• Structural Engineering and Mechanics
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• 제77권4호
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• pp.495-508
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• 2021

This study devises a novel approach, namely quadruple 1D convolutional neural network, for detecting connection stiffness reduction in steel truss bridge structure using experimental and numerical modal data. The method is developed based on expertise in two domains: firstly, in Structural Health Monitoring, the mode shapes and its high-order derivatives, including second, third, and fourth derivatives, are accurate indicators in assessing damages. Secondly, in the Machine Learning literature, the deep convolutional neural networks are able to extract relevant features from input data, then perform classification tasks with high accuracy and reduced time complexity. The efficacy and effectiveness of the present method are supported through an extensive case study with the railway Nam O bridge. It delivers highly accurate results in assessing damage localization and damage severity for single as well as multiple damage scenarios. In addition, the robustness of this method is tested with the presence of white noise reflecting unavoidable uncertainties in signal processing and modeling in reality. The proposed approach is able to provide stable results with data corrupted by noise up to 10%.

• Structural Engineering and Mechanics
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• 제86권1호
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• pp.93-107
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• 2023

In this paper, a density based topology optimization is proposed for generating of supports required in additive manufacturing to maintain the overhanging regions of main structures during layer by layer fabrication process. For this purpose, isogeometric analysis method is employed to model geometry and structural analysis of main and support structures. In order to model the problem two cases are investigated. In the first case, design domain of supports can easily be separated from the main structure by using distinct isogeometric patches. The second case happens when the main structure itself is optimized by using topology optimization and the supports should be designed in the voids of optimum layout. In this case, in order to avoid boundary identification and re-meshing process for separating design domain of supports from main structure, a parameterization technique is proposed to identify the design domain of supports. To achieve this, two density functions are defined over the entire domain to describe the main structure and supporting areas. On the other hand, since supports are under gravity loads while main structure and its stiffness is not completed during manufacturing process, in the proposed method, stiffness of the main structure is considered to be trivial and the gravity loads are also naturally applied to design support structures. By doing so, the results show reasonable supports are created to protect, continuously, overhanging surfaces of the main structure. Several examples are presented to demonstrate the efficiency of the proposed method and compare the results with literature.

• 대한물리의학회지
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• 제18권2호
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• pp.93-101
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• 2023

PURPOSE: The Western Ontario and McMaster Universities Arthritis (WOMAC) index has been used to measure the outcome of total knee replacement (TKR), but studies on its reliability and validity are limited. The present study examined the reliability and validity of this index for patients with knee osteoarthritis who underwent TKR. METHODS: Seventy-one inpatients and outpatients who underwent bilateral TKR for knee osteoarthritis were included in this study. The pain assessment scale and WOMAC index were used to evaluate the participants every two weeks to examine the test-retest reliability, internal consistency, and construct validity. RESULTS: The test-retest reliability scores for pain, stiffness, and physical function were .75-.92, .85-.90, and .75-.95, respectively. The corresponding intraclass correlation coefficients were .75-.88, .76-.88, and .71-.95, respectively. The internal consistency score in the first and second examinations was .92. Furthermore, the construct validity scores for pain, stiffness, and physical function were .83, .41, and .58, respectively. CONCLUSION: The application of the WOMAC index in patients who underwent TKR showed high test-retest reliability and internal consistency with the use of the WOMAC index and good validity with the use of the pain assessment scale.

• Journal of Acupuncture Research
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• 제41권1호
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• pp.69-73
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• 2024

This study evaluated a case of trigeminal nerve stimulation during acupotomy at a site 5 pun left of GV16. The study participant was a 52-year-old male suffering from upper neck pain and numbness, which was managed by acupotomy at a site 5 pun left of GV16. During acupotomy, the patient experienced unexpected numbness and stiffness of the left zygomatic bone. This area corresponds to the distribution of the maxillary nerve, which is the second branch of the trigeminal nerve. After approximately one month, symptoms of numbness and stiffness disappeared without rendering medical treatment. These side effects are presumed to be associated with the trigeminocervical complex and stimulation of the trigeminal nucleus within the spinal cord. Thus, during the acupotomy of the upper neck, especially at GV16, the needles should be inserted slowly, and the patient's response should also be monitored.

