• Wind and Structures
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• 제10권4호
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• pp.367-382
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• 2007

A nonlinear numerical method was developed to assess the stability of suspension bridge catwalks under a wind load. A section model wind tunnel test was used to obtain a catwalk's aerostatic coefficients, from which the displacement-dependent wind loads were subsequently derived. The stability of a suspension bridge catwalk was analyzed on the basis of the geometric nonlinear behavior of the structure. In addition, a full model test was conducted on the catwalk, which spanned 960 m. A comparison of the displacement values between the test and the numerical simulation shows that a numerical method based on a section model test can be used to effectively and accurately evaluate the stability of a catwalk. A case study features the stability of the catwalk of the Runyang Yangtze suspension bridge, the main span of which is 1490 m. Wind can generally attack the structure from any direction. Whenever the wind comes at a yaw angle, there are six wind load components that act on the catwalk. If the yaw angle is equal to zero, the wind is normal to the catwalk (called normal wind) and the six load components are reduced to three components. Three aerostatic coefficients of the catwalk can be obtained through a section model test with traditional test equipment. However, six aerostatic coefficients of the catwalk must be acquired with the aid of special section model test equipment. A nonlinear numerical method was used study the stability of a catwalk under a yaw wind, while taking into account the six components of the displacement-dependent wind load and the geometric nonlinearity of the catwalk. The results show that when wind attacks with a slight yaw angle, the critical velocity that induces static instability of the catwalk may be lower than the critical velocity of normal wind. However, as the yaw angle of the wind becomes larger, the critical velocity increases. In the atmospheric boundary layer, the wind is turbulent and the velocity history is a random time history. The effects of turbulent wind on the stability of a catwalk are also assessed. The wind velocity fields are regarded as stationary Gaussian stochastic processes, which can be simulated by a spectral representation method. A nonlinear finite-element model set forepart and the Newmark integration method was used to calculate the wind-induced buffeting responses. The results confirm that the turbulent character of wind has little influence on the stability of the catwalk.

• 한국치위생학회지
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• 제2권1호
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• pp.85-95
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• 2002

The purpose of this study was to examine dental hygienists' knowledge of implant operation, which is recently emerging as one of the important medical services in the dental treatment sector. It's ultimately intended to serve as a basis for the preparation of more effective, appropriate implant-education programs for dental hygienists and to help them, who take a crucial part in implant operation, provide better dental services to patients who are in need of implant operation. The subjects in this study were 368 selected dental hygienists who were working in the dental institutions in the region of Taegu. The results of this study were as below: 1. The largest number of the dental hygienists investigated, 34.1%, were at age 25 to 27. The second most common age was 24 and under, and the third most common age group was 28 to 30. For educational level, most of them, 91.0%, were junior-college graduates, and 9.0% were being in or graduated from four-year-course university. Concerning career, 52.7%, the greatest percentage, had worked for one to three years, and 41.3% had a four-year or higher career. 812%, most of them, were working in dental clinics, and 18.3% were serving in dental hospital or general hospital. 2. Many of the dental institutions were providing implant operation services, as the dental institutions where 64.9% of the subjects were working conducted implant operation. In relation to the necessity of implant operation, the dominant opinion, 73.0%, was thai it's needed to make oral slate healthier. So there was a strong tendency to ad mit implant as one of the necessary treatments in the dental treatment sector. 3. Their collective mean implant knowledge got $57.02{\pm}14.11$. And the collective average of 21 items was $2.7153{\pm}0.6720$ on the basis of 5 points, which was below the average(3 points of Likert scale). This meant that the dental hygienists didn't have a good knowledge or understanding of implant. When it's taken into account what role should be performed by dental hygienists, their implant knowledge should be increased. 4. As a result of examining the effect of the general characteristics on their implant knowledge, the educational level(t=-3.481, P=0.001) and the type of dental institution where they were working(F=16.476, P=0.001) made a significant difference. 5. Their implant knowledge was significantly different according to whether or not the dental institution they were serving conducted implant operation (t=7.199, P=0.001). And, whether or not they agreed to the necessity of implant operation also generated a significant difference to their implant knowledge(F=8.610, P=0.000).

