• Journal of applied mathematics & informatics
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• 제7권1호
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• pp.269-278
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• 2000

A Boolean function generates a binary sequence which is frequently used in a stream cipher. There are number of critical concepts which a Boolean function, as a key stream generator in a stream cipher, satisfies. These are nonlinearity, correlation immunity, balancedness, SAC(strictly avalanche criterion), PC(propagation criterion) and so on. In this paper, we present the algorithms for generating random nonlinear combining functions satisfying given correlation immune order and nonlinearity. These constructions can be applied for designing the key stream generators. We use Microsoft Visual C++6.0 for our program.

• 한국해양공학회지
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• 제2권1호
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• pp.46-58
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• 1988

The experimental investigations on the motion characteristics of a marine riser both in air and water were performed. The static deflections and natural frequencies of the riser in air including the effect of static offset, were obtained from the experiment. These results were compared with those of theoretical prediction by using a simple asymptotic formula. In order to investigate the nonlinear motion characteristics of the riser subject to nonlinear viscous drag and large displacement, the forced oscillation tests both in air and water were performed. In the forced oscillation tests in air, it was found that the transverse motion due to geometrical nonlinearity grows when the amplitude of in-line oscillation exceeds a certain critical value, say, order of 1-2 diameters. The planar motions of the riser in water due to vortex shedding and the geometrical nonlinearity were described. Some of these results were also compared with those of theoretical analysis, which uses a numerical perturbation technique based on the derived linear asymptotic solutions, and found to be generally in good agreement.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1997년도 봄 학술발표회 논문집
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• pp.240-247
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• 1997

Single-layer latticed domes, which ore consisted of slender linear elements, are able to transmit external loads to the structure by in-plane forces, therefore spatial structures can be constructed with the merit of its own lightweight. But, as external load reaches to any critical level at which each member has not material nonlinearity, the single-layer latticed dome shows unstable phenomenon. In particular, pin-connected single-layer latticed domes have much complicate unstable phenomena that are combined with nodal buckling and member buckling. Furthermore, single-layer latticed domes are very sensible to the initial imperfection which occurred inevitably in construction. In this study, we are going to grasp the characteristics of instability for the latticed dome by finite element method considering geometrical nonlinearity.

• Wind and Structures
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• 제17권5호
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• pp.553-564
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• 2013

By using the nonlinear aerostatic stability theory together with the method of mean wind decomposition, a method for nonlinear aerostatic stability analysis is proposed for long-span suspension bridges under yaw wind. A corresponding program is developed considering static wind load nonlinearity and structural nonlinearity. Taking a suspension bridge with three towers and double main spans as an example, the full range aerostatic instability is analyzed under wind at different attack angles and yaw angles. The results indicate that the lowest critical wind speed of aerostatic instability is gained when the initial yaw angle is greater than $0^{\circ}$, which suggests that perhaps yaw wind poses a disadvantage to the aerostatic stability of a long span suspension bridge. The results also show that the main span in upstream goes into instability first, and the reason for this phenomenon is discussed.

• Wind and Structures
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• 제25권5호
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• pp.415-432
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• 2017

The nonlinear aerodynamic instability of a tensioned plane orthotropic membrane structure is theoretically investigated in this paper. The interaction governing equation of wind-structure coupling is established by the Von $K\acute{a}rm\acute{a}n's$ large amplitude theory and the D'Alembert's principle. The aerodynamic force is determined by the potential flow theory of fluid mechanics and the thin airfoil theory of aerodynamics. Then the interaction governing equation is transformed into a second order nonlinear differential equation with constant coefficients by the Bubnov-Galerkin method. The critical wind velocity is obtained by judging the stability of the second order nonlinear differential equation. From the analysis of examples, we can conclude that it's of great significance to consider the orthotropy and geometrical nonlinearity to prevent the aerodynamic instability of plane membrane structures; we should comprehensively consider the effects of various factors on the design of plane membrane structures; and the formula of critical wind velocity obtained in this paper provides a more accurate theoretical solution for the aerodynamic stability of the plane membrane structures than the previous studies.

• 대한수학회보
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• 제53권3호
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• pp.667-680
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• 2016

We get a theorem which shows the multiple weak solutions for the bifurcation problem of the superquadratic nonlinear Hamiltonian system. We obtain this result by using the variational method, the critical point theory in terms of the $S^1$-invariant functions and the $S^1$-invariant linear subspaces.

