Xinshu Zhang

Design and performance simulation of a new solar continuous solid adsorption refrigeration and heating hybrid system

In this paper, the design of a new continuous solid adsorption refrigeration and heating hybrid system driven by solar energy was proposed, and its performance simulation and analysis were made under the normal working conditions. Some performance parameters of the system were obtained, and the effects of water mass in water tank on the systems COPcooling, COPheating etc. were discussed. The simulation indicated: the system could refrigerate continuously with such a design, and at the conditions of that the daily sun-radiation is 21.6 MJ, the mean ambient temperature is 29.9°C, the evaporating temperature is 5°C, the heat-collecting coefficient of upper bed η is 60%, and the heat-transfer coefficient between lower bed and ambient α is 2 W/m2 K, by day a hybrid system of single combined bed could furnish 30 kg hot water of 47.8°C, and had a mean COPcooling of 0.18, a mean COPheating of 0.34, a continuous mean SCPa of 17.6 W/kg, a continuous mean SCPc of 87.8 W/m2, and a continuous mean SHPc of 165.9 W/m2; and at night it had a cooling capacity of 0.26 MJ/kg of adsorbent, and a cooling capacity of 1.3 MJ/m2 of heat-collecting area.

Numerical simulation of heat transfer in regenerator of solid adsorption refrigeration system

In this paper a theoretical model of the heat-transfer processes in a solid adsorbent packed bed is established. Based on discretized energy control equations of the fluid in the heat-transfer coil and transient heat conduction equations of the adsorbent in the bed with unsteady boundary conditions, a numerical analysis is made. Through numerical computation, a coupling temperature distribution in the adsorbent and the heat-transfer coil is obtained. This will make for an optimal design of the solid adsorbent packed bed.

Wave force prediction effect on the energy absorption of a wave energy converter with real-time control

Real-time control has been widely adopted to enlarge the energy extraction of a wave energy converter (WEC). In order to implement a real-time control, it is necessary to predict the wave excitation forces in the close future. In many previous studies, the wave forces over the prediction horizon were assumed to be already known, while the wave force prediction effect has been hardly examined. In this paper, we investigate the effect of wave force prediction on the energy absorption of a heaving point-absorber WEC with real-time latching control. The real-time control strategy is based on the combination of optimal command theory and first order-one variable grey model. It is shown that a long prediction horizon is beneficial to the energy absorption, whereas the prediction deviation reduces extracting efficiency of the WEC. Further analysis indicates that deviation of wave force amplitude has little influence on the WEC performance. It is the phase deviation that leads to energy loss. Since the prediction deviation accumulates over the horizon, a moderate horizon is, thus, recommended.

Global motion and airgap computations for semi-submersible floating production unit in waves

Abstract We study the global hydrodynamic performance of a semi-submersible floating platform unit in order to optimize the hull form in the future. The hydrodynamic problem is solved by employing potential flow theory and Morison equation for modelling of the viscous effects. The added mass and damping coefficients, as well as the first-order motion responses, second-order mean drift forces, diffracted and radiated wave field, and airgap are computed to examine the hydrodynamic behavior of the floating production unit. The computational results show that the motion responses in short-crested waves are mostly smaller than those in long-crested waves. The maximum wave elevation occurs at WP45 in 45 ° wave heading in long-crested waves. In addition, the minimum airgap occurs at AG45 in 45 ° wave heading in linear waves, while the worst airgap point in nonlinear waves is AG0 in 0 ° wave heading. Extensive parametric studies have been performed to examine the dependence of the motion responses and the other key design criteria on the principal dimensions including hull draft, column width, column spacing, column corner radius, pontoon height, pontoon width, and the size of cakepiece. By comprehensive and systematic hydrodynamic computations and analyses, it is revealed that the combined vertical motion at the worst airgap location is almost in phase with the wave elevation in extreme wave condition with a peak wave period around 14–15xa0s. Moreover, it is found that the most efficient way to reduce the motion is to increase the hull draft, though the airgap may also decrease. Besides, reducing the pontoon height can achieve better motion performance and larger airgap simultaneously. This paper aims to provide a benchmark for future studies on automatic hull form optimization.

Investigation on long-term extreme response of an integrated offshore renewable energy device with a modified environmental contour method

Considering the massive simulations required by the full long-term analysis, the environmental contour method is commonly used to predict the long-term extreme responses of an offshore renewable system during life time. Nevertheless, the standard environmental contour method is not applicable to the wind energy device due to the non-monotonic aerodynamic behaviour of the wind turbine. This study presents the development of a modified environmental counter method and its application to the extreme responses of a hybrid offshore renewable system. The modified method considers the variability of the responses by checking multiple contour surfaces so that the non-monotonic aerodynamic behaviour of the wind turbine is considered. The hybrid system integrates a floating wind turbine, a wave energy converter and two tidal turbines. Simulation results prove that the modified method has a better accuracy.

Numerical Studies on Vortex-Induced Motions of a Semi-Submersible With Four Columns Based on IDDES Model

The vortex-induced motions (VIM) of deep draft semi-submersible platforms have been challenging engineering issues because of its impact to the fatigue life of mooring and riser systems. This paper presents numerical studies on the vortex-induced motions (VIM) of a deep draft semi-submersible. Numerical simulations are performed by using an improved delayed detached eddy simulation (IDDES). VIM amplitudes for in-line (surge), transverse (sway) and yaw motions and hydrodynamic force coefficients are obtained for different current incidence angles. The sensitivity analyses on grids and time step sizes are carried out to ensure convergences of the computational results. Comparisons with experimental data demonstrate the capability of the present numerical model. It is observed that the transverse motions for 22.5° current incidence are larger than those for 0° and 45° current incidences. The mean drag force coefficients for these simulated current incidence angles tend to grow as the transverse motion amplitudes increase. In addition, parametric studies have also been performed to examine the effects of the column corner radius on VIM.Copyright