Engineering Help Desk

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Questions:

How Can I Calculate the Stress of Saddle Clamp Bolts Supporting a Vertical Mast?

(Question moved to the bottom of page. StuRat 15:28, 12 September 2008 (UTC))

Where are the files I contributed six months ago?

Answer: Probably still at Wikibooksb:Main_Page or lost in the link maze locally. Only a few Custodians have been appointed and it will take a while to sort out the elements of the database being moved from Wikibooks to the new dedicated name spaces at permanent URL http://en.wikiversity.org. Please try a search either here or at Wikibooks.

Can I request special attention for the files I need to get started?

Answer: Yes. Request the files be transwiki'd here: http://en.wikiversity.org/wiki/Wikiversity:Import it may take a few hours as there are only a few appointed Custodians (synonmous with administrator, sysop).

Is any Free Engineering actually occurring at Wikiversity?

I am doing some at Lunar Boom Town. If you have some time ask me how and why I am developing pieces and I can give you some pointers to places where the data,tools,techniques, are starting to pool up and become self organizinng with emergent properties with growing participation. Some of the folks at googles sci.space.* groups can helpfully assess the potential and limitations inherent in distributed virtual companies. The eductainment is still being researched and developed .... need some effective data feedback and improving mechanisms. 70.110.62.240 19:40, 26 November 2007 (UTC)

Efficient Combuustion Needed

My parents will not allow me to have natural gas pipeline plumbed into the workshop areas I borrow and rent from them so I can operate a microfoundry for aluminum parts for engineering research and commercial network game opportunities I wish to pursue. Can sombody help me learn what some better or worse options might be? Mirwin 19:55, 26 November 2007 (UTC)

I suggest propane tanks. They are readily available for use with barbecue units. The 1900°C temp of a propane flame is more than enough to melt aluminum (which melts at around 660°C). However, aluminum fumes are toxic, so you will need a good exhaust fan and a smokestack so you release the fumes above the elevation where people might breathe them. This will also require that you locate in an area zoned for industrial usage. This type of activity would not be permitted in a residential area. Also, depending on the jurisdiction, special permits may be required, and "scrubbing" of the exhaust fumes may be expected to gain approval. The obvious fire hazard from using combustible gases will also likely bring about requirements for extra fire precautions, like sprinklers. StuRat 22:35, 26 November 2007 (UTC)

Excellent information StuRat! Thanks. I will investigate air scrubbers and local zoning requirements. It is possible there is some lower limit on size of activity that will allow a tiny quantity of tiny parts to be cast in a microfoundry. Point about air quality is still taken seriously by me and I will investigate options although 20 years ago in local high school no special precautions were taken in much larger pours other than an excellent ventilation system in a large volume shop area. Despite that shop training I retained no idea that aluminum fumes were toxic so I wish you to know that you have assisted me greatly here. Thanks again! Mirwin 19:58, 18 December 2007 (UTC)

You're welcome. See w:Aluminum#Health_concerns for info on aluminum toxicity. StuRat 20:12, 8 January 2008 (UTC)

Where to put Polymer technology?

Hello Wikiversity - people! I just joint this project and I have already my first question. In Germany "Polymer Technology" is considered a part of "Mechanical engineering". But in the english speaking part of the world it is considered a part of "Material Science". At which Portal should I start working. There is already a speciality "Polymers" in "Materials science and engineering". But that is more about the chemistry of polymers. But the "engineering part of polymers" is another thing than "engineering with steel" as there are quite a few special topics to consider. This won't be a problem for the next few weeks, as there is enough to learn about wikiversity itself and there definitely is a lot of material I'll contribute to the chemical side of polymer technology. But still I would like to have some opinions on that one. Yours Akinom 13:25, 8 January 2008 (UTC)

UPs. I think I may have found the solution. The german "Kunststofftechnik" isn't "Polymer Technology" but "Polymer engineering". Sorry for that one. But there comes the next question. Is "Polymer engineering" considered a department in the "School of Engineering" or is a subdivision of "Mechanical engineering"? Akinom 13:25, 8 January 2008 (UTC)

I have an engineering degree from the US and would break it down like this:

Mechanical engineering: Engineering subjects which do not depend on the material.

Material science: Mechanical properties of materials.

Chemistry: Chemistry of materials.

