• 호남수학학술지
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• 제40권2호
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• pp.265-280
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• 2018

In this study, we firstly define equations of motion based on the traditional model Newtonian mechanics in terms of the Frenet frame adapted to the trajectory of the moving particle in Lie groups. Then, we compute energy on the moving particle in resultant force field by using geometrical description of the curvature and torsion of the trajectory belonging to the particle. We also investigate the relation between energy on the moving particle in different force fields and energy on the particle in Frenet vector fields.

• Structural Engineering and Mechanics
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• 제51권4호
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• pp.651-662
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• 2014

The main goal of this study is to extend the domain of influence result to cover the micropolar thermoelastic diffusion. So, we prove that for a finite time t>0 the displacement field $u_i$, the microrotation vector ${\varphi}_i$, the temperature ${\theta}$ and the chemical potential P generate no disturbance outside a bounded domain $B_t$.

• 터널과지하공간
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• 제29권5호
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• pp.332-345
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• 2019

평사투영도에서 불연속면을 대표하는 유일한 점으로 정의되는 최대경사벡터를 해당 면의 경사와 경사방향에 의거하여 형성하였다. 평사투영해석에서 평면의 극점이 대원과 역방향에 제도되는 것에 비해 최대경사벡터는 대원의 최대 경사지점에 위치하여 불연속면의 미끄러짐 방향을 직접 투영도 상에서 지시한다. 투영도 상에서 불연속면의 거동방향을 직접적으로 지시하는 최대경사벡터를 활용하여 평면 및 전도파괴 양상을 직관적으로 확인하였다. 특히 평면 파괴의 경우 블록의 옆면을 형성하는 고 경사 절리의 존재를 확인하여 실제 미끄러짐 블록의 형성가능성을 산정하였다. 또한 사면 방향과 반대방향을 갖는 고경사절리들의 존재를 확인하여 3각형 단면을 갖는 미끄러짐 블록의 형성여부를 판별하고 안전율을 도출하였으며, 4각형 단면을 갖는 가장 취약한 블록의 안전율과 비교분석하였다. 쐐기파괴 경우에는 절리면 교차에 의해 형성되는 쐐기의 기저선 방향이 최대경사벡터 속성을 지니고 있어 쐐기파괴 영역을 평면 및 전도파괴 영역이 제도된 투영도 상에 함께 도시하여 분석을 수행하였다. 특히 쐐기 상부 면을 형성하는 절리를 추출할 수 있어 전체 쐐기형상을 추정하고 역학적 거동분석을 수행하는데 요구되는 쐐기의 기하학적 특성자료를 도출하는 토대를 확립하였다.

• Computers and Concrete
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• 제33권2호
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• pp.175-193
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• 2024

Researchers have embarked on an active investigation into the feasibility of adopting alternative materials as a solution to the mounting environmental and economic challenges associated with traditional concrete-based construction materials, such as reinforced concrete. The examination of concrete's mechanical properties using laboratory methods is a complex, time-consuming, and costly endeavor. Consequently, the need for models that can overcome these drawbacks is urgent. Fortunately, the ever-increasing availability of data has paved the way for the utilization of machine learning methods, which can provide powerful, efficient, and cost-effective models. This study aims to explore the potential of twelve machine learning algorithms in predicting the tensile strength of geopolymer concrete (GPC) under various curing conditions. To fulfill this objective, 221 datasets, comprising tensile strength test results of GPC with diverse mix ratios and curing conditions, were employed. Additionally, a number of unseen datasets were used to assess the overall performance of the machine learning models. Through a comprehensive analysis of statistical indices and a comparison of the models' behavior with laboratory tests, it was determined that nearly all the models exhibited satisfactory potential in estimating the tensile strength of GPC. Nevertheless, the artificial neural networks and support vector regression models demonstrated the highest robustness. Both the laboratory tests and machine learning outcomes revealed that GPC composed of 30% fly ash and 70% ground granulated blast slag, mixed with 14 mol of NaOH, and cured in an oven at 300°F for 28 days exhibited superior tensile strength.

• 대한기계학회논문집B
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• 제41권4호
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• pp.277-283
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• 2017

본 연구에서는 높이에 따른 점프 전략 변화를 이해하기 위해 반동을 이용한 수직 점프 시 상변화 시점에서의 지면반력 벡터가 높이에 따라 어떻게 변하는지 분석하였다; 반동과 추진 구간에서 유사한 힘 작용선을 갖는 수직 점프의 경우, 상변화 시점에서 반동의 이득을 나타내는 합력 벡터의 크기와 방향이 일정한 경향성을 가지고 높이에 따라 변화할 것이라 가정하였다. 9명의 청년군 모두는 정해진 5 종류의 높이를 총 5세트에 걸쳐 랜덤 방식으로 점프하였으며, 해당 높이를 유도하기 위해 지면으로부터 191 cm에서 221 cm 사이에 일정한 간격을 두고 마커를 배치하였다. 점프 높이가 증가함에 따라 반동 시 무게중심을 낮추고, 수평, 수직 방향의 힘을 증가시키는 것이 관찰되었는데, 이는 추진일을 증가시키기 위해 관절의 가용범위를 넓히고 초기 힘(또는 가속도) 이득을 늘리기 때문으로 생각된다.

