesized FRFs with the measured FRFs for the rectangular plate structure aided in calibrating the rectangular plate FE model. The techniques presented in this paper can be used to visually check if the test and analytical data are well correlated and for calculating FRAC metric to quantify the strength of correlation. | Techniques for Synthesizing FRFs from Analytical Models | 10.1007/978-3-319-04729-4_7 |
2014-01-01 | The paper addresses analytical, numerical and experimental aspects of the design of controlled fluid damper. The mathematical model served the development of a numerical model in MATLAB/Simulink environment. The selected important aspects of the tracked vehicles dynamic modelling process related to dynamics of the drive system and the suspension of selected tracked vehicles are presented. The main aim of the article was to present the investigation results of the experimental studies of a prototype rotary shock absorber at various magnitudes of control current was presented in this paper. Simulation and preliminary experimental results comprising resistance force values as a function of angular displacement and angular velocity are presented. | Tuning the Dynamic Characteristics of Tracked Vehicles Suspension Using Controllable Fluid Dampers | 10.1007/978-3-319-04624-2_15 |
2014-01-01 | Accumulating data indicates that following anti-cancer treatments, cancer cell death can be perceived as immunogenic or tolerogenic by the immune system. The former is made possible due to the ability of certain anti-cancer modalities to induce immunogenic cell death (ICD) that is associated with the emission of damage-associated molecular patterns (DAMPs), which assist in unlocking a sequence of events leading to the development of anti-tumour immunity. In response to ICD inducers, activation of endoplasmic reticulum (ER) stress has been identified to be indispensable to confer the immunogenic character of cancer cell death, due to its ability to coordinate the danger signalling pathways responsible for the trafficking of vital DAMPs and subsequent anti-cancer immune responses. However, in recent times, certain processes apart from ER stress have emerged (e.g., autophagy and possibly viral response-like signature), which have the ability to influence danger signalling. In this review, we discuss the molecular nature, emerging plasticity in the danger signalling mechanisms and immunological impact of known DAMPs in the context of immunogenic cancer cell death. We also discuss key effector mechanisms modulating the interface between dying cancer cells and the immune cells, which we believe are crucial for the therapeutic relevance of ICD in the context of human cancers, and also discuss the influence of experimental conditions and animal models on these. | Danger signalling during cancer cell death: origins, plasticity and regulation | 10.1038/cdd.2013.48 |
2014-01-01 | Stroke is among the most common diseases of advanced age and is becoming a steadily increasing financial healthcare problem in the industrialized world with the increasing longevity and aging of the population. The incidence of ischemic stroke is highest in the elderly population, representing one of the most common causes of disability and mortality worldwide. Over the past decades, a tremendous amount of research has been undertaken into developing effective therapeutic strategies for the treatment of acute stroke. Unfortunately, many neuroprotective agents that have shown successful results in treating animal models of acute stroke have failed to translate into clinical treatments. Only tissue plasminogen activator is currently licensed for use in the treatment of acute ischemic stroke. Increasing evidence shows that the central nervous system and the immune system interact in complex ways, and better insight into these interactions may be relevant to the treatment of patients with stroke and other forms of central nervous system injury. However, during recent years, promising findings suggest that systemic inflammation and neuroinflammation are central features in cerebrovascular disease. Atherosclerosis, autoimmune disease, and physiological stressors, such as infection or surgery, may be a risk factor for the initial development of cerebral ischemia. In addition, the immune system actively participates in the pathophysiological processes occurring during an ischemic stroke. Thrombosis and hypoxia trigger an intravascular inflammatory cascade which elicits an inflammatory response in the injured brain that is accompanied by a marked local inflammatory reaction that is initiated by ischemia- or hematoma-induced expression of cytokines, adhesion molecules, and other inflammatory mediators, including prostanoids, extracellular proteases, reactive oxygen species, and nitric oxide, leading to the accumulation of inflammatory cells, such as leukocytes and microglia, which is further augmented by the innate immune response to cellular damage occurring in the parenchyma. Many of these compounds are known to promote and sustain inflammatory responses at local and systemic level, producing a neuroinflammatory response and a systemic acute-phase response. The acute-phase inflammatory response after stroke is a reflection of an unspecific systemic inflammatory response syndrome. Classic acute-phase reactants and body temperature are also modified in stroke and may be useful in the prediction of events and outcome and as therapeutic targets. The activation of innate immunity after stroke sets the stage for an adaptive immune response directed against brain antigens. The pathogenic significance of adaptive immunity and its long-term effects on the postischemic brain remains unclear, but it cannot be ruled out that a persistent autoimmune response to brain antigens has deleterious and long-lasting consequences, such as the development of poststroke dementia. This immune activation causes secondary tissue injury, but it is unclear whether modulating the acute immune response to stroke can produce clinical benefits. Better understanding of the role of the postischemic-induced inflammatory response and its potential for modulation might have profound implications for patient treatment. Preclinical studies suggest that interventions that are aimed at attenuating such inflammation reduce the progression of brain damage that occurs during the late stages of cerebral ischemia. In particular, strategies that block the activity of inflammation-related enzymes reduce ischemic damage with an extended therapeutic window. Although, clinical trials using anti-inflammatory strategies did not show benefit in patients with ischemic stroke, there is a strong rationale for continuing to explore the efficacy of anti-inflammatory therapies in the treatment of the late stages of cerebral ischemia acting more on the modulation of these later events than targeting of specific steps in the ischemic cascade. | Neuroinflammation and Immune Regulation in Ischemic Stroke: Identification of New Pharmacological Targets | 10.1007/978-1-4939-1071-7_11 |
2014-01-01 | Active vibration control technologies are reaching maturity in many applications, in both periodic and transient operating regimes. Historically these systems have been designed without regard for the power they consume, which is not only inefficient and costly, but limits their adoption in applications where it is impractical to provide large power supplies. Strategies for reducing power consumption include semi-active and regenerative methods. The former limits the device action to dissipative forces, through adjustable spring and/or damping rates. The latter uses the dissipative portion of the cycle to store energy in a reservoir, which can then be used in the remainder of the cycle. This paper looks at the benefits of using hydraulic devices in this context instead of the prevalent electromechanical devices. A case study of regenerative hydraulic vibration control is presented using digital hydraulics concepts, analogous to the switching power supplies and amplifiers that have revolutionised the efficiency of modern electronic equipment. The limitations and trade-offs are examined and projections are made as to the performance that could be achieved as the limitations of contemporary hydraulic components are improved upon. | A Regenerative Approach to Energy Efficient Hydraulic Vibration Control | 10.1007/978-3-319-04729-4_17 |
2014-01-01 | Fluid-flow around mechanical structures can sometimes lead to catastrophic failures. Improved modelling of fluid/structure interaction is required for safety and mechanical considerations. In this contribution, concepts for modelling the interaction of structures and fluids are presented. Starting from excitation mechanisms and associated classifications, various model depth approaches are compared. Among them, the use of added coefficients for quasisteady problems is discussed. On the basis of potential flow theory, different approaches for determining fluid-induced additional mass are established and illustrated using an analytical example. Given the limitations of simplifying the engineering models, the second part of the paper provides a brief overview on computational methods for fluid-structure interaction and presents a monolithic modelling approach using space-time finite elements for discretisation of both fluid and structure. Applications from aero- and hydro-elasticity show the applicability of computational methods for problems involving flow-induced added mass, damping, and stiffness. | Modelling of Fluid-Structure Interaction – Effects of Added Mass, Damping and Stiffness | 10.1007/978-3-7091-1809-2_5 |
2014-01-01 | This paper introduces a novel type of passive control system designed to suppress unwanted vibrations in civil engineering structures subjected to base and lateral excitation. The new system configuration, inspired by traditional tuned mass dampers (TMD) where the mass element has been replaced with an inerter is presented. An inerter is a two-terminal flywheel device with the capacity to generate high apparent mass and it was initially developed for Formula 1 racing cars suspension systems. An analytical tuning procedure for inerter-based systems has been developed. This is inspired by traditional tuning rules for damped vibration absorbers. The inerter-based system performance is assessed in comparison to TMDs. It is shown that the new control system suppresses the response of all modes, which constitutes an advantage with respect to TMDs. Moreover, our analysis shows that the new system is most effective when located at ground storey level, which is advantageous for its installation. A multiple-degree-of-freedom structure is analysed numerically to verify our theoretical findings. This has been subjected to a range of excitation inputs, including wind and earthquake loads and its performance was similar or superior to that of TMDs, making the new device an attractive vibration-suppression method. | Design and Performance Analysis of Inerter-Based Vibration Control Systems | 10.1007/978-3-319-04546-7_53 |