So, polymer engineering would fall under materials science, in my opinion. I'd add links from the adjacent fields of chemistry and mechanical engineering, however, so everyone can find your material :-). StuRat 20:20, 8 January 2008 (UTC)

"The future is in plastics" they used to say...but those were the businessmen. Invented by Chemists, created by Chemical Engineers and mass Manufactured by Mechanical and Industrial engineers, I would indeed go so far as to create a branch of engineering called Polymer Engineering and to add it to the template. The information you have may be most suitable to Chemistry (science behind it) or Chemical Engineering (how to make it), Industrial Engineering (plastics in a larger scope), Mechanical Engineering (ways to use it), and/or Materials Science (how it behaves as a material). A good curriculum for a Polymers Engineer would include all of these courses. -71.159.31.220 04:01, 19 February 2008 (UTC)

Relating flow rate of compressed gas to pressure

Hi, folks. How much information is needed to find (even to within about 20%) the flow rate of a tank of gas compressed at a given pressure? Specifically, given a tank of 0.4m^3 helium compressed to 16500 kPa, is it possible to work out (on paper) what pressure to regulate it down to in order to achieve an initial flow rate of 15 lpm? Would I need to know the area of the narrowest part of the outlet? Thank you, Lsterling 06:56, 14 July 2008 (UTC)

Yes, you would need to know the cross sectional area of the narrowest restriction, but also the shape of that opening. A circular opening should allow for faster flow than a narrow slit of the same cross sectional area, for example. You would also need to know the type of fluid (helium, in this case) and pressure in the tank (16500 kPa, in this case) and the pressure in the target container. Other factors, like the fluid temperature, and the smoothness, length, and straightness of the connection hose, would have a minor effect (perhaps less than 20%) on the flow rate. You did use the term "initial flow rate", so it sounds like you already understand that the flow rate would decrease as the pressure in the tank decreases and (possibly) the pressure in the target container increases. The volume of the tank doesn't actually matter for finding the initial flow rate, but it will affect how quickly the pressure in the tank drops, which, in turn, affects how quickly the flow rate decreases. Similarly, the volume of the target container will also matter. Note that, for a flexible target container, like a balloon, a more complex relationship will exist between the quantity of gas and the back-pressure/flow rate. StuRat 22:52, 14 July 2008 (UTC)

Thanks, StuRat. (question moved to the bottom...) Lsterling 03:52, 24 October 2008 (UTC)

How Can I Calculate the Stress of Saddle Clamp Bolts Supporting a Vertical Mast?

I need to calculate the stress of a saddle clamp bolt supporting a vertical mast to the side of a building.

For a vertical cantilever mast, such as an antenna or flag pole, force due to wind pressure on the antenna or flag will cause a moment around the mast base. The moment can be calculated by multiplying the force on the mast by the distance from the base to the force.

$M=FL$

The stress on the mast at the base can be calculated by dividing the moment around the base by the section modulus of the mast.

$\sigma ={\frac {M}{I}}$

I am dealing with a slightly different situation as shown in this diagram.

The upper saddle clamp has two bolts holding the mast to the building. To calculate the stress in a single bolt, can I simply substitute the section modulus of the bolt?

There is a reason why I ask this question for a single bolt -- not two bolts. When the force on the mast is such that it loads the bolts in tension, it's reasonable to expect each to carry about half of the load. When the force on the mast is such that is loads the bolts in shear, this may not be the case. The bolts do not fit precisely into the saddle clamp. It's possible that one bolt would need to deform before both bolts are carrying the load. Therefore, I think the conservative approach is to consider the load in shear of a single bolt.

Anyway, can I simply use the section modulus of the bolt to calculate the stress in the bolt in this scenario?

--xquercus 10:43, 12 September 2008 (UTC)

I'd agree that you need to do your calculations as if a single bolt is present. See my diagrams below:

IF MAST IS VIEWED AS RIGID
--------------------------
 \ <- wind     wind ->/
  \                  / 
   \  +-+           /+-+
    \ | |          / | |
     \| |         /  | |
      +-+            +-+

IF MAST IS VIEWED AS FLEXIBLE
-----------------------------
  \ <- wind      wind ->/
   \                   / 
    \ +-+             /+-+
     || |             || |
     || |             || |
      +-+              +-+

So, if the mast is viewed as rigid, then, depending on the wind direction, most of the forces will apply either to the top or bottom bolt. If the mast is viewed as flexible, then the majority of the forces will always apply to the top bolt. In any scenario, we can't assume that the forces are distributed evenly. Therefore, I'd do the calculations for each bolt assuming that it's the only bolt. Otherwise, the bolt carrying the majority of the forces may fail, causing all the forces to apply to the second bolt, which may then fail as well.

