Why are engine blocks so robust apart from containing high pressure?

Lately, I've been pondering why some engine blocks are so bulky, I always thought intuitively it was because they had to last a long time whilst containing thousands of combustion cycles but the more, I look into the reality of engine design that understanding doesn't always hold up to the design of an engine. It seems cylinder walls have a set thickness which makes pretty good sense, then there is a water-jacket chamber for coolant which again, makes sense but then there is an outer shell of material that is sometimes even thicker than the cylinder walls themselves. This is where I become confused (An example image below) Surely, this outer shell doesn't need to be as thick as it is. In my mind all it's doing is containing a pressurized coolant which can't amount to more pressure than the combustion of the engine itself. So why is it sometimes as thick as the cylinder wall?

mechanical-engineering structural-engineering structural-analysis automotive-engineering vibration

If you were going to turn left 90 degrees, without turning the wheels, then you wind up dragging the wheels sideways while you turn. 16 seconds into this video shows exactly what I'm talking about . So every time you try to back out of your driveway, or a parking spot, or turn into a parking spot, or turn anywhere for any reason, you're going to lay down rubber because the tires are rotating quickly while remaining nearly stationary as you turn. Again, look at the wheel slip in the video I linked. You'd be hard pressed to find "four...

You want to let air into the pipe when you switch the pump off, without letting water out. Here's a few ways to do this. Make a pinhole in the highest point of the pipe. You will lose a bit of water this way, but if it is above the tank, the water will drip back in (provided it doesn't spray too far.) You could even put it just under the tank lid. Install a tee and riser at the highest point of the pipe. this will need to be high enough to avoid the pump pressure pumping water out...

Actually, handlebars and steering wheels are less similar than you might think. When a two-wheeled vehicle is moving fast enough to balance, the front wheel is never turned more than a few degrees. The primary mechanism for steering is leaning the vehicle, not turning the front wheel. For example, to turn right, you actually tug briefly on the left side of the handlebar. This causes the wheels to track to the left of the center of mass, which in turn causes the bike to lean to the right. This lean is what causes the direction to change, while maintaining balance...

If you consider only the static forces then indeed the thickness might seem over-engineered. However, engine blocks are not statically loaded. They operate in the range of a few hundred to a few thousand rpm (Revolution Per Minute), so there are dynamic considerations here. Fatigue When materials are subjected to cyclic loading they exhibit a reduction in the allowable stresses. See below for an example: In general, BCC (body-centered cubic) materials (like steel) show a marked drop in strength (close to 50% or more depending on the steel). For these material there is stress (called the endurance limit), for which...


Why doesn't a lightning strike destroy the lightning rod?

Lightning strikes have been known to cause massive amounts of damage . The stats on a lightning bolt are: current levels sometimes in excess of 400 kA, temperatures to 50,000 degrees F., and speeds approaching one third the speed of light These are massive numbers, but lightning protection systems are designed to draw the lightning away from the building or structure that they are protecting. Lightning protection systems can be simply thought of as lightning rods connected to the ground via cabling (downconductor). The NOAA specification for lightning protection requires that lightning rods be at least 0.5in (13mm) in diameter. The downconductor is a similar size copper cable ( 4/0 AWG or 12mm ). The allowable amperage for this type of wire is only about 250A for constant current. I realize that this is more of a heat limit rather than a instantaneous current capacity limit. From this paper on lightning protection (page 28): Positive feedback on the operation of a lightning protection system is seldom documented and most often not even noticed. Only in some rare cases can it be documented that a lightning protection system has been struck if it works properly and there is no damage. There is sometimes evidence at the strike termination point which can be noted during a careful inspection, but it is seldom cost effective for the owner of a lightning protection system to obtain the expertise necessary to conduct such a careful inspection. How can a seemingly small 0.5in (13mm) piece of metal handle a lightning strike with little or no visible damage much less without being completely destroyed?

As it happens, I just recently went through that calculation myself for a different site. Given the following facts from a quick web search, it isn't difficult to work out the numbers. The maximum efficiency of a (large) windmill is about 40%. The density of air is 1.225 kg/m 3 You need about 50 mW (10 mA at 5V) to light up an LED First, we'll need about 50 mW / 0.40 = 125 mW of air power flowing through the windmill to create the electricity we need (ignoring other factors such as the actual efficiency of a small windmill...

The loops are known as expansion loops. They need to be placed in pipelines to enable the pipelines to contend with thermal expansion and contraction and other forces that can affect the pipeline. They are typically placed in gas pipelines, irrespective of when the gas is hot or cold - natural gas or steam. The following quote is from Pipeline Design . It's near the end of the page under Pipe Expansion and Supports Steel piping systems are subject to movement because of thermal expansion/contraction and mechanical forces. Piping systems subjected to temperature changes greater than 50°F or temperature changes...

If I model this as a simply supported beam having load at mid span [...] I suspect that this is where your analysis went awry. First off, you should always model bridges with distributed loads, not a single concentrated load at midspan. The most significant load on a bridge will almost always be its own self-weight; load-trains are heavy but, well, so are bridges. Secondly, I assume you're thinking of the bridge like this: Indeed, we can see here that the bending moment is greater at midspan. However, that's not the bridge we're looking at, it's missing the cantilevers! So...

The current limit specification for a wire is limited by the heat that current will produce, and how much heat the wire can dissipate before getting too hot. "Too hot" depends on the circumstances. You will see higher current ratings for the same type of wire in chassis wiring applications than the electrical code allows for home installations, for example. This is mostly due to how hot too hot is. The ultimate limit for extreme applications is that the conductor not melt. Temperatures anywhere near that would be unsafe running along wooden supports inside a wall in a house. As...


Why are rear wheels not placed at the extreme rear of a bus?

In some cars, I have noticed the rear wheels are located at the extreme rear of the vehicle. However, I have noticed that the rear wheels of buses are always located about 1/4th of the way forward from the rear. What is the reason for this?

The loops are known as expansion loops. They need to be placed in pipelines to enable the pipelines to contend with thermal expansion and contraction and other forces that can affect the pipeline. They are typically placed in gas pipelines, irrespective of when the gas is hot or cold - natural gas or steam. The following quote is from Pipeline Design . It's near the end of the page under Pipe Expansion and Supports Steel piping systems are subject to movement because of thermal expansion/contraction and mechanical forces. Piping systems subjected to temperature changes greater than 50°F or temperature changes...

To slightly generalize I'll reform the question slightly. A ridged 2-D body (car) has a line $l$ that moves with it. The car can be linearly transformed as long as the instantaneous center of rotation lies along $l$ at least distance $R$ away from a point $c$ that also moves with the car. In this case point $c$ lies in the center of the rear axle and $l$ lies on the rear axle. Now imagine the car's domain is limited to a quarter plane with edges $A$ and $B$. It initially is placed against $A$, far from $B$ with $l$...

Some ideas: Wheel Load Distribution : The load is greater on the rear wheels providing the power; more force on the front ones bring no benefit and would provide less traction. Better manoeuvrability from having a shorter wheelbase. Better Ground Clearance in some conditions, especially for bumps and or up a increasing slope for instance. Better Driving : The front wheels now turn around a point closer to the C.G. than with the rear wheels. Not good with vehicle dynamics but this appears better than the rear end 'trailing' behind. Structural : As some people have pointed out, it's better...

It is more efficient to transmit DC using about the same infrastructure. This is because of several effects: Skin effect experienced with AC. There is no skin effect with DC. Higher voltage allowed with DC for the same transmission lines. The lines have to withstand the peak voltage. With AC, that is 1.4 times higher than the RMS. With DC, the RMS and peak voltages are the same. However, the power transmitted is the current times the RMS, not peak, voltage. No radiation loss with DC. Long transmission lines act as antennas and do radiate some power. That can only...


Why would you launch a large ship by dropping it sideways?

I'm referring to the process shown in this video: https://youtu.be/Quyr5R1Rbfw?t=20 Or this image from Wikipedia: In it, a large warship is launched into the water by essentially dropping it sideways down some ramps and off of a pier. The ship rolls hard to one side, and then oscillates back to the other, making the process seem like a fairly risky one. For instance, if it rolls back towards the pier too aggressively it might strike the structure and cause damage both to the pier and the shiny new warship. Or if it rolls too far on the initial drop, the ship might capsize. So my question is, what are the advantages of launching a large ship sideways like this, as opposed to, say, dropping or gently lowering it vertically into the water?

mechanical-engineering structural-engineering safety naval-engineering ships

Some ideas: Wheel Load Distribution : The load is greater on the rear wheels providing the power; more force on the front ones bring no benefit and would provide less traction. Better manoeuvrability from having a shorter wheelbase. Better Ground Clearance in some conditions, especially for bumps and or up a increasing slope for instance. Better Driving : The front wheels now turn around a point closer to the C.G. than with the rear wheels. Not good with vehicle dynamics but this appears better than the rear end 'trailing' behind. Structural : As some people have pointed out, it's better...

I think you are talking about roundabouts, not traffic circles. It is baffling to those of us in the UK that Americans think roundabouts are a new idea. In the UK we have so many variants, from mini-roundabouts all the way up to full motorway junctions (a giant roundabout above or below the motorway). So do roundabouts take up more space? Not necessarily, this is a mini roundabout: It's nothing more than a slightly domed area of paint on the road, no lights are necessary, you can actually drive straight over the top of it rather than around it, its...

