• Nuclear Engineering and Technology
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• 제56권3호
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• pp.873-879
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• 2024

A sodium-cooled fast reactor (SFR) core has a potential of prompt criticality due to a change of core material distribution during a severe accident, and the resultant energy release has been one of the safety issues of SFRs. In this study, the safety assessment of an unprotected loss-of-flow (ULOF) in a small SFR (SSFR) has been performed using the SIMMER-IV computer code, which couples the models of space- and time-dependent neutronics and multi-component, multi-field thermal hydraulics in three dimensions. The code, therefore, is applicable to the simulations of transient behaviors of extended disrupted core material motion and its reactivity effects during the transition phase (TP) of ULOF, including a potential of prompt-criticality power excursions driven by fuel compaction. Several conservative assumptions are used in the TP analysis by SIMMER-IV. It was found out that one of the important mechanisms that drives the reactivity-inserting fuel motion was sodium vapor pressure resulted from a fuel-coolant interaction (FCI), which itself was non-energetic local phenomenon. The uncertainties relating to FCI is also evaluated in much conservative way in the sensitivity analysis. From this study, the ULOF characteristics in an SSFR have been understood. Occurrence of recriticality events under conservative assumptions are plausible, but their energy releases are limited.

• Tribology and Lubricants
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• 제22권6호
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• pp.342-349
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• 2006

In this study, a dynamic behavior of rotor-bearing system used in CNG compressor has been investigated using the combined methodologies of finite elements and transfer matrices. The finite element is formulated including the field element for a shaft section and the point element for roller bearings. The Houbolt method is used to consider the time march for the integration of the system equations. The transient whirl response of rotating shaft supported on roller bearings is obtained, considering compression forces and unbalance forces at eccentric crank-pin part. And, the steady state displacements of the rotor are compared with a variation in stiffness coefficient of roller bearings. Results show that the loci of crankshaft considering unbalance forces and external compression forces are more severe in whirl motion than with only unbalance forces.

• Tribology and Lubricants
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• 제17권1호
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• pp.56-63
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• 2001

The dynamic behavior of rotor-bearing system used in swash plate compressor has been investigated using the combined methodologies of finite elements and transfer matrices. The finite element is formulated including the field element for a shaft section and the point element for swash plate, disk pulley and bearings. The Houbolt method is used to consider the time march for the integration of the system equations. The transient whirl response of rotating shaft supported on roller bearings is obtained, considering compression forces and unbalance forces at swash plate and driving pulley. And, the steady state displacements of the rotor are compared with a variation in unbalance mass. Results show that the loci of rotating shaft considering unbalance forces and external compression forces are more severe in flutter motion than with only unbalance forces.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제34회 추계학술대회 개최
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• pp.230-236
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• 2001

We developed a built-in sensor bearing to measure the rotor motion of a rolling piston type compressor for the air conditioner. Because of needs for the high efficiency and long life span of compressor, and the usage of alternative refrigerants, the operating condition of the compressor becomes more severe. The accurate measurement of the rotor motion of the compressor can contribute greatly to the design and analysis of the hydrodynamic bearing. However, it is difficult to measure accurately the shaft behavior of small compressor because of the small space for the sensor mount, high temperature and pressure of compressor, oil mixed with refrigerant, and electromagnetic noise of the motor. To overcome these difficulties, we develop the cylindrical capacitive sensor that is built in the hydrodynamic bearing and calibrate the built-in sensor bearing indirectly through measuring the oil relative permittivity. We measured the rotor motion as well as suction and discharge pressures in various conditions. The several experimental results show that the developed built-in sensor bearing can measure the rotor motion not only in steady state but also in transient state.

• 대한조선학회논문집
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• 제47권3호
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• pp.291-305
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• 2010

A three-dimensional time-domain calculation method is of crucial importance in prediction of the motions and wave loads of a ship advancing in a severe irregular sea. The exact solution of the free surface wave-ship interaction problem is very complicated because of the essentially nonlinear boundary conditions. In this paper, an approximate body nonlinear approach based on the three-dimensional time-domain forward-speed free-surface Green function has been presented. The Froude-Krylov force and the hydrostatic restoring force are calculated over the instantaneous wetted surface of the ship while the forces due to the radiation and scattering potentials over the mean wetted surface. The time-domain radiation and scattering potentials have been obtained from a time invariant kernel of integral equations for the potentials which are discretized according to the second-order boundary element method (Hong and Hong 2008). The diffraction impulse-response functions of the Wigley seakeeping model advancing in transient head waves at various Froude numbers have been presented. A simulation of coupled heave-pitch motion of a long rectangular barge advancing in regular head waves of large amplitude has been carried out. Comparisons between the linear and the approximate body nonlinear numerical results of motions and wave loads of the barge at a nonzero Froude number have been made.

