• Title/Summary/Keyword: Impact Velocity

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Qualitative Factor Analysis on Speed Reduction of Drivers in Expressways Tunnel Section (고속도로 터널구간 도로이용자 속도감소의 정성적 요인분석 연구)

  • Park, Jun-Tae;Lee, Soo-Beom;Kim, Tae-Ho
    • International Journal of Highway Engineering
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    • v.13 no.4
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    • pp.151-158
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    • 2011
  • Tunnel sections on the expressway are different from rest of sections on the expressway in terms of velocity, the number of passing cars, and vehicle density which, in particular, affect drivers' behavior before and after drivers pass through the tunnel. However, literature review reveals that former studies are too focused on quantitative indicator to consider qualitative aspects. Thus, this study tried to find out qualitative factors affecting speed reduction in tunnel sections based on questionnaire surveys and its analysis in tunnel sections selected by taking consideration of diverse conditions. Analysis showed that factors concerning tunnel configuration (lane width, shoulder width, and tunnel length) related to very long tunnels increasingly popular recently had some effects on reduced speed inside of tunnels. It appeared that visual environment such as visibility of tunnel entrance had an impact in speed reduction and vehicle speed tended to change according to lighting illumination level inside of tunnels. It is expected that continual investment would be made in technological development related to expressway tunnel design and service improvement based on this study.

Trajectory Studies of Methyl Radical Reaction with Iodine Molecule

  • Lee, Sang-Kwon;Ree, Jong-Baik;Kim, Yoo-Hang;Shin, Hyung-Kyu
    • Bulletin of the Korean Chemical Society
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    • v.26 no.9
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    • pp.1369-1380
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    • 2005
  • The reaction of methyl radical with iodine molecule on an attractive potential energy surface is studied by classical trajectory procedures. The reaction occurs over a wide range of impact parameters with the majority of reactive events occurring in the backward rebound region on a subpicosecond scale. A small fraction of reactive events take place in the forward hemisphere on a longer time scale. The ensemble average of reaction times is 0.36 ps. The occurrence of reactive events is strongly favored when the incident radical and the target molecule align in the neighborhood of collinear geometry. Since the rotational velocity of I2 is slow, the preferential occurrence of reactive events at the collinear configuration of $CH_3{\ldots}I{\ldots}$I leads to the reaction exhibiting an anisotropic dependence on the orientation of $I_2$. During the collision, there is a rapid flow of energy from the $H_3C{\ldots}$I interaction to the I-I bond. The $CH_3I$ translation and $H_3C$-I vibration share nearly all the energy released in the reaction, and the distribution of the vibrational energy is statistical. The reaction probability is $\cong$0.4 at the $CH_3$ and I2 temperatures maintained at 1000 K and 300 K, respectively. The probability is weakly dependent on the $CH_3\;and\;I_2$ temperatures between 300 K and 1500 K.

Management Strategies to Conserve Soil and Water Qualities in the Sloping Uplands in Korea (한국의 경사지 밭의 토양 및 물의 보전 관리 전략)

  • Yang, Jae-E.;Ryu, Jin-Hee;Kim, Si-Joo;Chung, Doug-Young
    • Korean Journal of Agricultural Science
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    • v.37 no.3
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    • pp.435-449
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    • 2010
  • Soils in the sloping uplands in Korea are subject to intensive land use with high input of agrochemicals and are vulnerable to soil erosion. Development of the environmentally sound land management strategy is essential for a sustainable production system in the sloping upland. This report addresses the status of upland agriculture and the best management practices for the uplands toward the sustainable agriculture. More than 60% of Korean lands are forest and only 21% are cultivating paddy and upland. Uplands are about 7% of the total lands and about 62% of the uplands are in the slopes higher than 7%. Due to the site-specificity of the upland, many managerial and environmental problems are occurring, such as severe erosion, shallow surface soils with rocky fragments, and loadings of non-point source (NPS) contaminants into the watershed. Based on the field trials, most of the sloping uplands were classified as Suitability Class III-V and the major limiting factor was slope and rock fragments. Due to this, soils were over-applied with N fertilizer, even though N rate was the recommendation. This resulted in decreases in yield, degradation of soil quality and increases in N loading to the leachate. Various case studies drew management practices toward sustainable production systems. The suggested BMP on the managerial, vegetative, and structural options were to practice buffer strips along the edges of fields and streams, winter cover crop, contour and mulching farming, detention weir, diversion drains, grassed waterway, and slope arrangement. With these options, conservation effects such as reductions in raindrop impact, flow velocity, runoff and sediment loss, and rill and gully erosion were observed. The proper management practice is a key element of the conservation of the soil and water in the sloping upland.

