Merging Disciplines and Models for Large Engine Structural Analyses
Structural requirements for large engine applications cover operational safety and comfort aspects. MAN Diesel & Turbo (MDT) therefore limits the engine vibration to an acceptable level applying numerical simulation in an early design stage. Long-term validated simulation workflows are applied for the crankcase simulation, the drivetrain simulation and the mounting simulation.
Noise and vibration requirements concerning engine integration into ships (or plants) mainly focus on the frequency range below the 10th engine order. Customer focus is comfort on board or ship underwater noise radiation. Engine mounting and genset configuration are discussed in this stage. For standard, decisions are made based on experience or on predictions using measurements at some engine/ foundation positions. For projects with small ship vibration safety margins, simulated engine vibrations at all engine mounts including phase relationships are used to predict ship structure vibrations.
In a project with AVL, the above mentioned frontloading disciplines are combined in a single model, which covers all relevant vibration effects for the engine-ship-integration. Beside MDT customers, the engine development benefits from reduced modeling effort with a minimum number of breaks in the toolchain.
The workflow uses one central tool for multi-body simulation (MBS) of the engine and drivelines till vehicle integration. Even sub-systems and components like EHD contacts (slider bearings) are handled inside the same simulation environment and interact with the overall dynamic behavior of the whole system. All simulation disciplines use the same graphic user interface and pre-processing tools, shared data only need to be defined once. Different modelling levels for single components as well as for entire system help to use an optimum balance of model depth in terms of required accuracy for the application target and the modelling and simulation time.
Targets of the project were the evaluation of engine vibration and structure borne noise on the foundation. In that respect, as the main outcome of the MBS simulation, the main results quantities in form of displacements, velocities, accelerations and forces are evaluated in time and frequency domain. These results are further interpreted and presented as the main bearings excitations (forces and moments), engine velocity levels, reactions at engine mounts, accelerations at auxiliaries etc. and assessed with respect to different performance attributes.
The MBS simulation results, as transient dynamic excitation loads, are additionally used in combination with assembly loads, for subsequent FEM durability analysis and assessment of engine components, like for crankshaft and crankcase lower structure parts (i.e. main bearing wall, oil pan) as well as for auxiliary supporting brackets (i.e. turbo chargers and piping system).
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