Physics Forums - Mechanical Engineering

Physics Forums - Mechanical Engineering http://www.physicsforums.com Mechatronics, Robotics, Engines, Drafting Aerospace Engineering - Automotive Engineering en Fri, 24 May 2013 22:34:11 GMT vBulletin 60 http://www.physicsforums.com/images/physicsforums/misc/rss.jpg Physics Forums - Mechanical Engineering http://www.physicsforums.com Turbomachinery: number of stages and power of steam turbine http://www.physicsforums.com/showthread.php?t=693491&goto=newpost Fri, 24 May 2013 21:56:49 GMT Please help! Steam turbine. Given parameters: turbine speed, steam flow, steam inlet and outlet pressures, nozzle and blade velocity coefficients,... Please help!
Steam turbine. Given parameters: turbine speed, steam flow, steam inlet and outlet pressures, nozzle and blade velocity coefficients, blade angles and blade velocity. I can find all efficiencies. How could I calculate number of stages required and the actual power produced? ]]> Mechanical Engineering Submarine http://www.physicsforums.com/showthread.php?t=693491 Motor for a project http://www.physicsforums.com/showthread.php?t=693454&goto=newpost Fri, 24 May 2013 18:29:05 GMT I do not know much about motors so I was wondering if you all could help me out a bit here. I am looking for a small electric motor that does not... I do not know much about motors so I was wondering if you all could help me out a bit here. I am looking for a small electric motor that does not need to accelerate fast, but can propel about 150lbs as fast as possible when connected to a 110mm wheel. It will need to be battery operated. I am a bit flexible on the dimensions, but would prefer it to be no larger than 100mm x 100mm x 100mm. I hope I explained it well enough for you all to understand. If not, let me know. Price at this point isn't an issue.

Thanks a bunch! ]]> Mechanical Engineering Securityman http://www.physicsforums.com/showthread.php?t=693454 Theory of Gearing http://www.physicsforums.com/showthread.php?t=693380&goto=newpost Fri, 24 May 2013 07:12:31 GMT Folks, I have a book Gear Geometry and Applied Theory by Litvin. It looks pretty hairy and the diagrams/schematics of the kinematic relations etc... Folks,

I have a book Gear Geometry and Applied Theory by Litvin. It looks pretty hairy and the diagrams/schematics of the kinematic relations etc are difficult to understand.
What branch of mathematics does this fall under, diferential geometry and topology?

I think I may need to get some introductory book before I delve into this gear theory...

Any suggestions?

Thanks ]]> Mechanical Engineering bugatti79 http://www.physicsforums.com/showthread.php?t=693380 Confusion with Motor Sizing http://www.physicsforums.com/showthread.php?t=693145&goto=newpost Wed, 22 May 2013 19:38:57 GMT Hello all, I an trying to size a motor to drive two mechanisms but am having some real trouble getting my head around the required torque. ... Hello all,

I an trying to size a motor to drive two mechanisms but am having some real trouble getting my head around the required torque.

First let me explain what we have. Basically there are two mechanisms where I have plotted the speed and torque requirements on this graph

as you can see the v230 mechanism only runs between 0 to 1500 RPM where as the v24 mechanism runs from 0 to 6000 RPM but with very different torque requirements.

I need to size a motor in terms of RPM and Torque that will run both mechanisms however I'll have to do something to limit the speed of the v230 mechanism to 1500 rpm.

What happens to the torque requirements in this situation? Are they added together? If a motor is driving one mechanism is the torque already present for the other mechanism or is additional torque required?

I am envisaging the mechanics somewhat like this

I soft of have the speeds sorted in as much as I believe they are correct but I am struggling with the amount of torque required by the motor.

Could someone please advise on this? Or maybe (i'm sure) there is a simpler way to achieve this in a less complicated fashion?

Thanks very much guys. ]]> Mechanical Engineering cosmarchy http://www.physicsforums.com/showthread.php?t=693145 Mass Spring Damper system http://www.physicsforums.com/showthread.php?t=692890&goto=newpost Tue, 21 May 2013 13:26:19 GMT Hello! I am taking a course in dynamics and have a question about a spring-mass-damper system (see the attached file) that I want to solve using... Hello!

