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A driveline system with a double Cardan joint may be subject to severe vibration due to fluctuations in angular speed determined by the degree of angular misalignment and the phasing of the joint yokes. The inner yokes of the two joints are usually in the same plane or in phase. In this study, the potential of an out-of-phase position displaced by a phase angle to attenuate torsional vibration of the driveline is investigated. The governing equations describing the torsional dynamics of the system are derived. The torsional vibration is indicated by a maximum and minimum value of the steady-state twist calculated over a range of input rotational speeds. When attenuating the vibration, the phase angle is set equal to the maximum twist that occurs during the in-phase position. Relative attenuation is used to study the percentage of attenuation of the twist due to phase angle effects. The effectiveness is investigated for different levels of angular misalignment. For the system considered, the results showed that the phase angle can attenuate the torsional vibration by more than 10 percent for angular misalignment greater than 20 degrees. [ABSTRACT FROM AUTHOR]

Reducing structural weight while increasing modal frequencies is very challenging in structural dynamics. Honeycomb sandwich panels are widely used as alternative structural components to achieve the goal in engineering assembled structures. This research investigates the modal parameters of an aluminium honeycomb sandwich panel with an aluminium square-shaped design that is characteristically susceptible to closely-spaced modal frequencies. The FE model of the honeycomb sandwich panel was carefully developed, and MSC Nastran was used to compute the modal parameters of the FE model. The computed modal parameters were compared with the modal parameters obtained from the FE model of a square-shaped solid thick panel. The comparison showed that the honeycomb sandwich panel successfully eliminated the closely-spaced modal frequencies in the square-shaped solid thick panel with an average percentage MAC value of 0.91. Furthermore, the honeycomb sandwich panel computed higher modal natural frequencies with an average percentage discrepancy of 16.77 per cent. This study reveals that honeycomb sandwich panels offer many advantages in engineering designs, especially, modal frequency improvements, weight reductions and closely-spaced modal modes are the design parameters of concern [ABSTRACT FROM AUTHOR]

Recently, laser stitch welds are prefered in automotive structure comparing with others joining methods when joining two or more substructures due to its capabilities producing high strength joint with low heat application. However, the vibration responses such as dynamic behaviour of laser stitch welded structure are complex and there is a variety of uncertainties in predicting the behaviour of the jointed structure. Therefore, fast-running meta-modelling tools such as response surface (RSM)-based model updating are needed in accurately predict the vibration responses of the welded structure. In this paper, FE modelling scheme for represent laser stitch welds and the use of RSM-modal updating method for improving the dynamic behaviour of the FE model are presented. Initially, element connectors such as CBAR, CQUAD and ACM2 format are implemented to model the laser stitch welds in the FE models. Then, the correlation of the dynamic behaviour obtained from the FE models are compared with the experimental counterparts. In order to improve the accuracy of the FE models in comparison with experimental data using fast-running optimization method, combination of model updating method (NASTRAN SOL 200) and RSM is used. The results show the capabilities of RSM in optimising the predicted dynamic behaviour of the welded structure. [ABSTRACT FROM AUTHOR]

The modal parameters of a laser spot welded hat plate are investigated using finite element analysis(FEA) and experimental modal analysis (EMA). A new scheme of FE modelling residual stress effects is proposed and evaluated. The modal parameters were characterised using impact testing and roving accelerometers under a free configuration. Normal modes analysis was performed to compute the modal parameters of the structure. NASTRAN SOL 200 was used to attempt to improve the FE modal parameters using the test model as a reference. The effectiveness of the proposed scheme was determined by comparing the improved FE model with the test model and calculating the percentage of overall discrepancy reduction. The Modal Assurance Criterion (MAC) analysis was performed to evaluate the improved FE mode shapes. The FE model developed based on the proposed scheme computed the modal parameters of the laser spot welded hat-plate structure with 95 per cent accuracy. [ABSTRACT FROM AUTHOR]

