Partial air cushion support catamaran (PACSCAT) is a new type of high-performance ship based on slender catamaran and supplemented by partial air-cushion support. Its bottom is flat and wide, and the air-cushion displacement volume accounts for about 30% of the whole ship. Due to the air cushion, the ship will have many nonlinear characteristics when sailing in the waves, influencing the motion performance of the hull heavily. The three-dimensional potential flow theory considers the three-dimensional effect of the flow field and it has been widely used in the field of ship hydrodynamics, so it can be effectively applied to the study of strong nonlinear motion characteristics of ships, which coincides with the study of nonlinear mechanics of hovercraft. The research was based on the rigid air seal form of the cushion system, and took into account the nonlinear characteristics of the air cushion. Therefore, in order to verify the form of numerical calculation method of PACSCAT with rigid seals, and study its movement characteristics in waves, this paper adopted the free surface method, and used overlapping grids and slip grids to analyze its performance in clam water. Furthermore, based on the best grid form, its navigation performance in regular waves was numerically simulated and compared with the experimental values, and then the calculation accuracy of the total hull resistance and the characteristics of the motion parameters under different wavelengths were studied. The results show that: overlapping grids have a higher hydrostatic resistance calculation accuracy than sliding grids, up to 5.2% when v=5.0 m/s. In the numerical calculation, the amplitude and average value of wave resistance are greater than the experimental value, and the error is the largest at the wavelength of 7.0 m. From the study of various wave motion parameters, it can be seen that there is no obvious difference between the duration curve of each motion parameter and the test value, and the calculated value of amplitude response is generally smaller than the experimental value, but the calculated value is obviously greater than the experimental value when λ/L is 2.33.
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The bow lines of a planing craft have a significant influence on its seakeeping performance, making their intelligent optimization design necessary.
This study focuses on a certain type of wave-piercing bow planing craft and uses the stem angle, second-order curve shape factors, and coordinates of the knuckle line bow control points as parameters for driving the deformation of the bow lines and carrying out the parametric modeling of the bow. It validates numerical calculation methods based on model test results and establishes a surrogate model according to the numerical results. It optimizes the still water resistance and motion response amplitude in regular waves at a speed corresponding to a volume Froude number of
The results under the constraint show that the still water resistance and the average wave-making resistance increase does not exceed 12% and the optimized hull form sees a reduction of about 20% in acceleration amplitude, heave amplitude, pitch amplitude, and heaving compared to the initial craft.
By optimizing the bow lines, the planing craft's low resistance is ensured while improving its motion response in regular waves, providing an intelligent optimization design method for planing craft lines.
Aiming at balancing the cost and accuracy of ship maneuvering motion prediction, a numerical calculation based prediction approach is presented, combined with the sensitivity analysis of hydrodynamic derivatives.
First, the numerical calculation is carried out by solving the RANS equations, employing the method of volume-of-fluid (VOF) to capture the free-water surface and putting constraints on the motion of DTMB 5415 model, additional comparison of the linear hydrodynamic derivatives obtained from the regression are conducted with the experimental data so as to verify the validity of the proposed numerical scheme. Furthermore, a ship maneuvering mathematical model of DTMB 5415 is established on the basis of the maneuvering mathematical model group (MMG) method, and the Runge-Kutta algorithm is utilized to solve the equations and the model's turning and zigzag maneuvering motions are simulated. Finally, the sensitivity of the hydrodynamic derivatives of the two maneuvering motions are analyzed.
The results show that the modelling results of ship motion trajectory and parameter for criteria obtained by the proposed methods are agree well with the experimental data, among which the average errors of the parameters of turning and zigzag maneuvering motion are 5.1% and 11.7% respectively. Compared with the results of the self-propelled ship model simulation using CFD, both the accuracy and cost are improved. The sensitivity analysis also verify that some nonlinear hydrodynamic derivatives have little influence on the maneuverability criterion, and can be estimated using empirical formulas.
The proposed method is feasible for ship maneuverability motions prediction, which can meet the engineering application precision and reduce the calculation cost greatly, especially suitable for the maneuverability motions prediction and optimization in ship design stage.
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