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shock accelerometer
Posted 2010年2月15日 GMT-5 01:00 1 Reply
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hello sir
i am doing project on shock accelerometer.i don't knw how to apply the pulses as a input to the system.(i.e for some period it should be on and remaining period it should be off).
what is the relation between vonmises stress and axial stress. and how to find the axial stress in comsol.could you please explain the above problems.
thanking you sir
i am doing project on shock accelerometer.i don't knw how to apply the pulses as a input to the system.(i.e for some period it should be on and remaining period it should be off).
what is the relation between vonmises stress and axial stress. and how to find the axial stress in comsol.could you please explain the above problems.
thanking you sir
1 Reply Last Post 2010年2月15日 GMT-5 02:27
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Posted:
1 decade ago
Hi
Well for applying a square, heaviside step or half sinus pulse or simiting similar in transient, you can either define a function, calling up the required comsol "functions" (typically dependent on the time "t" and with an output of "1", and then you multiply your desired amplitude by this time function).
Or you type the formula direrectin your load field the acceleration must be multiplied by the density to get to a "pressure" for domain loads, always check the units).
You can also use F0*(t>t_start)*(t<t_end) but such a square pulse is tough to model as the steps tend to destabilise the solvers, you can "smoothen" the setps with a "Heaviside" function (do an indexed search on your doc) or you make your sinus step by playing a little with the algebra, be sure your function is derivable number of times (in my opinion sinus functions are the simplest for shock analysis).
Mostly for shocks, I ensure a continuous "jerck" wich is the derivative of the acceleration (d^3/dt^3)(u)
Now for the tress, this is rather case dependent, Von Mieses stress is an average commonly used (I use it mostly too as a general "stress quality value"), but depending on the case you a looking for the detailed stress tensor is often of interest too.
I can only recommend to study books like:
www.amazon.com/Elasticity-McGraw-Hill-Classic-Textbook-Reissue/dp/0070858055/ref=sr_1_1?ie=UTF8&s=books&qid=1266218426&sr=8-1
or
www.amazon.com/Elasticity-Tensor-Dyadic-Engineering-Approaches/dp/0486669580/ref=pd_sim_b_5
there are many out there, in many languages
Note selecting the correct stress and understanding "stress concetrating" effects is crucial, many tragic accidents have happened as designers and manufacturer has forgotten to check carefully the stress concetration effects.
further readings:
www.amazon.com/Petersons-Stress-Concentration-Factors-Walter/dp/0470048247/ref=sr_1_1?ie=UTF8&qid=1266218754&sr=1-1-spell#reader_0470048247
Good luck
Ivar
Well for applying a square, heaviside step or half sinus pulse or simiting similar in transient, you can either define a function, calling up the required comsol "functions" (typically dependent on the time "t" and with an output of "1", and then you multiply your desired amplitude by this time function).
Or you type the formula direrectin your load field the acceleration must be multiplied by the density to get to a "pressure" for domain loads, always check the units).
You can also use F0*(t>t_start)*(t<t_end) but such a square pulse is tough to model as the steps tend to destabilise the solvers, you can "smoothen" the setps with a "Heaviside" function (do an indexed search on your doc) or you make your sinus step by playing a little with the algebra, be sure your function is derivable number of times (in my opinion sinus functions are the simplest for shock analysis).
Mostly for shocks, I ensure a continuous "jerck" wich is the derivative of the acceleration (d^3/dt^3)(u)
Now for the tress, this is rather case dependent, Von Mieses stress is an average commonly used (I use it mostly too as a general "stress quality value"), but depending on the case you a looking for the detailed stress tensor is often of interest too.
I can only recommend to study books like:
www.amazon.com/Elasticity-McGraw-Hill-Classic-Textbook-Reissue/dp/0070858055/ref=sr_1_1?ie=UTF8&s=books&qid=1266218426&sr=8-1
or
www.amazon.com/Elasticity-Tensor-Dyadic-Engineering-Approaches/dp/0486669580/ref=pd_sim_b_5
there are many out there, in many languages
Note selecting the correct stress and understanding "stress concetrating" effects is crucial, many tragic accidents have happened as designers and manufacturer has forgotten to check carefully the stress concetration effects.
further readings:
www.amazon.com/Petersons-Stress-Concentration-Factors-Walter/dp/0470048247/ref=sr_1_1?ie=UTF8&qid=1266218754&sr=1-1-spell#reader_0470048247
Good luck
Ivar