• 소음진동
• /
• 제11권2호
• /
• pp.329-335
• /
• 2001

The analytical model of the ground wave can be used for the prediction of the noise level from a source above a plain and homogeneous ground surface with no obstacles nearby. Sound propagation along the surface of the ground can be affected by the roughness of the ground surface and the direction of the wind. The effects of the ground surface and the wind can be formulated in terms of the ground coefficient and the noise source parameter. Upward and downward conditions can also be addressed by considering the direction of the wind. The ground coefficient and the noise source parameter are estimated using the measured noise levels of two points under particular environmental condition, and the noise levels of arbitrary points under the same environmental condition can be estimated. The proposed method can be utilized to estimate the noise level of specific noise environment and its validity was confirmed with the results of actual field measurement.

• 한국자동차공학회논문집
• /
• 제1권1호
• /
• pp.120-130
• /
• 1993

In the analysis of automobile exhaust system, the exciting forces from the engine determine the dynamic behavior of the system and the dynamic characteristics influence the riding quality. Therefore, the identification of the force in numeric value is quite important for the vibrational reduction. However, the value is difficult to obtain by experiments due to harsh conditions around the engine. In this research, an optimization technology is adopted to evaluate the exciting forces. An experimental method is conducted for the verification of the finite element modeling. Displacements on the end of the exhaust system are measured under the idling environment. cost function is set up to minimize the differences between the displacements of the numerical simulation and the experiment. Design variables are the components of the exciting forces. That is, optimization is utilized to estimate the forces with existing data. Excellent estimations have been calculated efficiently and the information is used again for the forced vibration of the exhaust system.

• Advances in materials Research
• /
• 제8권4호
• /
• pp.259-274
• /
• 2019

Flexoelectric effect has a major role on mechanical responses of piezoelectric materials when their dimensions become submicron. Applying differential quadrature (DQ) method, the present article studies dynamic characteristics of a small scale beam made of piezoelectric material considering flexoelectric effect. In order to capture scale-dependency of such piezoelectric beams, nonlocal elasticity theory is utilized and also surface effects are included for better structural modeling. Governing equations have been derived by utilizing Hamilton's rule with the assumption that the scale-dependent beam is subjected to thermal environment leading to uniform temperature variation across the thickness. Obtained results based on DQ method are in good agreement with previous data on pizo-flexoelectric beams. Finally, it would be indicated that dynamic response characteristics and vibration frequencies of the nano-size beam depends on the existence of flexoelectric influence and the magnitude of scale factors.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2011년도 제37회 추계학술대회논문집
• /
• pp.456-459
• /
• 2011

위성의 자세제어용 추력시스템에 대한 연료 공급용 솔레노이드 밸브의 국산화를 위해 Dual-Type의 솔레노이드 밸브를 개발하였다. Hydrazine을 연료로 사용하는 위성용 밸브는 반응속도, 유량, 누설 등의 기본성능 외에 수십만 번의 Cycle life, 충격 및 진동, 극저온 등의 환경 요인을 만족해야 한다. 본 논문에서는 설계 및 제작하고 질소 공압 장치를 이용한 성능 시험을 수행하였다.

• Journal of Astronomy and Space Sciences
• /
• 제16권1호
• /
• pp.79-88
• /
• 1999

인공위성은 로켓을 이용하여 궤도에 진입하며 발사과정 중 진동, 가속, 충격, 소음 등과 같은 극심한 발사환경을 경험하므로, 이와 같은 발사조건에 견딜 수 있도록 설계/제작 되어야 한다. 본 논문에서는 우리별 3호 비행모델의 구조체에 대해 소개하고, 발사과정에서 겪게 되는 환경을 지상에서 시험한 발사환경시험의 과정과 결과를 소개하고자 한다.

• 조명전기설비학회논문지
• /
• 제25권3호
• /
• pp.7-14
• /
• 2011

Many countries and researchers in the lighting field have focused on the LED light source as a solution to energy savings and environmental pollution. The LED light source consumes less power, has a long life and is highly economical. It is vibration and shock-resistant, and environment friendly as well. But LED lighting has some problems. In particular, the photobiological safety of LED light sources is emerging as an issue. Ultraviolet radiation from the LED light source emitted directly to the human body over a long period of time is harmful. In this paper, UV radiation from white LED was measured. Finally, the LED light source emits UV radiation, but it is relatively small when compared to others.

• 전자공학회논문지A
• /
• 제30A권10호
• /
• pp.1-11
• /
• 1993

A narrow-band dual TE$_{111}$ mode circular waveguide filter for Ku-Band satellite transponder was designed and manufactured based on a new model of the filter. We calculated the cavity size, pin polarizer depth and diameter, iris length and width, and used Bethe's Small Diffraction Theory and Chon's Correction Formular in order to obtain exact Result for each cavity. The designed dual model waveguide filter was manufactured with invar in order to maintain the thermal stability, and the filter performance was improved through the thermal test and vibration test to endure in the cosmic environment.

• 한국환경보건학회지
• /
• 제44권4호
• /
• pp.391-396
• /
• 2018

Objectives: The purpose of this study is to examine the level of community environmental perception of older adults and to identify the association between environmental perception and subjective health status among older persons. Methods: Analyses are based on data from Statistics Korea 2016 Social Survey. This study analyzed a total of 8,193 older adults aged 65 and over, and examined the association between environmental perception on air, water, soil, noise and vibration, and subjective health status using multiple regression analysis. Results: Study findings shown that environmental perception on water and soil had significant association with subjective health status of older adults. Specifically, older adults reported worse health status when they had more negative perceptions of water and soil environments in their communities. Conclusions: Results of this study suggested that efforts to enhance safety of drinking water and soil environments, and continuous research to identify relationship between environment and elderly health shoud be needed.

• 한국군사과학기술학회지
• /
• 제13권2호
• /
• pp.227-234
• /
• 2010

When a weapon system is developed, climate elements such as temperature, rainfall, and so on have an effect on development costs and a developing period. Therefore, effects of environment and climate must be examined throughly before the design of weapon systems and be applied to their developments. And so, operational and storage requirements for weapon systems are determined and are applied to related tests through analyzing not only environmental factors such as vibration, shock, and so on, but also climate factors. In this paper, the distribution and the frequency of occurrence of rainfall were analyzed and were suggested as a good guide to determine standards of tests for weapon systems when it's raining.

• 한국정밀공학회지
• /
• 제24권2호
• /
• pp.47-57
• /
• 2007

The vibration environment essentially companied by vehicle operation on the road is determined by the shape of road surface, which is called profile. In general, the profile and severity of unpaved road is an important issue in the reliability of durability test for vehicles. In order to maintain severity of unpaved road, it is necessary to develop profilometer system. We developed profilometer system which is composed of data processing computer, power unit, air compressor and sensors. This paper focuses on the severity management of unpaved test courses using neural networks. This paper presents the maintenance range for cross-country course in CPG(Chang-won Proving Ground) and the evaluation of similarity degree between unpaved roads.