• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
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• pp.221-226
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• 1999

Three-dimensional flow analysis and numerical optimization methods are presented for the design of an axial-flow fan. Steady, Incompressible, three-dimensional Reynolds-averaged Wavier-Stokes equations are used as governing equations, and standard k-$\epsilon$ turbulence model is chosen as a turbulence model. Governing equations are discretized using finite volume method. Steepest descent method, conjugate gradient method and BFGS method are compared to determine the searching directions. Golden section method and quadratic fit-sectioning method are tested for one dimensional search. Objective function is defined as a ratio of generation rate of the turbulent kinetic energy to pressure head. Sweep angle distributions are used as design variables.

• KIEE International Transaction on Systems and Control
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• 제12D권1호
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• pp.33-38
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• 2002

In this paper, the infinite time optimal regulation problem for weakly coupled bilinear systems with quadratic performance criteria is obtained by a sequence of algebraic Lyapunov equations. This is the new approach is based on the successive approximation. In particular, the order reduction is achieved by using suitable state transformation so that the original Lyapunov equations are decomposed into the reduced-order local Lyapunov equations. The proposed algorithms not only solve optimal control problems in the weakly coupled bilinear system but also reduce the computation time. This paper also includes an example to demonstrate the procedures.

• Journal of information and communication convergence engineering
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• 제17권4호
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• pp.255-260
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• 2019

A pendubot is a representative example of an underactuated system that has fewer actuators than the degree of freedom of the system. In this study, the characteristics of the pendubot are first reviewed; each part is then designed using Solidworks by dividing the pendubot into three parts: the base frame, first link frame, and second link frame. These three parts are then imported into the Simulink environment via a STEP file format, which is the standard protocol used in data exchange between CAD applications. A 3D model of the pendubot is then constructed using Simscape, and the usefulness of the 3D model is validated by a comparison with a dynamic equation derived using the Lagrangian formulation. A linearized model around an upright equilibrium position is finally obtained, and a sliding mode controller is designed based on the linear quadratic regulator. Simulation results showed that the designed controller effectively maintained upright balance of the pendubot in the presence of disturbance.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.876-876
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• 2001

Axisymmetric finite element model is developed to determine sound propagation characteristics in a circular duct lined with a poroelastic foam. The foam and air models are derived based on the Biot's theory and the Helmholtz equation respectively and finally result in a quadratic eigenvalue problem in the wave number. Some cross sectional mode shapes are shown and sound attenuations and phase speeds of some acoustic modes are given. Those of fundamental modes are compared with those by forced response solutions and those from measurement results. The influence of lining thickness is also described on sound propagation characteristics.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제19권3호
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• pp.327-364
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• 2015

In this paper, a generalized guidance law with an arbitrary pair of guidance coefficients for impact angle control is proposed. Under the assumptions of a stationary target and a lag-free missile with constant speed, necessary conditions for the guidance coefficients to satisfy the required terminal constraints are obtained by deriving an explicit closed-form solution. Moreover, optimality of the generalized impact-angle control guidance law is discussed. By solving an inverse optimal control problem for the guidance law, it is found that the generalized guidance law can minimize a certain quadratic performance index. Finally, analytic solutions of the generalized guidance law for a first-order lag system are investigated. By solving a third-order linear time-varying ordinary differential equation, the blowing-up phenomenon of the guidance loop as the missile approaches the target is mathematically proved. Moreover, it is found that terminal misses due to the system lag are expressed in terms of the guidance coefficients, homing geometry, and the ratio of time-to-go to system time constant.

• Structural Engineering and Mechanics
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• 제72권4호
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• pp.525-540
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• 2019

The purpose of the present work was to study the dynamic instability of a three-layered, symmetric sandwich beam subjected to a periodic axial load resting on nonlinear elastic foundation. A higher-order theory was used for analysis of sandwich beams with soft core on elastic foundations. In the higher-order theory, the Reddy's third-order theory was used for the face sheets and quadratic and cubic functions were assumed for transverse and in-plane displacements of the core, respectively. The elastic foundation was modeled as nonlinear's type. The dynamic instability regions and free vibration were investigated for simply supported conditions by Bolotin's method. The results showed that the responses of the dynamic instability of the system were influenced by the excitation frequency, the coefficients of foundation, the core thickness, the dynamic and static load factor. Comparison of the present results with the published results in the literature for the special case confirmed the accuracy of the proposed theory.