I am taking a course in dynamics and have a question about a spring-mass-damper system (see the attached file) that I want to solve using Lagrange equation (see attached file).

I am having trouble writing the equation of motion for this problem. At first I tried doing it the way I would for a system with two masses, connected by springs and dampers. This gave me a system of equations which I then used the State Space Approach on. I set the first mass=0, only to realize that I would not be able to get the homogenous solution this way.

Any help is appreciated! Thank you very much!

Attached Images

	Mass-spring-damper-system.JPG (21.4 KB)
	Lagrange.JPG (12.0 KB)

]]> Mechanical Engineering Lelak http://www.physicsforums.com/showthread.php?t=692890 Model Reduction and Substructuring in Dynamics, CMS http://www.physicsforums.com/showthread.php?t=692483&goto=newpost Sun, 19 May 2013 11:25:22 GMT Dear engineers and physicists, I would like to ask you a question about Component Mode Synthesis (CMS), which is the topic of my bachelor thesis.... Dear engineers and physicists,
I would like to ask you a question about Component Mode Synthesis (CMS), which is the topic of my bachelor thesis. My primary resource is the classical AIAA article "Coupling of Substructures for Dynamic Analyses: an Overview" by Prof. Craig.
For now I am considering a simple mechanical system consisting of two connected bodies (arms) according to the first picture. The individual bodies have been modeled in ANSYS and their mass, stiffness, nodal coordinates and adjacency matrices were imported to Matlab, where reduction and interconnection themselves are carried out.
First the FEM solution without reduction (i.e. in physical coordinates) is calculated for reference and then two CMS methods are implemented, namely the Craig-Bampton's (fixed-interface normal modes & constraint modes) and Rubin's (free-interface normal modes, rigid-body modes & residual flexibility modes).
Now to my question, which might be a bit funny, bacause I am complaining about the methods being too precise. :) It seems that the natural frequencies of both methods correspond exactly (!) to the FEM solution, errors being of the order 0.01% which can be accounted to numerical round-offs. If I keep 30 natural modes for each body corresponding to 30 lowest frequencies, the first 50 natural frequencies of the connected system are exact! Then the error increases and the last calculated frequency (60th) has an error of 20% (talking about the Craig-Bampton now). I was really surprised by this, do you somebody have an insight where this "exact" corresponence comes from? If I compare the normal modes of the assembled reduced model with the reference solution by the Modal Assurance Criterion (MAC), I get the expected inaccuracies (please see 2nd included picture for the 20 lowest freq. normal shapes).

Thank you very much for any answers, tips, further questions or any other form of reactions. All the best from the Czech Republic.

Attached Images

	Natural_mode_1.png (114.8 KB)
	MAC_Craig_Bampton.png (23.8 KB)

]]> Mechanical Engineering Zirkus http://www.physicsforums.com/showthread.php?t=692483 Stress analysis of quadcopter part http://www.physicsforums.com/showthread.php?t=692421&goto=newpost Sat, 18 May 2013 23:33:07 GMT Hi Everyone, I am a student studying civil engineering and want to do a stress analysis on a part I have made in Solidworks (CAD software).... Hi Everyone,

I am a student studying civil engineering and want to do a stress analysis on a part I have made in Solidworks (CAD software). However, it is somewhat complex for handcalculation purposes, so I have simplified it down. I want to run a full ansys simulation on the part, however I need a basis from the handcalculation to determine if the ansys analysis is credible or not. If anyone can give me some input onto if my assumptions are right that would be great.

I initially tried to use a plane stress approach 2d analysis, however this assumes the whole cross section is fixed. It is only fixed at the spots indicated. Attached is the part geometry with support and loads.

The fixed support holes I am concerned that the material will fail there, and at the beginning of the square cross section due to the bending moment.

I can't thank you enough for the help.

