• 대한조선학회논문집
• /
• 제57권6호
• /
• pp.322-330
• /
• 2020

This study deals with underwater explosion (UNDEX) characteristics of various non-explosive underwater shock sources for the development of non-explosive underwater shock testing devices. UNDEX can neutralize ships' structure and the equipment onboard causing serious damage to combat and survivability. The shock proof performance of naval ships has been for a long time studied through simulations, but full-scale Live Fire Test and Evaluation (LFT&E) using real explosives have been limited due to the high risk and cost. For this reason, many researches have been tried to develop full scale ship shock tests without using actual explosives. In this study, experiments were conducted to find the characteristics of the underwater shock waves from actual explosive and non-explosive shock sources such as the airbag inflators and Vaporizing Foil Actuator (VFA). In order to derive the empirical equation for the maximum pressure value of the underwater shock wave generated by the non-explosive impact source, repeated experiments were conducted according to the number and distance. In addition, a Shock Response Spectrum (SRS) technique, which is a frequency-based function, was used to compare the response of floating bodies generated by underwater shock waves from each explosion source. In order to compare the magnitude of the underwater shock waves generated by each explosion source, Keel Shock Factor (KSF), which is a measure for estimating the amount of shock experienced by a naval ship from an underwater explosionan, was used.

• Journal of Audiology & Otology
• /
• 제23권2호
• /
• pp.103-111
• /
• 2019

Background and Objectives: Dizzy patients with abnormal otolith function tests, despite a normal caloric response, are defined as having specific (isolated) otolith organ dysfunction. This study was performed to compare the differences in clinical presentation between isolated otolith dysfunction (iOD) patients with lab- and Sx-based iOD group and lab-based iOD symptoms. Subjects and Methods: The medical records of 23 iOD patients with normal caloric response but abnormal cervical vestibular evoked myogenic potential (VEMP), ocular VEMP, or subjective visual vertical were reviewed. Non-spinning vertigo was considered as otolith-related symptoms. The patients' age, onset of dizziness, Numeric Rating Scale on the severity of dizziness, and concomitant vestibular disorders were analyzed. Results: Patients in the lab-based iOD group were significantly older than those in the lab- and Sx-based iOD group. Known vestibular disorders were significantly more common in the lab-based iOD group (83.3%) compared to the lab- and Sx-based iOD group (18.2%). Despite the normal caloric response, catch-up saccade was found in the video head impulse test in more than half (54.5%) of the lab-based iOD group patients. There was no catch-up saccade in the lab- and Sx-based iOD group. There were no significant differences in gender ratio, frequency of dizziness attacks, and duration of illness. Conclusions: We propose new definitions of definite iOD (lab- and Sx-based iOD) and probable iOD (lab- or Sx-based iOD). These new definitions may help researchers to identify patients who are more likely to have true iOD, and facilitate comparisons of results between different studies.

• 대한청각학회지
• /
• 제23권2호
• /
• pp.103-111
• /
• 2019

Background and Objectives: Dizzy patients with abnormal otolith function tests, despite a normal caloric response, are defined as having specific (isolated) otolith organ dysfunction. This study was performed to compare the differences in clinical presentation between isolated otolith dysfunction (iOD) patients with lab- and Sx-based iOD group and lab-based iOD symptoms. Subjects and Methods: The medical records of 23 iOD patients with normal caloric response but abnormal cervical vestibular evoked myogenic potential (VEMP), ocular VEMP, or subjective visual vertical were reviewed. Non-spinning vertigo was considered as otolith-related symptoms. The patients' age, onset of dizziness, Numeric Rating Scale on the severity of dizziness, and concomitant vestibular disorders were analyzed. Results: Patients in the lab-based iOD group were significantly older than those in the lab- and Sx-based iOD group. Known vestibular disorders were significantly more common in the lab-based iOD group (83.3%) compared to the lab- and Sx-based iOD group (18.2%). Despite the normal caloric response, catch-up saccade was found in the video head impulse test in more than half (54.5%) of the lab-based iOD group patients. There was no catch-up saccade in the lab- and Sx-based iOD group. There were no significant differences in gender ratio, frequency of dizziness attacks, and duration of illness. Conclusions: We propose new definitions of definite iOD (lab- and Sx-based iOD) and probable iOD (lab- or Sx-based iOD). These new definitions may help researchers to identify patients who are more likely to have true iOD, and facilitate comparisons of results between different studies.

