• 해양환경안전학회지
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• 제23권3호
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• pp.313-319
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• 2017

Cylindrical shells are often used in ship structures at deck plating with a camber, side shell plating at fore and aft parts, and bilge structure part. It has been believed that such curved shells can be modelled fundamentally by a part of a cylinder under axial compression. From the estimations with the usage of cylinder models, it is known that, in general, curvature increases the buckling strength of a curved shell subjected to axial compression, and that curvature is also expected to increase the ultimate strength. We conduct series of elasto-plastic large deflection analyses in order to clarify the fundamentals in buckling and plastic collapse behaviour of cylindrical shells under axial compression. From the numerical results, we derive design formula for predicting the ultimate strength of cylindrical shell, based on a series of the nonlinear finite element calculations for all edges, simply supporting plating, varying the slenderness ratio, curvature and aspect ratio, as well as the following design formulae for predicting the ultimate strength of cylindrical shell. From a number of analysis results, fitting curve can be developed to use parameter of slenderness ratio with implementation of the method of least squares. The accuracy of design formulae for evaluating ultimate strength has been confirmed by comparing the calculated results with the FE-analysis results and it has a good agreement to predict their ultimate strength.

• 한국통신학회논문지
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• 제41권8호
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• pp.917-920
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• 2016

전통적 도래각 추정기법[1]과 별개로 2004년 이후 입사신호의 입사방향은 공간 영역에서 희소도(sparsity)를 가짐을 이용한 도래각 추정 기법이 제안되었다. 압축센싱 기반 도래각 추정 알고리즘인 SpSF 알고리즘에 이용되는 비용함수는 비선형 다변수 최적화문제이다. 적절한 변환을 통하여 해당 비용함수는 볼록 최적화 (convex optimization) 문제로 표현할 수 있다. 볼록 최적화 문제는 제한조건이 있는 최적화 문제이며 제한조건에 포함되는 상수를 지정해야 한다. 본 연구에서는 제한조건에 포함되는 사용자지정 상수값 결정법을 제안한다. 잡음의 실수부와 허수부가 서로 독립인 평균 0인 정규분포를 따름을 이용하여 제한조건에 포함되는 행렬의 Frobenius norm의 평균을 유도할 수 있으며, 이를 이용하여 제한조건에 포함되는 상수를 결정할 수 있다. 제안된 방법에 의해 결정된 상수를 이용한 SpSF 알고리즘이 실제로 동작함을 보였다.

• 한국자동차공학회논문집
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• 제22권3호
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• pp.114-122
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• 2014

Sensor fusion is the one of the main research topics. It offers the highly reliable estimation of vehicle movement by processing and mixing several sensor outputs. But unfortunately, every sensor has drift which degrades the performance of sensor. It means a single degraded sensor output may affect whole sensor fusion system. Drift in most research is ideally assumed to be zero because it's usually a nonlinear model and has sample variation. Plus, it's very difficult for the acceleration to separate drift from the output signal since it contains many contributors such as vehicle acceleration, slope angle, pitch angle, surface condition and so on. In this paper, modified spline interpolation is introduced as a dynamic temperature compensation method covering sample variation. Using the last known output and the first initial output is suggested to build and update compensation factor. When the system has more compensation data, the system will have better performance of compensated output because of the regression compensation model. The performance of the dynamic temperature compensation system is evaluated by measuring offset drift between with and without the compensation.

• 한국지능시스템학회논문지
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• 제21권5호
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• pp.555-563
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• 2011

영상의 왜곡보정은 영상 좌표계(이미지)와 전역 좌표계(대상체)의 상관관계를 규정하는 것이다. 기존의 왜곡영상에 대한 보정은 카메라의 광학적 특성을 모델링하여 영상 좌표계와 전역 좌표계의 물리적 관계를 찾는 방식이 주를 이루고 있다. 본 논문에서는 성능 지수기반 다항식 모델을 이용하여 왜곡영상의 보정을 시도하였다. 성능지수기반 다항식 모델은 영상 좌표계와 전역 좌표계 사이의 상관관계를 다항식으로 가정한 후, 이미지와 대상체의 좌표 데이터와 성능지수를 이용하여 다항식 모델의 계수와 차수를 결정하는 방식이다. 제안한 성능지수기반 다항식 모델을 이용하여 기존의 왜곡영상을 보정방식이 가진 과대적합 문제와 같은 한계를 극복하고자 한다. 제안한 방법을 레이저 스캔 카메라로 획득한 2차원 영상에 적용하여 모델의 유효성을 검증하였다.