• Geomechanics and Engineering
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• 제21권5호
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• pp.433-445
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• 2020

The weakening and softening behavior of soft clay subjected to cyclic loading due to the build-up of excess pore water pressure is well-known. During the design stage of the foundation of highways and coastal high-rise buildings, it is important to study the mechanical behavior of marine soils under cyclic loading as they undergo greater settlement during cyclic loading than under static loading. Therefore, this research evaluates the cyclic stress-strain and shear strength of untreated and treated marine clay under the effects of wind, earthquake, and traffic loadings. A series of laboratory stress-controlled cyclic triaxial tests have been conducted on both untreated and treated marine clay using different effective confining pressures and a frequency of 0.5 and 1.0 Hz. In addition, treated samples were cured for 28 and 90 days and tested under a frequency of 2.0 Hz. The results revealed significant differences in the performance of treated marine clay samples than that of untreated samples under cyclic loading. The treated marine clay samples were able to stand up to 2000 loading cycles before failure, while untreated marine clay samples could not stand few loading cycles. The untreated marine clay displayed a higher permanent axial strain rate under cyclic loading than the treated clay due to the existence of new cementing compounds after the treatment with recycled tiles and low amount (2%) of cement. The effect of the effective confining pressure was found to be significant on untreated marine clay while its effect was not crucial for the treated samples cured for 90 days. Treated samples cured for 90 days performed better under cyclic loading than the ones cured for 28 days and this is due to the higher amount of cementitious compounds formed with time. The highest deformation was found at 0.5 Hz, which cannot be considered as a critical frequency since smaller frequencies were not used. Therefore, it is recommended to consider testing the treated marine clay using smaller frequencies than 0.5 Hz.

• 한국시뮬레이션학회논문지
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• 제29권1호
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• pp.71-79
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• 2020

현대사회의 도시화 추세가 지속됨에 따라 인구의 집중으로 주거환경에 대한 도시문제의 중요성이 대두되고 있다. 다양한 도시문제 중에서 대표적인 문제 중 하나는 쓰레기 문제로 시민들의 주거환경 악화의 원인이 되며 시정 만족도에 대해 직접적으로 영향을 미치는 요인이다. 이와 같은 쓰레기 문제는 단순히 주거지역의 쓰레기 배출량에 대한 분석으로는 정확히 예측할 수 없으며 쓰레기의 주거지역에 분포하고 있는 거주민의 생활양식과 특징에 대한 분석이 필요하다. 본 연구에서는 주거지역 내의 거주민의 분포에 따라 발생할 수 있는 쓰레기 문제와 이에 대한 만족도 분석을 수행하기 위하여 이산사건 시스템 형식론을 활용한 에이전트 기반 거주민 모델링과 시뮬레이션 환경을 제안한다. 제안하는 연구는 주거민의 시계열적인 특성을 표현하기 위하여 원자모델을 사용하였으며 시뮬레이션 모델의 재사용성을 증대시키기 위한 결합모델을 사용하여 다가구와 다가구 주택을 모의하였다. 또한, 본 연구는 다가구 주택지역에 대한 시뮬레이션 모델링을 진행하고, 시뮬레이션을 수행하였다. 연구결과로 다가구 주택지역의 시뮬레이션에서는 거주민의 특성을 고려한 결과와 그렇지 않은 결과 사이에 뚜렷한 차이점을 발견할 수 있었으며 지역 문화적 특성과 시간적 특성을 고려한 시뮬레이션이 필요함을 확인할 수 있었다.

• 중소기업융합학회논문지
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• 제6권4호
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• pp.71-77
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• 2016

본 논문에서는 기존의 BIC(Bayesian Information Criterion) 기반 화자변화의 성능 향상을 위하여 GMM-UBM(Gaussian Mixture Model-Universal Background Model) 기반 KL(Kullback Leibler) 거리를 활용한 화자변화 검증을 제안하였다. 정보량의 차이에 민감한 기존의 BIC 기반 화자변화검출 알고리즘을 상대적으로 정보량 차이에 견인한 KL 거리 알고리즘으로 검증하였고, 정보량의 비대칭을 보상하기 위해서 GMM-UBM을 활용하였다. 기존의 BIC 기반 화자변화 검출은 1단계로 비유사도 d가 양수인 구간의 국소 최댓값인 지점을 화자변화 후보지점으로 검출하였고, 2단계로 검출된 화자변화 후보지점 중 ${\Delta}BIC$가 양수인 지점을 화자변화지점으로 결정하였다. 본 논문에서는 BIC 기반 화자변화 검출에 의해 결정된 화자변화지점에 대하여 GMM-UBM 기반 KL 거리 D가 문턱치(threshold)보다 높은 지점을 최종 화자변화 지점으로 검증하였다. 실험결과, MDR(Missed Detection Rate)이 0인 조건에서 문턱치 0.028일 때 FAR(False Alarm Rate) 60.4%로 성능이 향상되었다.

