# All Questions

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### Purpose of spheres and fins on submarine propeller

On a recently launched Russian diesel-electric submarine, the rear propeller has two distinct features. You can see spheres at the base of every propeller blade: Also, the trailing edge of the shaft ...
8k views

### Why is Mach 0.3 the threshold separating compressible and incompressible flow?

I've read that Mach 0.3 is pretty much the upper limit for treating air as an incompressible fluid. The sources I've read seem to treat this as a given, without proof or justification. Why is this ...
5k views

### How to prevent deposition of dust on ceiling fan blades

It is well known that dust gets deposited on a rotating ceiling fan because formation of a boundary layer over fan blades. The air layer next to blade surface is stagnant due to no-slip condition and ...
280 views

### What is it about the cabin electrical supply on cruise ships that makes surge protectors dangerous?

Surge protectors are banned on cruise ships, and so are confiscated during boarding. Extension cords and cube taps etc. are discouraged, but not banned. I'm asking specifically about surge protector ...
870 views

### Why does prestressing in trees make them stronger?

In "Structures: or Why Things Don't Fall Down" James Gordon talks about trees being prestressed with the outside in tension and the inside in compression. Why does it make a tree stronger to have it ...
79 views

### How do you ensure physical network interfaces always get the same interface name across reboots on an embedded Linux system?

For an embedded Linux system, if I have two or more network interfaces, how do I ensure that they always get the same interface names every boot In other words, I want, for example, eth0 to always ...
5k views

### Quantifying inertia on the electricity grid

A lot of discussion about the modernisation of electricity systems is about "inertia". This is usually a qualitative discussion about how turbines (in hydro, coal & gas plants) with lots of ...
3k views

### Derivation for bridge natural frequency estimate in Eurocodes

The Eurocodes gives the following equation for estimating a "simply supported bridge subject to bending only"*: $$n_0 = \frac{17.75}{\sqrt{\delta_0}}$$ Where $n_0$ is the natural frequency in hertz ...
1k views

### In aluminum machining, what are the most common factors that might cause a machined component to have warping issues?

I am currently having an issue where features of my machined parts are warping. I am using Alloy 7050 Type I and Type III in this particular case. Using a feeler gauge and a certified, calibrated ...
11k views

### How does pressure treatment affect the mechanical properties of lumber?

Pressure treated lumber is specified for many exterior applications because of its resistance to insect damage and fungal rot. But how does it compare to untreated wood, mechanically? For example, ...
1k views

### Why are hyperboloid towers not popular anymore?

Hyperboloid towers were very popular in the end of 19th and the first half of 20th centuries - water towers, powerline anchor towers, sometimes tall radio towers were built using this design. The ...
680 views

### What causes rechargeable batteries to age? What can be done to extend life of these batteries?

These days most of modern electronics use rechargeable batteries as a power source. Also, these days most modern rechargeable batteries are Lithium Ion or Lithium Polymer based. Like any other devices,...
13k views

### Affixing a thermocouple to a surface

I'm looking for advice on how to attach a thermocouple to a metal surface in a fashion that's relatively temperature resistant (more-so than) glue. I've got some very fine gauge wire on hand to make ...
293 views

### Modern method for teaching controls

Background When I took my first class in controls (2006-ish as taught by an aerospace professor for a mix of ME and EE students) it was basically all done in Laplace-transform, transfer functions etc....
518 views

### What are some cost-effective metal substances that can wet glass?

A highly desirable property of metals like gallium and indium is that they are able to wet glass. Normally, as metals, they wouldn't be able to form an airtight seal when in contact with glass. But ...
1k views

### Why are bird flight diverters shaped like a spiral?

I was out walking and saw these strange looking spirals on some power lines. When I got home I did some research and discovered that they are to prevent birds form hitting the power lines, mainly ...
650 views

### Can Zinc/Aluminum coated anchor rods be used in concrete?

Bolts and anchor rods that are very high strength ($F_u$ > 150ksi) are not supposed to be galvanized. This is because of concerns about hydrogen embrittlement. This includes ASTM A 490 bolts and ASTM ...
4k views

### What are the disadvantages of concentrated solar thermal power?

Concentrated solar power looks on the surface to be an excellent source of grid power. It's sustainable, has no obvious waste products to deal with either during construction or operation, and with ...
3k views

### How thick is it reasonable for the walls of a steel gas pipeline to be?

The TurkStream project site claims the gas pipeline will use pipes made from 39 millimeters of high-quality carbon manganese steel with additional plastic coatings on both sides. Yes, they claim 39 ...
694 views

### Is interference between aircraft an issue for fly-by-wireless technology?

I was reading up on fly-by-wire development, and I saw a short section about fly-by-wireless technology. It seems like a great idea, with the potential to lower costs, weight and complexity. I can see ...
924 views

### Why are three way bridges rare?

It's true that most bridges are "two directional." But three way bridges are pretty rare, globally. I can understand why there wouldn't be many for rivers, but if bridges are designed based on the ...
3k views

11k views

### Defining the heap and stack size for an ARM Cortex-M4 microcontroller?

I have been working on and off on small embedded systems project on and off. Some of these projects used an ARM Cortex-M4 base processor. In the project folder there is a startup.s file. Inside that ...
3k views

### Practical setup to measure angular velocity

I have got a spinning top from a Canadian manufacturer, and I am deeply amazed by how neatly it spins. My interest in physics has led me to try to find out at what top speed I can spin the top and ...

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