• Wind and Structures
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• 제36권1호
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• pp.61-73
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• 2023

In this article, a novel structural modal parameters identification methodology is developed to determine the natural frequencies and damping ratios of civil structures based on the symplectic geometry mode decomposition (SGMD) approach. The SGMD approach is a new decomposition algorithm that can decompose the complex response signals with better decomposition performance and robustness. The novel method firstly decomposes the measured structural vibration response signals into individual mode components using the SGMD approach. The natural excitation technique (NExT) method is then used to obtain the free vibration response of each individual mode component. Finally, modal natural frequencies and damping ratios are identified using the direct interpolating (DI) method and a curve fitting function. The effectiveness of the proposed method is demonstrated based on numerical simulation and field measurement. The structural modal parameters are identified utilizing the simulated non-stationary responses of a frame structure and the field measured non-stationary responses of a supertall building during a typhoon. The results demonstrate that the developed method can identify the natural frequencies and damping ratios of civil structures efficiently and accurately.

• Communications for Statistical Applications and Methods
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• 제7권2호
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• pp.427-433
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• 2000

In this paper, we review several two-stage randomized response techniques for gathering self-report data when persons are asked sensitive question. Also efficiencies and privacy protections based on the two-stage randomized response procedures are compared. Finally, we find optimal parameter conditions.

• Ocean Systems Engineering
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• 제7권3호
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• pp.179-193
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• 2017

Dynamic response analysis of offshore triceratops with stiffened buoyant legs under impact and non-impact waves is presented. Triceratops is relatively new-generation complaint platform being explored in the recent past for its suitability in ultra-deep waters. Buoyant legs support the deck through ball joints, which partially isolate the deck by not transferring rotation from legs to the deck. Buoyant legs are interconnected using equally spaced stiffeners, inducing more integral action in dispersing the encountered wave loads. Two typical nonlinear waves under very high sea state are used to simulate impact and non-impact waves. Parameters of JONSWAP spectrum are chosen to produce waves with high vertical and horizontal asymmetries. Impact waves are simulated by steep, front asymmetric waves while non-impact waves are simulated using Stokes nonlinear irregular waves. Based on the numerical analyses presented, it is seen that the platform experiences both steady state (springing) and transient response (ringing) of high amplitudes. Response of the deck shows significant reduction in rotational degrees-of-freedom due to isolation offered by ball joints. Weak-asymmetric waves, resulting in non-impact waves cause steady state response. Beat phenomenon is noticed in almost all degrees-of-freedom but values in sway, roll and yaw are considerably low as angle of incidence is zero degrees. Impact waves cause response in higher frequencies; bursting nature of pitch response is a clear manifestation of the effect of impact waves on buoyant legs. Non-impact waves cause response similar to that of a beating phenomenon in all active degrees-of-freedom, which otherwise would not be present under normal loading. Power spectral density plots show energy content of response for a wide bandwidth of frequencies, indicating an alarming behaviour apart from being highly nonlinear. Heave, being one of the stiff degrees-of-freedom is triggered under non-impact waves, which resulted in tether tension variation under non-impact waves as well. Reduced deck response aids functional requirements of triceratops even under impact and non-impact waves. Stiffened group of buoyant legs enable a monolithic behaviour, enhancing stiffness in vertical plane.

• 한국지반공학회논문집
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• 제36권11호
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• pp.21-33
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• 2020

본 연구에서는 국내 내진설계기준 공통적용사항(MOIS, 2017)의 지반증폭계수를 활용하여 지표면 최대가속도를 산출하는 방법의 적절성을 검토하기 위해 포항지역 전역의 시추공을 대상으로 1차원 등가선형해석프로그램을 통해 지반응답해석을 수행하였다. 지반응답해석을 위한 지진파는 내진설계기준 공통적용사항에 따라 지진 재현주기 500년, 1000년, 2400년의 표준설계응답스펙트럼에 맞추었고, 지반데이터는 국토지반정보 포털시스템을 활용하여 확보하였다. 그 결과 내진설계기준 공통적용사항에서 제시하는 응답스펙트럼과 지반응답해석에서 얻어진 응답스펙트럼은 지반분류에 상관없이 대략적으로 일치하는 것을 알 수 있었다. 하지만, 증폭계수를 활용하여 지표면최대가속도를 산출할 경우 지반응답해석에서 얻어진 결과와 상당한 차이를 나타내는 것을 알 수 있었다.

• 한국지반공학회논문집
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• 제36권6호
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• pp.17-34
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• 2020

일반적으로 잔교식 구조물의 내진설계를 위한 응답스펙트럼 해석 시 기준서들에서는 지진응답해석을 통해 증폭된 가속도를 입력가속도 활용하도록 제시하고 있으나, 기준서에 따라 방법이 상이하여 설계 시 혼란을 야기할 수 있다. 이에, 본 연구에서는 동적원심모형실험을 통해 지반 내 다양한 깊이에서 지반 가속도를 산정하였으며, 산정된 지반가 속도를 활용하여 응답스펙트럼 해석을 수행하였다. 이후 실험 및 해석을 통해 도출된 잔교식 안벽 구조물의 모멘트 결과를 비교하였으며, 응답스펙트럼 해석 시 적절한 입력지반가속도를 결정하기 위한 방법을 제시하고자 하였다. 실험 및 해석을 비교한 결과, 탄성 지반 스프링을 적용하는 경우 구조물의 고유주기를 가장 적절하게 모사하는 것으로 나타났으며, 상부 지표면에서 증폭된 지진파를 입력가속도로 활용하는 것이 사질토 지반에 관입된 구조물 응답을 가장 합리적으로 모사하는 것으로 나타났다.

