Sensors can be used to trigger entities based on certain criteria. The following image is a high-level steps involved to take advantage of sensors in LS-DYNA.
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Sensor Definitions in LS-DYNA
Published by May 18th, 2010 in LS-DYNA Bytes and LS-DYNA Output. 0 Comments*RIGIDWALL_{DISPLAY} option
Published by May 3rd, 2010 in LS-DYNA Bytes and LS-DYNA Elements. 0 CommentsRigidwalls are analytical representations of surfaces or volumes that are frequently used to represent stiff structures that are either stationary or in motion. Viewing of such analytical definitions in D3PLOTs were not possible for most rigidwalls. A new option in LS-DYNA named DISPLAY that can now be used to any *RIGIDWALL definitions which causes LS-DYNA to create an element that matches the dimensions of the rigidwall which can then be viewed alongside other elements. Optionally, a PID with material properties can be associated.
New Coordinate based Joint Definition – *CONSTRAINED_JOINT_COOR_{JOINT_TYPE}
Published by May 3rd, 2010 in LS-DYNA Connections. 0 CommentsSeveral joints are available in LS-DYNA that can be defined between two rigid bodies or nodal rigid bodies. The difficult part of the joint definition from the pre-processing point of view is the creating of nodes that defines the joint axes and subsequent merging of them to the respective rigid bodies. To simlpy this problem, LS-DYNA R5 59341 and later versions has a new keyword named *CONSTRAINED_JOINT_COOR_{JOINT_TYPE} that only requires the two rigid body IDs (or nodal rigid body ID) between which the joint is the modeled and the actual coordinates of the joint axis or points. Using this information, LS-DYNA will internally create all necessary nodes and assign them to the respective rigid bodies (or nodal rigid bodies).
A nice publication on hydrocodes by Dr. Benson .
I recently came across a nice blog written by QUI. It is remarkable that he is willing to share examples and his experiences in LS-DYNA. The broad spectrum of LS-DYNA applications can never be fully covered by a single blog or a small set of publications. It is great to see such new sites emerging and I hope more users come forward to share their experiences.
Suri Bala
This is a post by Guest Author Satish Pathy who works full time for LSTC
In *MAT_FABRIC, element formulation 4 & 14 will allow you to input unloading curve for the material. Recently in a model it was noticed, that when a large compressive stress develops in the fibers, lsdyna would release some of these stresses by inverting the elements and thus leading to numerical instability. This could be avoided by activating compressive stress elimination, CSE=1. However, it still does not improve the fabric behavior with the current unloading method.
A new option was implemented to overcome this. This option can be activated by using a “negative” unload curve. Unlike the current way where the unload curve will get shifted to the yield point, the unload curve is stretched along the x-axis to intersect the current yield point, so that the first data-point is always at (0,0). This will allow the stress to follow a more physically realistic unloading path, where the stress is positive and does not return to zero until the tensile strain reaches zero. Hence, this option does not require compressive stress elimination to be active and will also give a better correlation with actual fabric behavior compared to the current method.
The following picture shows the typical way of defining unloading curve for negative load curve option. The initial slope should be defined which will be lower than the loading curve, then the slope can gradually increase such that it intersects the loading curve at a positive strain value.
Figure 1. Unloading curve signature when using negative load curve option.
Figure 2. Animation with current input scheme for unloading.
Figure 3. Animation with new input scheme (negative load curve option) for unloading.
I would like to thank Dr. Lee Bindeman for his feedback and sharing information regarding the above discussed topic.
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