The hydrodynamic performance of a propeller in unsteady inflow was calculated using the surface panel method. The surfaces of blades and hub were discreted by a number of hyperboloidal quadrilateral panels with consta...The hydrodynamic performance of a propeller in unsteady inflow was calculated using the surface panel method. The surfaces of blades and hub were discreted by a number of hyperboloidal quadrilateral panels with constant source and doublet distribution. Each panel＇s comer coordinates were calculated by spline interpolation between the main parameter and the blade geometry of the propeller. The integral equation was derived using the Green Formula. The influence coefficient of the matrix was calculated by the Morino analytic formula. The tangential velocity distribution was calculated with the Yanagizawa method, and the pressure coefficient was calculated using the Bonuli equation. The pressure Kutta condition was satisfied at the trailing edge of the propeller blade using the Newton-Raphson iterative procedure, so as to make the pressure coefficients of the suction and pressure faces of the blade equal at the trailing edge. Calculated results for the propeller in steady inflow were taken as initialization values for the unsteady inflow calculation process. Calculations were carried out from the moment the propeller achieved steady rotation. At each time interval, a linear algebraic equation combined with Kutta condition was established on a key blade and solved numerically. Comparison between calculated results and experimental results indicates that this method is correct and effective.展开更多
In part I of this series, experimental investigation in EPFM （elastic-plastic fracture mechanics） had been discussed. In this paper, experimental investigation in LEFM （ linear elastic fracture mechanics） is given...In part I of this series, experimental investigation in EPFM （elastic-plastic fracture mechanics） had been discussed. In this paper, experimental investigation in LEFM （ linear elastic fracture mechanics） is given. Fracture toughness tests had been carried out on three different strength steels, using both through-cracked specimens with different α/W ratio and semi-elliptical cracked specimens with variable crack size and shape. Results show that the fracture toughness KIC increases with decreasing α/W when α/W 〈 0.3 for three-point-bend specimens, and that for α/W 〉 0.3, it is independent of α/W. Shallow crack specimens, both through-cracked and surface-cracked, gave markedly higher values than deeply notched specimens. However, the effect of crack shape on fracture toughness is negligible. Results also show that the LEFM approach to fracture is not tenable for design stresses where αc is often very small, far less than 2.5 （ KIC/σy）^2.展开更多
Radar cross section (RCS) reduction technologies are very important in survivability of the military naval vessels. Ship appearance shaping as an effective countermeasure of RCS reduction redirects the scattered energ...Radar cross section (RCS) reduction technologies are very important in survivability of the military naval vessels. Ship appearance shaping as an effective countermeasure of RCS reduction redirects the scattered energy from one angular region of interest in space to another region of little interest. To decrease the scattering electromagnetic signals from ship scientifically, optimization methods should be introduced in shaping design. Based on the assumption of the characteristic section design method, mathematical formulations for optimal shaping design were established. Because of the computation-intensive analysis and singularity in shaping optimization, the response surface method (RSM) combined genetic algorithm (GA) was proposed. The poly-nomial response surface method was adopted in model approximation. Then genetic algorithms were employed to solve the surrogate optimization problem. By comparison RCS of the conventional and the optimal design, the superiority and effectiveness of proposed design methodology were verified.展开更多
In naval engineering and offshore industry,the fluid-structure interaction(FSI)problem is a very common problem,and water entry is a very representative one.The hydroelasticity effects due to slamming are of great int...In naval engineering and offshore industry,the fluid-structure interaction(FSI)problem is a very common problem,and water entry is a very representative one.The hydroelasticity effects due to slamming are of great interest.In this paper,the water entry problem is simulated by the moving particle semi-implicit&finite element method(MPS-FEM)coupled method.The MPS method is used for the fluid because it is very suitable for the violent free-surface flow.The structure domain is solved by the FEM method because of the maturity in solving structural motion and deformation.The water entry of a rigid cylinder is numerically studied first and the results show good agreements with previous published data.After that,variable analysis is conducted in the water entry simulation of an elastic cylinder,including the structural elasticity and impact velocity.展开更多
基金Supported by the Doctoral Program of Higher Education Foundation under Grant No. 2006021702.
文摘The hydrodynamic performance of a propeller in unsteady inflow was calculated using the surface panel method. The surfaces of blades and hub were discreted by a number of hyperboloidal quadrilateral panels with constant source and doublet distribution. Each panel＇s comer coordinates were calculated by spline interpolation between the main parameter and the blade geometry of the propeller. The integral equation was derived using the Green Formula. The influence coefficient of the matrix was calculated by the Morino analytic formula. The tangential velocity distribution was calculated with the Yanagizawa method, and the pressure coefficient was calculated using the Bonuli equation. The pressure Kutta condition was satisfied at the trailing edge of the propeller blade using the Newton-Raphson iterative procedure, so as to make the pressure coefficients of the suction and pressure faces of the blade equal at the trailing edge. Calculated results for the propeller in steady inflow were taken as initialization values for the unsteady inflow calculation process. Calculations were carried out from the moment the propeller achieved steady rotation. At each time interval, a linear algebraic equation combined with Kutta condition was established on a key blade and solved numerically. Comparison between calculated results and experimental results indicates that this method is correct and effective.
文摘In part I of this series, experimental investigation in EPFM （elastic-plastic fracture mechanics） had been discussed. In this paper, experimental investigation in LEFM （ linear elastic fracture mechanics） is given. Fracture toughness tests had been carried out on three different strength steels, using both through-cracked specimens with different α/W ratio and semi-elliptical cracked specimens with variable crack size and shape. Results show that the fracture toughness KIC increases with decreasing α/W when α/W 〈 0.3 for three-point-bend specimens, and that for α/W 〉 0.3, it is independent of α/W. Shallow crack specimens, both through-cracked and surface-cracked, gave markedly higher values than deeply notched specimens. However, the effect of crack shape on fracture toughness is negligible. Results also show that the LEFM approach to fracture is not tenable for design stresses where αc is often very small, far less than 2.5 （ KIC/σy）^2.
基金the National Natural Science Founda-tion of China (No. 10672100)
文摘Radar cross section (RCS) reduction technologies are very important in survivability of the military naval vessels. Ship appearance shaping as an effective countermeasure of RCS reduction redirects the scattered energy from one angular region of interest in space to another region of little interest. To decrease the scattering electromagnetic signals from ship scientifically, optimization methods should be introduced in shaping design. Based on the assumption of the characteristic section design method, mathematical formulations for optimal shaping design were established. Because of the computation-intensive analysis and singularity in shaping optimization, the response surface method (RSM) combined genetic algorithm (GA) was proposed. The poly-nomial response surface method was adopted in model approximation. Then genetic algorithms were employed to solve the surrogate optimization problem. By comparison RCS of the conventional and the optimal design, the superiority and effectiveness of proposed design methodology were verified.
基金the National Key Research and Development Program of China(Grant No.2019YFB1704200)the National Natural Science Foundation of China(Grant Nos.51879159 and 52131102).
文摘In naval engineering and offshore industry,the fluid-structure interaction(FSI)problem is a very common problem,and water entry is a very representative one.The hydroelasticity effects due to slamming are of great interest.In this paper,the water entry problem is simulated by the moving particle semi-implicit&finite element method(MPS-FEM)coupled method.The MPS method is used for the fluid because it is very suitable for the violent free-surface flow.The structure domain is solved by the FEM method because of the maturity in solving structural motion and deformation.The water entry of a rigid cylinder is numerically studied first and the results show good agreements with previous published data.After that,variable analysis is conducted in the water entry simulation of an elastic cylinder,including the structural elasticity and impact velocity.
