• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.494-497
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• 2004

This paper presents the analysis results predicted by the upper bound approach in the limit analysis of concrete incorporating the original plastic and crack sliding solutions for short high-strength concrete beams that varied the compressive strength of concrete, and the shear span-to-depth and vertical shear reinforcement ratios. The significance of the distance away from the support to define the location where the yield line starts and the properties of cracked concrete, particularly related to high-strength concrete, is identified.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.177-181
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• 1996

A fundamental study for the production of an internal combustion engine piston by forging is performed through UBET(Upper Bound Elemental Technique) analysis and experiments. In UBET analysis, an optimal preform of the aluminum piston is predicted and the results are compared with the experimental results. The internal flow pattern and and the forging loads according to the different friction condition are investigated.

• Journal of Power Electronics
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• 제18권5호
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• pp.1380-1397
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• 2018

The synchronous reluctance motor (SynRM) servo-drive system has highly nonlinear uncertainties owing to a convex construction effect. It is difficult for the linear control method to achieve good performance for the SynRM drive system. The nonlinear backstepping control system using upper bound with switching function is proposed to inhibit uncertainty action for controlling the SynRM drive system. However, this method uses a large upper bound with a switching function, which results in a large chattering. In order to reduce this chattering, a nonlinear backstepping control system using an adaptive law is proposed to estimate the lumped uncertainty. Since this method uses an adaptive law, it cannot achiever satisfactory performance. Therefore, a nonlinear backstepping control system using a reformed recurrent Hermite polynomial neural network with an adaptive law and an error estimated law is proposed to estimate the lumped uncertainty and to compensate the estimated error in order to enhance the robustness of the SynRM drive system. Further, the reformed recurrent Hermite polynomial neural network with two learning rates is derived according to an increment type Lyapunov function to speed-up the parameter convergence. Finally, some experimental results and a comparative analysis are presented to verify that the proposed control system has better control performance for controlling SynRM drive systems.

• 대한토목학회논문집
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• 제13권2호
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• pp.237-242
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• 1993

기초 지반이 몇개의 토층으로 구성된 경우 그 지지력은 각 토층의 강성도와 두께 및 위치 등에 의해 영향을 받는다. 따라서 기초 설계시에 기초의 지지력을 정확히 구하고 파괴면을 예측하기 위해서는 토층의 상태를 지지력 계산에 고려해야 한다. 본 연구에서는 기초 지반이 사질지반이고 중간에 상대적으로 조밀한 지층을 포함하는 경우에 조밀한 층의 두께나 위치가 기초의 지지력 및 파괴모양에 미치는 영향을 극한 해석의 상한한계(upper bound)쪽에서 완전해에 가까운 해를 구하는 K.E.M(Kinematical Element Method)을 이용하여 검토 하였으며, 기초 폭(B)의 3/5 B보다 깊지 않은곳에 조밀한 층이 위치하는 경우에는 기초의 지지력 과 파괴모양이 조밀한 층의 영향을 받는 것으로 나타났다.

• 한국정밀공학회지
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• 제12권8호
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• pp.63-72
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• 1995

Closed-die forging of spur gears with hollow cylindrical billet has been analysed by using the upper-bound method. A kinematically admissible velocity field has been developed, wherein, an involute curve has been introduced to represent the forging die profile. In the analysis, the deformation region has been divided into nine zones. A constant frictional stress has been assumed on the contacting surfaces. Utilizing the formulated velocity field, numerical calculations have been carried out to investigate the effects of various parameters, such as module, number of teeth and friction factor, on the forging of spur gears. Hardness and accuracy of forged gears are measured. The following results have been obtained: (1) It is verified that an axisymmetric deformation zone exists between root circle and center of gear through forged gears. (2) The average relative forging pressure is predominantly dependent on the number of teeth and increases near the final filling stage as the addendum modification coefficient increases. (3) Close agreement was found between the predicted values of forging load and those obtained from experimental results.

• Geomechanics and Engineering
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• 제37권4호
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• pp.323-339
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• 2024

If the pressure exerted on the face of a tunnel excavated by TBM exceeds a threshold, it leads to failure of the soil or rock masses ahead of the tunnel face, which results in heaving the ground surface. In the current research, the upper bound method of limit analysis was employed to calculate the blow-out pressure of tunnels excavated in rock masses obeying the Hoek-Brown nonlinear criterion. The results of the proposed method were compared with three-dimensional finite element models, as well as the available methods in the literature. The results show that when σ_ci, m_i, and GSI increase, the blow-out pressure increases as well. By doubling the tunnel diameter, the blow-out pressure reduces up to 54.6%. Also, by doubling the height of the tunnel cover and the surcharge pressure exerted on the ground surface above the tunnel, the blow-out pressure increased up to 74.9% and 5.4%, respectively. With 35% increase in the unit weight of the rock mass surrounding the tunnel, the blow-out pressure increases in the range of 14.8% to 19.6%. The results of the present study were provided in simple design graphs that can easily be used in practical applications in order to obtain the blow-out pressure.

