Chang Yong Song

Estimation of submerged-arc welding design parameters using Taguchi method and fuzzy logic

Fuzzy logic with the Taguchi method is proposed for estimating submerged-arc welding design parameters. Design of experiments based on the submerged-arc welding simulation is applied to the proposed approach. The finite element analysis of a steel plate is carried out to simulate the submerged-arc welding process using thermomechanical and temperature-dependent material properties. Welding simulation results on thermal–mechanical coupled physical phenomena are compared with welding test. The proposed fuzzy model is generated with triangle membership functions and fuzzy if–then rules using training data obtained from design of experiments and the Taguchi method. The objective of the present study is to develop a Taguchi method-based fuzzy model to effectively approximate the optimized arc weld parameters. To validate the fuzzy model, an approximate model based on response surface method is generated from the Taguchi design data, and then the results are reviewed by the outcomes obtained from the fuzzy model. This proposed study facilitates a quantitative decision of weld factors such as speed and output of weld that are generally expressed by qualitative linguistic terms in the welding process.

Lateral pressure effect on average compressive strength of stiffened panels for in-service vessels

This paper presents the estimation of the average compressive strengths of three types of stiffened panels under axial compression and lateral pressure based on simplified formulae in the CSR for tankers (common structural rules for double hull oil tankers) and nonlinear finite element analyses (FEAs). Basic scenarios are determined based on the slenderness ratios of the stiffened panels used for in-service ships. Secondary scenarios are subdivided by external pressures that are applied to finite element model by increasing 1 bar, assuming 30 m water height. The total number of FEAs for flat bar (FB)-, angle bar (AB)- and tee bar (TB)-stiffened panels is 189. FEA results show that the existence of pressure can cause a significant reduction of ultimate strength, while CSR formulae do not take into account the effect of lateral pressure. The lateral pressure is more detrimental to the ultimate strength of stiffened panels with a higher column slenderness ratio than those with a smaller column slenderness ratio. A new concept of the relative average compressive strain energy, instead of the ultimate strength, is introduced in order to rationally compare the average compressive strength through a complete compressive straining history. The differences in the ultimate strengths between CSR formulae and FEA results are relatively small for FB- and AB-stiffened panels, but larger discrepancies of relative average compressive strain energies are obtained.

Fluid-Structure Interaction Analysis on the Deformation of Simplified Yacht Sails

Since most of yacht sails are made of thin fabric, they form cambered sail shape that can efficiently generate lift power by aerodynamic interaction and by external force delivered from supporting structures such as mast and boom. When the incident flow and external force alter in terms of volume or condition, the shape of sail also change. This deformation in shape has impact on the peripheral flow and aerodynamic interaction of the sail, and thus it is related to the deformation of the sail in shape again. Therefore, the precise optimization of aerodynamic performance of sail requires fluid-structure interaction (FSI) analysis. In this study, the simplified sail without camber was under experiment for one-way FSI that uses the result of flow analysis to the structural analysis as load condition in an attempt to fluid-structure interaction phenomenon. To confirm the validity of the analytical methods and the reliability of numerical computation, the difference in deformation by the number of finite element was compared. This study reproduced the boundary conditions that sail could have by rigs such as mast and boom and looked into the deformation of sail. Sail has non-linear deformation such as wrinkles because it is made of a thin fabric material. Thus non-linear structural analysis was conducted and the results were compared with those of analysis on elastic material.

Design of Stress Relief Groove on a Press-Fitted Assembly

The objective of this study is to propose the effective method of reducing the maximum contact pressure at the contact edge of press-fitted shaft by optimizing the location and the size of stress relief groove in hub face. Finite element analysis was performed in order to determine the contact pressure and stress state on a press-fitted assembly and optimization were applied to select optimal size and location of stress relief groove. In order to reduce the cost of optimization design, approximation optimization method is used and the optimum results obtained by Sequential Quadratic Programming and genetic algorithm are compared. Optimized results show that the maximum contact pressure at the contact edge of press-fitted shaft with optimal stress relief groove decreased about 30%. And the both optimization algorithms can effectively reduced the maximum contact pressure at the contact edge of press-fitted shaft.