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2015-03-01 | In the present paper, a linear model for multi-degree-of-freedom systems with rate-independent damping is proposed to the purposes of dynamic response prediction and identification. A viscoelastic model with memory, equivalent to the ideal hysteretic model as for the energy dissipation properties, but causal and physically consistent in both the time and the frequency domain, is developed by adopting the Maxwell–Wiechert kernel function and by requiring the loss modulus to be substantially independent of frequency in a specified range of interest. The finite element model of the equivalent viscoelastic system is constructed and its equations of motion are shown to be uncoupled, in terms of modal coordinates, by the real-valued eigenvectors of the conservative system. An augmented state-space formulation, which encompasses, besides the customary displacements and velocites, a number of internal variables devoted to represent the viscoelastic memory, is then provided for the sake of system identification. Mechanical and modal properties of the equivalent viscoelastic model are finally illustrated by means of numerical examples. | Modelling and identification of structures with rate-independent linear damping | 10.1007/s11012-014-0046-3 |
2015-03-01 | The seismic response of single-storey, one-way asymmetric building with passive and semi-active variable stiffness dampers is investigated. The governing equations of motion are derived based on the mathematical model of asymmetric building. The seismic response of the system is obtained by numerically solving the equations of motion using state-space method under different system parameters. The switching and resetting control laws are considered for the semi-active devices. The important parameters considered are eccentricity ratio of superstructure, uncoupled lateral time period and ratio of uncoupled torsional to lateral frequency. The effects of these parameters are investigated on peak lateral, torsional and edge displacements and accelerations as well as on damper control forces. The comparative performance is investigated for asymmetric building installed with passive stiffness and semi-active stiffness dampers. It is shown that the semi-active stiffness dampers reduce the earthquake-induced displacements and accelerations significantly as compared to passive stiffness dampers. Also, the effects of torsional coupling on effectiveness of passive dampers in reducing displacements and accelerations are found to be more significant to the variation of eccentricity as compared to semi-active stiffness dampers. | Seismic response of torsionally coupled building with passive and semi-active stiffness dampers | 10.1007/s40091-015-0080-y |
2015-03-01 | Timber frame buildings are well known as an efficient seismic resistant structure and they are used worldwide. Moreover, they have been specifically adopted in codes and regulations during the XVIII and XIX centuries in the Mediterranean area. These structures generally consist of exterior masonry walls with timber elements embedded which tie the walls together and internal walls which have a timber frame with masonry infill and act as shear walls. In order to preserve these structures which characterize many cities in the world it is important to better understand their behaviour under seismic actions. Furthermore, historic technologies could be used even in modern constructions to build seismic resistant buildings using more natural materials with lesser costs. Generally, different types of infill could be applied to timber frame walls depending on the country, among which brick masonry, rubble masonry, hay and mud. The focus of this paper is to study the seismic behaviour of the walls considering different types of infill, specifically: masonry infill, lath and plaster and timber frame with no infill. Static cyclic tests have been performed on unreinforced timber frame walls in order to study their seismic capacity in terms of strength, stiffness, ductility and energy dissipation. The tests showed how in the unreinforced condition, the infill is able to guarantee a greater stiffness, ductility and ultimate capacity of the wall. | Seismic behaviour of traditional timber frame walls: experimental results on unreinforced walls | 10.1007/s10518-014-9650-9 |
2015-03-01 | A single-mass mechanical system with harmonically changing rigidity at the parametric disturbance frequency, which approximately coincides with the double frequency of the natural oscillations of the system and contains an arbitrary nonlinear symmetrical force, is considered. Main parametric resonance occurs when the amplitude of steady-state oscillations reaches large values. To decrease the amplitude, active force vibration damping with a limited intensity is introduced into the system. Its structure and parameters are determined based on variation methods. It is shown that for some nonlinearity classes small amplitudes of oscillations can be reached at small intensity values of the vibration damping. | The effect of the strong suppression of parametric oscillations at a low intensity of vibration damping | 10.3103/S1052618815020065 |
2015-03-01 | The geometric nonlinearity of off-diagonal bracing system (ODBS) could be a complementary system to covering and extending the nonlinearity of reinforced concrete material. Finite element modeling is performed for flexural frame, x-braced frame and the ODBS braced frame system at the initial phase. Then the different models are investigated along various analyses. According to the experimental results of flexural and x-braced frame, the verification is done. Analytical assessments are performed in according to three dimensional finite element modeling. Nonlinear static analysis is considered to obtain performance level and seismic behaviour, and then the response modification factors calculated from each model’s pushover curve. In the next phase, the evaluation of cracks observed in the finite element models, especially for RC members of all three systems is performed. The finite element assessment is performed on engendered cracks in ODBS braced frame for various time steps. The nonlinear dynamic time history analysis accomplished in different stories models for three records of Elcentro, Naghan and Tabas earthquake accelerograms. Dynamic analysis is performed after scaling accelerogram on each type of flexural frame, x-braced frame and ODBS braced frame one by one. The base-point on RC frame is considered to investigate proportional displacement under each record. Hysteresis curves are assessed along continuing this study. The equivalent viscous damping for ODBS system is estimated in according to references. Results in each section show the ODBS system has an acceptable seismic behaviour and their conclusions have been converged when the ODBS system is utilized in reinforced concrete frame. | Finite Element Modeling and Nonlinear Analysis for Seismic Assessment of Off-Diagonal Steel Braced RC Frame | 10.1007/s40069-014-0089-9 |
2015-03-01 | Permanent magnet (PM) synchronous motors with starting cage, already developed in the 1960s for variable-speed textile drives, become increasingly important as energy-efficient PM line-start motors. Differing from the standard design with integrated magnets, a rotor design with surface-mounted magnets is presented. In the planning and design phase of drives with PM line-start motors, the simulation of switching on, running up, and pulling into step is essential. An analytical model is presented leading to voltage and mechanical differential equations that have to be solved simultaneously. Based on a prototype, the suitability of the presented model is demonstrated by direct comparison of simulated to measured data. Besides, the mean influence factors of the pulling-into-step behavior are identified and discussed. | Running up and pulling into step of PM line-start motors with surface-mounted magnets | 10.1007/s00202-014-0308-z |
2015-03-01 | We present a new and algebraic approach to the optimal damping of servo axes during commissioning. The approach is based on control of root loci of the denominator of the transfer function using algebraic elimination. The results are either explicit formulas for simple systems or descriptions of the optima via roots of univariate polynomials. The power of the result is demonstrated in examples. | Commissioning rules for optimal velocity controller damping of servo axes using elimination methods | 10.1007/s11081-014-9272-8 |
2015-03-01 | A Fourier transform-based method has been developed for calculating the response of a railway track as an infinitely long uniform periodic structure subject to moving or stationary harmonic loads. The track may become a non-uniform periodic structure by, for example, rail dampers which are installed between sleepers to control rolling noise and roughness growth. The period of the structure may become greater than the sleeper spacing. For those new situations, the current version of the method cannot be directly applied; it must be generalized and this is the aim of this paper. Generalization is performed by applying periodic conditions to each type of support and summarizing contributions from all types of support. Responses of the rail, sleeper, and damper are all formulated as an inverse Fourier transform from wavenumber domain to spatial domain. The generalized method is applied to investigate dynamics of a typical track with rail dampers of particular design. It is found that the rail dampers can significantly suppress the pinned–pinned vibration of the original track, widen the stop bands and increase vibration decay rate along the rail. However, it is also found that a new pinned–pinned mode is created by the dampers and between about 450 and 1,300 Hz dampers vibrate stronger than the rail, making noise radiation from the dampers a potential issue. These concerns must be fully investigated in the future. The formulae presented in this paper provide a powerful tool to do that. | Generalization of the Fourier transform-based method for calculating the response of a periodic railway track subject to a moving harmonic load | 10.1007/s40534-015-0066-2 |
2015-03-01 | This paper presents design, implementation and experimental results of active vibration control of a truss structure using a pair of piezoelectric ceramic stack actuators. To reduce the vibrations caused by an impulse force, two active strut members are installed along a vertical of the base bay of the truss. The active strut element consists of a piezoelectric ceramic actuator stack, a force transducer and mechanical interfaces. A self-organizing fuzzy controller (SOFC) is designed to suppress vibration of the truss. The SOFC, which uses the input and output history in its fuzzy rules, is designed to maximize modal damping of a constructed truss structure. Experimental results illustrate that the active piezoceramic strut actuators and the SOFC can effectively reduce vibration of the truss. | Active modal damping control of a smart truss structure using a self-organizing fuzzy controller | 10.1007/s40430-014-0174-7 |
2015-03-01 | In the last years, different active methods and devices have been proposed to suppress chatter vibrations. Among active control devices, inertial actuators have demonstrated their good behaviour in several studies. However, their dimensioning and tuning are not clear issues. This work proposes the utilization of a novel coupled model, based on experimental data, where the cutting process and the effect of an active inertial device are simulated in time domain. In this way, the model permits to simulate different control strategies, control filters and actuators. The location of the actuator and the collocation or not of accelerometer can be taken into account, as well. In this work, the mathematical formulation of the model is developed, several applications are shown and, finally, its predictions are verified by means of real cutting operations. | Coupled model for simulating active inertial actuators in milling processes | 10.1007/s00170-014-6469-0 |
2015-03-01 | Active vibration control based on state feedback using H _∞ criterion for two typical types of engineering equipment (machinery and sensitive equipment) is demonstrated here. Semi-active vibration control was implemented using a magnetorheological (MR) damper, which was guided by optimal output using the active method. Two control strategies based on error feedback are introduced here to achieve current regulation for the MR damper. The first method uses a conventional proportional-integral controller. Another method uses an adaptive fuzzy controller to account for the severe nonlinearity and uncertainty of the MR damper. This method is aimed at making improvements in fuzzy logic control for semi-active vibration control. Apart from this, a novel method was implemented to limit current in the case of the sensitive model used to predict output. Particle swarm optimization technique was used to optimize parameters used in this work. | Semi-active Vibration Control Using a Magneto Rheological (MR) Damper with Particle Swarm Optimization | 10.1007/s13369-015-1574-4 |
2015-03-01 | In this paper, vibration isolator of single degree of freedom systems having a nonlinear viscous damping is studied under force excitation. Stability of the steady state periodic response has been discussed. The influence of damping coefficients on the force transmissibility and displacement transmissibility is investigated. The relationship between amplitude and frequency is derived by using the averaging method. Results reveal that the performance of the nonlinear isolator has some beneficial effects compared with linear isolator in a certain range. Numerical simulations are presented to illustrate the results. | Analysis of the effects of nonlinear viscous damping on vibration isolator | 10.1007/s11071-014-1814-2 |
