Un-Chang Jeong

Evaluation of the Rattle Noise of a Vehicle Seat using the Coherence Analysis Technique

The complicated transfer path relationship between the vibrations of a seat and the noise at the locations of the driver’s ears was estimated from the residual spectrum. For accurate quantitative estimation of the rattle noise at the locations of the driver’s ears, in particular the partial coherence function of the pure inputs to the output was modelled by considering the correlation between the inputs and the input–output. Whenever a coherence analysis was performed with the noise sources in close proximity selected as the inputs and the noise at the locations of the driver’s ears modelled as the output, the partially coherent output spectrum as a quantitative contribution of the inputs to the output was determined. In this study, we applied a coherence analysis technique to identify the sources of the rattle noise of a seat by visualizing the noise sources with an acoustic camera while excitation of the seat was carried out using a hydraulic exciter. We were able to generate the rattle noise from the headrest stay, the recliner and the front part of the slide while excitation of the seat was obtained using a hydraulic exciter with white noise. We observed that the noise was generated by utilizing a hydraulic six-axis exciter positioned at the driver’s seat of a middle-sized manual transmission vehicle. We determined that the noise measured at the locations of the driver’s ears had a frequency of 58 Hz using acoustic visualization and a coherence technique. It was selected in particular as the target frequency since the 58 Hz resonant frequency caused by the twisting mode of the seat back was identical with the frequency of the rattle noise. Finally, it was verified through a modal test that the rattle noise at 58 Hz was generated by the vibration characteristics of the seat, which depended on gaps between the headrest stay and the guide.

Sound Quality Evaluation for Laundry Noise by a Virtual Laundry Noise Considering the Effect of Various Noise Sources in a Drum Washing Machine

The objective of this study is to determine the effect for the sound quality according to the noise source and to build the sound quality index of the laundry noise. In order to compare laundry noise among the influence of noise sources, we made virtual laundry noises by synthesizing an actual laundry noise and each noise source such as a dropping noise, water noise, motor noise and circulation pump noise. We conducted a listening test by customers using virtual laundry noises. As a result of listening test, we found that the dropping noise has a decisive effect on the sound quality of the laundry noise. We conducted the multi regression analysis of sound quality for the laundry noise using the statistical data processing. It is verified to the reliability of the multi regression index by comparison with listening results and index results of other actual laundry noises. This study is expected to provide a guide line for improvement of the laundry noise.

Identification of Moan-Noise Generation Mechanisms by an Experimental Method and Verification of the Mechanism by Finite Element Analysis

‘Moan’ noise in a vehicle is known to cause discomfort and anxiety to passengers. This abnormal noise is generated by a stick–slip phenomenon between the brake pad and the disc during breaking. The exciting force from the brake system is transmitted to a coupled torsion beam axle module through the brake pad, the caliper and an extra bracket. In this study, moan noise is reproduced during the vehicle’s operating test, and the parts of the coupled torsion beam axle module generating moan noise are identified. Further, it is verified that the resonance of the coupled torsion beam axle module due to the exciting force of the brake system is the main cause of moan noise. Coherence analysis and transfer path analysis were conducted to identify how the vibrations from the coupled torsion beam axle module are related to moan noise in the passenger compartments of vehicles. In the coherence analysis, the vibration accelerations of the brake pad, the caliper, the spindle bracket, the trailing arm and the V-beam are set as the inputs, and the output is the noise at the driver’s ear level. In terms of the frequency response, the results from a modal analysis of the coupled torsion beam axle module under the vehicle’s test conditions agreed well with those from a finite element modal analysis in which the boundary conditions of the vehicle were taken into consideration. The dynamic characteristics of the response from the coupled torsion beam axle module were identified using the exciting-force transfer mechanism of the brake system. The locations producing a large strain were determined by calculating the modal strain energy, and an improvement scheme with design modification was proposed for moan noise reduction.

