Numerical modelling of salinity variations due to wind and thermohaline forcing in the Persian Gulf

Salinity is an important component of the marine system. Due to shallow nature of the Persian Gulf, the salinity has been influenced by both wind driven and surface thermohaline fluxes (heat and moisture fluxes). In this study, the seasonal distribution of salinity and its variations due to wind stress and thermohaline forcing are investigated by using a three-dimensional hydrodynamic model, Coupled Hydrodynamical–Ecological Model for Regional and Shelf Seas (COHERENS). The simulation results show that the salinity in the Persian Gulf experiences dramatic spatial and temporal variations. The influence of the thermohaline forcing is considerably more than the wind stress on the salinity. The effect of the surface thermohaline fluxes over the salinity field is generally to increase the salinity for almost all the water column during the year. This effect is high during September–November where the evaporative surface salinity flux dominates over inflow of low-salinity values of Indian Ocean Surface Water. The wind forcing at the most regions of the Persian Gulf, in particular at the United Arab Emirate (UAE) coast and Bahrain–Qatar shelf, freshens the water all the year round. The wind and thermohaline forcing in March–June have strong potential to generate stratification in salinity structure. The model predictions, which are successful in simulating many features of observed pattern, indicate that the surface water of the Gulf is saltier in winter than that in spring and early summer. Both heat fluxes and wind stress play an important role for this seasonal cycle of the surface salinity.     

Studying the role of temperature and salinity anomalies in the formation of world ocean meridional circulation modes

A numerical model of the ocean circulation is considered for using in a coupled oceanice-atmosphere climatic model. Preliminary experiments conducted on a numerical grid with a coarse spatial resolution over a period of one thousand years reproduce the World ocean dynamics under climatic surface forcing. By introducing anomalies into the surface sources, the sensitivity of the global ocean circulation to thermohaline variability in the northern regions of the Atlantic Ocean is investigated.     

Study of storm surge due to Typhoon Linda (1997) in the Gulf of Thailand using a three dimensional ocean model

Numerical integrations using the three dimensional ocean model based on the princeton ocean model (POM) were applied for the study of both sea level elevation and ocean circulation patterns forced by the wind fields during typhoons that moved over the Gulf of Thailand (GoT). The simulation concerned a case of Typhoon Linda which occurred during November 1-4, 1997. Typhoon Linda was one of the worst storms that passed the Gulf of Thailand and hit the southern coastal provinces of Thailand on November 3, 1997. It caused flooding and a strong wind covering large areas of agriculture and fisheries, which destroyed households, utilities and even human lives. The model is the time-dependent, primitive equation, Cartesian coordinates in a horizontal and sigma coordinate in the vertical. The model grid has 37 × 97 orthogonal curvilinear grid points in the horizontal, with variable spacing from 2 km near the head of the GoT to 55 km at the eastern boundary, with 10 sigma levels in the vertical conforming to a realistic bottom topography. Open boundary conditions are determined by using radiation conditions, and the sea surface elevation is prescribed from the archiving, validation and interpretation of satellite oceanographic data (AVISO). The initial condition is determined from the spin up phase of the first model run, which was executed by using wind stress calculated from climatological monthly mean wind, restoring-type surface heat and salt and climatological monthly mean freshwater flux. The model was run in spin up phase until an ocean model reached an equilibrium state under the applied force. A spatially variable wind field taken from the European Centre for Medium-Range Weather Forecasts (ECMWF) is used to compute the wind stress directly from the velocity fluctuations. Comparison of tendency between the sea surface elevations from model and the observed significant wave heights of moored buoys in the Gulf of Thailand under Seawatch project is investigated. The model predicts the sea level elevation up to 68.5 cm at the Cha-Am area located in the north of where the typhoon strands to the shore. Results of sea level elevation show that there is an area of peak set-up in the upper gulf, particularly in the western coast, and the effects of the storm surge are small at the lower gulf. During the entire period of this study, the surge in the gulf was induced by the northeasterly wind blowing over it.     

