Numerical modeling of landslide-induced waves and their effects on downstream structures

Abstract

Impulse waves in reservoirs, lakes, bays and oceans may be generated by

landslides. The resulting impulse waves can propagate and cause disaster to the

downstream. Some studies are carried out to investigate such phenomenon but

most of them were based on either experimental observations or empirical/semiempirical

relationships in simulating the waves generated by landslides. Therefore,

the fundamental mechanism of such hazard is not got fully understood (complex

motions of landslides with arbitrary geometry and interactions of fluid with

landslides or shorelines). In addition, the effects of landslide-induced waves on

downstream structures are rarely reported. Therefore, it appears necessary that the

coupling numerical model is developed to simulate landslide-induced waves and

to investigate generated wave characteristics. Furthermore, their effects on

downstream structures should be investigated for mitigating hazard, such as the

estimations of wave run-up, rundown and wave overtopping.

This thesis presents the numerical modeling of landslide-induced waves and their

effects on the downstream structures based on the computational fluid dynamics

(CFD) package FLUENT. As there is no existing module to simulate water waves,

the redevelopment of FLUENT by the user defined function (UDF) is necessary.

For the problem of landslide-induced wave, two simplified numerical models are

developed, including piston-type model and inlet boundary-type model. These two

numerical models can rapidly assess the landslide-induced waves but be

appropriate for the simple cases, such as a vertical wall moving horizontally or

slump-type landslide whose particle velocities and free surface displacements at

the inlet boundary are known. In order to expand the available range of numerical

modeling, the block models aiming for rockslide are developed to investigate

landslide-induced waves. Four categories of landslides are considered, such as

horizontal landslide, vertical landslide, subaerial landslide and submarine

landslide. Except of horizontal landslide, the coupled block model is employed to

investigate water waves generated by vertical, subaerial and submarine landslides.

The coupling is based on an iterative procedure enforcing the principle of the

dynamic equilibrium of the fluid, the slide and their interfaces, and the interaction

between landslide and fluid are considered. The wave characteristics generated by

above-mentioned different types of landslides are investigated and discussed. For

their effects of landslide-induced wave on downstream structures, the focuses of

numerical modeling are the run-up and rundown of waves generated by subaerial

and submarine landslides and wave overtopping on the downstream structures.

The detailed numerical modeling illustrates that the present models can predict

fairly well landslide-induced waves and their effects on downstream structures.

The results of parametric study indicate that slide volume and impact Froude

number ( v / gh ) play important roles on generated wave characteristics. The

wave characteristics, propagation distance and geometric characteristics of

seaward structural wall (slope and crest freeboard) are major factors in

determining the characteristics of wave run-up, rundown and overtopping. Several

useful prediction relationships are provided.