Now, as for the question about using the section modulus of the bolt to determine if it will shear; yes, that seems reasonable, when the bolt is under a shear load. However, with different loads on the bolt it may fail in different ways. The head of the bolt may break off or the threads of the bolt (or material into which the bolt is screwed) may also strip. Vibrations and/or a twisting load may also cause the bolt to unscrew over time, so it may be best to weld the bolt in place or at least use an adhesive ("thread lock") to prevent this. StuRat 15:47, 12 September 2008 (UTC)

Thank you for your comments. I want to make sure I understand your comments and I may not have been clear. Each saddle clamp shown in the diagram has two hex bolts connecting the clamp and mast to the side of the building. When I refer to a single bolt, I am referring to a single hex bolt. The diagram above includes two sets of clamps, for a total of four bolts, as this is how I plan to do my installation. The following diagram includes a single clamp with a total of two hex bolts.

I believe in the above diagram, the forces are a bit more complicated. For example, there may be some torsional forces in the bolts. Ignoring these forces, I believe when the bolts are in tension, we can reasonably expect the bolts to share the load. When the bolts are in shear, I don't believe the tolerances are close enough that the load will be shared evenly between the two hex bolts. Thus, a conservative maximum load should be determined by the strength of a single hex bolt in shear.

As an aside, I've seen a general rule that the strength of a bolt in shear can be estimated by taking 60% of the strength in tension. I haven't found an authoritative source on this but am certainly looking for one.

Thank you for reminding me of the potential failures at the head or threads. When doing my calculations, I've been using data from various ASTM standards which specify the yield strength of my bolts. I need to do a bit more reading to insure that the yield strength includes possible failure of the threads.

My particular project is the installation of a vertical mast on the side of my house to support amateur radio antennas. I'm going through the entire process of calculating the maximum wind surface area the saddle clamps and bolts can handle using the Telecommunications Industry Association models for wind loading. The impact of a failure in this particular system is negligible however I'm preparing to erect a number of cantilever and guyed lattice towers. This exercise is a step in the learning process so I can understand the tower manufacturer's specifications and (if needed) my PE's calculations. --xquercus 23:53, 12 September 2008 (UTC)

Thanks for the clarifications. I'm still unclear on the form of the mast itself, however. It appears to be cylindrical with no holes, in your diagrams, is this correct ? Your method seems good provided the bolts actually go through the mast, although there the mast itself will be considerably weakened by the holes, if the holes were drilled for this purpose, the mast now being subject to corrosion. It's difficult to tell if this is what was meant from the diagram. If they only go on either side of the mast and rely on friction with the clamp to keep the mast from sliding downward, then that would be a far weaker design. Perhaps the best method of all would be if the top pair of bolts went on either side of the mast (to preserve the strength of the mast where it will experience the strongest forces) and the bottom pair of bolts went through the mast (to support it):

      |     |
+-----+-----+-----+
| / \ |     | / \ |
| \_/ |     | \_/ |
+-----+-----+-----+
      |  M  |
      |  a  |
      |  s  |
      |  t  |
      |     |
      | / \ |
      | \_/ |
      |     |
      | / \ |
      | \_/ |
      |     |
      +-----+

A comment on the final rotation of the bolts: The bottom pair is in a good orientation, but it would be best if the upper pair were rotated so that the flats are parallel to the sides of the mast. This will prevent the corners of the bolts from putting unwanted force concentrations on the bracket. Since it may be difficult to control the final rotation of the bolt heads, using circular washers between the bolt heads and bracket may be a better way to accomplish this. Ensure that the washers are wider than the corners of the bolt heads.

One last question, what material do the bolts screw into ? Beware that this material itself may fail, in that the bolts may strip out of it, or a piece of the material may break off, or the material may crack, or the entire piece may break off of the building (for example, if a bolt is screwed into a brick). If possible, arrange it so that each bolt screws into a different object, to distribute the forces widely. Attaching to the frame of the building would be the best way to go.