• 대한수학회논문집
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• 제37권1호
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• pp.137-161
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• 2022

In this article, we study the existence and multiplicity of homoclinic solutions for the following fourth-order differential equation (1) u⁽⁴⁾(x) + ωu''(x) + a(x)u(x) = f(x, u(x)), ∀x ∈ ℝ where a(x) is not required to be either positive or coercive, and F(x, u) = ∫^u₀ f(x, v)dv is of subquadratic or superquadratic growth as |u| → ∞, or satisfies only local conditions near the origin (i.e., it can be subquadratic, superquadratic or asymptotically quadratic as |u| → ∞). To the best of our knowledge, there is no result published concerning the existence and multiplicity of homoclinic solutions for (1) with our conditions. The proof is based on variational methods and critical point theory.

• 대한수학회지
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• 제60권5호
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• pp.931-957
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• 2023

For an arbitrary integer x, an integer of the form $$T(x)={\frac{x^2+x}{2}}$$ is called a triangular number. Let α₁, ... , α_k be positive integers. A sum ${\Delta}_{{\alpha}_1,{\ldots},{\alpha}_k}(x_1,\,{\ldots},\,x_k)=\{\alpha}_1T(x_1)+\,{\cdots}\,+{\alpha}_kT(x_k)$ of triangular numbers is said to be almost universal with one exception if the Diophantine equation ${\Delta}_{{\alpha}_1,{\ldots},{\alpha}_k}(x_1,\,{\ldots},\,x_k)=n$ has an integer solution (x₁, ... , x_k) ∊ ℤ^k for any nonnegative integer n except a single one. In this article, we classify all almost universal sums of triangular numbers with one exception. Furthermore, we provide an effective criterion on almost universality with one exception of an arbitrary sum of triangular numbers, which is a generalization of "15-theorem" of Conway, Miller, and Schneeberger.

• Journal of Ceramic Processing Research
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• 제13권spc2호
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• pp.241-245
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• 2012

The barrier rib on plasma display panel (PDP) is a typical 3D-patterned thick film with thickness of 120 ㎛ and it is hard to measure its dielectric constant in this state of the product. Because the porosity of ceramic thick film influenced the mechanical and dielectric characteristics, it was expected that there was the relationship between two properties. Therefore, the correlation analysis between porosity, hardness and dielectric constant of the barrier rib was studied and the exponential curve between porosity and hardness, and the quadratic curve between porosity and dielectric constant were drawn. The dielectric constant was well related to hardness by K400kHz = 0.5672 + 5.695 ln(Hv). The hardness was measured at five points on two real panels which sintered by two types of profiles and then dielectric constants and deviation were estimated by the above equation.

• 한국약용작물학회지
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• 제3권2호
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• pp.77-80
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• 1995

한국산 광릉쥐오줌풀에 대한 광합성 및 호흡특성과 아울러 광합성의 일중(日中)변화와 이와 관련된 특성 및 생육상황에 미치는 온도의 영향을 조사하였던 그 결과는 다음과 같다. 1. 온도와 쥐오줌풀 잎의 광합성간에는 고도로 유의한 2차곡선회귀가 인정되었으며, 이 회귀식에 의해 산출한 최대광합성을 위한 은도는 $17.7^{\circ}C$이었다. 2. 쥐오줌풀 잎의 기공수는 잎의 표면에서 약 $25/mm^2$, 이면에서 $85mm^2$이었으며 기공의 크기는 $21{\sim}30/{\mu}m$로 나타났다. 3. 온도와 쥐오줌풀의 엽폭 및 근중간에는 각각 고도로 유의한 2차곡선회귀가 인정되었으며 이 회귀식에 의해 산출한 근생장(根生長)의 최적온도는 약 $20.3^{\circ}C$이었다.