• 한국터널지하공간학회 논문집
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• 제20권1호
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• pp.211-224
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• 2018

터널의 지보패턴 설계는 터널의 안정성에 직접적인 영향을 끼치기 때문에 터널에 작용하는 다양한 하중들을 적절히 고려하여야 한다. 국내에서는 프로젝트에 따라 암반분류법을 기반으로 표준 지보패턴을 정의하고 있으며, 시공 시 터널거동을 고려하여 적절히 수정되어야 한다고 기술되어 있다. 본 연구에서는 내공변위제어법, 토압, 록볼트의 축력 및 숏크리트의 모멘트 등을 종합적으로 고려하여 지보패턴을 최적화할 수 있는 방법을 제시하고자 한다. 차분진화알고리즘(DEA)을 적용하여 터널 심도에 따라 록볼트의 길이 및 간격, 숏크리트의 두께를 최적화하였으며, 도출된 결과를 철도터널의 표준지보패턴(3등급)과 비교하였다. 천층지반에서 록볼트의 길이는 표준지보패턴보다는 짧아질 수 있으며, 간격은 넓어질 수 있다. 터널의 심도가 깊어질수록 숏크리트의 두께는 선형적으로 증가하는 것으로 나타났다. 따라서, 숏크리트의 두께는 심도가 깊어질수록 표준지보패턴보다는 두꺼워져야 터널의 안정성을 확보할 수 있는 것으로 나타났다.

• 한국터널지하공간학회 논문집
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• 제18권5호
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• pp.389-399
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• 2016

해저 터널의 안정성 평가는 계측 변위 이외에도 응력, 수압 그리고 지반강성(열화) 등 다른 계측 정보를 사용해서 역해석 알고리즘에 반영하면, 그 효율성이 증대될 수 있다. 본 연구에서는 FLAC3D 프로그램에 내장된 FISH 언어를 사용해서, 기 구축된 변위-응력 기반의 차분진화 알고리즘을 수정 및 확장하였다. 확장된 차분진화 알고리즘에는 변위, 응력 정보 외에도 수압 및 지반 및 라이닝 열화 정보도 입력 인자로 사용되었다. 해저 터널 안정성 평가에 추가적인 계측 정보를 활용하면, 터널 역해석에 대한 오차율이 감소함을 확인할 수 있었다.

• 한국터널지하공간학회 논문집
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• 제18권2호
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• pp.183-193
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• 2016

운영 중 터널의 역해석을 통한 안정성 평가는 다루기 어려운 개념이다. 특히, 해저터널처럼 라이닝이 상대적으로 두껍게 시공된 경우에 발생하는 내공변위가 작기 때문에, 일반적으로 터널 역해석에 사용되는 변위 기반의 터널 역해석에는 한계가 있을 것으로 판단된다. 여기서는 FLAC3D 프로그램에 내장된 FISH 언어를 사용해서, 다양한 역해석 알고리즘 중에 차분진화 알고리즘의 구축을 통한 터널 역해석에 대한 적용성을 확인하였다. 또한, 변위 기반의 알고리즘 구축과 더불어 응력 계측값 등 다양한 인자의 적합성을 확인하여 터널 라이닝의 안정성을 평가하고자 한다.

• Earthquakes and Structures
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• 제5권1호
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• pp.83-109
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• 2013

A simple damper optimization method is proposed to find optimal damper allocation for shear buildings under both target added damping ratio and interstorey drift ratio (IDR). The damping coefficients of added dampers are considered as design variables. The cost, which is defined as the sum of damping coefficient of added dampers, is minimized under a target added damping ratio and the upper and the lower constraint of the design variables. In the first stage of proposed algorithm, Simulated Annealing, Nelder Mead and Differential Evolution numerical algorithms are used to solve the proposed optimization problem. The candidate optimal design obtained in the first stage is tested in terms of the IDRs using linear time history analyses for a design earthquake in the second stage. If all IDRs are below the allowable level, iteration of the algorithm is stopped; otherwise, the iteration continues increasing the target damping ratio. By this way, a structural response IDR is also taken into consideration using a snap-back test. In this study, the effects of the selection of upper limit for added dampers, the storey mass distribution and the storey stiffness distribution are all investigated in terms of damper distributions, cost function, added damping ratio and IDRs for 6-storey shear building models. The results of the proposed method are compared with two existing methods in the literature. Optimal designs are also compared with uniform designs according to both IDRs and added damping ratios. The numerical results show that the proposed damper optimization method is easy to apply and is efficient to find optimal damper distribution for a target damping ratio and allowable IDR value.