• 한국구조물진단유지관리공학회 논문집
• /
• 제24권5호
• /
• pp.119-125
• /
• 2020

에폭시 계열의 합성수지와 골재를 혼합함으로써 진동저감 성능을 크게 증가시킨 고감쇠 콘크리트에 대한 연구가 활발히 진행되고 있는데, 이러한 폴리머 혼입 고감쇠 콘크리트는 배합 시, 시멘트와 물을 사용하지 않으므로, 일반 콘크리트에 비해 경화시간이 매우 짧고, 물리적 특성 및 동특성 등이 매우 우수하여, 층간소음 및 진동 저감이 요구되는 건축구조물에의 폭넓은 활용이 기대되고 있다. 한편, 폴리머 혼입 고감쇠 콘크리트의 활용성을 넓히기 위한 방안으로, 보강재 분야에 대한 연구가 다양하게 진행되어 왔으나, 폴리머 콘크리트가 일반 콘크리트 및 기존 방진보강재를 완전히 대체하기 위해서는 물리적 특성, 동적 물성, 생산성 및 현장 적용성 등을 고려하여 진동저감 성능에 대한 전반적인 검토가 필요한 실정이다. 본 연구에서는 폴리머 콘크리트의 에폭시 혼입비율별 물리적, 동적 특성을 일반 콘크리트와 비교한 결과, 탄성계수는 비슷한 반면, 압축, 인장, 휨강도가 상당히 우수한 결과를 보였으며, 특히 인장강도는 4~10배 이상 큰 차이를 보였으며, 주파수 응답함수와 감쇠비를 Modal 시험과 유한요소해석 모델을 통해 도출하여 검토한 결과, 폴리머 콘크리트의 동적 강성이 일반 콘크리트 보다 20% 크게 나타났고, 감쇠비는 약 3배 정도 높은 것으로 나타났다.

• 한국구조물진단유지관리공학회 논문집
• /
• 제24권5호
• /
• pp.135-142
• /
• 2020

구조물을 구성하고 있는 콘크리트의 경우, 진동에 대한 감쇠성능이 작아, 구조물에서 발생하는 다양한 진동 문제를 해결하는데 어려움이 있으므로, 이러한 문제를 해결하기 위해, 최근 폴리머 콘크리트와 복합구조 댐퍼를 혼합하여 댐핑 성능을 크게 증가시킨 고 감쇠 시스템에 대한 연구가 활발히 진행되고 있다. 한편, 폴리머 콘크리트는 배합 시, 시멘트와 물을 사용하지 않아, 경화시간이 매우 짧고, 물리적 특성 및 동특성 등이 매우 우수하여 진동저감이 요구되는 건축구조물에의 폭넓은 활용이 기대되는 구조재료이며, 복합구조 댐퍼는 파이프 관 내부에 위치한 쇠구슬의 충돌에 따른 운동에너지 소산과 점성유체의 에너지 소산 방식을 통해 진동을 저감하는 구조시스템이라 할 수 있다. 본 연구에서는 폴리머 콘크리트와 복합구조 댐퍼의 물리적, 동적 특성을 일반 콘크리트와 비교하였는데, 물리적 특성의 경우, 폴리머 콘크리트가 탄성계수 및 강도 특성에서 상당히 우수한 결과를 보였으며, 특히 인장강도는 6.5~10배 이상 큰 차이를 보였다. 또한, 동적 특성의 경우도 폴리머 콘크리트는 일반 콘크리트 대비 동적강성은 25%, 감쇠비는 약 3배 정도 증가하였으며, 복합구조 댐퍼는 동적강성은 비슷한 경향을 보였지만 감쇠비는 3.5배 이상 증가하여, 일반 콘크리트보다 진동 감쇠성능이 우수한 것으로 나타났다.