2014-01-01 | The theory of optimal control is concerned with operating a linear dynamic system at a minimum cost. It also provides the best possible performance with respect to given measure of performance index. This paper presents the design of an optimal control law for yaw damper of an aircraft model. This modern controller based on linear quadratic regulator (LQR) technique is stable, robust, and optimized with respect to energy. It is compared and analyzed with classical controller available in the literature. The classical controller uses washout filter which is well known in aircraft control design. The comparative assessment is based on time response specification performance for a yaw control system of an aircraft. The LQR-based controller has effectively taken care of Dutch roll mode which is an area of concern in lateral dynamics of aircraft. The performances of yaw control systems are investigated and analyzed based on common criteria of impulse response in order to identify which control strategy delivers better performance with respect to the desired bank angle and yaw rate. Simulation is carried out for 747 jet aircraft model using MATLAB and Simulink. According to simulation results, LQR controller delivers better performance than classical controller. | Design of an Optimal Yaw Damper for 747 Jet Aircraft Model | 10.1007/978-81-322-1157-0_81 |
2014-01-01 | The dynamical response of systems with shape memory alloy (SMA) or magnetorheological damper (MRD) presents a different behavior due to their nonlinear characteristics. Both systems have a nonlinear behavior due to adaptive dissipation related to their hysteretic behavior. This property is very attractive in engineering field. This paper investigates the nonlinear dynamical behavior of an SMA or MRD oscillator system. The LuGre mathematical model is used to represent the MRD behavior. On the other hand, the SMA model is based on a thermomechanical consistent model with four state variables. Numerical simulations show different aspects about these two systems. | Influence of Smart Material on the Dynamical Response of Mechanical Oscillator | 10.1007/978-3-319-08266-0_37 |
2014-01-01 | This Chapter investigates the statistical properties of residual errors induced by POD-based reduced order modeling. Such errors enter into the state space equations of the reduced systems in terms of system evolution and observation noise. A fundamental assumption made by recursive Bayesian filters, as exploited in this study, is the whiteness of the aforementioned noises. In this chapter, null hypothesis of the whiteness of the noise signals is tested by making use of the Bartlett’s whiteness test. It is shown that, no matter what the number of POMs retained in the analysis is, the null hypothesis of the whiteness is always to be rejected. However, the spectral power of the embedded periodic signals decreases rapidly by increasing the number of POMs. The speed-up gained by incorporating POD-based reduced models into Kalman observer of linear time invariant systems, is also addressed in this chapter. It is shown that the reduced models incorporated into the Kalman filter dramatically reduce the computing time, leading to speed-up of 300 for a POD model featuring 1 POM, which is able to accurately reconstruct the displacement time history of the structure. Moreover, it is revealed that the coupling of POD and Kalman filter can improve the estimations provided by POD alone. | POD-Kalman Observer for Linear Time Invariant Dynamic Systems | 10.1007/978-3-319-02559-9_4 |
2014-01-01 | This paper explores the optimisation technique of Damped Least Square Method also known as the Levenberg-Marquardt (LM) Algorithm for Iris recognition. The motive behind it is to show that even though there are many algorithms available which act as an alternative to the LM algorithm such as the simple gradient decent and other conjugate gradient methods be it the vanilla gradient decent or the Gauss Newton iteration, the LM algorithm outperforms these optimisation techniques due to the addressing of the problem by the algorithm as the Non-linear Least Square Minimisation. The results are promising and provide an insight into Iris recognition which are distinct pattern of individuals and are unique in case of every eye. | Optimisation Using Levenberg-Marquardt Algorithm of Neural Networks for Iris | 10.1007/978-3-319-02931-3_12 |
2014-01-01 | This chapter discusses the dynamics of a mass–damper–spring system with two rigid constraints and impact interactions. Impacting chatter and stuck phenomena are investigated for the mass with constraints and the corresponding conditions for such phenomena are determined. Analytical predictions are presented for the system to give a more precise and complete demonstration of the phenomena in the system. Finally, an analytical parameter map is given to show how the system changes for varying parameters. From these conditions, numerical simulations are performed to demonstrate these phenomena in the system. | Analytical Dynamics of a Mass–Damper–Spring Constrained System | 10.1007/978-3-319-01411-1_18 |
2014-01-01 | The present paper shall give some ideas to protect power plant machinery against seismic demands. The elastic support of turbine foundations, fans, boiler feed pumps and coal mills is a well-accepted strategy for the dynamic uncoupling from their substructures and for the vibration isolation. If the corresponding bearing systems are combined with certain strategies an efficient earthquake protection for the important machinery can be achieved. Seismic control may be obtained by increasing the fundamental period or increasing the damping or changing the shape of the fundamental mode of a structure. A combination of these measures could lead to an optimum seismic protection system as described in this contribution. Here, the first step consists of the choice of the required stiffness properties of the flexible support. Helical steel springs possess the possibility of providing a three-dimensional flexibility. Thus, it is possible to obtain a vertically and horizontally acting protection system. Depending on the seismic input the spring properties could be chosen in a specific range. The system frequency can be decreased and simultaneously, the damping ratio can be increased by incorporating viscous dampers at different locations of the spring supported structure. Internal stresses of important members, acceleration amplification as well as deformations due to seismic excitation can be decreased compared to a structure without any precautions. The possible damage after a severe earthquake can be reduced significantly, and the behaviour of the structural members could remain in the elastic range. Details of executed projects and corresponding results of numerical analyses document the effectiveness of the presented seismic protection strategies. Selected pictures demonstrate the general applicability of the applied systems. | Strategies for the Seismic Protection of Power Plant Equipment | 10.1007/978-3-658-02810-7_14 |
2014-01-01 | This paper aims at analyzing the shapes of the bounded traveling wave solutions for a class of nonlinear wave equation with a quintic term and obtaining its damped oscillatory solutions. The theory and method of planar dynamical systems are used to make a qualitative analysis to the planar dynamical system which the bounded traveling wave solutions of this equation correspond to. The shapes, existent number, and conditions are presented for all bounded traveling wave solutions. The bounded traveling wave solutions are obtained by the undetermined coefficients method according to their shapes, including exact expressions of bell and kink profile solitary wave solutions and approximate expressions of damped oscillatory solutions. For the approximate damped oscillatory solution, using the homogenization principle, its error estimate is given by establishing the integral equation, which reflects the relation between the exact and approximate solutions. It can be seen that the error is infinitesimal decreasing in the exponential form. | Shape analysis and damped oscillatory solutions for a class of nonlinear wave equation with quintic term | 10.1007/s10483-014-1777-7 |
2013-12-01 | By a special layout of the damper in a vibration isolation system, the velocity- n th power damping of the damper can be transformed into the velocity-displacement dependent damping in the moving direction due to geometric nonlinearity. This study is mainly concerned with the mechanism of this geometric nonlinear damping and tries to find some guidelines for designing isolators with high performance, regardless of the isolator is passive or active. The model used in this study is an unconstrained two-degree-of-freedom isolation system, which is suitable for investigating vibration isolation in space vehicles. The motion equation is solved by the averaging method to obtain the amplitude–frequency equation. The influence of damping coefficients on the force transmissibility is analyzed. Results show that this kind of damping has some advantages in improving isolation performance at both the resonance and higher frequencies. Meanwhile, it can also degrade the isolation performance if unreasonable parameters are chosen. | Study on the force transmissibility of vibration isolators with geometric nonlinear damping | 10.1007/s11071-013-1027-0 |
2013-12-01 | We analyze the convergence to equilibrium of solutions to the nonlinear Berger plate evolution equation in the presence of localized interior damping (also referred to as geometrically constrained damping ). Utilizing the results in (Geredeli et al. in J. Differ. Equ. 254:1193–1229, 2013 ), we have that any trajectory converges to the set of stationary points $\mathcal{N}$ . Employing standard assumptions from the theory of nonlinear unstable dynamics on the set $\mathcal{N}$ , we obtain the rate of convergence to an equilibrium. The critical issue in the proof of convergence to equilibria is a unique continuation property (which we prove for the Berger evolution) that provides a gradient structure for the dynamics. We also consider the more involved von Karman evolution, and show that the same results hold assuming a unique continuation property for solutions, which is presently a challenging open problem. | Decay Rates to Equilibrium for Nonlinear Plate Equations with Degenerate, Geometrically-Constrained Damping | 10.1007/s00245-013-9210-8 |
2013-12-01 | This paper presents results from an extensive set of frequency response measurements from a simple plate structure with a single bolt lap joint. The frequency response measurements are obtained from modal impact tests. Both damping ratios and natural frequencies are found to remain fairly constant for medium to high levels of bolt preload. At low levels of preload, damping ratios increase significantly by 25–75%, whereas natural frequencies decrease by only 1–2%. These results identify the monitoring of vibration damping as a means for detecting low preload and fastener loosening. Comparative tests with monolithic plate structures show the introduction of a single bolt lap joint results in an increase in damping and a decrease in frequency for the first three modes of vibration. Similar results are found for steel and aluminum plate materials with grade 5 and 8 fasteners. | Effect of Fastener Preload on Structural Damping | 10.1007/s11668-013-9740-z |