2015-03-01 | The issue of vibration damping occurs in many mechanical problems in the operation of various devices, in the automotive industry engineering, aerospace. In the case where damping by selection of the masses and dimensions is not possible due to various reasons or for other reasons it was abandoned, vibration dampers are used. Minimization of adverse impact of dynamic interaction effects is an important research and technical problem. Passive energy absorbers used today (complex of bumpers, passenger lifts buffers typically allows to the safe dissipation of energy within a certain range of loads. In the case of high-impact loading variability is desirable to use an adaptive energy absorption system capable of rapid change their dynamic characteristics. The main issue in the analysis of interactions impact of dynamic loads on objects is dispersion (dissipation) of kinetic energy during impact. In paper a description of model of internal damping was proposed with the proof the influence of component part of polynomial. For example elastomer material EPUNIT will be used to present prepare the buildings of model hyperdeform material. Was present conclusion of analyses systems hyperdeform composite materials. | Description of phenomena vibration in hyperdeform polymers materials | 10.1007/s40435-014-0069-6 |
2015-03-01 | This paper is concerned with vibration mitigation of a quarter car model using a semi-active magnetorheological (MR) damper. A nonlinear adaptive controller is proposed for vibration attenuation of the quarter car suspension system equipped with MR damper. Proposed adaptive controller can also compensate the uncertainties related to both quarter car model and the MR damper. Moreover, a nonlinear observer is designed to estimate an internal state variable of the MR damper. The mathematical model of the damper which is strongly nonlinear is used to predict the damping force based on velocity input, internal state and voltage input. An experimental test set-up is constructed to validate the MR damper parameters which are adapted by designed controller. Efficiency of adaptive controller is compared with separately designed linear $$\hbox {H}\infty $$ H ∞ controller and passive cases under bump, sine and C-grade road inputs. The proposed adaptive controller is able to achieve good performance in road holding and driving comfort despite uncertainties in model parameters. | Nonlinear adaptive control of semi-active MR damper suspension with uncertainties in model parameters | 10.1007/s11071-014-1844-9 |
2015-03-01 | We present an idealised model of the tidal response in a main channel with multiple secondary basins, co-oscillating with an adjacent sea. The sea is represented as a semi-infinite strip of finite width, anywhere between the limits of a channel extension (narrow) and a half-plane (wide). The sea geometry controls the extent to which radiative damping takes place and hence the type of conditions that effectively apply at the channel mouth. These conditions range between the two extremes of prescribing elevation (deep sea limit) and prescribing the incoming wave (sea as channel extension of the same depth, as done in an earlier study). The closer to this first extreme, the stronger the oscillations in the secondary basins may feed back onto the channel mouth and thus produce an amplified or weakened response in the system as a whole. The possibly resonant response is explained by analysing the additional waves that emerge on either side of the entrance of the secondary basin. Finally, we show that the simultaneous presence of two secondary basins may amplify or weaken the accumulated responses to these basins individually. | Resonance properties of tidal channels with multiple retention basins: role of adjacent sea | 10.1007/s10236-015-0809-y |
2015-03-01 | Formulas for calculating the dimensions of a dynamic low-frequency vibration damper are derived. The damper is designed as a circularly curved thin-walled plate. Bench tests demonstrated that the damper effectively reduces the amplitude of vibrations of the bearing of a high-power turbine-generator set in two directions simultaneously. | A Dynamic Low-Frequency Vibration Damper for Bearings of Turbine-Generator Sets | 10.1007/s10749-015-0560-z |
2015-03-01 | Influence of foundation conditions and typology in above-ground full containment liquefied natural gas (LNG) storage tank design makes it necessary to evaluate its structural response due to dynamic actions. Typical above-ground full containment LNG storage tanks are constituted of an outer tank made of reinforced and pre-stressed concrete, which provides support, protection and secondary containment in case of failure of the inner tank and a 9 % Ni steel inner tank, which acts as principal and main containment. Conceptual description of full containment LNG storage tanks is included in applicable normative EN 14620-1 . Foundation is a structural element, which acts as a dynamic excitation transmitter in case of earthquakes and modifies structure response. This effect is known as soil-structure interaction due to dynamic energy exchange, which affects the overall structural response. The soil-structure interaction under seismic loads has been implemented on the LNG storage tanks for, at least, the last 30 years. The term is widely used to consider the site effect taking into account the local soil characteristics instead of the simplified approach in a fixed-base analysis. A methodology based on the use of finite element modeling for evaluation of soil-structure interaction under horizontal seismic action is presented and results obtained are compared to methodology included in Veletsos and Damodaran Nair (J Struct Div ASCE 101:109–129, 1975 ) of characterizing the soil as the standard Voigt solid, which assumes the characteristics of a simulated 1 degree of freedom (DOF) oscillator. Besides, comparison with current formulae extracted from codes EN 1998-1 and ASCE 7-05 will be performed. | Finite element methodology for the evaluation of soil damping in LNG tanks supported on homogeneous elastic halfspace | 10.1007/s10518-014-9655-4 |
2015-03-01 | Passive control devices are often added to slender and flexible systems in order to increase their structural safety. Several types of devices have been proposed in order to reduce the dynamic responses of different kind of structural systems. Among them, the tuned liquid column damper (TLCD) proved to be very effective in reducing vibration of various type of structures by means of a combined action which involves the motion of the liquid mass within the tube. The restoring force, in particular, is produced by the force of gravity acting on the liquid and the damping effect is generated by the hydrodynamic head losses that arise during the motion of the liquid inside the TLCD. Since the increasing use of TLCD in practical realizations, an approximated simplified formulation, by means of a statistical linearization technique has been previously developed by the same authors. This direct and ready-to-use formulation is able to predict the effectiveness of TLCD on a structure subjected to random loads and has been numerically validated by means of a parametric analysis in a stochastic framework by comparison with the numerical Monte Carlo simulation based on the nonlinear complete system for a wide range of the system parameters. In this paper optimal TLCD parameters have been computed taking advantage of the proposed approximated formulation, by which a smooth function, defining the main system variance, can be formulated and easily minimized, resulting in a significant reduction of the computational time and a valuable tool for design purposes. Moreover, starting from the proposed formulation, optimal design charts have been created which enable for an easy and quick evaluation of the TLCD parameters design. | Optimal tuning of tuned liquid column damper systems in random vibration by means of an approximate formulation | 10.1007/s11012-014-0051-6 |
2015-03-01 | Hydrostatic guideways are used as an alternative to contact bearings due to high stiffness and high damping in heavy machine tools. To improve the dynamic characteristic of bearing structure, the dynamic modeling of the hydrostatic guidway should be accurately known. This paper presents a “mass-spring-Maxwell” model considering the effects of inertia, squeeze, compressibility and static bearing. To determine the dynamic model coefficients, numerical simulation of different cases between displacement and dynamic force of oil film are performed with fluent code. Simulation results show that hydrostatic guidway can be taken as a linear system when it is subjected to a small oscillation amplitude. Based on a dynamic model and numerical simulation, every dynamic model’s parameters are calculated by the Levenberg-Marquardt algorithm. Identification results show that “mass-spring-damper” model is the most appropriate dynamic model of the hydrostatic guidway. This paper provides a reference and preparation for the analysis of the dynamic model of the similar hydrostatic bearings. | Dynamic modeling of hydrostatic guideway considering compressibility and inertia effect | 10.1007/s11465-015-0331-4 |
2015-02-27 | In this work, we consider coupled nonlinear wave equations with degenerate damping and source terms. We will show the blow up of solutions in finite time with positive initial energy. This improves earlier results in the literature. | Blow up of positive initial-energy solutions for coupled nonlinear wave equations with degenerate damping and source terms | 10.1186/s13661-015-0306-8 |
2015-02-11 | In this paper, we consider the initial boundary value problem of the double dispersive-dissipative wave equation with nonlinear damping and source terms. By the combination of the Galerkin method and the monotonicity-compactness method, the existence of global solutions is obtained with the least amount of a priori estimates. Moreover, the asymptotic behavior of global solutions is investigated under some assumptions on the initial data. | Global existence and asymptotic behavior of solutions for the double dispersive-dissipative wave equation with nonlinear damping and source terms | 10.1186/s13661-015-0288-6 |
2015-02-01 | The earthquake-resistant design of prefabricated buildings is currently the focus of attention, especially for industrial buildings that require a high level of seismic protection. The standard design approach, based on ductility requirements, may succeed in preventing building collapse during a severe earthquake, but at the expense of accepting a high damage level at the column bases. To improve the seismic performance of such buildings, different innovative techniques have been proposed. However, these have not been widely implemented in engineering practice due, among others, to the lack of simple conceptual design methodologies. To achieve this goal, a methodology for the design of a roof isolation system is presented, where the roof isolation serves as non-conventional tuned mass damper (TMD), giving a significantly reduced response in terms of displacements and forces. To that effect, design expressions for the TMD period and damping, depending on the building and soil characteristics, are proposed: The expressions have been calibrated based on numerical parametric time history analyses considering Eurocode 8 spectrum—compatible accelerograms. The application of the proposed methodology is demonstrated for a two-story prefabricated building. | Roof Isolation with Tuned Mass-based Systems and Application to a Prefabricated Building | 10.1007/s13369-014-1537-1 |
2015-02-01 | We consider the attenuation of the oscillation of a flat spring due to the action of a granular damper. The efficiency of the damper is quantified by evaluating the position of the oscillator as a function of time using a Hall effect based position sensor. Performing experiments for a large abundance of parameters under conditions of microgravity, we confirm a recent theory for granular damping (Kollmer et al. in New J Phys 15:093023, 2013 ) and show that the theory remains approximately valid even beyond the limits of its derivation. | Probing the validity of an effective-one-particle description of granular dampers in microgravity | 10.1007/s10035-014-0539-8 |
2015-02-01 | In this paper, we consider the $$n$$ n -dimensional ( $$n\ge 2$$ n ≥ 2 ) damped models of incompressible fluid mechanics in Besov spaces and establish the global (in time) regularity of classical solutions provided that the initial data are suitable small. | Global Smooth Solutions to the n-Dimensional Damped Models of Incompressible Fluid Mechanics with Small Initial Datum | 10.1007/s00332-014-9224-7 |
