Operating Deflection Shape Analysis Research Articles

On the Cover: Experimental Modal Analysis and Operational Deflection Shape Analysis of a Cantilever Plate in a Wind Tunnel with Finite Element Model Verification

On the Cover: Experimental Modal Analysis and Operational Deflection Shape Analysis of a Cantilever Plate in a Wind Tunnel with Finite Element Model Verification

Mathematical modelling of friction induced high frequency noise and vibration mechanism in vehicle brake systems through experimental data

Friction induced brake squeal problem is not solved comprehensively despite several proposed theories about its mechanisms, and being frequently studied. Therefore, this study aims to make contribution to the relevant literature by obtained experimental data and built mathematical model. Firstly, experimental modal analysis of the brake disc, caliper, bracket and pads, are performed. Afterwards, disc and pads, which have critical roles in squeal mechanism, are numerically modelled by using finite element methods. Then, model updating is performed to reach good correlation between the experimental and computational resonant frequencies. Afterwards, high amount of brake squeal experiments are conducted by altering disc velocity, brake pressure and temperature on a laboratory set-up by acquiring sound pressure and acceleration data. Additionally, operational deflection shape analysis is executed on the system, during selected operation conditions. Lastly, a mathematical model, which focuses on the interactions between the disc and pad, is developed to explain squeal induction mechanisms that observed in the experiments. Experiments and mathematical model shows good agreement. It is concluded that the squeal dynamics and frequencies are depended on changing contact stiffness between the disc and pad due to changing brake pressure, and closely related to natural frequencies of the disc and caliper fingers.

Experimental Modal Analysis and Operational Deflection Shape Analysis of a Cantilever Plate in a Wind Tunnel with Finite Element Model Verification

Experimental Modal Analysis and Operational Deflection Shape Analysis of a Cantilever Plate in a Wind Tunnel with Finite Element Model Verification

Advancements on bifurcation behavior and operational deflection shapes of disk brake creep groan

Disk brake creep groan vibrations are friction-induced stick–slip vibrations. Their impulse-like excitation, caused by the physical properties of the frictional contacts, leads to strongly nonlinear vibrations of brake system, axle and also chassis parts. As with many nonlinear phenomena, theoretical and experimental investigations on the bifurcation behavior were already done. So-far performed experiments used either strongly reduced setups or were limited in the controllability of testing, leading to certain deviations and a reduced complexity compared to the real-world behavior of the full vehicle. In this work, an approach based on half-axle tests is presented. Here, tire and rim are part of the system. By running drum-driven test matrices, extended stability maps of the rest position were created. An operational deflection shape (ODS) analysis over all 72 operating points of the test matrix was performed. Together with the relative speeds in the friction contact, a novel classification of creep groan phenomena is presented. These results prove an interaction between longitudinal and rotational axle displacements during creep groan, which was already assumed in corresponding vehicle tests. The insights enable a clearer distinction of creep groan, which is necessary for the accurate objective rating of creep groan phenomena in industry. Furthermore, the ODS results suggest the structure for a sufficient minimal model.

A novel unknown-input and single-output approach to extract vibration patterns via a roving continuous random excitation

Operating deflection shape analysis allows investigating the dynamic behaviour of a structure during operation. It normally requires simultaneous, multi-point measurements to capture the response from an unknown excitation source (unknown-input and multiple-output), which can complicate its usage for structures without ease of access. A novel vibration pattern testing method is proposed based on a roving continuous random excitation employing a small robotic Hexbug device and a single-point measurement. The Hexbug introduces a random excitation in consecutive locations while roaming over the structure. The resulting multi-modal, time and location dependent response of the system is captured in a single location, and then analysed with a newly developed method based on empirical wavelet transform, multiscale morphological filtering and optimization to extract the excited vibration patterns. The efficiency of the proposed method is experimentally demonstrated on a free–free and a cantilevered beam with comparison to mode shapes extracted by hammer test. The validation highlights its ability to extract several vibration patterns from a long slender structure with good accuracy and robustness, with the general ability to expand the usability of an operating deflecting shape analysis.