Muscle Union Procedure in Patients with Paralytic Strabismus

To present the surgical outcomes of a muscle union procedure in patients with paralytic strabismus, this retrospective study included 27 patients with paralytic strabismus who underwent a muscle union procedure. In this procedure, the two vertical rectus muscles are united with the paralytic horizontal muscle without splitting the muscles. Postoperative ocular deviations, complications, surgical success rates, and reoperation rates were obtained by examining the medical records of the patients. Seventeen patients had a sixth cranial nerve palsy, seven patients had a third cranial nerve palsy, and three patients had a medial rectus muscle palsy after endoscopic sinus surgery. The mean preoperative angle of horizontal deviation in the primary position was 56 ± 21 prism diopters. The mean follow-up period was 12 ± 9 months. The mean final postoperative ocular deviation was 8 ± 13 prism diopters. The success rate was 74%, and the reoperation rate was 0%. No significant complications, including anterior ischemia, occurred in any of the patients. One patient exhibited an increase in intraocular pressure in the immediate postoperative period, but this resolved spontaneously within 1 week. Our muscle union procedure was effective in patients with paralytic strabismus, especially in patients with a large angle of deviation. This muscle union procedure is potentially a suitable option for muscle transposition in patients with paralytic strabismus who have large-angle deviation or a significant residual angle after conventional surgery.

Experimental Evaluation of a Variable Shear Modulus Characteristic for Magnetorheological Elastomer Due to Induced Current

The purpose of this study is to fabricate an anisotropic magnetorheological elastomer (MREs) based on natural rubber (NR) that has a more advanced MR effect than isotropic MREs by using an anisotropic mold. We evaluated variation in the shear modulus of the MREs in the frequency domain under a magnetic field with a continuously-variable induced current. An evaluation system is proposed that includes a magnetic flux generator, which generates a magnetic field via a continuously-variable induced current. One of the anisotropic MREs possessing 30 vol. %, 40 vol. %, and 50 vol. % carbonyl iron powder was expected to have the highest shear modulus variation as a function of the variable induced current. With the evaluation system, we identified the variation and maximum variation rate of the shear modulus of MREs with three different volume fractions of carbonyl iron powder (CIP) and continuously-variable induced current. The magnetic flux density generated by the magnetic flux generator (MFG) is optimized by electromagnetic finite element method (FEM) analysis and response surface method techniques. The values of each design factor determined by the response surface method (RSM) were applied to the redesign of the evaluation system, including the MFG. The proposed system is verified for the range in which MFG can generate magnetic flux density in order to determine the existence of magnetic saturation of the MFG by magnetic circuit analysis. Consequently, the appropriate volume fraction of CIP in MREs without inducing currents can be determined for any desired shear modulus. The desired volume fraction of CIP in the anisotropic MREs can be approximated to achieve an appropriate shear modulus variation rate. This study demonstrates that it is possible to obtain an appropriate volume fraction of CIP and induced current to achieve the desired shear modulus variation rate of an anisotropic MRE.

Noise reduction of the automobile multi-mode muffler using differential gap control and neural network control

In this study, a controllable multi-mode exhaust system was investigated by analysing the acoustic structure of a low-noise low-back-pressure air exhaust system and forming its controller. After selecting the exhaust system structure that considered the frequency characteristics of the vehicle’s exhaust noise with a large acoustic transmission loss, the basic muffler of the controllable multi-mode exhaust system was designed. The basic structure of the controllable multi-mode muffler with a curved side inlet and a curved side outlet was determined. The theoretical and experimental values of the acoustic transmission loss for straight pipes and for curved pipes were compared with no significant difference. To control the curved multi-mode exhaust system, a differential gap controller and a neural network controller were designed and simulated for control tests. The study findings reveal that the use of the proposed model for noise control achieves a noise reduction of 40–50% over systems with no noise control, proving that this exhaust system is effective in noise control. The feasibility of the noise-controllable multi-mode exhaust system was investigated using both a differential gap controller and a neural network controller.

