

January 19, 2024 at 8:53 ammdmech.mechSubscriber
Hello All,
I have modelled an oilfilled tank. It is subjected to a vibration of 25 mm/sec for a period of 2 seconds. I want to ensure that the designed component or parts are within the yield strength of the material. Can anyone suggest a procedure to perform the analysis? I don't know how to start this analysis. Some guidance would be very much appreciated.

January 19, 2024 at 2:13 pmpeteroznewmanSubscriber
Let me restate the vibration load.
 Peak velocity is 25 mm/sec for a sinusoidal ground motion.
 A period of 2 seconds is a frequency of 0.5 Hz.
You want to know the steady state response of the structure.
Let's put aside the fact that the tank is oilfilled for now because it makes the model slightly more complex and just focus on making a model to simulate the stress in an empty tank.
The analysis you want is called Harmonic Response.Â It requires a Modal analysis to build upon.
Take the free courses on Harmonic Response and Modal then come back when you have attempted that for the empty tank.
/courses/index.php/courses/harmonicresponseanalysisinansysmechanical/
/courses/index.php/courses/modalanalysisinansysmechanical/

January 24, 2024 at 5:08 ammdmech.mechSubscriber
Hi Peter,
As per your suggestion, i have completed the modal analysis course and the tank natural frequency extracted. While attempting to do the harmonic analysis followed by modal analysis, I could not able to insert the 25 mm/sec as a velocity for the frequency of 0.5 Hz. Can you please guide me for further process.

January 25, 2024 at 11:59 ampeteroznewmanSubscriber
Convert the velocity to acceleration by taking the derivative. The equation for the velocity is A*sin(w*t) where A is 25 mm/s and w is the circular frequency. Convert the 0.5 Hz frequency into a circular frequency. It's not important that the equation changes to a cos function.Â

January 28, 2024 at 4:57 ammdmech.mechSubscriber
Thank you Peter,
velocity (A) = 0.025 m/sec, w = circular frequency is 3.14159 rad/sec, from this acceleration I have got is 0.2467 m/s^2. Am I correct?Â
Mean while, how do I model the oil filled in the tank? Please suggest a procedure.
Thanks in advance


January 28, 2024 at 8:13 pmpeteroznewmanSubscriber
How did you come up with that number? I don't think it is correct.Â
Is the tank completely filled with fluid or is there a free surface with air or other gas at the top?

January 29, 2024 at 12:53 ammdmech.mechSubscriber
Hi Peter, From Internet, I have found a formula,
x = 0.025 m
acceleration =Â 4*Ï€^2*f^2*xÂ = 0.2467 m/s^2
I am not sure, which method is correct
As you suggested,
f = 0.5 Hz
A = 0.025 m/s
w = 2*pi*f = 3.14159 rad/sec
velocity = A*sin(w*t)
t = 2 seconds
acceleration = A*w*sin(w*t)  As you said I have taken the derivative
Â Â Â Â Â Â Â Â Â Â = A*(2 * pi * f) * sin(w*t)
Â Â Â Â Â Â Â Â Â Â Â = 0.025*(2*3.1416*0.5)*sin(3.1416 * 2)
Â Â Â Â Â Â Â Â Â Â Â = 0.00859 m/s^2
Please give me a suggestion as to which value of acceleration I should take.
The tank is half filled with free surface with air at the top.


January 29, 2024 at 6:57 pmpeteroznewmanSubscriber
The formula from the internet is to convert a displacement to acceleration. You have a velocity so you take the derivative of the velocity and you wrote a correct equation for acceleration.
The amplitude for the acceleration is A*w = 0.025*3.1416 = 0.07854 m/s^2.Â Don't evaluate the sin(w*t) term, which you got wrong because you didn't use radians, but you only want the amplitude anyway.
I will reply later after I find a reference for adding the fluid to the tank. That question has been asked before so you can try searching for it also.

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