2015-02-01 | In this study, the nonlinear, Hertz–Mindlin contact model and clumped particles were used in the discrete element method simulations of cyclic shear tests to obtain the shear modulus G and damping ratio D at a wide range of strain levels. The simulated G and D , which demonstrated similar behavior as observed by the experiments, can be derived from either (1) the traced energy or (2) the resulting hysteresis loop. As the particle number N _p in the numerical sample increased (i.e., the ratio of the particle size to the sample size decreased) while other sample parameters were fixed, including the same sample size and void ratio, the resulting G decreased whereas D increased. Increasing particle numbers indeed led to a decrease in the associated contact normal forces among particles, which in turn lowered the contact stiffness and therefore the shear modulus of the sample. The D responses were the results of interaction between the stored energy, which was related to the shear modulus, and the energy that mainly dissipated at the weak contacts where the contact normal forces F ^ n were smaller than the associated mean value $$ F_{\text{mean}}^{n} $$ F mean n . The G and D values of the samples became similar and almost independent of N _p when N _p was greater than 32,000 where the ratio of D _50 to the sample size was 0.029. Hence, this particle number was used in the simulations to obtain unbiased results. The G and D values can also be increased and decreased, respectively, by increasing the particle aspect ratio (i.e., by decreasing sphericity). The simulations regarding aging effects on G and D replicated the experimental observations. The contact normal forces among particles were found to become more homogenized after aging. This in turn increased the shear modulus and led to increasing contact normal forces at weak contacts, thereby reducing the frictional loss and damping ratio. The aged and unaged samples had similar shear moduli and damping ratios as the strain levels gradually increased. This is simply because contact forces homogenized during aging were progressively destroyed by subsequent shearing and associated structural changes. | DEM simulations of shear modulus and damping ratio of sand with emphasis on the effects of particle number, particle shape, and aging | 10.1007/s11440-014-0331-2 |
2015-02-01 | In this paper we consider an n -dimensional thermoelastic system with viscoelastic damping. We establish an explicit and general decay rate result without imposing restrictive assumptions on the behavior of the relaxation function at infinity. Our result allows a larger class of relaxation functions and generalizes previous results existing in the literature. | Energy decay in thermoelasticity with viscoelastic damping of general type | 10.1007/s10114-015-2687-0 |
2015-02-01 | This paper is concerned with the asymptotic behavior of the solution for quasilinear hyperbolic equations with nonlinear damping. The main novelty in this paper is that we obtain the L ^ p (2 ≤ p ≤ +∞) convergence rates of the solution to the quasilinear hyperbolic equations, and we need none of the additional technical assumptions for the nonlinear damping f ( v ) given by Li and Saxton (Q Appl Math 61:295–313, 2003 ). |
L
^
p
-convergence rates to nonlinear diffusion waves for quasilinear equations with nonlinear damping | 10.1007/s00033-013-0392-3 |
2015-02-01 | Shear step strain experiments with various strain amplitudes have been performed on poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) melts using both stress-controlled and strain-controlled rheometers. Firstly, the onset of the rheological nonlinearity, i.e., nonlinear stress damping behavior, occurring after a large step strain is found to be a phenomenological consequence of an abrupt stress decline within the transient period of strain actuation. Such a feature, analogous to the stress overshoot in a fast startup shear with sufficiently high rates, is interpreted based on theoretical frameworks concerning chain disentanglement/re-entanglement arising from chain retraction. Furthermore, this work infers that full technical considerations in step strain experiments are indispensable for acquisition of accurate stress relaxation data, as some common but easily overlooked technical problems are influential, probably introducing errors. For instance, a too long finite rise time and a stress overload enable to hinder the nonlinearity onset in the transient period, resulting in inaccurate experimental data. In this sense, the stress-controlled rheometer is advantageous relative to the strain-controlled one, although the inertia in the stress-controlled mode incurs a strain overshoot effect. Nevertheless, the amplitude-dependent strain overshoot offers a very subtle effect on the stress damping behavior. Moreover, transducer compliance problems need to be taken into account, especially for high stiffness polymers. Overall, the effects of such technical factors are dictated by their ability to influence the chain stretching/retraction and the disentanglement. A well-considered experimental methodology is necessary to achieve confidence windows in step strain experiments for analysis accuracy. | Experimental considerations on the step shear strain in polymer melts: sources of error and windows of confidence | 10.1007/s00397-014-0814-y |
2015-02-01 | This paper is an extended study on the model of the hysteretic dynamics of magnetorheological dampers based on a phenomenological phase transition theory (Wang and Kamath in Smart Mater. Struct. 15(6):1725–1733, 2006 ). It is demonstrated that, by appropriately choosing model parameters, the frequency dependence of the hysteretic dynamics can be captured very well by the model based on phase transition theory. Whilst by introducing an appropriate rescaling coefficient to account for the strength of the magnetized particle chains with various magnetic field strengths, the field strength dependence of the hysteretic dynamics can also be captured very well by the same differential equation with the same set of model parameters. There are in total eight model parameters introduced for capturing the hysteretic dynamics, including its dependence on the loading rate and field strength. | An investigation on the field strength and loading rate dependences of the hysteretic dynamics of magnetorheological dampers | 10.1007/s11043-014-9251-7 |
2015-01-13 | In this article, we study forced oscillatory properties of solutions to nonlinear fractional differential equations with a damping term. Based on the properties of the Riemann-Liouville fractional derivative, we establish a sufficient condition for oscillation of all solutions. | Forced oscillation of nonlinear fractional differential equations with damping term | 10.1186/s13662-014-0331-4 |
2015-01-10 | Based on a variational approach, we prove that a second-order singular damped differential equation has at least one periodic solution when some reasonable assumptions are satisfied. | Periodic solutions for a singular damped differential equation | 10.1186/s13661-014-0269-1 |
2015-01-01 | We investigated the damping mechanism of a granular material damping system applied to vibration reduction in structures that have a small vibration displacement. We devised a computational model of the movement of the primary system and the individual granules and obtained those motions by numerical simulation. Based on the fundamental idea that the damping effect of a granular material damper is governed by the motion of the granules, we classified the granular material as “equivalent added mass” and “relative motion mass”, and considered the relation of those mass classes to the damping characteristics. | Numerical Simulation of a Granular Material Damper | 10.1007/978-3-319-09411-3_55 |
2015-01-01 | The contents of this chapter focus on modelling the control valves in flow-mode MR dampers. The authors handle several constitutive models of non-Newtonian fluid models, and obtain equations governing their behaviour in planar flow. Special attention in given to the development of a non-dimensional modelling approach including all key variables. The scheme performance is then demonstrated based on several configurations of control valves of MR dampers. Electromagnetic coupling is provided through a magneto-static axisymmetric model of the control valve assembly or a (transient) lumped parameter model of the electromagnetic circuit of the control valve. A simple design algorithm for optimising the performance of the dampers is demonstrated in the chapter, too. | Modelling of Control Valves | 10.1007/978-3-319-13233-4_4 |
2015-01-01 | In an earlier paper, authors have investigated the static and dynamic stability of cracked concrete flanged conservative beam-columns. The cantilever column with a lumped mass at its free end is subjected to an axial compressive force and a lateral force. Two critical values each of the axial and lateral loads are defined. Loss of static stability is predicted to occur by excessive displacements or brittle buckling while dynamic instability called divergence is shown to occur by vanishing natural frequency. In this paper, the dynamic stability of highly damped concrete beams-columns is investigated. Two measures—damping ratio and damping coefficient—of structural damping have been employed. Critical loads and displacements are not affected by level of structural damping. Application of inadmissible set of loads results in dynamic instability by divergence at all levels of damping. In particular cases, higher damping has been predicted to destabilize even these conservative structures. Effects of initial conditions and higher damping on the inelastic stability, passive stability control and creep buckling of concrete beam-columns have been delineated. Theoretical significance and practical relevance of the paper are also discussed. | Stability of Highly Damped Concrete Beam-Columns | 10.1007/978-81-322-2187-6_179 |
2015-01-01 | The stability of semiconductor laser operation plays a crucial role in almost every possible application of these devices (Erneux, Glorieux, Laser dynamics, Cambridge University Press, UK, 2010) [ 1 ], (Lüdge, Nonlinear laser dynamics—from quantum dots to cryptography, Wiley, Weinheim, 2012) [ 2 ], (Chow, Jahnke, Prog Quantum Electron 37:109–184, 2013) [ 3 ], (Otto, Dynamics of quantum dot lasers—effects of optical feedback and external optical injection, Springer, Heidelberg, 2014) [ 4 ]. In most fields of operation, one would require a stable steady-state output with constant intensity that follows any change in external operating parameters instantaneously, thus enabling, e.g., arbitrarily fast switching of the laser output. In reality such requirements can naturally never be met. | Quantum-Dot Laser Dynamics | 10.1007/978-3-319-25805-8_3 |
2015-01-01 | The consideration of Rayleigh damping coefficients of α and β are an important aspect to determine damping matric in dynamic analysis. In this paper, finite element modal analysis is used on square natural damping rubber plate with various boundary conditions to determine its dynamic properties and damping coefficients α and β. Based on the finding, Rayleigh damping coefficient can be computed and different boundary conditions show different value of Rayleigh damping coefficient. | Determination of Rayleigh Damping Coefficient for Natural Damping Rubber Plate Using Finite Element Modal Analysis | 10.1007/978-981-287-290-6_62 |
2015-01-01 | In this chapter we discuss how to continue NLS solutions beyond the singularity. | Continuations Beyond the Singularity | 10.1007/978-3-319-12748-4_38 |
2015-01-01 | Series compensation of long transmission lines is an economic solution to the problem of enhancing power transfer and improving system stability. However, series compensated transmission lines connected to the turbo generator can result in Subsynchronous Resonance (SSR) leading to undamped Subsynchronous Oscillations (SSO). The advent of Flexible AC Transmission System (FACTS) controllers using high power semiconductors has made it possible to apply these controllers in conjunction with fixed series compensation, not only to improve system performance, but also to overcome the problem of SSR. FACTS controllers based on Voltage Source Converter (VSC) are emerging controllers that have several advantages over the conventional ones using thyristors. STATCOM is a shunt FACTS controller suitable for voltage regulation and damping of oscillations. This chapter describes the analysis and simulation of a series compensated system with STATCOM connected at the electrical center of the transmission line. The SSR characteristic of the combined system is discussed. A new technique of SSR damping is presented in which a STATCOM injects subsynchronous current. | Analysis and Damping of Subsynchronous Oscillations Using STATCOM | 10.1007/978-981-287-281-4_17 |
2015-01-01 | Rotor vibrations in electrical machines depend on structural damping and stiffness properties of the laminated cores. Structural damping determines torsional and transversal vibration amplitudes at resonances. Therefore, it is very important to know the structural damping and stiffness of the laminated cores to carry out structural dynamic simulations. In this paper, a measurement set-up is presented to determine the structural damping and direction-dependent stiffness for laminated cores and stacks. The dissipated damping energy is examined as a result of harmonic excitation of different excitation amplitudes, frequencies and axial pre-stressing conditions. Thereby, the measured structural damping factor is compared to the material damping factor from tables. To allow a conclusion for the reproducibility of the evaluated damping parameters, repeated measurements are carried out and the results are statistically analyzed using the Weibull distribution. | Experimental Investigation of Structural Damping of Laminated Stacks of Electrical Machine Rotors | 10.1007/978-3-319-06590-8_50 |
2015-01-01 | Large photovoltaic power generation facilities are installing in the world. These large power generation are required to contribute actively to ac power system operation. This paper presents basic study results for dynamic stability improvement by large photovoltaic power generation. | Basic Study on Contribution to Dynamic Stability by Large Photovoltaic Power Generation | 10.1007/978-3-319-15765-8_20 |
