• Computers and Concrete
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• 제25권3호
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• pp.225-244
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• 2020

The influence of boundary conditions on the bending and free vibration behavior of functionally graded sandwich plates resting on a two-parameter elastic foundation is examined using an original novel high order shear theory. The Hamilton's principle is used herein to derive the equations of motion. The number of unknowns and governing equations of the present theory is reduced, and hence makes it simple to use. This theory includes indeterminate integral variables and contains only four unknowns in which any shear correction factor not used, with even less than the conventional theory of first shear strain (FSDT). Unlike any other theory, the number of unknown functions involved in displacement field is only four, as against five, six or more in the case of other shear deformation theories. Galerkin's approach is utilized for FGM sandwich plates with six different boundary conditions. The accuracy of the proposed solution is checked by comparing it with other closed form solutions available in the literature.

• Geomechanics and Engineering
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• 제22권4호
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• pp.361-374
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• 2020

This paper is concerned with the thermoelastic bending of FG beams resting on two-layer elastic foundations. One of these layers is Winkler springs with a variable modulus while the other is considered as a shear layer with a constant modulus. The beams are considered simply supported and subjected to thermo-mechanical loading. Temperature-dependent material properties are considered for the FG beams, which are assumed to be graded continuously across the panel thickness. The used theories contain undetermined integral terms which lead to a reduction of unknowns functions. Several micromechanical models are used to estimate the effective two-phase FG material properties as a function of the particles' volume fraction considering thermal effects. Analytical solutions for the thermo-mechanical bending analysis are obtained based on Navier's method that satisfies the boundary conditions. Finally, the numerical results are provided to reveal the effect of explicit micromechanical models, geometric parameters, temperature distribution and elastic foundation parameters on the thermoelastic response of FG beams.

• 한국전자파학회논문지
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• 제10권5호
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• pp.786-795
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• 1999

다중경로가 존재하는 수중환경에서 표적으로부터 발생되는 신호의 도래방위를 정확히 예측하기 위한 방법으로써. 최근 이론이 정립된 Inverse beamforming(역빔형성) integral equation의 해인 역빔형성기에 대한 이론적 고찰 및 simulation에 의한 방위탐지 성능분석을 수행하였고, 표적 도래방위의 좌우 구분을 위한 Cardioid 빔형성에 역빔형성 알고리즘을 적용한 IBF -Cardioid 빔형성기법을 고안하여 성능분석을 수행하였다. 이상적인 조건하에서 역빔형성기는 Conventional beamformed고전빔형성기)에 비해 array noise gain 3dB 이상 향상됨을 이론적으로 검증하고. simulation을 통하여 이를 입증하였다. 도래방위 탐지의 정확도를 나타내는 빔폭도 고전빔형성기에 의한 빔폭의 0.68배 정도인 것으로 입증하였다. 역빙형성 알고리즘이 적용된 Cardioid 빔형성(IBF -Cardioid 빔형성)기법은 고전 알고리즘에 의한 탐지성능에 비해 탐지의 정확도, 분해능 의 탐지성능이 우세함을 입증하였고, 특히, endfire 방향에 대한 정확한 방위탐지와 탐지성능이 향상됨을 입증 하였다.

• Structural Engineering and Mechanics
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• 제71권6호
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• pp.627-641
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• 2019

The paper focuses on bending analysis of the functionally graded (FG) plates with arbitrary shapes and boundary conditions. The material property of FG plates is modelled by using the power law distribution. Based on the first order shear deformation plate theory (FSDT), the governing equations as well as boundary conditions are formulated and obtained by using the principle of virtual work. The coupled Boundary Element-Radial Basis Function (BE-RBF) method is established to solve the complex FG plates. The proposed methodology is developed by applying the concept of the analog equation method (AEM). According to the AEM, the original governing differential equations are replaced by three Poisson equations with fictitious sources under the same boundary conditions. Then, the fictitious sources are established by the application of a technique based on the boundary element method and approximated by using the radial basis functions. The solution of the actual problem is attained from the known integral representations of the potential problem. Therefore, the kernels of the boundary integral equations are conveniently evaluated and readily determined, so that the complex FG plates can be easily computed. The reliability of the proposed method is evaluated by comparing the present results with those from analytical solutions. The effects of the power index, the length to thickness ratio and the modulus ratio on the bending responses are investigated. Finally, many interesting features and results obtained from the analysis of the FG plates with arbitrary shapes and boundary conditions are demonstrated.

