Energy Evolution Principles of Shock-Wave in Sandstone under Unloading Stress

Yun Cheng,Zhanping Song,Xiaoxu Chang,Tong Wang 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.10

Excavation process often induces the unloading rock mass to be in different damage stages, thus changing the propagation and attenuation characteristics of shock-wave energy in rock mass. This paper involved an investigation on the energy dissipation principles during unloading stress process. First, the paper presented small disturbance impact tests to acquire shock-wave data using the modified split Hopkinson pressure bar device. Then we discussed the shock-wave characteristics under different unloading stresses, attenuation characteristics of shock-wave energy at distance and its effects on unloading stress on the attenuation characteristics of shock-wave energy. Results showed that the presence or absence of unloading stress in sandstone had significant effect on shock-waveform. The shock-wave energy showed a spatial exponential attenuation characteristic, and the decay coefficient indicated that the variation degree in low unloading stress region was significantly greater than that in high unloading stress region. The unloading stress cut-off point was σ/σc = 23.88%. The shock-wave energy at different locations declined with a trend of slight decrease and rapid attenuation, illustrated that the closer the incident end of the sandstone was, the greater the attenuation degree of the shock-wave energy would be. This paper also analyzed the attenuation rate of shock-wave energy and corresponding different sensitivity to unloading stress, showed that the relationship between attenuation rate and unloading stress could be exposed by a composite linear exponential equation. Therefore, the conclusions can provide reference for the attenuation evolution analysis of shock-wave energy in the excavated rock mass.

MR Insert를 이용한 구조물의 응력파 저감

강병우,김재환,최승복,김경수 한국소음진동공학회 2001 한국소음진동공학회 논문집 Vol.11 No.4

In this paper, stress wave propagation characteristics of MR(Magneto-rheological) inserts are experimentally investigated. Generally, stress waves of structures such as warships or submarines are induced by shock waves from underwater explosion. Their fatal effects on the shipboard equipments or structures damage the performance of warships. But, such a problem can be solved by controlling the stress waves propagating through structures by means of MR inserts. MR insert consists of two aluminum layers and MR fluid filled in between. Two piezoceramic disks are embedded on the host plate as a transmitter and a receiver of stress waves. Pulse waves are generated by the transmitter and they reach to the receiver through the MR insert. Permanent magnet and magnetic coil are used to produce magnetic field at the MR insert. In the presence of magnetic field, MR particles are arranged in chains parallel to the magnetic field such that the transmitted stress waves are reduced. Attenuation of stress waves is experimentally investigated.

와후류 저감을 위한 날개 끝 홈 형상의 수치해석

진정현,오세종,이관중,권기범 한국항공우주학회 2013 한국항공우주학회 학술발표회 논문집 Vol.2013 No.4

항공기의 이·착륙 시 선행 항공기의 날개에서 떨어져 나온 강한 와후류는 후행 항공기에 심각한 위험을 줄 수 있다. 이러한 와후류로 인한 위험도를 줄이기 위하여 본 연구에서는 날개 끝 홈 형상을 제안하고 이것의 기초적인 입증을 위하여 수치해석이 수행 되었다. 수치해석은 SIMPLE 알고리즘에 기반한 비압축성 Navier-Stokes 해석자를 사용하였다. 난류 효과를 평가하기 위하여 Reynolds stress model을 사용하였다. 날개 끝 홈 형상은 기본 형상에 비하여 와후류의 강도를 현저하게 저감시켰다. 본 연구의 다양한 날개 끝 홈 형상변화를 통하여 기본형상 대비 항력의 증가량과 와후류의 접선방향 속도성분의 감소량이 상반관계에 있음을 확인하였다. The shedding of strong vortices generated in take-off and landing poses serious hazard for the following aircraft. To circumvent the vortex wake hazard, a chipped wingtip shape was suggested and a series of numerical simulations were conducted to verify its conceptual validity. The numerical simulation was performed by using incompressible Navier-Stokes solver with pressure based SIMPLE algorithm. Reynolds stress model was employed to evaluate turbulence effects. It was found that the trailed vortices of chipped wingtip shapes were more dissipative than those of the baseline wingtip shape. It was found that there was a trade-off relationship between tangential velocity reduction and drag increase.

서해연안 돌제구조물 주위의 침퇴적 해석

서승원(Suh, Seung-Won),유경선(Yoo, Gyeong-Sun),이화영(Lee, Hwa-Young) 한국해안해양공학회 2007 한국해안해양공학회 논문집 Vol.19 No.4

대조시 조차가 6.6 m에 이르는 천해역인 전북 구시포 연안에 건설된 어항연육제방, 방류제 및 돌제 등 제방군 주위에서의 침퇴적을 이해하기 위한 초기의 연구가 시도되었다. 직접 해석방법으로 정선측량과 간이항공 측량에 의한 침퇴적 변화를 1년 6개월에 걸쳐 수행하였다. 간접적인 방법으로는 제방 인접지역에서의 침퇴적 성향을 파악하기 위하여 침수-노출을 고려한 2차원의 ADCIRC 모형을 적용하여 제방 건설 전후의 유속 및 해저응력의 변화를 비교 평가하였다. 연구 결과에 따르면 구시포어항 연육제방 부근 및 해수욕장 간사지는 퇴적이 다소 우세한 것으로 평가된다. 제방 건설로 유속이 둔화되고 shadow zone 등에서는 한계응력 이하로 급감하여 0.10~0.15N/m²으로 변하며 퇴적성향으로 전이되는 것이 모델링 결과로부터 분석되었다. 그러나 본 논문에서 제시하는 결과는 해저질의 물리적 특성을 충분히 고려하지 못한 제한적인 초기의 평가에 따른 것으로 이어지는 연구의 상세 침퇴적 모델결과와 비교 검토되어 충실한 결과가 도출되어야 할 것으로 사료된다. A sedimentation analysis has been attempted to figure out sedimentation environment due to construction of coastal jetties, such as fish harbor dike, flow guided dike and jetty in shallow Kusipo area, in which tidal range marks up to 6.6 meters in spring tide. As an initial approach of understanding field measurement were done on several stations along reference lines with total station and photo analysis taken by remote controlled small air craft far one and half years. Also numerical tests were done by 2-D ADCIRC model considering dry-wet treatment to evaluate flow and bottom shear stress variations. According to direct measurement, deposition seems to be dominant on Kusipo beach. Model results show bottom shear stress lessens to 0.10~0.15N/m² on most shadow zone of jetties and the inner zone is suffering sedimentation as a result of dike construction. However this is the first approach with limited analysis, thus it should be dealt further considering physical characteristics of bottom sediments in a complete sediment model on upcoming study.

