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Influence of marine main engine foundations on the results of vibration calculations

Murawski Lech

Journal of KONES

2019

Vol. 26, No. 1

95--101

The article presents an influence of foundations of slow-speed main engine body on the results of numerical analysis of the engine dynamic stiffnesses and thermal deformations. The engine body is much stiffer than its foundation pads and ship hull (double bottom) – boundary conditions of the engine. Especially for the high power, marine engines, the correct model of the boundary conditions plays a key role during the analyses. Therefore, modelling method of engine foundation (boundary conditions) of that kind of model is essential during the analyses. During shaft line alignment and crankshaft springing analyses, knowledge of dynamic stiffnesses characteristics and thermal displacements of radial (main) bearings is significant. Those data of marine main engine body are difficult to estimate because of lack of available documentation and complicated shape of the engine and ship hull. The article presents the methodology of the characteristics determination of the marine engine’s body as well as the example of computations for a MAN B&W K98MC type engine (power: 40000 kW, revolutions: 94 rpm) mounted on a 3000 TEU (twenty-foot container equivalent unit) container ship (length: 250 m). Numerical analyses were performed with usage of Nastran software based on Finite Element Method. The FEM model of the engine body comprised over 800 thousand degree of freedom.

Stiffness characteristics of main bearings foundation of marine engine

Murawski L.

Journal of KONES

2016

Vol. 23, No. 1

239--246

During shaftline alignment and crankshaft springing analyses, knowledge of stiffness of radial bearings is essential. Dynamic stiffness's characteristics of marine main body are difficult to estimate because of lack of available documentation and complicated shape of the body. In the literature, there is a lack of the detailed data on the stiffness of the crankshaft foundation in the frame of marine main engine. Those parameters are crucial for the shaft line alignment analysis as well as for the analysis of interactions between the shaft line and the crankshaft. Especially for the high power engines, the correct model of the boundary conditions plays a key role during the analysis. The paper presents the methodology of the characteristics determination of the marine engine’s body as well as the example of computations for a MAN B&W K98MC type engine mounted on a ~3000 TEU container ship. The model of main engine body is relatively big – it contains over 800 thousand degree of freedom. The elasticity of ship hull has been estimated and taken into account during analysis. It has been found, that static stiffness parameters recommended by the producer for the shaft line alignment are evaluated correctly, however they represent only the flexibility of the engine’s body, not taking into account the flexibility of the ship’s hull. What is more, the dynamic magnification of vibration amplitudes is not taken into account.

Analysis methods of crankshaft's stiffness characteristics

Murawski L., Charchalis A.

Journal of KONES

2013

Vol. 20, No. 1

219--226

Development of on-line diagnostic (monitoring) method of marine propulsion system working parameters is the authors' target. Crankshaft springing characteristics are one of the most important from the ships' main engines reliability point of view. Planned monitoring system will be able to verify crankshaft springing characteristics by continuous measurements of the crankshaft free-end's axial deformations. Development of the analysis methods of crankshaft's stiffness characteristics is the first step of planned SHM system. The main purpose of research is method developing of the springing analysis for the marine crankshafts in the high-power engines. Crankshaft modeling method, by Finite Element Method, has been discussed. Short overview of the crankshaft boundary conditions is presented. Bearings' oil film stiffness characteristics, ship hull stiffness characteristics and temperature deformation of the ship hull and main engine body are taking into account. Influence of the crankshaft's foundation stiffness on springing values is analysed. During the analyses it was proved that flexibility of engine foundation has a big influence upon the value of crankshaft springing. The authors' method of cylindrical mass and gas forces decompositions has been presented. Analysis of modeling precision of piston-crank system's forces has been performed. Results of calculations are well compatible in the terms of quality with the measurements data.