I suspect that the answer to this is that, ultimately the gear ratio comes from the ratio of diameters of the gears rather than the number of teeth, although in most circumstances practicality dictates that they are proportional. Say you have a 10 tooth cog and a 40 tooth chainwheel. It's fairly simple to imagine that you could remove every other tooth from the 40 tooth wheel while keeping the diameter the same and maintain exactly the same gear ratio. Similarly you could have a completely gearless wheel (putting aside issues of slippage) driving a chain which drove a geared...

A specific reason for doing this is simply when there isn't enough room to do a bow or stern first launch. This is often the case when a ship or boat is built in a yard on a river or canal either because the hull is especially long or the channel it is being launched into is narrow. There is also the consideration that a sideways launch can be done from any quay that will take the weight but a bow first launch requires a specially constructed slipway. There is also the consideration that if you go in sideways the...


I have assembled a small DIY drip-irrigation system for my terrace garden. Please have a look at the attached image. I switch on a small pump to start the drip-irrigation system and then switch it off. But even after that, the water keeps flowing through the system and stops only when I physically lift the pump out of water. How can I stop this water flow without requiring any physical action? Please note that I plan to automate the switch-on/off of the pump using a timer so that it functions without requiring my physical presence. ======================================================================== I tried the suggestion of "Making a pinhole in the highest point of the pipe." It worked like a charm and solved the issue I was facing. Completely loved it, more so, because it does not involve procuring new stuff. I also like the option of using a solenoid-valve, but have not tried it yet. Will use it when I install such a system again where the tank is at a considerably higher place than the plants. Thank you everyone who took the effort to write an answer, and that too with detailed explanations.

As other have pointed out, the main utility is to allow easier cleaning of the tank cars from sediment (solid precipitates). Usually, there is a drain in the lowest point. The reason that it is in the middle is that in this way, you can allow double the incline compared to if you had the drain at one of the ends for the same height. For example, if the allowed height difference is about 15 cm, and about 15 m length, then if you had the drain in: the edge, the angle would be $\arctan\left(\frac{0.15}{15}\right)=0.57^\circ$ or 1%. the middle ,...

Electricity production optimization is a very complex subject. It is also affected by many parameters , which I will try to outline below. TL;DR: Demand is constantly monitored and supply is constantly adjusted TL;DR 2: Lshaver's excellent post is a suggested reading after reading this, because it expands and explains what happens at timescales ranging from the micro-second to minutes timescales. Changes in energy demand during the day First of all, the energy demand during the day, week, month of year can change quite a lot. Below is a typical day in New England. Fluctuation in power energy consumption a...

I will expand on DKNguyen answer, because to my knowledge also the two reasons are: reduce contact/bearing stresses (having a significant effect on thin finishes live galvanisation) change the joint tightening characteristics (see joint diagram). reduce contact stresses on surfaces. The basic idea is that since contact stress is defined as: $$\sigma = \frac{F}{A}$$ Obviously the larger the area the less the stress. Also, like Nuclear Hoagie pointed out the area changes with a square law of the diameter. UPDATE 2 - Calculation for M6 bolt (thanks to BenC) *The question gathered enough interest for me to carry out a...


How do ball bearings not crack from a load concentrated on an infinitesimally small point?

How do ball bearings last? Most bearings in a standard hub (bottom of the image) are not actually taking a load. Only the single ball that happens to be at a particular location while spinning takes 100% of the load. If the bearings were cylindrical (top of the image) supporting a rolling plate, it would be slightly better, but not by much. Regardless of the load (in a bike hub), and even if it's just cyclist+bicycle, that the area is infinitesimally small would suggest that the stress skyrockets towards infinity. And that's before even talking of the higher loads in a car's bearings. How do ball bearings (in a bike hub) not crack from a load concentrated on an infinitesimally small point? This is a sequel question to a question I just asked on bicycles.SE about how much grease I should use after I overhaul bike hubs—whether I should put so little to keep the wheel spinning freely with minimal drag, or put so much that water ingress would be unlikely (the red areas in the image).

Nothing is rigid, the raceways and the ball in a ball-bearing are no exception. The contact area deflects and accommodates the ball in a small contact surface, not a point. Also, the balls take the load in groups. The digrams are from SKF ball-bearings. '

Some ideas: Wheel Load Distribution : The load is greater on the rear wheels providing the power; more force on the front ones bring no benefit and would provide less traction. Better manoeuvrability from having a shorter wheelbase. Better Ground Clearance in some conditions, especially for bumps and or up a increasing slope for instance. Better Driving : The front wheels now turn around a point closer to the C.G. than with the rear wheels. Not good with vehicle dynamics but this appears better than the rear end 'trailing' behind. Structural : As some people have pointed out, it's better...

If you consider only the static forces then indeed the thickness might seem over-engineered. However, engine blocks are not statically loaded. They operate in the range of a few hundred to a few thousand rpm (Revolution Per Minute), so there are dynamic considerations here. Fatigue When materials are subjected to cyclic loading they exhibit a reduction in the allowable stresses. See below for an example: In general, BCC (body-centered cubic) materials (like steel) show a marked drop in strength (close to 50% or more depending on the steel). For these material there is stress (called the endurance limit), for which...

I'm going to set aside the potential legal liability aspects of your question. In part because you didn't ask about them, but also because liability will vary based upon jurisdiction. Obviously, consult an attorney familiar with the relevant law. Ethically, I think you've done everything that you're obligated to do. You have contacted the customer and notified them of an unsafe situation or configuration of the product. And you have (strongly) advised them that they need to discontinue using the older product in the unsafe configuration. If the customer remains insistent about using the product in an unsafe manner, you...


What is the purpose of these "steps" in rivers?

I have seen a number of structures within rivers, which resemble steps, and which allow the water to cascade down them instead of flowing naturally down the course of the river. Example 1: River Avon in Bath Example 2: River Seine in Paris (from Les Miserables (2012)) What is the purpose of these structures?

The two photos in the post show the same structure: Pulteney Weir , downstream of Pulteney Bridge on the River Avon in Bath. The shot of the "Seine" in Les Miserables was filmed on location in Bath. Pulteney Weir was designed by architect Neville Conder , and built between 1968 and 1972. It's one component of the Bath Flood Prevention Scheme, which was carried out after the disastrous flood of December 1960 . The Bath in Time website has photos of the old weir (which descended in a single step) and of the new weir under construction ( 1968 ,...

It is a trench shield. It gets placed in a trench after the trench is dug to prevent workers from being hurt or killed in the event of a trench collapse. This picture from GMC trench shield shows a partially collapsed trench with a shield installed that would protect the workers installing the blue brute pipe.

Please note : I'm not a building designer by trade, but I have had to investigate related questions for other reasons. I'll let you in on a dirty secret about sanitation lines within buildings - The biggest concern is not about how fast things are flying, it's about maintaining air pressure and providing adequate ventilation. This guide presents a bit of a historical background to tall building design with respect to sanitation system design. This presentation provides some more recent perspective and goes into some of the research that is refining current building standards. The traditional viewpoint is that waste...


Why exactly does a washer help distribute the stress around a bolt?

Usually the reason for having a washer under a bolt head is stated to be that it helps to evenly distribute the stress to the clamped material surface. But why is this? I would understand if the washer was significantly larger than the bolt head. Then there would understandably be more surface area. But for a bolt like in the picture, the washer is only slightly larger than the bolt head, so why would it make much difference? EDIT: Thank you everyone for good discussion and answers! Didn't expect this to spark such a discussion.

mechanical-engineering civil-engineering stresses fasteners machine-elements

Car wheels have holes mostly due to weight and cost considerations. Each hole is a chunk of material that you aren't wasting and weighing down the wheel with. As another bonus, the holes help with cooling the brakes by allowing airflow between the inside and outside. The shape and size of the holes are calculated to have a minimal impact on the structural integrity of the wheel.

I would say that using a warm pressurized gas is not very feasible. Ratchet freak already mentioned how you can get much more volume out of heating water into steam than just heating up air until it's warmer. This touches on, but doesn't completely address an important factor about steam as power. Converting to steam includes a phase change from liquid to gas. This phase change actually acts as an additional storage of energy. You can draw this energy out of the steam later in the system (through a heat exchanger for example), converting it back into a liquid, which...

I will expand on DKNguyen answer, because to my knowledge also the two reasons are: reduce contact/bearing stresses (having a significant effect on thin finishes live galvanisation) change the joint tightening characteristics (see joint diagram). reduce contact stresses on surfaces. The basic idea is that since contact stress is defined as: $$\sigma = \frac{F}{A}$$ Obviously the larger the area the less the stress. Also, like Nuclear Hoagie pointed out the area changes with a square law of the diameter. UPDATE 2 - Calculation for M6 bolt (thanks to BenC) *The question gathered enough interest for me to carry out a...

Trees increase the turbulence of the air that reaches the turbines. That creates all sorts of uneven, rapidly-shifting loads on the blades and structure. That increases the maintenance costs, decreases availability, decreases the capacity factor, and decreases the life expectancy of the turbine. So, higher costs, lower revenue. One of the ways we measure the impact is the surface roughness coefficient $z_0$. Here are the figures from the book " Wind Energy - The Facts ". As you can see, forest and woodland has a much higher $z_0$ than open farmland - and that means higher turbulence. Open land also...


