• Title/Summary/Keyword: Dynamic Pressure

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Evaluation of Applicability of HMS-25 as the Railroad Roadbed Material (철도 노반재로서의 수경성 입도 조정 고로슬래그(HMS-25)의 적용성 평가)

  • 황선근;이성혁;이시한;최찬용
    • Journal of the Korean Geotechnical Society
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    • v.16 no.1
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    • pp.157-165
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    • 2000
  • The applicability and performance of HMS-25 as the railroad roadbed materials were evaluated through the model and laboratory tests. The uniaxial compression test of HMS-25, model soil box test, and combined resonant column and torsional shear test were performed for static and dynamic analysis of railroad roadbed. The uniaxial compression test result of HMS-25 shows steady increase in strength due to hardening chemical reaction between HMS-25 and water. The result of model soil box test reveals that railroad roadbed of HMS-25 is better than that of soil in several aspects such as bearing capacity and settlement. The combined resonant column and torsional that shear test result indicates that shear modulus of HMS-25 increases with the power of 0.5 to the confining pressure and that shear modulus increases with the increase of curing period.

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Static and Repeat Loads Model Test on Soft Clay Layer due to the Geotextile Reinforcement (토목섬유로 보강된 연약지반의 정.동적 모형실험)

  • Kim, Young-Su;Kwon, Sung-Mok;Kim, Yeun-Wook;Kim, Hyoung-Jun
    • Proceedings of the Korean Geotechical Society Conference
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    • 2005.03a
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    • pp.232-239
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    • 2005
  • Recently geosynthetics that can be constructed on soft ground have been used for reinforcement and separation in various ways. Through laboratory model tests and numerical analysis, in this study, estimated the suitability of cable elements and appropriate input factors considering loading effect in modeling of geosynthetics. First, in laboratory model tests, geosynthetics were constructed on the clay, and covered with the thickness, 7.5cm of sand mat. And then static and dynamic model tests were performed measuring loading, settlement, ground lateral displacement, and displacements of geosynthetics, but, for cyclic loading, bearing capacity increased linearly with stiff slop because cyclic loading with constant cyclic pressure compacted the ground. Numerical analysis were performed with FLAC 4.0 2D using Mohr-Coulomb and Modified Cam-Clay models, and they compared with the results of model tests. Cable elements of FLAC in modeling geosynthetics couldn't consider the characteristics of geosynthetics that increase shear strength between geosynthetics and clay according to the loading increase. Therefore, in this study, appropriate equation that can consider loading effects in Cable elements was proposed by Case Study.

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An Experimental Study on the Liquefaction Behavior under Various Loading Conditions (다양한 입력하중에서의 액상화 발생 특성 비교 연구)

  • Kim, Soo-Il;Hwang, Seon-Ju;Park, Keun-Bo;Choi, Jae-Soon
    • Proceedings of the Korean Geotechical Society Conference
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    • 2005.03a
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    • pp.320-327
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    • 2005
  • Liquefaction characteristics of saturated sand under various dynamic loadings such as sinusoidal, wedge, increasing wedge and real earthquake loading are investigated focusing on the excess pore water pressure build up instead of liquefaction resistance strength in this paper. There are large differences between two types of earthquake loading - impact and vibration in liquefaction characteristics. The angle of phase change line of sinusoidal loading is very close to the vibration type, whereas the cumulative deviator stress and cumulative plastic strain are larger than two types of real earthquake loadings. On the other hand, the liquefaction characteristics of increasing wedge loadings are located in the range between vibration and impact earthquake loadings. It is concluded that the sinusoidal loading overestimates the resistance of soil under real earthquake loading. Based on results obtained, the increasing wedge loading can reflect the liquefaction behavior under real earthquake loadings more efficiently than sinusoidal loading based on equivalent uniform stress concept.