2015-01-01 | The generalized damping based power flow mode theory [ 1 ] reveals natural power flow behaviours of a dynamic system based on the inherent characteristics of the system’s damping distribution, which provides insight into energy dissipation mechanisms of the dynamic system. In this paper, a new Power Flow Mode dynamic Topology OPtimization (PFMTOP) approach is proposed based on the developed power flow mode theory to achieve topologically optimised systems’ damping material distributions with enhanced vibration suppression capability. Conventional method of topology optimization focuses on minimizing the structural frequency response or dynamic compliance without considering structural damping. The new approach developed herein uses the trace of system’s characteristic damping matrix as design objective to find an optimal damping material layout that maximize the energy dissipation for a given volume of the material to achieve minimum power flow response. Topology optimal design of damping distributions of two-phase structures subject to dynamic loading is studied. Example presented demonstrates the applicability and efficiency of the new PFMTOP approach. The obtained results reveal that the proposed approach can significantly enhance vibration energy dissipation and provides an effective method for optimised systems’ damping material distributions with enhanced vibration suppression capability and reduced material usages. This new method can be readily extended to more complex structures to optimize the topology of damping material layer for improved vibrational power flow control. | Novel Approach for Structural Dynamic Topology Optimizations Based on Power Flow Mode Theory | 10.1007/978-3-319-09918-7_94 |
2015-01-01 | Damping plays an important role in bolted joints of assembled structures due to their significant capacity to dissipate energy. The underlying mechanisms of these dissipative phenomena are generally poorly understood and result from contact and friction effects within the joint interfaces. In order to provide useful virtual prototyping tools for reducing response levels, accurate model-based estimation of modal damping is required. The present study employs an energetic method to calculate the loss factor associated with the localized dissipative interfaces of a global linear structure. This method is based on the concept of the dissipated energy in the interfaces for which the closed-form expression of the loss factor is the ratio between dissipated energy and maximal potential energy, over a cycle of periodic vibration. The aim of this work is to investigate the advantages and drawbacks of this approach for particular conditions such as: modal projection, localized damping level and model density. Simulated academic examples, where accurate estimations of the exact solutions are available, will be used to illustrate the methodology and to explore the potential difficulties that may arise in more complex industrial applications. | Estimation of Modal Damping for Structures with Localized Dissipation | 10.1007/978-3-319-15048-2_17 |
2015-01-01 | A determination of the dynamic stiffness of the torque-speed curve of an electric drive is presented. Development of systems of control of an electric drive with elastic mechanics is described. The structure of a drive based on fuzzy-logic control and a state sensor is given. It is shown that the best damping of elastic oscillations with the distributed parameters of the mechanical part can be achieved by a system of control with neural networks. | Developing systems of control of electric drives with elastic mechanics | 10.3103/S1068371215010058 |
2015-01-01 | Artificial Neuro Fuzzy Inference System (ANFIS) is applied to design static synchronous series compensator based damping controller for the improvement of small signal stability. The proposed controller is implemented in the single machine system. The generated database from conventional static synchronous series compensator based damping controller is used for training the ANFIS. Bacterial foraging optimization algorithm (BFOA) is employed for optimal controller parameter selection. Simulation is done for four cases namely single machine without damping controller, with SSSC and without damping controller, with SSSC based damping controller and with SSSC based ANFIS controller. Simulation results shows that the SSSC based ANFIS controller provide efficient damping and improves the small signal stability of power system when compared to conventional damping controller. | Design of ANFIS Controller for Power System Stability Enhancement Using FACTS Device | 10.1007/978-81-322-2119-7_113 |
2015-01-01 | In the paper comparative rotor-dynamic analyses are carried out for various rotor-shaft systems supported on the classical journal-, rolling element- and on the passive magnetic bearings. The investigations are performed by means of the advanced 3D finite element model of the electrodynamic passive magnetic bearing and of the structural model of the rotor-shaft—bearing systems, using which proper Campbell diagrams, amplitude—frequency characteristics and complex eigenvalues have been determined as well as numerical simulations of rotor-shaft transient dynamic responses were carried out. The presented study is focused on the lateral vibration damping abilities realized by the mentioned above bearing types. In this way, advantages of the prospective passive magnetic bearing have been emphasized. | Dynamic Analysis of the High-Speed Flexible Rotors Supported on the Electrodynamic Passive Magnetic Bearings | 10.1007/978-3-319-06590-8_122 |
2015-01-01 | In order to make a bridge between the mathematical theory and the different applications of differential equations in real life, we begin by giving simple applications of differential equations. An object of mass m is released from a certain height h above the ground and falls under the force of gravity . We want to write a mathematical model that describe the change of the height h with respect to time t . We assume that at time t = 0 , we know the initial height h _0 and the initial velocity of the object $$v_{0}=\frac{dh}{dt}|_{t=0}$$ . Newton’s second law states that the mass of the object m times its acceleration $$\frac{d^{2}h}{dt^{2}}$$ equals the total forces acting on it. | Modelling and Definitions | 10.1007/978-3-319-25735-8_1 |
2015-01-01 | Tuned liquid column gas damper (TLCGD) show excellent vibration absorbing capabilities appropriate for applications in wind- and earthquake engineering. However, in the early regime of strong motion seismic excitation or to counteract strong wind gusts the performance of the passive device can be increased substantially by active elements obtained from adding a pressurized gas supply with input–output valves to the sealed ends of the TLCGD. To prove the working principle of active TLCGD several small scale laboratory experiments have been performed with single and multiple degree of freedom host structures. To obtain a desired dynamic behavior, a conventional feedback control law is used to compute small active pressure inputs to the TLCGD. The experiments have proven that the active device is able to substantially reduce the dynamic system response in a broad frequency range. In fact, dangerous structural resonances of lightly damped structures can be avoided even if the passive absorber is not tuned perfectly. For multiple degree of freedom host structures a suitable control enables a single active TLCGD to counteract several modes of vibrations thereby avoiding the need to install numerous passive devices. | Active Tuned Liquid Column Gas Damper in Structural Control | 10.1007/978-3-319-15248-6_47 |
2015-01-01 | Electrodynamic actuators and electromagnetic dampers (EMD) are used extensively in mechanical systems. They utilise the electromagnetic induction concept to generate eddy current and Lorentz forces for providing vibration suppression forces. In this research, these principles will be developed for vibration serviceability control of a civil engineering structure. An electrodynamic actuator is used in this research, together with a shunt resonant circuit, an RLC resonant circuit (a simple electronic circuit oscillator) which is needed to cascade with the EMD for closing the circuit and generating electrical damping forces. The EMD is set between the structure and the ground. The kinetic energy of the vibrating structure provides the input energy to activate the EMD. H _ ∞ optimisation (minimisation of the maximum response) and H _2 optimisation (minimisation of kinetic energy) are used to obtain the vibration suppression performance, which is compared against a conventional tuned mass damper (TMD). The EMD with shunt resonant circuit (EMDS) can have similar dynamic performance, which achieves suppression of resonant vibration amplitude of the primary structure down to two lower amplitude peaks in the frequency domain. Hence, this work shows that the EMDS can in principle achieve satisfactory vibration suppression performance. | Analysis of H
_
∞
and H
_2 Optimal Design Scheme for an Electromagnetic Damper with Shunt Resonant Circuit
| 10.1007/978-3-319-15233-2_21 |
2015-01-01 | In a composite lathe cutter, the influence of the handle design on the rigidity, temperature propagation, and damping of vibrations in cutting is analyzed. Metal cutters with horizontal holes in a checkerboard pattern and without such holes are considered. Software based on the finite-element method is used in the calculations. | Influence of the handle design on a composite lathe cutter | 10.3103/S1068798X15010220 |
2015-01-01 | Damping of the oscillating cantilever in dynamic atomic force microscopy contains valuable information about the local vibrational structure and elastic compliance of the substrate. We review Damping Force Spectroscopy which has successfully visualized atomically-resolved damping in supramolecular assemblies, capable of identifying the location and packing of inner molecules as well as local excitations of vibrational modes, dependent on outer molecules with specific geometry. We introduce the physical origin of damping in a microscopic model and quantitative interpretation of the practical observations by calculating the vibrational spectrum and damping of inner metallofullerene Dy@C $$_{82}$$ 82 molecules inside carbon nanotubes with different diameters using ab initio total energy and molecular dynamics calculations. | Revealing Subsurface Vibrational Modes by Atomic-Resolution Damping Force Spectroscopy | 10.1007/978-3-319-15588-3_8 |
2015-01-01 | In this paper an elasto-dynamic model of a defective sphere bearing is presented. This two-dimensional model can simulate local faults on the bearing races and rolling elements, and it is based on the non-linear Hertzian contact deformation of the rolling elements. In the model the outer race is supposed to be fixed, and the rolling elements are supposed to roll without slipping. These assumptions yield a total of z + 4 Degrees of Freedom (DOF), where z is the number of rolling elements: three DOF come from the inner race (two displacements and one rotation), one DOF from the cage (rotation) and one DOF from each rolling element (i.e., z radial displacements). Each contact between the spheres and the races is modelled by a non-linear spring (Hertz contact theory) and a damper proportional to the spring stiffness (Palmgren). The model uses a kinematic approach to calculate the trajectory of the rolling elements when passing over the defect. This trajectory is introduced into the equations of motion for the calculation of the rolling elements deformations; subsequently, the internal bearing forces are calculated. The model inputs are the bearing and defect geometry, the materials characteristics and the radial load. The model outputs the overall force transmitted to the outer race, which accurately reproduces the typical behaviour exhibited by a faulty bearing both in time and frequency domain. | Non-linear Elasto-dynamic Model of Faulty Rolling Elements Bearing | 10.1007/978-3-319-06590-8_35 |
2015-01-01 | This core chapter concerns the convergence problem in finite dimensions. We recall that even gradient systems in two dimensions may be divergent, and we show that this phenomenon can happen even for potentials which are almost as smooth as analytic functions. Analyticity, through the Łojasiewicz gradient produces convergence of bounded trajectories, for gradient systems and some classes of gradient-like systems as well. We illustrate all the results by carefully selected examples. | The Convergence Problem in Finite Dimensions | 10.1007/978-3-319-23407-6_10 |
