Sometimes, it is necessary to add mass to a model to reduce complexity, change the center of gravity, or update load cases. Radioss tracks two types of masses: Structural and Non-Structural. Structural mass is determined by the size of the element and material density. Non-structural mass is determined by the user and can be implemented using the /ADMAS keyword. This article provides an example model and explains the various input types for /ADMAS and how to use them in Radioss. Please see the example model files attached as they are referenced frequently in the article.
Summary of all input types in /ADMAS:
The following article:
- Presents the reference model
- Shows how to check the model mass summary in HyperWorks
- Explains the referenced model
- Provides details for each of the input types for the /ADMAS keyword.
Reference Model
The attached model referenced in this article is a simple steel plate modeled with 100 shell elements.
Model mass can be calculated in HyperWorks using the “Mass” feature in Validate ribbon:
- Select “Validate” ribbon
- Go to “check” group, click “Mass”
- Click “Compute” in the tool that appears.
See screenshot below of the model mass without using /ADMAS
Note that the values for “Non-Structural Mass” and “Lumped Mass” are both zero.
Structural Mass
In the attached examples, the Structural mass is 7.89 E-05 Mg. This is calculated using material density and element volume. You can see the structural mass listed using the mass function in HyperWorks, shown in the previous section:
Below is a contour plot showing the nodal masses for itr00, the baseline iteration with no extra mass added.
Please note that structural mass is assigned to each node based on area distribution and how many elements use that node.
Nodes on the corners of the plate are used by only one element and have ¼ the structural mass as the nodes used by 4 elements (for a regular mesh with 4-node shells).
Nodes on the edges of the plate are shared by 2 elements and receive ½ the structural mass as the nodes sharing 4 elements (for a regular mesh with 4-node shells).
/ADMAS/0
Whatever mass you enter will be added to each node contained in the specified node set.
In the attached itr01 folder. The starter file adds 1.21 E-04 Mg of nonstructural mass to a node set containing all nodes using input type “0”. Thus, each node receives 1.21 E-04 Mg of additional mass, and the total added mass is 1.21 E-04 Mg x 121 Nodes, or 1.4641 E-02 Mg.
Below is a contour plot showing the nodal masses for this iteration. Each node has 1.21 E-04 mass added.
/ADMAS/1
Whatever mass you enter will be divided equally among the nodes in the specified node set.
In the attached itr02 folder. The starter file specifies 1.21 E-04 Mg of mass to a node set containing all 121 nodes using input type “1”. Thus, the 1.21 E-04 Mg of mass is divided equally into 121 nodes, so each node receives an additional 1.00E-06 Mg of mass. The total added mass is equal to the mass specified in the /ADMAS card: 1.21 E-04 Mg.
Below is a contour plot showing the nodal masses for this iteration. Each node has 1.00 E-06 mass added to the existing structural mass.
/ADMAS/2
Requires that you specify a mass per unit area and a surface. Applies nodal mass based on surface area and specified mass/unit area.
In the attached itr03 folder. The starter file specifies a mass per area of 1.00 E-05 (Mg / mm) and a surface with an area of 1.00 E+04 mm². Thus, Radioss adds 1.00 E-01 Mg in total.
Below is a contour plot showing the nodal masses for this iteration. The mass is distributed to the nodes using the same formula as the distribution for structural mass. The mass is not split evenly among all nodes.
/ADMAS/3
Whatever mass you enter will be added to the nodes in the specified part set.
In the attached itr04 folder. The starter file specifies a total mass of 1.00 E-05 added to a part set containing only Sample_Comp_A. Radioss adds 1.00 E-05 Mg to Sample_Comp_A and adds no mass to Sample_Comp_B.
Below is a contour plot showing the nodal masses for this iteration. Sample_Comp_A is on the left and has higher mass. The mass is distributed to the nodes of Sample_Comp_A using the same formula as the distribution for structural mass. The mass is not split evenly among all nodes.
/ADMAS/4
Radioss will check the mass of the part set and then increase the nodal mass on each node in the part set so that the total mass of the part set is equal to the mass that you specify.
If the mass you specify is less than the inherent mass of the part set, the job will not run.
In the attached itr05 folder. The starter file specifies a total mass of 1.00 E-04 Mg and a part set containing only Sample_Comp_A. Radioss checks the structural mass of 7.89 E-05 Mg and adds 2.11 E-05 Mg of non-structural mass to achieve the final mass of 1.00 E-04 Mg.
Below is a contour plot showing the nodal masses for this iteration. Sample_Comp_A is on the left and has higher mass. The mass is distributed to the nodes of Sample_Comp_A using the same formula as the distribution for structural mass. The mass is not split evenly among all nodes.
In the attached itr06 folder. The starter file specifies a total mass of 6.89 E-05 Mg and a part set containing all the parts in the model. Radioss compares this to the structural mass of 7.89 E-05 Mg and terminates the job because the specified mass is less than the structural mass. The job terminates with the error shown below:
/ADMAS/5
Requires that you specify how much mass you want added to each node by entering the node ID and desired mass. Radioss adds the mass to each node by the specified amount.
In the attached itr07 folder. The starter file uses /ADMAS/5 to add a mass of 1.0 Mg to node 4. Node 4 is the only node affected and the total mass of the model increases by 1.0 Mg total. See screenshot of 0000.out file below:
Below is a contour plot showing the nodal masses for this iteration. Node 4 in the bottom left corner has 1.0 Mg mass added to the existing structural mass. All other nodes received zero added mass.
/ADMAS/6
Requires that the desired mass added to each part is entered along with the part ID. Radioss then distributes the mass to the nodes of the specified part.
In the attached itr08 folder. The starter file specifies a total mass of 1.00 E-05 Mg and Sample_Comp_A. Radioss adds 1.00 E-05 Mg to Sample_Comp_A only.
Below is a contour plot showing the nodal masses for this iteration. Sample_Comp_A is on the left and has higher mass. The mass is distributed to the nodes of Sample_Comp_A using the same formula as the distribution for structural mass. The mass is not split evenly among all nodes.
Please note that /ADMAS/6 is different from /ADMAS/3. In /ADMAS/3, the final mass is specified for a part set that can contain many parts. In /ADMAS/6, the final mass is specified for a single part only.
/ADMAS/7
Radioss will check the mass of the specified part and then add mass equally to each node in the part so that the total mass of the part is equal to the mass that you specify. If the mass you specify is less than the inherent mass of the part set, the job will not run.
In the attached itr09 folder. The starter file specifies a total mass of 1.00 E-03 Mg and part 1. Radioss compares this to the structural mass of 7.89 E-05 Mg and then adds 9.211 E-04 Mg.
Below is a contour plot showing the nodal masses for this iteration. Sample_Comp_A is on the left and has higher mass. The mass is distributed to the nodes of Sample_Comp_A using the same formula as the distribution for structural mass. The mass is not split evenly among all nodes.
In the attached itr10 folder. The starter file specifies a total mass of 1.89 E-05 Mg and part 1. Radioss compares this to the structural mass of 7.89 E-05 Mg and terminates the job because the specified mass is less than the structural mass. The job terminates with the error shown below:
Please note that /ADMAS/7 is different from /ADMAS/4. In /ADMAS/4, the final mass is specified for a part set that can contain many parts. In /ADMAS/7, the final mass is specified for a single part only.