Numerical modeling of hydrodynamic and hydrothermal characteristics in subtropical alpine lake

A three-dimensional, time-dependent hydrodynamic and hydrothermal model was performed and applied to the subtropical alpine Yuan-Yang Lake (YYL) in northeastern region of Taiwan. The model was driven with discharge inflow, heat, and wind stress to simulate the hydrodynamic and hydrothermal in the lake. The model was validated with measured water surface elevation, current, and temperature in 2008. The overall model simulation results are in quantitative agreement with the available field data. The validated model was then used to investigate wind-driven current, mean circulation, and residence time in the YYL. The modeling results reveal that the velocity field along the wind axis present the variations over depth with return current where the velocity at the surface layer is along the wind direction while it is opposite near 1 m below water surface. The simulated mean current indicates that the surface currents flow towards the southwest direction and form a clock-wise rotation. The calculated residence time is strongly dependent on the inflows and wind effects. Regression analysis of model results reveals that an exponential regression equation can be employed to correlate the residence time to change of discharge input. The residence time without wind stress is higher than that with wind effect, indicating that wind plays an important role in lake mixing. The calculated residence time is approximately 2-2.5 days under low inflow with wind effect.     

A stratified model of flow in a coastal trench

A stratified model of the circulation in a deep, narrow trench adjacent to a coast is described. The flow in the trench is driven by surface wind stress, coastal runoff and inflow at one end. The model is being developed to investigate the Norwegian coastal current flowing through the Norwegian Trench.     

基于X-12-ARIMA方法的迪拜原油价格季节性波动分析

油价时间序列往往受众多因素的影响,从而可以分解成各种成分.运用X-12-AR IM A方法分析迪拜原油价格的季节性波动,探讨油价运动规律,结果表明季节调整的整体效果较好,季节因素对中质高硫原油价格具有显著影响,夏、秋季推动油价上升,而春、冬季节使油价下跌,同时发现原油价格的短期变化主要由不规则事件和季节因素决定,而长期变化由趋势因素决定.     

Inflow Treatment for the Simulation of Subsonic Jets with Turbulent Nozzle Boundary Layers

The state of the boundary layer at the nozzle exit of a circular nozzle-jet configuration has an important influence on the development of the shear layer and the emitted sound. Of special interest is the acoustic near-field obtained when the nozzle exit boundary layer is fully turbulent. The turbulent inflow generation and the inflow boundary treatment are important issues to be addressed. We use the Synthetic Eddy Method (SEM) to generate a turbulent inflow which reproduces mean flow and Reynolds stress profiles of specified reference data. The spatially and temporally varying synthetic fluctuations are imposed in the simulation by a forcing term added to the governing equations which is active in a small region downstream of the inflow boundary. This forcing in combination with characteristic boundary conditions allows for passing of upstream-propagating acoustic waves and avoids an uncontrolled drift of mean-flow quantities. We employ this inflow boundary treatment for a subsonic nozzle-jet flow simulation at a Reynolds number of ∼ 9500 and Mach number of 0.9. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dynamics of the thermohaline circulation under uncertainty

The ocean thermohaline circulation under uncertainty is investigated by a random dynamical systems approach. It is shown that the asymptotic dynamics of the thermohaline circulation is described by a random attractor and by a system with finite degrees of freedom.     

Finite Element Simulation of Frost Wedging in Ice Shelves

Break-up events in ice shelves have been studied extensively during the last years. One popular assumption links disintegration events to surface melting of the ice shelf in conjunction with growing melt-water ponds, leading to hydro-fracture. As this explanation only holds during warm seasons [1], the possibility of frost wedging as forcing mechanism for autumn and winter break-up events is considered. Frost wedging can only occur if a closed ice lid seals the water inside the crack. Hence, the present study of frost wedging in a single crack uses ice lid thicknesses to evaluate the additional pressure on the crack faces. The investigation of the resulting stress intensity factor as a measure of crack criticality follows consequently. The results show that freezing water inside a crack can result in unstable crack growth of an initially stable water filled crack. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Existence of global weak solutions for Navier-Stokes equations with large flux

Global existence of weak solutions to the Navier-Stokes equations in a cylindrical domain under boundary slip conditions and with inflow and outflow is proved. To prove the energy estimate, crucial for the proof, we use the Hopf function. This makes it possible to derive an estimate such that the inflow and outflow need not vanish as t→∞. The proof requires estimates in weighted Sobolev spaces for solutions to the Poisson equation. Our result is the first step towards proving the existence of global regular special solutions to the Navier-Stokes equations with inflow and outflow.     