2015-01-01 | The flight mechanics is an important ingredient in vehicle and subsystem design, its performance evaluation and its validation. It deals with forces and moments acting on bodies and the response of the bodies to the applied forces and moments. Typical applications are trajectory design, optimum payload estimation, navigation, guidance and control (NGC) system algorithm design, estimation of loads on vehicle and various subsystems, mission design, vehicle sequencing, performance evaluations of subsystems, validation of NGC systems and evaluation of mission performance. Flight mechanics consists of two processes, namely, modelling and solution where the modelling represents subsystems, vehicle, forces and moments acting on it, their operating environment and the dynamics of vehicle and subsystem. The solution involves obtaining the solutions to the mathematical models, which truly represent the response of the vehicle and subsystems. To achieve the error-free design, the various models used for the vehicle, subsystems, environment, forces and moments generated by the respective systems as well as the dynamics of the systems under the influence of the forces and moments have to represent very close to the physical system and process. The systems models vary from simple three-dimensional model for the translational motion of the vehicle centre of gravity to the detailed six-degrees-of-freedom model along with the flexible vehicle structural dynamics. In addition, to evaluate the integrated system performance, the modelling of the vehicle onboard system elements such as sensors, navigation, guidance and control systems, the corresponding algorithms and signal flows simulating the delays in data transmission among various systems are required. In this chapter, the role of flight mechanics in the STS design process and the need for the integrated design approach are explained. The different coordinate systems used to represent the mathematical models, vehicle attitude sign conventions and the coordinate transformation to transfer the data between the reference frames are described. Subsequently, various models necessary for representing vehicle, subsystem and environment and the methodology for evaluating the system response are included. The usage of the flight mechanics models in the design process is also highlighted. | Flight Mechanics | 10.1007/978-81-322-2532-4_8 |
2015-01-01 | Many of the modern slender and flexible structures are highly susceptible to wind-and earthquake-induced vibrations, which may result in damage to these structures. Of late tuned liquid column dampers (TLCD) has drawn significant attention of researchers. In TLCD, the motion of liquid column in a U-tube container counteracts the forces acting on the structure resulting in reduction of structural response. The advantages of TLCD include low cost and maintenance. There are many varieties of TLCDs proposed for vibration control. In this study, the efficiency in vibration suppression of four different types of passive TLCDs has been compared. These are U-shaped TLCD, liquid column vibration absorber (LCVA), V-shaped TLCD and tuned liquid column ball damper (TLCBD). For this purpose, the response of an SDOF system with and without TLCD is evaluated when subjected to harmonic excitation of varying frequencies and excitation levels. Transfer functions are evaluated for uncontrolled and controlled (i.e., with TLCD) cases by using an equivalent linearization approach for the non-linear TLCD damping. Further, a numerical method is also used for solving equations of motion involving non-linear damping of TLCDs. Results are presented in terms of percentage reduction in SDOF system response. The results of this work demonstrate that TLCBD has better performance when compared to other TLCDs. | Comparison of Performance of Different Tuned Liquid Column Dampers (TLCDs) | 10.1007/978-81-322-2193-7_98 |
2015-01-01 | The high complexity and nonlinearity of power systems, together with their almost continuously time-varying nature, have presented a big challenge for control engineers, for decades. The disadvantages of the linear controllers/models, such as being dependent on the operating condition, sensibility to the disturbance such as parametric variations or faults can be overcome by using appropriate nonlinear control techniques. Sliding-mode control technique has been extensively used when a robust control scheme is required. This chapter presents the transient stabilization with voltage regulation analysis of a synchronous power generator driven by steam turbine and connected to an infinite bus. The aim is to obtain high performance for the terminal voltage and the rotor speed simultaneously under a large sudden fault and a wide range of operating conditions. The methodology adopted is based on sliding mode control technique. First, a nonlinear sliding mode observer for the synchronous machine damper currents is proposed. Next, the control laws of the complete ninth order model of a power system, which takes into account the stator dynamics as well as the damper effects, are developed. They are shown to be asymptotically stable in the context of Lyapunov theory. Finally, the effectiveness of the proposed combined observer-controller for the transient stabilization and voltage regulation is demonstrated. | Transient Stability Enhancement of Power Systems Using Observer-Based Sliding Mode Control | 10.1007/978-3-319-11173-5_16 |
2015-01-01 | The Hamiltonian formalism developed by Arnowitt, Deser, and Misner (ADM) is used to derive and discuss the higher order post-Newtonian dynamics and motion of compact binary systems in general relativity including proper rotation of the components. Various explicit analytic Hamiltonians will be presented for the conservative and dissipative dynamics, the latter resulting from gravitational radiation damping. Explicit analytic expressions for the orbital motion will be given. | Higher Order Post-Newtonian Dynamics of Compact Binary Systems in Hamiltonian Form | 10.1007/978-3-319-18335-0_18 |
2015-01-01 | Operational Modal Analysis (OMA) techniques provide in most cases reasonably accurate estimates of structural frequencies and mode shapes. In contrast though, they are known to often produce uncertain structural damping estimates, which is mainly due to inherent random and/or bias errors. In this paper a comparison is made of the effectiveness of two existing OMA techniques in providing accurate damping estimates for random stationary loading, varying levels of signal noise, number of added measurement channels and level of structural damping. The investigation is focusing on the two frequency domain techniques, the Frequency Domain Decomposition (FDD) and the Frequency Domain Polyreference (FDPR). The response of a two degree-of-freedom (2DOF) system is numerically established with specified modal parameters subjected to white noise loading. The system identification is evaluated with well separated and closely spaced modes. Finally, the results of the numerical study are presented, in which the error of the structural damping estimates obtained by each OMA technique is shown for a range of damping levels. From this, it is clear that there are notable differences in accuracy between the different techniques. | Evaluation of Damping Using Frequency Domain Operational Modal Analysis Techniques | 10.1007/978-3-319-15248-6_37 |
2015-01-01 | This chapter provides a comprehensive mathematical description of the system given by a set of partial differential equations which embeds individual submodels corresponding to the different levels of the drillstring. The upper extremity is accurately described by appropriate top boundary conditions including the actuators’ dynamics. Wave equation models involving viscous and viscoelastic Kelvin–Voigt internal damping are chosen to represent the axial and torsional propagating waves traveling along the drillstring; a distinction between the different sections composing the drilling rod, i.e., the series of drillpipes and the Bottom Hole Assembly (BHA), is made. The system trajectories at the bit level are characterized by the bottom boundary conditions involving a nonlinear term to represent the bit-rock contact from which undesirable vibrations arise. This chapter presents an accurate experience-based model of the frictional torque which considers the drilling surface characteristics and the bit geometry. | Comprehensive Modeling of a Vertical Oilwell Drilling System | 10.1007/978-3-319-15747-4_4 |
2015-01-01 | In this paper, we will show that under some smallness conditions, the planar diffusion wave $$\bar v\left( {\frac{{x_1 }} {{\sqrt {1 + t} }}} \right)$$ is stable for a quasilinear wave equation with nonlinear damping: v _ tt − Δ f ( v ) + v _ t + g ( v _ t ) = 0, x = ( x _1, x _2, ⋯, x _ n ) ∈ ℝ^ n , where $$\bar v\left( {\frac{{x_1 }} {{\sqrt {1 + t} }}} \right)$$ is the unique similar solution to the one dimensional nonlinear heat equation: $v_t - f(v)_{x_1 x_1 } = 0,f'(v) > 0$ , v (±∞, t ) = v _±, v _+ ≠ v _−. We also obtain the L ^∞ time decay rate which reads $\left\| {v - \bar v} \right\|_{L^\infty } = O(1)(1 + t) - \tfrac{r} {4} $ , where r = min{3, n }. To get the main result, the energy method and a new inequality have been used. | Stability of planar diffusion wave for the quasilinear wave equation with nonlinear damping | 10.1007/s10255-011-0100-z |
2015-01-01 | The main objective of this work is to contribute to a better understanding of the dynamic behavior of composite bars. In this work we propose an experimental modal analysis of Glass Fibers Reinforced Polymers (GFRP) bars. The objective is to characterize the damping properties of this material through vibration tests. It was found that these properties were acceptable especially for critical excitation such as earthquakes. | Damping Analysis of GFRP Bars | 10.1007/978-3-319-17527-0_60 |
2015-01-01 | Cantilevered piezoelectric devices under transverse base excitations, for generating usable power from ambient vibrations is a highly researched topic over the past decade. The commonly used rectangular shaped bimorphs require a large proof mass to drive sufficient power, and suffer from having a large stress concentration near the fixed end of the device. Tapering geometry provides a constant axial strain through the length of a triangular cantilever, and therefore provides the opportunity for more reliable operation due to enhanced efficiency. However, in order to make fair comparisons for power output, it is important to compare devices with matching resonance frequency, device volume, and inertial loads to study the effect of geometry. This study takes an experimental approach for designing such devices, and evaluates the effects of shape change with and without the presence of proof masses. While a mass-less triangular device does not outperform a rectangular counterpart for power output generation, tapering the geometry does increases the k_31 electromechanical coupling coefficient, while the damping ratios are nearly the same. The addition of a nominal 2 g proof mass increases the output power by an order of magnitude, and the triangular device outperforms its rectangular counterpart by 40 %; and a subsequent 30 % with 4 g of proof mass. With the addition of proof masses, the electromechanical coupling and damping ratio also increase, which are always greater in the case of the cantilevered triangular bimorphs, and these important parameters may be used as design parameters for better device design. | Shape Optimization of Cantilevered Devices for Piezoelectric Energy Harvesting | 10.1007/978-3-319-07004-9_3 |
2015-01-01 | We end up this book by considering different examples of systems with delay for which our abstract framework can be applied. | Systems with Delay | 10.1007/978-3-319-10900-8_5 |
2015-01-01 | This chapter overviews the theory of nonlinear dynamical systems. Next, it outlines differential geometry and Lie algebra-based control as the predecessor of differential flatness theory-based control. | Nonlinear Dynamical Systems and Global Linearizing Control Methods | 10.1007/978-3-319-16420-5_1 |
2015-01-01 | Many innovative, radical and respectable space debris remediation ideas are being proposed these days. Most of them are under constant development and many others have been taken up by space research organizations of different countries. But a good number of methods still suffer from technical and or financial imperfections. Space debris is a problem that hasn’t yet been contemplated by many countries. The Kessler Syndrome makes the situation even more serious for the ongoing space operations and manned activities in the Low Earth Orbit (LEO). This paper discusses major unconventional methods that are being taken into account by many concerned space institutes, professionals and students. The difficulties which these ideas face are discussed in this paper. A new concept of space debris removal, Deorbiting Cylindrical Orbiter (DeCOrb), is introduced along with its potential design and ability to take versatile forms. | Unconventional Methods for Space Debris Removal | 10.1007/978-3-319-15982-9_6 |
2015-01-01 | We investigated the specific features low-frequency (50–300 Hz) sound propagation in shallow-water areas to relatively small distances r ≈ 3 H –50 H from the sound source, where H is the waveguide depth. The bottoms of water areas were assumed to be fluid homogeneous gas-containing media. Situations were compared in which the sound velocity in the bottom is higher and lower than in the water layer (hard and soft bottom). It was confirmed in experiment that the average effective sound velocity in the bottom may have rather low values (≈100 m/s). The mode description of the acoustic field was used in calculations, and both propagating and outgoing modes, including quasi-modes, were taken into account. The averaged dependences of the field intensity decay on distance were obtained for different frequencies and sound velocities in the bottom. The sound damping factors β in the waveguide were found as functions of frequency and sound velocity in the bottom. It is shown that for a soft bottom, the value of β monotonically increases with an increase in the sound velocity in the bottom, while for a hard bottom, β monotonically decreases. The maximum of β depends on the sound frequency and is reached at the approximate equality of the sound velocities in the bottom and water. | Attenuation of sound in shallow-water areas with gas-saturated bottoms | 10.1134/S1063771015010029 |