• Composites Research
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• 제12권2호
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• pp.10-25
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• 1999

Fragmentation 시험법에 의한 섬유상 복합재료의 계면적 특성에 대한 새로운 평가방법이, 순차적으로 섬유간의 간격이 변하게 된 단계적 다섬유 복합재료를 사용하여 제시되었다. 섬유간의 간격이 증가함에 따라, 부서진 섬유들의 형상비는 감소하였으며, 섬유와 기지간의 계면전단강도는 증가함을 보여주었다. 섬유간 거리의 역수를 취했을 때에, 형상비와 계면전단강도 모두가 포화되는 값을 보여주었다. 이것은 단계적 다섬유 복합재료가 형상비에서의 상한값을 나타내고, 계면전단강도에서 하한값을 보여준다는 것을 의미한다. 이 fragmentation 시험법은 복합재료의 평가에 새로운 방법이 될 수 있다. 왜냐하면, 이 두 한계값의 차이를 줄이는 것이 복합재료의 강화에 효과적이기 때문이다. 또한, 섬유 파괴점 부근에서의 섬유응력 분포와 위의 결과를 관련시키기 위해 탄송-소성 유한요소 해석이 행해졌다. 단계적 다섬유 복합재료 시험에서 얻어진 한계값은 그룹형태의 다 섬유 파괴에 의해 야기된 응력집중과 밀접하게 관련되어 있다는 것이 입증되었다.

• 한국정보과학회논문지:정보통신
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• 제35권4호
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• pp.282-291
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• 2008

본 논문에서는 무선 노드의 이동성에 따른 링크 에러로 인한 Mobile Ad hoc Network (MANET) IP 자동 네트워크 프로토콜(Address Autoconfiguration Protocol: AAP)의 메시지 복잡도를 분석하고자 한다. 링크 에러로 인해 목적지까지 전달되지 못한 메시지는 재전송되어야 하고, 이러한 재전송 횟수 (S)를 링크 에러 확률 ($P_e$)에 따라 계산하는 알고리즘을 제안하였다. 또한, O-표기법에 따라 N개의 노드에 의해 발생된 메시지의 Upper Bound를 각 AAP에서 유도하였다. 본 연구에서 검토된 AAP는 Strong Duplicate Address Detection (DAD), Weak DAD with proactive routing protocol (WDP), Weak DAD with on-demand routing protocol (WDO), MANETconf이다. 컴퓨터 기반 시뮬레이션에서, 제안된 알고리즘에 의해 링크 에러가 있을 때, 각 AAP의 성능을 분석해본 결과, WDP가 가장 낮은 메시지 복잡도를 가졌고, MANETconf가 가장 높은 메시지 복잡도를 보였다.

• 품질경영학회지
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• 제26권3호
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• pp.71-81
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• 1998

In reliability analysis, the time difference between the expected next failure time and the current failure time or the Mean Time Between Failure(MTBF) is of significant interest. Until recently, in reliability growth studies, the reciprocal of the intensity function at current failure time has been used as being equal to MTBE($t_n$)at the n-th failure time $t_n$. That is MTBF($t_n$)=l/$\lambda (t_n)$. However, such a relationship is only true for Homogeneous Poisson Process(HPP). Tsokos(1995) obtained the upper bound and lower bound for the MTBF($t_n$) and proposed an estimator for the MTBF($t_n$) as the mean of the two bounds. In this paper, we provide the estimator for the MTBF($t_n$) which does not depend on the value of the shape parameter. The result of the Monte Carlo simulation shows that the proposed estimator has better efficiency than Tsokos's estimator.

• Architectural research
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• 제2권1호
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• pp.47-54
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• 2000

The critical load of a continuous compression member was determined by the beam-analogy method. The proposed method utilizes the stress-analysis results of the analogous continuous beam, where imaginary concentrated lateral load changing its direction is applied at each midspan. The proposed method gives a lower bound error of critical load and can predict the span that buckles first. The effective length factors for braced frame columns can be easily determined by the present method, but result in the upper bound errors in all cases, which can lead to a conservative structural design.