• Tribology and Lubricants
• /
• 제32권4호
• /
• pp.132-139
• /
• 2016

The piston of a marine diesel engine works under severe conditions, including a combustion pressure of over 180 bar, high thermal load, and high speed. Therefore, the analyses of the fatigue strength, thermal load, clamping (bolting) system and lubrication performance are important in achieving a robust piston design. Designing the surface profile and the skirt ovality carefully is important to prevent severe wear and reduce frictional loss for engine efficiency. This study performs flexible multi-body dynamic and elasto-hydrodynamic (EHD) analyses using AVL/EXCITE/PU are performed to evaluate tribological characteristics. The numerical techniques employed to perform the EHD analysis are as follows: (1) averaged Reynolds equation considering the surface roughness; (2) Greenwood_Tripp model considering the solid_to_solid contact using the statistical values of the summit roughness; and (3) flow factor considering the surface topology. This study also compares two cases of skirt shapes with minimum oil film thickness, peak oil film pressure, asperity contact pressure, wear rate using the Archard model and friction power loss (i.e., frictional loss mean effective pressure (FMEP)). Accordingly, the study compares the calculated wear pattern with the field test result of the piston operating for 12,000h to verify the quantitative integrity of the numerical analysis. The results show that the selected profile and the piston skirt ovality reduce friction power loss and peak oil film pressure by 7% and 57%, respectively. They also increase the minimum oil film thickness by 34%.

• Tribology and Lubricants
• /
• 제33권2호
• /
• pp.37-44
• /
• 2017

A DE-side LBP tilting pad journal bearing of a 1-stage overhung heat-pump compressor in a propylene process exhibited abnormal high-temperature behavior. Its temperature had been relatively high at $78^{\circ}C$ from the beginning of operation. In 2014, after three years of operation, it increased suddenly and reached $103^{\circ}C$. Installing a varnish removal equipment and others managed to stabilize the temperature at $95^{\circ}C$. We undertook a troubleshooting approach for reviewing the comprehensive status and integrity of the temperature design of the bearing. We performed lubrication and heat-balance analysis, based on the design engineering data and documents supplied by the OEM. For the base design data of DE-side TPJB, evaluating the effects of key design variables on bearing metal temperature showed that firstly, increasing the bearing clearance and supply oil flow-rate, and next, changing the oil type, and finally, increasing the machined pad clearance and offset, are more effective in reducing the bearing metal temperature. Furthermore, a clarification meeting with the OEM revealed that an incorrect decision had been made to decrease the bearing clearance to eliminate the SSV harshness issue, while not maintaining a sufficient oil flow-rate. We conducted a detailed retrofit design analysis, wherein we increased the oil flow-rate and bearing clearance by decreasing the preload. We predicted that the bearing temperature would decrease to $63^{\circ}C$ from $75.7^{\circ}C$ even at the rerate condition. Finally, after installing and operating a retrofit replacement bearing in 2015, the bearing temperature stabilized at a low temperature of $65^{\circ}C$. Currently (January. 2017), two year later, the bearing metal temperature remains at $65^{\circ}C$. Therefore, we can conclude that the abnormal high-temperature behavior of the bearing has been resolved completely.

• 한국압력기기공학회 논문집
• /
• 제13권2호
• /
• pp.75-83
• /
• 2017

In severe accident conditions of light water reactors, the loss of coolant may cause problems in integrity of zirconium fuel cladding. Under the condition of the loss of coolant, the zirconium fuel cladding can be exposed to high temperature steam and reacted with them by producing of hydrogen, which is caused by the failure in oxidation resistance of zirconium cladding materials during the loss of coolant accident scenarios. In order to avoid these problems, we develop a multi-metallic layered composite (MMLC) fuel cladding which compromises between the neutronic advantages of zirconium-based alloys and the accident-tolerance of non-zirconium-based metallic materials. Cold pilgering process is a common tube manufacturing process, which is complex material forming operation in highly non-steady state, where the materials undergo a long series of deformation resulting in both diameter and thickness reduction. During the cold pilgering process, MMLC claddings need to reduce the outside diameter and wall thickness. However, multi-layers of the tube are expected to occur different deformation processes because each layer has different mechanical properties. To improve the utilization of the pilgering process, 3-dimensional computational analyses have been made using a finite element modeling technique. We also analyze the dimensional change, strain and stress distribution at MMLC tube by considering the behavior of rolls such as stroke rate and feed rate.

