• 제목/요약/키워드: Wave Pressure

검색결과 2,082건 처리시간 0.028초

다공벽을 전파하는 압축파에 관한 수치해석적 연구 (Numerical Study of Compression Waves Propagating Through Porous Walls)

  • 김희동
    • 대한기계학회논문집B
    • /
    • 제21권11호
    • /
    • pp.1403-1412
    • /
    • 1997
  • When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates through the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. In the purpose of the impulsive noise reduction, the present study calculated the effect of porous walls on the compression wave propagating into a model tunnel. Two-dimensional unsteady compressible equations were differenced by using a Piecewise Linear Method. Calculation results show that the cavity/porous wall system is very effective for a compression wave with a large nonlinear effect. The porosity of 30% is most effective for the reduction of the maximum pressure gradient of the compression wave front. The present calculation results are in a good agreement with experimental ones obtained previously.

다공벽을 전파하는 압축파의 실험적 연구 (Experimental study of compression waves propagating porous walls)

  • 김희동;뢰호구준명
    • 대한기계학회논문집B
    • /
    • 제20권12호
    • /
    • pp.4036-4043
    • /
    • 1996
  • When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. In the purpose of the impulsive noise reduction, the present study tested the effect of porous walls on the compression wave propagating into a model tunnel. Experimental results were obtained using a shock tube with an open end. The results showed that the cavity/porous wall is very effective for the compression wave with a large nonlinear effect. The porosity of 30% is most effective for attenuation and pressure gradient reduction of the compression wave front. Also the impulsive noise reduction increases with increasing the length and height of the cavity, compared with the tunnel equivalent diameter.

중·저준위 방사성폐기물 고화체의 압축강도 평가를 위한 초음파속도 측정 (Measurement of Ultrasonic Speed for Evaluating Compressive Strength of Solidified Low & Intermediate-Level Radioactive Wastes)

  • 문균영;이태훈;문용식
    • 한국압력기기공학회 논문집
    • /
    • 제7권4호
    • /
    • pp.26-30
    • /
    • 2011
  • In order to ship low & Intermediate level radioactive waste drums, which have been temporarily stored on site, to a disposal facility, their physical and chemical properties should be evaluated and proven to meet the acceptance guideline prior to their shipment. Ultrasonic velocity method, which has been used to estimate the strength of concrete, can be suggested to evaluate the compressive strength of solidified radioactive waste, which is one of the evaluated properties. The strength is estimated from acoustic velocity. However, a guided wave traveling along a drum is generated when applying ultrasonic method to the drum, and this makes it difficult to analyze the signal due to overlap between transmitted wave through the contents in drum and the guided wave. This paper reported feasibility of ultrasonic method to evaluate of the compressive strength of the solidified LLW. It is observed that the guide wave is greater than transmitted wave, and ultrasonic velocity could be estimated from transmitted wave signal arriving prior to the guided wave

대동맥 반사파를 재현한 4 element 대동맥 혈압 모델을 이용한 혈압 기반 진단 기술의 평가 (Estimation of Blood Pressure Diagnostic Methods by using the Four Elements Blood Pressure Model Simulating Aortic Wave Reflection)

  • 최성욱
    • 대한의용생체공학회:의공학회지
    • /
    • 제36권5호
    • /
    • pp.183-190
    • /
    • 2015
  • Invasive blood pressure (IBP) is measured for the patient's real time arterial pressure (ABP) to monitor the critical abrupt disorders of the cardiovascular system. It can be used for the estimation of cardiac output and the opening and closing time detection of the aortic valve. Although the unexplained inflections on ABP make it difficult to find the mathematical relations with other cardiovascular parameters, the estimations based on ABP for other data have been accepted as useful methods as they had been verified with the statistical results among vast patient data. Previous windkessel models were composed with systemic resistance and vascular compliance and they were successful at explaining the average systolic and diastolic values of ABP simply. Although it is well-known that the blood pressure reflection from peripheral arteries causes complex inflection on ABP, previous models do not contain any elements of the reflections because of the complexity of peripheral arteries' shapes. In this study, to simulate a reflection wave of blood pressure, a new mathematical model was designed with four elements that were the impedance of aorta, the compliance of aortic arch, the peripheral resistance, and the compliance of peripheral arteries. The parameters of the new model were adjusted to have three types of arterial blood pressure waveform that were measured from a patient. It was used to find the relations between the inflections and other cardiovascular parameters such as the opening-closing time of aortic valve and the cardiac output. It showed that the blood pressure reflection can bring wide range errors to the closing time of aortic valve and cardiac output with the conventional estimation based on ABP and that the changes of one-stroke volumes can be easily detected with previous estimation while the changes of heart rate can bring some error caused by unexpected reflections.

