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Treatment of acoustic fluid-structure interaction by Localized Lagrange Multipliers and comparison to alternative interface coupling methods

Computer Methods in Applied Mechanics and Engineering

This paper is a sequel on the topic of localized Lagrange multipliers (LLM) for applications of fluid-structure interaction (FSI) between finite-element models of an acoustic fluid and an elastic structure. The prequel paper formulated the spatial-discretization methods, the LLM interface treatment, the time-marching partitioned analysis procedures, and the application to 1D benchmark problems. Here, we expand on formulation aspects required for successful application to more realistic 2D and 3D problems. Additional topics include duality relations at the fluid-structure interface, partitioned vibration analysis, reduced-order modeling, handling of curved interface surfaces, and comparison of LLM with other coupling methods. Emphasis is given to non-matching fluid-structure meshes. We present benchmark examples that illustrate the benefits and drawbacks of competing interface treatments. Realistic application problems involving the seismic response of two existing dams are considered. These include 2D modal analyses of the Koyna gravity dam, transient-response analyses of that dam with and without reduced-order modeling, incorporation of nonlinear cavitation effects, and the 3D transient-response analysis of the Morrow Point arch dam.

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TYPE Journal Article YEAR 2008
OSTI

Predicting the lifetime of fluorosilicone O-rings

Proposed for publication in Polymer Degradation and Stability.

Long-term (up to 1000 days) accelerated oven-aging studies on a commercial fluorosilicone o-ring seal are used to predict the sealing lifetime at room temperature (23 C). The study follows force decay (relaxation) on squeezed o-ring material using isothermal compression stress relaxation (CSR) techniques. The relaxation is normally a complex mix of reversible physical effects and non-reversible chemical effects but we utilize an over-strain approach to quickly achieve physical equilibrium. This allows us to concentrate the measurements on the chemical relaxation effects of primary interest to lifetime assessment. The long-term studies allow us to access a fairly broad temperature range (80-138 C) which results in improved modeling of the temperature dependence of the accelerated data. Non-Arrhenius behavior is observed with evidence of a significant lowering of the activation energy at the lowest accelerated aging temperature (80 C). This observation is consistent with numerous recent accelerated aging studies that probed temperature ranges large enough to observe similar non-Arrhenius behavior. The extrapolated predictions imply that significant loss of sealing force requires on the order of 50-100 years at 23 C. Field aging results out to 25 years at 23 C are shown to be in reasonable accord with the significant change in Arrhenius slope observed from the accelerated aging study.

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TYPE Journal Article YEAR 2008
OSTI
Results 76451–76475 of 99,299
Results 76451–76475 of 99,299