• Structural Engineering and Mechanics
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• 제66권5호
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• pp.583-594
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• 2018

A theoretical formulation based on the linearized potential theory, the Descartes' rule and the extremum optimization method is presented to calculate the critical distance of lifting points of the fully balanced hoist vertical ship lift, and to study pitching stability of the ship lift. The overturning torque of the ship chamber is proposed based on the Housner theory. A seven-free-degree dynamic model of the ship lift based on the Lagrange equation of the second kind is then established, including the ship chamber, the wire rope, the gravity counterweights and the liquid in the ship chamber. Subsequently, an eigenvalue equation is obtained with the coefficient matrix of the dynamic equations, and a key coefficient is analyzed by innovative use of the minimum optimization method for a stability criterion. Also, an extensive influence of the structural parameters contains the gravity counterweight wire rope stiffness, synchronous shaft stiffness, lifting height and hoists radius on the critical distance of lifting points is numerically analyzed. With the Runge-Kutta method, the four primary dynamical responses of the ship lift are investigated to demonstrate the accuracy/reliability of the result from the theoretical formulation. It is revealed that the critical distance of lifting points decreases with increasing the synchronous shaft stiffness, while increases with rising the other three structural parameters. Moreover, the theoretical formulation is more applicable than the previous criterions to design the layout of the fully balanced hoist vertical ship lift for the ensuring of the stability.

• Smart Structures and Systems
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• 제10권4_5호
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• pp.375-391
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• 2012

This paper reports the structural health monitoring benchmark study results for the Canton Tower using Bayesian methods. In this study, output-only modal identification and finite element model updating are considered using a given set of structural acceleration measurements and the corresponding ambient conditions of 24 hours. In the first stage, the Bayesian spectral density approach is used for output-only modal identification with the acceleration time histories as the excitation to the tower is unknown. The modal parameters and the associated uncertainty can be estimated through Bayesian inference. Uncertainty quantification is important for determination of statistically significant change of the modal parameters and for weighting assignment in the subsequent stage of model updating. In the second stage, a Bayesian model updating approach is utilized to update the finite element model of the tower. The uncertain stiffness parameters can be obtained by minimizing an objective function that is a weighted sum of the square of the differences (residuals) between the identified modal parameters and the corresponding values of the model. The weightings distinguish the contribution of different residuals with different uncertain levels. They are obtained using the Bayesian spectral density approach in the first stage. Again, uncertainty of the stiffness parameters can be quantified with Bayesian inference. Finally, this Bayesian framework is applied to the 24-hour field measurements to investigate the variation of the modal and stiffness parameters under changing ambient conditions. Results show that the Bayesian framework successfully achieves the goal of the first task of this benchmark study.

• 한국도로학회논문집
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• 제17권5호
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• pp.25-31
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• 2015

PURPOSES: The objective of this study is to analyze the relationship between the FWD back-calculated modulus and dynamic modulus of asphalt layers for existing asphalt pavements. METHODS: To evaluate the dynamic modulus of the asphalt mixture in the existing and new asphalt layers, the uniaxial direct tension test was conducted on small asphalt specimens obtained from the existing asphalt-covered pavements. A dynamic modulus master curve was estimated by using the uniaxial direct tension test for each asphalt layer. The falling weight deflectometer (FWD) testing was conducted on the test sections, and the modulus values of pavement layers were back-calculated using the genetic algorithm and the finite element method based back-calculation program. The relationship between measured and back-calculated asphalt layer moduli was examined in this study. The normalized dynamic modulus was adopted to predict the stiffness characteristics of asphalt layers more accurately. RESULTS: From this study, we can conclude that there is no close relationship between dynamic modulus of first layer and back-calculated asphalt modulus. The dynamic moduli of second and third asphalt layers have some relation with asphalt stiffness. Test results also showed that the normalized dynamic modulus of the asphalt mixture is closely related to the FWD back-calculated modulus with 0.73 of R square value. CONCLUSIONS: The back-calculated modulus of asphalt layer can be used as an indicator of the stiffness characteristics of asphalt layers in the asphalt-covered pavements.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.255-264
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• 2009

