船舶用 大型 디젤엔진 실린더 커버 스터드의 疲勞 및 振動 解析에 관한 硏究

Abstract

ylinder cover of low-speed marine engine is assembled and fastened with stud bolts at the upper part of cylinder liner. So, the stud is quite important for safe and reliability design of engine.

The cylinder cover stud receives axial force from the initial fastening torque and cyclic explosion pressure during combustion period in cylinder chamber. Due to the cyclic loading it is estimated to cause fatigue failure in the stud at much lower stress values than static yield strength of the material of the stud.

In this case, Fatigue Analysis Method is well corresponded to the Fatigue life estimation of the stud. In this study, it was accomplished the Fatigue Analysis for the stud considering loading type, mean stress effects, variable stress concentration, surface finish factor, reliability factor, temperature factor and size factor of the stud. The analysis was conducted using ANSYS code with solid modeling.

The results of the fatigue analysis showed that the stud have infinity fatigue life under normal operating conditions and the fatigue strength of the stud is sufficient.

The cyclic explosion pressure during combustion period in cylinder chamber is only considered as cyclic load for fatigue failure of the stud in previous study.

However, the cyclic load causes the harmonic excitation vibration to the stud. Also guide force moments caused by the transverse reaction forces acting on the crossheads of engine may excite engine vibrations, moving the engine top athwartships and causing a rocking (excited by H-moment) or twisting (excited by X-moment) movement of the engine.

So, in this study, to evaluate vibrational characteristics of the stud natural frequencies and mode shapes of the stud are analyzed and compared with potential sources of excitation.

The analysis, including natural frequency and mode shapes, for two(2) cases of the stud is conducted using ANSYS code with solid model.

The results in the study provides a updated framework for the further design of cylinder cover stud of low-speed marine engine.