Recently I was thinking about home improvement, and one idea that is haunting me is that I could use some kind of refrigerator for gaming consoles and laptops. The obvious benefit is that it maintains a constant low temperature. Also, the doors usually can be closed firmly and it won't let dust come inside, so there isn't any need to disassemble and clean hardware. That is a good thing in long term. Despite it makes airflow less intensive, according to my understanding it should not be a problem, as all that is needed for hardware is cooled air, not new air. And whenever I get what I consider a good idea, I usually stop for a minute and ask myself a question "why doesn't this exist yet?". So there are definitely big-scale expensive enterprise servers which could possibly use the same approach to reduce maintenance effort, but that is not the case. So the disadvantages I can think of is that refrigerators are just not designed to cool a source of constant heat for a long period of time and (probably) will break quickly. Another problem that came to mind is that refrigerator boxes tend to generate condensate and it might be harmful for hardware. Am I correct with my assumptions, or is it not that crucial and are there in fact similar solutions?

Those are counterweights . They work exactly the same as those lead counterbalance weights on the wheels of your automobile. If they left those out, then those connecting rods and bearings would create an out-of-balance condition, and the wheels would vibrate at higher speeds. That could very well damage the wheels. But as a couple of others have nicely pointed out, the violent shaking could derail the train .

When a reactor is shut down the core produces much less heat, but they do still produce heat through a mechanism known as decay heat . The fact that the core is producing less heat means that the coolant temperature is going to drop, but how far that temperature drops depends on the decay heat generation rate. This in turn is based on operating history, or the power at which the plant was operating before shutdown. This can be large for commercial plants, because they typically operate at or very near capacity and the power companies bring coal or natural...

We do. It's just an up-sized (i.e. more powerful) version of a refrigerator known as an air conditioning unit. Essentially all server rooms and most spaces where PCs are located (speaking for the U.S., at least) are air conditioned. Server rooms almost universally have dedicated HVAC systems and they will indeed be designed to keep the room at a more-or-less constant temperature (and typically humidity, too.) Other answers mention water blocks, heat sinks, fans, etc., but those are mostly just used to move the heat from the CPUs and other such hot components to the ambient air in the server...


What is a reason that handlebars fit to a motorcycle and steering wheel fit to a car?

What is the reason that handlebars are installed on motorcycles and steering wheels are installed on cars? Notice that the way to use both handlebars and steering wheels are quite similar, but a steering wheel allows for much more rotation than a handle bar when you control a vehicle. Please give me a reason why a massive vehicle should use a steering wheel and a light weight vehicle should use a handlebar? The reason maybe involve scientific reasons, safety reasons or designing reasons.

The turbulence model can make a big difference in your simulation . There are many turbulence models around. It becomes a tough job to select one out of them. There is no perfect turbulence model. It all depends on several parameters like Reynold's number, whether the flow is separated, pressure gradients, boundary layer thikness and so on. In this answer, brief information about a few popular models is given along with pros and cons and potential applications. However, interested users can see this excellent NASA website and references therein to know more about turbulence modeling. A) ONE EQUATION MODEL: 1....

Actually, handlebars and steering wheels are less similar than you might think. When a two-wheeled vehicle is moving fast enough to balance, the front wheel is never turned more than a few degrees. The primary mechanism for steering is leaning the vehicle, not turning the front wheel. For example, to turn right, you actually tug briefly on the left side of the handlebar. This causes the wheels to track to the left of the center of mass, which in turn causes the bike to lean to the right. This lean is what causes the direction to change, while maintaining balance...

Biggest advantage is that when connecting to trailers, there are no bleeding issues. Imagine having to connect hydraulic pipes and remove the air bubbles... As for the amount of air - the compressor and receiving tanks are designed for normal use. However if you wish to accompany AC/DC with the air brakes you will run out. Disc brakes already exist in an airbrake version for trucks - came out over 10 years ago IIRC. But one big difference is that if you lose hydraulics on a car braking system then you lose stopping power (except for handbrake etc) but with...

My first thought is that it might be intended to be a wing nut driver of some sort, but those are usually hollow cylinders with slots for the wings. Ah ... sure enough, it's described as such in this Ebay ad :


If you have a look at the car's wheels, you'll notice that they have holes which can be of different forms (mostly circular or rectangular). Why do they have such holes? Doesn't that reduce the stiffness of the wheels?

At the beginning of my career (1979) as a design engineer at HP, the mechanical engineer created the part design and then rendered it in pencil on paper, and then transferred it onto sheets of vellum paper held onto a huge flat tilting table called a drafting board which had a precision sliding arm on it with which parallel and right angle lines could be drawn anywhere on the sheet. Clever graphical rules were applied to the resulting drawings which permitted auxiliary views of the part to be generated so it could be viewed from any desired angle, as an...

Car wheels have holes mostly due to weight and cost considerations. Each hole is a chunk of material that you aren't wasting and weighing down the wheel with. As another bonus, the holes help with cooling the brakes by allowing airflow between the inside and outside. The shape and size of the holes are calculated to have a minimal impact on the structural integrity of the wheel.

As with all good things, it depends. If you can assume that your supports are totally stiff and that the loading on the shelf will be approximately uniform, then you basically have the following structure: A rectangular cross-section (such as a plank) will behave equally under positive or negative bending moment, so your objective should be to balance both. To do so, you want your main span to be $2\sqrt2 \approx 2.83$ times the cantilevers. This is found by calculating the cantilever required to offset half of the bending moment due to a uniform load along a simply supported beam:...


What's wrong with transporting a refrigerator on its side?

I tried to deliver a refrigerator and the customer saw that the refrigerator was lying down in the truck instead of standing up. He refused to accept it, claiming that the compressor would be damaged by having it on its side. I tried to explain that that made no sense, but his friend came to me and also said the same thing. Is transporting a refrigerator on its side a problem? If so, why?

After the 2014 ICCT report revealed that these light-duty passenger diesel vehicles were emitting too much NOx and US regulators confronted VW about the results, VW did some testing and proposed a voluntary software recall to recalibrate the various emissions control devices on the affected vehicles. From the California Air Resources Board's (CARB's) in-use compliance letter to Volkwagen AG, 2015-09-18 , following that recall: To have a more controlled evaluation of the high NOx observed over the road, CARB developed a special dynamometer cycle which consisted of driving the Phase 2 portion of the FTP repeatedly. This special cycle revealed...

After referring to some good online resources such this , I know why we shouldn't transport it laying down. Compressor is filled with oil which is critical to its operation. In the normal upright position gravity keeps the oil in the compressor. When we lay the refrigerator flat, some of the oil can leave the compressor and go into the cooling lines. The oil is a thick viscous fluid and can clog the cooling lines thus hampering the refrigerator's ability to cool. Lack of oil in the compressor can also damage the compressor. If we must lay the fridge down,...

When a reactor is shut down the core produces much less heat, but they do still produce heat through a mechanism known as decay heat . The fact that the core is producing less heat means that the coolant temperature is going to drop, but how far that temperature drops depends on the decay heat generation rate. This in turn is based on operating history, or the power at which the plant was operating before shutdown. This can be large for commercial plants, because they typically operate at or very near capacity and the power companies bring coal or natural...


How does turning off electric appliances save energy

We all know if we use less electricity we save energy. But the energy we're getting is result of burning (not necessarily the literal meaning) the fuel. Even if we don't use that energy that fuel is gone forever. (Except saving money on bills) My questions Am I wrong in above statement? If yes then how does actually electricity production work so that we're able to save it? Do power plant (or associate agencies) constantly monitor demand and reduce the production of electricity on real time thus saving fuel (hence energy)?

power energy power-engineering fuel-economy

Electricity production optimization is a very complex subject. It is also affected by many parameters , which I will try to outline below. TL;DR: Demand is constantly monitored and supply is constantly adjusted TL;DR 2: Lshaver's excellent post is a suggested reading after reading this, because it expands and explains what happens at timescales ranging from the micro-second to minutes timescales. Changes in energy demand during the day First of all, the energy demand during the day, week, month of year can change quite a lot. Below is a typical day in New England. Fluctuation in power energy consumption a...

I will expand on DKNguyen answer, because to my knowledge also the two reasons are: reduce contact/bearing stresses (having a significant effect on thin finishes live galvanisation) change the joint tightening characteristics (see joint diagram). reduce contact stresses on surfaces. The basic idea is that since contact stress is defined as: $$\sigma = \frac{F}{A}$$ Obviously the larger the area the less the stress. Also, like Nuclear Hoagie pointed out the area changes with a square law of the diameter. UPDATE 2 - Calculation for M6 bolt (thanks to BenC) *The question gathered enough interest for me to carry out a...

After the 2014 ICCT report revealed that these light-duty passenger diesel vehicles were emitting too much NOx and US regulators confronted VW about the results, VW did some testing and proposed a voluntary software recall to recalibrate the various emissions control devices on the affected vehicles. From the California Air Resources Board's (CARB's) in-use compliance letter to Volkwagen AG, 2015-09-18 , following that recall: To have a more controlled evaluation of the high NOx observed over the road, CARB developed a special dynamometer cycle which consisted of driving the Phase 2 portion of the FTP repeatedly. This special cycle revealed...

At the beginning of my career (1979) as a design engineer at HP, the mechanical engineer created the part design and then rendered it in pencil on paper, and then transferred it onto sheets of vellum paper held onto a huge flat tilting table called a drafting board which had a precision sliding arm on it with which parallel and right angle lines could be drawn anywhere on the sheet. Clever graphical rules were applied to the resulting drawings which permitted auxiliary views of the part to be generated so it could be viewed from any desired angle, as an...


Why do wooden gate designs recommend a brace under compression instead of tension?

