Observation and simulation of wind waves near a typical reef lagoon in South China Sea

Due to the inference of the uneven shallow water seabed and the surrounding islands,the wind-generated waves around or in a reef lagoon are rather complicated,and critical to the safety of floating structures deployed near islands or inside a lagoon.This paper aims to find a feasible analysis tool for the wave simulations near islands and reefs.The proposed three methods of grid techniques of WAVEWATCH III(WW3)are assessed by using on-site measured data which was collected and accumulated for about 5 years since August 2014 by a wave observation system deployed inside and outside a reef lagoon in South China Sea.In the assessments,the wave statistics including the correlation coefficients,root mean square errors,and their variances are used to quantify the precisions of the simulation results of the significant wave heights,mean wave periods,and peak wave directions at two sites.Among the three methods,the Multi-scale Zone and Multi-scale grid Technique(MZMGT)established on unstructured triangular grids exhibits better results in terms of the accuracy and CPU cost.In addition,the bimodal feature of wave spectra was observed at both sites of the reef lagoon in different typhoon events.The wave characteristics inside the reef lagoon and open sea are also analyzed.

An application of network modeling method to scientific research and demonstration platform-Connector load analysis

A new approach referred as“the network modeling method”was developed by the authors to analyze the behaviors of marine structures.In this paper the method is briefly described and applied to predict the loads acting on the connectors between the two modules of the Scientific Research and Demonstration Platform(SRDP),which was deployed in a complicated wave environment near islands and reefs in South China Sea.Based on this method,the response amplitude operators(RAOs)of the connector loads of the SRDP in regular waves,and the time variations of the connector loads of the SRDP in an on-site measured random sea state are predicted and presented.The significant stresses at 20 spots of the local connection structure induced by the connector loads in the sea state are further calculated.The comparisons between the predicted and the on-site measured stresses confirm that the network modeling method is feasible to some extent and especially useful for design of the connectors’arrangement,estimation of the connector loads and the related structural safety of a multi-module floating structure in early design stage.

Nonlinear dynamic characteristics of a multi-module floating airport with rigid-flexible connections

This paper studies the dynamics of a multi-module floating airport with flexible connectors using the network theory. A mathematical model for a chain-type topology structure is developed by using the wave theory, and the models of a single floating module and the connector and mooring system. The nonlinear dynamics of the floating airport and the connector force are studied. A remarkable phenomenon of amplitude death is observed, as a weak oscillation state of all floating modules, an important state for the system global dynamic stability. The parametric domain for the onset of amplitude death is identified, and the effects of the wave height and the number of the floating modules on the dynamic stability are discussed. An application of the network theory in the marine engineering is illustrated with the introduction of a new concept for global dynamic stability for the floating airport.

Three-dimensional numerical study of flow characteristics and membrane fouling evolution in an enzymatic membrane reactor

In order to enhance the understanding of the membrane fouling mechanism, the hydrodynamics of the granular flow in a stirred enzymatic membrane reactor is numerically investigated in the present paper. A three-dimensional Euler-Euler model, coupled with the k-ε mixture turbulence model and the drag function proposed by Syamlal and O＇Brien（1989） for the interphase momentum exchange, is built to simulate the two-phase（fluid-solid） turbulent flow. Numerical simulations of single-or two-phase turbulent flows at various stirring speeds are carried out. The numerical results agree very well with the published experimental data. Results include the distributions of the velocity, the shear stress and the turbulent kinetic energy. It is shown that the increase of the stirring speed not only enlarges the circulation loops in the reactor, but also increases the shear stress on the membrane surface and accelerates the mixing process for the granular materials. The time evolution of the volumetric function of the granular materials on the membrane surface can qualitatively explain the evolution of the membrane fouling.