2013-12-01 | This paper proposes a new scheme for piezoelectric energy harvesting maximization. The proposed enhancement relies on a new topology of splitting a specified dimension piezo composite bender into beams with smaller width and, therefore, higher quality factor (or Q factor). The increase of Q factor allows a much more effective energy conversion process. It is shown that the proposed method, based on single splitting, increases the harvested power by a factor of up to √6, and up to √7.62 for two even-splitting compared to with no splitting. The wideband operation is accomplished by using different resonating benders in such a way that individual benders are each tuned to a different resonance frequency. Taking the configuration of single even-splitting as an example, the power output of the prototype was 39 μW at 27.2 Hz with 8 Hz bandwidth under 2 mm peak-to-peak input displacement and 3 Hz variation in resonant frequency. This corresponds to more than 2 times of power output with no splitting as well as about 23% increase in bandwidth. Such power output is sufficient to power up electronics devices such as a “2 AA dry cells-powered” digital clock with the wider range operating frequency. | Increasing the output from piezoelectric energy harvester using width-split method with verification | 10.1007/s12541-013-0291-8 |
2013-12-01 | Studies in the past focused on the implementation of semi-passive damping techniques that could significantly reduce structural vibration. Recently, the performances of these damping techniques have been enhanced by artificially increasing the voltage amplitude delivered by the piezoelectric patches with an external voltage source. To maintain the stability of this damping method, an adaptive voltage source must be used. To satisfy this requirement, this study proposes an enhanced semi-passive damping technique based on pulse-width modulation. The proposed method allows the waveform of the piezoelectric voltage to adapt to the vibration velocity. Thus, this method can maintain its stability with a constant voltage source and simultaneously exhibit superior performance. This study consists of a theoretical part and an experimental proof-of-concept demonstration of the proposed damping technique. | Semi-passive piezoelectric structural damping based on a pulse-width modulation switching circuit | 10.1007/s12206-013-0906-0 |
2013-12-01 | Based on dynamic triaxial test, the mechanical properties of the weathered rock covered by loess were studied. The cohesion value of weathered mudstone is far below that of the weathered sandstone, while the internal friction angle values are basically equivalent, about 30°. Compared with the undisturbed sample, the cohesion value of remodeling weathered rock sample decreases significantly. With the increase of moisture content, the strength of weathered mudstone is obviously decreased due to the influence of the water softening effect. This results illustrate that the bearing stratum is not easily affected by external disturbance in comparison to weathered mudstone. In the engineering, in order to ensure the good mechanical properties of the soil, more attention should be paid to keeping the water content constant, even to reducing the water content. The experiments show that the relations between shear stress and strain of weathered rock were nonlinear and the behavior of weathered rock can be expressed by the hyperbolic model. The initial modulus of undisturbed weathered rock, under the same consolidation conditions, is much greater than that of remodeling samples. Meanwhile, the initial dynamic elastic modulus of sandstone is also greater than that of the mudstone. The dynamic shear modulus ratios of the undisturbed sandstone, the undisturbed mudstone, as well as the remodeling mudstone have the normalization characteristics with the increase of dynamic shear strain. The damping ratio of mudstone is larger than that of the sandstone, and the damping ratio of remolding sample is also greater than that of the undisturbed mudstone. The mudstone has the bad mechanical properties as bearing stratum. | Experimental study on mechanical properties of weathered rock covered by loess | 10.1007/s12204-013-1455-5 |
2013-12-01 | The effectiveness of viscous dampers in mitigating the seismic excitation impacts upon building structures has been widely proved. Recently, with reference to the specific case of equal mass, equal stiffness, shear-type structures, the authors developed a direct practical procedure which gives the mechanical characteristics of the manufactured viscous dampers capable of providing the frame structure with a prescribed value of the first damping ratio. In this paper, a comprehensive rational framework is presented, which allows to formally extend the validity of the proposed procedure to the more realistic case of a generic moment-resisting frame structure. Also the influence of various lateral stiffness distributions is investigated. | On the dimensioning of viscous dampers for the mitigation of the earthquake-induced effects in moment-resisting frame structures | 10.1007/s10518-013-9474-z |
2013-12-01 | This paper presents a hybrid active power filter (HAPF) comprising an active resistive damper (ARD). The ARD consists of three resistances connected to the grid through three bi-directional electronic switches (IGBTs). The ARD can rapidly damp over voltages or over currents under resonance conditions, when the active part (inverter) of the HAPF is disconnected from the grid due to electrical or non-electrical failures. To drive the bi-directional electronic switches of the ARD, a control method is presented in this paper. The control method is based on comparison of resonance over voltage magnitude with a reference voltage (voltage protection level) to control the bi-directional electronic switches. Also the magnitude–frequency characteristics and the control method of the HAPF based on source current detection strategy are analyzed in detail in this paper. Performance of the HAPF with and without the ARD is analyzed in this paper and the results are compared with each other. Finally, the simulation results are provided to validate the proposed topology. | Using an active resistive damper in hybrid active power filter to avoid resonance over-voltage | 10.1007/s00202-012-0256-4 |
2013-12-01 | This paper deals with the analysis of active constrained layer damping (ACLD) of geometrically nonlinear transient vibrations of skew laminated composite plates using skew or rectangular patches of the ACLD treatment. The constraining layer of the patch of the ACLD treatment is composed of the vertically/obliquely reinforced 1–3 piezoelectric composite material. The Golla–Hughes–McTavish method has been used to model the constrained viscoelastic layer of the ACLD treatment in the time domain. A coupled electromechanical nonlinear three dimensional finite element model of skew laminated thin composite plates integrated with the skew or rectangular patches of ACLD treatment has been derived. The performance of the patches is investigated for different configurations of their placements on the top surface of the skew substrate plates. The analysis reveals that the ACLD treatment significantly improves the active damping characteristics of the skew laminated composite plates over the passive damping for suppressing their geometrically nonlinear transient vibrations. It is found that even though the substrate laminated plates are skew, a rectangular patch of the ACLD treatment located at the centre of the top surface of the substrate should be used for optimum damping of geometrically nonlinear vibrations of skew laminated composite plates irrespective of their skew angles and boundary conditions. The effects of piezoelectric fiber orientation angle and the skew angles of the substrate plates on the control authority of the ACLD patches have been emphatically investigated. | Control of geometrically nonlinear vibrations of skew laminated composite plates using skew or rectangular 1–3 piezoelectric patches | 10.1007/s10999-013-9224-z |
2013-12-01 | It is proposed here to use a robust tracking design based on adaptive fuzzy control technique to control a class of multi-input-multi-output (MIMO) nonlinear systems with time delayed uncertainty in which each uncertainty is assumed to be bounded by an unknown gain. This technique will overcome modeling inaccuracies, such as drag and friction losses, effect of time delayed uncertainty, as well as parameter uncertainties. The proposed control law is based on indirect adaptive fuzzy control. A fuzzy model is used to approximate the dynamics of the nonlinear MIMO system; then, two on-line estimation schemes are developed to overcome the nonlinearities and identify the gains of the delayed state uncertainties, simultaneously. The advantage of employing an adaptive fuzzy system is the use of linear analytical results instead of estimating nonlinear system functions with an online update law. The adaptive fuzzy scheme uses a Variable Structure (VS) scheme to resolve the system uncertainties, time delayed uncertainty and the external disturbances such that H_∞ tracking performance is achieved. The control laws are derived based on a Lyapunov criterion and the Riccati-inequality such that all states of the system are uniformly ultimately bounded (UUB). Therefore, the effect can be reduced to any prescribed level to achieve H _∞ tracking performance. A two-connected inverted pendulums system on carts and a two-degree-of-freedom mass-spring-damper system are used to validate the performance of the proposed fuzzy technique for the control of MIMO nonlinear systems. | Robust tracking design based on adaptive fuzzy control of uncertain nonlinear MIMO systems with time delayed states | 10.1007/s12555-012-0543-x |
2013-12-01 | The damping-induced self-recovery phenomenon refers to the fundamental property of underactuated mechanical systems: if an unactuated cyclic variable is under a viscous damping-like force and the system starts from rest, then the cyclic variable will always move back to its initial condition as the actuated variables come to a stop. The regular momentum conservation phenomenon can be viewed as the limit of the damping-induced self-recovery phenomenon in the sense that the self-recovery phenomenon disappears as the damping goes to zero. This paper generalizes the past result on damping-induced self-recovery for the case of a single unactuated cyclic variable to the case of multiple unactuated cyclic variables. We characterize a class of external forces that induce new conserved quantities, which we call the damping-induced momenta. The damping-induced momenta yield first-order asymptotically stable dynamics for the unactuated cyclic variables under some conditions, thereby inducing the self-recovery phenomenon. It is also shown that the viscous damping-like forces impose bounds on the range of trajectories of the unactuated cyclic variables. Two examples are presented to demonstrate the analytical discoveries: the planar pendulum with gimbal actuators and the three-link planar manipulator on a horizontal plane. | On the Damping-Induced Self-Recovery Phenomenon in Mechanical Systems with Several Unactuated Cyclic Variables | 10.1007/s00332-013-9177-2 |