Looking at guides for building wooden frame gates I almost always find the following design recommendation: The idea is that the cross brace will distribute load from the top outside corner into the bottom of the hinge bracket. I understand this logic and am sure it works but wouldn't it be preferred to use a tension brace rather than a compression brace in this application? For example virtually every recommendation for a wire rope support shows the opposite: In this case the wire rope supports the far end under tension, but is there a reason a 2x4 couldn't also be used under tension rather than compression? Is the former design more effective for some reason? I realize that using the 2x4 for tension would require stronger joinery but it's certainly possible to secure it more than well enough to take the load. Additionally a common theme here seems to be that the load on the gate is too trivial to really care either way but I strongly disagree with that statement. Wooden gates almost never hold up to time, and we aren't talking decades here...most wooden gates will sag within 1-2 years. Wood is certainly a troublesome material but plenty of critical structures have been made from wood with proper engineering and have held up much longer than this. So maybe we should consider complicating things more? It's certainly cheaper and easier to use more complicated joinery/a 99 cent steel bracket and 2x4s than it is to fabricate an all steel gate frame. Are 2x4s just undersized to support a load like this or is it possible the bracing can make a difference?

The current limit specification for a wire is limited by the heat that current will produce, and how much heat the wire can dissipate before getting too hot. "Too hot" depends on the circumstances. You will see higher current ratings for the same type of wire in chassis wiring applications than the electrical code allows for home installations, for example. This is mostly due to how hot too hot is. The ultimate limit for extreme applications is that the conductor not melt. Temperatures anywhere near that would be unsafe running along wooden supports inside a wall in a house. As...

It is more efficient to transmit DC using about the same infrastructure. This is because of several effects: Skin effect experienced with AC. There is no skin effect with DC. Higher voltage allowed with DC for the same transmission lines. The lines have to withstand the peak voltage. With AC, that is 1.4 times higher than the RMS. With DC, the RMS and peak voltages are the same. However, the power transmitted is the current times the RMS, not peak, voltage. No radiation loss with DC. Long transmission lines act as antennas and do radiate some power. That can only...

The reason is simple: the load applied on the gate is pretty trivial, and the brace (be it a 2x4 or a wire) is mostly added for rigidity. Indeed, you could put that 2x4 in tension and it would work just as well (since the load is usually trivial, a 2x4 is probably 10x stronger than necessary in both tension and compression). However, as you mentioned, that would require more complex joinery, so... why bother? Obviously, when using a wire, it must be in tension, so you don't even have the choice. But with a 2x4, you can choose, so...


How does width and thickness affect the stiffness of steel plate?

I have a 2 mm thick steel plate which is 300 mm long and 30 mm wide, supported at either end. It supports a weight-bearing wheel that can roll along the plate. It currently supports the maximum weight that I expect it to support when the wheel is in the middle, but it flexes a little bit too much. Would making it wider help to support the weight and increase its stiffness, or do I need to make it thicker? Also is there a way to calculate how the stiffness will change with the thickness (or width if that would affect it)?

Short answer : make it thicker. Long answer : The moment of inertia affects the beam's ability to resist flexing. Use one of the many, free, online moment of inertia calculators (like this one ) to see how increasing the height of the beam will have an exponential effect on increasing the stiffness of the beam. And this site helps provide a pictorial view of the load(s) upon a beam depending upon differing configurations, such as where the supports are and where the load is applied. It also provides a calculator to determine the forces involved. Wikipedia has a decent...

The difference between the two equations The cavitation number is the ratio of the static pressure difference to the dynamic pressure difference. So, if you want to use the first equation, you would need to take the pressure using a Pitot tube to measure the total pressure, whereas if you want to use the second equation you will need to measure the freestream velocity, but I would recommend measuring it upstream rather than downstream because of possible effects of acceleration and boundary layer growth. Also, your $V$ should be $V_{in}$ such that it corresponds to the same location where $p_{in}$...

I suspect that the answer to this is that, ultimately the gear ratio comes from the ratio of diameters of the gears rather than the number of teeth, although in most circumstances practicality dictates that they are proportional. Say you have a 10 tooth cog and a 40 tooth chainwheel. It's fairly simple to imagine that you could remove every other tooth from the 40 tooth wheel while keeping the diameter the same and maintain exactly the same gear ratio. Similarly you could have a completely gearless wheel (putting aside issues of slippage) driving a chain which drove a geared...


How do engineers really use numerical simulation?

Disclaimer I'm an applied mathematician by training, not an engineer. My work research primarily focuses on creating new "methods" to solve different PDE's related to solid deformation (elasticity) and fluid mechanics. In this sense, i know how to solve a pde problem computationally. From my perspective, engineers use my work as "tools" to accomplish their work. However, due to my lack of education/experience in engineering, i admit i'm actually rather clueless on how numerical solutions to pde's are really used in an engineers actual practice. The primary source of my confusion is the following: I've been told that engineers never (or should never) conduct numerical simulations (e.g. finite element analysis, CFD, etc...) without knowing or having a good idea ahead of time what the simulation "should" look like. This helps engineers discriminate realistic results from questionable ones. However, i argue that if the engineer already knows what is supposed to happen in the simulation, then what's the point of simulation in the first place??? I've always assumed that simulations are needed for predictive purposes, which assumes ignorance of what is to come. That is, I think of a simulation as a stand-alone tool to predict the future when you don't know what to expect . What i'm looking for is a broader perspective into how/when/why engineers use numerical simulations like CFD and Finite Element Analysis, especially if good engineering practice dictates that you should already know what to expect when you're simulating?

Biggest advantage is that when connecting to trailers, there are no bleeding issues. Imagine having to connect hydraulic pipes and remove the air bubbles... As for the amount of air - the compressor and receiving tanks are designed for normal use. However if you wish to accompany AC/DC with the air brakes you will run out. Disc brakes already exist in an airbrake version for trucks - came out over 10 years ago IIRC. But one big difference is that if you lose hydraulics on a car braking system then you lose stopping power (except for handbrake etc) but with...

I have written mostly about CFD in this answer, however same points should also work for FEA or other simulation techniques. CFD is mostly used for design optimization and parametric study of the design. Following are a few examples showing how engineers use simulations Selection of a design : Read: A conceptual study of airfoil performance enhancement using CFD. This thesis shows use of CFD for selecting the best design out of a number of candidate designs. Engineers often go for simulations to select 'the one' out of many . Shape optimization using CFD : This paper gives an example...

The loops are known as expansion loops. They need to be placed in pipelines to enable the pipelines to contend with thermal expansion and contraction and other forces that can affect the pipeline. They are typically placed in gas pipelines, irrespective of when the gas is hot or cold - natural gas or steam. The following quote is from Pipeline Design . It's near the end of the page under Pipe Expansion and Supports Steel piping systems are subject to movement because of thermal expansion/contraction and mechanical forces. Piping systems subjected to temperature changes greater than 50°F or temperature changes...

Water meets the low compressibility requirement, but there are many other considerations in the design of a hydraulic system: Boiling point/vapor pressure: If the system warms up during operation, the fluid may boil, which results in high compressibility and thus decreased effectiveness of the hydraulic system. Hydraulic fluid has a higher boiling point than water to help combat this. Related to this is the concept of vapor pressure. Hydraulic systems often involve small orifices, which can cause cavitation (localized boiling). This cavitation has the same effects as boiling and can cause pitting damage to the components near the cavitated region....


What makes suspension bridges unsuitable for railways?

I recall reading in an old issue of Model Railroader an article about railroad bridges. In it, the author mentioned that you shouldn't have a model suspension bridge for a railroad track on your layout because no such arrangement would be prototypical. In his own words, "suspension bridges and trains don't mix." I realize that the author probably wasn't an engineer (at least in the sense of this site), but his remark did get me thinking. I am somewhat of a railroad buff, and I can't think of a suspension bridge for trains - the closest thing that comes to mind are the trolley tracks that were on the Brooklyn Bridge * . I understand that there wouldn't be many suspension bridges for trains, since other bridge types would be better suited (cheaper, easier to build, etc.) but why are they so rare? * Bear in mind, though, I live in the US, and am pretty unfamiliar with foreign railroad infrastructure.

There are a few main reasons why suspension bridges aren't used for railroads. The main reason is that suspension bridges are typically used where very long spans are needed. Trains are very heavy, especially when compared to lanes of highway traffic. This means that long spans require very strong support structures, which in the case of suspension bridges are cables and towers. The second reason goes along with the first; trains cause high dynamic loads as they move along the rail. This can increase the vertical loads by 30%. Third is that trains don't really have suspensions, especially freight trains....

Theoretically pontoon bridges with rope anchors keeping them to the bottom would work against wind and flow, overcoming the problem jhabbot mentioned in his answer (same as train length limit - stretching force). In practice these come with more problems of their own. They drift on water surface and as result, rise and fall with water waves. The larger the body of water they span, the higher the waves; at certain point in stormy weather the bridge would just launch the vehicles into the air. The anchoring isn't exactly simple if it's to withstand such forces. You could just as...

BS5950-1:2000 Clause 1.3.23 defines an H-section as having " an overall depth not greater than 1.2 times its overall width ", and Clause 1.3.25 defines an I section as having " an overall depth greater than 1.2 times its overall width ". Note that at exactly a ratio of 1.2, it would be an H section not an I section.


Why do cars turn by turning the front wheel?

Why do we design cars to turn by turning the front wheel? Wouldn't it better to keep all wheels straight and turn by rotating the wheels on one side of a car more then the wheels on the opposite side of the car, like tank tracks do? That way you can turn even if you are standing still. Why don't cars do this?

Note: This is specific to gasoline based engines. Assuming your car was produced after the ~1990's it is equipped with a Deceleration Fuel Cut-Off (DFCO) system which cuts the fuel flow to the engine when the gas pedal is not depressed and the car is in gear. In this case it is more fuel efficient to stay in gear because you are letting gravity run the engine instead of fuel. In addition, it saves wear on your brakes because the partial-vacuum created in the engine leads to engine-braking . In many states in the US it is actually required that...