Assumptions and simplifications in finite element (FE) modelling for structural vibration analysis contribute to discrepancies in numerical results. This paper presents FE model updating on components of a simplified model of an aircraft pylon. The components are tested under free-free boundary conditions. Impact testing is performed with roving accelerometers technique. Modal parameters are predicted numerically using NASTRAN SOL 103 normal modes analysis. NASTRAN SOL 200 optimisation for modal based updating method is subsequently used and successfully minimised the total error of the initial FE model from 19.17 per cent to 3.19 per cent. These satisfactory results could be confidently enhanced the quality of the FE model to be used for the further engineering analysis. [ABSTRACT FROM AUTHOR]

The laser spot weld is widely used to join automotive structural components due to the advantages of being inexpensive and more efficient. However, developing a reliable FE model of a laser spot weld for investigating a structure's modal parameters is very challenging. A repeated assessment of the welded joint model can significantly affect the efficiency of the finite element method, especially for a large complex structure that usually consists of huge numbers of degrees of freedom. This paper presents a wave-based substructuring method to speed up a modal parameters analysis of a laser spot welded structure. A reduced model is developed based on the wave-based substructuring scheme and compared with the full finite element model in computational time and accuracy. It was found that the proposed scheme was able to reduce the computational time of a modal parameters analysis significantly. The proposed scheme may provide advantages for research requiring high computational analysis. [ABSTRACT FROM AUTHOR]

Tungsten inert gas (TIG) welding is an electrical arc welding method that commonly used in the fabrication of engineering structure to join either ferrous or nonferrous metals due to great control over weld area comparing to other welding methods such as metal inert gas (MIG). A limited study can be found on finite element (FE) modelling technique of a structure that jointed by TIG welding method especially with a concerning of the dynamic analysis. This paper presents a systematic scheme to model the TIG weld of the welded structure in order to mimic experimental result of the TIG welded structure accurately using FE method. The welded joint of the FE model is developed by employing the area contact model (ACM2) format element connector. In order to evaluate the accuracy of the developed FE model, the predicted dynamic behaviour is compared with the experimental counterpart. The combination of impact hammer, roving accelerometers and free boundary conditions techniques are implemented in obtaining reliable experimental data for correlation analysis. For improving the accuracy of predicted model of the welded structure in light of experimental, FE model updating is utilised by coupled the response surface method with sensitivity analysis with minimisation of natural frequencies as objective function. The results obtained proved the capabilities of ACM2 model to represent as TIG welded joint. However, the requirement to identify updating parameters using sensitivity analysis for improving the predicted model is paramount importance. [ABSTRACT FROM AUTHOR]

Analytical modelling of composite structures is found to be difficult to develop especially to predict the structural vibration responses due to the complicated of components itself such as matrix-reinforcement element, fibre orientation and unknown properties fibre raw material during fabrication stages of composite structures. The uncertainties of the finish product of components then indirectly affect the initial analytical model of the composites in comparison to measured vibration responses. Therefore, this paper aim to investigate the accuracy of analytical model of composite structure using finite element (FE) method. There are two methods that been investigated in this work by implemented MSC Patran/Nastran software which are simplified shell element property card (PSHELL) and complicated layered composite element property card (PCOMP). The accuracy of the both models are compared with experimental results obtained by using experimental modal analysis (EMA). Then, FE model updating was utilized to enhance the quality of analytical models. The results show that the PSHELL model provide the simplest technique in composite structure modelling, however PSHELL providing inaccurate prediction especially when the model required optimisation steps. Meanwhile, good achievement in term of prediction accuracy can be achieved by utilising the PCOMP model. However, complexity of the PCOMP modelling technique could become cumbersome in the large and more complex geometry structure due to it requirement to define all the properties of plies. [ABSTRACT FROM AUTHOR]

Bolted joint structure is one of the complex types of the assembled structure that is applied in different sectors of industries. The benefit of the joining method using bolt and nut including low production cost, low maintenance and simplistic design of assembly. The prediction of dynamic behaviour of the bolted joins assembled structure is very challenging. The dynamic behaviour of the assembled structure such as bolted joined structure can be altered by the uncertainties of parameters such as material properties, structural geometry, and boundary conditions of the structure. The uncertainties that are inherited in the assembled structure can be analysed and evaluated using stochastic structural response by benchmarking the obtained results with the experimental data. In this study, a few bolted joint models are represented with RBE2, CBAR and CBEAM element connectors and initially constructed using finite element method (FEM). The initial response of the FE models with different type of element connectors in terms of natural frequencies and mode shapes are compared with experiment counterpart. The initial bolted joins assembled structure using CBEAM have shown the highest correlation response in terms of natural frequencies and mode shapes. The analysis using Stochastic Finite Element Method (SFEM) by utilising The Modified Extensible Lattice Sequence (MELS) algorithm is then used to predict stochastic responses from the initial FE model of the bolted joins structure. The result shows the adaptation of MELS algorithm on the analysis of the bolted joins assembled structure with CBEAM shows a better correlation to the experimental counterpart as higher number of samples applied to the structure. [ABSTRACT FROM AUTHOR]

