A main goal of supplemental control devices is to manage the energy dissipation in the system. Semi-active damping devices have emerged as a promising control device for application to civil structures as they are effective energy dissipators. The inclusion of structural non-linearities in control assessment simulations presents new challenges that must be considered in the application of semi-active control systems. This paper presents a semi-active control utilizing semi-active devices and investigates its ability to mitigate structural response in the presence of hysteretic, geometric and yielding non-linearities under various intensity level seismic hazard suites so as to examine control efficacy and seismic hazard statistics. Due to the non-linear models used, the permanent deformations that result from large excitations result in a time-varying equilibrium position. Hence, a key feature of this research is the inclusion of a moving-zero within the control law, effectively tracking the permanently deformed position about which the structure oscillates, and its impact on control efficacy.

Clusters of PCs are increasingly popular as cost-effective platforms for supercomputer-class applications. Given recent performance improvements in graphics accelerators, clusters are similarly attractive for demanding graphics applications. We describe the design and implementation of Lightning-2, a display subsystem for such a cluster. The system scales in both the number of rendering nodes and the number of displays supported, and allows any pixel data generated from any node to be dynamically mapped to any location on any display. A number of image-compositing functions are supported, including color-keying and depth-compositing. A distinguishing feature of the system is its platform independence: it connects to graphics accelerators via an industry-standard digital video port and requires no modifications to accelerator hardware or device drivers. As a result, rendering clusters that utilize Lightning-2 can be upgraded across multiple generations of graphics accelerators with little effort. We demonstrate a renderer that achieves 106 Mtri/s on an 8-node cluster using Lightning-2 to perform sort-last depth compositing.