Soils containing vanishing materials lead changes in the microstructure of particulate media due to water inflow. Thus, dissolution renders some local unstability. As the moisture contents decease, the component of the vanished materials may affects on the cementation of paniculate materials. This cementation phenomenon has a huge influence on the stiffness, strength and stability under lower stress level. The goal of this study is to introduce the cementation effects on a compressional wave velocity, a shear wave velocity, and the resonant frequency of shear waves. The glass bead and salt water with different mole contents are used. Test results show that the changes of shear and compressional wave velocities consist of three stages. In the first region, compressional wave velocities increase and shear wave velocities decrease with a decreases in reducing water contents from 100% to 90~95%. In the second region, shear and compressional wave velocities become stable at 90~95% to 10% of the water contents. In the third region, shear and compressional wave velocities increases dramatically with a decrease in the water content due to the capillary force and cementation of salt. Furthermore, the resonant frequency of the shear waves shows similar phenomenon. Specimens prepared by glass beads and salt water are proved to be able to provide a meaningful insight in under structural behaviors of the cementation.

• 한국항해항만학회지
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• 제36권3호
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• pp.215-223
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• 2012

플로팅 함체의 강성변화가 상부 철골모멘트연성골조에 미치는 영향을 확인하기 위해 함체의 높이를 1.5m, 2.0m, 2.5m로 변화시키면서 파랑하중 3초에서 15초에 대하여 동적 유체 해석과 그에 따른 파력을 산정하고 정적 구조 해석을 수행하였다. 해석결과, RAO-피치와 상부 골조의 모멘트 증가량이 선형적인 관계이고 함체의 곡률이 구조물의 강성과 반비례함을 확인하였다. 이러한 선형적 결과를 종합하여, 임의의 함체에 대한 상부골조의 해석 결과를 이용하여 함체 높이가 다른 경우에도 상부 골조의 모멘트를 추정하는 절차를 제안하였으며, 추정결과가 해석결과와 상당히 잘 일치함을 확인하였다.

• 디지털융복합연구
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• 제13권9호
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• pp.515-521
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• 2015

본 연구에서는 우리는 평균 연령이 높은 제주 해녀의 경-대퇴 맥파 전도 속도와 발목-상완지표를 측정하여 찬물에서 산소의 보조 없이 채취활동을 하는 제주 해녀의 동맥 혈관의 경직도를 측정하였으며, 결과는 다음과 같다. 첫째, 경-대퇴 맥파 전도 속도는 동연령대의 일반여성보다 유의하게 낮게 나타났다. 둘째, 발목-상완지표(ABI)는 해녀와 일반여성 모두 정상범위 안에 포함되어 있었으며, 일반여성보다 해녀집단이 높은 경향을 보였다. 이러한 결과는 고령의 나이임에도 불구하고 장기간 침수활동을 통해 신체의 적응이 이미 완료된 상태로써 저온 및 높은 수압환경에 대한 적응이 완료된 신체상태이며, 아울러 높은 신체활동 수준으로 인하여 말초혈관저항이 고연령임에도 불구하고 감소되지 않았으며, 오히려 동연령 여성들보다 양호한 수준임을 확인할 수 있었다. 하지만 해녀들의 고령화는 여전히 진행되고 있는 중요한 현상이기에 동맥혈관경직도에 대한 관심과 향후의 지속적인 연구는 반드시 더 필요할 것으로 보인다.