Experimental Analysis of the Parameters Governing Scour in Plunge Pool with Cohesionless Bed Material (침강지내 비점성하상의 세굴 지배인자에 대한 실험적 해석)

  • Son, Kwang Ik;Lee, Won Hwan;Cho, Won Cheol
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.13 no.4
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    • pp.123-129
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    • 1993
  • Because the existing scour prediction formulas for plunge pools of pipe culverts and spillways give a wide range of predicted scour depths, it is difficult to estimate actual scour depths. A review of literature showed that wide range of predicted values was caused mostly by lack of thorough analysis of the scour mechanism. In this study, the effects of the parameters govering scour were examined, and the scour potentials were measured. The major variables govering scour were the velocity and size of jet impinging into the plunge pool, the submerged weight of bed material, the ratio of jet size to bed material size, the tail watr depth of the plunge pool, and the angle of jet impact on water surface. The ratio of jet size to bed material size to bed material size was found to be another significant parameter affecting scour for larger bed materials. A densimetric Froude nember of the bed material in incipient motion was formulated. This number represented the scour potential of the jet at the point where the bed material was tested.

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Experimental Study of the Supersonic Free Jet Discharging from a Petal Nozzle (페탈노즐로부터 방출되는 초음속 자유제트에 관한 실험적 연구)

  • Lee, Jun-Hee;Kim, Jung-Bae;Gwak, Jong-Ho;Kim, Heuy-Dong
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.2133-2138
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    • 2003
  • In general, flow entrainment of surrounding gas into a supersonic jet is caused by the pressure drop inside the jet and the shear actions between the jet and the surrounding gas. In the recent industrial applications, like supersonic ejector system or scramjet engine, the rapid mixing of two different gases is important in that it determines the whole performance of the flow system. However, the mixing performance of the conventional circular jet is very low because the shear actions are not enough. The supersonic jet discharging from a petal nozzle is known to enhance mixing effects with the surrounding gas because it produces strong longitudinal vortices due to the velocity differences from both the major and minor axes of petal nozzle. This study aims to enhance the mixing performance of the jet with surrounding gas by using the lobed petal nozzle. The jet flows from the petal nozzle are compared with those from the conventional circular nozzle. The petal nozzles employed are 4, 6, and 8 lobed shapes with a design Mach number of 1.7 each, and the circular nozzle has the same design Mach number. The pitot impact pressures are measured in detail to specify the jet flows. For flow visualization, the schlieren optical method is used. The experimental results reveal that the petal nozzle reduces the supersonic length of the supersonic jet, and leads to the improved mixing performance compared with the conventional circular jet.

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A Numerical Analysis of the Binary Droplet Collision by Using a Level Set Method (레벨셋 방법을 이용한 액적 충돌에 대한 수치해석)

  • Lee, Sang-Hyuk;Hur, Nahm-Keon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.35 no.4
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    • pp.353-360
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    • 2011
  • The prediction of binary droplet collisions is important in the formation of falling drops and the evolution of sprays. The droplet velocity, impact parameter, and drop-size ratio influence the interaction between the droplets. The effect of these parameters results in complicated collision phenomena. Droplet collisions can be classified into four types of interactions: bouncing, coalescence, reflexive separation, and stretching separation. In the present study, the interfacial flow problem of the droplet collision was numerically simulated by using the level set method. 2D axisymmetric simulations on the head-on collisions and 3D simulation on the off-center collisions were performed. The numerical results of droplet behavior after the collision agreed well with the experimental and analytical results. The mixing of the mass of the initial droplets after the collision was also predicted by using different species index of colliding droplets.

A model to develop the porosity of concrete as important mechanical property

  • Alyousef, Rayed;Alabduljabbar, Hisham;Mohamed, Abdeliazim Mustafa;Alaskar, Abdulaziz;Jermsittiparsert, Kittisak;Ho, Lanh Si
    • Smart Structures and Systems
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    • v.26 no.2
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    • pp.147-156
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    • 2020
  • This numerical study demonstrates the porosity conditions and the intensity of the interactions with the aggressive agents. It is established that the density as well as the elastic modulus are correlated to ultrasonic velocity The following investigation assessed the effects of cement grade and porosity on tensile strength, flexural and compressive of Ultra High Performance Concrete (UHPC) as a numerical model in PLAXIS 2d Software. Initially, the existing strength-porosity equations were investigated. Furthermore, comparisons of the proposed equations with the existing models suggested the high accuracy of the proposed equations in predicting, cement grade concrete strength. The outcome obtained showed a ductile failure when un-corroded reinforced concrete demonstrates several bending-induced cracks transfer to the steel reinforcement. Moreover, the outcome also showed a brittle failure when wider but fewer transverse cracks occurred under bending loads. Sustained loading as well as initial pre-cracked condition during the corrosion development have shown to have significant impact on the corrosion behavior of concrete properties. Moreover, greater porosity was generally associated with lower compressive, flexural, and tensile strength. Higher cement grade, on the other hand, resulted in lower reduction in concrete strength. This finding highlighted the critical role of cement strength grade in determining the mechanical properties of concrete.