• Smart Structures and Systems
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• 제13권2호
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• pp.281-303
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• 2014

In order to suppress the wind-induced vibrations of the Canton Tower, a pair of active mass driver (AMD) systems has been installed on the top of the main structure. The structural principal directions in which the bending modes of the structure are uncoupled are proposed and verified based on the orthogonal projection approach. For the vibration control design in the principal X direction, the simplified model of the structure is developed based on the finite element model and modified according to the field measurements under wind excitations. The AMD system driven by permanent magnet synchronous linear motors are adopted. The dynamical models of the AMD subsystems are determined according to the open-loop test results by using nonlinear least square fitting method. The continuous variable gain feedback (VGF) control strategy is adopted to make the AMD system adaptive to the variation in the intensity of wind excitations. Finally, the field tests of free vibration control are carried out. The field test results of AMD control show that the damping ratio of the first vibration mode increases up to 11 times of the original value without control.

• 한국음향학회지
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• 제42권3호
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• pp.169-180
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• 2023

수중음향통신의 성능은 다중경로 전달과 도플러 확산에 크게 영향을 받는다. 본 논문은 다중경로 전달 환경에서 강인한 기존의 Sweep Spread Carrier(SSC) 기법을 변형하여, 새로운 통신기법인 Triangle Spread Carrier(TSC) 기법을 제안한다. 제안한 TSC 기법은 상승-처프와 하강-처프 신호가 반복되는 반송파를 갖는 형태이며, 각각의 상관함수 특성을 활용하여 수신 신호의 도플러 천이 주파수를 추정하고 보정한다. 제안된 TSC 기법의 성능을 입증하기 위하여 수중 채널 시뮬레이터를 이용한 모의실험과 동해에서 수행된 해상실험을 결과를 제시한다. 해상실험 결과 추정된 도플러 천이 주파수만을 이용하여 복조하였을 때 비부호화 된 비트 오류율은 최대 0.194였지만, 제안한 방법을 적용하였을 때 비부화화된 비트 오류율이 0.001로 감소하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제17권6호
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• pp.1530-1544
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• 2023

Data monitoring is an important foundation of modern science. In most cases, the monitoring data is time-series data, which has high application value. The deep learning algorithm has a strong nonlinear fitting capability, which enables the recognition of time series by capturing anomalous information in time series. At present, the research of time series recognition based on deep learning is especially important for data monitoring. Deep learning algorithms require a large amount of data for training. However, abnormal sample is a small sample in time series, which means the number of abnormal time series can seriously affect the accuracy of recognition algorithm because of class imbalance. In order to increase the number of abnormal sample, a data augmentation method called GANBATS (GAN-based Bi-LSTM and Attention for Time Series) is proposed. In GANBATS, Bi-LSTM is introduced to extract the timing features and then transfer features to the generator network of GANBATS.GANBATS also modifies the discriminator network by adding an attention mechanism to achieve global attention for time series. At the end of discriminator, GANBATS is adding averagepooling layer, which merges temporal features to boost the operational efficiency. In this paper, four time series datasets and five data augmentation algorithms are used for comparison experiments. The generated data are measured by PRD(Percent Root Mean Square Difference) and DTW(Dynamic Time Warping). The experimental results show that GANBATS reduces up to 26.22 in PRD metric and 9.45 in DTW metric. In addition, this paper uses different algorithms to reconstruct the datasets and compare them by classification accuracy. The classification accuracy is improved by 6.44%-12.96% on four time series datasets.

