• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.26 no.7
• /
• pp.836-843
• /
• 2016

This study investigates the vibro-acoustic characteristics of an automotive brake drum given free boundaries using the hybrid approach combining numerically obtained structural properties with analytical solution for acoustic radiation. Structural vibrations of the drum are investigated with the finite element method, and modal displacements on the outer surfaces of the drum are idealized as simple mathematical expressions. Based on the expressions, modal sound radiations of the drum are calculated using the Rayleigh integral method. Structural and acoustic responses of the drum for a harmonic excitation are obtained from above results using the modal expansion technique. The results are confirmed with numerical analyses using the boundary element method. Based on these results, it can be concluded that the vibro-acoustic characteristics of a brake drum can be accurately investigated with the process used in this study. Also, many noise and vibration problems in drum brake can be addressed using the procedure proposed in this study.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.26 no.1
• /
• pp.20-26
• /
• 2016

This study investigated noise characteristics of air cleaners and humidifiers in terms of frequency domains and measurement directions. Noise levels of 31 air cleaners and 36 humidifiers were measured in an anechoic chamber according to the related group standards. As for air cleaners, 5 receiving points of 1 m off from front, rear, left, right and top surfaces of the product were considered. In case of humidifiers, 4 receiving points without the rear position were considered in the same manner as air cleaners. In each case, A-weighted equivalent continuous sound level was measured three times for 1 min. As a results, most of the measured air cleaners and humidifiers showed the highest noise levels at top directions due to the air ventilating location. In case of air cleaners, averaged noise levels of top and rear positions were 49.9 and 48.2 dB(A), respectively, whereas averaged noise level of other positions was all 45.2 dB(A). In case of humidifiers, averaged noise level of top position was 44.1 dB(A) whereas averaged noise levels of other positions were 38.7 to 39.1 dB(A). In addition, high frequency content of 1 kHz and 3.15 kHz to 4 kHz for air cleaners and middle frequency content of 500 Hz to 1.6 kHz for humidifiers showed significant contribution to determination of overall noise levels with correlation coefficient of 0.9 and above.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.26 no.6_spc
• /
• pp.714-720
• /
• 2016

Rubbing and misalignment are the most usual faults that occurs in rotating machinery and with them severe effect on power plant availability. Especially blade rubbing is hard to detect on FFT spectrum using the vibration signal. In this paper, the possibility of feature analysis of vibration signal is confirmed under blade rubbing and misalignment condition. And the lab-scale rotor test device provides the blade rubbing and shaft misalignment modes. Feature selection based on GA (genetic algorithm) is processed by the extracted feature of the time domain. Then, classification of the features is analyzed by using SVM (support vector machine) which is one of the machine learning algorithm. The results of features selection based on GA compared with those based on PCA (principal component analysis). According to the results, the possibility of feature analysis is confirmed. Therefore, blade rubbing and shaft misalignment can be diagnosed by feature of vibration signal.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.05a
• /
• pp.852-855
• /
• 2004

This experimental study describes the propagation characteristics of the impulse noise emitted from the exit of a straight pipe attached to the open end of a simple shock tube. The sound pressure level and directivity of the impulse noise propagating from the exit of pipe with several different diameters are measured in the far sound fold for the range of the incident shock wave Mach number between 1.07 and 1.26. The experimental results showed that the peak values of impulse noises had a strong dependance on the exit diameter of a pipe and the shock wave Mach number. The impulse noise had the directivity propagating toward to the pipe axis and the characteristics of inverse square law of propagation distance. Moreover, it was shown that the one-third octave band SPL of impulse noise was almost constant regardless of the frequency band.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.26 no.7
• /
• pp.875-880
• /
• 2016

A new hybrid permanent magnet biased magnetic levitation actuator (maglev) is developed. This new maglev actuator is composed of two C-core electromagnetic cores separated with two permanent magnets. Compared to the conventional hybrid maglev actuators, the new actuator has unique flux paths such that bias flux paths are separated with control flux paths. The control flux paths have minimum reluctances only developed by air gaps, so the currents to produce control fluxes can be minimized. The gravity load can be compensated with the permanent magnet bias fluxes developed at off-centered air gap positions while external disturbances are controlled with control fluxes by currents. The consumed power to operate this levitation system can be minimized. 1-D magnetic circuit model is developed for this model such that the flux densities and magnetic forces are extensively analyzed. 3-D finite element model is also developed to analyze the performances of the maglev actuator.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.26 no.7
• /
• pp.814-819
• /
• 2016