• International Journal of Automotive Technology
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• 제6권6호
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• pp.615-623
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• 2005

In this research, an effective technique was examined to improve the drift running performance. Concretely, the driver model by which the counter steer was done was assumed to the model by which the vehicle body slip angle (and the vehicle body slip angle velocity) was feed back. Next, the effectiveness of the system which added the assist steer angle corresponding to the steering wheel angle velocity to a front wheel steer angle was clarified as a drift running performance improvement technique of the vehicle. As a result, because the phase advances when the differentiation steer assistance is added, it has been understood to be able to cover the delay of the counter steer when the drift running. Therefore, it has been understood that the drift control does considerably easily. Moreover, it has been understood that the differentiation steer assistance acts effectively at the drift cornering by which the drift angle is maintained in cornering and the severe lane change with a drift at a situation. That is, it was understood to be able to settle to the drift angle of the aim quickly at the time of the drift cornering because the delay of the control steer angle of the counter steer was improved. Moreover, it was understood for the transient overshoot of the vehicle tracks to be able to decrease, and to return to the state of stability quickly at the severe lane change.

• 해양환경안전학회지
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• 제25권3호
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• pp.306-312
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• 2019

This paper investigates to design a controller for maritime autonomous surface ship (MASS) by means of adaptive super-twisting algorithm (ASTA). A input-out feedback linearization method is considered for multi-input multi-output (MIMO) system. Sliding Mode Controller (SMC) is suitable for MASS subject to ocean environments due to its robustness against parameter uncertainties and disturbances. However, conventional SMC has inherent disadvantages so-called, chattering phenomenon, which resulted from the high frequency of switching terms. Chattering may cause harmful failure of actuators such as propeller and rudder of ships. The main contribution of this work is to address an appropriate controller for MASS, simultaneously controls surge and yaw motion in severe step inputs. Proposed control mechanism well provides convergence bewildered by external disturbances in the middle of steady-state responses as well as chattering attenuation. Also, the adaptive algorithm is contributed to reducing non-overestimated value of control gains. Control inputs of surge and yaw motion are displayed by smoother curves without excessive control activities of actuators. Finally, no overshoot can be seen in transient responses.

• Clinics in Shoulder and Elbow
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• 제1권2호
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• pp.167-174
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• 1998

Since the first description by Cotton, there have been sporadic reports about the inferior subluxation of the shoulder. Nevertheless there is still a lack of consensus regarding the mechanism of occurrence, evolution and treatment. We have experienced six cases of inferior sublusation(five cases after trauma and one case after surgery) which resolved over time. Analysis of the clinical informations including serial radiographs, data from clinical examination and electromyography(EMG) revealed the following results. All the five post-traumatic inferior subluxations were noted in women with an average age of 59 years after direct trauma resulting in fracture of the proxiaml hrnerus(4) or clavicle(1), of which nerve injury was proven by EMG in three. One case occurred after Bankart repair by stretch injury to the axillary nerve. The presenting symptom was unusually severe pain on passive motion. Absence of anterior or posterior displacement wasl confirmed by radiographs. All the cases seemed to have delayed onset of subluxation except one. The subluxed hu.meral head was concentrically reduced at an average 11 weeks(range 3-23 weeks) from the supposed time of occurrence and the acromiohumeral interval measUred on the standing anteroposterior radiographs decreased to 9.4 mm ftom 23 mm. Improvement of pain paralled the reduction. In conclusion, the most common cause of transient inferior subluxation was nerve injury in ou~ series and the prognosis was excellent, however protraction of recovery or leaving permanent subluxation would be possible if .the injured nerve is unrecoverable.

