• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.481-487
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• 1997

The development of transportation and construction equipment has required higher engine power and lower operation cost. The sound which the engine emits often degrade the performance of the whole system which adopts that engine. Specially the marine engine requires high restriction on the noise level for the customer's comfort and safety. The noise and vibration of Diesel engine must be carefully considered in the early design step. The double antivibration system is effective to increase the efficiency of antivibration, and the acoustic enclosure for reducing the noise level. 2 DOF model was effective to estimate the antivibration performance, which allows to determine the mass of the engine bed and the specification of the engine mount. The mass distribution of the enclosure system can be considered effectively by using the FEM model. The design contains structurally rigid engine bed by FEM, which is for reducing the influence of the flexible vibration, rubber mount selection as well as the acoustic enclosure design.

• Proceedings of the KSR Conference
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• 1998.05a
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• pp.280-286
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• 1998

In recent years, the interest in noise increases gradually and the low noise level becomes one of the important performances in electrical equipment for railway vehicle. In the auxiliary power supply, most of the noise is made by the current ripple of alternating current reactor(ACL) which filters the output voltage. And this current ripple results from the voltage harmonics across the ACL. So the noise can be reduced by eliminating the voltage harmonics across the ACL. This paper shows harmonic eliminating technique which is making gating signals of upper and lower inverter have a phase difference in the 12-step inverter type auxiliary power supply. This technique was proved by testing on the developed 180KVA auxiliary power supply using IGBT.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.91-97
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• 1996

We have all heard sounds that did not sound "right" while riding in an automobile. Objectionable sounds are difficult to find and understand because the sound field is complex and dynamic in the near field of an automobile. Many different noise sources and transmission paths must be understood before an engineering change can be recommended. This paper reviews the fundamental characterization of sound and chscusses the Sound Intensity measurement technique. Sound intensity measurements locate sources and sinks of acoustic energy. Used with narrowband analysis equipment, acoustic noise sources can be identified. Sound intensity measurements are made -in-situ and do not require specmi anechoic facilities. The measurement results in a vector representation of the near field sound field and can discriminate between multiple sound sources.d sources.

• Transactions of The Korea Fluid Power Systems Society
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• v.6 no.3
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• pp.1-9
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• 2009

Noise reduction for hydraulic pump is strongly demanded in the market with its efficiency and durability. In order to meet this demand, it is necessary to reveal mechanism for noise and relationship between the important factors. In this paper, mathematical model for cylinder pressure which is primary reason of pulsation and sound noise were established, and examined its pressure profile by simulation. Also, the valve plate of three kind types are manufactured and tested for piston pressure, pressure pulsation, and sound power level based on the tentative standard which is officially recognized.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.6
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• pp.137-144
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• 1995

The purpose of this study is to obtain a foundation data for chassis design and road noise reduction of automobiles. Using the combination of the automobile, radial tires and instrumentation equipment, experimental investigation was carried out to examine the characteris- tics of the structural vibration of tire as the key to obtaining the effective parameters for reducing road noise. From the results of this studies it has been confirmed that the specific ranges of natural frequency of tire exciting the suspension and chassis system. And the tire, axle and chassis natural frequency of automobile govern the road noise. Results show that material properties of tire and experimental condition are major parameter for shifting of tire natural frequency. These results would be utilized as basic materials for the design of chassis design with papametric study, which enables a designer of an automobile to foresee the influence of the various design factors or operating conditions.

• Journal of dental hygiene science
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• v.15 no.5
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• pp.603-611
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• 2015

This research is aimed at cutting off hearing loss and other harmful factors due to noise and providing basic material for noise reduction plan. As the research method, this research assessed noise by measuring acoustic pressure level and frequency in various situation of non-treatment and treatment. As the measurement result, average noise degree of high speed handpiece of non-treatment, ultrasonic waves scaler, and low speed handpiece showed 58~66 dB(A). Average noise degree of scaling of treatment, tooth elimination, and denture adjust showed 73~81 dB(A). The result is inferior to recognized standards of noise induced hearing loss. But the result of assessing this with (noise rating) NR curve was NR-73~78, which exceeded general workplace noise standard. This level can cause hearing loss when exposed to a long time. Therefore, treatment office noise during dental treatment can cause psychological and physical damage in dental clinic employees, and it is urgently required to establish systematic and active noise reduction plan.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.1634-1641
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• 2008

The shock absorbing equipment for railway rolling is one of the most important components. It's effects on the safety of both passengers and vehicle itself and reduce shock, vibration and noise. The shock absorber equipment is mainly consisted of the yoke, plate and rubber draft gear. The objective of the this paper is to evaluation of structure and strength for the yoke in railway vehicles. Structure and strength analysis has been performed by use of finite element method and experimental stress analysis.

• Journal of Korean Association for Spatial Structures
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• v.8 no.2
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• pp.63-72
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• 2008

One of the most important matters in keeping membrane structures in healthy condition is to maintain the proper tension distribution over the membrane. However, it is not easy to know the real stress level in the membrane quantitatively after completion of the structures. Authors suggested measurement method that can measure membrane stress using sound wave, and have been holding experimental tests of membrane stress measurement that used the sound external excitation with sine wave and white noise. The concept of the method is the fact that measurement of resonance frequency by vibrating membrane having rectangular boundary by audible frequency can measure membrane stress indirectly. In this paper, through the experimental tests it is proved that the equipment can be used for not only the membrane material of type A but also for types B and C. In addition, it is proved that the developed measurement equipment is available to stably measure the membrane stress which exists in the membrane material of the actual membrane structures.

• Progress in Medical Physics
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• v.13 no.3
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• pp.156-162
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• 2002

In this study, we attempted in preparing high precision EEG measuring equipment. To measure EEG in high efficiency, pre-amplifier should get high performance common mode rejection ratio. Also, separation amplifier is essential to eliminate common line noise. So, our study were pointed at elevating the efficiency of eliminating noise, user safety and low noise characteristics. Prepared high precision pre-amplifier for EEG was A/D converted to automatically classify $\alpha$ wave, $\beta$ wave and $\theta$ wave. And converted data were Fast Fourier Transformed with real time DSP (Digital Signal Processing). Clinical demonstrations were carried out with healthy students, aged between 20 to 26 who has no histories of illness. To recognize the efficiency of the EEG, prepared EEG were used with MS equipment in low stimulated state and high stimulated state. Then, we studied at the effect of sensitivity on brain wave. From this study, it is known that our EEG equipment is efficient in sensitivity evaluation and suitable stimulations for each psychological state are required.

• International Journal of Ocean System Engineering
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• v.1 no.4
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• pp.205-210
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• 2011

High data-rate underwater communications is demanded. This demand imposes stringent requirements on underwater communication equipment of phase-locked-loop (PLL). Phase noise in PLL is unwanted and unavoidable. In this paper, we investigate the PLL phase noise effect on high order QAM for underwater communication systems. The phase noise model using power spectral density is adopted for performance evaluation. The phase noise components considered in PLL are reference oscillator, voltage controlled oscillator (VCO), filter and divider. The filters in PLL noise are assumed to be second order active and passive low pass filters. Through simulation, we analyze the phase noise characteristics of the four components and then investigate the performance improvement factor of each component. Consequently, we derive specifications of VCO, phase detector, divider to meet performance requirement of high data-rate communication using QAM under phase noise influence.