Modelling Joints in Radioss
Altair EmployeeAnswers
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Hi Ramakiran,
The easiest way to model joints in RADIOSS is to use a /PROP/TYPE8 spring. Provide high stiffness to all degrees of freedom those are fixed and zero stiffness in the direction which you want to be free.Unfortunately no webinars are available on this topic as of now, but a sample solver deck is attached for your reference.
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Thank you sir.
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Hi George,
Can we assign a local coordinate system with a spring?
How the coordinate system for spring acts? Like does it take x-along the direction of spring.
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Hi Gopal,
By default for Type 8 and Type 13 it works as per the global co-ordinate system. If you want it to work in any particular local direction then you have to create a local system and assign it to this spring in Iskew option. Type 4 spring is a spring property with one translational DOF, and spring’s X direction is defined using nodes N1 and N2 of the spring.
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Hi,
In the type 13 spring, does K_tension term takes it along the x- axis of the global coordinate system or along the spring node to node direction.
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Hi Gopal,
It takes with respect to the global coordinate system.
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Hi,
Thank you for your reply.
So we can consider it as movement of global coordinate system to one of the nodes of spring. Kindly correct me if I am wrong.
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Hi Gopal,
If no local skew is provided for Type 13 spring then it will work with respect to the global coordinate system and so the nodes connected to the spring will also follow the global coordinate system.
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Hi,
Thank you.
Do you have any sample file for type 13 spring failure due to displacement.
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Hi. I am doing Door Slam test.
My door latch is with revolute joint about Y axis in Door Open Condition and in door closed condition, it's revolute about X axis.
How to Model that change? Can modeling with local co-ordinate system will be correct in this case (Coz, local co-ordinate system is also changing/ rotating here).
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Hi,
you can use Type 13 spring referencing a local coordinate system (defined by nodes).
Revolute joints can also be modeled with KJOINT2:
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So it means, Local co-ordinate system will not get affected due to Rotation of the door. It will always consider direction accommodating the door revolution irrespective of Direction with respect to Global Co-ordinate system. Correct if I am wrong.
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Yes in case the local coordinate system is created by (appropriately selected) node reference and provided in the spring property.
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Actually, type 13 spring is non-zero length and works in the local coordinate system by default:
Spring type 13 works only if the length is not equal to zero. Nodes 1 and 2 are always used to define the local X-axis. Local Y direction is defined at time t=0 and its position is updated at each cycle, taking into account the mean X rotation. Initially, the Y-axis can be defined in different ways. A third node can be used for beam elements. It is also possible to use the local Y-axis of a skew frame. If a skew frame and third node are not defined, global Y-axis replaces the Y skew axis. If the Y skew axis is co-linear with the local X-axis, the local Y-axis and Z-axis are put in an arbitrary position. The Z-axis is finally computed as the cross product of X-axis and Y-axis.
Type 8 spring is zero length and works in the global coordinate system by default:
The local coordinate system is not associated with the nodes positions, if no local skew is specified (moving or fixed), the global coordinate system is used.
Sorry for the confusion.
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