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Design of a Turbine System for Liquid Rocket Engine (액체로켓용 터빈시스템 설계)

  • Choi, Chang-Ho;Kim, Jin-Han;Yang, Soo-Seok;Lee, Dae-Sung;Woo, Yoo-Cheol
    • 유체기계공업학회:학술대회논문집
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    • 2000.12a
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    • pp.145-152
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    • 2000
  • A turbopump system composed of two pumps and one turbine is considered. The turbine composed of a nozzle and a rotor is used to drive the pumps while gas passes through the nozzle, potential energy is converted to kinematic energy, which forces the rotor blades to spin. In this study, an aerodynamic design of turbine system is investigated using compressible fluid dynamic theories with some pre-determined design requirements (i.e., pressure ratio, rotational speed, required power etc.) obtained from liquid rocket engine (L.R.E.) system design. For simplicity of turbine system, impulse-type rotor blades for open type L.R.E. have been chosen. Usually, the open-type turbine system requires low mass flow rate compared to close-type system. In this study, a partial admission nozzle Is adopted to maximize the efficiency of the open-type turbine system. A design methodology of turbine system has been introduced. Especially, partial admission nozzle has been designed by means of simple empirical correlations between efficiency and configuration of the nozzle. Finally, a turbine system design for a 10 ton thrust level of L.R.E is presented.

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Model for Estimating CO2 Concentration in Package Headspace of Microbiologically Perishable Food

  • Lee, Dong-Sun;Kim, Hwan-Ki;An, Duck-Soon;Yam, Kit L.
    • Preventive Nutrition and Food Science
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    • v.16 no.4
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    • pp.364-369
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    • 2011
  • Levels of carbon dioxide gas, a metabolite of microbial growth, have been reported to parallel the onset of microbial spoilage and may be used as a convenient index for a packaged food's shelf life. This study aimed to establish a kinetic model of $CO_2$ production from perishable food for the potential use for shelf life control in the food supply chain. Aerobic bacterial count and package $CO_2$ concentration were measured during the storage of seasoned pork meat at four temperatures (0, 5, 10 and $15^{\circ}C$), and their interrelationship was investigated to establish a mathematical model. The microbial growth at constant temperature was described by using model of Baranyi and Roberts. $CO_2$ production from the stored food could be explained by taking care of its yield and maintenance factors linked to the microbial growth. By establishing the temperature dependence of the microbial growth and $CO_2$ yield factor, $CO_2$ partial pressure or concentration in package headspace could be estimated to a limited extent, which is helpful for controlling the shelf life under constant and dynamic temperature conditions. Application and efficacy of the model needs to be improved with further refinement in the model.

Statistical analysis of SC-associated geosynchronous magnetic field perturbations

  • Kim, Gwan-Hyeok;Park, Jong-Seon;Lee, Dong-Hun;Jin, Ho
    • The Bulletin of The Korean Astronomical Society
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    • v.37 no.1
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    • pp.91.2-91.2
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    • 2012
  • Kokubun (1983) reported the local time variation of normalized amplitude of sudden commencement (SC) with a strong day-night asymmetry at geosynchronous orbit with 81 SC events. Further careful inspection of Kokubun's local time distribution reveals that the normalized SC amplitudes in the prenoon sector are larger than those in the postnoon sector. That is, there is a morning-afternoon asymmetry in the normalized SC amplitudes. Until now, however, there are no studies on this SC-associated morning-afternoon asymmetry at geosynchronous orbit. Motivated by this previous observation, we investigate a large data set (422 SC events in total) of geosynchronous SC observations and confirm that the geosynchronous SC amplitudes is larger in the morning sector than in the afternoon sector. This morning-asymmetry is probably caused by the enhancement of partial ring current, which is located in the premidnight sector, due to solar wind dynamic pressure increase. We also examine the latitudinal and seasonal variations of the normalized SC amplitude. We find that the SC-associated geosynchronous magnetic field perturbations are dependent on the magnetic latitude and season of the year. This may be due to the location of the magnetopause and cross-tail currents enhanced during SC interval with respect to geosynchronous spacecraft position.

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On the Penetration Phenomena for Thin and Multi-Layered Finite Thickness Plates by a Long Rod Penetrator (긴 관통자에 의한 유한박판 및 적층표적재의 관통현상 연구)

  • 이창현;홍성인
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.7
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    • pp.1759-1772
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    • 1994
  • In this study, we re-examined the Tate's modified Bernoulli equation to study penetration phenomena for long rod projectile into single or multi-layered finite thickness plates. We used the force equlibrium equation at mushroomed nose/target interface instead of conventional pressure equation at the stagnation point. In our penetration model, we considered the velocity dependent $R_t$ value for semi-infinite target and considered only the back face effect for finite target. To compensate for $R_t$ value according to target's thickness and back face effect, we used the spherical cavity expansion theory for semi-infinite plate and used the cylindrical cavity expansion theory for finite plate. Also we developed the experimental technique using make screen to measure the penetration duration time at each layered plate. In 3-layered laminated RHA/mild steel/ A1 7039 plate, we observed that spall had occured around the back face of A1 7039 plate by the stress wave interaction. Through the comparison between theoretical and experimental data including Lambert's results, we conform that our study has good confidences.

