• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.7
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• pp.58-65
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• 2019

Polymer concrete is expected to be widely used as a building material because it has a shorter hardening time and excellent compression, tensile, bending, bond strength, frictional resistance and abrasion loss compared to general concrete. The polymer concrete has excellent vibration damping performance and research on the use of various reinforcing materials is being conducted. However, in order to completely replace the general concrete and the general anti-vibration reinforcement, such polymer concrete requires an overall review of vibration reduction performance considering physical properties, dynamic properties, productivity and field applicability. In this study, the physical and dynamic properties of polymer concrete by epoxy mixing ratio were compared with those of general concrete. It was appeared that compression, tensile, bending and bond strengths of polymer concrete by epoxy mixing were significantly higher than those of general concrete. Especially, the tensile strength was more than 4 ~ 6.5 times. Based on the basic physical properties of polymer concrete, the damping ratio, which is a dynamic characteristic according to the epoxy mixing ratio, was derived through analytical models and experiments. As a result, the dynamic stiffness of polymer concrete was 20% higher than that of general concrete and the loss rate was about 3 times higher.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.92-102
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• 2020

Porous pavement (PP) has attracted attention as a new alternative measure against road traffic noise. PP refers to pavement that reduces the fines in the asphalt mixture to form voids. These voids can reduce traffic accidents and friction noise. For active application, verification of the noise reduction effect is required. In this study, the noise reduction of single-layer PP(SLPP) and double layer PP(DLPP) was analyzed. First, the Sejong section was selected, and traffic noise was measured using the SPB method on the roadside. The traffic volume, speed, and mixing ratio of large vehicles were measured. As a result, the DLPP was evaluated to be 7.95 dB(A) smaller on average and 7.57dB(A) smaller at the 95% reliability level than the SLPP. The traffic volume was more influential than the speed and the mixing rate of large vehicles. As the traffic volume increased, the noise increased, but the difference in noise between the two pavements decreased gradually. The results showed that the most effective way to reduce road traffic noise is to change the road pavement rather than reduce traffic speed, restrict traffic for heavy vehicles, or reduce traffic volume.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.46-46
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• 2015

강우가 지역별 계절별로 편중되어 있는 우리나라는 수자원의 안정적인 확보와 이용을 위해 다양한 형태의 댐을 건설하여 운영하고 있다. 그러나 대부분의 댐건설을 통해 형성된 저수지들은 탁수 장기화 및 녹조 발생 등의 환경, 생태적인 문제를 겪고 있으며, 그에 따른 사회적 우려로 인해 신규댐 건설을 통한 수자원확보는 더 이상 어려운 실정이다. 이러한 문제에 대응하기 위한 대안으로 기존 댐 저수지들(안동호-임하호)의 구조적 연계운영방안이 진행되고 있다. 본 연구의 목적은 2차원 CE-QUAL-W2모형을 활용하여 안동호와 임하호의 구조적 연결에 따른 탁수의 이동과 각 저수지 내에서의 유동 변화를 해석하는데 있다. 저수지 연계 시나리오는 EL. 138 m 위치에 길이 2 km, 직경 5.5 m 의 콘크리트관(마찰계수 0.05)이 안동호 좌안인 임동면 마리와 임하호 우안 망천리를 연결하는 것으로 가정하였다. 모델의 보정은 실측자료가 풍부한 2006년도 수문사상을 대상으로, 개별 저수지에 대해 수행하였고, 탁수 유동 시나리오 해석은 임하호에 심각한 탁수장기화 문제가 발생했던 2002년을 대상으로 댐 연계 탁수모의를 수행하였다. 안동호와 임하호의 댐 앞에서 모의값과 실측값을 오차를 분석한 결과 탁수예측오차는 AME 0.5~24 mg/L, RMSE 0.7~30.2mg/L의 범위로 비교적 실측값을 잘 반영한 것으로 나타났다. 임하댐의 경우 탁수층의 위치와 두께, 그리고 최고 탁도값을 적절히 재현 하였지만, 안동댐은 최고 탁도값 예측에서 다소 오차가 발생하는 것으로 나타났다. 안동호와 임하호 단독 운영시와 연계 운영시의 탁수변화 파악을 위해 초기 홍수사상이 발생한 8월 이후부터 저수지내의 TSS농도 분포를 비교하였다. 안동호의 경우 댐앞지점의 탁수분포는 수온성층구조에 영향을 받아, 단독 운영시(EL. 130 m)보다 연계운영시(EL. 140 m)에 탁수의 중심이 높은 위치에 형성되었다. 단독 운영시 10월 이후에 전도현상으로 인해 침강되지 않은 잔류 탁수층이 저수지 하부로 확산되었지만, 연계 운영시에는 재부상 되어 상층으로 확산되는 것으로 모의되었다. 또한 연계운영시 유량이동으로 인해 안동호의 탁수 댐앞 도달시간이 짧아지는 것으로 나타났다. 반면 임하호는 연계 운영시 안동댐으로 유출이 생기면서 중층에서 탁수량이 저감되는 것으로 모의되었다. 저수지 내 탁수량 분석을 위해 SS 15 mg/L 이상의 잔류 탁수량을 분석한 결과, 연계운영시 안동호의 평균 잔류탁수량 비율은 11.8% 증가, 임하호의 경우 11.7% 감소하였다. 또한, 탁수의 댐하류 방류일수도 SS 15 mg/L 기준 임하호 9일 저감, 안동호는 70일 증가하여 임하호의 탁수가 안동호의 탁수 장기화에 영향을 주는 것으로 나타났다.