2015-01-01 | The rotor of a 3-stage axial turbine designed for an ORC plant, supported by two axial/radial lubricated roller bearings, has some axial clearance in between the outer bearing ring shoulder in the casing to allow for thermal expansion. The rotor can move freely within the clearance before the bearings on both sides are able to apply a restoring force. In order to avoid axial vibrations excited by possible operating fluid pressure fluctuations, an unilateral axial squeeze film damper has been designed. CFD calculations have allowed to characterize the damper, which is highly non-linear. The damper has been introduced in the model of the machine and its performance has been analyzed by comparing the behavior of the damped rotor to the un-damped rotor, at the different exciting frequencies. The comparison has been performed necessarily in the time domain due to the presence of two non-linearity: unsymmetrical damper and non-linear elastic restoring force. The results of the comparison have shown the efficiency of the damper especially in conditions close to resonance. | Controlling Non-linear Axial Vibrations of a Turbine Rotor | 10.1007/978-3-319-06590-8_147 |
2015-01-01 | In this chapter, we first introduce the basic principles of seismic tomography and discuss the common features and differences between seismic tomography and the medical CT-scan. Considering the fact that many different kinds of tomographic studies have been made and a large number of tomography-related technical terms are used in the literature, we present a classification of seismic tomography. Then we explain the meaning of multiscale seismic tomography, and discuss how to interpret the obtained tomographic images. Finally, the scope and contents of this book are outlined. | Methodology of Seismic Tomography | 10.1007/978-4-431-55360-1_2 |
2015-01-01 | The paper deals with optimization of dynamic characteristics of smart structures based on piezoelectric materials with external electric circuits comprising resistance, capacitance and inductance. The dynamic parameters to be optimized are resonance frequencies and damping properties. For numerical estimation of the dynamic characteristics of the model system, a natural vibration problem of an electroviscoelastic solid with differing external electric circuits is proposed. Model examples are given to demonstrate the efficiency of the natural vibration problem in finding dynamically optimum piezoelectric smart structures with external electric circuits. | Optimization of the Damping Properties of Electro-Viscoelastic Objects with External Electric Circuits | 10.1007/978-3-319-17118-0_4 |
2015-01-01 | A method of absolute calibration of electrodynamic seismic sensors by single-sensor displacement is theoretically justified. It is shown that the method can be implemented using simple mechanical devices and a recording system. The required mathematical processing of the step-test impact can also be carried out using only standard software on any modern PC. A practical implementation of the method is shown by the example of calibration of a 10 Hz geophone. Features of the test technology and the mathematical processing of the obtained record are presented. The method is recommended for the calibration of sensors (velocimeters) with natural frequencies from 0.5 to 30 Hz. | Absolute calibration of seismic sensors using a displacement jump: Theory and practice | 10.3103/S0747923915010053 |
2015-01-01 | This chapter describes the experimental work and numerical simulations performed for the purpose of monotube damper model verification. To validate the modelling scheme for the material contained in previous chapters, several monotube damper prototypes were subjected to a range of velocity, displacement and commanded current inputs. The acquired data have formed basis for the presented modelling work. The tested damper prototypes vary in their low-velocity performance characteristics. The contents of this chapter is split into two related parts. First, experimental work including all three prototype dampers is presented and results discussed. Finally, based on the prototype geometry and the properties of the fluid and damper component materials, the authors carry out simulations of the damper behaviour and compare them against the real-life data. | Experimental Verification of an MR Monotube Damper Model | 10.1007/978-3-319-13233-4_8 |
2015-01-01 | In this thesis, the dynamics of semiconductor quantum-dot optoelectronic devices has been investigated. The complex charge-carrier dynamics due to the coupling of localized electronic quantum-dot states and the surrounding continuum reservoir states has been found to crucially influence the dynamic response of the quantum-dot devices to external perturbations. | Summary and Outlook | 10.1007/978-3-319-25805-8_5 |
2015-01-01 | A contraction semi-group on a real Banach space is either made of operators of norm equal to 1 for all times, or exponentially decaying in norm. Exponential decay is established in relevant norms for the heat equation and the wave equation with dissipation in a bounded domain. | Uniformly Damped Linear Semi-groups | 10.1007/978-3-319-23407-6_4 |
2015-01-01 | This paper describes modeling and simulation of spur gear pair in Adams–View. Initially, virtual model of an ideal gear pair is created in Adams and variation of the dynamic force is obtained by considering the tooth mesh stiffness and mesh damping coefficient. The magnitude of force variation thus obtained is confirmed with the design calculations. The dynamic force magnitudes thus obtained and those found in Adams are closely matching. Later on, tooth profile error is introduced in the gear pair by removing part of involute surface from one of the gears making one tooth surface as flat. Dynamic force variation is now obtained for the defective gear pair. After comparing the dynamic forces for defect free and defective gear pairs, it is found that change in dynamic force pattern is a good indicator of tooth profile error in spur gears. | Modeling and Dynamic Force Simulation for Detection of Profile Error in Spur Gear Pair | 10.1007/978-3-319-09918-7_97 |
2015-01-01 | The damping properties of materials, joints, and assembled structures can be modeled efficiently using fractional derivatives in the respective constitutive equations. The respective models describe the damping behavior accurately over broad ranges of time or frequency where only few material parameters are needed. They assure causality and pure dissipative behavior. Due to the non-local character of fractional derivatives the whole deformation history of the structure under consideration has to be considered in time-domain computations. This leads to increasing storage requirements and high computational costs. A new concept for an effective numerical evaluation makes use of the equivalence between the Riemann–Liouville definition of fractional derivatives and the solution of a partial differential equation (PDE). The solution of the PDE is found by applying the method of weighted residuals where the domain is split into finite elements using appropriate shape functions. This approach leads to accurate results for the calculation of fractional derivatives where the numerical effort is significantly reduced compared with alternative approaches. Finally, this method is used in conjunction with a spatial discretization method and a simple structure is calculated. The results are compared to those obtained from alternative formulations by means of accuracy, storage requirements, and computational costs. | Implementation of Fractional Constitutive Equations into the Finite Element Method | 10.1007/978-3-319-06980-7_13 |
2015-01-01 | Turbine blades are critical components in thermal power plants and their design process usually includes experimental tests in order to tune or confirm numerical analyses. These tests are generally carried out on full-scale rotors having some blades instrumented with strain gauges and usually involve a run-up and/or a run-down phase. The quantification of damping in these conditions is rather complicated, since the finite sweep velocity produces a distortion of the vibration amplitude with respect to the Frequency-Response Function that would be expected for an infinitely slow crossing of the resonance. In this work, we demonstrate through a numerical simulation that the usual identification procedures procedure lead to a systematic overestimation of damping due both to the finite sweep velocity, as well as to the variation of the blade natural frequency with the rotation speed. An identification procedure based on the time-frequency analysis is proposed and validated through numerical simulations. | Damping Estimation for Turbine Blades Under Non-stationary Rotation Speed | 10.1007/978-3-319-15048-2_14 |
2015-01-01 | Understanding the dynamic response of accelerometers is critical to interpreting data obtained in impulsive loading conditions. While this information is commonly provided by manufacturers, the estimated properties are typically obtained at levels below the full range of the sensor. Using high bandwidth operating data of varying amplitudes, the damping ratio and principle resonant frequency of shock accelerometers are estimated using a simple dynamic model. While the resonance is shown to be essentially amplitude-invariant, the damping ratio is shown to vary with the excitation amplitude. Possible causes related to the frequency content of the excitation and the presence of repeated roots are discussed. | Estimation of Amplitude-Dependent Resonance and Damping in MEMS Shock Accelerometers | 10.1007/978-3-319-15233-2_11 |
2015-01-01 | In the last couple of decades the use of energy dissipation devices for earthquake mitigation has gained much attention. Most research in that field, however, focused on frame buildings. This chapter is based on (Lavan, Earthq Eng Struct Dyn 41(12):1673–1692) and discusses the possibilities of using energy dissipation devices, or more specifically viscous dampers, in wall structures to result in viscously coupled shear walls (VCSWs). In turn, insight to their behaviour, as well as simplified approximate tools for their analysis and initial design are presented. While very simple to use, those rely on a strong theoretical background. | On the Seismic Behaviour of Viscously Coupled Shear Walls | 10.1007/978-3-319-06394-2_13 |
2015-01-01 | This note gives a concise summary of results concerning the well-posedness and long-time behavior of (Reissner)–Mindlin–Timoshenko plate equations as presented in Pei et al. (Local and global well-posedness for semilinear Reissner–Mindlin–Timoshenko plate equations, 2013 and Global well-posedness and stability of semilinear Mindlin–Timoshenko system, 2013 ). The main feature of the considered model is the interplay between nonlinear viscous interior damping and nonlinear source terms. The results include Hadamard local well-posedness, global existence, blow-up theorems, as well as estimates on the uniform energy decay rates. | Well-Posedness and Stability of a Mindlin–Timoshenko Plate Model with Damping and Sources | 10.1007/978-3-319-12577-0_36 |
2015-01-01 | The response of two adjacent single degree-of-freedom (SDOF) structures connected by nonlinear viscous damper under base excitation, modeled as stationary white-noise random process is investigated. Considering nonlinear force-deformation phenomenon of nonlinear viscous damper, the dynamic response of connected structures is obtained using the equivalent linearization technique. A parametric study is carried out to examine the influence of system parameters such as mass ratio and frequency ratio on optimum damping of damper and corresponding response. It is found that frequency ratio affects the performance of damper and corresponding response significantly, whereas, the effect of mass ratio is marginal. | Dynamic Response of Adjacent Structures Coupled by Nonlinear Viscous Damper | 10.1007/978-81-322-2193-7_85 |
2015-01-01 | The attributes, relevant to earthquake resistant design, are described. The reader will get acquainted with properties of reinforced concrete and masonry units to the extent that they relate to cyclic loading. Other attributes that are described in detail are damping, ductility, mass, lateral stiffness and strength. After a precise definition of degree of freedom, the methods of evaluating distortions under various modes of vibration are explained. Examples at end of the chapter illustrate the methods for evaluation of various damping parameters such as critical damping, logarithmic decrement and damping coefficient. These examples cover evaluation of energy dissipation, obtaining damped and undamped frequencies of vibration and calculation of various forms of ductility such as curvature ductility, rotational ductility, etc., as well as frequencies of vibration along six degrees of freedom. | Important Attributes for Seismic Design | 10.1007/978-81-322-2319-1_2 |
2015-01-01 | The opportunities to energize a broad range of devices by use of energy available almost anywhere and in many forms are almost unlimited. A major advantage of energy harvesting is the manufacture of small autonomous electronic devices with no need for power supply and maintenance. Shunt damping circuits, although unfavorably affected by the size and mass of bulky coil inductors, started to base on synthetic inductors losing their passivity. In this paper we report a study of the feasibility of powering shunt damping circuits by use of thermal energy otherwise irrevocably lost from a bearing. The heat generated in the bearing is converted thermoelectrically into electric energy which is then used to power synthetic inductance circuitry. We show that the power demand of such circuit can be satisfied by use of a thermoelectric generator paired with a moderately loaded bearing. | Integration of Thermal Energy Harvesting in Semi-Active Piezoelectric Shunt-Damping Systems | 10.1007/s11664-014-3194-2 |
