Buhm Park

Determination of effective mass density and modulus for resonant metamaterials.

This work presents a method to determine the effective dynamic properties of resonant metamaterials. The longitudinal vibration of a rod with periodically attached oscillators was predicted using wave propagation analysis. The effective mass density and modulus were determined from the transfer function of vibration responses. Predictions of these effective properties compared favorably with laboratory measurements. While the effective mass density showed significant frequency dependent variation near the natural frequency of the oscillators, the elastic modulus was largely unchanged for the setup considered in this study. The effective mass density became complex-numbered when the spring element of the oscillator was viscoelastic. As the real part of the effective mass density became negative, the propagating wavenumber components disappeared, and vibration transmission through the metamaterial was prohibited. The proposed method provides a consistent approach for evaluating the effective parameters of resonant metamaterials using a small number of vibration measurements.

Force generation characteristics of standard heavyweight impact sources used in the sound generation of building floors

Several heavyweight impact sources have been used in applying standardized excitation forces to evaluate the noise generation characteristics of building floors. In this study, heavyweight sources (a bang machine and an impact ball) were filmed with a high-speed camera on the period of deformation and restitution of the impact. The generated impact force was measured, and the effects of the taken deforming shapes were investigated. Experimental modal analysis was performed to determine the natural frequencies and mode shapes of the impact sources. With respect to deforming shapes during impacts, the influence of the mode shapes was clearly demonstrated, especially for the impact ball. Using the measured modal properties, the impact force was predicted and compared to the measured excitation force. By comparing the transient variation of the excitation force and its frequency spectrum, the influence of the modal characteristics of the source on the generated impact force was investigated.

Sound Quality Characteristics for Interior Noise of High Speed Train

In Korea, the high-speed train is one of the most important mass transportation. Due to its fast speed, the interior noise level is high and it is one of major reason for passenger complaints. In this study, the response of passengers to interior noise was evaluated using sound quality parameters. The effects of various parameters, such as train types, travel speed, rail road, on the calculated sound quality were investigated. The characteristics of interior noise were identified. The obtained results were compared to auditory experimental data. For precise comparison of noises of similar loudness but with different characteristics, paired comparison method was used. From the comparison, important parameters that have influence on the annoyance and loudness of the noise were determined.

Artificial Engine Sound Synthesis Method for Modification of the Acoustic Characteristics of Electric Vehicles

Sound radiation from electric motor-driven vehicles is negligibly small compared to sound radiation from internal combustion engine automobiles. When running on a local road, an artificial sound is required as a warning signal for the safety of pedestrians. In this study, an engine sound was synthesized by combining artificial mechanical and combustion sounds. The mechanical sounds were made by summing harmonic components representing sounds from rotating engine cranks. The harmonic components, including not only magnitude but also phase due to frequency, were obtained by the numerical integration method. The combustion noise was simulated by random sounds with similar spectral characteristics to the measured value and its amplitude was synchronized by the rotating speed. Important parameters essential for the synthesized sound to be evaluated as radiation from actual engines were proposed. This approach enabled playing of sounds for arbitrary engines. The synthesized engine sounds were evaluated for recognizability of vehicle approach and sound impression through auditory experiments.

Bi-directional homogenization equivalent modeling for the prediction of thermo-mechanical properties of a multi-layered printed circuit board (PCB)

Warpage of multi-layered printed circuit boards (PCB) during the reflow process is a serious problem which affects the reliability of solder ball connections between the PCB and the mounted semi-conductor packages in electronic devices. It is essential to predict the warpage of the PCB accurately; however, the complicated copper patterns in multi-layered PCBs render a full modeling analysis impossible due to the excessive computing time required. To overcome this problem, we have developed analytical equations of three Cu patterns (line, square, and grid) for the application of thermo-mechanical properties simply by equivalent modeling of Cu patterns. In the proposed equations, the effect of thermo-viscoelastic properties as well as the influence of surrounding layers such as woven glass fabric/BT (bismaleimide triazine), composite laminate (BT core), and photoimageable solder resist (PSR) were considered. To verify the developed equations, vibration tests based on the wave propagation approach were performed at various temperatures. Good agreement was observed between the equivalent model and the experimental results.

Analysis of Annoyance of Various Train Pass-by Noise Using Binaural Recording

ABSTRACT Pass-by noises of various trains were recorded by binaural recorder. The measured noises were evaluated using a sound pressure level and psychoacoustic metrics objectively. To analyze a binaural effect on annoyance that can be caused by train noise, auditory experiments were performed. Through the experiments, the annoyance differences between monaural and binaural train noises, the annoyance differences due to measurement angle and the annoyance differences due to kinds of train and measurement distance were determined. A correlation analysis was conducted to determine which index can affect the annoyance more strongly. As the result, a maximum rate of change of sharpness difference between left and right channels was proposed to predict the annoyance. * 1. 서 론 철도차량은 2012년 말 기준 영업거리 5571 km에 이르며 2015년 호남고속철도(182.3 km), 수도권고속철도(61.0 km)에 이어 2017년 원주∼강릉간 고속철도(120.0 km) 등이 개통될 예정이다. 이처럼 철도구간이 늘어나고 그에 따른 철도차량운행이 많아짐에 따라 철도에 인접한 주민들의 소음에 대한 민원도 점차 많아지고 있다.현재 우리나라는 환경부 고시 제 2010-73호 별표 2에 소음레벨에 의해 철도소음을 명시된 소음한도에 의해 권고하고 있다. 하지만 기준치 이내로 제시된 지역에서도 지속적으로 철도소음에 대한 민원이 발생함으로써 법적인 dBA 산출량으로 평가하는 방법의 한계성이 제시되고 있기 때문에 철도차량에 의한 성가심의 원인을 규명하고 해소할 수 있는 과학적 근거자료가 매우 요구되고 있다. 철도차량에 의한 성가심의 원인을 규명하고자 여러 연구들이 진행되고 있으며 Mellet 등

Annoyance evaluation of interior vehicle motor noise by impulse response method

In this study, the annoyance of EPS(Electronic Power Steering system) motor noise in a vehicle was evaluated through the anechoic chamber test. Evaluation during actual operation installed in vehicles allows in-situ annoyance tests, but requires a great deal of labor and time. Therefore anechoic chamber test is required to automate the evaluation process under consistent test condition. However vehicle noise test is significantly different from anechoic chamber test from different sound generation and propagation. Due to these discrepancies, the evaluated results among motors open differ between two test results. For consistent test results compared to those obtained from the actual vehicle environment, impulse response of both the vehicle interior and anechoic chamber was measured, and produced a simulated motor noise by using recorded signal in the anechoic chamber. The important peak noises at 1/3 octave bands to take into account of the tonal components were selected for evaluation of its noisiness. F...

Sound quality characteristics for transient noise of high speed railway interior

This study presents interior noise characteristics of Korean high-speed train under different operation conditions. The interior noise was measured for various operating conditions such as different speeds, concrete and ballast track, and open and tunneled track, passing by another moving train. The transient variation of the sound pressure was recorded. The objective and subjective sound quality evaluation of the interior noise was performed. For quasi-static sounds measured for open lands and in tunnel, Zwickers loudness has dominant impact on the annoyance. When there are transient variations in the sound pressure encountered during entrance, exit, and passing by, the sharpness and roughness also have significant impact on the perceived annoyance. The obtained data are useful for the design of interior of the train since the transient variation of the sound pressure level is influenced also by the sound environment in the room.