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An exhaust structure is experienced dynamic loads caused by engine operational and road surface condition that affected its durability and dynamic performance. Hence, the purpose of this study is to perform finite element (FE) modelling of exhaust structure and the used of updating approach to improve its dynamic behaviour. Due to its design, exhaust structure is built-up from several parts connected with welded joints. These welded joints significantly contribute to the dynamic behaviour of the structure. Four types of element connector that are RBE2, CBAR, CBEAM and CELAS have been used to replicate FE model of welded joint on the structure. Modal parameters (natural frequency and mode shape) of the FE model have been obtained from normal mode analysis using finite element analysis (FEA) software, MSC. Nastran/Patran. The precision of numerical predicted result from FEA is compared with its measured counterpart. The measured test data obtained through experimental modal analysis (EMA) using impact hammer and roving accelerometers under free-free boundary conditions. Under correlation process, CBAR element connector was chosen to model the welded joint due to its accurate prediction of natural frequency and contains updating parameters. FE model updating process was performed to improve the correlation between EMA and FEA. Ahead of updating process, sensitivity analysis was done to select the most sensitive updating parameter. As a result, total percentage error of natural frequency for updated CBAR model is reduced significantly from 8.74 % to 3.45 %. Consequently, CBAR element connector was chosen as the most reliable joint element in FE model to represent welded joint on exhaust structure.

Bolted joint commonly being used as a mechanical joint to connect two or more mechanical components which bring an interest to this study. The complexity of joint element plays an important role in the dynamic investigation. Structural damage happens and often it's too late to react to it and early detection of structure failure (damage) is beneficial. This paper aims to study the differences between undamaged and damage frame structure with bolted joints. Frame structure consists of 4 angle bar and 16 flat bars fabricated with stainless steel material is used. Total of 32 pcs of M6 screw and nuts are used together with structure. Damage often alter the mode shapes and reduce the natural frequencies. Natural frequencies and mode shapes of both undamaged and damaged data obtained by experimental modal analysis is correlated. Frequency drop is observed on natural frequencies after being correlated and as well as the mode shapes changed occurs on the undamaged and damages structure. Frame structure with damage on the joints able to detect the frequency drops and alter the modes shapes.

The dynamic motion of internal fluid flow caused an interaction between the fluid's dynamic forces and a structure’s inner wall. This phenomenon will induce unstable vibration into the system and recently called flow-induced vibration. In this study, an experimental analysis was performed to identify the changes in the characteristics of vibration measured on an automotive radiator resulting from internal flow in a circular heated tube. The vibration result is presented in terms of Power Spectral Density (PSD) that shows the strength of the energy variations as a function of frequency. Water was used as the working fluid operate with engine temperature range from 80 to 90 ℃. The air flow velocities of radiator cooling fan were varied from 1.0 to 1.9 m/s and the water flowrates were 2.2, 2.8, 3.2 and 3.8 l/min. Experimental results are presented and indicated that PSD values are dependant to the fluid flowrate. It is also analysed that relationship between vibrations (PSD) and flowrate is influenced by the change of radiator cooling fan speed. Apart from that, the paper also develops a set of vibration features that will assist in identifying low flow conditions in automotive radiator. 1

The aim of the this paper is to develop the tool life prediction model for P20 tool steel with aid of statistical method and find the optimisation values with partial swarm optimisation (PSO), using coated carbide cutting tool. By using Response Surface Method (RSM), first and second order models were developed with 95% confidence level. The tool life model was developed in terms of cutting speed, feed rate, axial depth and radial depth, using RSM. It was found that the feedrate, cutting speed, axial depth and radial depth played a major role. Tool life increases with a reduction in cutting speed and feedrate. For end-milling of P20 tool steel, the optimum conditions obtained from PSO are: cutting speed of 100 m/s, federate of 0.1 mm/tooth, axial depth of 1.9596 mm and radial depth of 2 mm. Using these parameters, a tool life of 40.52 min was obtained.