2015-01-01 | A finite element model of a car front subframe has been calibrated against test data. Stepped-sine testing has been used to give frequency response function estimates on an ensemble of seemingly identical subframes. Therefore, the deviation between test data and simulation results can be compared in a meaningful way by the outcome of model calibration and cross-validation. Emphasis has been put on the preparation of the test pieces for high fidelity testing and on bettering the chances of getting a calibration outcome that provides insight into the physical processes that govern the subframe dynamics. The front subframe model has more than 200,000 degrees-of-freedom and 17 model calibration parameters. The efficiency of the calibration procedure under these conditions is reported. To achieve efficiency, a calibration with a smooth deviation metric is used together with a damping equalization method that eliminates the need for matching of experimental and analytical eigenmodes. The method is combined with surrogate model frequency response evaluation based on model reduction for increased speed. The Matlab based open-domain software tool FEMcali that employs the Levenberg-Marquardt minimizer with randomized starts has been used for calibration and an unregularized Gauss-Newton minimizer has been used in the cross-validation. | Calibration and Validation of a Car Subframe Finite Element Model Using Frequency Responses | 10.1007/978-3-319-15251-6_2 |
2015-01-01 | This paper focuses on vibrations attenuation of an electromechanical system flexibly coupled with a baseplate by cylindrical helical springs and damped by an element that can work either in inertia or impact regime. 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. The nonlinearities that significantly influence behavior of the system are impacts if the impact regime is set on. Several important results were obtained by means of computational simulations. Character of the system motion and amplitude of its oscillations strongly depend on the width of clearances between the damping element and the rotor frame. The damping element operating in inertia regime must have precisely chosen mass and reduces efficiently the oscillations amplitude only in a narrow frequency interval. In contrast, the damping device working in impact regime attenuates vibrations of the rotor frame in a wide range of the excitation frequency and the system is showing periodic, quasi periodic and chaotic movements. | On Dynamics of an Electromechanical System Supported by Cylindrical Helical Spring Damped by an Impact Damper | 10.1007/978-3-319-10759-2_19 |
2015-01-01 | The response of two adjacent single degree-of-freedom (SDOF) structures connected by viscous damper under base excitation, modeled as non-stationary random process is investigated. To study the effect of amplitude non-stationary characteristics of earthquake excitation, the ground motion is modeled as a uniformly modulated stationary Gaussian random process with zero-mean. The non-stationary response of coupled structure is obtained for modulating function having different strong motion duration and compared with the corresponding stationary response. The peak value of root mean square (RMS) response of the connected structures for other model of earthquake excitation such as Kanai-Tajimi and white noise is compared for stationary and tow non-stationary conditions. It is observed that stationary response is achieved in a very short time. The peak value of RMS response under non-stationary ground motion is nearly same as that of the stationary response. The result indicates that the peak value of responses for stationary and two non-stationary cases is quite comparable with each other. Thus, the random response of coupled structure can be obtained by considering stationary model of earthquake ground motion. | Random Response Analysis of Adjacent Structures Connected by Viscous Damper | 10.1007/978-81-322-2193-7_88 |
2015-01-01 | Non-linear damped vibrations of a cylindrical shell subjected to the different conditions of the combinational internal resonance are investigated. Its viscous properties are described by Riemann-Liouville fractional derivative. The displacement functions are determined in terms of eigenfunctions of linear vibrations. The procedure resulting in decoupling linear parts of equations is proposed with the further utilization of the method of multiple time scales for solving nonlinear governing equations of motion, in so doing the amplitude functions are expanded into power series in terms of the small parameter and depend on different time scales. It is shown that the phenomenon of internal resonance can be very critical, since in a circular cylindrical shell the internal additive and difference combinational resonances are always present. The influence of viscosity on the energy exchange mechanism is analyzed. It is shown that each mode is characterized by its damping coefficient connected with the natural frequency by the exponential relationship with a negative fractional exponent. | Analysis of Non-linear Vibrations of a Fractionally Damped Cylindrical Shell Under the Conditions of Combinational Internal Resonance | 10.1007/978-3-319-15765-8_3 |
2015-01-01 | Reduction of whirling vibration amplitudes in rotordynamic systems resulting from unbalance force during the passage through the critical speeds is very important for preventing propagation of fatigue cracks, excessive noise and instability problems. In this paper, numerical investigations of passive targeted energy transfer (TET) to mitigate the whirling vibration amplitude in rotor systems at the critical speeds are performed by applying nonlinear energy sinks (NESs) to the rotor systems. The three-degree-of-freedom hollow shaft-NES system has been modeled based on Lagrange’s method. Numerical simulations have been performed to optimize the NES parameters in order to obtain the optimum performance for vibration reduction. The influence of critical parameters, including the angle between the unbalance mass and the NES, the NES damping and the unbalance mass on the NES performance in whirling vibration reduction, is also investigated. Additionally, the application of the NES is compared with that of the tuned mass damper (TMD). Numerical results show that the NES is able to efficiently reduce the resonant amplitude of the rotor systems when the stiffness and mass ratios are optimized appropriately. Furthermore, it is found that, unlike the NES, the TMD requires an offset distance from the shaft centerline to be able to reduce the resonant amplitude; otherwise, it fails in mitigating the whirling amplitude. Identifying this offset for the TMD requires pre-knowledge of the exact unbalance value and its eccentricity from the shaft centerline. However, the NES does not require a priori knowledge of the unbalance value which is an advantage of the NES compared to the TMD. The TMD, applied here with an offset distance able to mitigate the resonant vibration, only works as a balancer when positioned opposite to the location of the unbalance mass, which limits its application in vibration reduction of rotor systems. | Vibration reduction in unbalanced hollow rotor systems with nonlinear energy sinks | 10.1007/s11071-014-1684-7 |
2015-01-01 | One of the important advantages of IEPE accelerometers is their small noise permitting them to measure small vibration signals at frequency range from about 0.001 Hz to 20 kHz. Specifically, some modern ultra-low-noise IEPE accelerometers feature a noise floor (equivalent input noise acceleration spectral density) estimated at a few dozen n g ∕ H z $$ \mathrm{ng}/\sqrt{\mathrm{Hz}} $$ at frequency 1 Hz and a few n g ∕ H z $$ \mathrm{ng}/\sqrt{\mathrm{Hz}} $$ at frequency 100 Hz [1–4]. Designers of IEPE sensors try to decrease their noise more and more. In this matter, the question about the fundamental noise limit of an IEPE accelerometer becomes vital. This chapter describes noise of the PE transducer as the fundamental noise limit of the IEPE accelerometer [5]. Most literature sources on noise of vibration and acoustic sensors describe the mechanical-thermal noise of a damped harmonic oscillator as the only noise source determining the sensor’s noise limit [6–10]. A few other literature sources present the electrical-thermal noise of a piezoelectric (PE) element (crystal) caused by its loss factor as the only noise limit for a PE transducer [11, 12]. But a few, if any, literature sources describe the complete noise analysis of the PE transducer. In this chapter, both noise sources of the PE transducer mentioned above are considered for determination of the fundamental noise limit of the IEPE sensor. The chapter content is based on the author’s work [5]. | Fundamental Noise Limit of an IEPE Accelerometer | 10.1007/978-3-319-08078-9_6 |
2015-01-01 | Poor and devastating performance of the soft storey buildings during earthquakes always advocated against the construction of such buildings with soft ground storey. Increasing construction of multistoried buildings with soft ground story however indicates that the practical need of an open space to provide car parking space far overweighs the advice issued by the engineering community. In past, several researchers have addressed the vulnerability of soft storey due to seismic loading Seismic loading . As the conventional local/member level strengthening techniques (steel jacketing, concrete jacketing, steel caging, FRP jacketing, etc.) may not be feasible to enhance the seismic performance of the deficient reinforced concrete structures beyond a certain limit, the improvement of seismic performance of this type of deficient structures by reducing the seismic demand through the supplemental energy dissipation mechanisms has warranted the focus of the researchers. In recent years efforts have been made by researchers to develop the concept of energy dissipation or supplemental damping into a workable technology, and a number of these devices have been installed in structures, throughout the world. The effectiveness of sliding friction damper, in improving the seismic performance of the soft storey reinforced concrete frame building, has been investigated in this paper. The response parameters, such as absolute acceleration, interstorey drift and base shear have been investigated for the example soft storey frame equipped with friction damper. The present study demonstrates the effectiveness of the friction damper in controlling the response behavior of the soft storey frame building due to significant energy dissipation by the friction damper at the soft storey level. | Seismic Protection of Soft Storey Buildings Using Energy Dissipation Device | 10.1007/978-81-322-2193-7_102 |
2015-01-01 | This paper presents a numerical model of how a visco-elastic support affects the dynamical response of a 42 MW Kaplan turbine that is experiencing resonance problems. The supports are placed between the bearing bracket and the supporting concrete structure. Since the supports are nonlinear, the nodal displacements are solved using a Runge-Kutta time integration method where the visco-elastic supports are implemented as a nonlinear force. To reduce calculation time the number of degrees of freedom of the rotor model is reduced using the Improved Reduction System. Excitation of the system is implemented as a stationary force in the runner with varying frequency. The resulting nodal displacement from the transient simulation is then compared to the system simulated without the supports to show how the machine dynamics are affected. The simulations show that the visco-elastic supports efficiently reduces the displacements in the lower vibration modes. The reduced vibration levels should decrease the probability of resonance problems occurring when running at operating speed. | Modeling of Visco-elastic Supports for Hydropower Applications | 10.1007/978-3-319-06590-8_180 |
2015-01-01 | Depending on their types and sizes, MW-scale wind turbines are usually designed to be operational for wind speeds between 4 and 25 m/s. In order to reach this goal, most of the turbines utilize active pitch control mechanisms where the angle of the blade (pitch angle) is changed as a function of wind speed. Similarly, the whole rotor is rotated toward the effective wind direction by using the yaw mechanism. The ability of the turbine to adapt to the changes in operating conditions plays a crucial role in ensuring maximum energy production and the safety of the structure during extreme wind loads. This on the other hand makes it more difficult to investigate the system from the dynamic analysis point of view. Unlike ordinary engineering structures, the modal damping ratios identified for wind turbines are not constant; they change depending on wind speed, rotor speed, and blade pitch angle. Unexpected resonance problems due to dynamic interactions among the aeroelastic modes and/or excitation forces can always be encountered. Therefore, within the design wind speed interval, for each velocity increment, it has to be proven that there are no risks of possible resonance problems and that the structure is dynamically stable. This work presents the results of in-field vibration tests and the corresponding data analysis performed on a 2.5 MW, 80 m diameter wind turbine. Within the scope of the research, 12 different modes were identified for the turbine at parked conditions. Similarly, seven different aeroelastic modes were extracted for the rotating turbine. These results were then qualitatively compared with a reference study in literature which includes in-field vibration tests and aeroelastic stability analysis performed on a similar size and capacity wind turbine. | Dynamic Stability Analysis of Wind Turbines Through In-Field Vibration Tests | 10.1007/978-3-319-17031-2_70 |