2013-12-01 | The integration of large amount of wind power into a power system imposes a new challenge for the secure and economic operation of the system. It is necessary to investigate the impacts of wind power generation on the dynamic behavior of the power system concerned. This paper investigates the impacts of large amount of wind power on small signal stability and the corresponding control strategies to mitigate the negative effects. The concepts of different types of wind turbine generators (WTGs) and the principles of the grid-connected structures of wind power generation systems are first briefly introduced. Then, the state-of-the-art of the studies on the impacts of WTGs on small signal stability as well as potential problems to be studied are clarified. Finally, the control strategies on WTGs to enhance power system damping characteristics are presented. | Small signal stability analysis of power systems with high penetration of wind power | 10.1007/s40565-013-0028-9 |
2013-12-01 | The model, experimental equipment, and test program are briefly described. A method of determining the aerodynamic characteristics of the model on the facility with free oscillations is presented. Aerodynamic derivatives of the pitching moment of the model are obtained for two positions of the axis of rotation and Mach numbers M_∞ = 2, 4, and 6. At M_∞ = 2, the model with the rear position of the axis of rotation is not balanced at low angles of attack, whereas irregular self-sustained oscillations of the model with the frontal position of the axis of rotation arise. | Aerodynamic derivatives of the model of the jettisonable module of the emergency rescue system at hypersonic velocities | 10.1134/S0869864313060103 |
2013-12-01 | This paper introduces the design of a new combination of friction/hysteretic damper installed in the middle of cross bracing for dissipating seismic energy. Due to its relative simplicity and easy application, with no need for any special material or technology, this high-performance system has gained more attention than any other energy dissipation devices. Choosing appropriate slip load and maximum sliding movement values in this system, in comparison with its counterpart i.e. circular ring yielding dissipator, this combined system may inherit the advantages of both friction and steel yielding damper. In weak-to-moderate ground motions, it dissipates energy by friction and in strong ground motions, it absorbs energy by yielding These circular damper systems can be used to rehabilitate existing buildings whose slender braces are only designed based on resistance of tension forces. Also because of failure localization in this simple-type system, a distorted and damaged damper can be promptly replaced with a new one after a strong earthquake. | A hybrid friction-yielding damper to equip concentrically braced steel frames | 10.1007/s13296-013-4001-2 |
2013-12-01 | The aim of this study was to determine how the violinist robot could produce a good quality of violin sounds. We began our study with the basic physics of producing sound with a violin. We found three parameters that influenced the quality of the sound produced by the violin; the bowing force, the bowing velocity and the sounding point. In particular, the bowing force was found to be the most important parameter in producing good sounds. Furthermore, to produce such sounds, a same amount of the bowing force must be applied on the contact point between a bow and a string. However, it is hard to keep a same amount of the bowing force on the contact point due to inherent characteristics of a bow. Thus, we primarily focused on the bowing force by considering bowing a string as a spring-mass system. Then, we devised a passive damper device to offset variables in the spring-mass system that may result in changing the bowing force on the contact point. We then validated our methodology with the violinist robot, a human-like torso robot. | Improvement of Violinist Robot using a Passive Damper Device | 10.1007/s10846-012-9799-x |
2013-12-01 | For a large floating vessel in waves, radiation damping is not an accurate prediction of the degree of roll unlike other degrees of freedom motion. Therefore, to get the knowledge of roll motion performance of deepwater pipelay crane vessels and to keep the vessel working safety, the paper presents the relationship between a series of dimensionless roll damping coefficients and the roll response amplitude operator (RAO). By using two kinds of empirical data, the roll damping is estimated in the calculation flow. After getting the roll damping coefficient from the model test, a prediction of roll motion in regular waves is evaluated. According to the wave condition in the working region, short term statistics of roll motion are presented under different wave parameters. Moreover, the relationship between the maximal roll response level to peak spectral wave period and the roll damping coefficient is investigated. Results may provide some reference to design and improve this kind of vessel. | Roll motion analysis of deepwater pipelay crane vessel | 10.1007/s11804-013-1217-7 |
2013-12-01 | Improvement in mechanical damping of SBR-modified cement pastes had been evaluated by dynamic mechanical analyzer. Specimens were fabricated and tested under 3-point flexure clamp at frequencies of 0.5–50 Hz or temperatures of −30 to 70 °C. Significant improvement in damping was observed in cementitious-SBR composite specimens when SBR latex to cement ratio was 0.12, which is hypothesized to occur due to improvements in viscosity of cement paste. Furthermore, the SBR-modified cement pastes showed a decreased damping variation tendency with an increase of frequency. They also showed a peak damping variation tendency under the effect of the glass transition temperature. Based on the three element model, mechanical parameters are calculated by fitting the dynamic modulus of SBR-modified cement pastes. | Study of the mechanical damping behavior of SBR-modified cement pastes by dynamic mechanical analyzer | 10.1007/s10973-013-3165-5 |
2013-12-01 | The present paper studies the forced damped pendulum equation, equipped with Hubbard’s parameters (Hubbard in Am Math Mon 8:741–758, 1999 ). With the aid of rigorous computations, his 1999 conjecture on the existence of chaos was proved in Bánhelyi et al. (SIAM J Appl Dyn Syst 7:843–867, 2008 ) but the problem of finding chaotic trajectories remained entirely open. In order to approximate a wide range of chaotic trajectories with arbitrary precision, the present paper establishes an optimization method capable to locate finite trajectory segments with prescribed geometrical behavior. | An optimization technique for verified location of trajectories with prescribed geometrical behaviour in the chaotic forced damped pendulum | 10.1007/s10100-012-0256-5 |
2013-11-19 | We study oscillatory behavior of a class of second-order differential equations with damping under the assumptions that allow applications to retarded and advanced differential equations. New theorems extend and improve the results in the literature. Illustrative examples are given. MSC: 34C10, 34K11. | Oscillation of second-order damped differential equations | 10.1186/1687-1847-2013-326 |
2013-11-11 | Shear wall has been considered as a major lateral load-resisting element inmultistoried building located in wind- or earthquake-prone zone. The behavior ofshear wall under various loading conditions has been the subject of intenseresearch for the last few decades. The behavior of shear walls without openingsis completely well understood and well documented in literature. The use ofsquat shear wall has been found in many low-rise buildings. On the other hand,squat shear walls may also be provided with openings due to the functionalrequirement such as placement of doors/windows in the building. The size andlocation of the opening play a significant role in the response of the shearwall. Even though it is intuitively known that the size of opening hassignificant effects on the behavior of a shear wall, it is desirable to know thelimiting size of opening in the shear wall, beyond which the shear walls mayfail or become unserviceable, especially when subjected to severe earthquakeground motions. In this study, the materially nonlinear dynamic response of theshear wall, with and without openings for different damping ratios, subjected toEL Centro earthquake has been captured. For dynamic analysis, constantacceleration Newmark β method of direct time integration has been used.From the study, it was observed that the presence of opening results in severedisplacements and stresses on the shear wall and also results in stressconcentration near the opening tip. Hence, the presence of damping has beenconsidered to be vital for large opening under severe dynamic loadingconditions. | Nonlinear finite element dynamic analysis of squat shear wall with openings | 10.1186/2008-6695-5-27 |
2013-11-07 | In this paper, by using the mountain pass theorem, we investigate the existence of subharmonic weak solutions for a class of second-order impulsive Lagrangian systems with damped term under asymptotically quadratic conditions. Some new existence criteria are established. Finally, an example is presented to verify our results. MSC: 37J45, 34C25, 70H05. | Subharmonic solutions for a class of second-order impulsive Lagrangian systems with damped term | 10.1186/1687-2770-2013-218 |
2013-11-01 | Interaction of a moving body with a compressible fluid is considered in light of electrodynamic analogies. For a sphere-shaped body, the “relativistic” correction to the added mass and radiation damping force is calculated. Motion with small velocities, as well as the case of near-sonic motion, is considered. For comparison with the 3-D case, the 1-D problem of the motion of a barge in a canal is solved, with the nontrivial dispersion of the surface gravity waves taken into account. The question of a stationary solution is discussed, taking into account dispersion and nonlinearity. | Radiation damping and acoustic relativism of a solid body motion through a compressible medium | 10.1134/S1063771013060055 |
2013-11-01 | The discontinuous deformation analysis (DDA) is a numerical method for modeling discontinuous deformation behaviour of jointed rocks. In this paper, two basic problems are discussed related to kinetic energy dissipation and the convergence criterion for the DDA method when it is applied to geotechnical engineering. In view of the fact that the deformation and progressive failure can be treated as a quasi-static process with low kinetic energy dissipation rates, this paper introduces a viscous damping component to absorb discrete blocks’ kinetic energy, establishes the global equations of motion of the discrete block system that take damping effects into account, investigates the energy dissipation mechanism when solving a static or quasi-static problem, and defines the convergence criteria of displacement, kinetic energy and unbalanced force for DDA solutions when the system arrives at a stable state. | Kinetic Energy Dissipation and Convergence Criterion of Discontinuous Deformations Analysis (DDA) for Geotechnical Engineering | 10.1007/s00603-012-0356-5 |
