• International Journal of Advanced Culture Technology
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• 제3권1호
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• pp.90-100
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• 2015

Green technologies such as renewable energy resources, Electric Vehicles and Plug-in Hybrid Electric Vehicles (EVs/PHEVs), electric locomotives, etc. are continually increasing at the existing power network especially distribution levels, which are Medium Voltage (MV) and Low Voltage (LV). It can be noted that the increasing level of green technologies is driven by the reduction emission policies of carbon dioxide ($CO_2$). The green technologies can affect the quality of power, and hence its impacts of are analysed. In practical, the environment such as wind, solar irradiation, temperature etc. are uncontrollable, and therefore the output power of renewable energy in that area can be varied. Moreover, the technology of the EVs/PHEVs is still developed in order to improve the performance of supply and driving systems. This means that these developed can cause harmonic distortion as the control system is mostly used power electronics. Therefore, this paper aims to analyse the voltage variation and harmonic distortion in distribution power network in urban area in Europe due to the combination between wind turbine, hydro turbine, photovoltaic (PV) system and EVs/PHEVs. More realistic penetration levels of SSDGs and EVs/PHEVs as forecasted for 2020 is used to analyse. The dynamic load demands are also taken into account. In order to ensure the accurate of simulation results, the practical parameters of distribution system are used and the international standards such as Institute of Electrical and Electronics Engineers (IEEE) standards are also complied. The suggestion solutions are also presented. The MATLAB/Simulink software is chosen as it can support complicate modelling and analysis.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2001년도 춘계학술대회 논문집
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• pp.119-126
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• 2001

The potential pollution problems resulting from tanker collision necessitate the requirement for an effective structural design and the development of relevant safety regulation. During a few decades, the great effort has been made by International Maritime Organization and the Administration, etc, to reduce oil spillage from collision accidents. However there is still a need for investigation in the light of structural evaluation method for the experiments and rational analysis, and design development for an operational purpose of ships. This study is aimed at investigating a complicated structural response of bow structures of oil carriers for assessing the energy dissipation and crushing mechanics of striking vessel through a methodology of the numerical analysts for the various models and its design changes. Through this study an optimal bow construction absorbing great portion of kinetic energy in the least penetration depth prior to reach to the cargo area and an effective location of collision bulkhead are investigated. In order to obtain a rational results in this study, three stages of response analysis procedures are performed as follows; 1). 16 simplified ship models are used to investigate the structural response against bow collision with variation of primary and secondary members. Mass and speed are also varied in two conditions. 2). 21 models conisted of 5 size of full scaled oil carriers are used to perform the collision simulation with the various sizes and deadweight delivered in a recent which are complied with SOLAS and MARPOL. 3). 36 models of 100k oil carrier are used to investigate the structural response and its influence to the collision bulkhead against bow collision in variation with location of collision bulkhead, primary mombers, framing system and colliding conditions, etc.

• 한국지반공학회논문집
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• 제19권3호
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• pp.23-31
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• 2003

지난 반세기 동안 검측공 탄성파시험은 시험 장비 및 그 배치에 따라 크로스홀, 다운홀, 서스펜션로깅과 같은 시험으로 발전하였다. 이런 현장시험은 장비와 시험기법이 꾸준히 개선되어 지반 및 지진공학 분야의 부지특성규명에 매우 값진 기술이 되었다. 그러나 이 기술은, 공학적 의의와 중요성에도 불구하고, 표준관입 시험처럼 실무에 보편적으로 적용되지 못하고 있다. 그 이유는 장비가 복잡 정교할 뿐만 아니라, 사용하기 어렵고 비싸기 때문이다. 이 연구에서는 경제적이고 실용적인 지반의 동적물성치 계측 기술 개발을 목표로 하여 인홀 시험법을 연구하였다. 이 연구에서 개발한 인홀장비 시작품은 NX 크기의 검측공에 사용하고 맨손으로 다룰 정도로 작고 가볍다. 이 장비의 발진장치는 여러 현장에서 크로스홀시험을 통하여 그 성능을 검증하였고 꾸준히 개선되고 있다. 세 현장에서 인홀시험을 수행하고 그 결과를 크로스홀시험 결과와 비교하여 타당성을 검증하였다.