• Advances in aircraft and spacecraft science
• /
• 제5권2호
• /
• pp.225-237
• /
• 2018

The difficulties of satellite vibration testing are due to the commonly expressed qualification requirements being incompatible with the limited performance of the entire controlled system (satellite + interface + shaker + controller). Two features cause the problem: firstly, the main satellite modes (i.e., the first structural mode and the high and low tank modes) are very weakly damped; secondly, the controller is just too basic to achieve the expected performance in such cases. The combination of these two issues results in oscillations around the notching levels and high amplitude beating immediately after the mode. The beating overshoots are a major risk source because they can result in the test being aborted if the qualification upper limit is exceeded. Although the abort is, in itself, a safety measure protecting the tested satellite, it increases the risk of structural fatigue, firstly because the abort threshold has been already reached, and secondly, because the test must restart at the same close-resonance frequency and remain there until the qualification level is reached and the sweep frequency can continue. The beat minimum relates only to small successive frequency ranges in which the qualification level is not reached. Although they are less problematic because they do not cause an inadvertent test shutdown, such situations inevitably result in waiver requests from the client. A controlled-system analysis indicates an operating principle that cannot provide sufficient stability: the drive calculation (which controls the process) simply multiplies the frequency reference (usually called cola) and a function of the following setpoint, the ratio between the amplitude already reached and the previous setpoint, and the compression factor. This function value changes at each cola interval, but it never takes into account the sensor signal phase. Because of these limitations, we firstly examined whether it was possible to empirically determine, using a series of tests with a very simple dummy, a controller setting process that significantly improves the results. As the attempt failed, we have performed simulations seeking an optimum adjustment by finding the Least Mean Square of the difference between the reference and response signal. The simulations showed a significant improvement during the notch beat and a small reduction in the beat amplitude. However, the small improvement in this process was not useful because it highlighted the need to change the reference at each cola interval, sometimes with instructions almost twice the qualification level. Another uncertainty regarding the consequences of such an approach involves the impact of differences between the estimated model (used in the simulation) and the actual system. As limitations in the current controller were identified in different approaches, we considered the feasibility of a new controller that takes into account an estimated single-input multi-output (SIMO) model. Its parameters were estimated from a very low-level throughput. Against this backdrop, we analyzed the feasibility of an LQG control in cancelling beating, and this article highlights the relevance of such an approach.

• 한국수소및신에너지학회논문집
• /
• 제25권5호
• /
• pp.509-515
• /
• 2014

At the fuel processing system (FPS) of fuel cell vehicle, hydrogen recirculation blower (HRB) is used for the recirculation of remained hydrogen after reaction. In this paper, noise and vibration improvement of HRB is studied by changing design and control. It is checked the campbell diagram and critical speed for stability of rotor, and housing stiffness is improved using simulation of frequency response function (FRF). A method is suggested that can decrease the unbalance amount of the rotor and impeller which main source of noise and vibration. In order to reduce the noise during deceleration of blower, electrical braking is applied and tested the risk impact of durability. Founded the optimum switching frequency of the motor control, and reduced the idle rpm by increasing of aerodynamic performance. The superiority of paper is proved by measurement of the improved product's noise and vibration.

