Anyone here work on composite structures and if so, what methods do you use to solve for deflections, stresses and strains?

I have made code to solve for thin laminates using CLT, but as I usually work with sandwich structures. the assumptions in CLT can only get so far. As shear deformation is dominant in relatively thick composite structures with short spans, I was wondering if people working in the industry developed their own code using FSDT or just work with FEA packages to model thicker composites

I'm a structural (bridge) engineer, and I'm trying to find some active online boards or groups for discussing various topics related to bridge, structural, or civil engineering. I realize the obvious answer is "why not here?", and maybe it is a good answer. But I'm looking for other recommendations, in particular I'm looking for resources specific to my field or to civil engineering as a whole. Most of the places I can find are either deserted, based in the middle east or east Asia, or overrun with spam. It would be great to find some active communities based primarily in the US. And recommendations?

Hi

I have a jewelry drill press that I want to modify to slow down the rpms ( currently 660 rpm). It is driven by an AC motor and some pulleys that give some spindle speed control but it is already on the lowest setting.

I have googled that putting in a variable resistor could help with this but I am looking for something off the shelf with proper packaging for safety.

Would a dimmer switch from a lamp cord work?

Hello everyone, I don't know if this post belongs here but I found 5 of these bulbs in my late grandpa's garage and I'm trying to identify what it is, does, and if it's of any value anymore. I've seen 2 listings on eBay, one for 600 and one for 2750 so I'm a little confused on what the value is. Any info is appreciated, thank you.

Intro

Welcome to the weekly career discussion thread, where you can talk about all career & professional topics. Topics may include:

• Professional career guidance & questions; e.g. job hunting advice, job offers comparisons, how to network

• Educational guidance & questions; e.g. what engineering discipline to major in, which university is good,

• Feedback on your résumé, CV, cover letter, etc.

• The job market, compensation, relocation, and other topics on the economics of engineering.

[Archive of past threads]

Guidelines

1. Before asking any questions, consult the AskEngineers wiki. There are detailed answers to common questions on:

• Job compensation
• Cost of Living adjustments
• Advice for how to decide on an engineering major
• How to choose which university to attend

1. Most subreddit rules still apply and will be enforced, especially R7 and R9 (with the obvious exceptions of R1 and R3)

2. Job POSTINGS must go into the latest Quarterly Hiring Thread. Any that are posted here will be removed, and you'll be kindly redirected to the hiring thread.

3. Do not request interviews in this thread! If you need to interview an engineer for your school assignment, use the list in the sidebar.

Resources

• The AskEngineers wiki

• The AskEngineers Quarterly Salary Survey

• For students: "What's your average day like as an engineer?" We recommend that you spend an hour or so reading about what engineers actually do at work. This will help you make a more informed decision on which major to choose, or at least give you enough info to ask follow-up questions here.

• For those of you interested in a career in software development / Computer Science, go to r/cscareerquestions.

My boss wants me to put some feelers out for potential solutions or workarounds for this problem that we have with stainless drums. I've contacted some local machine shops to see if they won't laugh at us, but I figured someone here might have a good idea or might get a good laugh out of it.

Long story short, we purchased these 50L drums for a drum press we had designed that have a beveled bottom and are incompatible with the platen. We didn't know ahead of time the drums were going to have the bevel because the spec sheet said they were flat and the 20L drums we used previously were pretty flat.

I found the actual manufacturer of the drum from China and they gave me a drawing of a flat bottom 50L but actually don't offer it as a product for some reason.

So now what we're looking to do is salvage these drums by modifying them in some way to "give" them a flat bottom. I am open to any and all suggestions, even "Don't even bother this is the stupidest things I've ever heard."

I thought perhaps we could get someone to cut off the bottom and weld on a flat stainless plate, or weld a trapezoid thing on the inside to just not use the tapered section, or maybe cast something on the inside to fill the space in.

Anyway, here's the full album of pics https://imgur.com/a/ow6x5IW. Happy to answer any questions.

Edit: to be more explicit about the problem statement. We store our product in these drums and use the drum press to transfer product out to a filling machine. We need the platen to go as far down as possible in the drum to maximize recovery, the taper prevents this. The platen has two holes at the bottom, one for a vent valve and the other for the main outlet connected to a hose. We cannot return the drums.

I work at a chemical plant in Belgium where we have a CHP (gas turbine) and we inject a big amount of the leftover electricity.

Some days it will be beneficial to inject, but some days or hours the market price will be so low that we need to inject as little as possible to minimize losses. But I need to know this 2 days in advance.