• 한국수학사학회지
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• 제25권4호
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• pp.53-67
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• 2012

오늘날, 우주비행궤도의 정밀계산은 매우 실용적인 학문이 되었다. 프엥카레의 천체역학의 주요 키워드는 적분불변, 주기해, 점근해, 특성지수, 단일값을 갖는 새로운 적분의 불가능성등으로 볼 수 있다. 적분불변은 모든 시간에 걸쳐서 일정한 적분 값을 유지하는 것을 말한다. 곡선의 호상에서 취한 적분은 2, 3차원으로 확장하였다. 고유치는 궤적의 형식에 따라서 분류되는 바 매듭, 초점들, 말 안장점, 중심과 같은 것이다. 주기해에서는 고유값에 해당하는 특성지수에 따라서 주기해를 갖는다고 하였다. 주기해의 안정성은 특성지수의 성질을 조사하는 것과 동일한 것이다. 분지라고 불리는 천체궤도의 카오스적 존재 가능성을 프엥카레는 예외적 궤도의 존재로 주장하였고, 이는 아다마르의 견해대로 우연에 의한 확률적 궤도의 존재를 말하는 것이다. 호모크리닉점의 존재는 삼체문제의 이중 점근해를 말하고, 이것은 궤적이 카오적임을 말해주는 것이다. 주어진 조건에 따라서 엑스포넨셜 함수의 고유값인 특성지수가 계속 변함으로, 매우 작은 간격에서도 분지들은 얻게 되고, 원래의 주기와는 다소 멀어지는 것이다. 주기해의 안정성문제는 특성지수를 연구하는 것과 같다. 프엥카레는 궤적의 거동이 선형변환의 고유값 성질에 의존하고 이 고유값들과 서로 다른 특이점들 사이에 매우 밀접한 관련이 있음을 발견하였다. 뷔른스, 질덴, 순드만, 힐, 다윈, 벌코프, 하이테커, 아다마르등의 이론전개는 프엥카레의 이론과 불가분의 관계를 갖는다.

• Geomechanics and Engineering
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• 제14권6호
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• pp.519-532
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• 2018

In this work, two dimensional (2D) and quasi three-dimensional (quasi-3D) HSDTs are proposed for bending and free vibration investigation of functionally graded (FG) plates using hyperbolic shape function. Unlike the existing HSDT, the proposed theories have a novel displacement field which include undetermined integral terms and contains fewer unknowns. The material properties of the plate is inhomogeneous and are considered to vary continuously in the thickness direction by three different distributions; power-law, exponential and Mori-Tanaka model, in terms of the volume fractions of the constituents. The governing equations which consider the effects of both transverse shear and thickness stretching are determined through the Hamilton's principle. The closed form solutions are deduced by employing Navier method and then fundamental frequencies are obtained by solving the results of eigenvalue problems. In-plane stress components have been determined by the constitutive equations of composite plates. The transverse stress components have been determined by integrating the 3D stress equilibrium equations in the thickness direction of the FG plate. The accuracy of the present formulation is demonstrated by comparisons with the different 2D, 3D and quasi-3D solutions available in the literature.

• 대한기계학회논문집
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• 제14권6호
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• pp.1408-1416
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• 1990

본 연구에서는 과도 연성 열탄성문제의 해를 구할때 사용되는 직접시간적분방 법과 Laplace 변환방법은 상호 장 단점을 가지고 있다. 각 방법들의 장단점은 서로 배타적이므로 서로의 장점을 살리는 수치방법이 필요하다. 그런데, 대부분의 과도 열탄성문제는 급격한 온도변화로 인한 물체의 변형에 관심이 있기때문에 이 형태의 문 제를 효율적으로 다루는 데 주안점을 두고 본 연구를 수행하였다. 유도된 유한요소 방정식은 결국 열탄성 지배 방정식 중 열전달방정식인 에너지보존식은 Gurtin의 범함 수로부터 유도된 원래의 형태를 사용하나 수치적 안정성(numerical stability)을 보장 하기 위하여 운동방정식은 시간에 대한 2차미분 형태로 수정하였다. 에너지보존식은 시간에 대한 합성적분(convolution)형태로 표현되므로 온도의 시간미분항이 소거되므 로 경계에서의 급격한 온도변화로 인한 수치 해석적 문제점은 간단히 해결된다. 그 러므로, 제안된 수치해법은 직접시간적분방법의 일종이나 결과식인 유한요소방정식은 기존의 문헌들과 상당한 차이가 있다. 과도 연성 열탄성해석을 위한 새로운 근사수 치해법의 장점을 이론적으로 설명하기보다 수치계산면에서의 안전성, 정확성 및 효율 성이 있음을 증명하기 위하여 이미 발표된 문헌들에서 다룬 예제를 선정하여 해석결과 를 비교하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권1호
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• pp.240-263
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• 2021