Adopting dynamic substructuring methods to predict the dynamic behaviour of a combined structure is a common practice in the field of structural dynamics. This method has the capability and versatility to combine different sources of data; experimental and analytical, via the frequency based substructuring (FBS) method. This paper investigates the dynamic behaviour of a structure with doubled bolted joints using the frequency based substructuring (FBS) method. In the analysis the substructures are combined in the frequency domain, and the frequency response functions of the substructures are analytically derived and experimentally measured. However, the accuracy of the FBS method is highly dependent on experimental rotational degrees of freedom (DOF) which are always found to be very difficult to measure accurately. Therefore, a new approach - namely single-axis multipoint connection through which the need for the rotational DOF in the FBS method can be neglected entirely is presented in this study. The actual test structure used in this study is an assembled structure consisting of two substructures, a simple beam (numerical model) and an irregular plate steel (experimental model) structure. The FRFs of both substructures are combined via the FBS method. This study reveals that the use of the FBS method with the proposed approach is capable of representing the experimental frequency function response accurately even without rotational degrees of freedom data. [ABSTRACT FROM AUTHOR]

The accuracy of the predicted dynamic behaviour of a structure is highly dependent on the accurate properties used in the analytical model. The predicted results computed from the finite element method used to develop the model are often found not to be in good agreement with the experimental results due to the erroneous assumptions made in the finite element modelling. One way to systematically correct the finite element model is to use model updating methods. The main goal of this study was to systematically improve the predicted dynamic behaviour of a car trunk lid using the modal based updating method. HyperWorks and Leuven Measurement System (LMS) test were used for the finite element modelling and modal testing respectively. In order to evaluate the capability of the modal based updating in improving the finite element model, the natural frequencies and mode shapes computed from the updated finite element model of the trunk lid were compared with the corresponding experimental results. The comparison of the results showed that the total error of 65.48 percent predicted from the initial finite element model of the trunk lid has been successfully reduced to 4.74 percent. In conclusion, modal based updating has been successfully used to reconcile the initial finite element model with the physical model of the trunk lid. [ABSTRACT FROM AUTHOR]

Structural dynamic modification (SDM) techniques are important in structural optimisation of the system to modify the dynamics behaviour of the structure. It can be implemented by utilising the dynamic test data to alters the dynamic behaviour of the structure. However, there are some concern in the design process in which the undesirable mode shapes movement of structure are occurred along side with desired natural frequencies. Therefore, the SDM technique can be used as to varying the predicted dynamic behaviour of structure to solve noise, vibration and harshness problems (NVH). In order to be well predicted the modified dynamic behaviour of structure, the optimisation method via finite element (FE) model updating is used to obtain a reliable and accurate unmodified FE model. The main goal of this research is to change or altered the mode shapes movement of the mild steel bar structure due to the mass modification without shifting the natural frequencies away from unmodified value. In this research, the FE model of the mild steel bar structure was constructed using MSC software and the predicted dynamic behaviour were compared with the experimental modal analysis (EMA) data. The measured data was obtained using an impact hammer testing and roving accelerometers under free-free boundary conditions with data were extracted from LMS SCADAS software. Then, reconciliation process via FE model updating method is carried out in order to reduce the inaccuracy of initial FE model based on the measured data where the initial error has been reduced from 24.81 percent to 7.71 percent. Finally, the updated FE model was used for SDM technique using mass modification. The results reveal that the mode shapes of the structure can be change by manipulating the mass. It is agreed that by adding a reasonable mass with a right position to the structure the mode shapes can be change without shifting the natural frequencies away from unmodified values. [ABSTRACT FROM AUTHOR]