# Multibody Simulation for the Vibration Analysis of a Turbocharged Diesel Engine
## 1 Introduction
In [14], an experimentally validated diesel engine simulation code is used to study and evaluate the importance of a notable engine dynamic issue, i.e., the crankshaft torsional (angular) deformations during turbocharged diesel engine operation, owing to the difference between instantaneous engine and load (resistance) torques. The analysis aims ultimately in studying the phenomena under the very demanding, and often critical, transient operating conditions. Details are provided concerning the underlying mechanism of the crankshaft torsional deformations during steady state and transient operation. In [15], a methodology for predicting the piston to liner contact in running engines by means of MBD (Multi-Body Dynamics) and FEM is presented. In addition to the mathematical modeling of the excitation, the paper describes the transfer mechanisms of the piston slap phenomenon. Thus, the model is extended in order to analyze vibration transfer via engine structure. Results of simulation work show structure surface velocity levels and their contribution to integral levels in different frequency bands. In [16], the mathematical modeling of body structures and the calculation of the non-linear connecting forces resulting from elastohydrodynamic contacts between piston-liner and shaft-bearing is described. Results of parametric studies, e.g., the influence of piston surface profile on the contact mechanism between piston and liner, are shown. In [17], the coupling of elastic multibody simulations (including elastohydrodynamic interactions) with finite element based vibration and acoustic analysis is presented. In [18], the emphasis is on the integration of the kinetic reactions arising from the tribological conjunction of the dynamics of engine subsystems, piston, and crankshaft. In [19], the CAE capabilities in the simulation of the dynamic and acoustic behavior of an engine, with a focus on the relative merits of modification and full-scale structural/acoustic optimization of engine, are presented. In [20], an investigation of the diesel engine combustion-related fault detection capability of crankshaft torsional vibrations is presented: the torsional vibration amplitudes are used to superimpose the mass and gas torque; further mass and gas torque analysis is used to detect fault in the operating engine. The engine dynamics are analyzed with a focus on the low frequency range and low engine speeds, when vibration transmission through engine mounts becomes critical. In [21; 22], a detailed multi-body numerical model of an engine prototype is used to characterize the whole engine dynamic behavior in terms of forces and velocities. A combined usage of FEM and multi body methodologies is adopted for the dynamic analysis: both crankshaft and cylinder block are considered as flexible bodies, whereas all the other components are considered as rigid elements. The focus of this work is related to industrial aspects because, for an existing and commercialized engine, a numerical and experimental complex study has been performed to enable design improvements aimed at reducing noise emission and vibrations. Existing procedures and algorithms are combined here to reach the abovementioned objectives in the most efficient way.