• Journal of Advanced Marine Engineering and Technology
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• 제24권6호
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• pp.7-14
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• 2000

Nowadays, the viscous damper using high viscosity oil was much to be used for engine shafting system to reduce the excessive additional stress by torsional vibration. In general, it was assumed that the viscous damper could be modelled having only damping coefficient, that is to say, whose stiffness be ignored. But it is found that there exists a jump phenomenon, as a kind of non-linear vibration, in the actual engine shafting system with a damper of high viscosity. Therefore the damper ring and the casing are modelled as two mass elastic system with a complex viscosity. Also, to analyze a non-linear phenomenon, it is assumed that the viscous damper has a linear stiffness coefficient in proportion to the angular amplitude and a non-linear stiffness coefficient in proportion to cube of the angular amplitude. For the analysis, Quasi-Newton method with BFGS(Broyden-Fletcher-Goldfarb-Shanno) formula is used. Both calculated and measured values are provided in this paper which confirm the possibility of applying non-linear theory to engine shafting system with viscous damper.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.1018-1025
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• 2003

The diesel engine is often a serious excitation source in ships. Both the varying cylinder gas forces and the reciprocating and rotating mass forces associated with the crank and the connecting rod mechanism produce ample possibilities for excitation of the engine structure itself, the shafting, the surrounding substructures as well as the hull girder. This paper presents a guide for optimization of excitation forces produced by the marine propulsion 2-stroke diesel engine. The computational program for predicting the excitation forces is developed and applied to 2-stroke in-line engines. The object function is defined as the work done by every cylinder excitation force which is related to the mode shape of the diesel engine system, especially in the torsional vibration of the shafting. As a practical application of the presented method, the crank angle of 7 cylinder 2-stroke engine is optimized to reduce torsional vibration stresses on the shafting. Compared with the regular firing angle, about 60% of the 4th order torsional vibratory stress on the propeller shaft can be reduced by optimizing the crank angle irregularly. The usefulness of the presented optimization method is confirmed by the measurements.

• 한국소음진동공학회논문집
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• 제14권8호
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• pp.709-717
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• 2004

The diesel engine is often a serious excitation source in ships. Both the varying cylinder gas forces and the reciprocating and rotating mass forces associated with the crank and the connecting rod mechanism produce ample possibilities for excitation of the engine structure itself, the shafting, the surrounding substructures as well as the hull girder. This paper presents a guide for optimization of excitation forces produced by the marine propulsion 2-stroke diesel engine. The computational program for predicting the excitation forces is developed and applied to 2-stroke in-line engines. The object function is defined as the work done by every cylinder excitation force which is related to the mode shape of the diesel engine system, especially in the torsional vibration of the shafting. As a practical application of the presented method. the crank angle of 7 cylinder 2-stroke engine is optimized to reduce torsional vibration stresses on the shafting. Compared with the regular firing angle, about 60 ％ of the 4th order torsional vibratory stress on the propeller shaft can be reduced by optimizing the crank angle irregularly. The usefulness of the presented optimization method is confirmed by the measurements.

• Structural Engineering and Mechanics
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• 제19권3호
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• pp.281-295
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• 2005

An analytical method is presented to solve the elastodynamic problem of finitely long hollow cylinder subjected to torsional impact often occurs in engineering mechanics. The analytical solution is composed of a solution of quasi-static equation satisfied with the non-homogeneous boundary condition and a solution of dynamic equation satisfied with homogeneous boundary condition. The quasi-static solution is obtained directly by solving the quasi-static equation satisfied with the non-homogeneous boundary condition. The solution of the non-homogeneous dynamic equation is obtained by means of finite Hankel transform on the radial variable, r, Laplace transform on time variable, t, and finite Fourier transform on axial variable, z. Thus, the solution for finitely long, hollow cylinder subjected to torsion impact is obtained. In the calculating examples, the response histories and distributions of shear stress in the finitely long hollow cylinder subjected to an exponential decay torsion load are obtained, and the results have been analyzed and discussed. Finally, a dynamic finite element for the same problem is carried out by using ABAQUS finite element analysis. Comparing the analytical solution with the finite element solution, it can be found that two kinds of results obtained by means of two different methods agree well. Therefore, it is further concluded that the analytical method and computing process presented in the paper are effective and accurate.