The Stockbridge damper is used to control the aeolian vibration of a overhead transmission line due to the natural wind under a low velocity, between 1 m/s to 7 m/s. The damper model can be simply derived with several design parameters and the location of eigenvalues of design parameters are important to determine the efficiency of energy dissipation by excitation itself with two counterweights. First, the importance of resonance frequencies of Stockbridge damper was reviewed through the analysis of frequency response function of damper system. Then, the best selection of design parameters was investigated with the introduction of objected function that minimize the distance between the calculated eigenvalues and target frequency points. The best choice of design parameters was reviewed using the simulated results from the objective function and the effectiveness of selected design case was discussed at the point view of practical implementation.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.26 no.4
• /
• pp.469-474
• /
• 2016

Abnormal sound was heard from a heat exchanger of condensate water system in a nuclear power plant, which was identified as impact sound of a loose part later. Nuclear power plants are normally equipped with loose part monitoring system for primary water system, but not for secondary water system. The abnormal sound was analyzed by using the impact signal-processing methodology based on the Hertz theory. The predicted results for impact location and size of the loose part showed good agreement with those of the actual loose part found during the overhaul period in the plant. So, this analysis methodology for the impact signal will be widely utilized for the primary and secondary side of the nuclear power plant.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.26 no.4
• /
• pp.428-435
• /
• 2016

In this paper, high-performance and low-noise centrifugal fan used to circulate cold air inside a household refrigerator is developed by reducing the vortex flow observed near the tip of fan hub. First, the performance of the existing centrifugal fan is investigated through the experiment using a fan tester and the characteristics of detailed flow field obtained from the CFD simulation are closely examined. The strong vortex flow is observed in the vicinity of the tip of fan hub. Based on this result, new design is devised to reduce this vortex flow. As a result, it is numerically and experimentaly found that the volume flow rate of the new fan increases and the radiated noise decreases in comparison with the existing fan at the same rotation speed.

• Journal of the Korean Society of Industry Convergence
• /
• v.26 no.2_2
• /
• pp.327-332
• /
• 2023

As interest in eco-friendly and fuel-efficient electric vehicles has increased globally, there has also been a growing interest in the efficiency, vibration, and noise of motors for electric vehicles Electric vehicles generally have significantly lower driving ranges per charge compared to the maximum driving range per fueling of internal combustion engine vehicles. Additionally, there are issues with various vibrations and noise generated by the motor that can cause discomfort for passengers. Therefore, research is necessary to reduce losses, vibration, and noise of the motor to improve the driving range of electric vehicles. IPMSM with a purchased design can obtain additional reluctance torque by utilizing the difference in inductance between the d and q axes. However, due to this reluctance torque, torque ripple occurs larger than other motors. The increase in torque ripple also increases noise and vibration. Since the reluctance torque, which is the main cause of torque ripple, is determined by the shape of the motor components, torque ripple can be reduced through shape optimization. In this paper, a rotor shape for reducing torque ripple and core loss that causes vibration, noise, and efficiency to decrease of IPMSM for electric vehicles was proposed. Optimization design was carried out by changing the shape of the q-axis path of the rotor to reduce the difference in inductance of the d and q-axis of the rotor. Finally, in order to verify the validity of the design variables derived through the optimal design, the original model and the improved model were compared through the FEM. Compared to the original model, the improved model's torque verifying ripple was reduced by about 62% and core loss was reduced by about 29%, the superiority of the improved model.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.26 no.2
• /
• pp.217-224
• /
• 2016

In this study, a transfer matrix method (TMM) for a twisted uniform beam considering the effect of rotary inertia is developed, and the differential equation and the displacements and forces are derived from Hamilton's principle. The particular transfer matrix is derived by applying the distributed mass and transcendental function while using a local coordinate system. In addition, the results obtained from this method are independent for a number of subdivided elements, and this method can determine the exact solutions for the free vibration characteristics of a twisted uniform Rayleigh beam. To validate the accuracy of the proposed TMM, the computed results are compared with those reported in the existing literature, and the comparison results indicate notably good agreement. In addition, the method is used to investigate the effects of rotary inertia for a twisted beam.