High-vibration diagnosis of gas turbines: An experimental investigation

Rotordynamics is a very challenging field because of machine complexities. Many internal and external factors contribute toward change in the structural dynamic characteristics. One of these factors is broad-band high-vibration amplitudes. In this article, a similar high vibration issue on a gas turbine is investigated using bode, orbit, and shaft centerline plots. Data from proximity probes installed on turbine generator system are captured and analyzed against any factor contributing toward high vibration issue. Fish bone diagram was used for root cause investigation. Main components investigated for the root cause of high vibration issue include generator rotor and casing. Rotor behavior has been examined by capturing orbit and shaft centerline diagrams, whereas casing contribution has been investigated by conducting operating deflection shape analysis. A comparison is drawn between a machine suffering from high vibration issue and a normal machine. Resonance was identified as the root cause, and stiffness enhancement was recommended to change the natural frequency of casing. Based on investigations, recommendations are given and a final comparison is drawn after structural modification was done. In addition to early fault finding, reduction in maximum vibration was 38% after implementation of the fix that confirmed the accuracy of the root cause investigation process.

An experimental investigation of resonance sources and vibration transmission for a pure electric bus

Electric vehicles generally have a better noise, vibration, and harshness quality than traditional vehicles due to the relatively quiet electric motors. By contrast, the noise, vibration, and harshness issues of the driveline system become more outstanding and significant in the absence of the “masking effect” by the engine. The electrification of the powertrain has also brought many changes in the sources or transmission of vibration, which has led to some new noise, vibration, and harshness issues. Specifically, the intense vibration of the prototype bus appears when driving in third gear, which makes the passengers uncomfortable. This paper presents an efficient analytical strategy for identifying the resonance sources and vibration transmission for a pure electric bus. The strategy incorporates order analysis, operating deflection shape, and transfer path analysis. Order analysis shows that the resonance is primarily caused by the second-order excitation associated with the driveline, and the vibration sources are further identified using operating deflection shape analysis. Moreover, the vibration transfer paths from the driveline to the bus floor are quantitatively determined by the transfer path analysis method. The results show that the coupling vibration of the powertrain and the rear drive axle, which amplifies the resonance of the whole driveline, is transmitted to the bus floor primarily through powertrain mounts and V rods. Based on the results, the design and structure modifications of the driveline and transfer paths are recommended to handle this issue. The proposed identification strategy would be beneficial for accurate and efficient engineering troubleshooting on the vibration issues.

Study for the Identification of Dominant Frequencies and Sensitive Structure on Machine Tools Using Modal Decoupling and Structural Sensitivity Analysis

The research on machine tool vibration has significant impact to improve the processing quality of the processed parts. The vibration response on the surface quality is quite different based on different modes of vibration. Current study proposed a new approach of modes decoupling based on Operational Deflection Shape (ODS) and structural sensitivity analysis, which used to identify the structural vibrations on surface topography in manufacturing process. Method According to the modes decoupling based on the ODS method, the dominant vibration frequencies of machine tool are identified in a wide range of frequency band. Furthermore, the modal mass distribution matrix analysis is used to determine the sensitive structures that cause greater machining errors. A milling process is used to conduct experiments. The experimental and theoretical results indicate that (i) the contribution of dominant vibration frequency to the vibration of machine tool is larger than weak modes vibration and (ii) the sensitive structure has higher vibration energy than the insensitive structures. The multimode vibration at dominant frequencies of the sensitive structures (MVDFSS) directly can determine the surface topography of the products.

Non-Destructive Testing and Diagnostic of Rotating Machinery Faults in Petrochemical Processing Plant

