Abstract When optimizing the hydrodynamic performance of a propeller, a sufficient sample space for optimization calculations needs to be established and parametric modeling of the initial propeller needs to be implemented. In this paper, the parametric modeling of the propeller is programmed based on the F-spline curve fitting principle, and the radial parameter distributions of the propeller are fitted with one F-spline curve each. The idea of using fewer control variables to fit the curve accurately and minimizing the variance of the fitted points is added to the curve fitting, which greatly reduces the error between the fitted curve and the original curve. Based on the fitted propeller radial parameter curves, the parent propeller shape can be accurately described and the propeller geometry in the generated sample space is guaranteed to be smooth. The fitted curve is then used to write a program that integrates the modeling process and eliminates the need to manually complete the propeller 3D model. The implementation of parametric modeling of the propeller allows for better establishment of the relationship between propeller geometric features and propeller performance. The closed-loop nature of this modeling method ensures efficient propeller hydrodynamic performance forecasting and optimization, and improves the propeller hydrodynamic performance optimization system.
The industry demand for ice-classed tankers is rapidly increasing as a result of the growing exports of oil from Russia. There has been a trend toward allowing for alternative designs using direct calculation approaches. However, no complete procedure is available. This paper presents a procedure for designing ice-strengthened structures of tankers using direct calculation approaches. It addresses the main issues, including ice load definition, material modeling, structural modeling and acceptance criteria. The paper summarizes a recent joint ABS-SHI project that will become the basis of the future, refined design practice.
The properties of turbulence subgrid-scale stresses are studied using experimental data in the far field of a round jet, at a Reynolds number of R λ ≈ 310. Measurements are performed using two-dimensional particle displacement velocimetry. Three elements of the subgrid-scale stress tensor are calculated using planar filtering of the data. Using a priori testing, eddy-viscosity closures are shown to display very little correlation with the real stresses, in accord with earlier findings based on direct numerical simulations at lower Reynolds numbers. Detailed analysis of subgrid energy fluxes and of the velocity field decomposed into logarithmic bands leads to a new similarity subgrid-scale model. It is based on the ‘resolved stress’ tensor L ij , which is obtained by filtering products of resolved velocities at a scale equal to twice the grid scale. The correlation coefficient of this model with the real stress is shown to be substantially higher than that of the eddy-viscosity closures. It is shown that mixed models display similar levels of correlation. During the a priori test, care is taken to only employ resolved data in a fashion that is consistent with the information that would be available during large-eddy simulation. The influence of the filter shape on the correlation is documented in detail, and the model is compared to the original similarity model of Bardina et al. (1980). A relationship between L ij and a nonlinear subgrid-scale model is established. In order to control the amount of kinetic energy backscatter, which could potentially lead to numerical instability, an ad hoc weighting function that depends on the alignment between L ij and the strain-rate tensor, is introduced. A ‘dynamic’ version of the model is shown, based on the data, to allow a self-consistent determination of the coefficient. In addition, all tensor elements of the model are shown to display the correct scaling with normal distance near a solid boundary.
Mooring system design of a floating offshore structure in the arctic region is considered to be extremely important. This paper aims at investigating an optimal mooring system for the Kulluk platform operating in the Beaufort Sea, which has ice-free and ice-covered conditions during the whole year time. In order to complete the layout design of the mooring system to satisfy the year-round operation, both the effect of wave loads and ice loads should be considered. The research establishes a coupled numerical production system composed of the Kulluk platform and mooring system. Wave load is solved by potential flow theory. The slender finite element method is used to compute the tension of the mooring system. The nonlinear finite element method, discrete element method, and empirical formula are compared to analyze ice load. Finally, the discrete element method is selected for the analysis of the Kulluk, and the simulated results are compared reasonably with the field data. When studying the mooring line configurations, quantitative time-domain analysis is carried out, including tension of mooring lines and the motions of the platform under different working conditions. The research work in this paper will provide a reference for the optimal design of the mooring system of the platform operating in the Arctic Sea.
The recent surge of interest in potential oil and gas reserves in the Arctic has resulted in vital technological developments in the field of Arctic shipping. New, larger vessels of novel designs are entering the region where the industry has limited experience. The design of these large vessels presents new challenges for designers and operators. ABS, DSME, and BMT Fleet have collaborated in a joint project focusing on the development of a 107,000 DWT Arctic crude oil tanker designed to comply with the IACS Polar Class PC4. Structural strength assessments of the bow and three midbody configurations subject to ice loads derived from the PC rules and several other ship-ice interaction scenarios were conducted. This paper presents the procedure and results of static nonlinear finite element analysis (FEA) and plastic grillage analysis used to simulate several identified high-risk ship-ice interaction scenarios.
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