How to creat a concentrated mass that is distributed over an area in Hyperworks/Hypermesh Radioss

Praveen Kalloli_20515

erdem.keskin

In Altair HyperMesh (Radioss profile), the recommended way to create a concentrated mass that is distributed over an area is to use Non-Structural Mass (NSM) rather than assigning a single nodal mass.

If the goal is to represent additional weight (e.g., coating, adhesive, trim, or an equivalent lumped mass) over a shell area, follow this approach:

Recommended Method – Non-Structural Mass on Shell Property

1. Identify the shell elements representing the area.
2. Go to Model Browser → Properties.
3. Edit (or create) the shell property assigned to those elements.
4. In the Radioss property card, define:
   • Non-structural mass per unit area (NSM)
     or
   • Direct mass per unit area, depending on your card image.
5. Calculate the value as:
   [
   \text{Mass per area} = \frac{\text{Total Mass}}{\text{Total Area}}
   ]

This method automatically distributes the mass to all connected nodes through the element formulation. It does not introduce artificial stiffness and is fully consistent for explicit dynamic and crash analyses in Radioss.

Alternative – Distributed Nodal Mass (/ADDMASS)

If you need purely inertial mass without any property modification:

1. Calculate:
   [
   \text{Nodal mass} = \frac{\text{Total mass}}{\text{Number of nodes}}
   ]
2. Create a /ADDMASS card.
3. Select all nodes in the area.
4. Assign the calculated nodal mass.

Use this method when the mass should be purely lumped and independent of element properties.

Best Practice Recommendation

• For realistic physical representation of area-based additional mass → Use NSM on the property.
• For simplified inertial loading → Use /ADDMASS distributed to nodes.
• For rigid components (e.g., equipment, battery, engine) → Use /RBODY + /ADDMASS at CG including inertia terms.

In most practical Radioss models, NSM at the property level is the cleanest and most robust solution.