Machinery fault detection as part of predictive maintenance based on the machine vibration has been practiced comprehensively in oil and gas industry and power generation plant for maintaining the reliability of the machineries. Despite the advantages, the efforts of identifying machinery fault earlier may lead to inaccurate interpretation and diagnosis due to lack of knowledge, skill and experience. Conventional vibration data acquisition and analysis using single axis accelerometer are time consuming. Therefore, an approach which relies on the visualisation of machine vibration motion technique is proposed. The visualisation of machine vibration motion was performed through a simplified Operating Deflection Shape (ODS) analysis. ODS analysis on a 4 measurement points is enough to show the motion of general machinery arrangement which consist of 2 bearings on the drive side and another 2 bearings on the driven side. The effectiveness of the simplified technique was tested in a laboratory condition before being applied in oil and gas industry. The results show vibration data acquisition is more efficient and time saving by using tri-axis accelerometer and relative phase technique. Furthermore, machinery fault diagnosis can be identified easily, faster and more accurate through visualising the machine vibration motion using a simplified 4-point ODS. This simplified technique is seen as practical approach to be proposed and integrated into conventional machinery fault detection and predictive maintenance based on the machine vibration.

Analysis and control of structure-borne noise for a trimmed body by using panel acoustic participation method

This paper is aimed to analyze and control the structure-borne noise of a trimmed body (TB) under excitation by three engine mounts using panel acoustic participation (PAP) method. For each TB panel, the acoustic frequency response function is applied to obtain critical frequencies of interest under each excitation. The PAP analysis is then carried out at all critical frequencies. Panels of acoustic significance are identified by the correlation coefficient matrix (CCM) method for all excitations. The acoustic contributions from those panels may be positive or negative. It is found the control of the total interior noise level can be achieved by suppressing the vibration of positive contribution panels or by increasing the vibration of negative contribution panels. It is verified by installing dynamic vibration absorbers at selected positions on the positive contribution panel to reduce the vibration to control noise level and on the negative contribution panel to reduce the vibration to increase noise level. The PAP method is also compared with the other methods such as the operational deflection shape (ODS) analysis and the structural vibration modal analysis. It is concluded that the PAP method is more effective to control the structure-borne noise.

Identification of optimum Calophyllum inophyllum bio-fuel blend in diesel engine using advanced vibration analysis technique

Bio-fuel causes less pollution to the environment as compared with diesel fuel. However, sound and vibration resulting from the combustion in bio-fuel-powered engines adversely affect users. In this study, non-edible bio-fuel, i.e., Calophyllum inophyllum, and its blends were investigated for their performance as alternative fuel and were compared by using vibration as the engine parameter. Previous studies used overall engine vibration to determine the optimum bio-fuel blends with minimal vibration. Overall vibration could consist of vibration components due to combustion as well as other external vibration sources. This condition limits its effectiveness in identifying an optimum fuel blend mainly due to vibration caused by combustion effect. Advanced vibration analysis technique, which consists of time-domain, frequency-domain, and motion visualization analyses (i.e., operating deflection shape analysis), is first performed to isolate the effect of external vibration source due to torque from the overall vibration. Bio-fuel-powered engines at full speed and with the lowest engine torque are more suitable for the identification of an optimum fuel blend with minimal engine vibration. Bio-fuel blend B20 has the least vibration in overall root mean square acceleration at full speed compared with pure diesel and other bio-fuel blends.

Damage detection of a bridge model based on operational dynamic strain measurements

Vibration data analysis reserves a significant place in structural health monitoring practice since it can be employed for certain engineering problems such as locating damage and assessing damage severity by means of vibration signature interpretation. In this study, a damage detection study is carried out in light of vibration data analysis methods on a four-span bridge model by exploiting strain measurements. The concept of strain operating deflection shape along with an extraction method based on frequency and spatial domain decomposition is proposed. The damage-induced state of the bridge model is compared with the baseline state to detect and locate the damage. The result of strain analysis is also compared with acceleration analysis by simultaneous measurements of strain and acceleration. The power spectrum matrix of responses is estimated using digital signal processing principles. Besides the operating deflection shape analysis, operational modal analysis and correlation analysis of strain modes are conducted to identify and locate the damage.

Failure analysis of flow-induced vibration problem of in-serviced duplex stainless steel piping system in oil and gas industry

Failure of the duplex stainless steel piping system in oil and gas industry can have disastrous effects. In this study, a novel method of failure analysis of flow-induced vibration problem of in-serviced duplex stainless steel piping system is proposed. The proposed non-destructive technique is able to determine a suitable operating condition for continuous operation without failure. The technique relies on the combined operation of operational modal analysis, operating deflection shape analysis and linear elastic finite element analysis. The effect of different operating conditions for two distinct valve opening cases (i.e. fully opened and partially opened) on the dynamic stress is examined, and they are utilised for forecasting purpose in failure analysis. The result shows that maximum operating conditions are 360 and 400 mmscfd for fully opened and partially opened flow control valves, respectively. Beyond this limit, the piping system most likely will fail.