Beware that certain combinations of metals cause corrosion since one material acts as an anode and the other as a cathode. If you are near salt-water, special precautions will be needed for dealing with salt-water spray. Painting the bracket, bolts, washers, and mast (near the holes) with an outdoor paint may help to slow failure due to corrosion. Also, be sure to use hardware rated for outdoor use. The antenna mast will also need to be grounded to protect the house from lightning strikes. StuRat 10:09, 13 September 2008 (UTC)

Helium flow rate compared to argon

I'm trying to control a helium (97%, air 3%) tank using a flowmeter calibrated for argon. From rough experiments it seems that the helium is flowing at about 2.5x the marked rate. Is there a general theoretical reason that would confirm or correct this number, or would it depend largely on the specific configuration of the equipment? (Or maybe this is a chemistry question?) Cheers, Lsterling 03:52, 24 October 2008 (UTC)

I'd say experimental methods are probably the best way to establish the different flow rates. Differences will be caused by the atomic masses of the elements, the radius of the atoms (which depends on the electron configuration), what molecules they form (monoatomic or diatomic, for example), any charge they have, etc. You could theoretically combine all this info together to come up with a flow rate, but it sounds like more work than the experimental method, to me. StuRat 02:16, 28 October 2008 (UTC)

The first thing to ask is what type of flow-meter is this? Is it a magnetic, optical or manometric (pressure-based) meter? Various things will foul up the readings of each of these types of meters. Calculate viscosity to evaluate how much these vary. Similarly, evaluate temperature. If any one of these varies much from the other... Density will screw-up magnetic and manometric flow-meters while turbidity or impurity may easily disrupt optical flow measurements. --71.137.197.23 02:15, 15 December 2008 (UTC)

Mechanical joint problem

Note: I'll do my best to make this clear, but I can't promise anything.
I'm having troubles engineering a joint for the following scenario:
Imagine two equal-length arms (flat steel) that are connected to one another by a pivot point where they meet. They are in the same line, similar to clock hands at 25 past 11. Now, there is a force applied to the minute hand that rotates it anti clockwise. The joint ensures that the hour hand turns with it, so that they are still in the same line at 20 past 10. At this point, the join allows the minute hand to continue to turn until pointing at 2, while the hour hand remains at 10.

On the return (the minute hand is spring loaded to return when no force is applied), the minute hand moves from 2 to 3 turning the hour hand with it (back to its starting position). When the minute hand reaches 4, it then moves on its own (ie the hour hand is now stationary) back to 5.
Essentially the motion goes like this:
Force applied: Both move - minute hand moves alone
Force not applied (returning to starting position): Both move - minute hand moves alone.

It sounds like you need some absolute limits on the motion of the "hour hand", such as stops extending up from a face plate below the hour hand. Then you could have some rubber "blades" (like the blades of a windshield wiper) that extend down from the minute hand and up from the hour hand. Those will cause the two hands to move together until they hit a stop. Here's a pic that shows the stops and an exploded view of the hands in the 12 o-clock position:

              +-----+
              | MIN |
              +--+--+
                 |
RUBBER BLADES ->                    END
                 |                  VIEW
 +-+          +--+--+          +-+
 | |          |HOUR |          | |
 |S|          +-+P+-+          |S|
++T+------------+I+------------+T++ 
| O             |V|   FACE      O |
| P             |O|   PLATE     P |
+---------------+T+---------------+
                +-+

+---------------------------------+
|                                 |
|             +-----+             |  
|\            | M H |            /|
| \           | I O |           / |
| LEFT        | N U |       RIGHT |
| STOP        |   R |       STOP  | TOP
|             |     |             | VIEW
|             | | | |             |
|             |     |             |
|             | T B |             |
|             | O T |  FACE       |
|             | P M |  PLATE      |
|             |  O  |             |
|             |PIVOT|             |
|             +-----+             |
|                                 |
+---------------------------------+

The face plate can be minimized considerably to only extend to the stops, so long as it's anchored so it can't move when the hour hand moves.

