• Journal of Electrical Engineering and Technology
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• 제9권6호
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• pp.2036-2041
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• 2014

In this paper, a thermal model is developed for the bus bar system to predict the temperature variation during the transient time period and to calculate both the steady-state and transient electrical current carrying capacity (ampacity) of bus bar. The bus bar system installed in the power house of Kumaraguru College of Technology, Coimbatore has been considered. Temperature variation predicted in the modelling is validated by observing the current and steady state temperatures in different feeders of the bus bar. Magnetic field of the extreme phases R and B induces more current in the middle phase Y. Hence, the steady state temperature in the phase Y is greater than other two phases. The transient capabilities of the bus bar are illustrated by calculating the variations in the bus bar temperature when it is subjected to a step change in current during the peak hours due to increase in hostel utilities and facilities (5.30 pm to 10.30 pm). The physical and geometrical properties of the bus bar and temperature variation in the bus bar are used to estimate the thermal time constants for common bus bar cross-sections. An analytical expression for the time constant of the bus bar is derived.

• 한국안광학회지
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• 제4권2호
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• pp.51-55
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• 1999

안구운동의 회선점을 중심으로 한 안구운동은 직각좌표의 좌표축 회전변환에 의한 회전행렬 $R_x$, $R_y$, $R_z$로 표현할 수 있으며, 6가지의 눈의 주된 회전 형태인 외-내전, 상-하전, 내-외방 회선 등으로 기술된다. 제1안위에서 제3안위까지의 안구운동은 회전행렬의 조합으로 구성되고, 6가지의 주회전과 8가지의 보조회전으로 6개의 외안근 운동을 표현 할 수 있다. 안구운동에 의한 동공점인 각막정점의 위치를 각각좌표의 회전행렬을 구좌표$(r,{\theta},{\phi})$로 전환하여 9가지로 기술된다.

• Computers and Concrete
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• 제9권2호
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• pp.153-169
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• 2012

The contribution of steel fibers on the 28-day compressive strength of high-performance steel fiber reinforced concrete was investigated, is presented. An extensive experimentation was carried out over water-cementitious materials (w/cm) ratios ranging from 0.25 to 0.40, with silica fume-cementitious materials ratios from 0.05 to 0.15, and fiber volume fractions ($V_f$= 0.0, 0.5, 1.0 and 1.5%) with the aspect ratios of 80 and 53. Based on the test results of 44 concrete mixes, mathematical model was developed using statistical methods to quantify the effect of fiber content on compressive strength of HPSFRC in terms of fiber reinforcing index. The expression, being developed with strength ratios and not with absolute values of strengths, is independent of specimen parameters and is applicable to wide range of w/cm ratios, and used in the mix design of steel fiber reinforced concrete. The estimated strengths are within ${\pm}3.2%$ of the actual values. The model was tested for the strength results of 14 mixes having fiber aspect ratio of 53. On examining the validity of the proposed model, there exists a good correlation between the predicted values and the experimental values of different researchers. Equation is also proposed for the size effect of the concrete specimens.

• Environmental Engineering Research
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• 제16권4호
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• pp.243-252
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• 2011

Several mathematical relationships have been developed to describe bacterial responses to UV irradiation. Pseudomonas aeruginosa was taken as a bacterial model. The results obtained showed that the kinetics of disinfection is far to be as uniform. In fact, application of the model of Chick-Watson in its original form or modification, taking into account the speed change during the disinfection process, has not significantly improved results. The application of both models of Collins-Selleck and Hom constitute a major opportunity to simulate goodly the kinetics of UV disinfection. The results obtained showed that despite the major advantage held by applying the Hom model in this process of disinfection and for all strains studied, the model of Collins-Selleck gave the best results for the description of the UV inactivation process. The design of reactors, operating in continuous disinfection system, requires taking into account the hydrodynamic behaviour of water in the reactor. Knowing that a reduction of 4-log is necessary in the case of wastewater reuse for irrigation, a model integrating the expression of disinfection kinetics and the hydrodynamics through the UV irradiation room was proposed. The results highlight the interest to develop reactors in series working as four perfectly mixed reactors.

• 한국항행학회논문지
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• 제2권2호
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• pp.126-131
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• 1998

광학적 스캐닝 홀로그래피에 있어서, 물체의 3차원 홀로그래픽 정보는 2차원적 광스캐닝에 의해서 생성되며, 광스캐닝 광선은 time-dependent한 Gaussian 형태의 Fresnel 윤대판(zone plate)이다. 본 기술에서 홀로그래픽 정보는 그 자체로서 전기적인 신호로서 발생하기 때문에 전자광선 addressed - spatial light modulator을 사용하여 영상 재생이 가능하다. 이 기법의 응용분야로서 3-차원 원거리 광 센서로서 사용될 수 있으며, 특히 비행물체 확인에 응용될 수 있다. 본 논문에서, 우리는 먼저 광스캐닝 홀로그래피에 대해 간략한 기술과 본 기술 시스템에 있어서 광스캐닝 빔의 해상도를 먼저 유도하고, 그 다음으로 Gaussian 원리를 이용하여 홀로그래픽 image 재생을 위해 필요한 실상(real image) 및 허상(virtual image)에 대한 수학적 표현을 제시하고자 한다.