2013-11-01 | In this paper, we study the dissipative dynamics of the phase damped Jaynes–Cummings model with gravity under Markovian approximation in the presence of the Lamb shift parameter. The model consists of a moving two-level atom simultaneously exposed to the gravitational field and a single-mode traveling radiation field in the presence of a phase damping mechanism. We first present the master equation for the reduced density operator of the system under Markovian approximation in terms of a Hamiltonian describing the atom-field interaction with gravity in the presence of Lamb-shift parameter. Then, by making use of the super-operator technique, we obtain an exact solution of the master equation. Assuming that initially the radiation field is prepared in a Glauber coherent state and the two-level atom is in the excited state, we investigate the influence of Lamb shift parameter on the temporal evolution of collapses and revivals of the atomic population inversion, atomic dipole squeezing and atomic momentum diffusion in the presence of phase damping. | Influence of Lamb Shift Parameter on Dissipative Dynamics of the Phase Damped Jaynes–Cummings Model with Gravity Under Markovian Approximation | 10.1007/s10773-013-1704-2 |
2013-11-01 | The coupled problem of the forced axially symmetric vibrations and self-heating of clamped and hinged flexible circular plates with viscoelastic piezoelectric layers as sensors and actuators is solved. The mechanical and electric excitation of vibrations and the damping of mechanical vibrations by applying the appropriate potential difference to the electrodes of the actuators are studied. The effect of geometrical nonlinearity on the frequency-dependence of the deflection, self-heating temperature, and sensor voltage of a plate under harmonic electromechanical loading at principal bending resonance is analyzed | Forced Monoharmonic Vibrations and Self-Heating of Viscoelastic Flexible Circular Plates with Piezoelectric Layers | 10.1007/s10778-013-0605-7 |
2013-11-01 | For the inverse vibration problem, a differential-algebraic equation (DAE) method is proposed to simultaneously estimate the time-dependent damping and stiffness coefficients by using two sets of displacement and velocity as input data. We combine the equations of motion and the supplemental data into a set of DAEs. We develop an implicit $\mathit{GL}(n,\mathbb{R})$ scheme and a Newton iterative algorithm to stably solve the DAEs to find the unknown structural coefficients. The unknown force is also recovered by the present method. A linear oscillator and a non-linear Duffing oscillator are used as testing examples. The estimated results are rather accurate and robust against random noise; hence, the new method can be used in the solutions of non-linear inverse vibration problems. | An iterative
$\mathit{GL}(n,\mathbb{R})$
method for solving non-linear inverse vibration problems | 10.1007/s11071-013-0997-2 |
2013-11-01 | The dynamics of a circular film membrane with attached current-carrying conductors in zero gravity is studied. Equations are derived which describe the vibrations of the membrane stabilized by the Ampère force. The spectrum of natural vibrations and their corresponding strains are calculated. Constrained vibrations of the membrane are studied. The effect of the geomagnetic field on the stability of the membrane and the damping of its vibration is investigated for unsteady modes of application of mechanical forces in zero gravity. | Vibrations of a frameless film membrane stabilized by the Ampère force in zero gravity | 10.1134/S0021894413060035 |
2013-11-01 | In this paper, the asymptotic stability with probability one of multi-degree-of-freedom (MDOF) nonlinear oscillators with fractional derivative damping parametrically excited by Gaussian white noises is investigated. A stochastic averaging method and the Khasminskii’s procedure are employed to evaluate the largest Lyapunov exponent, whose sign determines the stability of the system. As an example, two coupled nonlinear oscillators with fractional derivative damping is worked out to demonstrate the proposed procedure and to examine the effect of fractional order on the stochastic stability of system. In particular, the case of factional order more than 1 is studied for the first time. | Asymptotic stability with probability one of MDOF nonlinear oscillators with fractional derivative damping | 10.1007/s11433-013-5053-1 |
2013-11-01 | A number of interesting phenomena at fluid-solid interfaces can be observed when the incident angle approaches the Rayleigh angle, including Schoch displacement and leaky Rayleigh waves. Besides the experimental and theoretical research on these problems, numerical tools have been more and more widely used for these complex problems. Based on previous experimental and numerical researches, a 2D finite element model has been built to reproduce the Schoch effects. With the same model, the minimum reflection profile is investigated for the feasibility of material characterization, especially for residual stress evaluation. Residual stress is one of the important properties for structures, and its measurement is a popular research topic in nondestructive evaluation. However, it is not possible to put the residual stress into the numerical model directly. According to the relation of residual stress with mechanical properties, the material damping and wave speed have been alternatively adopted in this work. The influence of minimum reflection profile by residual stress has been shown by the change of wave speed and damping factor. Simulation results show that the minimum reflection profile is a potential method for residual stress evaluation. | Numerical simulation of ultrasonic minimum reflection for residual stress evaluation in 2D case | 10.1007/s12206-013-0843-y |
2013-11-01 | Methods of calculating processes of discharge and suction in a displacement pump with gas damper are developed and the basic results of calculations of suction and discharge pressure in the working cavity of a pump as a function of the turning angle of the crankshaft (disregarding or based on the speed of the fluid) are presented. | Mathematical Modeling of Processes of Suction and Discharge in a Displacement Pump with Gas Damper | 10.1007/s10556-013-9774-9 |
2013-10-17 | Background Passive prosthetic devices are set up to provide optimal function at customary walking speed and thus may function less effectively at other speeds. This partly explains why joint kinetic adaptations become more apparent in lower-limb amputees when walking at speeds other than customary. The present study determined whether a trans-tibial prosthesis incorporating a dynamic-response foot that was attached to the shank via an articulating hydraulic device ( hy A-F) lessened speed-related adaptations in joint kinetics compared to when the foot was attached via a rigid, non-articulating attachment ( rig F). Methods Eight active unilateral trans-tibial amputees completed walking trials at their customary walking speed, and at speeds they deemed to be slow-comfortable and fast-comfortable whilst using each type of foot attachment. Moments and powers at the distal end of the prosthetic shank and at the intact joints of both limbs were compared between attachment conditions. Results There was no change in the amount of intact-limb ankle work across speed or attachment conditions. As speed level increased there was an increase on both limbs in the amount of hip and knee joint work done, and increases on the prosthetic side were greater when using the hy A-F. However, because all walking speed levels were higher when using the hy A-F, the intact-limb ankle and combined joints work per meter travelled were significantly lower; particularly so at the customary speed level. This was the case despite the hy A-F dissipating more energy during stance. In addition, the amount of eccentric work done per meter travelled became increased at the residual knee when using the hy A-F, with increases again greatest at customary speed. Conclusions Findings indicate that a trans-tibial prosthesis incorporating a dynamic-response foot reduced speed-related changes in compensatory intact-limb joint kinetics when the foot was attached via an articulating hydraulic device compared to rigid attachment. As differences between attachment conditions were greatest at customary speed, findings indicate a hydraulic ankle-foot device is most effectual at the speed it is set-up for. | Walking speed related joint kinetic alterations in trans-tibial amputees: impact of hydraulic 'ankle’ damping | 10.1186/1743-0003-10-107 |
2013-10-01 | A new model for a smart shell of revolution treated with active constrained layer damping (ACLD) is developed, and the damping effects of the ACLD treatment are discussed. The motion and electric analytical formulation of the piezoelectric constrained layer are presented first. Based on the authors’ recent research on shells of revolution treated with passive constrained layer damping (PCLD), the integrated first-order differential matrix equation of a shell of revolution partially treated with ring ACLD blocks is derived in the frequency domain. By virtue of the extended homogeneous capacity precision integration technology, a stable and simple numerical method is further proposed to solve the above equation. Then, the vibration responses of an ACLD shell of revolution are measured by using the present model and method. The results show that the control performance of the ACLD treatment is complicated and frequency-dependent. In a certain frequency range, the ACLD treatment can achieve better damping characteristics compared with the conventional PCLD treatment. | Modeling and Dynamics Analysis of Shells of Revolution by Partially Active Constrained Layer Damping Treatment | 10.1016/S0894-9166(13)60042-7 |
2013-10-01 | The joint interface plays a significant role in machine tools and other machineries. A novel type of joint which consists of oily porous material was proposed. The equivalent stiffness and damping of oily porous joint could be divided into solid and liquid parts, and the two parts are shunt connection. Theoretically, the stiffness and damping of solid part were established using Hertz contact and fractal theory, and the liquid counterpart was also deduced from the average flow of generalized Reynolds equation through a correlation parameter A _r. It was concluded from simulation and calculation that the total equivalent stiffness of oily joint is increased with D and decreased with increased G . The experiment was carried out to compare the normal characteristics of porous material–steel oily joint with non-media steel–steel joint, and the result was that the joint which contains an oil film interlayer formed by porous and steel is superior to the joint with non-media formed by steel in stiffness and damping characteristics. In the case of the same preload, the former’s stiffness is increased by about 30 %, and the damping is increased about five to six times meanwhile. | A fractal model of normal dynamic parameters for fixed oily porous media joint interface in machine tools | 10.1007/s00170-013-4825-0 |
2013-10-01 | A new boundary element (BEM) formulation is proposed for wave load analysis of submerged or floating bodies. The presented formulation, through establishing an impedance relation, permits the evaluation of the hydrodynamic coefficients (added mass and damping coefficients) and the coefficients of wave exciting forces systematically in terms of system matrices of BEM without solving any special problem, such as, unit velocity or unit excitation problem. It also eliminates the need for scattering analysis in the evaluation of wave exciting forces. The imaginary and real parts of impedance matrix give, respectively, added mass and damping matrices whose elements describe the fluid resistance against the motion of the body. The formulation is explained through the use of a simple fluid-solid system under wave excitations, which involves a uniform fluid layer containing a solid cylindrical body. In the formulation, the solid body is taken first as deformable, then, it is specialized when it is rigid. The validity of the proposed method is verified by comparing its result with those available in literature for rigid submerged or floating bodies. | A new boundary element formulation for wave load analysis | 10.1007/s00466-013-0846-7 |