How do you handle this at your company? I am looking for some insights and learn from how others handle this.

Extra info: At this moment I try to look at predicted energy production of Belgium in the coming days (solar and wind which is publicly available) and at the predicted consumption (which is also publicly available). If production almost matches load, gas plants will not be turned on and price will be low (because most expensive production determines the price and then we only have solar, wind and nuclear). If production is low I look at some of the neighbouring countries. Eventually I'm planning to automate this with something like python.

I am currently teaching a Numerical Analysis course for engineers at undergraduate level. The course is mandatory for *many* branches of engineering (mechanical, industrial, physics, electrical, agricultural, etc.) There are many problems with the course at the moment, one of them being that the content of the course has not changed much since the beginning of the 90s. I agree that since it is a maths course after all, some very old things are still valid today (e.g. Newton's or Euler's method), but I believe some parts of the course should be focused on tools that are modern and actually used by engineers in their practice. Moreover, the book used in the course is very mathematically focused and most of the students struggle to understand the goal of learning all of those very niche mathematical concepts.

Me and another teacher are trying to give some kind of makeover to the course. For instance, we have chapter on cubic splines, that we barely touch (only a short introduction) and we feel that the plus-value of this chapter is very low because we doubt actual engineers care for the theory behind cubic splines in their work. Either we flush it completely, or maybe go more in depth to other kinds of more modern interpolation techniques (NURBS maybe?)

The thing is: we are both mathematicians. Sure, our work is very applied and we collaborate with industrial partners and engineers, but still we have a hard time to know what numerical methods and what knowlege of numerical analysis is actually required for engineers in their practice.

My question: in your work, what do you feel you should need to take away from a numerical analysis course? Are there any methods or techniques that are absolutely essential for you (in simulations, for instance)? What subfields of maths/num. analysis have you used or do you use currently in your carrer?

TL;DR - What do they mean by "the bending moment per unit length MA is caused only by discontinuity, because there is no effect of difference of pressure between adjacent tubes"? Where exactly is the moment acting and how do you calculate it (I understand how to calculate moments, but this one is, weird)?

​

I've been reading through "Fundamental Concepts of Liquid-Propellant Rocket Engines" by Alessandro de laco Veris [1] and "Modern Engineering For Design of Liquid-Propellant Rocket Engines" by Huzel and Huang [2] since I enjoy rocket engineering. And while the books are fantastic at breaking it down and giving you the knowledge of how to engineer an engine, they both are lacking one very important step.

​

They describe the maximum combined tensile stress as two possible equations, depending on whether the cooling jackets are circular or are more of a rectangle with rounds on the ends. I have taken the liberty and pasted below screenshots of the pages with information that is useful for this problem. The issue to pay attention for is solving MA and M'A.

Cross Section A-A and general cooling tube arrangement [1]

Stress Equations (σ t only for circular tubes) and Explanations Given [1]

Stress Equation and M'A for Non-Circular Tubes [1]

Maximum Compressive Stress [1]

σ t - Sample Calculation 1 Solving For M.A_MAX [1]

σ t - Sample Calculation 2 Solving For M.A_MAX [1]

σ t Equation With Descriptions [2]

σ t Equation (Non-Circular) With Descriptions [2]

Full Sample Problem P.1 [2]

Full Sample Problem P.2 [2]

Full Sample Problem P.3 [2]

They, as in both books, describe the bending moment MA as "the bending moment per unit length MA is caused only by discontinuity, because there is no effect of difference of pressure between adjacent tubes" and M'A as "combined bending moment".

​

The issue is how they describe it. What exactly do they mean by caused by discontinuity in cross section A-A? We have a pressure inside the nozzle, a pressure inside each tube, a velocity in the nozzle along the center axis, and a velocity in each tube going parallel to the center axis (simplified, technically it is actually at an angle since the tubes run along the shape of the nozzle). A difference in pressure between tubes makes sense for adding stresses, which is accounted for as part of M'A. But nowhere else am I seeing a possible bending moment MA. Especially with how small of a moment that usually is there.

​

As you can see in the sample calculations, it is standard to calculate the maximum allowed for the material used and then confirm whether MA or M'A is indeed below the max. However, in all the examples given, the author uses their "experience" saying the design is good but not actually calculating the moments. While that may be a fine design practice for them with writing a book, anyone working on even just a "paper" engine needs to prove that the moment is under the allowed or have sufficient supporting evidence to treat it as a non-critical calculation.

​

What do you all think? I don't want to chalk this up as "usually below the allowable" and want to be able to calculate this value. Any ideas on what exactly they are talking about and how to go about calculating it?

