• Advances in aircraft and spacecraft science
• /
• 제3권3호
• /
• pp.317-330
• /
• 2016

Nowadays, the interest of aerospace and automotive industries on virtual testing of medium-frequency vibrational behavior of shallow shell structures is growing. The development of software capable of predicting the vibrational response in such frequency range is still an open question because classical methods (i.e., FEM, SEA) are not fully suitable for the medium-frequency bandwidth. In this context the Variational Theory of Complex Rays (VTCR) is taking place as an ad-hoc technique to address medium-frequency problems. It is a Trefftz method based on a weak variational formulation. It allows great flexibility because any shape function that satisfies the governing equations can be used. This work further develops such theory. In particular, orthotropic materials are introduced in the VTCR formulation for shallow shell structures. A significant numerical example is proposed to show the strategy.

• Nonlinear Functional Analysis and Applications
• /
• 제28권1호
• /
• pp.205-235
• /
• 2023

In this paper, we introduce and study an iterative technique for solving quasimonotone split variational inequality problems and fixed point problem in the framework of real Hilbert spaces. Our proposed iterative technique is self adaptive, and easy to implement. We establish that the proposed iterative technique converges strongly to a minimum-norm solution of the problem and give some numerical illustrations in comparison with other methods in the literature to support our strong convergence result.

• Nonlinear Functional Analysis and Applications
• /
• 제27권1호
• /
• pp.189-201
• /
• 2022

The aim of the current work is to investigate the numerical study of a nonlinear Volterra-Fredholm integro-differential equation with initial conditions. Our approximation techniques modified adomian decomposition method (MADM) and variational iteration method (VIM) are based on the product integration methods in conjunction with iterative schemes. The convergence of the proposed methods have been proved. We conclude the paper with numerical examples to illustrate the effectiveness of our methods.

• 정보보호학회논문지
• /
• 제28권6호
• /
• pp.1463-1474
• /
• 2018

퍼징이란 유효하지 않은 값이나 임의의 값을 소프트웨어 프로그램에 입력하여, 보안상의 결함을 찾아내는 소프트웨어 테스팅 기법 중 하나로 이러한 퍼징의 효율성을 높이기 위한 여러 방법들이 제시되어 왔다. 본 논문에서는 필드를 기반으로 퍼징을 수행하면서 커버리지, 소프트웨어 크래쉬와 연관성이 높은 필드가 존재한다는 것에 착안하여, 해당 필드 부분을 집중적으로 퍼징하는 새로운 방식을 제안한다. 이 때, Variational Autoencoder(VAE)라는 딥 러닝 모델을 사용하여 커버리지가 높게 측정된 입력 값들의 특징을 학습하고, 이를 통해 단순 변이보다 학습된 모델을 통해 재생성한 파일들의 커버리지가 균일하게 높다는 것을 보인다. 또한 크래쉬가 발생한 파일들의 특징을 학습하고 재생성 시 드롭아웃을 적용하여 변이를 줌으로써 새로운 크래쉬를 발견할 수 있음을 보인다. 실험 결과 커버리지가 퍼징 도구인 AFL의 큐의 파일들보다 약 10% 정도 높은 것을 확인할 수 있었고 Hwpviewer 바이너리에서 초기 퍼징 단계 시 발생한 두 가지의 크래쉬를 사용하여 새로운 크래쉬 두 가지를 더 발견할 수 있었다.

• 대한수학회지
• /
• 제54권3호
• /
• pp.1015-1030
• /
• 2017

This paper is concerned with the following Klein-Gordon-Maxwell system: $$\{-{\Delta}u+{\lambda}V(x)u-(2{\omega}+{\phi}){\phi}u=f(x,u),\;x{\in}\mathbb{R}^3,\\{\Delta}{\phi}=({\omega}+{\phi})u^2,\;x{\in}\mathbb{R}^3$$ where ${\omega}$ > 0 is a constant and ${\lambda}$ is the parameter. Under some suitable assumptions on V (x) and f(x, u), we establish the existence and multiplicity of nontrivial solutions of the above system via variational methods. Our conditions weaken the Ambrosetti Rabinowitz type condition.

• 한국군사과학기술학회지
• /
• 제14권5호
• /
• pp.957-964
• /
• 2011

New time schemes based on the FEM were developed and their performances were tested with 2D wave equation. The least-squares and weighted residual methods are used to construct new time schemes based on traditional residual minimization method. To overcome some drawbacks that time schemes based on the least-squares and weighted residual methods have, ad-hoc method is considered to minimize residuals multiplied by others residuals as a new approach. And variational method is used to get necessary conditions of ad-hoc minimization. A-stability was chosen to check the stability of newly developed time schemes. Specific values of new time schemes are presented along with their numerical solutions which were compared with analytic solution.

• Water Engineering Research
• /
• 제2권3호
• /
• pp.171-178
• /
• 2001

There are three methods for analyzing flow and pressure distribution in looped water distribution networks (the loop method, the node method, the element method) taking into consideration hydraulic parameters chosen as unknown. For all these methods the non-linear system of equations can be solved by iterative procedures. The paper presents a different approach to this problem by using the method of variational formulations for hydraulic analysis of water distribution networks. This method has the advantage that it uses a specialized optimization algorithm which minimizes directly an objective multivariable function without constraints, implemented in a computer program. The paper compares developed method to the classic Hardy-Cross method. This shows the good performance of the new method.

• 대한조선학회논문집
• /
• 제40권1호
• /
• pp.63-68
• /
• 2003

Systematic geometrical variation method of hull forms, such as "1 -Cp", "Swinging" and "Lackenby" are widely used in the early stage of a new design from those of a similar parent ship, which shows a better performance through the model test and/or sea trials. This method is simple and easy to modify original hull forms without changing the main characteristics. The shape of the prismatic curie can be easily varied by these methods, however, the frame line shape in the body plan can′t be generated easily, when the section shapes are complicated or have discontinuities or the mismatch of the body plan and the stem and stern profiles. To overcome this drawback of the hull form variations, a simple and useful method has been proposed in the present study.

• Smart Structures and Systems
• /
• 제13권1호
• /
• pp.111-135
• /
• 2014

Based on the Reissner mixed variational theorem (RMVT), finite rectangular layer methods (FRLMs) are developed for the three-dimensional (3D) linear buckling analysis of simply-supported, fiber-reinforced composite material (FRCM) and functionally graded material (FGM) sandwich plates subjected to bi-axial compressive loads. In this work, the material properties of the FGM layers are assumed to obey the power-law distributions of the volume fractions of the constituents through the thickness, and the plate is divided into a number of finite rectangular layers, in which the trigonometric functions and Lagrange polynomials are used to interpolate the in- and out-of-plane variations of the field variables of each individual layer, respectively, and an h-refinement process is adopted to yield the convergent solutions. The accuracy and convergence of the RMVT-based FRLMs with various orders used for expansions of each field variables through the thickness are assessed by comparing their solutions with the exact 3D and accurate two-dimensional ones available in the literature.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2005년도 추계학술발표대회 논문집
• /
• pp.198-201
• /
• 2005

This study investigates the difference between single-cell and multi-cell cross-sections of thin-walled beams. The variationally and asymptotically consistent theory is used in order to model the two-cell thin- walled beam. The theory is based on an asymptotical analysis of two-dimensional shell energy. In addition, the method allows for the development of closed-form expressions for the displacement, stress field and beam stiffness coefficients. The numerical results show the difference between the cross-sectional stiffness of single-cell and that of multi-cell.