Note, on rereading your question, I think I may have misunderstood. It sounds like you may want the two hands to move together at times when they aren't directly on top of each other. Is that correct ? If so, I'll need to come up with a modified design. Perhaps the stops can remain, but the rubber blades can be replaced with circular plates on the hour and minute hands, near the pivot, such that they contact each other with a moderate amount of friction (enough so they move together normally, but can move separately when the limits are reached on the hour hand). A way to have friction between the plates, without wearing them our quickly, would be to use a very thick grease between them. This would work as long as this mechanism doesn't move very fast, in which case heat could build up. StuRat 20:21, 10 December 2008 (UTC)

Pressure Drop Across a Constricted Annulus and the Venturi Effect

I am looking at a pump wear ring application, think of a concentric ring on a shaft with a clearance gap between the shaft and ring.

My question is this:

Due to any venturi effects, can the pressure profile in the clearance gap ever be less than the pressure on either end of the ring (entrance and exit)?

The differential pressure across the ring is 100 psi with the actual pressure numbers varying depending on what stage of the pump you are looking at.

   _______________
   |              |
A  |______________|  B
 ____Clearance Gap______
 |                     |
 |                     |
 |                     |
-------  --  --  ---------

Pressure A = 200psi (for example)

Pressure B = 100psi (for example)

(All flow must go thru the clearance gap)

Shaft diameter = 4.000 in

Ring inner diameter = 4.012 in

I think you're right, the venturi effect does apply here, so the pressure could be lower than 100 PSI, probably close to the 100 PSI side. StuRat 06:16, 13 February 2009 (UTC)

I NEED HELP PLEASE!!!!!!!!!!!!!!!!!!! (Bird house)

I have constructed a Martin birhouse 2'x2'x2' and it weighs 30 pounds. It is mounted on top of a 16' pressure treated 4"x4" post. I now need to have the bottom of the post 2' off the ground and erect it vertical ( so the birds will come live in it). I figure I need to use concrete and some more lumber. But how??? so mother nature won't destroy it????

HELP!!!!HELP!!! PLEASE!!! My name is Paul

Perhaps the biggest threat will come from animals trying to get to the martins, their eggs, and any food they have in their house. Unfortunately, just about any animal can climb a wooden post (maybe not dogs), so a metal pole would be a better choice. That would discourage most animals, and you could even grease the pole if some keep trying to climb it. One other problem with a square, wooden post is that it may cause the unit to fall over in heavy winds. A circular pole with a smaller diameter would greatly reduce this effect.

But, let's assume you're stuck with the square, wooden post. My suggestions for mounting it are as follows:

1) Get a metal pole to mount into the ground and in the center of the square, wooden post. Perhaps a 6 foot long metal fence pole would work, if you expect 2' in the ground, and 4' above (with 2' of those 4' inserted into the square, wooden post).

2) Drill a hole in the end of the post for the pole, and test it to make sure the wooden post slides nicely over the metal pole, all the way in. You may need a special tool to drill this hole. If so, go to a home improvement store and ask. They may either rent you the tool or drill the hole for you. Obviously, it's very important that the hole be vertical and in the center.

3) Dig a hole for the metal post and concrete. The same home improvement store will probably rent fence-pole-hole digging equipment. You can also dig the hole with a shovel, but that requires more work and concrete as the sides will be more like a 45 degree angle using a shovel. The hole should go below the frost-line for your area, so you won't get W:frost heaving, which can cause the bird house to lean.

4) Place the metal pole in the final position, stuck in the dirt at the bottom of the hole. Use stakes and ropes to tie the pole into it's final position, and use a level on top to ensure that the pole is truly vertical. Avoid doing this on a windy day, as it will be more difficult to keep the pole stationary while the concrete sets.

5) Get some concrete and follow the instructions very carefully. The mix of ingredients is critical, as is the temperature, humidity, etc. You also must use it fairly quickly after you mix it, and must rinse off any tools or containers before the concrete hardens on them.