Greetings I am setting up a vegtable "farm" on my balcony. I will have several large grow beds that will have individual watering needs. I have bought several soilmoisture sensors (b-parasite if you wanna look it up) that will monitor each zone and trigger watering when needed. I have also made a large watertank that will hold enough water for hopefully atleast a week. I have also bought a drip-water kit. The only thing I am missing is the pumps/valves.

So my question to you is what solution you think is most suitable for me.

Option1: 1 pump with a pressure sensor. 1 valve for each zone. The pressure is held high between pump and valves. When valve opens the pressure drops and pump starts pumping. Valves controlled with esp32.

Option 2: No valves, 1 pump for each zone. Pumps controlled with esp32 and Motor controll card.

I am estimating that I will have between 6 and 10 zones. ~10litres of water a day split between the zones. I want to water more water less often, rather than little water very often. Maybe 2-3 waterings per zone, per day.

The idea from the start was to have a gravity fed system so no pump and only valves. But I have no possiblity of getting enough water to a high enough point for that to work.

So what do the great minds of reddit think? I am leaning towards many pumps and no valves, the only issue with that is the cost (pumps are more expensive than valves) and the pumps I have found are all for quite thick tubing, while the tube I have for the drip nozzles is 4mm ID and 7mm OD. Any suggestions or ideas? Other options I havnt considered?

Thank you all. If you know a better subreddit for this question please let me know.

Ps: Please dont suggest hydroponics, thats another project entirely.

I'm trying to design a system that will have glass bottles upside down filled with liquid. They will be pressurized via a bulkhead air input and will dispense through bulkhead liquid output.

Here is a crude drawing of the system concept

The bulkheads are 1/4" Push-to-Connect fittings, I asked a mechE friend if i could simply use a one-way check valve like these in between the bulkhead and the air pump but he said there will likely still be backflow issues (he didn't elaborate why).

What is the standard method for preventing backflow for a system like this?

As a side question: Is there any mechanism i can employ so that i can remove the bottle, fill it, put the cap with bulkheads back on. Then have it not dispense anything until i push it into the main unit. Basically, a bulkhead that doesn't let anything flow until its connected on both sides, or like a press-and-turn system on the entire bottle to "activate" the bulkheads. This would make refilling the bottles easier. Is there such a thing as a double-halfed bulkhead, where both need to connect before it opens up? I'm imagining something like a uniseal except it's fully-sealed and does not allow flow when a tube isn't inserted, that way you can push the entire bottle down onto the tubes to start the flow and beforehand you can hold the bottle upside down without any leakage.

I'm trying to design a system that will have glass bottles upside down filled with liquid. They will be pressurized via a bulkhead air input and will dispense through bulkhead liquid output.

Here is a crude drawing of the system concept

The bulkheads are 1/4" Push-to-Connect fittings, I asked a mechE friend if i could simply use a one-way check valve like these in between the bulkhead and the air pump but he said there will likely still be backflow issues (he didn't elaborate why).

What is the standard method for preventing backflow for a system like this?

Hi all,

I'm looking for a rather unique actuator, and the closest I can find is piezo, but they're generally far too small for this application.

The key feature I need is that the actuator operates on voltage (IE higher voltage, higher displacement) and doesn't draw a lot of holding amps. When voltage is removed it has to return to its neutral position without a control system (failsafe).

The tricky part is I need displacement of around 5mm and a force of around 15kN. I don't need particularly high speed or accuracy though.

Is there any type of actuator I've missed that fits these requirements?

Thanks!

I have currently 3D printed a clip to attach the electronics and battery to the lower frame of the racquet, but due to the rigid nature of 3d printing, and the fairly violent action of hitting a ball, the clip keeps either breaking or coming off. I was hoping you guys would have a different way of approaching this issue, as nothing I have tried has worked.

Intro

Welcome to the weekly career discussion thread, where you can talk about all career & professional topics. Topics may include:

• Professional career guidance & questions; e.g. job hunting advice, job offers comparisons, how to network

• Educational guidance & questions; e.g. what engineering discipline to major in, which university is good,

• Feedback on your résumé, CV, cover letter, etc.

• The job market, compensation, relocation, and other topics on the economics of engineering.

[Archive of past threads]

Guidelines

1. Before asking any questions, consult the AskEngineers wiki. There are detailed answers to common questions on:

• Job compensation
• Cost of Living adjustments
• Advice for how to decide on an engineering major
• How to choose which university to attend

1. Most subreddit rules still apply and will be enforced, especially R7 and R9 (with the obvious exceptions of R1 and R3)

2. Job POSTINGS must go into the latest Quarterly Hiring Thread. Any that are posted here will be removed, and you'll be kindly redirected to the hiring thread.