• 한국산학기술학회논문지
• /
• 제13권1호
• /
• pp.333-342
• /
• 2012

이 논문에서는 인간 청각 시스템에 기반한 모음 개시 지점 (VOP) 탐지 방법을 제시하였다. 이 방법을 통해 '지각의' 주파수 범위, 즉 선형 음향 주파수에서의 Mel Scale을 보여준 후 일련의 삼각 Mel-weighted Filter Bank를 만들어 인간의 청각 시스템에서 대역 필터링 기능을 시뮬레이션하였다. 이러한 비선형 임계 대역 Filter Bank는 데이터 차원수를 크게 감소시키고 비선형적으로 간격을 둔 Mel 스펙트럼에서 더욱 효과적으로 포먼트를 생성하기 위해 조파들의 영향을 제거해준다. Mel 스펙트럼의 첨두 에너지 합은 각 프레임의 특징으로 추출하고 에너지 진폭이 급격히 상승하기 시작할 때의 특성은 Gabor 윈도우를 사용하여 VOP로 탐지한다. 실험 결과를 통해서 다른 종류의 자음들과 연결된 12개의 모음들을 포함하는 한 단어 데이터베이스에 대한 제안된 방법의 평균 정확도는 단시간 에너지와 zero-crossing 비율에 기반을 둔 다른 모음 탐지 방법들보다 높은 72.73% 이상임을 확인하였다.

• Journal of Pharmaceutical Investigation
• /
• 제39권5호
• /
• pp.345-351
• /
• 2009

Organic cation transporters (OCTs) are important for absorption, elimination of many endogenous small organic cations as well as a wide array of drugs and environmental toxins. This gene is located in a cluster on chromosome 6 and OCTs are in major organs such as intestine, liver, kidney, brain and placenta. Therefore, expression levels and function of OCTs directly affect plasma levels and intracellular concentrations of drugs and thereby determine therapeutic response. The aim of this study was to investigate the frequency of the SNPs on OCT1 (C181T and C1022T) and OCT2 (G808T) to analyze haplotype frequency in healthy Korean population. Human subjects have been genotyped for OCT1 (C181T for 195 subjects and C1022T for 825 subjects), using polymerase chain reaction-based diagnostic tests (RFLP). And for OCT2 (G808T), a total of 861 subjects have been genotyped, using pyrosequencing method. Haplotype was statistically inferred using an algorithm based on the expectation-maximization (EM). OCT1 C181T genotyping showed 100% homozygous wild-type (C/C). OCT1 C1022T genotyping showed wild-type (C/C), heterozygous (C/T) and homozygous mutant-type (T/T) and each accounted for 72.1, 24.5 and 3.4%, respectively. OCT2 G808T genotyping results also showed homozygous wild-type (G/G), heterozygous (G/T) and homozygous mutant-type (T/T) and each took 81.8, 17.9 and 0.3%, respectively. Based on these genotype data, haplotype analysis between OCT1 C181T and OCT1 C1022T has proceeded. The result has revealed that linkage disequilibrium between alleles is not obvious (P=0.0122).

• 대한전자공학회논문지
• /
• 제22권3호
• /
• pp.23-30
• /
• 1985

디지탈 필터의 구성이 차분방정식에 근거하였을 때, 그 주파수 특성을 구하는 방법은 계산에 의해 할 수 있는 식이 없으므로 Z-변환식으로 미루어 짐작하거나 실험에 의해 측정하는 방법 밖에 없다. 본 논문에서는 차분방정식으로 표현된 함수의 주파수 응답 진폭특성을 계산하는 방법을 Parseval의 정리를 도입하여 제시하고, 이 식의 타당성을 확인하기 위해 실제로 두 종류의 디지탈 필터를 설계 제작하고 실험 측정하였다. 측정된 결과와 Z-변환식에 의한 계산값, 본 논문에서 제시한 계산식에 의한 값을 서로 비교하였다. 그 결과 차분방정식에 의해 계산된 값이 훨씬 실제 측정값에 접근하였다. 또한 Z-변환식에 의한 결과보다 예리한 roll-off 특성을 보여 줌을 확인했다. 따라서 차분방정식을 기초로 하여 구성된 디지탈 필터의 진폭응답 특성은 Z-변환식보다 차분방정식에 의한 계산이 보다 나은 실제적인 결과를 예측해 준다.