If you were going to turn left 90 degrees, without turning the wheels, then you wind up dragging the wheels sideways while you turn. 16 seconds into this video shows exactly what I'm talking about . So every time you try to back out of your driveway, or a parking spot, or turn into a parking spot, or turn anywhere for any reason, you're going to lay down rubber because the tires are rotating quickly while remaining nearly stationary as you turn. Again, look at the wheel slip in the video I linked. You'd be hard pressed to find "four...

Please note : I'm not a building designer by trade, but I have had to investigate related questions for other reasons. I'll let you in on a dirty secret about sanitation lines within buildings - The biggest concern is not about how fast things are flying, it's about maintaining air pressure and providing adequate ventilation. This guide presents a bit of a historical background to tall building design with respect to sanitation system design. This presentation provides some more recent perspective and goes into some of the research that is refining current building standards. The traditional viewpoint is that waste...

After the 2014 ICCT report revealed that these light-duty passenger diesel vehicles were emitting too much NOx and US regulators confronted VW about the results, VW did some testing and proposed a voluntary software recall to recalibrate the various emissions control devices on the affected vehicles. From the California Air Resources Board's (CARB's) in-use compliance letter to Volkwagen AG, 2015-09-18 , following that recall: To have a more controlled evaluation of the high NOx observed over the road, CARB developed a special dynamometer cycle which consisted of driving the Phase 2 portion of the FTP repeatedly. This special cycle revealed...


Why does the Channel Tunnel enter the ground around 10 km from the coast?

I know that digging tunnels is always much more costly than building ways or train above ground. Why doesn't the Channel Tunnel start around the coastline? Why does it have an around 10 km long portion under land on the British side?

civil-engineering geotechnical-engineering rail tunnels

From the point of view of the driver of a car, impacting another car is about as bad as crashing against an ideal wall (a wall with zero deformation whatsoever). If there were a plane reflection between the two cars, then vs. Car would be exactly equal to vs. Wall (the contact points between both cars would all be on the same plane, due to reflection, so each car could be considered a wall for the other). But this plane reflection does not exist: What we have instead is a 2-fold rotational reflection . Let's say the left part of...

The picture, below, of the exaggerated long section of the Channel Tunnel was taken from Wikipedia . Full-sized image here . Some of the limiting factors for the Channel Tunnel are: Railways don't like steep gradients The tunnels comprising the Channel Tunnel were excavated using tunnel boring machines (TBMs). Like railways, they cannot tolerate steep gradients. The tunnel was excavated in chalk marl (green coloured material in the picture). This was due to its depth (not being too shallow and not being too deep) and its ability to be easily dug but also it would cause major support issues for...

If I model this as a simply supported beam having load at mid span [...] I suspect that this is where your analysis went awry. First off, you should always model bridges with distributed loads, not a single concentrated load at midspan. The most significant load on a bridge will almost always be its own self-weight; load-trains are heavy but, well, so are bridges. Secondly, I assume you're thinking of the bridge like this: Indeed, we can see here that the bending moment is greater at midspan. However, that's not the bridge we're looking at, it's missing the cantilevers! So...


Why would a train automatically derail if a signal is passed at danger?

In a recent incident in London Network Rail said an empty train had travelled past a red signal, which resulted in an automatic derailment. No one was injured. [link] The derailment has caused quite a bit of damage, and a lot of travel disruption along this track. My reading of the National Rail statement is that the derailment was a feature of the system, a response to the signal being passed at danger. While I'm sure it caused less damage than a train collision, it still seems dangerous and expensive. Things like train stops , to trigger the brakes exist, or one could imagine diverting the train into a sand trap. Why weren't options like these used instead of derailing?

When a reactor is shut down the core produces much less heat, but they do still produce heat through a mechanism known as decay heat . The fact that the core is producing less heat means that the coolant temperature is going to drop, but how far that temperature drops depends on the decay heat generation rate. This in turn is based on operating history, or the power at which the plant was operating before shutdown. This can be large for commercial plants, because they typically operate at or very near capacity and the power companies bring coal or natural...

Firstly, the incident happened as the train was leaving a siding passing a shunt signal. These provide less authorisation than a normal signal does, even when they are not at danger (the train can permit as far as the line is clear or the next signal , there is no guarantee the track ahead is clear). Now, in the UK, there are four train protection systems: AWS, TPWS, ATP, and ETCS. However, these are all primarily designed for trains on normal running lines, rather than those on sidings. I'll examine each of these in turn insofar as they protect signals:...

If the receiver does not detect the sub-carrier for the "colour burst" signal which is transmitted during the horizontal blanking period the receiver switches on the "colour-killer" circuit so the set reverts to black and white mode. The colour-burst signal - 8 to 10 cycles of 3.85 MHz - is unlikely to be generated by random noise. Figure 1. The colorburst signal is transmitted on the "back porch" between the horizontal blanking pulse and the start of that line's luminance signal. The colorburst signal is used to synchronise the QAM (quadrature amplitude modulation) oscillator which can hold its frequency accurately...


Does a roadway bridge experience more load when vehicles are parked or when they are moving?

Bridges are designed for the loads that come from the vehicles that are expected to cross them. This includes the weight the vehicle and any dynamic loads that may be introduced from movement of the vehicle. Dynamic loads may be from "bouncing" or from hitting a joint or pothole. Initially it would seem obvious that more load is applied to a bridge while the vehicles are in motion (weight of vehicle plus dynamic load). The dynamic loads are proportional to the travelling speed of the vehicles, but as vehicles go faster, they typically are spaced farther apart. When vehicles are stopped, they typically are much more closely spaced than when they are moving. Can there be a situation where more load is on a bridge because of closely spaced parked vehicles than from moving vehicles that are farther apart? Are these two situations covered in bridge design?

This is to make sure they know what the foundation is made of. For all they knew there may have been an old tunnel underneath that would have collapsed when the new building is put on top. London is built on top of an old marsh, this type of soil is very prone to sinking and uneven settling, digging down and reinforcing the foundation alleviates that. It also ensures the foundation is uniform under the building to avoid a new tower of Pisa. Given the age of the city it may have been to scour the land for potential archaeological...

Parked vehicles vs moving vehicles Closely spaced parked (or slow moving) vehicles are definitely more onerous, as stated on page 89, Appendix 2.A, Clause 2.A.1 of the South African bridge design code TMH7 : It is generally accepted and can readily be shown that except in the very small span range, the worst loading condition occurs under congested (bumper to bumper) conditions caused by a traffic blockage and that the dispersion of traffic at speed caused by increased vehicular inter-spacing, more than off-sets the effects of impact. However, this is only true by inspection for an unlimited number of vehicles...


What material is used to hold molten iron in a furnace?

When iron is melted, I guess it has to be transported and contained. I think the container in which it is has to be able to withstand higher temperatures than what you want to melt. According to this webiste , "Iron, Wrought" has a melting temperature of 1482 - 1593 °C. There are a couple of other metals which have higher melting points (e.g. Wolfram (tungsten) with over 3400 °C), but all I can think of are much more expensive. So what material is the oven / "bottle" / "basin" (or however you call it) made of? (Side question: Iron has been melted for quite a while now. I guess this has changed over the years. Of which materials was it before?)

Please note : I'm not a building designer by trade, but I have had to investigate related questions for other reasons. I'll let you in on a dirty secret about sanitation lines within buildings - The biggest concern is not about how fast things are flying, it's about maintaining air pressure and providing adequate ventilation. This guide presents a bit of a historical background to tall building design with respect to sanitation system design. This presentation provides some more recent perspective and goes into some of the research that is refining current building standards. The traditional viewpoint is that waste...

Summary Crucibles are lined with refractory materials. Steel processing makes use of graphite or a combination of chromite and magnesite for direct contact with the melt. Cast iron processing often uses engineered clays, also known as alumina-magnesia-silica mixtures. Graphite is harder to form than clay-type refractories. To be suitable as a refractory, a material must meet a number of property requirements to be both economical and safe. Refractory Materials As you noted, iron has a high-end melting point of about 1,540 °C on the far left side of the $\textrm{Fe-C}$ phase diagram below, in the form of pure iron. There...

This will at least depend on the: Rate of Cooling Magnetic field strength Exact composition The magnetic field will alter the microstructure as you can read in, for example, Yudong Zhang, Nathalie Gey, Changshu He, Xiang Zhao, Liang Zuo, Claude Esling, High temperature tempering behaviors in a structural steel under high magnetic field, Acta Materialia, Volume 52, Issue 12, 12 July 2004, Pages 3467-3474, ISSN 1359-6454, http://dx.doi.org/10.1016/j.actamat.2004.03.044 . G.M. Ludtka, R.A. Jaramillo, R.A. Kisner, D.M. Nicholson, J.B. Wilgen, G. Mackiewicz-Ludtka, P.N. Kalu, In situ evidence of enhanced transformation kinetics in a medium carbon steel due to a high magnetic field,...


Why does it take so long to restart a nuclear power plant?

I have heard a couple of times that an operating nuclear power plant which was shut down (non-emergency; e.g. for a regular check) needs over 24 hours (up to 72 hours?) to get up running again. Why does it take that long?

The loops are known as expansion loops. They need to be placed in pipelines to enable the pipelines to contend with thermal expansion and contraction and other forces that can affect the pipeline. They are typically placed in gas pipelines, irrespective of when the gas is hot or cold - natural gas or steam. The following quote is from Pipeline Design . It's near the end of the page under Pipe Expansion and Supports Steel piping systems are subject to movement because of thermal expansion/contraction and mechanical forces. Piping systems subjected to temperature changes greater than 50°F or temperature changes...