Inventory control as a discrete system control for the fixed-order quantity system

This paper shows how to model a problem to find optimal number of replenishments in the fixed-order quantity system as a basic problem of optimal control of the discrete system. The decision environment is deterministic and the time horizon is finite. A discrete system consists of the law of dynamics, control domain and performance criterion. It is primarily a simulation model of the inventory dynamics, but the performance criterion enables various order strategies to be compared. The dynamics of state variables depends on the inflow and outflow rates. This paper explicitly defines flow regulators for the four patterns of the inventory: discrete inflow – continuous/discrete outflow and continuous inflow – continuous/discrete outflow. It has been discussed how to use suggested model for variants of the fixed-order quantity system as the scenarios of the model. To find the optimal process, the simulation-based optimization is used.     

Incompressible flows in elastic domains: an immersed boundary method approach

This study illustrates how the immersed boundary method may be applied to perform the numerical simulation of incompressible flows in two-dimensional domains bounded by elastic boundaries. It presents the basic intermediate steps involved in the derivation of a solution methodology, from a scientific motivation to the numerical results, which can be applied for both steady and transient problems, even when the boundaries have an arbitrary shape. Its motivation, briefly presented, was borne in a bioengineering problem: the numerical simulation of the performance of ventricular assist devices. The mathematical model is composed by the Navier–Stokes equations, where the forcing term contains singular forces which arise from the elastic stresses acting on the boundaries. The incompressibility constraint is modified to introduce the inflow and outflow conditions into the problem through the use of sources and sinks. The methodology is applied to simulate two problems: the steady flow between two parallel plates, for which the exact solution is known and can be used to validate the approach, and the periodic flow in a winding channel, a transient problem in a non-trivial domain.     

Shallow water model for lakes with friction and penetration

We deduce a shallow water model, describ‐ ing the motion of the fluid in a lake, assuming inflow–outflow effects across the bottom. This model arises from the asymptotic analysis of the 3D dimensional Navier–Stokes equations. We prove the global in time existence result for this model in a bounded domain taking the nonlinear slip/friction boundary conditions to describe the inflows and outflows of the porous coast and the rivers. The solvability is shown in the class of solutions with L_p‐bounded vorticity for any given p∈(1,∞]. Copyright © 2009 John Wiley & Sons, Ltd.     

基于分层贝叶斯时空模型的雾霾天气过程计数分析

本文以北京市8个行政区(东城区、西城区、石景山区、海淀区、朝阳区、昌平区、顺义区、怀柔区)的PM2.5指数计算各区逐月雾霞天气过程计数频数为研究对象,选择考虑包括地表温度、相对湿度、平均风速、SO_2质量浓度和NO_2质量浓度在内的5个影响因素。本文定义雾霾天气过程,构建分层贝叶斯时空模型,在一个统计模型中对诸多影响因素进行分析,并从计数分析的角度对北京市雾霾天气现象的时空分布、影响因素进行深入讨论。通过分析得出,温度、湿度、污染物浓度对于雾霾天气过程发生具有促进作用,平均风速对于雾霾天气过程发生具有抑制作用。从时空角度分析,从时间维度上看雾霾天气过程的发生具有明显的季节性特征,冬季(1月、2月)以及3月雾霾天气过程发生次数最高,春季(4月、5月)发生次数最低,秋季发生次数略高于夏季。从空间维度上来看,中心城区(东城区、西城区、石景山、海淀区、朝阳区)雾霾天气过程发生次数明显高于郊区(顺义、昌平、怀柔),以东城区、西城区和朝阳区最为严重。     

