## General Mechanical

#### Beam subjected to a vertical mobile harmonic vertical force

• RHYLANE
Subscriber
Hello community!nI need your help please.nI want to do the following simulation but I didn't know how to do it on ANSYS Workbench.nMy simulation consists in calculating the displacement as a function of time of a point of a beam subjected to a mobile harmonic vertical force.nIn the first case, I have to consider that the harmonic force crosses the beam at a speed of 10m / s.nIn the second case, I must consider that the harmonic force crosses the beam at a speed of 20 m / s. n
• peteroznewman
Subscriber
nPlease insert an image of the beam and the direction the harmonic force is traveling.n
• RHYLANE
Subscriber
Thank you so much for your answer sir. This is the picture of the beam and the direction of the harmonic force.nThe frequency of the force is about 10 hz.n
• peteroznewman
Subscriber
nIn the future, please insert the image into the post because ANSYS staff are not permitted to download attachments.nYou gave the two velocities. Now it would be helpful to know how long the beam is and what the first natural frequency of the beam is.nDoes the oscillating force start at one end and move to the other, or does is start in the center?n
• RHYLANE
Subscriber
You're right sir. nThe length of my beam is 90m. The force starts from the first end of the beam and arrives at the other end with a speed v so that the maximum amplitude will be reached when the force reaches x = L / 2. L is the length of the beam in question. After x = L / 2, the amplitude decrease again until the force reaches 0N.nConcerning the first natural frequency, if you will allow me, I will carry out a modal analysis right now to answer you. nThank you very much sir for your support. n
• RHYLANE
Subscriber
Hello Sir This is the result of the modal analysis of the beam.nn
• peteroznewman
Subscriber
nIt doesn't look like this beam has been fixed to ground. When objects in 3D are not fixed to ground, the first six modal frequencies are zero. Request more than 6 modes, such as 10, or properly fix the beam to ground and rerun the analysis.n
• RHYLANE
Subscriber
i changed the extremities into fixed support and i've got this result sir .nfor the intermediate nodes, only the vertical motion is allowed.
• peteroznewman
Subscriber
nThe period of the first mode is 156 seconds. Does that seem right?nAt 10 m/s, it will only take 9 seconds to go from one end of the beam to the other so there is little chance of a harmonic force exciting much of the first mode.nCheck the profile of the beam, does it have the correct dimensions?n
• RHYLANE
Subscriber
Oh i see sir you say right. 156 second is the inverse of the first natural frequency.nConcerning the dimensions, i've choosed those values arbitrarly just for trying the case of the harmonic traveling force on the beam in ansys workbench. Now i changed the cross section dimensions and now i have those results:nThe new period of the first mode is 15 seconds. At 5 m/s, it will take 18 seconds to go from one end of the beam to the other. I think it can work now right?nn n