2013-10-01 | In this paper, stability and bifurcations in a simply supported rotating shaft are studied. The shaft is modeled as an in-extensional spinning beam with large amplitude, which includes the effects of nonlinear curvature and inertia. To include the internal damping, it is assumed that the shaft is made of a viscoelastic material. In addition, the torsional stiffness and external damping of the shaft are considered. To find the boundaries of stability, the linearized shaft model is used. The bifurcations considered here are Hopf and double zero eigenvalues. Using center manifold theory and the method of normal form, analytical expressions are obtained, which describe the behavior of the rotating shaft in the neighborhood of the bifurcations. | Dynamic stability and bifurcation of a nonlinear in-extensional rotating shaft with internal damping | 10.1007/s11071-013-0974-9 |
2013-10-01 | A long-span structure is a common type of public building, but its seismic characteristics are distinct from other types of buildings because of its long span. Calculation models considering multi-point excitation are required in the seismic analysis of long-span structures. However, correlative studies have already clearly shown that important but often overlooked errors exist in previously developed multi-point excitation calculation models. The process of establishing displacement and acceleration models for multi-point seismic analysis is reviewed. Error sources and criteria of the two models are explained using rigorous theoretical derivation. Error characteristics and distributions in multiple structural types, such as ordinary structures without dampers and damper-installed structures with concentrated damping, are also described. Modifications for multi-point excitation displacement and acceleration models, for time history and stochastic analysis, respectively, are proposed, and these modified models are used to assess errors in the conventional models. Numerical examples are solved using conventional displacement and acceleration models and two corresponding modified models. The properties, components and distribution of errors in the conventional models are demonstrated. The findings presented in this paper can provide a sound basis for the practical application of multi-point excitation calculation models in seismic analysis. | Possible existing seismic analysis errors of long span structures and bridges while utilizing multi-point earthquake calculation models | 10.1007/s10518-013-9462-3 |
2013-10-01 | The dynamic mechanical properties of high density polyethylene (HDPE) and teak wood flour (TWF) composites at varying volume fraction ( Φ _f) of TWF from 0.00 to 0.32 have been studied. In HDPE/TWF composites, storage modulus ( E ′) decreased at Φ _f = 0.05, then increases with Φ _f; however, values were lower than HDPE up to Φ _f = 0.16, due to a pseudolubricating effect of filler. Loss modulus ( E ″) values were higher than HDPE in β and α relaxation regions while in γ relaxation region values were marginally equal to HDPE. Tan δ value decreases with Φ _f which may be due to enhanced amorphization and decreased crystallinity of HDPE. In presence of maleic anhydride grafted HDPE (HDPE-g-MAH), E ′ values were lower than HDPE/TWF composites. In HDPE/TWF/HDPE-g-MAH, E ″ were slightly higher than HDPE/TWF due to slippage of HDPE chains facilitated by the extent of degradation of coupling agent. Tan δ were higher for both systems than the rule of mixture. | Dynamic mechanical properties of high density polyethylene and teak wood flour composites | 10.1007/s00289-013-0941-0 |
2013-09-01 | In this paper, the possibility of the development of a new kind of low frequency shaker was discussed. In order to prove the possibility, a series of tests was performed using a direct-made experimental setup which contains a metal plate, springs and varying dampers. The frequency of the harmonic force variation and damper variation was set as f_1 and f_2. The plate center displacement achieves a peak point in the frequency component f_1 and the rotational displacement achieves a peak point in the frequency components f_1 + f_2 and f_1 − f_2. In the experiment, the damper variation changed due to the damping constant value and current magnitude. Meanwhile, research on the natural frequency of the rotational displacement will continue. The inference of the reason for absence of frequency component related to rotational displacement natural frequency f_nr is that the MR damper shows non-linear phenomenon in this experiment. | Development of a low frequency shaker using MR dampers | 10.1007/s12541-013-0222-8 |
2013-09-01 | An ideal model of two immiscible liquids is analyzed, the lower of which is viscous and the upper one, moving with a constant velocity parallel to the interface, is ideal. It is shown that, in the linear approximation, the role of the viscosity of the two liquids results in the decrement of the damping of waves on the interface. | On the role of the viscosity of liquids in the realization of Kelvin-Helmholtz instability | 10.3103/S1068375513050116 |
2013-09-01 | Dowel and screw connections in timber structures behave nonlinearly, even at loads which would be experienced in a structure in normal service. They exhibit hysteresis and creep as a result of both the viscoelastic behaviour of the timber itself and the frictional interaction between the timber and connecting elements, and stress concentrations are created which behave plastically, even at loads well below the nominal yield force of the connection. A fundamental process in the load transfer through such a connection is the embedment of the connector into the timber that surrounds it, and the frictional, nonlinear and time-dependent properties in that process are investigated here. A simple rheological model, a combination of Kelvin–Voigt viscoelastic elements, was fitted to the measured response of a block of timber in embedment by a plain dowel or screw. Experiments were performed in which an oscillating force was applied to the screw or dowel, representative of in-service vibration in a timber structure. The effects of plasticity and viscoelasticity were quantified by comparing equivalent linear stiffnesses for an oscillating load, a short-term change in static load, and an initial static loading. The results showed a stiffness, on average, 3.8 times higher under oscillating load than under initial static loading with the same peak force. By quantifying and modelling viscoelastic behaviour in timber around a connector, this work contributes to the development of damping and stiffness models for joints under oscillating load. Such models could be used to determine the contribution of connections to the dynamic response of long spans and tall buildings in timber. Dübel- und Schraubverbindungen in Holzkonstruktionen weisen auch bei Belastungen, welche unter normalen Praxisbedingungen auftreten, ein nichtlineares Verhalten auf. Aufgrund des viskoelastischen Verhaltens von Holz als auch der Reibung zwischen dem Holz und dem Verbindungsmittel kommt es zu Hysterese und Kriechen, und es treten Spannungskonzentrationen auf, welche sich sogar bei Belastungen weit unter der nominalen Fließgrenze der Verbindung plastisch verhalten. Ein wesentliches Element der Kraftübertragung in solch einer Verbindung ist die Bettung des Verbindungsmittels im umliegenden Holz, und die reibungsbedingten, nichtlinearen und zeitabhängigen Eigenschaften in diesem Prozess werden hier untersucht. Ein einfaches rheologisches Modell, eine Kombination viskoelastischer Kelvin–Voigt Elemente, wurde an Lochleibungsversuche mit einem Bolzen oder einer Schraube angepasst. Es wurden Versuche durchgeführt, bei denen eine für Holzkonstruktionen unter Praxisbedingungen typische Schwellbelastung auf die Schraube oder den Bolzen aufgebracht wurde. Bestimmt wurde der Einfluss der Plastizität und der Viskoelastizität mittels Vergleich entsprechender Steifigkeiten bei Schwellbelastung, bei kurzzeitig wirkender Last und bei länger wirkender statischer Belastung. Die Ergebnisse zeigten, dass bei gleicher Spitzenbeanspruchung die Steifigkeit unter Schwellbelastung durchschnittlich 3,8 Mal höher war als unter länger wirkender statischer Belastung. Durch Bestimmung und Modellierung des viskoelastischen Verhaltens von Holz im Bereich eines Verbindungsmittels trägt diese Arbeit zur Entwicklung eines Dämpfungs- und Steifigkeitsmodells für Verbindungen bei dynamischer Beanspruchung bei. Solche Modelle könnten dazu dienen, um die Wirkung von Verbindungen auf das dynamische Verhalten hoher Holzgebäude und von Gebäuden mit großen Spannweiten zu bestimmen. | Viscoelastic embedment behaviour of dowels and screws in timber under in-service vibration | 10.1007/s00107-013-0720-5 |
2013-09-01 | This article describes the results of an investigation concerning the power absorbed at mechanical resonance for a single degree of freedom vibration system. Regarding the experimental purposes, the article proposes a cantilever beam set-up actuated by a voice-coil actuator and a computer-aided power monitoring technique. The absorbed power is evaluated in a steady-state regime for different values of excitation frequency around the resonance (the first mode of vibration). The experimental results are afterwards compared to the theoretical predictions. In addition, some transient regimes generated by beat vibrations are explored. The negative absorbed power has been observed. The article proposes an active vibration damping technique, based on actuation with a negative modal power supply. | Experimental investigations of the power absorbed at mechanical resonance | 10.1111/j.1747-1567.2011.00759.x |
2013-09-01 | The active-passive hybrid piezoelectric network (APPN) is investigated to reduce the vibration of cantilever beam. Hamilton’s principle with the Rayleigh-Ritz method is used to derive the equations of motion of the beam with the APPN. Only one piezoelectric actuator is bonded on the cantilever beam, so in the segment of the beam where the piezoelectric actuator is attached, the neutral axis is not the geometric center of the beam. This change on the neutral axis is considered in the process of deriving equations. Selecting RL circuit as passive shunt circuit, open-loop analysis is performed to gain insight into the passive damping features. Velocity feedback control is then employed to analyze the characteristics of the closed-loop system. Numerical results show that the APPN has a significant effect on vibration suppression, especially at narrow frequency bands. On this basis, variable RL circuit is proposed and analyzed for broadband vibration attenuation. Numerical simulations illustrate that this scheme is effective and feasible. | Modeling and analysis of cantilever beam with active-passive hybrid piezoelectric network | 10.1007/s11431-013-5320-4 |