암반에 전달된 밀장전 발파입력의 획률론적 예측 II - 최대압력 도달시간 예측을 중심으로 - (Probabilistic estimation of fully coupled blasting pressure transmitted to rock mass II - Estimation of rise time -)

  • 박봉기;이인모;김상균;이상돈;조국환
    • 한국터널지하공간학회 논문집
    • /
    • 제6권1호
    • /
    • pp.25-40
    • /
    • 2004
  • 밀장전한 암반발파공에서 화약폭발로 전파되는 초음속 충격파는 암반중에 전파되면서 차자로 저음속 충격파, 소성파, 탄성파로 변화된다. 이 연구는 발파압력파의 최대압력 도달시간 산정에 중점을 두었고 연계된 논문 I (the companion paper)에서는 최대 발파업력 산정에 중점을 두었다. 이 연구에서 최대압력 도달시간을 화약밀도, 단열지수, 폭광파속도, 감쇠지수, 동적항복강도, 소성파속도, 암반밀도, 탄성파속도, Hugoniot 상수의 함수식으로 유도하였다 최대합력 도달시간에 대한 매개변수분석 결과 암반특성치가 화약특성치보다 더 크게 영향을 미쳤다. 최대압력 도달시간의 확률분포는 화약과 암반 특성치의 확률분포로부터 Rosenblueth 확률모델로 조합하여 산출되었다. 화약과 암반특성의 불확정성이 발파진동의 불확정성에 미치는 영향을 수치해석으로 분석하였다. 불확정성 분석결괴 화약특성보다 암반특성의 불확정성이 발파진동에 더 크게 영향을 미쳤다. 수치해석 분석결괴 최대 발파양력과 최대양력 도달시간의 바인 하중재하율이 발파진동에 큰 영향을 미쳤다. 또한 화약특성보다 암반특성이 하중재하율에 더 크게 영향을 미쳤다.

  • PDF

극초고압 디젤분무의 충격파가 디젤분무특성에 미치는 영향 (Effect of Shockwave on Diesel Spray Characteristics in Ultra High Pressure Injection)

  • 정대용;이종태
    • 한국분무공학회지
    • /
    • 제10권1호
    • /
    • pp.10-16
    • /
    • 2005
  • To investigate the effect of shockwave on diesel spray characteristics under ultra high pressure injection, the velocity of spray tip and shock wave were investigated using the visualization of spray by schlieren method. Spray characteristics such as the spray radius, height, and droplets size were analyzed. It is found in this study that shock wave, produced by ultra high injection pressure, propagates faster than spray tip. Spray radius of right side of nozzle tip was shorter than that of left side and spray height of right side of nozzle tip was thicker than that of left side. Droplets sue was increased at 414MPa in injection pressure because of pressure gradient between inner and outer of tile spray caused by shockwave.