The Mechanical Effect of Rod Contouring on Rod-Screw System Strength in Spine Fixation

  • Acar, Nihat;Karakasli, Ahmet;Karaarslan, Ahmet A.;Ozcanhan, Mehmet Hilal;Ertem, Fatih;Erduran, Mehmet
    • Journal of Korean Neurosurgical Society
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    • v.59 no.5
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    • pp.425-429
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    • 2016
  • Objective : Rod-screw fixation systems are widely used for spinal instrumentation. Although many biomechanical studies on rod-screw systems have been carried out, but the effects of rod contouring on the construct strength is still not very well defined in the literature. This work examines the mechanical impact of straight, $20^{\circ}$ kyphotic, and $20^{\circ}$ lordotic rod contouring on rod-screw fixation systems, by forming a corpectomy model. Methods : The corpectomy groups were prepared using ultra-high molecular weight polyethylene samples. Non-destructive loads were applied during flexion/extension and torsion testing. Spine-loading conditions were simulated by load subjections of 100 N with a velocity of $5mm\;min^{-1}$, to ensure 8.4-Nm moment. For torsional loading, the corpectomy models were subjected to rotational displacement of $0.5^{\circ}\;s^{-1}$ to an end point of $5.0^{\circ}$, in a torsion testing machine. Results : Under both flexion and extension loading conditions the stiffness values for the lordotic rod-screw system were the highest. Under torsional loading conditions, the lordotic rod-screw system exhibited the highest torsional rigidity. Conclusion : We concluded that the lordotic rod-screw system was the most rigid among the systems tested and the risk of rod and screw failure is much higher in the kyphotic rod-screw systems. Further biomechanical studies should be attempted to compare between different rod kyphotic angles to minimize the kyphotic rod failure rate and to offer a more stable and rigid rod-screw construct models for surgical application in the kyphotic vertebrae.

Finite element analysis for 3-D self-contact problems of C.v.joint rubber boots (3차원 자체접촉을 위한 유한요소해석에 의한 등속조인트 고무부트의 변형해석)

  • Lee, H.W.;Kim, S.H.;Lee, C.H.;Huh, H.;Lee, J.H.;Oh, S.T.
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.12
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    • pp.2121-2133
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    • 1997
  • A finite element code is developed for 3-D self-contact problems, using continuum elements with a SRI(Selective Reduced Integration) scheme to prevent locking phenomenon by the incompressibility of rubber. Contact treatment is carried out in two ways : using the displacement constraints in case of rigid contact ; and imposing the same contact forces on two contact boundaries in case of self-contact. The finite element code developed is applied to the deformation analysis of C.V.joint boots which maintain lubrication conditions and protect the C.V.joint assembly from impact and dust. The boot accompanies large rotation depending on the rotation of the wheel axis and leading to the self-contact phenomena of the boot bellows. Since this contact phenomenon causes wear of the product and has great influence on the endurance life of the product, it is indispensable to carry out stress analysis of the rubber boots. In case of self-contact, various methods for determining contact forces have been suggested with an appropriate contact formulation. Especially, the types of penetration in self-contact are modularized to accelerate conputation with a contact algorithm.

Surface Roughness Impact on Francis Turbine Performances and Prediction of Efficiency Step Up

  • Maruzewski, Pierre;Hasmatuchi, Vlad;Mombelli, Henri-Pascal;Burggraeve, Danny;Iosfin, Jacob;Finnegan, Peter;Avellan, Francois
    • International Journal of Fluid Machinery and Systems
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    • v.2 no.4
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    • pp.353-362
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    • 2009
  • In the process of turbine modernizations, the investigation of the influences of water passage roughness on radial flow machine performance is crucial and validates the efficiency step up between reduced scale model and prototype. This study presents the specific losses per component of a Francis turbine, which are estimated by CFD simulation. Simulations are performed for different water passage surface roughness heights, which represents the equivalent sand grain roughness height. As a result, the boundary layer logarithmic velocity profile still exists for rough walls, but moves closer to the wall. Consequently, the wall friction depends not only on roughness height but also on its shape and distribution. The specific losses are determined by CFD numerical simulations for each component of the prototype, taking into account its own specific sand grain roughness height. The model efficiency step up between reduced scale model and prototype value is finally computed by the assessment of specific losses on prototype and by evaluating specific losses for a reduced scale model with smooth walls. Furthermore, surveys of rough walls of each component were performed during the geometry recovery on the prototype and comparisons are made with experimental data from the EPFL Laboratory for Hydraulic Machines reduced scale model measurements. This study underlines that if rough walls are considered, the CFD approach estimates well the local friction loss coefficient. It is clear that by considering sand grain roughness heights in CFD simulations, its forms a significant part of the global performance estimation. The availability of the efficiency field measurements provides an unique opportunity to assess the CFD method in view of a systematic approach for turbine modernization step up evaluation. Moreover, this paper states that CFD is a very promising tool for future evaluation of turbine performance transposition from the scale model to the prototype.