6) After you pour the concrete, wait the recommended amount of time for it to set, then place the wooden post over the metal pole. This may take two people. This design may allow the bird house to be rotated (depending on the shaft/hole tolerance). I'd think you would want to rotate it so the opening is pointing away from the prevailing winds, to make it the nicest for the martins. It should stay in position normally, but extreme winds may rotate it, in which case you can rotate it back. StuRat 15:22, 1 April 2009 (UTC)

microprocessor based EPROM programmer

Hello. Any one interested in this learning project? or if anyone has completed this project contact me ASAP by sending me a mail on jigsaw.18june@gmail.com or post it here

thanks

Below is the project statement :

Design a microprocessor based EPROM programmer to program 2716.The EPROM can be programmed by applying 25V at VPP and 5V at OE pin. Initially all data of EPROM will be 1's and the user should make the bits zero selectively. The bit parallel data is applied to the data output pins (D0-D7). The address for the EPROM is provided through the address pins. To program the address of each location to be programmed should be stable for 55ms.When address and data are stable, a 50ms active high pulse is applied to CE input.

Reply 1: Though you need to be more specific about what problems are you facing. This is a common university project, and can be accomplished with many microcontrollers - starting from the simplest 8051 core to more complex uC available today.

Manufacturing steel tubes

Friends, I am new to this portal and i have a very specific question in my mind.Which is the best method to manufacture hollow steel tubes of about 8 mm internal diameter & 40 mm outer diameter. the answer to this question is important to me as this has got connected to my livlihood now. hope to get answers from you all soon.thanks & regards ajay.

Let's look at some ways to form tubes and determine which might work for you:

1) Start with flat sheet metal, then bend it into a tube and weld the seam. This is appropriate for thin-walled tubes, though, not for yours.

2) Cast each section in two pieces, then weld them together. Probably not appropriate for tubes made to withstand high pressures, as the welds may fail (or the metal right around the welds).

3) Start with a solid cylinder, then drill out the hole. This would be appropriate for thick-walled tubes with small inner diameters and short length. You didn't specify the lengths needed.

4) Extrude the tube with the hole inside it. The supports for the bullet shaped form used to create the hole will sever the tube wall, so it will need to be hot enough to rejoin after. This method can be used to form very long tubes. Here's a rough drawing of what the center of the form for the extrusion might look like, with 3 supports:

                FRONT       SIDE
                   /           |\
                - O        |     >
                   \           |/

So, I'd expect the 4th approach would work the best for you, although the 3rd could also work for short tubes and the 2nd could work as long as the pressure requirements aren't very high. StuRat 05:19, 14 April 2009 (UTC)

Grain Growth

I have no idea how to start this. Please help! Grain growth rate (change in grain size with time) is proportional to the inverse of the grain size (the change in area is the critical parameter, but the linear rate will be normalized to the volume). Based on this fact derive the grain growth equationwhere n=2. (d^2-do^2=Kt)

Underwater ROV

UNDERWATER ROV I need to come up with an idea on a ROV that can go down to the bottom of a pool and collect 125 mL of water and then bring it back up. Any ideas??!!

How to calculate the temperature change of fluid inside a casing

Hi Everyone,

I am attempting to calculate the temperature of a casing circulating fluid that is heated from the formation. After reviewing articles from the Society of Petroleum Engineers such as: SPE 3605, SPE 1484, and SPE 105437, the answer was not clear. The following is an example question that I have gathered information from SPE 1484.

Fluid = water Casing Inner Diameter = 4.892 inches Casing Outer Diameter = 5.50 inches Fluid thermal conductivity = 0.37 BTU/(foot * Fahrenheit) Fluid Density = 8.34 pounds per gallon Formation specific heat = 0.21 BTU/(pounds * Fahrenheit) Formation thermal conductivity = 1.30 BTU/(foot * Fahrenheit) Formation temperature = 160 Fahrenheit Water temperature prior to exposure = 100 Fahrenheit Section of pipe = 10 feet

There are a few formulas at http://www.engineersedge.com/heat_transfer/conduction_cylidrical_coor.htm that is:

How would I determine the temperature of the fluid inside the casing after 1 minute of contact time?

Thanks for your help!

Are Velocity (mm/s) measurements obtained using an accelerometer comparable to those obtained using a Geophone?

I have performed some ground borne vibration tests using an accelerometer and obtained mm/s data (the vibration meter has a Velocity filter incorporated). I have noticed the results I'm getting are different from another geophone instrument I am also using in a comparative style. Are the peak velocity measurements I'm obtained from my accelerometer not analagous to those Peak Particle Velocity (PPV) measurements my geophone is yielding? Does a correction need to be applied? The accelerometer results are significantly greater than those from the geophone.