2013-09-01 | This paper describes an application study of Magneto-Rheological (MR) grease damper to a structure with three stories. MR fluid is known as one of successful smart materials whose rheological properties can be varied by magnetic field strength, and has been applied to various kinds of device such as dampers, clutches, engine mounts, etc. However, ferromagnetic particles dispersed in MR fluid settle out of the suspension after a certain interval due to the density difference between the particles and their career fluid. To overcome this defect, we have developed a new type of controllable working fluid using grease as the career of magnetic particles. Network of thickener in grease is expected to hold the magnetic particles and prevent them from settled down. No or little sedimentation was observed in MR grease whose characteristics could be controlled by the magnetic field strength. MR grease was introduced into a cylindrical damper and its performance was studied. As a result, it was confirmed that the damping force of MR grease damper could be controlled by the applied electric current to the coil in the cylinder of damper. Furthermore, vibration response of a three-story model structure equipped with MR grease damper was investigated experimentally, and it was shown that MR grease damper worked effectively as a semi-active damper. | Vibration control of a structure using Magneto-Rheological grease damper | 10.1007/s11465-013-0268-4 |
2013-09-01 | The possibility of recycling ambient energies with electric generators instead of using batteries with limited life spans has stimulated important research efforts over the past years. The integration of such generators into mainly autonomous low-power systems, for various industrial or domestic applications is envisioned. In particular, the present work deals with energy harvesting from mechanical vibrations. It is shown here that direct piezoelectric energy harvesting (short circuiting on an adapted resistance, for example) leads to relatively weak energy levels that are insufficient for an industrial development. By coupling an electric field and mechanical excitation on Ericsson-based cycles, the amplitude of the harvested energy can be highly increased, and can reach a maximum close to 100 times its initial value. To obtain such a gain, one needs to employ high electrical field levels (high amplitude, high frequency), which induce a non-linearity through the piezoceramic. A special dynamic hysteresis model has been developed to correctly take into account the material properties, and to provide a real estimation of the harvested energy. A large number of theoretical predictions and experimental results have been compared and are discussed herein, in order to validate the proposed solution. | Energy harvesting based on piezoelectric Ericsson cycles in a piezoceramic material | 10.1140/epjst/e2013-01958-0 |
2013-09-01 | Brittle nature and poor resistance in front of vibrational waves despite of good mechanical strength have limited widespread use of epoxy resins in industry. In current study a new combination of thermoplastic and particulate nanofiller is used as modifier to enhance simultaneously tensile strengths and damping properties in first and second modes of epoxy-based nanocomposite. High impact polystyrene (HIPS) as thermoplastic phase and silica nanoparticles as particulate phases incorporately used to obtain ternary epoxy-based nanocomposite. In current study solution blending as dispersion mechanism is used to prepare homogenous mixture and brings good molecular level of mixing. Tensile and damping properties in first and second modes were the two different mechanical tests investigated in order to achieve higher toughness strengths without attenuating desired mechanical properties. Also central composite design is employed to present mathematical models for predict mechanical behaviors of epoxy/HIPS/silica nanocomposite as function of physical factors. The effective parameters investigated were HIPS, SiO_2, and hardener contents. Based on mathematical functions obtained from central composite design model, the genetic algorithm as one of powerful optimization tools is applied to find optimum values of mentioned mechanical properties. From the results it can be found that combination of HIPS and silica nanoparticles significantly increased tensile and damping strengths of epoxy resin up to 69, 42, and 91%, respectively. The morphology of fracture surface is also studied by scanning electron microscopy. | Preparation, Modeling, and Optimization of Mechanical Properties of Epoxy/HIPS/Silica Hybrid Nanocomposite Using Combination of Central Composite Design and Genetic Algorithm. Part 1. Study of Damping and Tensile Strengths | 10.1007/s11223-013-9499-1 |
2013-09-01 | For the first time, systematic investigations of the damping parameter A of gold nanoparticles as a function of photon energy are presented. A is an essential parameter that quantifies the size-dependent optical properties of metal nanoparticles in the dielectric function. To determine the damping parameter, the dephasing time T _2 of gold nanoparticles has been systematically determined under ultrahigh vacuum conditions as a function of photon energy. Dephasing times ranging from $T_2 = 5$ fs to $T_2 = 17$ fs were measured, and subsequently, the damping parameter has been extracted. We found a strong resonance-like damping of the plasmon resonance in the vicinity of the onset of the interband transition. While the damping parameter scatters statistically around a value of $A = 0.19$ nm/fs for photon energies below $h\nu = 1.70$ eV, it increases rapidly to 0.32 nm/fs for $h\nu = 1.85$ eV. For higher photon energies, A decreases steadily to $A = 0.24$ nm/fs at $h\nu = 2.15$ eV. A comparison to former measurements as well as to theoretical predictions reveals surface scattering and a discretizing and broadening of the band structure that influences the interband transition as the most dominant size-dependent damping mechanisms. The latter, i.e., a damping via increased interband transitions, assumes a coherent damping process of the oscillating electrons and, as a consequence, the plasmon is treated as a two-level system. Thus, the results deliver new physical insight to the fundamental understanding of surface plasmons. | Increased Damping of Plasmon Resonances in Gold Nanoparticles Due to Broadening of the Band Structure | 10.1007/s11468-013-9536-8 |
2013-09-01 | The free vibrations of a thin elastic orthotropic open cylindrical shell (panel) with one edge free and the other three clamped are considered. Dispersion equations to find the natural frequencies of possible types of vibrations are derived using the classical theory of elasticity. An asymptotic relation between the dispersion equations of the problem under consideration and the similar problem for an orthotropic rectangular plate is established. It is also proved that the dispersion equations of the problem are in asymptotic relationship with the dispersion equations for a semi-infinite open orthotropic cylindrical shell with one free end and two clamped longitudinal edges. Open orthotropic and isotropic shells of different length are considered as an example to obtain approximate values for the dimensionless natural frequency and damping factors for the vibration modes | Vibrations of an Orthotropic Cylindrical Panel with Various Boundary Conditions | 10.1007/s10778-013-0588-4 |
2013-09-01 | A floor isolation system installed in a single floor or room in a fixed base structure is designed to protect equipment. With this configuration, the input motions to the floor isolation from the ground motions are filtered by the structure, leaving the majority of the frequency content of the input motion lower than the predominant frequency of the structure. The floor isolation system should minimize the acceleration to protect equipment; however, displacement must also be limited to save floor space, especially with long period motion. Semi-active control with an H _∞ control was adopted for the floor isolation system and a new input shaping filter was developed to account for the input motion characteristics and enhance the effectiveness of the H _∞ control. A series of shake table tests for a semi-active floor isolation system using rolling pendulum isolators and a magnetic-rheological damper were performed to validate the H _∞ control. Passive control using an oil damper was also tested for comparison. The test results show that the H _∞ control effectively reduced acceleration for short period motions with frequencies close to the predominant frequency of the structure, as well as effectively reduced displacement for long period motions with frequencies close to the natural frequency of the floor isolation system. The H _∞ control algorithm proved to be more advantageous than passive control because of its capacity to adjust control strategies according to the different motion frequency characteristics. |
H
_∞ control in the frequency domain for a semi-active floor isolation system | 10.1007/s11709-013-0214-x |
2013-08-01 | This article deals with self-excited vibrations, attractivity of stationary solutions, and the corresponding bifurcation behavior of two-dimensional differential inclusions of the type $\mathbf{M}\mathbf{q}'' + \mathbf{D}\mathbf{q}' + (\mathbf{K} + \bar{\mu}\mathbf{N})\mathbf{q} \in-\mathbf{R}\operatorname{Sign}(\mathbf{q}')$ . For the smooth case R = 0 , the equilibrium may become unstable due to non-conservative positional forces stemming from the circulatory matrix N . This type of instability is usually referred to as flutter instability and the loss of stability is related to a Hopf bifurcation of the steady state, which occurs for a critical parameter $\bar{\mu}= \bar{\mu}_{\mathrm{crit}}$ . For R ≠ 0 , the steady state is a set of equilibria, which turns out to be attractive for all values of the bifurcation parameter $\bar{\mu}$ . Depending on $\bar{\mu}$ , the basin of attraction of the equilibrium set can be infinite or finite. The transition from an infinite to a finite basin of attraction occurs at the stability threshold $\bar{\mu}_{\mathrm{crit}}$ of the underlying smooth problem. For the finite basin of attraction, its size is proportional to the Coulomb friction and inverse-proportional to $(\bar{\mu}- \bar{\mu}_{\mathrm{crit}})$ . By adding Coulomb damping the notion of steady state stability for the smooth problem is replaced by the question whether the basin of attraction of the steady state is infinite or finite. Simultaneously, the local Hopf-bifurcation is replaced by a global bifurcation. This implies that in the presence of Coulomb damping the occurrence of self-excited vibrations can only be investigated with regard to the perturbation level. | On the effect of non-smooth Coulomb damping on flutter-type self-excitation in a non-gyroscopic circulatory 2-DoF-system | 10.1007/s11071-013-0907-7 |