• The Korean Journal of Pain
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• 제20권1호
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• pp.26-30
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• 2007

Background: Epidural steroid injections (ESI) are a common treatment for spinal disorders. Previous research has shown that aspiration of the syringe is not a sensitive test for placement of an intravascular needle. Serious complications have been reported from injection of steroids and local anesthetics into the vascular space. In addition to safety concerns, the efficacy may decline with partial injection outside the desired epidural location. We hypothesized that incidence of vascular problems is increased in patients who undergo spine surgery compared with the patients who don't undergo spine surgery. We investigated the incidence of vascular problems during lumbosacral transforaminal ESI and we compared the difference of vascular problems between the patients who undergo spinal surgery and those patients who don't undergo spinal surgery. Methods: Two hundreds and three patients were consecutively recruited and they received 299 fluoroscopically guided lumbosacral transforaminal ESIs. Injection of contrast was performed under live dynamic fluoroscopy with using digital substraction analysis. The observed uptake pattern was classified into one of three categories: flashback, aspirated, and positive contrast with negative flashback and aspiration. Results: The vascular incidence rate was 20.4%. Transforaminal ESIs performed at S1 had avascular incidence rate of 27.8% compared with 17.7% for all the other lumbar injection sites. The sensitivity of spontaneous observation of blood in the needle hub or blood aspirate for predicting an intravascular injection in lumbar transforaminal ESIs was 70.4%. Conclusions: There is a high incidence of intravascular problems when performing transforaminal ESIs, and this is significantly increased in patients with previous spine surgery. Using a flash or blood aspiration to predict an intravascular injection is not sensitive therefore; a negative flash or aspiration is not reliable. Fluoroscopically guided procedures without contrast confirmation are prone to instill medications intravascularly. This finding confirms the need for not only fluoroscopic guidance, but also for contrast injection instillation when performing lumbosacral transforaminal ESIs, and especially for patients with previous spine surgery.

• 에너지공학
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• 제24권1호
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• pp.132-136
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• 2015

바이오디젤은 재생가능한 친환경적인 연료로서 화석연료의 대체에너지로 수송분야에서 각광받고 있다. 따라서 바이오디젤의 사용량은 향후 꾸준히 증가할 것으로 보이며, 이에 대한 연구가 필요하다. 따라서 본 연구에서는 순수 디젤 대비 바이오디젤이 질량기준으로 0%, 5%, 20%, 50%, 100% 혼합된 연료를 사용하여 분무 및 연소실험을 진행하고, 분무각, 평균 입경, 열발생율 등의 특성을 도출하였다. 실험 결과, 바이오디젤의 혼합률이 증가할수록 연료의 점도 및 밀도가 증가하여 분무각과 특정 위치에서의 평균 입경이 작아지는 것을 확인할 수 있었으며, 바이오디젤의 함산소 특성으로 인해 초기 연소가 촉진되며, 이로 인해 연소 종료 시점이 앞당겨 지는 것을 볼 수 있었다.

• Nuclear Engineering and Technology
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• 제50권2호
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• pp.218-222
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• 2018

An oxide-dispersion-strengthened (ODS) layer was formed on Zircaloy-4 tubes by a laser beam scanning process to increase mechanical strength. Laser beam was used to scan the yttrium oxide ($Y_2O_3$)-coated Zircaloy-4 tube to induce the penetration of $Y_2O_3$ particles into Zircaloy-4. Laser surface treatment resulted in the formation of an ODS layer as well as microstructural phase transformation at the surface of the tube. The mechanical strength of Zircaloy-4 increased with the formation of the ODS layer. The ring-tensile strength of Zircaloy-4 increased from 790 to 870 MPa at room temperature, from 500 to 575 MPa at $380^{\circ}C$, and from 385 to 470 MPa at $500^{\circ}C$. Strengthening became more effective as the test temperature increased. It was noted that brittle fracture occurred at room temperature, which was not observed at elevated temperatures. Resistance to dynamic high-temperature bursting improved. The burst temperature increased from 760 to $830^{\circ}C$ at a heating rate of $5^{\circ}C/s$ and internal pressure of 8.3 MPa. The burst opening was also smaller than those in fresh Zircaloy-4 tubes. This method is expected to enhance the safety of Zr fuel cladding tubes owing to the improvement of their mechanical properties.