• Smart Structures and Systems
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• 제31권4호
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• pp.421-436
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• 2023

This paper presents a vibration displacement measurement and damage identification method for a space truss structure from its vibration videos. Features from Accelerated Segment Test (FAST) algorithm is combined with adaptive threshold strategy to detect the feature points of high quality within the Region of Interest (ROI), around each node of the truss structure. Then these points are tracked by Kanade-Lucas-Tomasi (KLT) algorithm along the video frame sequences to obtain the vibration displacement time histories. For some cases with the image plane not parallel to the truss structural plane, the scale factors cannot be applied directly. Therefore, these videos are processed with homography transformation. After scale factor adaptation, tracking results are expressed in physical units and compared with ground truth data. The main operational frequencies and the corresponding mode shapes are identified by using Subspace Stochastic Identification (SSI) from the obtained vibration displacement responses and compared with ground truth data. Structural damages are quantified by elemental stiffness reductions. A Bayesian inference-based objective function is constructed based on natural frequencies to identify the damage by model updating. The Success-History based Adaptive Differential Evolution with Linear Population Size Reduction (L-SHADE) is applied to minimise the objective function by tuning the damage parameter of each element. The locations and severities of damage in each case are then identified. The accuracy and effectiveness are verified by comparison of the identified results with the ground truth data.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권11호
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• pp.5489-5511
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• 2019

The performance of evolutionary algorithms can be seriously weakened when constraints limit the feasible region of the search space. In this paper we present a constrained multi-objective optimization algorithm based on adaptive ε-truncation (ε-T-CMOA) to further improve distribution and convergence of the obtained solutions. First of all, as a novel constraint handling technique, ε-truncation technique keeps an effective balance between feasible solutions and infeasible solutions by permitting some excellent infeasible solutions with good objective value and low constraint violation to take part in the evolution, so diversity is improved, and convergence is also coordinated. Next, an exponential variation is introduced after differential mutation and crossover to boost the local exploitation ability. At last, the improved crowding density method only selects some Pareto solutions and near solutions to join in calculation, thus it can evaluate the distribution more accurately. The comparative results with other state-of-the-art algorithms show that ε-T-CMOA is more diverse than the other algorithms and it gains better in terms of convergence in some extent.

• 천문학회보
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• 제41권2호
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• pp.66.2-66.2
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• 2016

KASI and NAOJ are making collaborating efforts to implement faster mapping capability into the new 275-500 GHz Atacama Submillimeter Telescope Experiment focal plane array (FPA). Feed horn antenna is one of critical parts of the FPA. Required fractional bandwidth is almost 60 % while that of traditional conical horn is less than 50 %. Therefore, to achieve this wideband performance, we adopted a horn of which the corrugation depths have a longitudinal profile. A profiled horn has features not only of wide bandwidth but also of shorter length compared to a linear-tapered corrugated horn, and lower cost fabrication with less error can be feasible. In our design process the flare region is represented by a cubic splined curve with several parameters. Parameters of the flare region and each dimension of the throat region are optimized by a differential evolution algorithm to keep >20 dB return loss and >30 dB maximum cross-polarization level over the operation bandwidth. To evaluate RF performance of the horn generated by the optimizer, we used a commercial mode matching software, WASP-NET. Also, Gaussian beam (GB) masks to far fields were applied to give better GB behavior over frequencies. The optimized design shows >23 dB return loss and >33 dB maximum cross-polarization level over the whole band. Gaussicity of the horn is over 96.6 %. The length of the horn is 12.5 mm which is just 57 % of the ALMA band 8 feed horn (21.96 mm).