• Nuclear Engineering and Technology
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• 제55권11호
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• pp.4274-4281
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• 2023

Blanket is of vital importance for engineering application of the fusion reactor. Nuclear heat deposition in materials is the main heat source in blanket structure. In this paper, the three-dimensional method for thermal-hydraulics/neutronics coupling analysis is developed and applied for the full-scale module of the helium-cooled ceramic breeder tritium breeding blanket (HCCB TBB) designed for China Fusion Engineering Test Reactor (CFETR). The explicit coupling scheme is used to support data transfer for coupling analysis based on cell-to-cell mapping method. The coupling algorithm is realized by the user-defined function compiled in Fluent. The three-dimensional model is established, and then the coupling analysis is performed using the paralleled Coupling Analysis of Thermal-hydraulics and Neutronics Interface Code (CATNIC). The results reveal the relatively small influence of the coupling analysis compared to the traditional method using the radial fitting function of internal heat source. However, the coupling analysis method is quite important considering the nonuniform distribution of the neutron wall loading (NWL) along the poloidal direction. Finally, the structure optimization of the blanket is carried out using the coupling method to satisfy the thermal requirement of all materials. The nonlinear effect between thermal-hydraulics and neutronics is found during the blanket structure optimization, and the tritium production performance is slightly reduced after optimization. Such an adverse effect should be thoroughly evaluated in the future work.

• 한국환경보건학회지
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• 제32권4호
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• pp.304-315
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• 2006

This study is performed to reexamine the association between ambient air pollution and daily mortality in seven major cities of Korea using a method of meta-analysis with the data filed for the period 1998-2001. These cities account for half of the Korean population (about 23 million). The observed concentrations of carbon monoxide (CO, mean=1.08 ppm), ozone ($O_3$, mean=33.97 ppb), particulate matter less than 10 ${\mu}m$ ($PM_{10},\;mean=57.11\;{\mu}g/m^3$), nitrogen dioxide ($NO_2$, mean=25.09 ppb), and sulfur dioxide ($SO_2$, mean=9.14 ppb) during the study period were at levels below Korea's current ambient air quality standards. Generalized additive models were applied to allow for the highly flexible fitting of seasonal and long-term time trends in air pollution as well as nonlinear associations with weather variables, such as air temperature and relative humidity. Also, we calculated a weighted mean as a meta-analysis summary of the estimates and its standard error. In city-specific analyses, an increase of $41.17{\mu}g/m^3(IQR)\;of\;PM_{10}$ corresponded to $1{\sim}12%$ more deaths, given constant weather conditions. Like most of air pollution epidemiologic studies, this meta-analysis cannot avoid fleeing from measurement misclassification since no personal measurement was taken. However, we can expect that a measurement bias be reduced in district-specific estimate since a monitoring station is better representative of air quality of the matched district. Significant heterogeneity was found for the effect of all pollutants. The estimated relative risks from meta-like analysis increased compared to those relative risks from pooled analysis. The similar results to those from the previous studies indicated existence of health effect of air pollution at current levels in many industrialized countries, including Korea.

• Structural Engineering and Mechanics
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• 제83권3호
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• pp.305-326
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• 2022

To realize the recycling utilization of waste concrete and alleviate the shortage of resources, 11 specimens of steel reinforced recycled concrete (SRRC) filled circular steel tube columns were designed and manufactured in this study, and the cyclic loading tests on the specimens of columns were also carried out respectively. The hysteretic curves, skeleton curves and performance indicators of columns were obtained and analysed in detail. Besides, the finite element model of columns was established through OpenSees software, which considered the adverse effect of recycled coarse aggregate (RA) replacement rates and the constraint effect of circular steel tube on internal RAC. The numerical calculation curves of columns are in good agreement with the experimental curves, which shows that the numerical model is relatively reasonable. On this basis, a series of nonlinear parameters analysis on the hysteretic behaviors of columns were also investigated. The results are as follows: When the replacement rates of RA increases from 0 to 100%, the peak loads of columns decreases by 7.78% and the ductility decreases slightly. With the increase of axial compression ratio, the bearing capacity of columns increases first and then decreases, but the ductility of columns decreases rapidly. Increasing the wall thickness of circular steel tube is very profitable to improve the bearing capacity and ductility of columns. When the section steel ratio increases from 5.54% to 9.99%, although the bearing capacity of columns is improved, it has no obvious contribution to improve the ductility of columns. With the decrease of shear span ratio, the bearing capacity of columns increases obviously, but the ductility decreases, and the failure mode of columns develops into brittle shear failure. Therefore, in the engineering design of columns, the situation of small shear span ratio (i.e., short columns) should be avoided as far as possible. Based on this, the calculation model on the skeleton curves of columns was established by the theoretical analysis and fitting method, so as to determine the main characteristic points in the model. The effectiveness of skeleton curve model is verified by comparing with the test skeleton curves.