This study presents the effect of the spot weld and sheets thickness on the fatigue life of the of the spot-weld joints to predict the lifetime and location of the weakest spot-welds due to the variable amplitude loading conditions. A simple model was used to illustrate the technique of spot-weld fatigue analysis. Finite element model and analysis were carried out utilizing the finite element analysis commercial codes. Linear elastic finite element analysis was carried out to predict the stress state along the weld direction. It can be seen from the results that the predicted life greatly influence the sheet thickness, nugget diameter and loading conditions of the model. Acquired results were shown the predicted life for the nugget and the two sheets around the circumference of the spot-weld at which angle the worst damage occurs. The spot-welding fatigue analysis techniques are awfully essential for automotive structure design.

Structural joints provide connection between structural element (beam, plate etc.) in order to construct a whole assembled structure. There are many types of structural joints such as bolted joint, riveted joints and welded joints. The joints structures significantly contribute to structural stiffness and dynamic behaviour of structures hence the main objectives of this paper are to review on method of model updating on joints structure and to discuss the guidelines to perform model updating for dynamic analysis purpose. This review paper firstly will outline some of the existing finite element modelling works of joints structure. Experimental modal analysis is the next step to obtain modal parameters (natural frequency & mode shape) to validate and improve the discrepancy between results obtained from experimental and the simulation counterparts. Hence model updating will be carried out to minimize the differences between the two results. There are two methods of model updating; direct method and iterative method. Sensitivity analysis employed using SOL200 in NASTRAN by selecting the suitable updating parameters to avoid ill-conditioning problem. It is best to consider both geometrical and material properties in the updating procedure rather than choosing only a number of geometrical properties alone. Iterative method was chosen as the best model updating procedure because the physical meaning of updated parameters are guaranteed although this method required computational effort compare to direct method.

In this paper, the vibrations of structures are investigated via force appropriation method in which modes are excited individually by forces. Multivariate mode indicator function (MMIF) is used in the modal testing for investigating the prospective nonlinearities in the structures. The method is applied to simulate two degree of freedom with simple nonlinearities. The results are presented and evaluated to indicate that the method has advantages when it comes to involving in mode by mode identification. Results calculated from modal assurance criteria (MAC) and modal purity indicator (MPI) show that the qualities of evaluating a pure normal mode are in satisfactory. This suggests that force appropriation method for nonlinear structures is reliable and efficient, particularly in terms of the isolation of individual modes and determination of high quality modal parameters.

Biodiesel is an alternative fuel that is used in a diesel engine as a substitute for diesel fuel. However, using biodiesel without a modified engine can cause higher NOx emissions. Therefore, to reduce harmful emissions some strategy must be proposed or or a change in the injection is performed. In this study, injection schemes and engine performance injection time, emissions and firing characteristics of biodiesel mixing results in engines were investigated by using GT-POWER simulation. The simulations in this study were conducted on diesel engines to observe the accuracy in experimental results . The engines were tested at speeds of 1100 rpm, 1300 rpm, and 1500 rpm by using a biodiesel-diesel fuel mixture. The simulation results showed that NOx emissions were found to drop below 100 ppm when biodiesel fuel was used for all performed operations. Meanwhile CO emissions were also decreased by 10%-15% when biodiesel fuel was used, and the thermal efficiency level increased by 2% and 3.5% as compared to pure diesel. The ratio of NOx reduction rates of biodiesel and diesel was 11%-14% as compared to 9.5% with pure diesel. Based on the simulation result, it was shown that the accuracy level of simulation data with experiment was 97%. So this result can be the future testing standard and simulation by using GT-POWER could also be used especially for the automotive industry.

This paper aims to analyse the noise and vibration of the automotive radiator specifically focused on its cooling fan for different fan conditions and different coolants used namely Ethylene Glycol (EG) water-based and Titanium Oxide (TiO2) nanofluid. Noise source identification is carried out by utilizing the sound intensity mapping method while an accelerometer is used to measure the vibration results. Both of these experiments are conducted when the fan was both in static and working conditions. The maximum cooling fan speed for the working fan detected by a tachometer for EG water-based is 1990 rpm while TiO2 nanofluid is 2030 rpm. The difference in speed is due to the different physical properties such viscosity of each coolant has where TiO2 nanofluid has lower viscosity than EG water-based. The maximum sound power level produced by EG water-based is 53.73 dB while TiO2 nanofluid is 101.94 dB. Meanwhile, the vibration frequencies of EG water-based are higher than TiO2 nanofluid. The noise level increases with the cooling fan speed but decreases with the vibration frequency. Apart from studying the noise and vibration of the automotive radiator, this research also analysed the potential application using nanofluid due to its great properties according to its major use in the heat transfer enhancement. As a conclusion, nanofluid as a radiator coolant could improve heat transfer rate, and could also reduce the presence of vibration in the automotive cooling system.