2015-01-01 | The clamping length of holder-tool often changes with the machining conditions and is the main factor affecting the stiffness and damping values of holder-tool interface. To avoid the need for repeating the measurements, the previous studies identify the joint stiffness-damping parameters based on genetic algorithm and calculate the joint parameters per unit area of holder-tool interface for response prediction. This paper proposes a simplified method to identify the joint parameters by simplifying the continuous contact interface to contact points in side of the clamping part. The equivalent joint stiffness-damping parameters are calculated by an inverse calculation method along the whole frequency band, which is more efficient than the genetic algorithm. The responses of holder-tool assembly with different clamping length are predicted based on the assumption of linear relationship between the stiffness-damping values and clamping length. At last, the experiment cases were carried out to verify the effective of the simplified method. | A Simplified Method to Identify the Equivalent Joint Parameters of Holder-Tool Interface | 10.1007/978-3-319-22876-1_51 |
2015-01-01 | The destabilization effect of damping on a class of general dynamical systems is discussed. The phenomenon of jump in the critical value of the bifurcation parameter, in passing from undamped to damped system, is view in a new perspective, according to which no discontinuities manifest themselves. By using asymptotic analysis, it is proved that all subcritically loaded undamped systems are candidate to become unstable, provided a suitable damping matrix is added. The mechanism of instability is explained by introducing the concept of modal dampings, as the components of the damping forces along the unit vectors of a non-orthogonal eigenvector basis. Such quantities can change sign while the load changes the eigenvectors of the basis, thus triggering instability. A paradigmatic, non-physical, minimal system has been built up, admitting closed-form solutions able to explain the essence of the destabilizing phenomenon. Series expansions carried out on the exact solution give information on how to deal more complex systems by perturbation methods. | A paradigmatic minimal system to explain the Ziegler paradox | 10.1007/s00161-014-0363-8 |
2015-01-01 | Industrial structures are mainly assemblies with complex geometries and non-linear characteristics. Friction and joint preload added to fabrication imperfections lead to a substantial gap between numerical models and real structures. In order to develop accurate generic models, it is then necessary to quantify the behavior variability, especially the one related to the joint conditions. The first part of this paper describes the iterative sizing procedure of an academic assembly which characteristics may vary depending on several input variables (e.g. value of the bolt torque, number and position of preloaded bolts, etc.). The properties of the bolted joint were optimized in order to satisfy a set of conditions in terms of tangential slipping, normal displacement and maximum stress level. The second part concerns the experimental modal analysis of the assembly. The main purpose is to characterize the relationship that exists between the input variables and the measured eigenfrequencies and modal damping of the assembly. | Variability of a Bolted Assembly Through an Experimental Modal Analysis | 10.1007/978-3-319-15224-0_18 |
2015-01-01 | The nonlinear dynamics of a two-degree-of-freedom (2-DOFs) vibrating energy harvester (VEH) based on magnetic levitation is modeled and investigated. The equations of motion have been derived while taking into account the magnetic nonlinearity and the electro-magnetic damping. The associated linear eigenvalue problem has been analyzed and optimality conditions have been expressed in term of distance minimization between the two eigenfrequencies of the considered system. The resulting optimal design parameters have been substituted into the coupled nonlinear equations of motion which have been numerically solved. It is shown that the performances of a classical single degree of freedom VEH can be significantly enhanced up to 270 % in term of power density, up to 34 % in term of frequency bandwidth and up to 10 % in term of resonance frequency attenuation. | Nonlinear 2-DOFs Vibration Energy Harvester Based on Magnetic Levitation | 10.1007/978-3-319-15233-2_5 |
2015-01-01 | Peat soils impose special problems in Geotechnical Engineering design as well as Civil Engineering and constructions. Most of researchers conducted investigations on the dynamic loading of soft soils such as sand and clay, but only a few had discovered the behaviour of peat in terms of static and dynamic loadings. Hence, this paper presents the behaviour of peat soil located in Pontian, Johor as well as to obtain the dynamic parameters of peat soil such as shear modulus and damping ratio by using different frequencies. The index properties test, static test and cyclic test have been performed to determine the characteristics and also the parameters required by using stress-controlled cyclic triaxial test of 1 and 2 Hz loading frequencies. All tests were conducted in RECESS, UTHM. The findings explained that Pontian peat behaves differently during the frequencies of 1 and 2 Hz. The shear modulus behaviour on the Pontian peat increase as the loading frequency and effective stresses increased. The results show that the maximum shear modulus of Pontian peat was 1.19 MPa for the frequency of 1 Hz and 1.4 MPa for 2 Hz. Both at effective stress of 100 kPa. Meanwhile, damping ratios show a reduction in the increasing of effective stress and loading frequency applied. The maximum damping ratio in 1 Hz frequency was noted at 44 % and the maximum value for 2 Hz was 35 %. Both at effective stress of 13 kPa. For further research, the cyclic loading can be conducted with different frequencies to show clearly the behaviour of peat in terms of dynamic loading and the cause of frequency influences should also be stated as it would affect the results pattern. | The Characteristics of Pontian Peat Under Dynamic Loading | 10.1007/978-981-287-290-6_43 |
2015-01-01 | This paper investigates the influence of combined fast external excitation and internal parametric damping on the amplitude and the onset of the quasi-periodic galloping of a tower submitted to steady and unsteady wind flow. The study is carried out considering a lumped single degree of freedom model and the cases where the turbulent wind activates different excitations are explored. The method of direct partition of motion followed by the multiple scales technique are applied to derive the slow flow dynamic near the primary resonance. The influence of the combined loading consisting in external excitation and parametric damping on the quasi-periodic galloping onset is explored. The performance of the combined loading is compared with the cases where the external excitation and the parametric damping are introduced separately. The results show that the performance of the combined loading on retarding the quasi-periodic galloping Quasi-periodic galloping onset and quenching the corresponding amplitude is better in all cases of the turbulent wind excitations. | Quasi-Periodic Galloping of a Wind-Excited Tower Under External Forcing and Parametric Damping | 10.1007/978-3-319-19851-4_7 |
2015-01-01 | This study investigates the experimental validation of transverse flux linear motors (TFLMs) with permanent magnet excitation and the dynamic simulation of the developed TFLM created using the optimal design. Our research challenge is to use the developed direct drive TFLM to substitute the rack and pinion in a rotary motor because the rack and pinion lacks speed and thrust. The electromagnetic field characteristics are calculated using 3D finite element method analyses, and the dynamic characteristics are simulated using mechanical balance equations. After calculating the integral parameters, the dynamic behavior of the machine is simulated. The Matlab/Simulink model for solving motion equations is used. The peak currents obtained from simulations and experiments are very closely matched within 1%, which is the estimation error. The structural stability is evaluated using structural analyses that consider the load and moment of a robot. In order to reduce the structure-borne noise radiated from the main driving frame, damping materials are applied and the sound pressure level decreases by approximately 8.5 dB(A). Finally, the repetitive position accuracy is considered and measured using an API laser tracker T3. The measured repetitive position accuracy is within 0.1 mm at a speed of 3 m/s. | Development of thrust force 6 kN class transverse flux linear motor with synchronous control for direct drive applications | 10.1007/s12541-015-0025-1 |
2015-01-01 | The great twentieth century mathematician, John von Neumann, once said, “At a great distance from its empirical source, or after much abstract inbreeding, a mathematical subject is in danger of degeneration. Whenever this stage is reached the only remedy seems to me to be the rejuvenating return to the source: the reinjection of more or less empirical ideas.” This wisdom is especially applicable to the field of structural dynamics. The present paper takes a look at the historical and empirical bases of key aspects of structural dynamic phenomena including damping of materials and built-up assemblies, behavior of viscoelastic materials, interaction of structures and fluids, and general parametric uncertainties. Migration of misconceptions in engineering practice and, in particular, commercial software products are cited. Illustrative examples of the benefits of recollection of fundamentals in aerospace, marine and civil applications are described. | Structural Dynamic Modeling: Tales of Sin and Redemption | 10.1007/978-3-319-15048-2_6 |
2015-01-01 | Tip timing blade vibration measuring systems have become nowadays common for monitoring blade vibrations, due to rather easy and non-intrusive installation of sensors. The data collected by the sensors must be heavily processed in order to get the vibration time histories of all blades at rated speed or during a run up or run down transient. In the paper a real case of tip timing measurement for a steam turbine is shown. Resonant/natural frequencies, amplitude and phase of each blade vibration with respect to the synchronous reference, are identified. The first measurement results shown are related to asynchronous vibrations of a steam turbine last stage blade row due to an instability. The second results are instead transient synchronous vibrations when passing a blade row resonance during a run up of the steam turbine. It is further shown how synchronous vibrations, although non stationary, allowed to identify damping and excitation amplitudes by means of an original approach based on modal analysis. | Blade Vibration Measurements and Excitation Force Evaluation | 10.1007/978-3-319-06590-8_6 |
2015-01-01 | In the cardiovascular interventional operation, the surgeon steers the tip of a long-thin guidewire to reach the clinical targets while traveling through the inner of blood vessels, and performs a wide range of minimally invasive procedures. However, real-time simulating the physical deformation behaviours of guidewire caused by a large areas of frictional contact between guidewire and vasculature during insertion is a challenge task. From the microscopic view, this paper built a novel multi-frictional contact dynamics model based on flexible multi-body system to address the multi-frictional interaction between them. In the model, guidewire and vascular formed a flexible multi-body system and the process of contact and collision could be divided into three stages, including contact detection, contact handling and separation. In the first stage, a continuous collision detection algorithm based on an adaptive layer was proposed to obtain a set of “point-surface” contact pairs quickly. After confirming the contact areas, a multi-frictional contact dynamics algorithm based on nonlinear equivalent spring damping was put forward. In the normal direction, nonlinear spring damping model was used to compute the spring restoring force and nonlinear damping force. In the tangential direction, sliding friction, static friction and rolling friction were calculated during the collision between two bodies by coulomb friction model. Finally, all frictional forces in the contact areas were added to the physical models of guidewire for further simulating various non-linear deformation behaviors. The experimental results show that this algorithm is feasible and could simulate the multi-frictional interaction between guidewire and blood vessles very well with real-time performance. | Modeling and Simulation of Multi-frictional Interaction Between Guidewire and Vasculature | 10.1007/978-3-319-21963-9_48 |
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