Study on Flow Field Around Vertical Breakwater Under Different Overtopping Conditions Based on Numerical Simulation

A numerical wave flume is constructed based on the Reynolds Averaged Navier-Stokes （RANS） equations with turbulence closure by a modified k - ε model to study the viscous interactiorrs of waves with vertical breakwaters for different overtopping cases. The goveruing equations, the turbulence model, boundary conditions, and solution method for the nu- merical wave flume are introduced briefly. The reliability of the numerical wave flume is examined by comparing the nu- merical results with the experimental measurements, and good agreements between them indicate the validity of the pre- sent model. The developments of mean velocity fields, the contours of vorticity, and the influences of wave nonlinearity on turbulence field as wave passing through vertical breakwaters are discussed in detail based on the numerical results. It is noted that the vortices at the rear of the lower submerged breakwater are close to the bottum and maytbe induce the scouring to the leeside toe of marine structure in practice. Over all, a conclusion can be obtained from this study that the turbulence in wave field around structure is induced directly by the development of boundary layer on the solid boundary, the nonlinear interaction of free surface with obstaele, and the plunging of overtopping waves.

OBJECTIVITY REQUIREMENT FOR FLUID DYNAMICS

A new flow theory is established through the objectivity requirement on the fluid dynamics. It was known that inhomogeneous fluid motion gave rise to viscous force while the selection of observers on different space_time points would change such an inhomogeneous character.Therefore,when the viscous force was considered as an objective existence foreign to the selection of observers,the form invariances of viscous force and momentum equation under local rotation transformation required a new dynamic field,namely the vortex field to be introduced.Then the dynamical equations of all flow fields were obtained through constructing the Lagrangian density of fluid system and using the variational approach of energy.

Gao's interacting shear flows( ISF) theory and its inferences and their applications

Gao＇s viscous/in-viscid interacting shear flows （ISF） theory, proposed by professor Gao Zhi in Institute of Mechanics, China Academy of Science, and its inferences and their applications in computational fluid dynamics （CFD） are reviewed and some subjects worthy to be studied are pro- posed in this paper. The flow-field and motion law of ISF, mathematics definition of strong viscous shear layer flow in ISF, ISF equations, wall-surface compatibility criteria （Gao＇s criteria ）, space scale variety law of strong viscous shear layer reveals flow mechanism and local space small scale triggered by strong interaction that cause some abnormal severe local pneumatic heating phenomenon in hypersonic flow. Gao＇s ISF theory was used in near wall flow, free ISF flow simulation and design of computing grids, Gao＇s wall-surface criteria were used to verify calculation reliability and accuracy of near wall flows, ISF theory approximate analytical result of shock waves-boundary layer interac- tion and ISF equations were used to obtain the numerical exact solution of local area flow （ such as stationary point flow）. Some new subjects, such as, improving near-wall turbulent models according to the turbulent flow simulation satisfying the wall-criteria and illustrating relation between grid-con- vergence based on the wall criteria and other convergence tactics, are suggested. The necessity of applying Gao＇s ISF theory and wall criteria is revealed. Difficulties and importance of hypersonic vis- cous/in-viscid interaction phenomenon were also emphasized.