Generally, solutions to improve the noise problems in enclosure are to redesign or modifying the system such as increasing the thickness of the wall panels, enhancing the elasticity of the structure, and increase the damping mechanism of the wall structure. In this paper, the application of vibroacoustic modelling of enclosure coupled to a flexible wall was presented. The sound pressure characteristics of rigid walled enclosure, such as natural frequency and mode shape were determined using two approaches which are finite element simulation of Ansys® and mathematical model. The mathematical equations derived in Matlab® such as rigid walled enclosure and rigid walled enclosure coupled to flexible wall were used to validate finite element analysis (FEA). The result indicates that the theory and FEA display in a good agreement. Thus, proved that the FE model was accurate and can be applied in further research such as sound pressure and noise attenuation in enclosure.

Structural joints offer connection between structural element (beam, plate, solid etc.) in order to build a whole assembled structure. The complex behaviour of connecting elements plays a valuable role in characteristics of dynamic such as natural frequencies and mode shapes. In automotive structures, the trustworthiness arrangement of the structure extremely depends on joints. In this paper, top hat structure is modelled and designed with spot welding joint using dissimilar materials which is mild steel 1010 and stainless steel 304, using finite element software. Different types of connector elements such as rigid body element (RBE2), welding joint element (CWELD), and bar element (CBAR) are applied to represent real connection between two dissimilar plates. Normal mode analysis is simulated with different types of joining element in order to determine modal properties. Natural frequencies using RBE2, CBAR and CWELD are compared to equivalent rigid body method. Connection that gives the lowest percentage error among these three will be selected as the most reliable joining for resistance spot weld. From the analysis, it is shown that CWELD is better compared to others in term of weld joining among dissimilar plate materials. It is expected that joint modelling of finite element plays significant role in structural dynamics.

Resistance spot welding (RSW) is a proficient joining method commonly used for sheet metal joining and become one of the oldest spot welding processes use in industry especially in the automotive. RSW involves the application of heat and pressure without neglecting time taken when joining two or more metal sheets at a localized area which is claimed as the most efficient welding process in metal fabrication. The purpose of this project is to perform model updating of RSW plate structure between mild steel 1010 and stainless steel 304. In order to do the updating, normal mode finite element analysis (FEA) and experimental modal analysis (EMA) have been carried out. Result shows that the discrepancies of natural frequency between FEA and EMA are below than 10 %. Sensitivity model updating is evaluated in order to make sure which parameters are influences in this structural dynamic modification. Young's modulus and density both materials are indicate significant parameters to do model updating. As a conclusion, after perform model updating, total average error of dissimilar RSW plate is improved significantly.

Vibrations are undesired phenomenon and it can cause harm, distress and unsettling influence to the systems or structures, for example, aircraft, automobile, machinery and building. One of the approach to limit this vibration by introducing passive vibration absorber attached to the structure. In this paper, the adequacy of utilizing passive vibration absorbers are investigated. The vibration absorber system is designed to minimize the vibration of a thin plate fixed along edges. The plate's vibration characteristics, such as, natural frequency and mode shape are determined using three techniques: theoretical equations, finite element (FE) analysis and experiment. The results demonstrate that the first four natural frequencies of fixed-fixed ends plate are 48, 121, 193 and 242 Hz, and these results are corroborated well with theoretical, FE simulation and experiment. The experiment work is further carried out with attached single and multiple vibration absorbers onto plate by tuning the absorber's frequency to match with the excitation frequency. The outcomes depict that multiple vibration absorbers are more viable in lessening the global structural vibration. Refereed/Peer-reviewed

A methodology is proposed to apply an endurance function model with a genetic algorithm to estimate the fatigue life of notched or smooth components. The endurance function model is based on stress tensor invariants and deviatoric stress invariants. In the proposed methodology, FEA is used to simplify the application of the endurance function model. Experimental results from published literature are considered for the case studies to evaluate the proposed methodology. The results show that the proposed methodology simplified the application of the endurance function model, particularly by reducing the need for notch sensitivity factors, and the stress invariants can be calculated directly from the stresses at the critical point. The comparison with experimental results shows that, with proper calibration, the model can predict fatigue life accurately.

