Simulation of Engine Vibration on Nonlinear Hydraulic Engine Mounts

In this paper, vibration behavior of engine on nonlinear hydraulic engine mount including inertia track and decoupler is studied. In this regard, after introducing the nonlinear factors of this mount (i.e. inertia and decoupler resistances in turbulent region), the vibration governing equations of engine on one hydraulic engine mount are solved and the effect of nonlinearity is investigated. In order to have a comparison between rubber and hydraulic engine mounts, a 6 degree of freedom four cylinders V-shaped engine under inertia and balancing masses forces and torques is considered. By solving the time domain nonlinear equations of motion of engine on three inclined mounts, translational and rotational motions of engines body are obtained for different engine speeds. Transmitted base forces are also determined for both types of engine mount. Comparison of rubber and hydraulic mounts indicates the efficiency of hydraulic one in low frequency region.

Direct and Indirect Vibro-Acoustic Measurements for Road Noise NVH Predictions

This paper describes vibro-acoustic direct and indirect measurements for road noise NVH predictions from a complete car. Attention is devoted to the dynamic response of the structure and interior pressure field toward tire patch displacement inputs. The direct measurements exploited the Team Corporation CUBE™ high frequency 6 degree-of-freedom (DOF) shaker recently installed at the KULeuven Vehicle Technologies Laboratory; the input was provided directly at the tire contact patch, while the responses were measured as accelerations and pressures on the structure. In the indirect measurements a low-mid frequency volume velocity source (LMFVVS) was used to acoustically excite the structure in the reverse path direction from the inside of the interior car cavity, while accelerations on the car and forces/torques where acquired by a 6-DOF dynamometer at the tire patch. From both types of excitations Frequency Response Functions (FRF) were calculated in the frequency range [0–500 Hz]. The non-linearity of the full car system was investigated with different direct and indirect measurement tests, in order to assess the feasibility of the reciprocity principle in such a complex structure. Measurement set-ups, results and comparisons are described and discussed in detail.

Frequency Response Analysis of Piecewise Nonlinear Vibration Isolator

Non-smooth piecewise functional isolators are smart passive vibration isolators that can provide effective isolation for high frequency/low amplitude excitation by introducing a soft primary suspension, and by preventing a high relative displacement in low frequency/high amplitude excitation by introducing a relatively damped secondary suspension. In this investigation a linear secondary suspension is attached to a nonlinear primary suspension. The primary is assumed to be nonlinear to model the inherent nonlinearities involved in real suspensions. However, the secondary suspension comes into action only during a short period of time, and in mall domain around resonance. Therefore, a linear assumption for the secondary suspension is reasonable. The dynamic behavior of the system subject to a harmonic base excitation has been analyzed utilizing the analytic results derived by applying the averaging method. The analytic results match very well in the transition between the two suspensions. A sensitivity analysis has shown the effect of varying dynamic parameters in the steady state behavior of the system.

Multi Mode Vibration Control and Broder Band Motion Control of Three Dimensional Shaking Table

This paper deals with a new system design method for motion and vibration control of a three-dimensional flexible shaking table. An integrated modeling and controller design procedure for flexible shaking table system is presented. An experimental three-dimensional shaking table is built. “Reduced-Order Physical Model” procedure is adopted. A state equation system model is composed and a feedback controller is designed by applying LQI control law to achieve simultaneous motion and vibration control. Adding a feedforward, two-degree-of-freedom control system is designed. Computer simulations and control experiments are carried out and the effectiveness of the presented procedure is investigated. The robustness of the system is also investigated.

Optimizing Distributed-Contact Friction in Ring Dampers

This paper describes the vibration analysis and optimization of a base structure and a beam-like attached damper sub-system that couple in vibration through distributed-contact friction damping. The objective is to tune the characteristics of the damper sub-system to maximize energy dissipation, and therefore to control vibration of the base structure. Applications of the concept to noise and vibration phenomena associated with automotive disk brake rotors are discussed. Per-cycle energy dissipation is examined as a function of damper preload for two classes of sub-systems: dampers that are split rings, and dampers that are continuous rings. End-effects and the manner in which energy dissipation is distributed spatially along the damper are also discussed. Of potential technological application, for a given excitation frequency, the damper sub-system’s design can be optimized to reduce vibration of the base structure.

Railway Bridges Identification Techniques

Output-only methodologies are nowadays well established to extract modal parameters in many areas of engineering, such as civil, mechanical and aeronautical. In the past, civil engineering tests have been mainly developed for road bridges, with the vehicle passage over the bridge deck representing the main source of excitation with some contribution given by the ambient noise. In the road bridge cases, the excitation is considered to be a function of the road surface roughness, the vehicles speed, the weight and suspension vehicles characteristics, and also the random access of the vehicles over the bridge, whilst for the railway case, not all these issues are correctly addressed, and other characteristics rise-up, possibly advantageous for a correct identification process; to demonstrate this statement, we can bear in mind how the random access of the vehicles becomes meaningless for railway bridges, the single train being a quasi deterministic source; furthermore, the influence of the train weight should be considered if compared to usual road vehicles. Since output-only techniques are conceived for random excitation noise, their use in these conditions is considerably stressed and special care, or alternative techniques, has to be considered to avoid errors. In this sense, the bridge reference model becomes more important and some special techniques have to be developed.