Dynamic Behavior Analysis of the Heart Valve Prostheses Considering Squeeze Film Effect During Closing Phase (스퀴즈필름효과를 고려한 인공심장밸브의 닫힘시 동적거동 해석)

  • 천길정
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.2
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    • pp.443-450
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    • 1995
  • An analysis of the dynamics of a mechanical monoleaflet heart valve prosthesis in the closing phase is presented. Employing the moment equilibrium principles on the occluder motion and the squeeze film dynamics of the fluid between the occluder and the guiding strut at the instant of impact, the velocity of the occluder tip and the impact force were computed. The dynamics of fluid being squeezed between the occluder and the guiding struts is accounted for by Reynold's equation. The effect of the fluid being squeezed between the occluder and the guiding strut was to reduce the velocity of the occluder tip at the instant of valve closure as well as dampen the fluttering of the occluder before coming to rest in the fully closed position. The squeeze film fluid pressure changed rapidly from a high positive value to a relatively large negative value in less than 1 msec. The results of this study may be extended for the analysis of cavitation inception, mechanical stresses on the formed elements and valve components as well as to estimate the endurance limits of the prosthetic valves.

A Molecular Dynamics Study of Thermophysical Properties and Stability of Nanoscale Liquid Thread (분자동역학 해석을 이용한 액체 극미세사의 열역학적 물성과 안정성 연구)

  • Kim, Byeong-Geun;Choi, Young-Ki;Kwon, Oh-Myoung;Park, Seung-Ho;Lee, Joon-Sik
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.1366-1371
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    • 2003
  • Molecular dynamics (MD) simulations are conducted to investigate the thermophysical characteristics and the stability of liquid threads for various conditions. A cylindrical thread in the simulation domain is made of Lennard-Jones molecules. The surface tension of liquid threads can be determined from local densities, local normal and transverse components of the pressure force. In order to understand the effects of thread radii on surface tensions, the Tolman equation is modified on the basis of the cylindrical coordinates for prediction of surface tensions. Surface tensions calculated from the MD simulation agree with the prediction from the modified Tolman equation. In addition, surface tensions decrease linearly with increasing system temperature. For a binary system, the surface tension decreased linearly compared to that for a pure system with increasing binary ratio of solute molecules which have relatively large value of the affinity coefficient. For a fixed binary ratio, the surface tension increased slightly with the affinity coefficient and the maximum value appear around where the affinity coefficient is 1.5 and decreased rapidly for upper value of 1.5. In addition, the critical wavelengths of perturbations are proven to be directly proportional to the equimolar dividing radii of the liquid threads.

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A Study on Effect of Temperature of Press Forging on AZ31 Magnesium Alloy

  • Hwang, Jong-Kwan;Kang, Dae-Min
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.3 no.1
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    • pp.66-71
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    • 2004
  • Magnesium alloys have been widely used for many structural components of automobiles and aircraft because of high specific strength and good cast-ability in spite of hexagonal closed-packed crystal structure of pure magnesium. In this study, it is studied about the forming characteristics of press forging of AZ31 magnesium alloy by MSC/MARC in case of material having one boss and MSC/Supeiforge in case of material having multi-boss with heat transfer analysis during deformation at elevated temperature. For these results it is simulated about temperature distribution, strain distribution, and stress distribution of AZ31 Magnesium alloy. During the press forging, foot regions of bosses showed greater temperature rise than other areas of AZ31 sheet. Finally the plastic strain of AZ31 sheet did not remarkably vary with increasing temperature from 373 to 473K, while it significantly increased as the forming temperature increased from 473 to 573K, which is related with the change in micro-structures, such as dynamic re-crystallization occurring during the deformation process.

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