两层非静压高效波浪模型在缓坡前滩上的验证

摘要

在海岸工程问题的物理模型试验中，人们借助前滩与过渡坡，在指定位置获得所需的波浪条件——既包括谱参数，也包括波高分布。数值模型可用于预测：在给定的物理模型布置与波浪驱动条件下，目标波浪条件能否达到。XBeach 非静压两层模型是一个计算高效的数值模型，已针对谱波浪参数完成验证，却缺少对波高分布的验证；而当所关注的过程涉及波浪力或波浪爬高时，波高分布十分重要。本文利用缓坡前滩上空间密度很高的波浪水槽实测资料，验证该数值模型同时再现谱波浪参数与波高分布的能力。所用资料涵盖波陡为 1.0%、2.5% 与 5.0% 的深水波浪条件。研究导出了数值模型中波浪破碎的最优参数设置，建议 maxbrsteep 与 reformsteep 分别取 0.40 与 0.20。由验证结果可以得出：该数值模型无法再现深水波陡为 5.0% 的验证试验，其原因可能在于这类工况在造波边界上对应的 kpd 数偏高；因此不推荐在模型边界处 kpd ≥ 2 的条件下使用该数值模型。对于深水波陡为 1.0% 与 2.5% 的试验，XBeach 非静压两层模型的表现要好得多，谱波浪参数得到了很好的表征；在相对水深变得很小之前，相应的波高分布也表征得较为理想。对更浅的水，预期该模型会低估较高的波浪。此外，研究还表明，该数值模型对波高分布的再现优于一个常用的经验公式。

Abstract

In the physical modelling of coastal engineering problems, use is made of foreshores and transition slopes to obtain the desired wave conditions - both spectral parameters and wave height distribution - at a given location. Numerical models can be used to predict whether the target wave conditions are met for a given physical model layout and wave forcing. The XBeach non-hydrostatic two-layer model is a computationally efficient numerical model that has been validated for spectral wave parameters, but lacks validation of wave height distributions which are important when processes such as wave forces or wave run-up are of interest. In this work, wave flume data with high spatial density over a sloping foreshore is used to validate the ability of this numerical model to reproduce both spectral wave parameters and wave height distributions. This data contains offshore wave conditions with 1.0%, 2.5%, and 5.0% wave steepness. Optimal settings have been derived for the wave breaking in the numerical model, resulting in recommended values for maxbrsteep and reformsteep of 0.40 and 0.20 respectively. From the results of the validation it is concluded that the numerical model is unsuccessful in reproducing the validation tests with 5.0% offshore wave steepness, potentially due to the associated higher kpd numbers on the generating model boundary. Hence, using the numerical model with values of kpd not smaller than 2 on the model boundary is not recommended. The XBeach non-hydrostatic two-layer model performs much better for the 1.0% and 2.5% offshore wave steepness tests, where the spectral wave parameters are represented well. The corresponding wave height distributions are represented reasonably well up to the point that the relative water depth gets very shallow. For shallower water, the model is expected to underestimate the higher waves. Additionally, the numerical model is shown to reproduce the wave height distribution better than a commonly used empirical formulation.