Model Updating Using a Quadratic Form

The paper presents a method for model updating, called Quadratic Compression Method (QCM). The updated model has a fixed structure with some free parameters. Algebraic manipulations of the eigenvalue equation lead to a simplified equation with a lower dimension. This equation is then solved in a Least Squares sense. The method is shown to belong to the class of Minimization of the Error in the Characteristic Equation (MECE), with a particular choice of the weighting matrix. The paper presents also a weighted version of the method, called WQCM, which is motivated by reducing the effect of measuring noise. In addition to the theoretic analysis, the superior robustness to noise properties of QCM and WQCM are demonstrated by simulations and experimentally.

Random Loads Fatigue: The Use of Spectral Methods Within Multibody Simulation

The evaluation of the fatigue damage performed by using the Power Spectral Density function (PSD) of stress and strain state is proving to be extremely accurate for a family of random processes characterized by the property of being stationary. The present work’s original contribution is the definition of a methodology which extracts stress and strain PSD matrices from components modelled using a modal approach (starting from a finite element modelling and analysis) within mechanical systems modelled using multibody dynamic simulation and subject to a generic random load (i.e. multiple-input, with partially correlated inputs). This capability extends the actual stress evaluation scenario (principally characterised by the use of finite element analysis approach) to the multibody dynamic simulation environment, more powerful and useful to simulate complex mechanical systems (i.e. railway, automotive, aircraft and aerospace systems). As regards the fatigue damage evaluation, a synthesis approach to evaluate an equivalent stress state expressed in terms of the PSD function of Preumont’s “equivalent von Mises stress (EVMS)”, starting from the complete stress state representation expressed in terms of PSD stress matrix and easily usable in the consolidated spectral methods, is proposed. This approach allows and has allowed the use of the above methods such as the Dirlik formula as a damage evaluation method. An additional result is the conception and implementation of a frequency domain method for the component’s most probable state of stress, allowing quickly identification of the most stressed and damageble locations. The described methodologies were developed and embedded into commercial simulation codes and verified by using as a test case a simple reference multibody model with a simple flexible component.

Machine Fault Detection Using Genetic Programming

Applications of genetic programming (GP) include many areas. However applications of GP in the area of machine condition monitoring and diagnostics is very recent and yet to be fully exploited. In this paper, a study is presented to show the performance of machine fault detection using GP. The time domain vibration signals of a rotating machine with normal and defective gears are processed for feature extraction. The extracted features from original and preprocessed signals are used as inputs to GP for two class (normal or fault) recognition. The number of features and the features are automatically selected in GP maximizing the classification success. The results of fault detection are compared with genetic algorithm (GA) based artificial neural network (ANN)- termed here as GA-ANN. The number of hidden nodes in the ANN and the selection of input features are optimized using GAs. Two different normalization schemes for the features have been used. For each trial, the GP and GA-ANN are trained with a subset of the experimental data for known machine conditions. The trained GP and GA-ANN are tested using the remaining set of data. The procedure is illustrated using the experimental vibration data of a gearbox. The results compare the effectiveness of both types of classifiers with GP and GA based selection of features.

Non-Linear Dynamic Analysis of a Cable-Stayed Beam

The dynamic behaviour of a simple clamped beam suspended at the other end by an inclined cable stay is surveyed in this paper. The sag due to the cable weight, as well as the non-linear coupling between the cable and the beam motions are taken into account. The formulation for in-plane vibration follows closely that of Gattulli et al. [1] and confirms their findings for the overall features of the equations of motion and the system modal properties. A reduced non-linear mathematical model, with two degrees of freedom, is also developed, following again the steps of Gattulli and co-authors [2,3]. Hamilton’s Principle is evoked to allow for the projection of the displacement field of both the beam and the cable onto the space defined by the first two modes, namely a “global” mode (beam and cable) and a “local” mode (cable). The method of multiple scales is then applied to the analysis of the reduced equations of motion, when the system is subjected to the action of a harmonic loading. The steady-state solutions are characterised in the case of internal resonance between the local and the global modes, plus external resonance with respect to either one of the modes considered. A numerical application is presented, for which multiple-scale results are compared with those of numerical integration. A reasonable qualitative and quantitative agreement is seen to happen particularly in the case of external resonance with the higher mode. Discrepancies should obviously be expected due to strong non-linearities present in the reduced equations of motion. That is specially the case for external resonance with the lower mode.