March 14, 2022 at 7:29 pm

Rameez_ul_Haq

Subscriber

,fixed support at left end and 1 N force along =Z direction on right end. [Material = Aluminum Alloy, Large Deflection = OFF].

Well, yes. The deformations are different for both of these mesh sizes. So it means that the mesh size actually affects the stiffness of the body, and it just not depend on the unmeshed geometric dimensions of the body; infact mesh size plays a vital role here as well. Okay, so now I understand that the natural freqs would change if mesh size is changed, since overall stiffness of the body changes.

My basic concern was that why is this not an acceptable approximation to just idealize the complete body as a single point mass 'm' and then apply the relevant stiffness to it (calculated by hand), apply the support and then use analytical equation to find out the natural freq and mode shapes of it. But I think that this is not the greatest way to opt for; a single point mass could have 6 DOF's in total, so I would be able to only observe the deformation behavior or pattern of only the center of mass of the body at the respective mode and not of the complete body. By breaking the body into several mesh elements (which are infact all joined together by relevant stiffnesses), I would be able to observe the behavior of each of the nodes at that certain natural freq (which make up the complete body), and thus I am observing the overall behavior of the complete body at that natural freq.

The only question which remains now is that, okay, I mean I understand that the deformation behavior of the body can be observed by mode shapes at a certain natural freq from the modal analysis results, but assume I don't want to gain information about mode shape but only the natural freqs of my system. So in this case idealize the body as a single point mass (and then using analytical equations to calculate the natural freqs) would be an acceptable approach or not?

Plus, assume I conduct a modal analysis and I get first natural freq of, say, 10 Hz. We know that the total number of DOFÃ”Ã‡Ã–s for a FEA model will result in as much natural freqs (and mode shapes). So the node associated with this natural freq of 10 Hz is supposed to have the highest amplitude (when behaving at the shape of the relevant mode) than all the other nodes when, say, is exicted by an external force of this much freq?

Well, yes. The deformations are different for both of these mesh sizes. So it means that the mesh size actually affects the stiffness of the body, and it just not depend on the unmeshed geometric dimensions of the body; infact mesh size plays a vital role here as well. Okay, so now I understand that the natural freqs would change if mesh size is changed, since overall stiffness of the body changes.

My basic concern was that why is this not an acceptable approximation to just idealize the complete body as a single point mass 'm' and then apply the relevant stiffness to it (calculated by hand), apply the support and then use analytical equation to find out the natural freq and mode shapes of it. But I think that this is not the greatest way to opt for; a single point mass could have 6 DOF's in total, so I would be able to only observe the deformation behavior or pattern of only the center of mass of the body at the respective mode and not of the complete body. By breaking the body into several mesh elements (which are infact all joined together by relevant stiffnesses), I would be able to observe the behavior of each of the nodes at that certain natural freq (which make up the complete body), and thus I am observing the overall behavior of the complete body at that natural freq.

The only question which remains now is that, okay, I mean I understand that the deformation behavior of the body can be observed by mode shapes at a certain natural freq from the modal analysis results, but assume I don't want to gain information about mode shape but only the natural freqs of my system. So in this case idealize the body as a single point mass (and then using analytical equations to calculate the natural freqs) would be an acceptable approach or not?

Plus, assume I conduct a modal analysis and I get first natural freq of, say, 10 Hz. We know that the total number of DOFÃ”Ã‡Ã–s for a FEA model will result in as much natural freqs (and mode shapes). So the node associated with this natural freq of 10 Hz is supposed to have the highest amplitude (when behaving at the shape of the relevant mode) than all the other nodes when, say, is exicted by an external force of this much freq?