• Structural Engineering and Mechanics
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• 제63권3호
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• pp.361-370
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• 2017

Through the use of finite element analysis and acoustic emission techniques we have evaluated the interfacial failure of a carbon fiber reinforced polymer (CFRP) repair patch on a notched aluminum substrate. The repair of cracks is a very common and widely used practice in the aeronautics field to extend the life of cracked sheet metal panels. The process consists of adhesively bonding a patch that encompasses the notched site to provide additional strength, thereby increasing life and avoiding costly replacements. The mechanical strength of the bonded joint relies mainly on the bonding of the adhesive to the plate and patch stiffness. Stress concentrations at crack tips promote disbonding of the composite patch from the substrate, consequently reducing the bonded area, which makes this a critical aspect of repair effectiveness. In this paper we examine patch disbonding by calculating the influence of notch tip stress on disbond area and verify computational results with acoustic emission (AE) measurements obtained from specimens subjected to uniaxial tension. The FE results showed that disbonding first occurs between the patch and the substrate close to free edge of the patch followed by failure around the tip of the notch, both highest stress regions. Experimental results revealed that cement adhesion at the aluminum interface was the limiting factor in patch performance. The patch did not appear to strengthen the aluminum substrate when measured by stress-strain due to early stage disbonding. Analysis of the AE signals provided insight to the disbond locations and progression at the metal-adhesive interface. Crack growth from the notch in the aluminum was not observed until the stress reached a critical level, an instant before final fracture, which was unaffected by the patch due to early stage disbonding. The FE model was further utilized to study the effects of patch fiber orientation and increased adhesive strength. The model revealed that the effectiveness of patch repairs is strongly dependent upon the combined interactions of adhesive bond strength and fiber orientation.

• Smart Structures and Systems
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• 제20권1호
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• pp.61-74
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• 2017

One of the most reliable and simplest tools for structural vibration control in civil engineering is Tuned Mass Damper, TMD. Provided that the frequency and damping parameters of these dampers are tuned appropriately, they can reduce the vibrations of the structure through their generated inertia forces, as they vibrate continuously. To achieve the optimal parameters of TMD, many different methods have been provided so far. In old approaches, some formulas have been offered based on simplifying models and their applied loadings while novel procedures need to model structures completely in order to obtain TMD parameters. In this paper, with regard to the nonlinear decision-making of fuzzy systems and their enough ability to cope with different unreliability, a method is proposed. Furthermore, by taking advantage of both old and new methods a fuzzy system is designed to be operational and reduce uncertainties related to models and applied loads. To design fuzzy system, it is required to gain data on structures and optimum parameters of TMDs corresponding to these structures. This information is obtained through modeling MDOF systems with various numbers of stories subjected to far and near field earthquakes. The design of the fuzzy systems is performed by three methods: look-up table, the data space grid-partitioning, and clustering. After that, rule weights of Mamdani fuzzy system using the look-up table are optimized through genetic algorithm and rule weights of Sugeno fuzzy system designed based on grid-partitioning methods and clustering data are optimized through ANFIS (Adaptive Neuro-Fuzzy Inference System). By comparing these methods, it is observed that the fuzzy system technique based on data clustering has an efficient function to predict the optimal parameters of TMDs. In this method, average of errors in estimating frequency and damping ratio is close to zero. Also, standard deviation of frequency errors and damping ratio errors decrease by 78% and 4.1% respectively in comparison with the look-up table method. While, this reductions compared to the grid partitioning method are 2.2% and 1.8% respectively. In this research, TMD parameters are estimated for a 15-degree of freedom structure based on designed fuzzy system and are compared to parameters obtained from the genetic algorithm and empirical relations. The progress up to 1.9% and 2% under far-field earthquakes and 0.4% and 2.2% under near-field earthquakes is obtained in decreasing respectively roof maximum displacement and its RMS ratio through fuzzy system method compared to those obtained by empirical relations.

• Journal of Plant Biotechnology
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• 제44권1호
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• pp.97-106
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• 2017

일반적으로 유전자를 재조합하는 생명공학기술이 널리 이용되고 있는 것은 유전자변형 작물 분야이다. LM 제품에 대한 의존도가 높아짐에 따라 한국에서는 LMO의 안전성에 대한 우려가 지속적으로 증가하고 있다. 따라서, 우리는 자연환경 내 비의도적으로 방출된 LMO를 판별할 수 있는 검출기법을 확립하였다. JRC 정보를 토대로 6개 LM 이벤트(캐놀라 1, 옥수수 1, 콩 4개)의 유전자를 검출할 수 있는 PCR 조건을 확립하였다. 각 LM 시료에서 genomic DNA를 분리하였고, 이벤트 특이적인 프라이머를 사용하여 PCR 실험을 수행하였다. 또한 자체적으로 확립된 검출법에 의해 모든 LMO의 이벤트 특이적 유전자가 검출되었다. LM 유전자의 삽입 위치를 분석하기 위해 PCR 생성물을 이용하여 염기서열을 분석하였다. 이 결과는 LM 이벤트의 특이적인 유전자를 효율적으로 검출할 수 있음을 나타낸다. 게다가 본 연구결과 확립된 검출기법은 자연환경 내 LM 작물의 모니터링 및 사후 관리에 활용될 것이다.