English

Previous impact force identification has focused on collocated cases because noncollocated cases tend to be ill-posed. Considering the impact location is inaccessible, impact force identification using remote responses away from the impact location must be developed. This study initiates an effort to examine impact force identification for non-collocated case. A methodology utilizing operating deflection shape analysis, modal analysis and the modal transformation method (MTM) is presented to identify the unknown dynamic force. The performance of this approach is examined via experimental verification. The objective of this study is to examine the effectiveness of impact force identification by using MTM for both collocated and non-collocated cases. By measuring the response and frequency response function of the test rig, the time history of the unknown force is recovered by the force identification method where the impact location is known. The proposed method is examined at Points 1 and 15, which have satisfactory and poor curve fitting results respectively. It is found that force accuracy improves when the curve fitting result is enhanced. Experimental results show that impact force identification via MTM is applicable in both collocated and noncollocated cases, only if the curve fitting results satisfactory.

Impact Force Identification by Using Modal Transformation Method for Automobile Test Rig

In the automobile industry, impact force is the main cause for material fatigue in lightweight vehicles. Bump-excited impact force is the most common case, which causes damage to vehicles and reduces the quality of the ride. Force identification is important to reflect the structure's health so that action such as structure modification can be taken before material fatigue. However, direct measurement by using force transducer is not practical due to difficulty in force sensor configuration. A methodology utilizing Operating Deflection Shape (ODS) analysis, Frequency Response Function (FRF) measurement and Modal Transformation Method (MTM) to evaluate the dynamic force is proposed here. This method is called indirect force measurement by using inverse technique. The performance of this approach was demonstrated via experiment. From the measured responses and measured dynamic characteristics of an automobile test rig, a real time mathematical manipulation can generate the systems input force. The force location is known in priori for impact excitation and therefore the inverse problem is well-posed. This method was tested using different force location with unique input force. It shows that high quality of curve fitting to extract the modal parameters such as damped natural frequency, modal damping and residue mode shape is essential to obtain a high accuracy force determination result.

Impact force identification with pseudo-inverse method on a lightweight structure for under-determined, even-determined and over-determined cases

Force identification using inverse technique is important especially when direct measurement through force transducer is not possible. Considering the effects of impact excitation force on the integrity of a lightweight structure, impact force identification has become the subject of several studies. A methodology utilising Operating Deflection Shape (ODS) analysis, Frequency Response Function (FRF) measurement and pseudo-inverse method to evaluate the dynamic force is presented. A rectangular plate with four ground supports was used as a test rig to simulate the motions of a simple vehicle body. By using the measured responses at remote points that are away from impact locations and measured FRFs of the test rig, unknown force locations and their time histories can be recovered by the proposed method. The performance of this approach in various cases such as under-determined, even-determined and over-determined cases was experimentally demonstrated. Good and bad combinations of response locations were selected based on the condition number of FRF matrix. This force identification method was examined under different response combinations and various numbers of response locations. It shows that in the over-determined case, good combination of response locations (i.e. low average of condition number of FRF matrix) and high number of response locations give the best accuracy of force identification result compared to under-determined and even-determined cases.

