Absorbing boundaries, soil-structure interaction and dam analysis capabilities in LS-DYNA

The latest R5.1.1 release of LS-DYNA v971 has new capabilities for modeling wave propagation on unbounded domains, and for modeling soil-structure interaction and dam-water-foundation rock interaction under earthquake excitation directly in the time domain.

LS-DYNA can now model unbounded domains using perfectly matched layers (PML), an absorbing layer model that provides near-perfect absorption of outgoing waves. This presents a significant improvement over the existing Lysmer dashpot non-reflecting boundary available as *BOUNDARY_NON_REFLECTING. The fundamental theory and implementation of PML for elastic waves has been described in the following papers:

1. U. Basu and A. K. Chopra. Perfectly matched layers for time-harmonic elastodynamics of unbounded domains: theory and finite-element implementation. Computer Methods in Applied Mechanics and Engineering, 192(11–12):1337–1375, March 2003.
2. U. Basu and A. K. Chopra. Perfectly matched layers for transient elastodynamics of unbounded domains. International Journal for Numerical Methods in Engineering, 59(8):1039–1074, February 2004. Erratum: Ibid. 61(1):156–157, September 2004.
3. U. Basu. Explicit finite element perfectly matched layer for transient three-dimensional elastic waves. International Journal for Numerical Methods in Engineering, 77(2):151–176, January 2009.

The PML boundary is available for elastic, elastic fluid and acoustic media, accessible using one of the following cards:

• *MAT_PML_ELASTIC (example: quarter-mesh model of an elastic half-space)
• *MAT_PML_ELASTIC_FLUID (example: semi-infinite channel)
• *MAT_PML_ACOUSTIC (example: acoustic waveguide)

LS-DYNA can also now incorporate earthquake excitation into the soil-structure system using the effective seismic input method developed by Bielak and co-workers in the following papers:

1. J. Bielak, P. Christiano. On the effective seismic input for non-linear soil-structure interaction systems. Earthquake Engineering and Structural Dynamics, 12(1):107–119, January 1984.
2. M. G. Cremonini, P. Christiano, J. Bielak. On the effective seismic input for non-linear soil-structure interaction systems. Earthquake Engineering and Structural Dynamics, 16(4):615–625, May 1988.

This method computes effective forces at and near the soil-structure interface using only the free-field ground motions at the soil-structure interface. The method is equivalent to propagating the earthquake from the source to the site, and does not require any deconvolution of ground motion down to depth. The transient soil-structure interaction analysis may be started from a static state of the structure, thus allowing analysis of a non-linear structure. This method may be employed using the following cards to define the soil-structure interface:

• *INTERFACE_SSI (example: building on soil box, transient analysis following a static analysis, or purely dynamic analysis)
• *INTERFACE_SSI_STATIC (example: static analysis of building on soil box)

The examples above use the El Centro ground motion (load curve files: x-acceleration, y-acceleration, and z-acceleration)

These capabilities have also been extended to the earthquake analysis of dams, where both the impounded water and the foundation rock are unbounded. The ideas are outlined in the in the slides of a talk and the accompanying movie, and these new features are currently being validated.

Please use the latest release version from our ftp site to use these features.

Please contact Ushnish Basu < ubasu at lstc dot com > if you have any questions or comments regarding the material on this page.