  • PDF

천이 경계층 유동의 벽면 변동 압력에 관한 실험적 연구 (Experimental Study of Wall Pressure Fluctuations in the Regions of Flow Transition)

  • 홍진숙;전재진;김상윤;신구균
    • 한국소음진동공학회논문집
    • /
    • 제12권4호
    • /
    • pp.280-286
    • /
    • 2002
  • It has been long suspected that the transition region may give rise to local pressure fluctuations and radiated sound that are different from those created by the fully-developed turbulent boundary layer at equivalent Reynolds number. Experimental investigation described in this paper concerns the characteristics of pressure fluctuations at the transition. Flush-mounted microphones and hot wires are used to measure the pressure fluctuations and local flow velocities within the boundary layer in the low noise wind tunnel. From this experiment we could observe the spatial and temporal development process of T-S wave using Wigner-Ville method and find the relations between the characteristic frequency of T-S wave and free stream velocity and the boundary layer thickness based on nondimensional pressure spectra scaled on outer variables.

The dynamic stability of a nonhomogeneous orthotropic elastic truncated conical shell under a time dependent external pressure

  • Sofiyev, A.H.;Aksogan, O.
    • Structural Engineering and Mechanics
    • /
    • 제13권3호
    • /
    • pp.329-343
    • /
    • 2002
  • In this research, the dynamic stability of an orthotropic elastic conical shell, with elasticity moduli and density varying in the thickness direction, subject to a uniform external pressure which is a power function of time, has been studied. After giving the fundamental relations, the dynamic stability and compatibility equations of a nonhomogeneous elastic orthotropic conical shell, subject to a uniform external pressure, have been derived. Applying Galerkin's method, these equations have been transformed to a pair of time dependent differential equations with variable coefficients. These differential equations are solved using the method given by Sachenkov and Baktieva (1978). Thus, general formulas have been obtained for the dynamic and static critical external pressures and the pertinent wave numbers, critical time, critical pressure impulse and dynamic factor. Finally, carrying out some computations, the effects of the nonhomogeneity, the loading speed, the variation of the semi-vertex angle and the power of time in the external pressure expression on the critical parameters have been studied.

컴프레션웨어의 압박감 측정 방법 비교 연구 (Comparison of evaluation methods for measuring pressure of compressionwear)

  • 박지혜;천종숙
    • 복식문화연구
    • /
    • 제21권4호
    • /
    • pp.535-545
    • /
    • 2013
  • The aim of this study was comparing measuring tools for detecting physical comfortness with variation of garment pressure. The measuring tools for detecting physical comfortness were EEG and survey questionnaire. Two low-pressure compressionwears and a commercial compressionwear (girdle) were tested. Results showed that the questionnaire survey well detected suffocation or motion comfortness. But it did not discrete the appropriate tightness of the compressionwears. The results of EEG analysis show that the absolute power of ${\alpha}$-wave value was elevated with the low-pressure compressionwears. It also showed lower stress value. The high-pressure compressionwear presented decreased absolute power of ${\alpha}$-wave value. It showed higher stress value. These results implicate that EEG can appropriatly indicate the change of physical comfortness of compressionwear. The appropriate tightness of compressionwear can be measured with EEG analysis rather than survey questionnaire.

탄성관을 삽입한 관로에서의 비정상류에 관한 연구 (Study on Transient Flow in Pipeline with Flexible Tube)

  • 김영준;총본관
    • 유체기계공업학회:학술대회논문집
    • /
    • 유체기계공업학회 2005년도 연구개발 발표회 논문집
    • /
    • pp.825-828
    • /
    • 2005
  • Experimental and numerical study was done to confirm the effect of the flexible tube in pipeline on transient flow oscillation. Experiment was made for a pipeline with and without deformable flexible tube using a single pumping system of main stainless pipe. The wave speeds of main pipe and flexible tube were calculated from the pipe material properties, structures, and boundary conditions. Time dependent pressure fluctuations were calculated for the pipeline using the simple and the Kelvin-Voigt viscoelastic models for the deformation of main pipe and flexible tube. Pressure calculated by the Kelvin-Voigt viscoelastic model showed better agreement with measured one than pressure by the simple model. Experimental and numerical results show that the maximum pressure as well as amplitude of pressure oscillation was decreased by inserting short flexible tube in pipeline. Hence, inserted short flexible tube to pipeline was found to be effective for the suppression of strong pressure oscillation. Moreover, the wave speed in pipe was discussed based on numerical and experimental results.

  • PDF