3. Do not request interviews in this thread! If you need to interview an engineer for your school assignment, use the list in the sidebar.

Resources

• The AskEngineers wiki

• The AskEngineers Quarterly Salary Survey

• For students: "What's your average day like as an engineer?" We recommend that you spend an hour or so reading about what engineers actually do at work. This will help you make a more informed decision on which major to choose, or at least give you enough info to ask follow-up questions here.

• For those of you interested in a career in software development / Computer Science, go to r/cscareerquestions.

I have learned enough about transmission line impedance matching to worry about the integrity of some of my analog signals, but not enough to convince myself that it doesn't matter for the frequency range of my input data. I would greatly appreciate input from an EE who isn't trying to sell me something.

To bound the problem: I have a ±10V sensor, responding to a transient event, that I normally sample at 100 kHz for a few seconds at a time. I am highly oversampling my input signal at 100 kHz, but Nyquist says the max I could expect to pickup is a 50 kHz sine wave.

Would a 50-ohm to a 75-ohm coaxial cable mismatch cause noticeable reflections/signal degradation of a 50 kHz sine wave? Or, would DIY cable splices from a 50-ohm BNC to a 150-ohm cable cause any issues? I really don't want to have to impedance match everything I'm doing, but if there is reason to believe that it would help then I could just setup an experiment to prove it's worth the time/cost. I bemoan my lack of a function generator that could help me answer my own question.

I have a project which will use standard framed wood walls (2'x6' framing). The center of the wall will be foamed will closed cells rigid expanded foam. This will add alot of rigidity. Is there somme standard calculations that allow to calculate the rigidity of such walls? (Both in bending and in torsion rigidity). I saw some studies on sandwich panels with foam core, most of them are very thin, not wall thick with wood framing. However, I don't see any standard calculations for walls.

This calculation shows 2.3meters of head with .00126m3/s of flow through a 30% efficient turbine is 8.4watts output

But when i run the number myself for HP on my system specifications the formula is Power (HP) = Torque (lb.in) x Speed (RPM) / 63,025

2.8lbf-in * 21 rpm / 63,025 = .00093hp --> .68watts of power

What am i doing wrong here, why is this number so different than the calculation?

I can't seem to find the right standard that discusses Bill of material find numbers for assembly drawings. Can someone point me in the right direction?

Greetings!

I am seeking your expert opinion regarding a software recommendation for conducting basic piping system calculations, sizing pumps and pipes, and adhering to marine regulations and materials. The software should have the capability to handle fresh and saltwater, fuel oil, lubricating and hydraulic oils, and occasionally slurries.

Currently, I am using an outdated version of AFT Fathom, which restricts me from attending seminars or webinars organized by AFT, due to their focus on the latest software, which differs significantly from what I am using. The cost of upgrading Fathom and attending a seminar is approximately $7k.

I would be grateful if you could suggest a cost-effective alternative for both software and training that meets my requirements.

Thank you for your time and expertise.

Hello everybody. Just wondering if there are any websites that you all use to keep your engineering skills sharp. I’m looking for anything really; I’m trying to improve the way I spend my time and what better way than doing some good op engineering problems. Any general advice is welcomed too. Thank you for your input and I hope you have a wonderful day.

Has anyone ever quit a project because you don't agree with the design? (Or process, or standard, etc.) This is not necessarily about the intent of its function, politics or interpersonal issues. Purely the technical design.

Let's say at the beginning of a project, your team is brainstorming system architectures for a mechanism. You work on it for a while and come up with many layouts, but ultimately your organization's top management chooses a completely different design, or your least favorite one. This design is complicated, inefficient, costly, and/or just plain silly.

You are still the responsible engineer for this component and now have to see this design through bids, procurement, build, and test. It's a costly program and you still don't like this design. It's funky (for whatever real technical reason) and schedule keeps slipping. You thought this was a bad idea from the beginning and frankly as time goes on you're becoming more apathetic.

What do you do in this situation?

TL;DR advice, examples or warnings about part numbering for telecom engineering, specifically in fiber optics.

My current method is "[COMPANY]-[PRODUCT LINE]-[DWG NO.]-[COMPONENT]" while avoiding I, O, Q, S, and Z.

