深水波破碎特征的试验及模型化研究

Deep-water- breaking wave(DWBW) play a very important role on wind wave development, ocean surface mixing and surface current structure. There are still many problems to be solved in the existing wave model and the ocean circulation model concerning the quantization of DWBW by source terms. Aiming at these problems, laboratory experiment is employed as the main research method and some field measurements will be implemented too. Two main research contents are concentrated: 1) Experimental study on the features of energy dissipation and momentum transfer caused by DWBW and the corresponding parameterization in the wind wave model; 2) Experimental study on the features of turbulence caused by DWBW and the corresponding parameterization in ocean circulation model. The following key scientific problems will be solved: 1) The method of measuring the current field with strong aeration and the turbulence induced by surface wave breaking; 2) The estimation method of pure energy loss caused by DWBW; 3) The influencing factors of momentum transfer induced by DWBW and its quantification method; 4) The relationship between turbulent features induced by DWBW and wave parameters and its quantification method. It is expected that a new expression for the dissipation caused by DWBW will be proposed and be applied to SWAN model in stead of the original whitecapping term. The better prediction of spectrally averaged wave periods is attempted. The influence of the momentum transfer caused by DWBW will be added as stress terms in the momentum equations of the ocean circulation model. The original source terms in turbulent kinetic energy and its dissipation rate equations will be improved. The higher accuracy in simulating sea surface velocity and turbulence mixing by the improved ocean circulation model is expected.

深水波浪破碎对海浪的成长、海洋表面的混合和海表海流结构分布起着重要的作用。现有的波浪模型和环流模型中深水波浪破碎以源项形式采用经验式的量化方法存在较多问题亟待解决。本项目以实验室试验为主要手段，结合现场观测，重点开展深水破碎波能量耗散和动量转移特征的试验及其在风浪和环流模型中的模型化研究；深水破碎波紊动特征的试验及其在环流模型中的模型化研究。研究中拟解决基于BIV技术的表面破碎波强掺气流场及紊动特征量的测量方法；破碎波能量损失估算方法；破碎波动量转移特征的影响因素及其量化方法；破碎波紊动特征与波浪参量的关系及其量化方法等几个关键问题。提出深水破碎波耗散新的表达式，改进风浪模型SWAN中的白冠耗散项，提高风浪模型对海浪特征周期的模拟精度。在环流模型的动量方程中以应力项形式添加深水破碎动量转移的影响；改进原紊动动能及其耗散率方程中的深水破碎源项，提高环流模型对海表流速和垂向混合的模拟精度。

波浪破碎对海浪的成长过程、海洋表面的混合和近表海流结构分布等起着重要的作用。然而波浪破碎及其湍流混合由于复杂性和研究手段的制约一直是极具挑战性的难题。目前广泛应用的波浪模型和环流模型中深水波浪破碎主要以源项形式采用经验式的量化方法存在较多问题有待解决。对深水破碎波浪过程的深入研究和合理量化是改进风浪模型、环流模型和海洋混合模式的基础。课题针对以上问题开展了深水波破碎特征的试验及模型化研究，取得了以下进展：.1）在深水波浪破碎物理模型试验的测量技术上实现了两个突破：提出了可控深水破碎波实验室生成方法，实现了深水单次破碎波的精准生成；发展了PIV和BIV的耦合测速新方法，解决了强掺气表面破碎波大面积流场高效测量的难题。开发了两项新的试验数据预处理手段：提出了图像自动拼接、破碎区自动识别方法，实现了破碎影响区域内速度场的批量自动重构；开发了新的波面追踪程序以获得精确的波面数据。.2）在1）中测量技术和数据预处理手段的基础上，完成了系列深水破碎波的物理模型试验。系统地研究了不同破碎类型、波浪破碎形态参数和运动特征参数的演化差异；细致的分析了破碎前后波浪能量在频率间的损失和转移特征，为波浪破碎模型化改进提供基础。.3）利用物理试验和现场实测数据对深水破碎波的紊动特征进行了研究。量化了深水波浪破碎有效影响深度和破碎含能水团输移速度；利用实测的近海表湍动能耗散率分布，验证了几种常用的湍动能耗散率模式，为深水破碎波紊动特征的模型化提供基础。.4）提出了更准确反映谱型的整合因子QPW及更适合风浪破碎判据的谱特征参数WSP。WSP反映了谱型对波浪稳定性的影响，可以更准确地判断波浪破碎、易于参数化至海浪模型、更准确地反应能量耗散大小。利用QPW修正了ST6白冠耗散模式中的破碎判据项，以此提出了白冠耗散项的改进方案。该方案将谱型对波浪破碎阈值的影响反映到源项中，改进模式能够在保持原ST6周期预测准确度的同时，解决其过高估计有效波高的问题。