Nodal control of grass trimmer handle vibration

Imposing node technique is applied to the grass trimmer shaft in order to achieve very low vibration (node) at the handle location. The optimum tuning frequencies of the two tuned vibration absorbers (TVAs) attached at 0.74L and 0.85L along the shaft of the grass trimmer are determined using the imposing node technique. Transverse deflection, experimental modal analysis and operating deflection shape analysis of the grass trimmer were carried out, and the results indicated that nearly zero deflection (node) was induced at the position very close the loop handle location. Moreover, the vibration along the segment of the shaft (0.70L–0.94L) was also found to have relatively small amplitude. The TVAs were found to have best performance with 71% reduction on the frequency weighted rms acceleration at the loop handle and 72% for the rear handle. The results from the experimental modal analysis and operating deflection shape revealed that the presence of the two TVAs has successfully reduced the large deformations of the loop and rear handle where the node was shifted nearer to the handle location. The effects of TVAs were also evaluated during the field test involving grass trimming operation and subjective rating. The results indicated that average reduction of frequency-weighted rms acceleration was by 25%, 69%, 17%, 58% in Xh-, Yh-, Zh- axes and vibration total value respectively during the cutting operation. From the field test, subjective rating of vibration perception consistently rate better for the controlled grass trimmer. Relevance to industryLarge numbers of workers are employed to perform grass trimming job in maintenance of parks and areas with undergrowth. This paper presents the imposing node technique to control handle vibration to the lowest value.

Tuned vibration absorber for suppression of hand-arm vibration in electric grass trimmer

Prolonged use of electric grass trimmer exposes the user to the risk of hand-arm vibration syndrome. A simple approach for the suppression of hand-arm vibration in electric grass trimmer is presented. The proposed system is a tuned vibration absorber (TVA). Modal analysis and operating deflection shape analysis of the electric grass trimmer were carried out and a TVA was designed and fabricated for testing. The results indicated that minimum vibration level was related to the position of the TVA on the shaft of electric grass trimmer. The TVA was found to have best performance with 95% reduction on the acceleration level at position 0.025L. The results from modal analysis and operating deflection shape revealed that the presence of TVA has successfully reduced the large deformations of the handle where the node was shifted nearer to the handle location. The effect of TVA was also evaluated during field test involving grass trimming operation and subjective rating. The results indicated that average reduction of frequency-weighted rms acceleration in the Z h- axis was 84% and 72% in X h- axis for the cutting operation. For the no cutting operation, the reduction is 82% in Z h- axis and 67% in X h- axis. The presence of TVA in the electric grass trimmer has amplified the vibration level in Y h- axis by 19% (no cutting) and 21% (cutting). From the field test, subjective rating of vibration perception consistently rate better for controlled electric grass trimmer. Relevance to industry The tuned vibration absorber when installed to the electric grass trimmer attenuated the vibration total value by 67%. This significantly reduces the risk of hand-arm vibration syndrome.

Evaluation of stiffeners for reducing noise from horizontal vibrating screens.

Sound levels around vibrating screens in coal preparation plants often exceed 90 dB(A). The National Institute for Occupational Safety and Health (NIOSH) is developing noise controls to reduce noise generated by horizontal vibrating screens. NIOSH determined the vibration mechanism housings and the screen body to be the dominant noise sources on a horizontal vibrating screen. Researchers used beamforming, experimental modal analysis, and operating deflection shape analysis to examine noise radiated by the screen body. Based on these results, finite element analysis and a NIOSH-written program were used to estimate the sound power level reduction resulting from adding rib stiffeners to key locations on the screen sides. Rib stiffeners made from two sizes of steel channel and two different cross-sections, C and T, were evaluated. In addition, the effects of orienting the stiffeners horizontally and vertically were examined. Finally, the stiffeners were evaluated with the ends welded to the existing ribs on the screen sides and with the ends free. The results indicate that for a broadband input, the smaller T cross-section oriented vertically with the ends welded to the existing ribs was the best option. This configuration reduced the predicted A-weighted sound power level by 7 dB.

Identification of the interior noise generated by sport utility vehicle axles and structural modification of the axle system for noise reduction

This paper presents experimental and analytical methods for reducing the interior noise generated by the axle system of a sport utility vehicle. The test vehicle has a whine noise problem at the passenger seats. To identify the transfer path of the interior noise caused by the axle system, a vibration path analysis, modal analysis, and operational deflection shape analysis are systematically employed. It has been found that the interior noise generated by the axle system was airborne noise. To predict and reduce the whine noise generated by the axle system, structural modifications for the axle system are performed by using the finite element method and the boundary element method techniques. Throughout this modification the whine noise was reduced by 3—4 dBA.