As other have pointed out, the main utility is to allow easier cleaning of the tank cars from sediment (solid precipitates). Usually, there is a drain in the lowest point. The reason that it is in the middle is that in this way, you can allow double the incline compared to if you had the drain at one of the ends for the same height. For example, if the allowed height difference is about 15 cm, and about 15 m length, then if you had the drain in: the edge, the angle would be $\arctan\left(\frac{0.15}{15}\right)=0.57^\circ$ or 1%. the middle ,...


Windmills in empty fields. Why no trees?

I have noticed that windmills are generally built in empty fields with no trees around, and I've been wondering why... A windmill is generally way taller than trees and I can imagine that trees don't actually affect the flow (see picture). But is this the reason why there is nothing around or is there something else that makes them waste so much space around? And is the velocity profile from the first figure a realistic one? If I search for the theory of external convection, the velocity profile looks like this for flow over a plateau: In the second case, wouldn't the velocity be higher if there is an obstacle? Or is it because the obstacle is a porous medium that damps the flow? And lastly, is the velocity profile at earth level looking like that? Is there really an origin to it, or is it fully turbulent all the way?

mechanical-engineering fluid-mechanics thermodynamics heat-transfer

Trees increase the turbulence of the air that reaches the turbines. That creates all sorts of uneven, rapidly-shifting loads on the blades and structure. That increases the maintenance costs, decreases availability, decreases the capacity factor, and decreases the life expectancy of the turbine. So, higher costs, lower revenue. One of the ways we measure the impact is the surface roughness coefficient $z_0$. Here are the figures from the book " Wind Energy - The Facts ". As you can see, forest and woodland has a much higher $z_0$ than open farmland - and that means higher turbulence. Open land also...

After the 2014 ICCT report revealed that these light-duty passenger diesel vehicles were emitting too much NOx and US regulators confronted VW about the results, VW did some testing and proposed a voluntary software recall to recalibrate the various emissions control devices on the affected vehicles. From the California Air Resources Board's (CARB's) in-use compliance letter to Volkwagen AG, 2015-09-18 , following that recall: To have a more controlled evaluation of the high NOx observed over the road, CARB developed a special dynamometer cycle which consisted of driving the Phase 2 portion of the FTP repeatedly. This special cycle revealed...

For long freight trains and those that will be climbing to stations at higher altitudes, an extra or two locomotives are attached to the front. I've always wondered why. As usual there are multiple issues. Most important is landscape. If more power than a single locomotive can provide is not needed for the whole trip, but only a short stretch, like climbing or crossing a mountain range, then it would be a huge waste of resources to attach them the whole trip. For example, take a 10 hour trip time, where all, except for a 1 hour stretch, can be...

Those are counterweights . They work exactly the same as those lead counterbalance weights on the wheels of your automobile. If they left those out, then those connecting rods and bearings would create an out-of-balance condition, and the wheels would vibrate at higher speeds. That could very well damage the wheels. But as a couple of others have nicely pointed out, the violent shaking could derail the train .


What are the engineering principles for a train to get electricity from the railway

How many general methods are there for transferring electricity from the railway to a train? I could see that some trains are connected by a pantograph and some have a third rail. Are there any other methods? What is the general engineering principle behind each? What are the basic differences (pros and cons) of each method? I was looking for these questions but could not find a good review. If anyone has a reference or could answer them kindly do. Also, is it possible to build a small model of such a system and scale it up? I am not talking about a commercial model train. I am aiming at self-designing the same engineering principals and demonstrating them on a scalable small model. If so, I would be happy to have a nice tutorial reference. I am focusing on Electric multiple units (EMU) .

The current limit specification for a wire is limited by the heat that current will produce, and how much heat the wire can dissipate before getting too hot. "Too hot" depends on the circumstances. You will see higher current ratings for the same type of wire in chassis wiring applications than the electrical code allows for home installations, for example. This is mostly due to how hot too hot is. The ultimate limit for extreme applications is that the conductor not melt. Temperatures anywhere near that would be unsafe running along wooden supports inside a wall in a house. As...

Pantograph and third rail are pretty much it. Engineering principles: both have a conducting surface on the train (moving) in contact with the stationary rail/wire, in both cases you need a material that's resilient and conductive. The contact strip is a wear material . Differences: overhead catenary wires are flexible and will move around when a train drives underneath them. At high speeds, the pantograph can set up waves in the catenary wire, if these waves aren't damped sufficiently, the pantograph will start bouncing. third rail is limited to low voltages to reduce the risk of arcing between the rails....

If the receiver does not detect the sub-carrier for the "colour burst" signal which is transmitted during the horizontal blanking period the receiver switches on the "colour-killer" circuit so the set reverts to black and white mode. The colour-burst signal - 8 to 10 cycles of 3.85 MHz - is unlikely to be generated by random noise. Figure 1. The colorburst signal is transmitted on the "back porch" between the horizontal blanking pulse and the start of that line's luminance signal. The colorburst signal is used to synchronise the QAM (quadrature amplitude modulation) oscillator which can hold its frequency accurately...


Can we change steel properties by application of magnetic field while quenching?

Austenite is non magnetic while $\alpha$-ferrite and pearlite are magnetic . ( Magnetic properties of pearlite vary as a function of carbon content ) If a strong magnetic field is applied in a particular direction while the steel is being quenched (rather, austenite is being quenched!), would the grain structure change? Is it possible to get superior grain structure and hence tougher steel by application of cyclic magnetic field? My speculation is that, at the eutectoid point while quenching the steel, as low carbon zone of pearlite has more permeability, that zone should align itself to the strong magnetic field by pushing the carbon in orthogonal direction, so grain boundaries should take a different shape. Will it actually happen?

steel process-engineering materials metallurgy magnets

This will at least depend on the: Rate of Cooling Magnetic field strength Exact composition The magnetic field will alter the microstructure as you can read in, for example, Yudong Zhang, Nathalie Gey, Changshu He, Xiang Zhao, Liang Zuo, Claude Esling, High temperature tempering behaviors in a structural steel under high magnetic field, Acta Materialia, Volume 52, Issue 12, 12 July 2004, Pages 3467-3474, ISSN 1359-6454, http://dx.doi.org/10.1016/j.actamat.2004.03.044 . G.M. Ludtka, R.A. Jaramillo, R.A. Kisner, D.M. Nicholson, J.B. Wilgen, G. Mackiewicz-Ludtka, P.N. Kalu, In situ evidence of enhanced transformation kinetics in a medium carbon steel due to a high magnetic field,...

I'm going to set aside the potential legal liability aspects of your question. In part because you didn't ask about them, but also because liability will vary based upon jurisdiction. Obviously, consult an attorney familiar with the relevant law. Ethically, I think you've done everything that you're obligated to do. You have contacted the customer and notified them of an unsafe situation or configuration of the product. And you have (strongly) advised them that they need to discontinue using the older product in the unsafe configuration. If the customer remains insistent about using the product in an unsafe manner, you...

This is an admittedly North American response. MGT In the US, how much traffic goes over a given track in a year is measured in Million Gross Tons (MGT) e.g. 1 MGT = 2 000 000 000 lbs [spaces instead of commas to be world-friendly]. This is a measure of the total weight of cargo and vehicles but not necessarily the number of individual trains. Rail Life The life of a typical railroad rail is between 1300 MGT and 380 MGT depending on if the rail is on a straight (tangent) track or in a curve. There is more friction...

Short answer : make it thicker. Long answer : The moment of inertia affects the beam's ability to resist flexing. Use one of the many, free, online moment of inertia calculators (like this one ) to see how increasing the height of the beam will have an exponential effect on increasing the stiffness of the beam. And this site helps provide a pictorial view of the load(s) upon a beam depending upon differing configurations, such as where the supports are and where the load is applied. It also provides a calculator to determine the forces involved. Wikipedia has a decent...


How does a traffic light sense the proximity of vehicles?

Some traffic lights don't operate periodically but instead detect when a car is close by and then turns green. I have heard that they use a magnetic sensor embedded in the road to sense cars as they come near. Is this correct? Do they use other means as well?

I can understand your concern. This is going to be difficult for two reasons: Finding out the agency that is responsible for the maintenance may be next to impossible for a layperson. Note that I said "maintenance", because this might be a different entity than the owner due to agreements. Due to the number of complaints that the public agencies receive, it is very likely that your comment will get ignored. This often has nothing to do with whether or not your concern has merit. Public vs. Private Public agencies will be the easiest to contact. In a city, calling...

If you consider only the static forces then indeed the thickness might seem over-engineered. However, engine blocks are not statically loaded. They operate in the range of a few hundred to a few thousand rpm (Revolution Per Minute), so there are dynamic considerations here. Fatigue When materials are subjected to cyclic loading they exhibit a reduction in the allowable stresses. See below for an example: In general, BCC (body-centered cubic) materials (like steel) show a marked drop in strength (close to 50% or more depending on the steel). For these material there is stress (called the endurance limit), for which...

As others stated before, induction loops are the primary - most reliable method: the coils (usually just several loops of wire) embedded in the road; fed given frequency from a generator, in presence of metal the frequency of the LC circuit changes and the sensor circuitry detects the change of frequency, producing a presence signal. In some cases these may fail to detect bicycles, but they are by far most common as they aren't affected by weather (or more precisely, the detection circuit tunes in to slow changes of frequency caused by weather) and are immune to accidental false positives....