• 대한수학회보
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• 제59권4호
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• pp.961-977
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• 2022

In this paper, we consider the following Kirchhoff type equation on the whole space $$\{-(a+b{\displaystyle\smashmargin{2}{\int\nolimits_{{\mathbb{R}}^3}}}\;{\mid}{\nabla}u{\mid}^2dx){\Delta}u=u^5+{\lambda}k(x)g(u),\;x{\in}{\mathbb{R}}^3,\\u{\in}{\mathcal{D}}^{1,2}({\mathbb{R}}^3),$$ where λ > 0 is a real number and k, g satisfy some conditions. We mainly investigate the existence of ground state solution via variational method and concentration-compactness principle.

• 대기
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• 제17권3호
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• pp.231-240
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• 2007

The flow regimes of continuously stratified flow over a double mountain and the effects of a double mountain on wave breaking, upstream blocking, and severe downslope windstorms are investigated using a mesoscale numerical model (ARPS). According to the occurrence or non-occurrence of wave breaking and upstream blocking, three different flow regimes are identified over a double mountain. Higher critical Froude numbers are required for wave breaking and upstream blocking initiation for a double mountain than for an isolated mountain. This means that the nonlinearity and blocking effect for a double mountain is larger than that for an isolated mountain. As the separation distance between two mountains decreases, the degree of flow nonlinearity increases, while the blocking effect decreases. A rapid increase of the surface horizontal velocity downwind of each mountain near the critical mountain height for wave breaking initiation indicates that severe downslope windstorms are enhanced by wave breaking. For the flow with wave breaking, the numerically calculated surface drag is much larger than theoretically calculated one because the region with the maximum negative perturbation pressure moves from the top to the downwind slope of each mountain as the internal jump propagating downwind occurs.

• Wind and Structures
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• 제26권6호
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• pp.355-367
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• 2018

This paper studies the aerodynamic stability of a tensioned, geometrically nonlinear orthotropic membrane structure with hyperbolic paraboloid in sag direction. Considering flow separation, the wind field around membrane structure is simulated as the superposition of a uniform flow and a continuous vortex layer. By the potential flow theory in fluid mechanics and the thin airfoil theory in aerodynamics, aerodynamic pressure acting on membrane surface can be determined. And based on the large amplitude theory of membrane and D'Alembert's principle, interaction governing equations of wind-structure are established. Then, under the circumstance of single-mode response, the Bubnov-Galerkin approximate method is applied to transform the complicated interaction governing equations into a system of second-order nonlinear differential equation with constant coefficients. Through judging the frequency characteristic of the system characteristic equation, the critical velocity of divergence instability is determined. Different parameter analysis shows that the orthotropy, geometrical nonlinearity and scantling of structure is significant for preventing destructive aerodynamic instability in membrane structures. Compared to the model without considering flow separation, it's basically consistent about the divergence instability regularities in the flow separation model.

• Structural Engineering and Mechanics
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• 제67권1호
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• pp.53-67
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• 2018

The changes of parameters of pressure and velocity of propagation of elastic pressure and shear waves in uniformly deformed solid compressible media are studied within the nonclassically linearized approach (NLA) of nonlinear elastodynamics to create a new theoretical basis of the geomechanical interpretation of various groups of geophysical observational and experimental data. The cases of small and large deformations are considered while their describing by various elastic potentials, i.e., problems considering the physical and geometric nonlinearity. Convenient analytical formulae are obtained to calculate the indicated parameters in the deformed isotropic media within the nonclassical linear and nonlinear solution in the NLA. Specific numerical experiments are conducted in case of overall compression of various materials. It is shown that the method (generally accepted in the studies of mechanics of standard constructional materials) of additional linearization (relative to the pressure parameter) in the basic correlations of the NLA introduces substantial quantitative and qualitative errors into the results at significant preliminary deformations. The influences of the physical and geometric nonlinearity on the studied characteristics of the medium are large in various materials and differ qualitatively. The contribution of nonlinear components to the values of the considered parameters prevails over linear components at large deformations. When certain critical values of compression deformations in the medium are achieved, elastic waves with actual velocity cannot propagate in it. The values of the critical deformations for pressure and shear waves differ within different elastic potentials and variants of the theory of initial deformations.