• 한국방사성폐기물학회:학술대회논문집
• /
• 한국방사성폐기물학회 2003년도 가을 학술논문집
• /
• pp.229-232
• /
• 2003

고준위 방사성폐기물 처분장에서 적용하고 있는 다중 방벽의 한 부분인 처분 용기는 벤토나이트 완충재의 팽윤과 지압으로부터 폐기물을 역학적으로 안전하게 보호함과 동시에 일정 기간 방사성폐기물의 유출을 억제하는 역할을 한다. 용기는 엄격한 재질 선정과 품질 보증을 거쳐 건전성을 확보하나 보수적인 관점에서 보면 용기 제작 과정이나 수송 중 예상치 못한 사건으로 인해 불량품이 발생할 개연성이 있다. 본 연구에서는 이와 같은 사고 시나리오를 가정할 경우 불량 용기를 포함한 전체 용기에 거치된 방사성폐기물의 시간에 따른 환경 위해도를 평가하였다. 본 연구결과 일부 처분 용기에 초기 파손이 발생하더라도 규제치를 잘 만족하는 것으로 판명되었다.

• Nuclear Engineering and Technology
• /
• 제38권4호
• /
• pp.375-382
• /
• 2006

Characterization tests (load vs. displacement curve) are conducted for the springs of Zirconium alloy spacer grids for an advanced LWR fuel assembly. Twofold testing is employed: strap-based and assembly-based tests. The assembly-based test satisfies the in situ boundary conditions of the spring within the grid assembly. The aim of the characterization test via the aforementioned two methods is to establish an appropriate assembly-based test method that fulfills the actual boundary conditions. A characterization test under the spacer grid assembly boundary condition is also conducted to investigate the actual behavior of the spring in the core. The stiffness of the characteristic curve is smaller than that of the strap-wised boundary condition. This phenomenon may cause the strap slit condition. A spacer grid consists of horizontal and vertical straps. The strap slit positions are differentiated from each other. They affords examination of the variation of the external load distribution in the grid spring. Localized legions of high stress and their values are analyzed, as they may be affected by the spring shape. Through a comparison of the results of the test and FE analysis, it is concluded that the present assembly-based analysis model and procedure are reasonably well conducted and can be used for spring characterization in the core. Guidelines for improving the mechanical integrity of the spring are also discussed.

• 한국전산구조공학회논문집
• /
• 제29권1호
• /
• pp.1-8
• /
• 2016

본 논문에서는 원심식 대형 압축기 구동용 모터 베이스 프레임의 구조해석 및 콘크리트 타설에 따른 구조안전성 평가를 수행하였다. 먼저 모터 베이스 프레임에 적용되는 네 가지 하중조건에 따른 구조해석을 진행하고 최대 비틀림 에너지 이론 및 Mohr-Coulomb 이론을 통하여 구조안전성을 평가하였다. 구조해석 결과에서 취약한 구조안전성을 나타낸 연결부 등의 불연속적인 부분에서 발생하는 국부응력에 대하여 ASME VIII Div. 2에 따른 구조안전성 평가를 적용함으로써 좀 더 합리적으로 구조안전성 평가를 수행할 수 있었다. 또한, 모터 베이스 프레임 내부에 콘크리트 타설 및 미타설에 따른 구조해석 및 ASME 구조안전성 평가를 통하여 모터 베이스 프레임의 구조안전성을 정량적으로 비교하여 콘크리트 타설로 인한 구조 안전성의 향상을 확인하였다.

