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There are some misunderstanding. By equilibrium, I refer to the state that forces and moments are balanced and no accleration due to total loads. Nothing to do with "damping". Is it "common" that air vehicles in flight have translational/rotational accleration and the forces and moments are...

Thanks for the reply. It is common that there are many flight maneuver that the air vehicle is not in static/dynamic equilibrium. By "equilibrium", I mean that sum of all the external forces and moments are not zero. For example, to obtian a Diving condition, there is a pitching down moment...

Onda, Thank you again! I understand what you said. My point is that I need to analyze the condition, in which the forces and moments are not in a equilibirum state. I know that I can change thrust, control surface loads to balance forces and moments, which is a steady state. As we know, there...

Thanks a lot, Onda! I only apply a gravity acceleration to my model. Except that, I also have aerodynamic and dynamic loads. My question is that the sum of external forces and moments are not zero, which means that rotational/translational acceleration exist for the system (considering freebody...

Thanks for the reply. For PARAM, INREL, -2, no constraint is needed. For PARAM, INREL, -2, constraint need to be specified. My problem is that I need to analyze critical flight conditions-the forces and moments are not balanced. I don't know if it is working for inertia relief.

Can I use Nastran Inertia Relief to analzye an unconstrained system with unbalanced froces and moments? The system is not supported and not constrained (for example, an aircraft in flight), and have translational/rotational accelerations due to nonzero total forces and moments? I am not able...

Slumdogengineer and eelco71, thank you for the reply. Actually, I have more than one hundred lines to divide to three segments. If I don't change the number of the original line, I will get a new number of the new line. Then, I can divide the new line into two. What does "L1=lsnext(0)" mean...

Thank you for the reply. I don't know how to write a macro for this. I use APDL. Everytime I divide a line into two lines, the new line will be given a new number. It is not possible to get the line No of many lines. I can not get the line number to write APDL code. "*do loop" is not working...

Thank you very much. I have been searching for this for a long time and could not find it.

Is there any keyboard shortcuts for zoom/in/out/rotate in Patran?

I try to divide a line into three unequal segments. The ratio is 0.1, 0.8, 0.1. Is there any way of doing it in one command instead of dividing the line by two times. New lines after the old line is divided. Since I have to perform this operation on many lines, it will greatly simplify my model...

Thanks for the reply. I can not use analytical formulas to calculate because there is a large force applied on the top. I changed the thickness and found that even linear static analysis is working. That's the problem of excessive deflection, which is also too big for nonlinear analysis.

I use COSMOSWORKS to model a pressure vessel (like cylindrical shape) made of fabric having a large force applied on the top partial flat surface and internal pressure inside. The thickness is very small, and diameter-thickness ratio is around 4*10^4. I first use linear static analysis and it...

Gurmeet, thank you for the reply. Where did you get this 3-2-1 rule? Is it a conventional method in constrain specification? Drej, thank you for the reply. Just check in ANSYS. There is an inertia relief command. I didn't know before.

Thanks for the reply. Basically, I try to model a new type of aircraft flying in the sky. The loads are aerodynamic loads (control surface loads, distributed pressure) and aerostatic loads (weight). There is no contact involved in this model. I don't have experience of aircraft modeling. Not...

I have built a structural model for an air vehicle. As it contains tension-only element, nonlinear analysis need to be applied. I don't know how to constrain six degrees of freedom in order to remove rigid body motion. There are some symmetric conditions existing, but I still can not constrain...

Hi, Cbrn, Thank you again! I tried it. You are right. I imported IGES file with only curves into ANSYS. I used to think that IGES only works for surfaces. The ANSYS geometry generation is not very powerful.

It depends on how you draw your model in Solidworks. I imported IGES files of the same geometry but with different way of drawing. Some lines showed up in one model, and some lines didn't show up. Especially, for complicated curve surface, there might be problems for IGES file to generate solid.

Cbrn, Thank you for the answer. 1. I used Command instead of GUI to assign the real constants to the two types of elements. So, there are two different sets of real constants for two types of elements which share the same nodes. These elements don't need to have the same real constants, right...

Hi, Cbrn! Thank you for the suggestion. It is very helpful. Actually, I divided the lines to small segements, and I meshed the surface and its edge by specifying element size on lines. I tried to use hard point, but it didn't work for 3D curve surface. I still have a few questions. 1. The...