Topology Optimization of Wave Barriers

Abstract

Wave barriers are a common mitigation measure when dealing with environmentally induced vibrations. These wave barriers generally consist of stiff vertical walls buried in the soil to impede waves on their path from the source to the receiver. The geometries of the wave barriers that are used in practice are very simple. More complex geometries have not often been considered as it is difficult to estimate which changes would increase the effectiveness.

In literature, topology optimization was explored as a method to design wave barriers. This method was applied while modelling the soil as a homogeneous elastic half-space. The resulting wave barriers showed a significant increase in the achieved vibration reduction. However, the designs were often very complex and hard to manufacture. In this thesis the method was improved by introducing a layered soil and by ensuring the manufacturability of the designed wave barriers.

The improved method was then applied to multiple situations in order to investigate aspects of wave barrier design and effectiveness. Optimization of a wave barrier for a two-layered soil model showed the significance of implementing a layered soil model. The interface between two layers resulted in reflections that could diminish the effectiveness of a wave barrier if not accounted for. The optimization algorithm responded to these reflections by placing material in the path of waves that would otherwise reflect back to the surface.

A wave barrier optimized for a three-layered soil model that consisted of a softer layer embedded in a stiff layer and a stiff half-space showed a different approach to reflections. The wave barrier appeared to use the softer layer as a waveguide in order to reduce the energy at the surface.

The manufacturability was increased by adding constraints. This resulted in wave barriers with a more manufacturable design at the cost of a decrease in vibration reduction. In three of the four cases, the optimized wave barrier still performed significantly better than the reference wave barrier. In one case, the final design reverted back to the reference wave barrier when the manufacturability conditions were applied.

The goals set at the start of the thesis were largely accomplished. The model was able to more accurately reflect soil profiles found in practice by using a layered soil model and the topology optimization algorithm resulted in wave barriers that are relatively easy to manufacture while still showing a significant improvement over the standard reference wave barriers. The possible use of
soft embedded layers as waveguides was discovered during the optimization. Future research into this possibility could prove valuable. Some concerns are posited with regards to the reliability of the wave barriers. In some cases, the optimized wave barrier appeared to abuse the idealized representation of the interface between layers. An initial investigation showed that in those cases,
the effectiveness of the wave barrier was sensitive to changes of the interface depth. Further investigation would be required to determine the sensitivity of the designed wave barriers to other parameters related to the idealized representations of the interfaces.