象山港内三维动边界潮流的数值模拟  

3D variable-boundary numerical modeling of tidal current in the Xiangshangang Bay

作　　者：吴晓燕[1] 管卫兵[1] 

机构地区：[1]卫星海洋环境动力学国家重点实验室,国家海洋局第二海洋研究所,浙江杭州310012

出　　处：《海洋学研究》2009年第2期23-31,共9页Journal of Marine Sciences

基　　金：国家自然科学基金资助项目(40206014);国家重点基础研究发展规划资助项目(2006CB400602);我国近海海洋综合调查与评价专项资助项目(908-02-01-04);海洋公益性行业科研专项经费资助项目(200705013);国家海洋局第二海洋研究所基本科研业务专项资金资助项目(JT701);宁波市重大科技攻关择优资助项目(2006C100030)

摘　　要：象山港是一具有广阔潮滩和大潮差区域的半封闭型海湾,进行数值模拟时必须引入动边界技术来考虑露漫滩的影响。在二维模式中引入动边界技术相对成熟一些,而将这些二维模式使用的露漫滩处理方法简单地搬入三维模式中,常遇到由于边界不连续变动而产生的数值"噪音"及计算不稳定现象。原始POM(Princeton ocean model)模型采用固定边界,没有使用动边界技术,故无法模拟漫滩流。借鉴BURCHARD et al 2004年的研究工作,在原始POM模型的基础上,突破其为固定边界模式的局限,基于尽量使模式物理上满足流动简化需要的原则,引入了一种较为自然的动边界处理技术,使得在非常浅水处和复杂的地形情况下,应用合理的数学表达式体现该物理过程。当总水深大于设定的临界水深时,体现的数学方程是通常形式的动量方程;而当总水深接近设定的最小允许水深时,模型的动量方程被简化为变化率、摩擦力和正压梯度等项之间的平衡关系,此时由于摩擦力占优,相应的流速也会趋于0,这样可以有效避免计算中出现负水深。除在非常浅水处对动量方程作简化外,对于陡坡地形附近的露漫滩问题,当发生一个网格点上的水位低于相邻格点海床的现象时,还需对正压梯度的求解作一个简单的数值处理,以避免不合理值的出现。此外,通过修改原始POM模型的底摩擦系数表达式,可使模型在模拟露漫滩过程时计算更加稳定。改进后的POM模型被用来模拟象山港海域内的三维潮流场,模型计算结果与2个潮位站、1个锚系站和2个船测连续站资料进行了比较,符合良好。整个模型很好地再现了象山港内大区域三维涨、落潮流特征和变化规律,同时象山港顶区域涨憩、落急、落憩和涨急4个特征时刻的流场水平和垂直分布变化过程反映该模型能很好地反映涨、落潮造成的潮间带的露漫滩过程,由此说�The Xiangshangang Bay is a typical narrow semi-enclosed bay in the middle of the Zhejiang Province, located at the south edge of the Changjiang River Delta. Along its axis from southwest to northeast, the Xiangshangang Bay extends about 60 km with a water area of 563 km2, in which 171 km2 is tidal flat （above the base level of theoretical depth）. The tidal range in the bay is large. It increases gradually from the entrance inwards with a mean value of above 3 m. At the innermost part it reaches a maximum of 6 m with a mean range of 4 m or so. The water area of the mudflats changes markedly with tide. When the water level is high, the whole bay is merged by water, and when the water level falls, the shallow areas are exposed. Therefore, the influence of drying and flooding of the mudflats should be considered when a numerical model is applied for such a region with wide mudflats and large tidal range. Various drying and of flooding algorithms have been developed very well for 2D models. However, if those algorithms used in 2D models are directly introduced into 3D models, the numerical oscillations or instability could occur, and thus it is necessary to find an easy and feasible mobile boundary technique for 3D models. The original POM （Princeton Ocean Model） with a fixed boundary cannot deal with the overbank flow. Base on the work of Burchard et al in 2004, the fixed boundary in original POM was replaced with a naturally variable boundary following a strategy to let the physics do the best to meet the requirement of flow reduction. Some simplifications of the model physics will be applied for very shallow water in order to describe the physical process in a proper way. In this method, a dimensionless damping factor, which varies linearly between unity （deep water） and zero （very shallow water）, was introduced to the horizontal advection, horizontal diffusion, Coriolis force and baroclinicity terms of the momentum equations. When the whole water depth is larger than the set critical water depth, u

关 键 词：三维数值模拟 动边界 潮流 象山港 

分 类 号：P731.23[天文地球—海洋科学] O242.1[理学—计算数学]