• Journal of the Korean Geotechnical Society
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• v.31 no.11
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• pp.49-60
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• 2015

Open-water sediment disposal has many applications in costal construction. Dumping of sediment in open water can be divided into descending stage under water and sedimentation stage on the seabed, and retained rate is evaluated from analyzed results of these two successive stages. Descending particle cloud have two distinct thermal and swam phase, and trajectory equations for each phase are derived to describe settling velocity and radius of particle cloud. For sedimentation stage, a numerical simulator is used to calculate growth factors for particle fiction angle and current velocity. Retained rate is defined as a mass rate of remained sediment inside the circle which has a center at dumping point on the sea level and user-defined effective radius. Retained rate map for Singapore coast is presented with water depth of 20 m, current velocity of 0.0~1.5 m/s, and effective radius of 5 m. It will decrease sediment mass loss during disposal operation and minimize surrounding environmental pollution.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.973-978
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• 2010

In this paper, we studied the shimmy phenomena of an aircraft nose landing gear considering free-play. Shimmy is a self-excited vibration in lateral and torsional directions of a landing gear during either the take-off or landing. This phenomena is caused by a couple of conditions such as low torsional stiffness of the strut, friction and free-play in the gear, wheel imbalance, or worn parts, and it may make an aircraft unstable. Free-play non-linearity is linearized by the described function for a stability analysis in a frequency domain, and time marching is performed using the fourth-order Runge-Kutta method. We performed the numerical simulation of the nose landing gear shimmy and investigated its linear and nonlinear characteristics. From the numerical results, we found limit-cycle-oscillations at the speed under linear shimmy speed for the case considering free-play and it can be concluded that the shimmy stability can be decreased by free-play.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.5
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• pp.673-678
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• 2013

Creep groan noise occurs at low frequencies immediately after releasing brake pressure or when a car stops. This noise can be used to predict problems in not only the brake system but also the vehicle system. Because of its complexity, it is difficult to determine its characteristics. Therefore, most improvements are conducted by changing the brake pad, and it still remains difficult to conduct a test using a vehicle. In this study, the characteristics of creep groan noise and the effects from a vehicle system are investigated by using vehicles and an NVH chassis-dynamometer through various tests. A new evaluation method for creep groan noise by using a vehicle is proposed, and the possibility of reduction schemes from the viewpoint of the vehicle system is confirmed from the results mentioned above.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.863-868
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• 2009