2013-08-01 | Tree failure may cause significant economic and societal disruptions in urban environments. A better understanding of the relationship between branches and stem as they affect the dynamic response of decurrent trees under wind loading is needed to reduce the risk of tree failure. Finite element (FE) models were used to identify the parameters that primarily impact tree response. A base model was developed using data from a sugar maple ( Acer saccharum L.) located in Belchertown, MA, USA, from which parametric models were subsequently developed. Confidence in the base model was gained by comparing the natural frequency of this tree with experimental results. Results from a parametric study incorporating changes in eight different tree parameters (stem diameter, slenderness ratio of branches, number of branches, damping ratio, branch attachment heights, branch attachment angles, branch azimuth angles, and elastic modulus) are then presented to help identify critical model properties that affect the dynamic amplification factor (Rd) of the tree. A single parameter was varied in each model while keeping others unchanged from the base model. Parameters with the greatest effect on Rd included stem diameter, number and slenderness of branches in the crown, elastic modulus of stem and branches, and damping ratio. Thus, it may be possible to use pruning to alter crown architecture to reduce the risk of tree failure. | The effect of crown architecture on dynamic amplification factor of an open-grown sugar maple (Acer saccharum L.) | 10.1007/s00468-013-0867-z |
2013-08-01 | An equivalent visco-elastic model of saturated soft clay was studied under unconsolidated undrained (UU) condition, which can be used to evaluate the stability of ocean foundation. Cyclic triaxial compression and extension tests were conducted to study the parameters of the model. Results showed that the relationships of the damping ratio and the octahedral shear modulus with the octahedral cyclic shear strain were nearly unique, when the initial octahedral shear stress ratios of specimens were equal to 0.3, 0.5 and 0.7. The relationships of the damping ratio and the octahedral shear modulus with the octahedral cyclic shear strain determined from the cyclic triaxial compression tests were basically the same as those determined from the cyclic triaxial extension tests. Furthermore, the relationships were not related to the initial stress condition, the test stress state and the octahedral cyclic shear stress ratio. The relationships determined from the cyclic triaxial tests under no deviatoric stress were basically the same as those determined from the cyclic triaxial tests under deviatoric stress. The change of the octahedral cyclic accumulative strain with the number of cycles was unique under different tests stress states. An equivalent visco-elastic constitutive model of saturated soft clay under UU condition was initially established. | Constitutive model of saturated soft clay with cyclic loads under unconsolidated undrained condition | 10.1007/s12209-013-2026-4 |
2013-08-01 | A number of studies have been carried out to investigate the performance of viscoelastic dampers (VEDs) and magnetorheological dampers (MRDs) in controlling the seismic response of buildings, but very few of them regarding the effect of temperature on the behavior of those dampers. The energy absorption properties of the VEDs are dependent on the ambient temperature, excitation frequency and strain amplitude. Several mathematical models have been investigated for reproducing the experimental behavior of single degree of freedom VEDs and MEDs. Of these, only the fractional derivative model can reflect the influence of temperature which is, however, so complex that it is difficult to apply in structural analysis. In order to verify the effect of temperature, two case studies of structural element have been conducted: once using VED and once using MRD. Kelvin–Voigt mathematical model applied, they were investigated and after analyzing the results, the force vs. displacement showed that MRD achieved a high force capacity and a better performance than VED. Furthermore, the effect of the temperature in case of VED observed via plotting the dissipated energy hysteresis at different temperatures. These results validate the effect of the temperature as the lower the temperature the more viscous the dashpot element becomes, hence improving damping, but this is up to a specific low temperature. | Performance of viscoelastic dampers (VED) under various temperatures and application of magnetorheological dampers (MRD) for seismic control of structures | 10.1007/s11043-012-9180-2 |
2013-08-01 | We investigate classical motions of cold atoms in three types (harmonic, linear, and Gaussian) of off-axis rotating traps in the presence of damping forces. When the radius of rotation of the trap is within the trap volume, the atoms are always attracted towards the rotation’s origin if the damping rate Γ is larger than the trap frequency ω ( i.e. , Γ > ω ). This is opposed to being repelled by the centrifugal force in a rotating reference frame. Contrarily, when the trap’s rotation radius is larger than the trap size, the atoms experience a time-averaged ring-shape trap at a high rotational frequency. These anomalous properties can be used to realize high-speed rotation sensors and effective static ring-trap potentials for manipulating cold atoms. | Manipulating cold atoms with off-axis rotating traps | 10.3938/jkps.63.938 |
2013-08-01 | This paper is concerned with estimations of solutions of the Sturm–Liouville equation $$\big(p(x)y'(x)\big)'+\Big(\mu^2 -2i\mu d(x)-q(x)\Big)\rho(x)y(x)=0, \ \ x\in[0,1],$$ ( p ( x ) y ' ( x ) ) ' + ( μ 2 - 2 i μ d ( x ) - q ( x ) ) ρ ( x ) y ( x ) = 0 , x ∈ [ 0 , 1 ] , where $${\mu\in\mathbb{C}}$$ μ ∈ C is a spectral parameter. We assume that the strictly positive function $${\rho\in L_{\infty}[0,1]}$$ ρ ∈ L ∞ [ 0 , 1 ] is of bounded variation, $${p\in W^1_1[0,1]}$$ p ∈ W 1 1 [ 0 , 1 ] is also strictly positive, while $${d\in L_1[0,1]}$$ d ∈ L 1 [ 0 , 1 ] and $${q\in L_1[0,1]}$$ q ∈ L 1 [ 0 , 1 ] are real functions. The main result states that for any r > 0 there exists a constant c _ r such that for any solution y of the Sturm–Liouville equation with μ satisfying $${|{\rm Im}\, \mu|\leq r}$$ | Im μ | ≤ r , the inequality $${\|y(\cdot,\mu)\|_C\leq c_r\|y(\cdot,\mu)\|_{L_1}}$$ ∥ y ( · , μ ) ∥ C ≤ c r ∥ y ( · , μ ) ∥ L 1 is true. We apply our results to a problem of vibrations of an inhomogeneous string of length one with damping, modulus of elasticity and potential, rewritten in an operator form. As a consequence, we obtain that the operator acting on a certain energy Hilbert space is the generator of an exponentially stable C _0-semigroup. | Estimations of Solutions of the Sturm– Liouville Equation with Respect to a Spectral Parameter | 10.1007/s00020-013-2071-3 |
2013-07-16 | In this paper, we investigate the Cauchy problem for the generalized damped Bq equation. By applying fixed point theorem, we prove the global existence and asymptotic decay estimate of solutions for all space dimensions n ≥ 1 provided that the initial value is suitably small. MSC: 35L30, 35L75. | Asymptotic decay estimate of solutions to the generalized damped Bq equation | 10.1186/1029-242X-2013-323 |
2013-07-01 | A robust nonlinear controller is designed for the trajectory tracking of a model-scaled helicopter with uncertain parameters (including uncertain inertial parameters, uncertain structural parameters and uncertain aerodynamic parameters). The proposed controller is based upon the backstepping technique, with modifications to accommodate helicopter dynamics. Aerodynamic uncertainties are addressed by dynamic inverters, and derivatives of virtual controls in the backstepping process are calculated through command filters to avoid complex analytical solutions. Errors resulted from dynamic inverters, command filters, and uncertain parameters are then regarded as disturbances, and treated by nonlinear damping terms. With the proposed controller, it can be proved that tracking errors of the closed-loop system are ultimately bounded with tunable ultimate bounds. Performances of the proposed controller are evaluated by simulation results. | Robust nonlinear control for a model-scaled helicopter with parameter uncertainties | 10.1007/s11071-013-0858-z |
2013-07-01 | In the present study, free vibration of a vibratory system equipped with an impact damper, which incorporates the Hertzian contact theory, is investigated. A nonlinear model of an impact damper is constructed using spring, mass, and viscous damper. To increase accuracy of the solution, deformation of the impact damper during the collision with and the main mass is considered. The governing coupled nonlinear differential equations of a cantilever beam equipped with the impact damper are solved using the parameter expanding perturbation method. Contact durations, which are obtained using the presented method, are compared with previous results. Gap sizes of the impact dampers are classified to two main parts. The effects of selecting the gap sizes regarding to the discussed classification are investigated on the application of the impact dampers. Based on types of collision between colliding masses, the so-called “effectiveness” is defined. Finally, it is shown variation of the damping inclination with the gap size is similar to variation of the effectiveness. | Free vibration analysis of nonlinear resilient impact dampers | 10.1007/s11071-013-0775-1 |
2013-07-01 | The self-oscillations (surging) of a single-stage centrifugal pump working in a hydraulic system in the cavitation regime before the stall of the water feed were investigated. The character of change in these oscillations with change in the value of the acoustic capacitance positioned at the input of the pump was determined. The damping of the indicated self-oscillations with the use of an acoustic liquid damper connected to the hydraulic system was investigated. The impossibility of realization of a model of cavitation self-oscillations for a single-stage impeller pump was substantiated. | Self-Oscillations (Surging) of a Single-Stage Centrifugal Pump in the Cavitation Regime and Their Damping | 10.1007/s10891-013-0911-2 |
2013-07-01 | The problem of the interaction of surface and flexural-gravity waves with a vertical barrier is solved in a two-dimensional formulation. It is assumed that the fluid is ideal and incompressible, has infinite depth, and is partially covered with ice. The ice cover is modeled by an elastic plate of constant thickness. The eigenfrequencies and eigenmodes of oscillation of the floating elastic ice plate, the deflection and deformation of ice, and the forces acting on the wall are determined. | Interaction of surface and flexural-gravity waves in ice cover with a vertical wall | 10.1134/S0021894413040160 |
2013-07-01 | A two-step iterative scheme based on the multiplicative splitting iteration is presented for PageRank computation. The new algorithm is applied to the linear system formulation of the problem. Our method is essentially a two-parameter iteration which can extend the possibility to optimize the iterative process. Theoretical analyses show that the iterative sequence produced by our method is convergent to the unique solution of the linear system, i.e., PageRank vector. An exact parameter region of convergence for the method is strictly proved. In each iteration, the proposed method requires solving two linear sub-systems with the splitting of the coefficient matrix of the problem. We consider using inner iterations to compute approximate solutions of these linear sub-systems. Numerical examples are presented to illustrate the efficiency of the new algorithm. | On the multi-splitting iteration method for computing PageRank | 10.1007/s12190-013-0645-5 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.