Korean pine (Pinus koraiensis Sieb. et Zucc.) is one of the highly commercial woody species in Northeast China. In this study, six nonlinear equations and artificial neural network (ANN) models were employed to model and validate height-diameter (H-DBH) relationship in three different stand densities of one Korean pine plantation. Data were collected in 12 plots in a 43-year-old even-aged stand of P. koraiensis in Mengjiagang Forest Farm, China. The data were randomly split into two datasets for model development (9 plots) and for model validation (3 plots). All candidate models showed a good perfomance in explaining H-DBH relationship with error estimation of tree height ranging from 0.61 to 1.52 m. Especially, ANN models could reduce the root mean square error (RMSE) by the highest 40%, compared with Power function for the density level of 600 trees. In general, our results showed that ANN models were superior to other six nonlinear models. The H-DBH relationship appeared to differ between stand density levels, thus it is necessary to establish H-DBH models for specific stand densities to provide more accurate estimation of tree height.
The classical approaches using CFD software to calculate the hydrodynamic performance of catamaran planing vessel still need to rely on the model test or empirical formula to make sure of the running attitude. So a theoretical calculate method of resistance performance of catamaran planing vessel is proposed in this paper based on RANS equations and the VOF method to couple six degrees of freedom equation of the catamaran planing vessel. Numerical simulation results indicate that using RANS equations can better forecast hydrodynamic performance of catamaran planing vessel at high speed, which provides a practicable numerical method for optimization design of the catamaran planing vessels hull.
This paper describes the hydrodynamic performance prediction of ship hull with propeller by using CFD techniques. As an attempt in investigating the flow features around ship hull equipped with a rotating propeller, open water test, resistance test, and self-propulsion test were conducted. The paper discusses also the applicability of different turbulence models which are used to predict the hydrodynamic performance of the propeller, the hull, and the interaction hull-propeller. The hydrodynamic performance prediction method was gotten and was validated. The computational results were validated against the existing experimental data.
At present, the prediction of energy saving effect of energy saving devices, which still has some difficulties to solve in numerical methods, still depends on model test. Based on CFD technology, this paper will give a numerical prediction method of energy saving effect for compensating ducts. Firstly, the wake field of one full form ship is predicted, which includes the bare hull and hull with compensating ducts. After studying the numerical prediction method of analyzing the interaction between hull and propellers, the energy saving effect of compensating ducts is predicted with the interaction of hull and propeller. The calculation results show that the method is feasible to predict the energy saving effect of compensating ducts. The efficiency of the propeller is improved remarkably when ship hull is installed the compensating ducts.
Due to the special hull shape of the catamaran planing vessel, the shiplines optimization design and the hydrodynamic performance prediction of the catamaran planing vessel are mainly carried out by model tank tests and the empirical formula at present. The numerical prediction method of the hydrodynamic performance of catamaran planing vessel has been a big difficulty for a long time. In this paper, the influence of the key channel design parameters on the catamaran planing vessel hydrodynamic performance is studied based on the CFD technology. Some beneficial conclusions are obtained which is helpful for the optimization design of catamaran planing vessel. The work of this paper provides a numerical research method for the optimization design of the catamaran planing vessels hull.
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