• 한국산학기술학회논문지
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• 제19권5호
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• pp.176-183
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• 2018

기후변화, 급속한 도시화, 인구집중 및 SOC 시설물 구축 등으로 우리나라를 비롯한 전 세계 재난 재해 발생빈도와 피해규모는 점차 대형화, 복잡화 되는 추세이다. 특히 최근에는 자연재난, 인위재난 및 사회적 재난 등이 복합적으로 연계되어 발생하는 대형복합재난 발생이 국내외적으로 증가하고 있으며 인명피해 및 재산피해도 급속도로 늘어나고 있는 상황이다. 국내에서는 국가 R&D 및 정보화 사업을 통해 지진, 풍수해, 태풍, 대설, 가뭄 등 개별 자연재난에 대한 피해예측 및 대응기술개발에 많은 진전이 있었으나, 대형복합재난의 효율적 대응 및 관리를 위한 제도적 기반은 크게 미흡한 실정이다. 이에 본 연구에서는 기존 자연 및 사회재난의 대표적 사례와 관련 재난별 국내 재난대응관리시스템 사례를 조사 분석하여 시사점을 제시하고, 복합재난 관리정책을 위한 법제도 개선 및 대응매뉴얼 보완방안을 제안하며, 효율적 대응을 위한 통합지휘체계로 의 전환추진 및 부처/부서간 협력체계 구축과 재난대응역량 향상을 위한 교육 및 훈련체계 강화방안을 제시한다.

• Structural Engineering and Mechanics
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• 제64권4호
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• pp.449-459
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• 2017

High-rise buildings are generally sensitive to strong winds. The evaluation of wind loads for the structural design, structural health monitoring (SHM), and vibration control of high-rise buildings is of primary importance. Nevertheless, it is difficult or even infeasible to measure the wind loads on an existing building directly. In this regard, a new inverse method for evaluating wind loads on high-rise buildings is developed in this study based on a discrete-time Kalman filter. The unknown structural responses are identified in conjunction with the wind loads on the basis of limited structural response measurements. The algorithm is applicable for estimating wind loads using different types of wind-induced response. The performance of the method is comprehensively investigated based on wind tunnel testing results of two high-rise buildings with typical external shapes. The stability of the proposed algorithm is evaluated. Furthermore, the effects of crucial factors such as cross-section shapes of building, the wind-induced response type, errors of structural modal parameters, covariance matrix of noise, noise levels in the response measurements and number of vibration modes on the identification accuracy are examined through a detailed parametric study. The research outputs of the proposed study will provide valuable information to enhance our understanding of the effects of wind on high-rise buildings and improve codes of practice.

• Structural Engineering and Mechanics
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• 제66권3호
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• pp.411-421
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• 2018

Although a rubber isolation cushion can reduce the dynamic response of a structure itself, it has little influence on the height of a sloshing wave and even may induce magnification action. Vertical baffles are set into a base-isolated Concrete Rectangular Liquid Storage Structure (CRLSS), and baffles are opened as holes to increase the energy dissipation of the damping. Problems of liquid nonlinear motion caused by baffles are described using the Navier-Stokes equation, and the space model of CRLSS is established considering the Fluid-Solid Interaction (FSI) based on the Finite Element Method (FEM). The dynamic response of an isolated CRLSS with various baffles under an earthquake is analyzed, and the results are compared. The results show that when the baffle number is certain, the greater the number of holes in baffles, the worse the damping effects; when a single baffle with holes is set in juxtaposition and double baffles with holes are formed, although some of the dynamic response will slightly increase, the wallboard strain and the height of the sloshing wave evidently decrease. A configuration with fewer holes in the baffles and a greater number of baffles is more helpful to prevent the occurrence of two failure modes: wallboard leakage and excessive sloshing height.

• 한국환경복원기술학회지
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• 제9권2호
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• pp.72-80
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• 2006

This study was conducted to evaluate the influence of dried swine excrement on the germination of Pinus thunbergii seeds, the growth response of seedlings of Pinus thunbergii and the uptaken of nitrogen and phosphorous by seedlings of Pinus thunbergii. The germination rate of seeds of Pinus thunbergii tends to decrease according to the increasing of application amount of dried swine excrement and the application amounts of dried swine excrement which is more than 3%(w/w %) makes the rate of germination to much more decreased. Contents of nitrogen and phosphorus are much higher in a way that the dried swine excrement was treated in nursery soil. 179 days after seeds of Pinus thunbergii were sowed, nitrogen contents in soil was decreased more than 70% and phosphorus was decreased 20 to 45%. Growth response of Pinus thunbergii was much higher in treatment of dried swine excrement than in control. But growth response was not affected by increasing of application amounts of dried swine excrement. Growth response of Pinus thunbergii was the highest in 2%(w/w %) application but its growth response was decreased in treatment more than 3% (w/w %) of dried swine excrement.

• 디지털산업정보학회논문지
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• 제16권3호
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• pp.37-47
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• 2020

The In the 4^th industrial revolution, cyber space will evolve into hyper-connectivity, super-convergence, and super-intelligence due to the development of advanced information and communication technologies, which will connect the nation's core infrastructure into a single network. As applying the 4^th industrial revolution technology to the cyber attack technique, it is evolving in an intelligent and sophisticate method. In order to response intelligent cyber attacks, it is difficult to guarantee self-defense in cyberspace by policy-oriented, preplanned-centric and hierarchical cyber response strategies. Therefore, this research aims to propose a situation-flexible & action-oriented cyber response mechanism that can respond flexibly by selecting the most optimal smart security solution according to changes in the cyber attack steps. The proposed cyber response mechanism operates the smart security solutions according to the action-oriented detailed strategies. In addition, artificial intelligence-based decision-making systems are used to select the smart security technology with the best responsiveness.