• 한국전산구조공학회논문집
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• 제31권6호
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• pp.373-380
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• 2018

본 논문에서는 다중적층 유리의 고속 충돌체에 의한 충돌/침투 파괴 현상을 해석하기 위해 페리다이나믹 동적 해석 기법을 적용한다. 대부분의 다중적층 유리 구조물들은 다수의 주요 유리층들이 상대적으로 매우 얇은 탄성 필름으로 접착되어서 만들어진다. 따라서 다중적층 구조물의 수치해석 모델을 구성하는 것은 까다롭고 비용이 많이 든다. 본 연구에서는 실제 절점을 대신하여 가상의 절점들을 주요층들 사이에 위치시키고 상호작용시키는 비국부 가상 층간구조 모델링을 도입하여 보다 효율적으로 다중적층 구조를 모델링하였다. 또한 고속 충돌체와의 충돌 및 침투 현상을 해석하기 위해 페리다이나믹 비국부 접촉 모델이 고려되었다. 7개의 유리층과 하나의 탄성 백킹층이 폴리비닐부티랄 필름으로 부착된 다중적층 유리의 충돌 파괴 해석을 통해 제안된 해석 모델의 손상 파괴 적용 가능성을 확인하였다.

• 대한금속재료학회지
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• 제47권12호
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• pp.834-841
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• 2009

A study on the welding of electrogalvanized TRIP (Transformation-Induced Plasticity) steels was done to compare the life of the electrode and the alloying phenomena on the electrode tip surface using singlephase AC and inverter-DC resistance welding processes. A longer life of the electrode (>200 welds) was achieved using the inverter-DC welding process. The tensile shear strength was higher in the electrode life test when welded with the inverter DC welding machine it maintained a higher value even when the welding nugget diameter was smaller than specified. When spot-welding was conducted using the single-phase AC welding process, a higher wear rate of the electrode was observed compared to that with the inverter-DC process. An alloying layer used to determine the rate of electrode growth showed differences in the metallurgical features of the surface alloying and Zn penetration depending on whether the single-phase AC process or the inverter-DC welding process was used. Moreover, changes in the dynamic resistance during the electrode life test were correlated with the electrode wear (or growth) rate.

• Structural Engineering and Mechanics
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• 제77권3호
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• pp.329-342
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• 2021

In this paper, the effect of different steel bar configurations on the quasi-static punching and impact response of concrete slabs was studied. A total of forty RC square slab specimens were cast in two groups of concrete strengths of 40 and 63 MPa. In each group of twenty specimens, ten specimens were reinforced at the back face (singly reinforced), and the remaining specimens were reinforced on both faces of the slab (doubly reinforced). Two rebar spacing of 25 and 100 mm, with constant reinforcement ratio and effective depth, were used in both singly and doubly reinforced slab specimens. The specimens were tested against the normal impact of cylindrical projectiles of hemispherical nose shape. Slabs were also quasi-statically tested in punching using the same projectile, which was employed for the impact testing. The experimental response illustrates that 25 mm spaced rebars are effective in (i) decreasing the local damage and overall penetration depth, (ii) increasing the absorption of impact energy, and (iii) enhancing the ballistic limit of RC slabs. The ballistic limit was predicted using the quasi-static punching test results of slab specimens showing a strong correlation between the dynamic perforation energy and the energy required for quasi-static perforation of slabs.

• Advances in nano research
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• 제12권5호
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• pp.529-547
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• 2022

Graphene is one of the strongest, stiffest, and lightest nanoscale materials known to date, making it a potentially viable and attractive candidate for developing lightweight structural composites to prevent high-velocity ballistic impact, as commonly encountered in defense and space sectors. In-plane twist in bilayer graphene has recently revealed unprecedented electronic properties like superconductivity, which has now started attracting the attention for other multi-physical properties of such twisted structures. For example, the latest studies show that twisting can enhance the strength and stiffness of graphene by many folds, which in turn creates a strong rationale for their prospective exploitation in high-velocity impact. The present article investigates the ballistic performance of twisted bilayer graphene (tBLG) nanostructures. We have employed molecular dynamics (MD) simulations, augmented further by coupling gaussian process-based machine learning, for the nanoscale characterization of various tBLG structures with varying relative rotation angle (RRA). Spherical diamond impactors (with a diameter of 25Å) are enforced with high initial velocity (V_i) in the range of 1 km/s to 6.5 km/s to observe the ballistic performance of tBLG nanostructures. The specific penetration energy (E_p^*) of the impacted nanostructures and residual velocity (V_r) of the impactor are considered as the quantities of interest, wherein the effect of stochastic system parameters is computationally captured based on an efficient Gaussian process regression (GPR) based Monte Carlo simulation approach. A data-driven sensitivity analysis is carried out to quantify the relative importance of different critical system parameters. As an integral part of this study, we have deterministically investigated the resonant behaviour of graphene nanostructures, wherein the high-velocity impact is used as the initial actuation mechanism. The comprehensive dynamic investigation of bilayer graphene under the ballistic impact, as presented in this paper including the effect of twisting and random disorder for their prospective exploitation, would lead to the development of improved impact-resistant lightweight materials.