• Nuclear Engineering and Technology
• /
• 제42권3호
• /
• pp.249-258
• /
• 2010

Recently, many utilities have considered interim dry storage of spent nuclear fuel as an option for increasing spent fuel storage capacity. Foreign nuclear regulatory committees have provided some regulatory and licensing requirements for relatively low- and medium-burned spent fuel with respect to the prevention of spent fuel degradation during transportation and interim dry storage. In the present study, the effect of cladding creep and hydride distribution on spent fuel degradation is reviewed and performance tests with high-burned Zircaloy-4 and advanced Zr alloy spent fuel are proposed to investigate the effect of burnup and cladding materials on the current regulatory and licensing requirements. Creep tests were also performed to investigate the effect of temperature and tensile hoop stress on hydride reorientation and subsequently to examine the temperature and stress limits against cladding material failure. It is found that the spent fuel failure is mainly caused by cladding creep rupture combined with mechanical strength degradation and hydride reorientation. Hydride reorientation from the circumferential to radial direction may reduce the critical stress intensity that accelerates radial crack propagation. The results of cladding creep tests at $400^{\circ}C$ and 130MPa hoop stress performed in this study indicate that hydride reorientation may occur between 2.6% to 7.0% strain in tube diameter with a hydrogen content range of 40-120ppm. Therefore, it is concluded that hydride re-orientation behaviour is strongly correlated with the cladding creep-induced strain, which varies as functions of temperature and stress acting on the cladding.

• Nuclear Engineering and Technology
• /
• 제46권2호
• /
• pp.169-182
• /
• 2014

High-performance research reactors require fuel that operates at high specific power to high fission density, but at relatively low temperatures. Research reactor fuels are designed for efficient heat rejection, and are composed of assemblies of thin-plates clad in aluminum alloy. The development of low-enriched fuels to replace high-enriched fuels for these reactors requires a substantially increased uranium density in the fuel to offset the decrease in enrichment. Very few fuel phases have been identified that have the required combination of very-high uranium density and stable fuel behavior at high burnup. U-Mo alloys represent the best known tradeoff in these properties. Testing of aluminum matrix U-Mo aluminum matrix dispersion fuel revealed a pattern of breakaway swelling behavior at intermediate burnup, related to the formation of a molybdenum stabilized high aluminum intermetallic phase that forms during irradiation. In the case of monolithic fuel, this issue was addressed by eliminating, as much as possible, the interfacial area between U-Mo and aluminum. Based on scoping irradiation test data, a fuel plate system composed of solid U-10Mo fuel meat, a zirconium diffusion barrier, and Al6061 cladding was selected for development. Developmental testing of this fuel system indicates that it meets core criteria for fuel qualification, including stable and predictable swelling behavior, mechanical integrity to high burnup, and geometric stability. In addition, the fuel exhibits robust behavior during power-cooling mismatch events under irradiation at high power.

• 한국전산구조공학회논문집
• /
• 제31권5호
• /
• pp.243-250
• /
• 2018

본 논문에서는 복합재 판 스프링의 설계 최적화를 위해 유전자 알고리즘을 사용한 적층 최적화 과정을 제시하였다. 다목적 소형 승합 자동차 판 스프링을 유한요소모델로 구성하여 초기 설계를 검증한 이후, 유전자 알고리즘을 통해 복합재료의 적층수와 적층각도를 최적화하는 과정을 기술하였다. 최적화 과정을 통해 판 스프링의 하중 감소과정, 반복수에 따라 강 구조의 해석 결과와 비교하였다. 더불어 유전자 알고리즘을 통해 최적화된 적층 시퀀스를 구조에 적용하여 구조의 건전성을 검증하기 위해 유한요소 모델로 구성하여 안전여유를 계산하였다. GA를 적용할 때, 복합재료 판 스프링의 적층 두께와 적층 각을 획득하였으며, 이는 적절한 강도와 강성으로 최소 무게를 달성하는데 기여한다. 동일한 설계 매개 변수 및 최적화 조건에서 강철된 판 스프링을 복합재 판 스프링으로 교체하면 65.6%의 중량이 감소한다.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2007년도 동계학술발표대회 논문집
• /
• pp.305-309
• /
• 2007

FTL(Fuel Test Loop) is a facility that confirms performance of nuclear fuel at a similar irradiation condition with that of nuclear power plant. FTL construction work began on August, 2006 and ended on March, 2007. During Construction, ensuring the worker's safety was the top priority and installation of the FTL without hampering the integrity of the HANARO was the next one. The installation works were done successfully overcoming the difficulties such as on the limited space, on the radiation hazard inside the reactor pool, and finally on the shortening of the shut down period of the HANARO. The Commissioning of the FTL is to check the function and the performance of the equipment and the overall system as well. The FTL shall start operation with high burn up test fuels in early 2008 if the commissioning and licensing progress on schedule.