- Date:
**9 January 2008**
- Author:
**Suri Bala**

LS-DYNA provides three ways to account for the non-structural-mass lumping on structures.

** 1. Traditional Node Based Mass Lumping using ELEMENT_MASS_{OPTION} **

This method relies on the preprocessors to compute the node-based additional mass that is to be lumped based on the total non-structural-mass that is to be included. The input (into a preprocessor) would simply be the desired additional NSM that is to be lumped on a set of nodes or elements.

Optionally, users can include an optional PID which would then allow users to track the lumped mass by PID. Option allows for a single node (default) or a set of nodes to which the mass is to be lumped. When the OPTION is set to SET, then equal amounts of mass is lumped to all nodes that belong to the SET.

** 2. New Part Based Mass Lumping using ELEMENT_MASS_PART_{OPTION} **

Using this new keyword, users can directly pick a single part or a set of parts, and specify the amount of added mass using ADDMADD that must be lumped to the parts. LS-DYNA would then internally compute the node based mass value using area-weighted distribution method. Starting R3 of 971, a final mass FINMASS can be input which causes LS-DYNA to subtract the original mass of the the parts from the FINMASS to compute the additional mass that is to be lumped to the parts.

** 3. MAREA in SECTION_SHELL **

In this method, mass per unit area of the non-structural part can be directly input using the MAREA in the SECTION_SHELL keyword.

A simple example demonstrating the above methods are available in the D3VIEW datamanager at Non-Structural-Mass Lumping . Each of the simulations can be added to a simulation cart to compare the added NSM mass.

** Node **

It must noted that the timestep of elements are not affected by the addition of non-structural mass.

*Related*

Suri,

Similarly, *SECTION_BEAM has a card for NSM (non-structural mass) and some preprocessors may miss it when calculating the mass of that beam part.

Jai