• Journal of Advanced Marine Engineering and Technology
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• 제39권6호
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• pp.620-625
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• 2015

IMO MEPC에서는 지구온난화를 늦추기 위해서, 선박에서 배출되는 GHG(Green House Gas)인 $CO_2$를 줄이기 위한 방안으로 선속을 다운시켜 운항할 것을 제안한바 있으며, 해운회사에서도 연료비 절감을 위해서 자발적으로 감속운항(Low steaming)을 하고 있어, 국제항해에 종사하고 있는 대부분의 컨테이너선들이 감속운항을 하고 있다. 또한, 날로 증가되고 있는 해운 물동량 증가로 선박의 연료비 부담이 증가되고 있어 연료비 절감 기술개발이 절실히 요구되고 있다. 따라서 본 연구에서는 디젤엔진의 성능을 향상시킬 수 있는 연료첨가제(유용성 칼슘계 유기금속화합물)를 일정량 투입(사용 연료량의 0.025%) 하여 연료비를 절감하는 방법을 시도하였다. 실험의 정확도를 위해서 육상 발전소에 설치된 2행정 대형 디젤엔진을 실험 대상으로 하였다. 실험 엔진의 부하는 저, 중 및 고 부하(50, 75, 100%)로 나누어서 실시하였으며, 연료첨가제의 투입 전과 투입 후의 엔진성능(출력, 연료소비율, 최고연소압력(P-max), 배기온도)을 비교 분석 하였다. 본 실험을 통해서 연료첨가제를 투입함으로써 저부하(50%) 에서 2% 이상의 연료비 절감 효과를 확인 할 수 있었으며, 최고연소압력은 상승하는 반면에 배기온도는 하강함을 알 수 있었다.

• Advances in aircraft and spacecraft science
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• 제5권2호
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• pp.225-237
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• 2018

The difficulties of satellite vibration testing are due to the commonly expressed qualification requirements being incompatible with the limited performance of the entire controlled system (satellite + interface + shaker + controller). Two features cause the problem: firstly, the main satellite modes (i.e., the first structural mode and the high and low tank modes) are very weakly damped; secondly, the controller is just too basic to achieve the expected performance in such cases. The combination of these two issues results in oscillations around the notching levels and high amplitude beating immediately after the mode. The beating overshoots are a major risk source because they can result in the test being aborted if the qualification upper limit is exceeded. Although the abort is, in itself, a safety measure protecting the tested satellite, it increases the risk of structural fatigue, firstly because the abort threshold has been already reached, and secondly, because the test must restart at the same close-resonance frequency and remain there until the qualification level is reached and the sweep frequency can continue. The beat minimum relates only to small successive frequency ranges in which the qualification level is not reached. Although they are less problematic because they do not cause an inadvertent test shutdown, such situations inevitably result in waiver requests from the client. A controlled-system analysis indicates an operating principle that cannot provide sufficient stability: the drive calculation (which controls the process) simply multiplies the frequency reference (usually called cola) and a function of the following setpoint, the ratio between the amplitude already reached and the previous setpoint, and the compression factor. This function value changes at each cola interval, but it never takes into account the sensor signal phase. Because of these limitations, we firstly examined whether it was possible to empirically determine, using a series of tests with a very simple dummy, a controller setting process that significantly improves the results. As the attempt failed, we have performed simulations seeking an optimum adjustment by finding the Least Mean Square of the difference between the reference and response signal. The simulations showed a significant improvement during the notch beat and a small reduction in the beat amplitude. However, the small improvement in this process was not useful because it highlighted the need to change the reference at each cola interval, sometimes with instructions almost twice the qualification level. Another uncertainty regarding the consequences of such an approach involves the impact of differences between the estimated model (used in the simulation) and the actual system. As limitations in the current controller were identified in different approaches, we considered the feasibility of a new controller that takes into account an estimated single-input multi-output (SIMO) model. Its parameters were estimated from a very low-level throughput. Against this backdrop, we analyzed the feasibility of an LQG control in cancelling beating, and this article highlights the relevance of such an approach.