One of the biggest challenges that the software industry is facing today is to create highly efficient applications without affecting the quality of healthcare system software. The demand for the provision of software with high quality protection has seen a rapid increase in the software business market. Moreover, it is worthless to offer extremely user-friendly software applications with no ideal security. Therefore a need to find optimal solutions and bridge the difference between accessibility and protection by offering accessible software services for defense has become an imminent prerequisite. Several research endeavours on usable security assessments have been performed to fill the gap between functionality and security. In this context, several Multi-Criteria Decision Making (MCDM) approaches have been implemented on different usability and security attributes so as to assess the usable-security of software systems. However, only a few specific studies are based on using the integrated approach of fuzzy Analytic Network Process (FANP) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) technique for assessing the significant usable-security of hospital management software. Therefore, in this research study, the authors have employed an integrated methodology of fuzzy logic, ANP and TOPSIS to estimate the usable - security of Hospital Management System Software. For the intended objective, the study has taken into account 5 usable-security factors at first tier and 16 sub-factors at second tier with 6 hospital management system softwares as alternative solutions. To measure the weights of parameters and their relation with each other, Fuzzy ANP is implemented. Thereafter, Fuzzy TOPSIS methodology was employed and the rating of alternatives was calculated on the foundation of the proximity to the positive ideal solution.

• International Journal of Computer Science & Network Security
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• 제22권12호
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• pp.91-97
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• 2022

Analyzing the psychological and pedagogical literature, we showed the interest of researchers in the problem posed. The concept of competence is considered, which is interpreted as giving the key to solving a wide range of educational and life tasks. Research competence implies the ability to cooperate, enter into contacts, readiness for changes, for self-determination and is an integral quality of the individual, expressed in the readiness and ability to independently search for solutions to new problems and creative transformation of reality based on a set of personal and meaningful knowledge, skills, methods of activity and value attitudes.The article offers conditions that certify the improvement of forms and methods of training students in the formation of research competence of future specialists. The use of innovative technologies contributes to improving the level of training of future specialists: students are better prepared for classes, take an active part in the assimilation of program material in laboratory classes. It is noted that this creates a subject-subject relationship between the student and the teacher, and changes the attitude of students to classes. In the process of such organization of educational activities, students are convinced of the need for knowledge and its effectiveness, learn to compare, generalize, classify, establish cause-and-effect relationships, express opinions, defend their point of view, they ensure success in their studies, and develop research competence. It is proved that in order to apply the latest technologies, the teacher himself must know them well, that is, constantly improve himself, master new methods, techniques, ideas, which will help him create new pedagogical technologies and implement them in the educational process.

• Computers and Concrete
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• 제25권6호
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• pp.551-563
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• 2020

This paper investigates the artificial neural network (ANN) to predict the dimensionless parameters for the maximum contact pressures and contact areas of a contact problem. Firstly, the problem is formulated and solved theoretically by using Theory of Elasticity and Integral Transform Technique. Secondly, the contact problem has been extended based on the ANN. The multilayer perceptron (MLP) with three-layer was used to calculate the contact distances. External load, distance between the two quarter planes, layer heights and material properties were created by giving examples of different values were used at the training and test stages of ANN. Program code was rewritten in C++. Different types of network structures were used in the training process. The accuracy of the trained neural networks for the case was tested using 173 new data which were generated via theoretical solutions so as to determine the best network model. As a result, minimum deviation value (difference between theoretical and C++ ANN results) of was obtained for the network model. Theoretical results were compared with artificial neural network results and well agreements between them were achieved.