Frame structure is widely used in many engineering structures. Besides, vibrational problem is one of the main challenges in industry. Bolted joints are commonly used in industry to connect two or more mechanical parts and it plays a significant role in the dynamics characteristic of the structure. This study aims to perform a model updating procedure on a portal frame structure which consists of bolted joints. Modal parameters such as the natural frequencies, mode shapes and damping ratios are gathered through finite element analysis (FEA) and experimental modal analysis (EMA). Frame structure is set to be fixed-free boundary condition and equivalence of nodes is performed at the area of bolted joints. Correlation between these two sets of data is carried out. With the selected parameters identified to perform model updating on the structure by using sensitivity analysis, the discrepancies in natural frequencies were reduced between FEA and EMA.

Bicycle frames have to bear variety of loads and it is needed to ensure the frame can withstand dynamic loads to move. This paper focusing on dynamic study for bicycle frame structure with a purpose to avoid the problem regarding loads on the structure and to ensure the structure is safe when multiple loads are applied on it. The main objectives of dynamic study are to find the modal properties using two method; finite element analysis (FEA) and experimental modal analysis (EMA). The correlation between two studies will be obtained using percentage error. Firstly, 3D model of mountain bike frame structure has been draw using computer-aided design (CAD) software and normal mode analysis using MSC Nastran Patran was executed for numerical method meanwhile modal testing using impact hammer was performed for experimental counterpart. From the correlation result, it show that percentage error between FEA and EMA were below 10% due to noise, imperfect experiment setup during perform EMA and imperfect modeling of mountain bike frame structure in CAD software. Small percentage error differences makes both of the method can be applied to obtain the dynamic characteristic of structure. It is essential to determine whether the structure is safe or not. In conclusion, model updating method is required to reduce more percentage error between two results.

Laser cutting is one of the advances machining on material remover process.This paper explores the prediction model of surface roughness (Ra) and roughness height (Rz) of laser beam cutting on acrylic sheets. Box-Behnken design based Response Surface Method (RSM) was used to predict the effect of laser cutting parameters which are laser power, cutting speed and tip distance on Ra and Rz. The predictive models are good agreement with experimental results. The first order equation revealed that the power requirement was the dominant factor followed by tip distance and cutting speed respectively. This observation indicates that the potential of using RSM in predicting cutting parameters thus eliminating the need for exhaustive cutting experiments to obtain the optimum cutting condition and enhance the surface roughness.

This paper presents the development of mathematical models for torque and power in milling 618 stainless steel using coated carbides cutting tool. Response surface method was use to predict the effect of power and torque in the end-milling. From the model, the relationship between the manufacturing process factors including the cutting speed, feed rate, axial depth and radial depth with the responses such as torque and power can be developed. Beside the relationship, the effect of the factors can be investigated from the equation developed. It can seen that the torque increases with decreases of cutting speed while increase of the feed rate, axial depth and radial depth. The acquired results also shown that the power increases with the increases of cutting speed, feed rate, axial depth and radial depth .It can be found that the second order is more accurate based on the variance analysis and the predicted value is closely match with the experimental result. Third- and fourth- order model generated for both response to investigate the 3- and 4-way interaction between the factors. The third and fourth order model shows that 3- and 4-way interaction found less significant for the variables.

Polymeric foam is widely used as core materials in various applications such as cushioning, padding, insulating, structural use and buoyancy. This is because of its ability to provide high bending stiffness tied with lightweight in composite sandwich construction. The purpose of this paper is to present the behaviour of polyurethane foam, which is fabricated in various orientation angles. Five different orientation angles have been studied i.e. 0o, 30o, 45o, 60o and 90o. Three mechanical tests were performed under tension, compression and shear loads to investigate the polyurethane foam (PU) behaviour. Electron microscope was used to capture the microstructure of the specimens before and after the tests. Comparisons have been made between different orientation angles in fracture modes and mechanical properties. Deformation and failure occur during foam crushing are discussed according to experimental evidence. Since the main application of foam materials are for energy absorption, foam response under considerable compression has been studied intensively. At angle of 90o, it permits more localised failure with high-energy absorption and in contrary, 0o which posses the lowest of energy absorption. Energy absorption for PU foam material tends to increase when the orientation of angle is increased.