Attached Images

QUADCOPTER PART.JPG (38.4 KB)

]]> Mechanical Engineering sciencerocks http://www.physicsforums.com/showthread.php?t=692421 Rquired bolt size to support gantry http://www.physicsforums.com/showthread.php?t=692349&goto=newpost Sat, 18 May 2013 14:46:52 GMT Hello all, Just thinking of this in my head, and maybe over thinking it. First a description of the problem,If i have two upright I beams, and an I... Hello all,
Just thinking of this in my head, and maybe over thinking it. First a description of the problem,If i have two upright I beams, and an I beam spanning from one to the other. The horizontal beam isnt sitting on top of the two uprights, but bolted to the face of them. In calculating the force acting downwards at each end of the horizontal beam, do i just treat this as a simply supported at both ends and calculate the upward reactions at each, and use this as the force to calculate the shear stress in the bolts.
Thanks in advance for all replies ]]> Mechanical Engineering blizzard95 http://www.physicsforums.com/showthread.php?t=692349 ANSYS APDL help for 3D Thermal problem http://www.physicsforums.com/showthread.php?t=692316&goto=newpost Sat, 18 May 2013 08:27:00 GMT Hello, Greetings! How do I get the convective surface matrix from ANSYS for 3D thermal problem. Consider a volume, where some of its surfaces... Hello,
Greetings! How do I get the convective surface matrix from ANSYS for 3D thermal problem. Consider a volume, where some of its surfaces are subjected to convective boundary conditions. What is the way to get those (only convective surface) matrices generated by ANSYS. Any help in this direction is very much appreciated.

Thank you
Stacky ]]> Mechanical Engineering Stacky http://www.physicsforums.com/showthread.php?t=692316 Load versus deflection plot and MOE http://www.physicsforums.com/showthread.php?t=692305&goto=newpost Sat, 18 May 2013 06:22:45 GMT I should be able to calculate the MOE and MOR after a four point Bending test in lumber wood. I have all the data for develop a plot load versus... I should be able to calculate the MOE and MOR after a four point Bending test in lumber wood. I have all the data for develop a plot load versus deflection. The data provided was: load, cylinder, string and bridge. I have been doing the plot using the bridge as deflection, but I didn´t get the typical plot for load versus deflection.Which of them should I take for the deflections in order to calculate the MOE?

Load (lbs.)
169.9829

Cylinder (in.)
-0.0006

String (in.)
0

Bridge (in.)
-0.0001

thanks for your help ]]> Mechanical Engineering Pahoo http://www.physicsforums.com/showthread.php?t=692305 <![CDATA[What are the most popular Universities' Thermofluid Labs in the UK?]]> http://www.physicsforums.com/showthread.php?t=692257&goto=newpost Fri, 17 May 2013 20:11:10 GMT Hi, I am trying to decide about my postgraduate I was wondering which universities have a reputation on thermofluid mechanics? Can you name 5-6 of... Hi,
I am trying to decide about my postgraduate I was wondering which universities have a reputation on thermofluid mechanics?
Can you name 5-6 of them?
Thanks ]]> Mechanical Engineering socrates_1 http://www.physicsforums.com/showthread.php?t=692257 Instantaneous Center of Velocity http://www.physicsforums.com/showthread.php?t=692238&goto=newpost Fri, 17 May 2013 17:30:28 GMT Hello, I am trying to find the angular velocity of a link in a 4 link mechanism problem but I have reached a scenario which is new to me. Please... Hello,
I am trying to find the angular velocity of a link in a 4 link mechanism problem but I have reached a scenario which is new to me. Please look at the attached image.
I already know the velocity of the slider which is 3m/s. I have indicated in the diagram a line parallel to AB to indicate that all points on AB have the same velocity, hence AB undergoes only translation.
My problem is finding the velocity at point D because when I try to draw the instantaneous Center of velocity of points C and D they two velocities are concurrent. I seem to have a lot of ways to interpret it which is the problem. One way I can look at it is to say that C is the ICV which is absurd since I have already established that C, being on AB which is a rigid rod already has a velocity of 3.
Please enlighten me !

