Haicheng Zhang

On Study of Nonlinear Network Dynamics of Flexibly Connected Multi-Module Very Large Floating Structures

The very large floating structure (VLFS) designed for a floating airport and giant operating platform on sea consists of multiple floating modules with flexible connectors, which is a typical nonlinear dynamic network involving complex collective dynamics. The study focuses on the typical behaviors of amplitude death (AD) that is significantly important to the global dynamic stability of the VLFS system. A nonlinear dynamic model for a chain-formed VLFS with piecewise-nonlinear-coupling is developed. We investigate the onset of amplitude death in design parametric domain, and discuss the mechanism of the phenomenon corresponding to the coupling strengths. The numerical results show that by varying coupling strengths, a weak periodic oscillation can be rapidly bifurcated into high-order periodic or chaotic motions with large oscillations. The amplitude death is illustrated in the parametric domain of coupling strengths, which provide a new insight and theoretical guidelines for the VLFS safety design.

Response control of a floating airport in heading waves with output saturation

This paper presents a nonlinear control strategy to stabilize the response of a floating platform in waves. The floating platform consists of multiple floating modules connected in sequence with flexible connectors. A nonlinear dynamic model with a number of controllers is developed for the stability control of the chain-shape floating structure. The backstepping method in conjunction with the Lyapunov stability criteria is proposed to derive the control law for each of the control actuators where the actuator forces are limited with output saturation. The numerical experiments illustrate the feasibility and effectiveness of the control strategy in various conditions of heading waves. The performance of the control method is discussed, especially associated with the saturated output.

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.