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Recent content by alinalin

  1. alinalin

    Inertia Relief Analysis of Nastran

    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...
  2. alinalin

    Inertia Relief Analysis of Nastran

    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...
  3. alinalin

    Inertia Relief Analysis of Nastran

    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...
  4. alinalin

    Inertia Relief Analysis of Nastran

    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...
  5. alinalin

    Inertia Relief Analysis of Nastran

    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.
  6. alinalin

    Inertia Relief Analysis of Nastran

    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...
  7. alinalin

    how to divide a line into three unequal segments

    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...
  8. alinalin

    how to divide a line into three unequal segments

    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...
  9. alinalin

    Patran keyboard shortcuts for zoom out/in/rotate

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

    Patran keyboard shortcuts for zoom out/in/rotate

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

    how to divide a line into three unequal segments

    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...
  12. alinalin

    Nonlinear modeling of pressure vessel

    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.
  13. alinalin

    Nonlinear modeling of pressure vessel

    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...
  14. alinalin

    how to remove rigid body motion of an air vehicle

    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.
  15. alinalin

    how to remove rigid body motion of an air vehicle

    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...
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