Attached Images

ba.jpg (48.1 KB)

]]> Mechanical Engineering medwatt http://www.physicsforums.com/showthread.php?t=692238 Igntion system suggestions/considerations http://www.physicsforums.com/showthread.php?t=692096&goto=newpost Thu, 16 May 2013 20:46:49 GMT Hi, We are building a turbojet engine / gas turbine engine for our graduation project. We were looking out for ignition system for the... Hi,

We are building a turbojet engine / gas turbine engine for our graduation project.

We were looking out for ignition system for the combustion chamber.
The fuel is LPG (20% propane 80% butane)

What can be the best way to ignite a spark to light the flame in the combustion chamber to start the engine?

We think that a lighter will not work because it has very little ignition energy.
And we also think that holding a flame from a source such as matchstick or any other source cannot work, since airflow will extinguish the flame before combustion gets self sustaining in the combustion chamber.

Suggestions?
Is there a simple way to use spark plug? ]]> Mechanical Engineering sgvaibhav http://www.physicsforums.com/showthread.php?t=692096 <![CDATA[Engaged/disengaged flywheel's effect on a shaft`s work/power]]> http://www.physicsforums.com/showthread.php?t=692089&goto=newpost Thu, 16 May 2013 20:00:23 GMT A flywheel is to be rotated by a shaft through a clutch mechanism (assuming no friction or losses). In the begining, the flywheel is floating (not... A flywheel is to be rotated by a shaft through a clutch mechanism (assuming no friction or losses). In the begining, the flywheel is floating (not engaged to the shaft). The clutch mechanism from time to time engages/disengages the flywheel to/from the shaft trying to keep the shaft`s angular velocity steady. The flywheel is to accelerate and deaccelerate the shaft as it stores/releases energy.

I`d like to calculate the work done by the shaft when rotating the flywheel and also the effect of the flywheel on the overall shafts' work/power when the flywheel engages and disengages.

I understand that at the first engagement (flywheel's velocity is zero), the shaft starts to rotate the flywheel, and hence the shaft slows down, the work done by the shaft is the difference in the kinetic energy of the flywheel (1/2*I*ω(2)^2 - 1/2*I*ω(1)^2 ==> 1/2*I*ω(2)^2 since ω(1)=0). Am I wrong ?

Then the flywheel disengages from the shaft by the clutch mechanism, and when it is engaged again the flywheel may speed up the shaft(if its angular velocity higher than that of the shaft) or slow down the shaft (if its angular velocity lower than that of the shaft). What equation should I use to add the effect of the flywheel on the shaft`s work/power at the moment of the engagement ? is the difference in the kinetic energy of the flywheel (as above), represents the work done on or by the shaft ? or the effect of the flywheel can be included by adding the inertia of the flywheel to the shaft's power calculation ?

Sorry if I stated something wrong, I`m not good in physics, many thanks for your help.

Regards ]]> Mechanical Engineering Shune2001 http://www.physicsforums.com/showthread.php?t=692089 FEA Thermal Stress Factor of Safety Question http://www.physicsforums.com/showthread.php?t=692033&goto=newpost Thu, 16 May 2013 14:12:06 GMT Hi Guys

I'm analysing a heat exchanger based on an existing commercial model in SolidWorks Simulation. The same materials etc have been applied to it in the Static analysis.

Deflection on the heat exchanger is very small. The one thing that baffles me though is how, regardless of even when I increase the wall thickness considerably, the factor of safety whenever I apply a temperature to the heat exchanger is always really small.

The factor of safety is calculated based on Maximum von Mises stress and yield strength as a default.

Are the FOS results I'm getting actually quite realistic? I have a feeling that something is quite wrong here. If you would concur, could anybody explain to me why? It seems there is very little improvements that can be made besides actually changing the temperature.

Thanks for any help you can offer.

David ]]> Mechanical Engineering big_bird http://www.physicsforums.com/showthread.php?t=692033