I've tried to find an industry standard, or even simply something commonly used, but found nothing. There really does not seem to be a standardized system for part numbering in telecom components, especially in fiber optics.

The system I am replacing simply uses manufacturer ID which is a whole can of worms in of itself. (Half the time they look like an MSN messenger chatroom OMGTTYL;]XDLOL)

​

https://preview.redd.it/me1gitrs81va1.png?width=625&format=png&auto=webp&v=enabled&s=592a51658fa7e3c4637832a293e9b7f792f86da7

Based on my research, a 100% renewable electric power system for California will require an aggregate energy storage capacity of about 1,000 GWh and a power output/input capacity in the hundreds of gigawatts. The utility-scale energy storage technologies currently in service are batteries and pumped hydro storage systems. The energy storage system for 100% renewable energy will likely be a mix of various technologies; however, I am convinced that the main technology for “baseload” energy storage will be pumped hydro since it is a synchronous machine technology which will make it far easier to integrate into the existing electric grid.

The largest pumped storage facility in California is Helms Pumped Storage Facility. It has an energy storage capacity of 90 GWh and a power capacity of 1.2 GW. I have found several locations throughout California to build pumped storage facilities.

Below are the top three locations for discussion. The energy storage computations were conservative and based on the top 25% volume of the reservoir. The true storage capacity of these locations are likely many times larger.

1. Kern River Canyon. Using Google Earth, I found a location for an upper and lower reservoir in Kern River Canyon where we can build a pumped storage facility with an energy storage capacity of over 1,700 GWh. The upper reservoir dam is 583 meters tall and 1300 meters wide. The lower reservoir dam is 318 meters tall and 1121 meters wide.
2. Monterey. Another location is in Monterey County on the coast where we can build a pumped storage facility with an energy storage capacity of over 500 GWh. The upper reservoir dam is 366 meters tall and 1801 meters wide. The lower reservoir dam is 213 meters tall and 1367 meters wide.
3. San Luis Obispo. The last location is in San Luis Obispo County on the coast where we can build a pumped storage facility with an energy storage capacity of over 350 GWh. The upper reservoir dam is 359 meters tall and 1784 meters wide. The lower reservoir dam is 273 meters tall and 1476 meters wide.

One advantage of the Monterey and San Luis Obispo locations is that downstream from the dam is the ocean, with no population centers on the coast. This means that if the dam were to collapse, all of the water would flow into the ocean. Another benefit of coastal pumped storage facilities is that we can desalinate ocean water and pump it to fill the reservoirs.

This table contains more data for your reference. The purpose of this post is to discuss technical aspects of these systems and not environmental or financial concerns. I understand these systems are excessive. I am not promoting these exact designs or locations. I am simply sharing what is technically feasible from an engineering standpoint.

My company doesn't have any safety standards or training. We're about 150 people, and I'd say about 100 have science or engineering degrees.

There is no workshop training, no safety glasses or hearing protection signs in the workshop, no culture of saying no to lifting a 50kg weight up 2 meters on a ladder.

I'm certain my supervisor would allow me to give a presentation on workplace safety things like goggles and steel toed boots, but I don't know where to find sample SOPs.

Can anyone suggest some, or an online presentation, or something?

Intro

Welcome to the weekly career discussion thread, where you can talk about all career & professional topics. Topics may include:

• Professional career guidance & questions; e.g. job hunting advice, job offers comparisons, how to network

• Educational guidance & questions; e.g. what engineering discipline to major in, which university is good,

• Feedback on your résumé, CV, cover letter, etc.

• The job market, compensation, relocation, and other topics on the economics of engineering.

[Archive of past threads]

Guidelines

1. Before asking any questions, consult the AskEngineers wiki. There are detailed answers to common questions on:

• Job compensation
• Cost of Living adjustments
• Advice for how to decide on an engineering major
• How to choose which university to attend

1. Most subreddit rules still apply and will be enforced, especially R7 and R9 (with the obvious exceptions of R1 and R3)

2. Job POSTINGS must go into the latest Quarterly Hiring Thread. Any that are posted here will be removed, and you'll be kindly redirected to the hiring thread.

3. Do not request interviews in this thread! If you need to interview an engineer for your school assignment, use the list in the sidebar.

Resources

• The AskEngineers wiki

• The AskEngineers Quarterly Salary Survey

• For students: "What's your average day like as an engineer?" We recommend that you spend an hour or so reading about what engineers actually do at work. This will help you make a more informed decision on which major to choose, or at least give you enough info to ask follow-up questions here.

• For those of you interested in a career in software development / Computer Science, go to r/cscareerquestions.