The current limit specification for a wire is limited by the heat that current will produce, and how much heat the wire can dissipate before getting too hot. "Too hot" depends on the circumstances. You will see higher current ratings for the same type of wire in chassis wiring applications than the electrical code allows for home installations, for example. This is mostly due to how hot too hot is. The ultimate limit for extreme applications is that the conductor not melt. Temperatures anywhere near that would be unsafe running along wooden supports inside a wall in a house. As...


How many train passes can railway tracks endure?

I know that the rubber on car and truck tires wear, and the road concrete wears out. I wondered: While steel is hard and elastic, it still causes friction (interaction between molecules) and therefore abrasion. Let's say we have on average 20-30 wagons with four axles with a full load of 50-60 tons on each wagon and a traction vehicle. How many train passes can a railway rail endure before it must be replaced? What is the equivalent time frame in which this number of passes is achieved on average?

civil-engineering materials rail transportation

This is an admittedly North American response. MGT In the US, how much traffic goes over a given track in a year is measured in Million Gross Tons (MGT) e.g. 1 MGT = 2 000 000 000 lbs [spaces instead of commas to be world-friendly]. This is a measure of the total weight of cargo and vehicles but not necessarily the number of individual trains. Rail Life The life of a typical railroad rail is between 1300 MGT and 380 MGT depending on if the rail is on a straight (tangent) track or in a curve. There is more friction...

Biggest advantage is that when connecting to trailers, there are no bleeding issues. Imagine having to connect hydraulic pipes and remove the air bubbles... As for the amount of air - the compressor and receiving tanks are designed for normal use. However if you wish to accompany AC/DC with the air brakes you will run out. Disc brakes already exist in an airbrake version for trucks - came out over 10 years ago IIRC. But one big difference is that if you lose hydraulics on a car braking system then you lose stopping power (except for handbrake etc) but with...

The problem is that the formula $P=I\ V$ is correct when dealing with DC circuits or with AC circuits where there is no lag between the current and the voltage. When dealing with realistic AC circuits, the power is given by $$ P=I\ V\ \cos(\phi), $$ where $\phi$ is the phase difference between the current and the voltage. The unit kVA is a unit of what is called 'apparent power' whereas W is a unit of 'real power'. Apparent power is the maximum possible power attainable when the current and voltage are in phase and real power is the actual...

It is a trench shield. It gets placed in a trench after the trench is dug to prevent workers from being hurt or killed in the event of a trench collapse. This picture from GMC trench shield shows a partially collapsed trench with a shield installed that would protect the workers installing the blue brute pipe.


How should I position two shelf supports for the best distribution of load?

I'd like to mount a shelf on the wall. I have two shelf supports to do so, like this: Relative to the shelf, where do I place the (blue) supports to achieve the best distribution of load?

Please note : I'm not a building designer by trade, but I have had to investigate related questions for other reasons. I'll let you in on a dirty secret about sanitation lines within buildings - The biggest concern is not about how fast things are flying, it's about maintaining air pressure and providing adequate ventilation. This guide presents a bit of a historical background to tall building design with respect to sanitation system design. This presentation provides some more recent perspective and goes into some of the research that is refining current building standards. The traditional viewpoint is that waste...

As with all good things, it depends. If you can assume that your supports are totally stiff and that the loading on the shelf will be approximately uniform, then you basically have the following structure: A rectangular cross-section (such as a plank) will behave equally under positive or negative bending moment, so your objective should be to balance both. To do so, you want your main span to be $2\sqrt2 \approx 2.83$ times the cantilevers. This is found by calculating the cantilever required to offset half of the bending moment due to a uniform load along a simply supported beam:...

The torsion constant $J_T$ relates the angle of twist to applied torque via the equation: $$ \phi = \frac{TL}{J_T G} $$ where $T$ is the applied torque, $L$ is the length of the member, $G$ is modulus of elasticity in shear, and $J_T$ is the torsional constant. The polar moment of inertia on the other hand, is a measure of the resistance of a cross section to torsion with invariant cross section and no significant warping . The case of a circular rod under torsion is special because of circular symmetry, which means that it does not warp and it's...


Just by taking a train ride across my home city I can see truss bridges like the one in above picture everywhere. There are numerous variations, but the most common design seems to be this. But why are they built specifically this way? I can intuitively kind-of see why such a design probably is strong, but is there any kind of in-depth reason? I would be interested to know the answer as much from the physics side of things as possible. Googling didn't help much; I could find information on the different variations and many examples, but none really covered what is it about this design specifically that makes it so popular.

Those are counterweights . They work exactly the same as those lead counterbalance weights on the wheels of your automobile. If they left those out, then those connecting rods and bearings would create an out-of-balance condition, and the wheels would vibrate at higher speeds. That could very well damage the wheels. But as a couple of others have nicely pointed out, the violent shaking could derail the train .

That looks like a Pratt truss . These trusses have diagonals which go from the outer-top nodes to the inner-bottom nodes (i.e. they connect to the top chord on the node furthest from the center of the span, and to the bottom chord on the node closest to the center). This design means that the diagonals are under tension and the verticals are under compression. Another famous design is the Allan truss , which is the exact opposite: the diagonals go from the inner-top nodes to the outer-bottom nodes, which means that the diagonals are under compression and the verticals...

Please note : I'm not a building designer by trade, but I have had to investigate related questions for other reasons. I'll let you in on a dirty secret about sanitation lines within buildings - The biggest concern is not about how fast things are flying, it's about maintaining air pressure and providing adequate ventilation. This guide presents a bit of a historical background to tall building design with respect to sanitation system design. This presentation provides some more recent perspective and goes into some of the research that is refining current building standards. The traditional viewpoint is that waste...


What is the purpose of building foundations?

According to many sources, one of the purposes of building's foundations is "To distribute the weight of the structure over large area so as to avoid over-loading of the soil beneath." (Wikipedia) On the Wikipedia page on foundations, there is the following picture: So the foundation seems to consist of some type of "legs", with a larger surface area on the bottom. But if the point is to distribute the weight of the building over an area, why not put the bottom of the building in contact with ground? Isn't the bottom of the building itself a much larger contact area than the area the foundation can provide? In the picture, the bottom of the building does seem to rest at ground, so why do we require the foundation to have these large surface area rectangles at the bottom if the whole weight of the building is already resting on ground? Here is another picture from the same page: This seems to be some sort of lodge or a cabin, with stones used as foundation. Here it is evident that the building itself is raised above ground with the stones used as a contact to ground. But now the small stones suffer all the weight of the structure. Wouldn't they be under quite a heavy load over small contact area and possibly sink into the ground? Why not simply have the building's floor, a much larger contact area, rest on the ground?

That looks like a Pratt truss . These trusses have diagonals which go from the outer-top nodes to the inner-bottom nodes (i.e. they connect to the top chord on the node furthest from the center of the span, and to the bottom chord on the node closest to the center). This design means that the diagonals are under tension and the verticals are under compression. Another famous design is the Allan truss , which is the exact opposite: the diagonals go from the inner-top nodes to the outer-bottom nodes, which means that the diagonals are under compression and the verticals...

Down, Not Out Building foundations don't always have to spread the load out to a larger area. Sometimes the load only needs to be transferred to a stronger (harder) layer. This layer may be deep in the earth and have a softer layer on top of it. Layers Say you want to build a building in an area that has a lot of soft clay at the surface. This clay will not support much of anything (especially when it is wet). Underneath this layer is hard bedrock. You now have two choices: Add a basement to your building so that...

Biggest advantage is that when connecting to trailers, there are no bleeding issues. Imagine having to connect hydraulic pipes and remove the air bubbles... As for the amount of air - the compressor and receiving tanks are designed for normal use. However if you wish to accompany AC/DC with the air brakes you will run out. Disc brakes already exist in an airbrake version for trucks - came out over 10 years ago IIRC. But one big difference is that if you lose hydraulics on a car braking system then you lose stopping power (except for handbrake etc) but with...


How are passive houses made in very hot regions (like Saudi Arabia)?

I think, here is the main problem the difference between the internal and the external temperature. For example, in Saudi Arabia, in 50 C, a passive house needed probably much sophisticated planning as in Paris. Compared to the traditional cooling systems, in the second case is enough only to get a cooling system with bigger power. I think, they are much more scalable. Is it anyways possible?

If I model this as a simply supported beam having load at mid span [...] I suspect that this is where your analysis went awry. First off, you should always model bridges with distributed loads, not a single concentrated load at midspan. The most significant load on a bridge will almost always be its own self-weight; load-trains are heavy but, well, so are bridges. Secondly, I assume you're thinking of the bridge like this: Indeed, we can see here that the bending moment is greater at midspan. However, that's not the bridge we're looking at, it's missing the cantilevers! So...

If the receiver does not detect the sub-carrier for the "colour burst" signal which is transmitted during the horizontal blanking period the receiver switches on the "colour-killer" circuit so the set reverts to black and white mode. The colour-burst signal - 8 to 10 cycles of 3.85 MHz - is unlikely to be generated by random noise. Figure 1. The colorburst signal is transmitted on the "back porch" between the horizontal blanking pulse and the start of that line's luminance signal. The colorburst signal is used to synchronise the QAM (quadrature amplitude modulation) oscillator which can hold its frequency accurately...

A yahkchal is an example of a type of passively cooled building in Iran They utilise a combination of passive evaporative cooling and thick thermally insulating walls in order to keep the interior temperatures low enough. First, wind is directed into underground aquifers known as qanat . They are then cooled due to the low humidity desert air causing water to evaporate. The cooled air then flows through the interior of the yakhchal, cooling the interior. The thick insulating walls (filled with earth and various insulating materials such as straw and feathers) help to insulate the cool interior from the...