The drag reduction(DR) for Betaine+Amin and Xantan Gum as kinds of surfactant and Polyacrylamide as kinds of polymer solution according to the fluid velocity, temperature and surfactant concentration were compared experimentally. For this study, two kinds of experimental apparatus for short time and long time measurement were established. Each experimental appratus was equipped with hot water storage tanks, pumps, testing pipe network, flowmeter, two pressure gauges and data logging system was built for them. Results showed that Betaine+Amin and Xanthan Gum as kinds of surfactant had appeared optimal DR around 200-500 ppm and their DR tended to be decreased when flow velocity increased but Polyacrylamide as kinds of polymer solution showed the opposite trend to be increased when flow velocity increased. The both of them showed above 40% DR in the case of better condition by the short term measurement. But Polyacrylamide as kinds of polymer solution showed more degradation than Betaine+Amin and Xanthan Gum as kinds of surfactant by the long term measurement. As a result, Betaine+Amin and Xanthan Gum as kinds of surfactant showed better materials to use to the district heating system.

• Tribology and Lubricants
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• v.30 no.5
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• pp.303-310
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• 2014

In order to reduce friction and improve reliability, researchers have applied various surface texturing methods to highly sliding machine elements such as mechanical seals and piston rings. Despite extensive theoretical research on surface texturing, previous numerical results are only applicable to isothermal and iso-viscous conditions. Because the lubricant flow pattern of textured bearing surfaces is much more complicated than that for non-textured bearings, the Navier?Stokes equation is more suitable than the Reynolds equation for the former. This study carries out a thermohydrodynamic (THD) lubrication analysis to investigate the lubrication characteristics of a single micro-dimpled parallel thrust bearing cell. The analysis involves using the continuity, Navier?Stokes, energy, temperature?viscosity relation, and heat conduction equations with the commercial computational fluid dynamics (CFD) code FLUENT. This study discretizes these equations using the finite volume method and solves them using the SIMPLE algorithm. The results include finding the streamlines, pressure and temperature distributions, and variations in the friction force and leakage for various dimple radii and depths. Increasing the dimple radius and decreasing the depth causes a recirculation flow to form because of a strong vortex, and the oil temperature greatly increases compared with the non-textured case. The present numerical scheme and results are applicable to THD analysis of various surface-textured sliding bearings and can lead to further study.

• Journal of the Korean Geosynthetics Society
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• v.4 no.4
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• pp.3-11
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• 2005

In this study, a large-scale laboratory model test and 2-D numerical analysis were conducted to verify the reinforcement effect by utilizing geotextile bag on the railway roadbed. Static loading which simulated train load was applied on the geotextile-reinforced railway roadbed and also unreinforced railway roadbed. Computer program named Pentagon 2-D which is a part of FEM programs was used in the numerical analysis. Based on the results of laboratory test and 2-D numerical analysis, the effect of load distribution and settlement reduction was found to be depending on the geotextile characteristics, tensile strength of geotextile, and interface friction angle between geotextile bags. In general, the result of 2-D numerical analysis shows lower value than that of laboratory test.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.1
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• pp.75-82
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• 2016

As spreading of train concrete ballast leads to the increase resounding friction noise, an porous sound absorbing block is applied in urban train tunnel as a counterparts against the friction noise. Three steps of major variables tests for an optimal mix design of the block are conducted to pursue the light weight of the block. Pilot property tests of the block for the cases of the fly-ash only as lightweight aggregates are carried satisfying KRT(Korean Rail Transit) and new KRS(Korean Railway Standards). Based on the results of pilot tests, required structural strength and admixture effects are evaluated. Additionally, typical lightweight aggregates are replaced so that lightweight and strength are improved for serviceability of poor working conditions and proper maintenance in urban train tunnel.