Model updating is a process of making adjustment of certain parameters of finite element model in order to reduce discrepancy between analytical predictions of finite element (FE) and experimental results. Finite element model updating is considered as an important field of study as practical application of finite element method often shows discrepancy to the test result. The aim of this research is to perform model updating procedure on a composite structure as well as trying improving the presumed geometrical and material properties of tested composite structure in finite element prediction. The composite structure concerned in this study is a plate of reinforced kenaf fiber with epoxy. Modal properties (natural frequency, mode shapes, and damping ratio) of the kenaf fiber structure will be determined using both experimental modal analysis (EMA) and finite element analysis (FEA). In EMA, modal testing will be carried out using impact hammer test while normal mode analysis using FEA will be carried out using MSC. Nastran/Patran software. Correlation of the data will be carried out before optimizing the data from FEA. Several parameters will be considered and selected for the model updating procedure.

Nonlinear structural identification is essential in engineering. As new materials are being used and structures become slender and lighter, nonlinear behaviour of structures becomes more important. There have been many studies into the development and application of system identification methods for structural nonlinearity based on changes in natural frequencies, mode shapes and damping ratios. A great challenge is to identify nonlinearity in large structural systems. Much work has been undertaken in the development of nonlinear system identification methods (e.g. Hilbert Transform, NARMAX, and Proper Orthogonal Decomposition), however, it is arguable that most of these methods are cumbersome when applied to realistic large structures that contain mostly linear modes with some local nonlinearity (e.g. aircraft engine pylon attachment to a wing). In this paper, a multi-shaker force appropriation method is developed to determine the underlying linear and nonlinear structural properties through the use of the measurement and generation of restoring force surfaces. One undamped mode is excited in each multi-shaker test. Essentially, this technique is a derivative of the restoring surface method and involves a non-linear curve fitting performed in modal space. A reduced finite element model is established and its effectiveness in revealing the nonlinear characteristics of the system is discussed. The method is demonstrated through both numerical simulations and experiments on a simple jointed laboratory structure with seeded faults, which represents an engine pylon structure that consists of a rectangular wing with two stores suspended underneath.

This paper is a review of information and related studies concerning topic of model updating in structural dynamics. It is purposed to introduce and explain the important concept of the discussed subject in model updating area as well as to summarize the development and available guidance and method of conducting the study in this area. The review is structured by presenting an overview of general concept of finite element model updating in structural dynamics and the capabilities of finite element method as a tool in model updating. After the concept introduction, the reliable methodology to perform model updating, the limitation and the critical issues in model updating is discussed. The limitation and problems arise concerning correcting inaccurate finite element model is also discussed. This lead to issue of parameterization and regularization which the limitation and uncertainty in choosing the updating parameter is shown able to be overcome. Further studies on the elimination of systematic errors from both the measurements and the finite element model so that it can provide more reliable model updating is recommended.

This paper explores and investigates the dynamic characteristics of car chassis structure by using experimental modal analysis (EMA) method and modal testing. Dynamic characteristics are divided into three parameters include natural frequency, damping factor and mode shape. In this study, modal testing was performed on the car chassis including the impact hammer and shaker test. Data analyzer was used to convert the response signal from the sensor, which was in the time domain to frequency domain. Result obtained from both methods, is compared on each axis (X, Y and Z axis). However, small discrepancy was observed in terms of natural frequency, which is within the range of 5%. Based on the results, interpretation and comparison were made for both methods.

The crankshaft is a very crucial part in an internal combustion engine. This paper presents the findings of the mode shape and natural frequency of 3 cylinder 4 stroke engine crankshafts. Both experimental and computational methods were carried out to determine the modal parameter or dynamic characteristics, which are natural frequency, damping factor and mode shape. The prediction of the dynamic properties of the chassis is of great significance in determining the natural frequencies of the structure. The experiment is done by using an impact hammer to excite the crankshaft and data is recorded using a data acquisition system (DAS) connected to a sensor located on the crankshaft. Computational modal analysis on the crankshaft structure is simulated using finite element software. It can be seen from the results that there is a good agreement between the experimental and computational results in terms of modal parameter with a small discrepancy. The modal analysis techniques are essential for automotive crankshaft structure design.