• 전자공학회논문지
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• 제53권12호
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• pp.88-93
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• 2016

본 논문에서는 유한체의 수학적 성질과 그래프이론을 바탕으로 GF(P)상의 선형디지털스위칭함수구성을 효과적으로 구성하는 한가지 방법을 제안하였다. 제안한 방법은 주어진 임의의 디지털스위칭함수의 입출력 사이의 연관관계특성으로 부터 DCG를 도출한 후에 노드의 개수를 인수분해한다. 이때 행렬방정식을 해당 차수보다 낮은 기약다항식으로 인수분해하여 그 결과를 부분회로실현한 다음 선형결합함으로써 최종 선형디지털스위칭함수를 구성하였다. 그 결과 기존의 방법에 비해 선형디지털스위칭함수구성을 상당히 간단화 할 수 있었으며 회로구성은 유한체 GF(P)내에서 정의된 가산기와 계수곱셈기를 사용하여 용이하게 실현 할 수 있다.

• 한국정밀공학회지
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• 제21권10호
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• pp.127-136
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• 2004

This paper is the first of two companion papers concerning the analysis and design of a pneumatic vibration isolation system. The design optimization of the pneumatic vibration isolation system is required for the reduction of cost, endeavor and time, and it needs modeling and calculation algorithm. The nonlinear models are devised from the fluid mechanical expression for components of the system and the calculation algorithm is derived from the mathematical relationship between the models. It is shown that the orifice makes the nonlinear property of the transmissibility curve that the resonant frequency changes by the amplitude of excited vibration. Linearization of the nonlinear models is tried to reduce elapsed time and truncation error accumulation and to enable the transmissibility calculation of the system with multi damping chambers. The equivalent mechanical models generated by linearization clarify the function of each component of the system and lead to the linearized transfer function that can give forth to the transmissibility exactly close to that of nonlinear models. The modified successive under-relaxation method is developed to calculate the linearized transfer function.

• 한국정밀공학회지
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• 제32권5호
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• pp.415-422
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• 2015

Ballscrews are important motion transfer and positioning units of industrial machinery and precision machines. Positioning accuracy of the feed drive system depends upon axial stiffness of ballscrew systems. As the nut stiffness depends upon preload and operating conditions, analytical modeling of the stiffness is performed through the contact and body deformation analysis. For accurate contact analysis, the contact angle variation between balls and grooves is incorporated in the developed model. To verify the developed mathematical stiffness model, experiments are conducted on the test-rig. Through the uncertainty analysis according to GUM (Guide to the expression of Uncertainty in Measurement), it is confirmed that the formulated stiffness model has over 85% estimation accuracy. After constructing the ballscrew DB, a quick turnaround system for the nut stiffness estimation has been developed in this research.

• Structural Engineering and Mechanics
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• 제16권2호
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• pp.153-176
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• 2003

From the equation of motion of a "bare" non-uniform beam (without any concentrated elements), an eigenfunction in term of four unknown integration constants can be obtained. When the last eigenfunction is substituted into the three compatible equations, one force-equilibrium equation, one governing equation for each attaching point of the concentrated element, and the boundary equations for the two ends of the beam, a matrix equation of the form [B]{C} = {0} is obtained. The solution of |B| = 0 (where ${\mid}{\cdot}{\mid}$ denotes a determinant) will give the "exact" natural frequencies of the "constrained" beam (carrying any number of point masses or/and concentrated springs) and the substitution of each corresponding values of {C} into the associated eigenfunction for each attaching point will determine the corresponding mode shapes. Since the order of [B] is 4n + 4, where n is the total number of point masses and concentrated springs, the "explicit" mathematical expression for the existing approach becomes lengthily intractable if n > 2. The "numerical assembly method"(NAM) introduced in this paper aims at improving the last drawback of the existing approach. The "exact"solutions in this paper refer to the numerical results obtained from the "continuum" models for the classical analytical approaches rather than from the "discretized" ones for the conventional finite element methods.

• 한국태양에너지학회 논문집
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• 제34권2호
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• pp.1-7
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• 2014

Generally, buck converter controller is designed to control the output voltage of the converter. However, design of the controller in a photovoltaic power conditioning system is different from theoretical design guideline. The controller in a photovoltaic power conditioning system controls the input voltage of the converter (the output voltage of the solar cell) to meet a maximum power point tracking (MPPT) performance. In this study, a new model for buck converter used in a photovoltaic power conditioning system is proposed, which is linearized after state-space averaging in each period. Also, mathematical expression of the modeled buck converter is interpreted separately as small and large signals; therefore its appropriateness is measured to design linear voltage and current controller.