• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.3
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• pp.183-189
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• 2013

In this paper, uncertainties and failure criteria of structure are mathematically expressed by random variables and a limit state equation. A limit state equation is approximated by Fleishman's 3rd order polynomials and the theoretical moments of an approximated limit state equation are calculated. Fleishman introduced a 3rd order polynomial in terms of only standard normal distiribution random variables. But, in this paper, Fleishman's polynomial is extended to various random variables including beta, gamma, uniform distributions. Cumulants and a normalized limit state equation are used to calculate a theoretical moments of a limit state equation. A cumulative distribution function of a normalized limit state equation is approximated by a Pearson system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.1
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• pp.98-111
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• 1995

The objective of this work is to investigate the form of equations of state for specific refrigerants. In particular, equations of the extended van der Waals form have been studied. As a result, a new equation of state has been developed and tested over ranges of pressure and density up to 5 and 1.5 times critical, respectively. The equation of state separates the compressibility factor into two parts. One is the repulsive compressibility factor and the other is attractive. The former is in the same form of Carnahan-Starling's repulsive term with constant hard-sphere volume. The latter is based on a combination of two different functions linear to density. The equation of state developed here has 12 adjustable parameters and correlates PVT data successfully. All properties are in reduced forms.

• 전기의세계
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• v.22 no.2
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• pp.40-44
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• 1973

A method for obtaining state equation for nonlinear time-varying RLC networks is presented. The nonlinear time-varying RLC elements are decomposed by using Murata method to formulate nonlinear state equation. A nonlinear time-varying RLC network containing twin tunnel diode is solved as an example. In consequence of solving the examjple, simple methods are presented for revising the original network model so that the formulation of state equation is simplified.

• Journal of the Korean Chemical Society
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• v.56 no.2
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• pp.207-211
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• 2012

Using Carnahan-Starling equation for hard spheres and a lattice model with an attractive potential, a new twoparameter equation of state for pure gases is derived. Using this equation, compressibility factors are calculated and compared with Nelson-Obert generalized compressibility factor charts. The results show that the agreement of this equation with the experimental Nelson-Obert charts is similar to that of Redlich-Kwong equation in the average. But parameters and terms of the new equation have physical meanings which are more definite than those of Redlich-Kwong equation.

• Journal of the Korean Chemical Society
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• v.44 no.6
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• pp.587-591
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• 2000

Many theories have been suggested to obtain an equation of state for polymeric liquids. Most of them are based on the concepts of cell, hole, free volume or lattice etc. One of the most succesful theories is an equation of state theory of Flory and his coworkers based on the concept of free volume. In this work, van der Waals potential used in Flory's theory was modified, giving a new equation of state for polymeric liquids. The calculated results showed that the new equation of state gave better agreement with experimental PVT data than Flory's theory.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.12
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• pp.579-587
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• 2014

This paper deals with precise analytical state equation modeling of a variable speed refrigeration system (VSRS) for optimum control in state space. The VSRS is described as multi-input and multi-output (MIMO) system, which has two controlled variables and two control inputs. First, the Navier-Stokes equation and mass flow rate were applied to each component of the basic refrigeration cycle to build a dynamic model. The dynamic model, represented by a differential equation, was transformed into the state equation formula. Next, a full-order state observer was built to estimate all of the state variables to compose an optimum control system. Then, an optimum controller was designed to minimize an evaluation function that has input energy and control error. Finally, simulations and experiments were conducted to verify the validity of the proposed modeling and designed optimum controller to regulate target temperature and superheat in a 1RT oil cooler system. The results show that the proposed method, state equation modeling and optimum control, is efficient to ensure optimal control performance of the VSRS.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.3
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• pp.39-51
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• 2010

Theoritical principles about the real gas equation of state are investigated and comparisons for the thermophysical properties of oxygen, hydrogen, and methane as the propellants of liquid rocket engine are carried out for the various conditions of pressure and temperature including supercritical conditions. The properties obtained using the real gas equation of state(Soave modification of Redlich-Kwong, Peng-Robinson equation of state, and extended corresponding states principle) have been compared with the results of applying the ideal gas equation of state. Differences of thermophysical properties among the models specifically at the liquid phase regime and their error ranges are addressed.

• Journal of the Korean Institute of Gas
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• v.1 no.1
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• pp.41-48
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• 1997

The equation of state is widely utilized as a simple model for the prediction of gas properties. There are several equations of state and they often make diverse and hard to believe output of gas properties. In this study, We show a reliability of equation of state for nitrogen, oxygen and argon in pressure range from 1 bar to 30 bar and temperature range from liquefaction to room temperature. We use three equations of state such as Soave-Redlich-Kwong, Peng-Robinson and BWR-LS' equation of state which provided in the Aspen plus. The results were compared with literatures and virial equation. Finally, We report the differences of process calculation of distillation column and expansion turbine in cryogenic air separation plant with change of equation of state.

• Bulletin of the Korean Chemical Society
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• v.29 no.1
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• pp.33-37
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• 2008

A phenomenological theory of viscosity previously proposed by the present authors8 is applied to the corresponding state theory for the viscosity of liquid. Through the process of the formulation of the corresponding state equation, we can find the simple viscosity equation with no parameters in a reduced form. The liquid viscosities of various substances can be calculated using this equation when we know only the values of the molecular weight and critical constant of substances. A corresponding state equation for the viscosity of liquid from this theory may be applicable to predicting viscosities of various substances under varying temperature and pressure. As a result, this equation may be widely applied to chemical engineering.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.3
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• pp.399-406
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• 1996

This paper presents a method of hierarchical state estimation of the time-varying linear systems via Block-pulse function(BPF). When we estimate the state of the systems where noise is considered, it is very difficult to obtain the solutions because minimum error variance matrix having a form of matrix nonlinear differential equations is included in the filter gain calculation. Therefore, hierarchical approach is adapted to transpose matrix nonlinear differential equations to a sum of low order state space equation from and Block-pulse functions are used for solving each low order state space equation in the form of simple and recursive algebraic equation. We believe that presented methods are very attractive nd proper for state estimation of time-varying linear systems on account of its simplicity and computational convenience. (author). 13 refs., 10 figs.