Stoneley wave propagation in nonlocal isotropic magneto-thermoelastic solid with multi-dual-phase lag heat transfer

Parveen Lata,Sukhveer Singh 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.38 No.2

In the present paper we have investigated the Stoneley wave propagation at the interface of two dissimilar homogeneous nonlocal magneto-thermoelastic media under the effect of hall current applied to multi-dual-phase lag heat transfer. The secular equations of Stoneley waves have been derived by using appropriate boundary conditions. The wave characteristics such as attenuation coefficients, temperature distribution and phase velocity are computed and have been depicted graphically. Effect of nonlocal parameter and hall effect are studied on the attenuation coefficient, phase velocity, temperature distribution change, stress component and displacement component. Also, some particular cases have been discussed from the present study.

한반도 남동부에서 부지효과를 고려한 스펙트럼 감쇠상수 χ 추정 및 강지진동의 추계학적 모사

조남대,박창업 한국지진공학회 2003 한국지진공학회논문집 Vol.7 No.6

한반도 남동부에서 관측된 지진기록을 이용하여 스펙트럼 감쇠상수 \chi와 응력강하상수를 계산하였다. 특히, 스펙트럼 감쇠상수 \chi는 관측소별로 부지고유의 특성을 반영하여 새로운 방법으로 계산하였다. 이 방법은 2단계의 계산과정으로 구성된다. 첫 번째 단계에서는 코다(coda)파 정규화법을 이용하여 광역적 상수인 비탄성감쇠 Q를 역산하고, 이로부터 스펙트럼의 거리종속적인 감쇠효과를 일으키는 \chi_{q}값을 계산한다. 두 번째 단계에서는 앞서 계산된 \chi_{q}값을 관측소별로 동일하게 적용하여 거리와 무관한 스펙트럼 감쇠효과인 부지고유의 \chi_{s}값을 추정한다. 관측소에 관계없이 평균적으로 계산된 \chi값의 진원거리(R)에 따른 경향은 0.016+0.000157R이다. 응력강하상수는 1999년 경주근방에서 세 차례 발생한 지진의 관측자료를 이용하여 조남대와 박창업 방법으로 계산하였으며, 그 결과는 92-bar이다. 이들 상수를 이용하여 추계학적 모사법으로 한반도 남동부에서 발생 가능한 강지진동의 최대지반운동과 주파수에 따른 특성을 간접적으로 추정하였다. 이러한 추계학적 모사의 결과를 바탕으로 진원거리에 따른 지진동 감쇠공식을 유도하였으며 기존의 국내연구와 비교, 분석하였다.하였다

Effect of vaccination against foot-and-mouth disease on growth performance of Korean native goat (<i>Capra hircus coreanae</i>)

Jo, N. C.,Jung, J.,Kim, J. N.,Lee, J.,Jeong, S. Y.,Kim, W.,Sung, H. G.,Seo, S. American Society of Animal Science 2014 Journal of Animal Science Vol.92 No.6

<P>The objectives of this study were 1) to evaluate the effects of vaccination against foot-and-mouth disease (FMD) on growth performance, nutrient digestibility, hematological parameters, and behavior in a ruminant animal and 2) to investigate a possible strategy for reducing its adverse effect. A total of 12 Korean native goats (<I>Capra hircus coreanae</I>; 19.8 ± 2.9 kg) were used in a crossover design with 3 experimental periods and 3 treatments, randomized and balanced for counteracting possible carry-over effects. The treatments were 1) control, 2) co-injection with a commercially available dipyrone (CADI), and 3) supplementation with γ-amino butyric acid (GABA) at 10 g/kg in concentrate mix. Each period lasted 4 wk, and the vaccination against FMD was performed at 2 wk after the start of each period. The goats were individually housed in a metabolic cage and fed ad libitum with a diet consisting of bermuda grass and commercial concentrate mix (6:4, wt/wt). Dry matter intake, ADG, nutrients digestibility, hematological parameters, and behavioral activities of the goats were measured before and after vaccination. Although DMI was not decreased (<I>P</I> > 0.05), ADG was decreased by the vaccination to the goats (<I>P</I> < 0.01). The total number of leukocytes was increased while that of erythrocytes was decreased by the FMD vaccination (<I>P</I> < 0.01). The vaccination shortened standing time while extended lying time and the time spent in drinking (<I>P</I> < 0.05). The treatment by CADI reduced the adverse effect of vaccination on ADG and goat behavior compared with control and GABA treatment (<I>P</I> < 0.05). We concluded that the FMD vaccination decreased ADG of the goats without depression of diet intake, and CADI may attenuate the adverse effect of the FMD vaccination.</P>