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권4호
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• pp.263-273
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• 2011

The diffuse interface model of Saurel et al. (2008) is used for the computation of compressible cavitating flows around underwater missiles. Such systems use gas injection and natural cavitation to reduce drag effects. Consequently material interfaces appear separating liquid and gas. These interfaces may have a really complex dynamics such that only a few formulations are able to predict their evolution. Contrarily to front tracking or interface reconstruction method the interfaces are computed as diffused numerical zones, that are captured in a routinely manner, as is done usually with gas dynamics solvers for shocks and contact discontinuity. With the present approach, a single set of partial differential equations is solved everywhere, with a single numerical scheme. This leads to very efficient solvers. The algorithm derived in Saurel et al. (2009) is used to compute cavitation pockets around solid bodies. It is first validated against experiments done in cavitation tunnel at CNU. Then it is used to compute flows around high speed underwater systems (Shkval-like missile). Performance data are then computed showing method ability to predict forces acting on the system.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2018년도 학술발표회
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• pp.327-327
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• 2018

돌발홍수, 집중호우 등 강우가 발생 원인되는 자연재해에 효과적으로 대응하기 위한 연구가 활발히 이루어지고 있으나 강우의 시공간 변동성과 발생과정의 복잡한 물리과정으로 인해 강우 추정에 한계를 가진다. 일반적으로 강우 추정은 물리적, 추계학적 모형을 이용하며 추계학적 모형의 점과정(point process)을 이용하여 강우를 생산한다. 추계학적 강우 모형은 관측 강우의 시간 스케일, 강우발생 빈도, 강우 강도 등 강우 구조의 특성을 반영 할 수 있다는 장점을 가지고 있으나 생산되는 강우의 구조가 추정되는 매개변수에 크게 의존한다는 점에서 실제 강우에 적합한 매개변수 추정이 중요하다. 본 연구에서는 낙동강 유역내에 있는 20개의 강우관측 지점을 대상으로 1973년-2017년까지의 강우 관측자료를 수집하였으며 추계학적 강우생성 모형으로 점과정을 이용하는 추계학적 강우생성 모형인 NSRPM(Neymann-Scott rectangular pulse model)을 선정하였다. NSRPM모형의 매개변수를 추정하기위한 최적기법으로 DFP(Davidon-Fletcher-Powell), GA(genetic algorithm), Nelder-Mead, DE(differential evolution)를 이용하여 추정된 매개변수의 적합성을 분석하고 지역특성을 고려한 매개변수 추정 기법을 제시하였다. 추정된 모형의 매개변수를 분석한 결과 DE와 Nelder-Mead 기법이 높은 적합성을 보였으며 DFP, GA기법이 상대적으로 낮은 적합도를 보였다.

• Smart Structures and Systems
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• 제24권1호
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• pp.95-110
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• 2019

The semi-active impact damper (SAID) is proposed to improve the damping efficiency of traditional passive impact dampers. In order to investigate its damping mechanism and vibration control effects on realistic engineering structures, a 20-story nonlinear benchmark building is used as the main structure. The studies on system parameters, including the mass ratio, damping ratio, rigid coefficient, and the intensity of excitation are carried out, and their effects both on linear and nonlinear indexes are evaluated. The damping mechanism is herein further investigated and some suggestions for the design in high-rise buildings are also proposed. To validate the superiority of SAID, an optimal passive particle impact damper ($PID_{opt}$) is also investigated as a control group, in which the parameters of the SAID remain the same, and the optimal parameters of the $PID_{opt}$ are designed by differential evolution algorithm based on a reduced-order model. The numerical simulation shows that the SAID has better control effects than that of the optimized passive particle impact damper, not only for linear indexes (e.g., root mean square response), but also for nonlinear indexes (e.g., component energy consumption and hinge joint curvature).