• Structural Engineering and Mechanics
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• 제77권5호
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• pp.571-586
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• 2021

The present paper studies the influence of the inhomogeneous initial stresses in the bi-layered hollow cylinder and it is assumed that these stresses are caused by the hydrostatic pressures acting on the interior and outer free surfaces of the cylinder. The study is made by utilizing the version of the three-dimensional linearized theory of elastic waves in bodies with initial stresses for which the initial stress-strain state in bodies is determined within the scope of the classical linear theory of elasticity. For the solution to the corresponding eigenvalue problem, the discrete-analytical method is employed. Numerical results are presented and analyzed for concrete selected pairs of materials. According to these results and their analyses, it is established that, unlike homogeneous initial stresses, the influence of the inhomogeneous initial stresses on the torsional wave dispersion has not only quantitative but also qualitative character. For instance, in particular, it is established that as a result of the initial stresses caused by the hydrostatic pressure acting in the interior free surface of the cylinder, the cut-off frequency appears for the fundamental dispersive mode and the values of this frequency increase with the intensity of this pressure.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.772-785
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• 2021

Container ships has a transverse section in the form of an open profile, making it very sensitive to torsion phenomena. To minimize this effect, a structure known as a torsion box exists, which is subject to high stresses influenced by the fatigue phenomenon and the existence of cut-outs, for the passage of the longitudinal stiffeners, acting as stress concentrators. The aim of this study is to propose a two-stage design methodology to aid designers in satisfying the structural requirements and contribute with to a better understanding of the considered structure. The transverse webs of a torsional box structure are examined by comparing different cut-out geometries from numerical models with different regular load conditions to obtain the variables of the fatigue safety factor through linear regression models. The most appropriate geometry of the torsion box is established in terms of minimum weight, from nonlinear multivariable optimization models.

• 한국해양공학회지
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• 제19권2호
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• pp.53-59
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• 2005

The effect of pH on the corrosion characteristics in the dissimilar friction welded zone of IN713LC-SCM440 in the loaded torsional stress was studied. The corrosion experiment was performed for 120 hours on the specimens with five steps of pH. The surface corrosion pattern of the SCM440 area showed global corrosion and narrow pitting, which was caused by galvanic corrosion between friction welded IN713LC and SCM440, but corrosion did not proceeded from the IN713LC area. The average relative electrode potential gradually tends to decrease with the elapse of the immersion time in the acidity area. The average corrosion current also gradually tend to decrease The corrosion rate showed a larger value when the average relative electrode potential was higher and the average relative current was lower. The corrosion rate showed a larger value when the average relative electrode potential was higher in the acidity area, and it showed large when the average relative electrode potential was lower in the alkalinity area.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권4호
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• pp.1041-1063
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• 2014

Some results on the hydroelasticity of ultra large container ships related to the beam structural model and restoring stiffness achieved within EU FP7 Project TULCS are summarized. An advanced thin-walled girder theory based on the modified Timoshenko beam theory for flexural vibrations with analogical extension to the torsional problem, is used for formulation of the beam finite element for analysis of coupled horizontal and torsional ship hull vibrations. Special attention is paid to the contribution of transverse bulkheads to the open hull stiffness, as well as to the reduced stiffness of the relatively short engine room structure. In addition two definitions of the restoring stiffness are considered: consistent one, which includes hydrostatic and gravity properties, and unified one with geometric stiffness as structural contribution via calm water stress field. Both formulations are worked out by employing the finite element concept. Complete hydroelastic response of a ULCS is performed by coupling 1D structural model and 3D hydrodynamic model as well as for 3D structural and 3D hydrodynamic model. Also, fatigue of structural elements exposed to high stress concentration is considered.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 가을 학술발표회 논문집
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• pp.3-10
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• 2002

Recently, arches are used structurally because of their high in-plane stiffness and strength, which result from their ability to transmit most of the applied loading by axial forces actions, so that the bending actions are reduced. On the other hand, the resistances of arches to (out-of-plane,) flexural-torsional behavior depend on the rigidities EI/sub y/, for lateral bending, GJ for Uniform torsion, and EI/sub w/ for warping torsion which are related to axial stress for flexural-torsional behavior. The resistance of an arch to out-of-plane behavior may be reduced by its in-plane curvature, and so it may require significant lateral bracing. Thus. it is supposed that In-plane preloading which cause an axial stress, have an effect on out-of-plane free vibration behavior of arches. Because axial stresses caused increase or decrease out-of-plane stiffness. But study about this substance is insufficient. In this thesis, We will study an effect of preloading on lateral free vibration of arches, using finite element method based on Kang and Yoo's curved beam theory (about curved beam element have 7 degree of freedom including warping) with FORTRAN programming.

• 한국강구조학회 논문집
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• 제16권2호통권69호
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• pp.215-224
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• 2004

에너지법을 이용하여 보-기둥 및 기둥의 비탄성 좌굴거동을 해석하였다. 미국에서 생산되는 I 형강에 적용되는 단순형 잔류응력 모델을 우리나라에서 생산되는 I 형강에 적용하였다. 먼저, 집중 압축 축하중과 균등 휨을 동시에 받는 I 형강에 대하여 비탄성 횡-비틀림 좌굴거동을 알아보고 보-기둥에서의 잔류응력의 영향을 해석하였다. 또한 기둥의 경우에 대하여 해석하였으며 얻어진 결과를 강구조편람에 의한 설계 시의 값과 비교하였다. 결론적으로 강구조편람에 의한 설계는 과설계가 됨을 알 수 있었다.