• Smart Structures and Systems
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• 제12권3_4호
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• pp.327-344
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• 2013

Beam string structure (BSS) is introduced as a new type of hybrid prestressed string structures. The composition and mechanics features of BSS are discussed. The main principles of wavelet packet transform (WPT), principal component analysis (PCA) and support vector machine (SVM) have been reviewed. WPT is applied to the structural response signals, and feature vectors are obtained by feature extraction and PCA. The feature vectors are used for training and classification as the inputs of the support vector machine. The method is used to a single one-way arched beam string structure for damage detection. The cable prestress loss and web members damage experiment for a beam string structure is carried through. Different prestressing forces are applied on the cable to simulate cable prestress loss, the prestressing forces are calculated by the frequencies which are solved by Fourier transform or wavelet transform under impulse excitation. Test results verify this method is accurate and convenient. The damage cases of web members on the beam are tested to validate the efficiency of the method presented in this study. Wavelet packet decomposition is applied to the structural response signals under ambient vibration, feature vectors are obtained by feature extraction method. The feature vectors are used for training and classification as the inputs of the support vector machine. The structural damage position and degree can be identified and classified, and the test result is highly accurate especially combined with principle component analysis.

• Structural Engineering and Mechanics
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• 제27권4호
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• pp.409-424
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• 2007

In this paper, an identification method of impact force is proposed for composite structures. In this method, the relation between force histories and strain responses is first formulated. The transfer matrix, which relates the strain responses of sensors and impact force information, is constructed from the finite element method (FEM). Based on this relation, an optimization model to minimize the difference between the measured strain responses and numerically evaluated strain responses is built up to obtain the impact force history. The identification of force history is performed by a modified least-squares method that imposes the penalty on the first-order derivative of the force history. Moreover, from the relation of strain responses and force history, an error vector indicating the force location is defined and used for the force location identification. The above theory has also been extended into the cases when using acceleration information instead of strain information. The validity of the present method has been verified through two experimental examples. The obtained results demonstrate that the present approach works very well, even when the internal damages in composites happen due to impact events. Moreover, this method can be used for the real-time health monitoring of composite structures.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 Proceedings of 2004 Korea-Japan Joint Seminar on Particle Image Velocimetry
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• pp.1-13
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• 2004

A scanning stereo-PIV system was developed to measure the three-dimensional distribution of three-component velocity in a turbulent round jet. A laser light beam produced by a high repetition rate YLF pulse laser was expanded vertically by a cylindrical lens to form a laser light sheet. The light sheet is scanned in a direction normal to the sheet by a flat mirror mounted on an optical scanner, which is controlled by a programmable scanner controller. Two high-speed mega-pixel resolution C-MOS cameras captured the particle images illuminated by the light sheet, and stereoscopic PIV method was adopted to acquire the 3D-3C-velocity distribution of turbulent round jet in an octagonal tank filled with water. The jet Reynolds number was set at Re=1000 and the streamwise location of the measurement was fixed at approximately x = 40D. Time evolution of three-dimensional vortical structure, which is identified by vorticity, is visualized. It revealed that the existence of a group of hairpin-like vortex structures was quite evident around the rim of the shear layer of the jet. Turbulence statistics shows good agreement with the previous data, and divergence of a filtered (unfiltered) velocity vector field was $7\%\;(22\%)$ of root-me an-squared vorticity value.

• Structural Engineering and Mechanics
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• 제19권5호
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• pp.477-501
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• 2005

In this study, a new smart beam finite element is proposed for the finite element modeling of beam-type smart structures that are equipped with bonded plate-type piezoelectric sensors and actuators. Constitutive equations for the direct piezoelectric effect and converse piezoelectric effect of piezoelectric materials are considered in the formulation. By using a variational principle, the equations of motion for the smart beam finite element are derived. The proposed 2-node beam finite element is an isoparametric element based on Timoshenko beam theory. The proposed smart beam finite element is applied to the free vibration control adopting a constant gain feedback scheme. The electrical force vector, which is obtained in deriving an equation of motion, is the control force equivalent to that in existing literature. Validity of the proposed element is shown through comparing the analytical results of the verification examples with those of other previous researchers. With the use of smart beam finite elements, simulation of free vibration control is demonstrated by sensing the voltage of the piezoelectric sensors and by applying the voltages to the piezoelectric actuators.

• Nuclear Engineering and Technology
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• 제50권6호
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• pp.890-898
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• 2018

Nondestructive inspection (NDI) is an integral part of structural integrity analyses of dry storage casks that house spent nuclear fuel. One significant concern for the structural integrity is stress corrosion cracking in the heat-affected zone of welds in the stainless steel canister that confines the spent fuel. In situ NDI methodology for detection of stress corrosion cracking is investigated, where the inspection uses a delivery robot because of the presence of the harsh environment and geometric constrains inside the cask protecting the canister. Shear horizontal (SH) guided waves that are sensitive to cracks oriented either perpendicular or parallel to the wave vector are used to locate welds and to detect cracks. SH waves are excited and received by electromagnetic acoustic transducers (EMATs) using noncontact ultrasonic transduction and pulse-echo mode. A laboratory-scale canister mock-up is fabricated and inspected using the proposed methodology to evaluate the ability of EMATs to excite and receive SH waves and to locate welds. The EMAT's capability to detect notches from various distances is evaluated on a plate containing 25%-through-thickness surface-breaking notches. Based on the results of the distances at which notch reflections are detectable, NDI coverage for spent nuclear fuel storage canisters is determined.