How does measurement uncertainty combine with tolerances?

Given a tolerance within which your workpiece should be manufactured, say some length should be $10\pm1$mm. If you determine that your uncertainty in measuring this length is $0.2$mm (at 95%). How should a measurement of $9.1$mm be treated? Clearly there is a significant probability that this value will actually be outside of tolerance. Do you need to decrease you tolerance range based on the uncertainty in your measurement?

You need to ensure that even in the worst case scenario, you still meet your measurement spec of $10 \pm 1\text{mm}$. If your tolerance is $0.2\text{mm}$ of your measurement, then a measurement of $11\text{mm}$, while may look like it meets spec, it doesn't because it could be $11.1\text{mm}$. So the worst case that still meets your spec is a measurement of $10.9\text{mm}$, because then with a max tolerance of $0.2\text{mm}$, you still meet $11\text{mm}$. With a $0.2\text{mm}$ tolerance, your $10 \pm 1\text{mm}$ spec becomes $10 \pm 0.9\text{mm}$. How should a measurement of $9.9\text{mm}$ be treated? So revised spec is between...

Answering the question: What are possible types of low cost sensors I can use? There are several types of sensors that can provide millimeter level accuracy. "Low cost" is a very relative term, so you'll need to do some shopping around based on your specific budget. Optical sensors- Included here are those of the type you listed, though it's a very cheap sensor meant more to provide a "yeah something is in front of me, about yay-far-away". There are also laser sensor systems which can provide millimeter level accuracy. Ultrasonic Sensors- Most ultrasonic sensors have relatively low accuracy; in the...

Trees increase the turbulence of the air that reaches the turbines. That creates all sorts of uneven, rapidly-shifting loads on the blades and structure. That increases the maintenance costs, decreases availability, decreases the capacity factor, and decreases the life expectancy of the turbine. So, higher costs, lower revenue. One of the ways we measure the impact is the surface roughness coefficient $z_0$. Here are the figures from the book " Wind Energy - The Facts ". As you can see, forest and woodland has a much higher $z_0$ than open farmland - and that means higher turbulence. Open land also...

It is more efficient to transmit DC using about the same infrastructure. This is because of several effects: Skin effect experienced with AC. There is no skin effect with DC. Higher voltage allowed with DC for the same transmission lines. The lines have to withstand the peak voltage. With AC, that is 1.4 times higher than the RMS. With DC, the RMS and peak voltages are the same. However, the power transmitted is the current times the RMS, not peak, voltage. No radiation loss with DC. Long transmission lines act as antennas and do radiate some power. That can only...


Can wifi signal reception be improved by opening a door?

A wifi user is in a different room than the router. The computer is having a hard time connecting and receiving the wifi signal. Can the wifi signal from the router to the computer be improved by opening a door to the room where the computer is?

The picture, below, of the exaggerated long section of the Channel Tunnel was taken from Wikipedia . Full-sized image here . Some of the limiting factors for the Channel Tunnel are: Railways don't like steep gradients The tunnels comprising the Channel Tunnel were excavated using tunnel boring machines (TBMs). Like railways, they cannot tolerate steep gradients. The tunnel was excavated in chalk marl (green coloured material in the picture). This was due to its depth (not being too shallow and not being too deep) and its ability to be easily dug but also it would cause major support issues for...

Can the wifi signal from the router to the computer be improved by opening a door to the room where the computer is? Maybe, but probably not to a noticeable degree. All structures, including doors, impede the wireless signal from the router by some amount. Generally, the amount of impedance added by the door is a negligible amount and would not be sufficient to noticeably improve the quality of the signal. That said, differing types of door construction have differing impacts on the signal. A hollow core, wooden door won't impede the signal all that much at 4 dB. A...


While browsing a local news site, I stumbled upon this picture of a broken bus door. The glass was fractured due to a rock impact. As far as i know there are no heating elements on the window section in the picture. Now, what interests me is the apparent periodicity and structure of the fracture pattern. Are periodic fractures something commonly encountered in tempered glass? Is the mechanism that generates such fractures understood? Is it a consequence of the manufacturing process? Perhaps the way the glass is affixed to the door? Thanks in advance

It's an artifact of production - in particular, the construction of the conveyor belt of the machine performing the quenching process. The pattern can be observed through a polarizing filter in the undamaged glass: source and it's a result of the structure of the conveyor belt through which the surface of the glass is cooled to generate the stress that gives it the special properties: source The contact area of the glass with the conveyor is small enough that it doesn't negatively impact the process - all throughout the surface the stress is introduced in sufficient amount, but the amount...

The problem is that the formula $P=I\ V$ is correct when dealing with DC circuits or with AC circuits where there is no lag between the current and the voltage. When dealing with realistic AC circuits, the power is given by $$ P=I\ V\ \cos(\phi), $$ where $\phi$ is the phase difference between the current and the voltage. The unit kVA is a unit of what is called 'apparent power' whereas W is a unit of 'real power'. Apparent power is the maximum possible power attainable when the current and voltage are in phase and real power is the actual...


About all those oil tankers off the coast of California … | Grist The giant ships burn fuel to keep lights on, power equipment, and heat the large volumes of crude oil resting in their tanks. I'm assuming that crude oil can't be heated in steel frac tanks , places other than salt caverns , and salt caverns . While underground caverns may not seem like the best place to store an emergency oil supply, they're actually very secure. For one thing, since they're 2,000 to 4,000 feet (610 to 1,219 meters) underground, the extreme pressure prevents cracks from forming and leading to leaks [source: DOE ]. Also, the natural temperature difference between the top and bottom of each cavern encourages the oil to circulate, which maintains its quality.

As Solar Mike's answer says, crude oil is viscous - too viscous to easily pump. Crude oil has a "pour point:" the lowest temperature where it will flow under gravity. Heating the crude oil keeps it above the pour point, so it can be pumped. With the large volume of oil in a tanker, it makes more sense to keep it fluid, rather than letting it cool down and then heat it (very slowly) back up). I found one article (PDF) that recommends tankers keep the oil at least 10°C above the pour point to promote circulation within the tank,...

Those are counterweights . They work exactly the same as those lead counterbalance weights on the wheels of your automobile. If they left those out, then those connecting rods and bearings would create an out-of-balance condition, and the wheels would vibrate at higher speeds. That could very well damage the wheels. But as a couple of others have nicely pointed out, the violent shaking could derail the train .

Trees increase the turbulence of the air that reaches the turbines. That creates all sorts of uneven, rapidly-shifting loads on the blades and structure. That increases the maintenance costs, decreases availability, decreases the capacity factor, and decreases the life expectancy of the turbine. So, higher costs, lower revenue. One of the ways we measure the impact is the surface roughness coefficient $z_0$. Here are the figures from the book " Wind Energy - The Facts ". As you can see, forest and woodland has a much higher $z_0$ than open farmland - and that means higher turbulence. Open land also...


I was having a discussion today, which led to the question why do heavy trucks still use air brakes? To my knowledge, it has been used for at least 40 years (I remember that as a kid), and apparently (I was told today but I haven't gotten around to verify it) they are still widely used. From what I remember, one of the things I was cautioned was that if you repeatedly pressed on the air brakes, then after a while the air buffer would empty and it would take time to fill up (thus losing braking capacity). Anyway, I wanted to know what are the benefits and disadvantages of air brakes compared to other technologies, e.g. hydraulic lines, or electrical system, (even KERS systems for more modern electrical vehicles). UPDATE : From the answers I understand that the main issue is reliability and "technical debt". I want to push a bit further and understand, what's stopping air brakes from being used in other vehicles. E.g. is it cost, performance, inability to accompany AC/DC drum rhythm?

The turbulence model can make a big difference in your simulation . There are many turbulence models around. It becomes a tough job to select one out of them. There is no perfect turbulence model. It all depends on several parameters like Reynold's number, whether the flow is separated, pressure gradients, boundary layer thikness and so on. In this answer, brief information about a few popular models is given along with pros and cons and potential applications. However, interested users can see this excellent NASA website and references therein to know more about turbulence modeling. A) ONE EQUATION MODEL: 1....

Short answer : make it thicker. Long answer : The moment of inertia affects the beam's ability to resist flexing. Use one of the many, free, online moment of inertia calculators (like this one ) to see how increasing the height of the beam will have an exponential effect on increasing the stiffness of the beam. And this site helps provide a pictorial view of the load(s) upon a beam depending upon differing configurations, such as where the supports are and where the load is applied. It also provides a calculator to determine the forces involved. Wikipedia has a decent...

Biggest advantage is that when connecting to trailers, there are no bleeding issues. Imagine having to connect hydraulic pipes and remove the air bubbles... As for the amount of air - the compressor and receiving tanks are designed for normal use. However if you wish to accompany AC/DC with the air brakes you will run out. Disc brakes already exist in an airbrake version for trucks - came out over 10 years ago IIRC. But one big difference is that if you lose hydraulics on a car braking system then you lose stopping power (except for handbrake etc) but with...

If you consider only the static forces then indeed the thickness might seem over-engineered. However, engine blocks are not statically loaded. They operate in the range of a few hundred to a few thousand rpm (Revolution Per Minute), so there are dynamic considerations here. Fatigue When materials are subjected to cyclic loading they exhibit a reduction in the allowable stresses. See below for an example: In general, BCC (body-centered cubic) materials (like steel) show a marked drop in strength (close to 50% or more depending on the steel). For these material there is stress (called the endurance limit), for which...