• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
• /
• pp.205-210
• /
• 2000

An optimum design algorithm of PSC box girder bridges using design sensitivity analysis is proposed in this paper. For the efficiency of the proposed algorithm, approximated reanalysis techniques using design sensitivity analysis are introduced. And also to save the numerical efforts, an efficient reanalysis technique through approximated structural responses is proposed. A design sensitivity analysis of structural response is executed by automatic differentiation(AD). The efficiency and robustness of the proposed algorithm, compared with conventional algorithm, is successfully demonstrated in the numerical example.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 1998년도 춘계학술대회논문집; 용평리조트 타워콘도, 21-22 May 1998
• /
• pp.492-497
• /
• 1998

Thermoacoustic oscillation is a significant problem in cylindrical-type combustors such as common internal combustion engines, industrial furnaces, gas turbine, etc. This kind of low frequency oscillation can give rise to serious troubles such as the destruction of system or producing of a strong noise. Accurate numerical simulation of thermoacoustic phenomena is a complex and challenging problem. Especially, considering the reaction of mixture intensifies the difficulty of analysis. Like as other simulations of the aerodynamics and aeroacoustics, direct computation of thermoacoustic phenomena requires that the Navier-Stokes equations be solved using accurate numerical differentiation and time-marching schemes, with non-reflecting boundary conditions. In this study,, numerical approach aims at qualitative analysis and efficient prediction of problem, not at the development of an accurate scheme. Overally speaking, numerical prediction is reasonably matched with experimental result.

• 대한화학회지
• /
• 제22권3호
• /
• pp.128-132
• /
• 1978

산화환원 전위차 적정에 있어, 수치미분법으로 얻은 적정곡선의 2차 미분이 0이 되는 점을 얻어 종말점으로 삼을 때, 그 오차의 성격을 전자계산기를 사용하여 계산하였다. 그 결과로부커 당량점이 포함되는 시약첨가량의 어느 부분에 당량점이 존재하는 가에 따라 종말점의 오차가 변화함을 알 수 있다. 오차는 그 중심점에서 당량점이 벗어남에 따라 증가하여 최대 오차는 첨가량의 약 1/2이다. 따라서 수치미분법으로 영 2차미분점을 얻는 경우에는 적정곡선의 최대 기울기의 점을 얻어 두 값을 비교해 보는 것이 바람직스럽다. 또 종말점 부근에서는 묽은 시약을 사용하여 적정하는 방법으로 오차를 작게 할 수 있다.

• 한국통신학회논문지
• /
• 제33권8B호
• /
• pp.615-623
• /
• 2008

무선랜은 MAC 프로토콜과 스케줄링 알고리듬과 같은 다양한 기술을 이용하고 있으며 이런 기술 대부분은 주로 공평성과 서비스 차등화를 주로 다루고 있다. 그러나 대부분의 무선랜 시스템은 하나의 QoS 측면만을 고려하고 있기 때문에 이러한 기술을 동시에 제공하기 어렵다. 따라서 본 논문에서는 공평성과 차등서비스를 동시에 제공하기 위해서 Distributed Fair Scheduling(DFS)기법과 Enhanced Distributed Coordinated Function(EDCF) 기법을 이용하여 빠른 처리를 요구하는 트래픽의 처리뿐만 아니라 같은 우선순위를 갖는 트래픽의 공평성을 보장할 수 있는 F-EDCF를 제안하고 Markov 프로세스를 이용한 성능평가를 통하여 그 타당성을 검토한다. 성능평가에서 기존의 BDCF 방식보다 평균 전송량과 공평성뿐만 아니라 지연시간 또한 개선됨을 확인 할 수 있다.

• The Journal of the Acoustical Society of Korea
• /
• 제16권1E호
• /
• pp.29-34
• /
• 1997

Numerical prediction of aerodynamic noise radiated by subsonic rotors are carried out. A computer program has been developed which incorporates both the discrete frequency noise as well as the broadband noise arising from the ingestion of turbulence. Acoustic analogy is used in conjunction with Homicz's formulation of turbulence ingestion noise. Formulation 1A of Farassat is used to enhance the numerical analysis performance of Ffowcs-Williams Hawkings equation by eliminating the numericla time differentiation. Homicz's trubulence ingestion noise prediction technique is used to understand the characteristics of broadband noise radiated by isotropic trubulence in gestion. Numerical predictions are carried out for a number of rotor configurations and compared with experimental data. Monopole consideration of transonic rotor agrees well with both the experimental data and the linear theory. Noise radiation characteristics of rotor at lifting hover are investigated utilizing simple blade loading obtained by thin wing section theory. By incorporating discrete noise prediction of steady loading with broadband spectrum, much better agreement with experimental data is obtained in the low frequency region. The contributions from different noise mechanisms can also be analyzed through this method.