Thermally Enhanced Motions of Variable-Inflow Surface Gravity-Driven Flows

In this paper, we report on theoretical and numerical studies of models for suddenly initiated variable-inflow surface gravity currents having temperature-dependent density functions when these currents are subjected to incoming radiation. This radiation leads to a heat source term that, owing to the spatial and temporal variation in surface layer thickness, is itself a function of space and time. This heat source term, in turn, produces a temperature field in the surface layer having nonzero horizontal spatial gradients. These gradients induce shear in the surface layer so that a depth-independent velocity field can no longer be assumed and the standard shallow-water theory must be extended to describe these flow scenarios. These variable-inflow currents are assumed to enter the flow regime from behind a partially opened lock gate with the lock containing a large volume of fluid whose surface is subjected to a variable pressure. Flow filament theory is used to arrive at expressions for the variable inflow velocity under the assumptions of an inviscid and incompressible fluid moving through a small opening under a lock gate at one end of a large rectangular tank containing the deep slightly more dense ambient fluid. Finding this time-dependent inflow velocity, which will then serve as a boundary condition for the solution of our two-layer system, involves solving a forced Riccati equation with time-dependent forcing arising from the surface pressure applied to the fluid in the lock.
The results presented here are, to the best of our knowledge, the first to involve variable-inflow surface gravity currents with or without thermal enhancement and they relate to a variety of phenomena from leaking shoreline oil containers to spring runoff where the variable inflow must be taken into account to predict correctly the ensuing evolution of the flow.     

Banerjeeet al’s characterization theorem in thermohaline convection and its magnetorotatory extensions

The paper mathematically establishes that magnetorotatory thermohaline convection of the Veronis [7] type cannot manifest itself as oscillatory motions of growing amplitude in an initially bottom heavy configuration if the thermohaline Rayleigh numberR _s, the Lewis number τ, the thermal Prandtl number σ, the magnetic Prandtl number σ₁, the Chandrasekhar numberQ and the Taylor numberT satisfy the inequality \(R_s 4\pi ^4 \left[ {1 + \frac{\tau }{{\sigma \pi ^2 }}\left\{ {\pi ^2 - \left( {O\sigma _1 + \frac{T}{{\pi ^2 }}} \right)} \right\}} \right]\) when both the boundary surfaces are rigid thus achieving magnetorotatory extension of an important characterization theorem of Banerjeeet al (1992) on the corresponding hydrodynamic problem. A similar characterization theorem is mathematically established in the context of the magnetorotatory thermohaline convection of the Stern (1960) type.     

Discontinuous periodic behaviour in a looped macroscopic model of traffic dynamics

A whole link model of traffic flow in which the link trip time varies linearly with link volume is investigated in the case where a fraction of the flow exiting the link is ‘re-injected’ as inflow, thus forming the link into a loop. The scenario where the fraction of flow re-injected linearly decreases as the volume of traffic on the link increases is considered. It is found that for certain parameter choices a continuous periodic inflow can lead to sharp post-transient discontinuities in periodic outflow. The conditions under which this type of behaviour can occur are considered.     

A new method of describing bottom stress in two-dimensional hydrodynamical models of shallow homogeneous seas, estuaries, and lakes

A new expression for bottom friction is developed for use in two-dimensional hydrodynamical models of shallow homogeneous seas, estuaries, and lakes. Bottom stress is provided by a single relaxation approximation which can be used to replace the conventional parametrization in any existing explicit time-stepping model. The method produces the correct steady state flow for wind-driven circulation in shallow systems. It derives the bottom stress from the vertical eddy viscosity which can have any prescribed variation through the water column. The single relaxation approximation uses a recursive relation for bottom stress involving only values at the previous time step and a pair of precomputed coefficients at each grid point.     

转臂式离心机工作室内的瞬态温度求解与分析

考虑大型转臂式离心机圆柱形工作室各墙壁(顶板、底板和侧壁)的瞬态导热,建立各墙壁的瞬态温度控制方程,对控制方程进行Laplace变换并求解,得到了透过墙壁内表面的总热流量与工作室内空气温度的关系.同时,综合考虑离心机驱动系统输出功率与工作室内空气和固体部件吸热、墙壁系统的吸热和导热、出风口带出的热量,以及动能与进风口带入的热量和动能之差等供能与耗能之间的平衡关系,建立工作室内瞬态温度控制方程,导出了工作室内空气瞬态温度的Laplace变换像函数的解析表达式.然后,采用求解Laplace逆变换的展开定理,导出了工作室内空气瞬态温度随时间变化的级数型显式表达式.最后,以一台多用途离心机为例,进行了工作室内空气温度的理论计算,与以前只考虑墙壁稳态导热的理论计算相比,瞬态计算结果与实测结果更加接近.所建瞬态温度公式提高了工作室温度的预测精度,有助于提升大型转臂式离心机工作室温控设计的水平.