DOI: 10.17603/ds2p66h
title: Debris impact experiments
title: in NHERI Debris Impact Experiments

description: In the last decade, natural disasters such as tsunami events in Indonesia (2004), Samoa (2009), Chile (2010), and Japan (2011) have caused hundreds of thousands of deaths and billions of dollars in damage to coastal communities. Although there is a strong need for design guidelines for tsunamis, there are still significant knowledge gaps pertaining to tsunami forces, specifically dealing with debris laden flow. Although several studies have addressed the effect of tsunami loads on structures, and bridges in particular, few have examined the influence of debris carried by the tsunami. This is because of difficulties resolving complex contact interactions between solids and fluids that are not easily accommodated using typical fluid-oriented or solid-oriented numerical frameworks. This project  aims to establish new design guidelines for evaluating tsunami-driven debris loads on structures based on robust numerical simulations and experimental results. This requires to develop advanced numerical tools capable of capturing the complex 3D interaction between tsunami-driven debris and structural elements. It also requires valid  experimental results for verification and validation. For this purpose this project includes experimental and numerical components. 

The numerical component involves simulating fluid-drive debris interaction problems using MPM. The Material Point Method (MPM) is a numerical technique that is best suited for modeling history dependent materials in a dynamic, large deformation setting. The formulation tracks moving points relative to stationary nodes, and can be used to capture the behavior of both fluids and solids in a unified framework. The standard implementation solves the governing equation of motion at fixed nodes that collectively form a grid. Each body or phase in the analysis is represented by a collection of discrete points known as material points or particles. Each particle represents a portion of the total mass, and thus carries an implied volume as well as state variables that depend on the application. Due to the combination of Lagrangian (computational particles) and Eulerian (stationary grid) reference frames, the MPM shares many similarities with many other numerical schemes making it simple to couple with other tools. Within this context our current work includes validating recently proposed smoothing techniques within MPM and developing/implementing a pressure implicit MPM program (iMPM) which would then be validated against experimental results. 

The experimental part involves planning and conducting debris impact experiments and studying the experimental results. Early in 2017 experiments were conducted at the O.H.Hinsdale Wave Research Laboratory’s Large Wave Flume(LWF) to study the impact of debris carried by waves on a calibrated instrumentation box. While the dimensions of individual pieces of debris are the same, the number of debris, the orientation of debris and the relative layout of multiple debris pieces are changed. The main parameter of interest is the force recorded through nine load cells strategically located on the instrumentation box to record forces in different directions on the box. Statistical analysis of the data will be carried out to extract useful results. Debris velocities at the time of impact will be evaluated using image analysis on high speed video recordings.