LS Dyna

LS Dyna

Some questions about * IGA keywords and Nurbs 3D

    • Ming han Jia

      When using Nurbs 3D to generate a Nurbs mesh for a solid, why only the three * IGA keywords shown in the first figure are generated instead of the keywords of the topological relationship shown in the second figure,such as *IGA_FACE_UVW? (My version of LS-PrePost is 4.9)

       In addition, there are a few more questions I would like to ask:
        1: In the *LOAD series of keywords, I found the two keywords *LOAD_FACE_XYZ and *LOAD_FACE_UVW, which keyword should we use when we apply a uniform pressure to a surface of a solid? 

        2:   *LOAD_FACE_XYZ and *LOAD_FACE_UVW need to be associated with *IGA_FACE_XYZ and *IGA_FACE_UVW respectively. But "Nurbs 3D" cannot generate *IGA_FACE_XYZ and *IGA_FACE_UVW keywords. How should these keywords be generated? Do users need to manually write keywords content by themselves?

        3:Taking the *LOAD_FACE_XYZ keyword as an example, where should we determine the direction of the uniform pressure action?

    • Andreas Koutras
      Ansys Employee

      Hello Ming,

      The IGA developer provided the following answers.

      Writing out the complete set of *IGA keywords is apparently not done in LSPP. I would try version 4.10 just to make sure it is not there. If it is missing there too, we will inform the developers and let them know about the issue.

      1: The *LOAD_FACE_XYZ keyword is only meant to apply pressure on the entire surface of a (trimmed) shell. In contrast, the*LOAD_FACE_UVW keyword is meant to apply pressure on parametric faces (*IGA_FACE_UVW) comprised in the boundary representation (*IGA_2D_BREP) of a solid (*IGA_3D_NURBS_XYZ). 

      In addition, the *LOAD_FACE_UVW keyword can be used to apply pressure on a partial surface of a (trimmed) shell or a solid. These parametric faces are not used in the definition of a shell discretization or of a solid's boundary description. Consequently, they should be defined separately, collected to a single set  (*SET_IGA_FACE_UVW), and the set ID should be referenced using FSID in Card 1 of either the *IGA_FACE_XYZ or the *IGA_VOLUMNE_XYZ keyword.

      2:  Ideally, the pre-processor should take care of this. Development efforts are on the way in both LSPP and ANSA from BETA CAE.

      3: The standard convention is applied, i.e. positive pressure is acting opposite to the surface normal vector.

      • Ming han Jia

        Thank you very much for your help. In the process of static compression simulation of entities using the *IGA keyword, I still encounter the following problem. I hope you can give me some help:

        This k file ends normally in LS-RUN, but when I open the K file after running, the problem shown above appears. Some points where boundary conditions were applied could not be found. What is the reason for this problem? In the first picture below, we want to impose a fixed support constraint on the point set, and the second picture is the situation where some points are lost after running.Is this situation caused by setting parameters incorrectly during the refinement process?Thanks!


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