• Earthquakes and Structures
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• 제11권5호
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• pp.905-924
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• 2016

Several two-dimensional analytical beam column joint models with varying complexities have been proposed in quantifying joint flexibility during seismic vulnerability assessment of non-ductile reinforced concrete (RC) frames. Notable models are the single component rotational spring element and the super element joint model that can effectively capture the governing inelastic mechanisms under severe ground motions. Even though both models have been extensively calibrated and verified using quasi-static test of joint sub-assemblages, a comparative study of the inelastic seismic responses under nonlinear time history analysis (NTHA) of RC frames has not been thoroughly evaluated. This study employs three hypothetical case study RC frames subjected to increasing ground motion intensities to study their inherent variations. Results indicate that the super element joint model overestimates the transient drift ratio at the first story and becomes highly un-conservative by under-predicting the drift ratios at the roof level when compared to the single-component model and the conventional rigid joint assumption. In addition, between these story levels, a decline in the drift ratios is observed as the story level increased. However, from this limited study, there is no consistent evidence to suggest that care should be taken in selecting either a single or multi component joint model for seismic risk assessment of buildings when a global demand measure such as maximum inter-storey drift is employed in the seismic assessment framework.

• 대한핵의학회지
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• 제38권3호
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• pp.225-232
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• 2004

목적 : 관상동맥질환을 가진 환자에서는 운동부하 후 일시적인 심근기절로 인하여 좌심실의 벽운동이상과 좌심실구혈률 감소가 발생될 수 있다. 본 연구는 운동 후 좌심실기능저하를 보이는 환자와 그렇지 않은 환자의 관상동맥조영술과 운동부하 심근관류 SPECT소견을 비교분석 하고자 하였다. 대상 및 방법 : 운동부하심전도, 관상동맥조영술 및 심근관류 SPECT를 시행한 환자 중 게이트 SPECT로 구한 좌심실구혈률이 운동 후 5%이상 감소된 36명 (기절심근군)과 운동부하 후 좌심실구혈률 변화가 1%이하인 16명 (비기절심근군)을 대상으로 하였다. 답차를 이용한 운동부하중 심전도검사를 시행하고, 최대 운동부하시 Tc-99m MIBI 740MBq을 투여한 후 이중헤드 감마카메라(Vertex Plus, ADAC)로 부하 심근관류영상을 얻었다. 심혈관조영술은 위 검사로 부터 1개월내에 시행되었다. 결과 : 기절심근군은 비기절심근군에 비해 고콜레스테롤혈증의 빈도가 유의하게 높았으며(45.5 대 7.1%, p=0.01), 당뇨병의 빈도가 높은 경향을 가졌으며, 고혈압의 빈도는 낮은 경향을 가졌으나 통계적으로 유의하지 않았다. 비기절심근군에 비해 기절심근군에서 SPECT 검사상 관류결손의 범위 (18.2% 대 9.1%, p=0.029)와 정도 (13.5 대 6.9, p=0.04)는 더 컸으며, 가역성정도 (7.9 대 4.8, p=0.09)는 더 큰 경향을 가졌으며, 운동부하심전도상 허혈양성 소견의 빈도가 높은 경향을 가졌다(82.9% 대 64.3%, p=0.095). 심혈관조영술상 중증 ($80{\sim}99%$)의 관상동맥협착의 빈도가 높은 경향을 보였으나 (64.7% 대 35.7%, p=0.064), 다혈관질환의 빈도 (62.5% 대 46.2%, p=0.279), 협착정도 (75.8% 대 66.8%, p=0.468)에는 유의한 차이가 없었다. 기절심근군 중 관류결손이 발견되지 않았던 4명 (11.1%) 모두에서 유의한 관상동맥협착이 있었고 혈관재개통술이 시행되었다. 결론 : 운동부하로 5%이상의 좌심실구혈률의 감소를 보이는 환자는 그렇지 않은 환자에 비하여 심근관류 SPECT상 관류결손 크기와 정도가 크며, 가역성이 더 높은 경향을 나타내었으며, 혈관조영술상 관상동맥협착 정도가 중증인 경향을 가지고 있으며, 비록 관류 SPECT상 결손이 없더라도 관상동맥조영술상 혈관 재개통술이 필요할 정도의 유의한 협착이 있어, 이러한 환자에서는 적극적인 진단과 치료적 개입이 필요할 것으로 생각된다.