• Journal of applied mathematics & informatics
• /
• 제6권2호
• /
• pp.523-538
• /
• 1999

A new preconditioning method is investigated to reduce the roundoff error in computing derivatives using Chebyshev col-location methods(CCM). Using this preconditioning causes ration of roundoff error of preconditioning method and CCm becomes small when N gets large. Also for accuracy enhancement of differentiation we use a domain decomposition approach. Error analysis shows that for this domain decomposition method error reduces proportional to the length of subintervals. Numerical results show that using domain decomposition and preconditioning simultaneously gives super accu-rate approximate values for first derivative of the function and good approximate values for moderately high derivatives.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1992년도 하계학술대회 논문집 B
• /
• pp.567-569
• /
• 1992

Design sensitivity analysis is proposed for the optimal shape design of three dimensional magnetostatic problems. The direct differentiation method is introduced for design sensitivity analysis and the boundary element method with reduced magnetic scalar potential as the state variable is used to analyze the magnetic characteristics. In the direct differentiation method, the design sensitivity, defined as the total derivative of the objective function with respect to the design variables, is calculated based on the variation of the state variable with respect to the design variable. And the variation of He state variable is calculated by differentiating the both sides of the system matrix equation obtained by applying boundary element method. Through the numerical example with simple electromagnet, the usefullness is proved.

• 대한기계학회논문집A
• /
• 제20권5호
• /
• pp.1458-1467
• /
• 1996

A direct differentiationmethod is presented for the shape design sensitivity analysis of axisymmeetric elastic solids. Based on the exisymmetric boundary integralequaiton formulation, a new boundary ntegral equatio for sensitivity analysis is derived by taking meterial derivative to the same integral identity that was used in the adjoint variable melthod. Numerical implementation is performed to show the applicaiton of the theoretical formulation. For a simple example with analytic solution, the sensitivities by present method are compared with analytic sensitivities. As an application to the shape optimization, an optimal shape of a gas turbine disc toinimize the weight under stress constraints is found by incorporating the sensitivity analysis algorithm in an optimizatio program.

• Interaction and multiscale mechanics
• /
• 제2권4호
• /
• pp.333-352
• /
• 2009

We introduce a radial basis collocation method to solve axially moving beam problems which involve $2^{nd}$ order differentiation in time and $4^{th}$ order differentiation in space. The discrete equation is constructed based on the strong form of the governing equation. The employment of multiquadrics radial basis function allows approximation of higher order derivatives in the strong form. Unlike the other approximation functions used in the meshfree methods, such as the moving least-squares approximation, $4^{th}$ order derivative of multiquadrics radial basis function is straightforward. We also show that the standard weighted boundary collocation approach for imposition of boundary conditions in static problems yields significant errors in the transient problems. This inaccuracy in dynamic problems can be corrected by a statically condensed semi-discrete equation resulting from an exact imposition of boundary conditions. The effectiveness of this approach is examined in the numerical examples.

• Journal of Mechanical Science and Technology
• /
• 제19권spc1호
• /
• pp.350-356
• /
• 2005

A method of dynamic analysis of mechanical systems considering probabilistic properties is proposed in this paper. Probabilistic properties that result from manufacturing tolerances can be represented by means and standard deviations (or variances). The probabilistic characteristics of dynamic responses of constrained multi-body systems are obtained by two ways : the proposed analytical approach and the Monte Carlo simulation. The formerpaper, necessitates sensitivity information to calculate the standard deviations. In this a direct differentiation method is employed to find the sensitivities of constrained multi-body systems. To verify the accuracy of the proposed method, numerical examples are solved and the results obtained by using the proposed method are compared to those obtained by Monte Carlo simulation.