Update / Fix the Nodal Weights Dialog

[saainsworth]

Please fix the Nodal Weights dialog. It has a number of issues that make it difficult to use.

1) A better name would be "Nodal Mass" since that is what is really being added.

2) The units for Mass moment of inertia are not correct. When set to mass You get N*s^2*m which is a force unit.

When set to force you get N*m^2 which is not a correct unit of inertia. The correct unit is kg*m^2 -- a mass unit. The English

units are similarly messed up.

3) When switching unit systems the values update. However, when switching from Mass to Force units within the dialog it does

calculate the conversion. If someone enters a value and then switches the input mode the value is then wrong. This makes no sense

and certainly is not would be expected in quality software.

4) Provide an option to specify the mass moment of inertia about either the model coordinate system or the center of mass (at the node).

Currently is not clear which is being specified. The help file does not clarify this.

[AstroJohnPE]

A few comments.

1) I think this is a matter of personal preference. Do more users "think" in terms of mass or weight? The net effect is the same.

2) I agree that the mass moment of inertia units should be mass * length^2 when entering in mass units, where the mass unit is as-shown on the unit system dialog. So in SI units, would have kg*m^2. In English inch, the unit would be (lbf*s^2/in)*in^2. Technically, N*s^2*m (or force*time^2*length in general) is a valid but unusual unit for the mass moment of inertia. weight/gravity = mass, so weight = mass*gravity. Thus, N*s^2*m = (kg*(m/s^2))*s^2*m = kg*m^2

The concept of W*k^2 (weight times radius of gyration squared) is quite common for the mass moment of inertia, at least in the U.S. So units of force*distance^2 is acceptable when using force units in the dialog.

3) There is an important word missing. It should read "However, when switching from Mass to Force units within the dialog it does NOT calculate the conversion." I agree that it would be a nice feature for the dialog to convert the entered numbers between mass units and force units.

4) I can see how this would be handy. But instead of an option for the mass moment of inertia to be about the model coordinate system (0,0,0), there should be three input boxes for the user to enter the coordinate. After all, how many CAD models are positioned properly with respect to 0,0,0?

John Holtz, PE