Reduction in the Moan Noise by Frequency-Response-Function-Based Substructuring and Optimization Techniques

‘Moan’ noise in a vehicle causes discomfort and anxiety to passengers. In the previous study, the causes of moan noise were identified, and a coherence analysis of the components was conducted. It was found that moan noise was generated by the attribution of resonance when the exciting force produced by the stick–slip motion in a brake system was transmitted to a coupled torsional beam axle module. The analysis involved calculation of the response of the coupled torsional beam axle module on a full suspension brake system reconstructed by consideration of the transfer functions and the joint conditions of the coupled torsional beam axle module and the brake system. Each transfer function is decomposed by a frequency-response-function-based substructuring technique. In this study, when using the sensitivity analysis and optimization techniques for moan-noise reduction, the frequency-response-function-based substructuring technique was performed to calculate the response of the modified coupled torsional beam axle module by considering the joint conditions and the transfer functions of the brake system. Highly sensitive design parameters regarding the response of the coupled torsional beam axle module were identified after the sensitivity analysis. The most sensitive design parameters were selected to enhance the efficiency and the robustness of optimization. The optimal values for the design variables were obtained by applying a progressive quadratic response surface method as a optimization algorithm. The application of an optimization technique was possible using the finite element model and the results of the finite element analysis from the previous study. After optimization, a prototype was re-designed, manufactured and tested. Finally, it was verified that the moan noise was reduced, as the natural frequency of 387 Hz for the coupled torsional beam axle module was moved to a higher frequency.

A Newly Advanced Anti-Vibration Pad With a Phase Balancer Designed by Analysis of Washing Machine Behaviors

This study proposed an anti-vibration pad with a phase balancer that helps reduce wood floor vibrations from a washing machine as well as the vibrations of the machine itself. When a washing machine is installed just on anti-vibration pads, the floor vibrations can be reduced, but consequently the machine’s left–right vibrations become more violent. Accordingly, in order to identify the mechanism by which anti-vibration pads generate left-right vibrations in washing machines, the present study proposed a two-point measurement method that can determine vertical washing machine vibrations and phase differences. In addition, we proposed an optimal phase balancer designed by a finite element analysis-based response surface method for reducing vibrations using a phase difference. As a result, the anti-vibration pad with a phase balancer, when applied to washing machines, greatly contributed to simultaneously reducing the actual vibrations of washing machines and the vibration transfer to the floor.

Application magnetorheological elastomer to dynamic vibration absorber for vibration reduction by avariable-unbalance excitation

This paper presents a concept of dynamic vibration absorber (DVA) applied magnetorheological elastomers (MREs) for vibration reduction. Elastic modulus of MRE significantly increases due to the induced magnetic field. Elastic modulus changes the stiffness of DVA. Thus, the DVA can work effectively in a wide frequency range instead of a narrow bandwidth as a conventional dynamic vibration absorber does. Numerical simulations of avariable-unbalance excitation system are used to validate its effectiveness. Thus, the MRE-DVA will be applicable to the vibration reduction.

Design of piezoelectric energy harvesting system using cantilever beam

In this paper, a design for an energy harvesting device using cantilever beam will be investigated and experimental results will be presented to validate the design. The energy harvesting device in the study is 31-unimorph piezoelectric which was used to convert small amplitude mechanical vibration from a specific machine application into an electrical energy source that could be used for electronic devices with low power requirements. The primary purpose of the design is to illustrate a method to design a cantilever beam that is optimized for attached position of piezoelectric by Experiment and FEM. From the given vibration data a range of frequencies where the energy harvesting device will generate the greatest amount of energy is determined. The device is then designed specifically targeting that frequency range with sinusoidal wave about resonant frequency. And results of this study show the change trend of output voltage according to changing circuit elements. This approach is presented as part of a ...