• Architectural research
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• v.12 no.2
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• pp.93-98
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• 2010

This paper describes a numerical method for estimating the elastic moduli of cement paste. The cement paste is modeled as a unit cell which consists of three components: the unhydrated cement grain, the gel, and the capillary pore. In the unit cell, the volume fractions of the constituents are quantified using a single kinetic function calculating the degree of hydration. The elastic moduli of cement paste are calculated from the total displacements of constituents when a uniform pressure is applied to the gel contact area. The cement paste is assumed to be a homogenous isotropic matrix. Numerical simulations were conducted through the finite element analysis of the three-dimensional periodic unit cell. The model predictions are compared with experimental results. The predicted trends are in good agreement with experimental observations. This approach and some of the results might also be relevant for other technical applications.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.8
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• pp.670-677
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• 2012

In this paper, mechanical property of biomorphic C/SiC composite was calculated by unit cell analysis. The microstructural arrangements of carbonized pine and radiata pine which were impregnated with silicon, were idealized as square and hexagonal arrays. Unit cell was then defined and equivalent elastic constants were calculated. A single and double unit cell structures were considered. The effect of void distribution was also studied by monte carlo simulation.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.181-188
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• 2004

Structural analysis for materials containing regularly spaced in-homogeneities is usually executed by using averaged material properties. For the homogenization process, a unit cell is defined and loaded somehow, and its response is investigated to evaluate the properties. The imposed loading conditions should accord to the behavior of unit cell immersed in the macroscopic structure in order to guarantee the accuracy of the effective properties. Each unit cell shows periodic variation of strain if the material is loaded uniformly, and in this study, direct implementation of this characteristic behavior is attempted on FE models of unit cell. Conventional finite element analysis tool can be used without any modification, and the boundary of unit cell is constrained in a way that the periodicity is satisfied. The proposed method is applicable to skew arrayed in-homogeneity problems. The flexibility matrix relating tonsorial stress and strain components in skewed rectilinear coordinate system is transformed so that the required engineering constants can be evaluated. Effective properties are computed for the materials with square and skew arrayed circular holes, and its accuracy is examined.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.5
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• pp.623-631
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• 2011

Metallic sandwich panels based on a truss core structure have been developed for a wide range of potential applications with their lightweight and multi-functionality. Structural performance of sandwich panels can be predicted from the studies on mechanical behavior of a unit cell of truss core structures. Analytical investigations on the unit cell provide approximated guidelines for the design of overall core structures for a specific application in short time. In this study, the effects of geometrical parameters on mechanical behavior of a pyramidal shape of unit cell were investigated with analytical models. The unit cell with truss member angle of 45 degree was considered as reference model and other models were designed to have the same weight and projected area but different truss member angle. All truss members were assumed to be connected with pin joint in analytical models. Under the assumptions, the equivalent strength and stiffness of the unit cell under compressive and shear loads were predicted and compared. And finally, the optimum core member angle to have maximum mechanical property could be calculated and verified with FE analysis results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.12
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• pp.1950-1957
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• 2004

Analysis for structures composed of materials containing regularly spaced in-homogeneities is usually executed by using averaged material properties. In order to evaluate the effective properties, a unit cell is defined and loaded somehow, and its response is investigated. The imposed loading, however, should accord to the status of unit cells immersed in the macroscopic structure to secure the accuracy of the properties. In this study, mathematical description for the periodicity of the displacement field is derived and its direct implementation into FE models of unit cell is attempted. Conventional finite element code needs no modification, and only the boundary of unit cell should be constrained in a way that the periodicity is preserved. The proposed method is applicable to skew arrayed in-homogeneity problems. Homogenized in-plane elastic properties are evaluated for a few representative cases and the accuracy is examined.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1997.10a
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• pp.35-41
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• 1997

Unit cell analyses were peformed to study the engineering properties of satin weave textile composites. Two 5-harness satin weave layers with fiber tow shifts were modeled by unit cells and repeating boundary conditions were applied at the outer surface of the unit cells. Multi-field macroelements were employed to consider the microstructure details and to effectively reduce computer memory requirements. Preliminary results indicated that the engineering properties of 5-harness satin weave textile composites can vary significantly according to the manner how the adjacent fiber tows were arranged in stacking.

• Proceedings of the Safety Management and Science Conference
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• 2003.11a
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• pp.351-357
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• 2003

The optimum polymer gel electrolyte composition ratio was 23 : 66 : 11 wt% of P(VdF-co-HFP) : PVP =20 : 3), (PC: EC =44 : 22) and TEABF$_4$. And the optimal thickness of polymer gel electrolyte was 50 ${\mu}{\textrm}{m}$. The electrochemical characteristics result of unit cell were 31.41 Fig of specific capacitance, and 3.21$\times$10$^{-3}$ S/cm of ion conductivity. Ion conductivity of polymer gel electrolytes decreased according to added PVP through impedance analysis, and it was higher in 7 wt%, but electrochemical characteristics of unit cell were better in 3 wt% PVP. And for excellent ion conductivity of polymer gel electrolytes, the use of a thin layer electrolyte(20 $\mu\textrm{m}$) was an effective method, but with unit cell application, the best thickness was 50 $\mu\textrm{m}$. Unit cell showed higher capacitance and more stable electrochemical performance when hot pressed between polymer gel electrolyte and electrode. This results from enhancement of the physical contact between the electrode and the polymer gel electrolyte and good accessibility of the liquid electrolyte to the electrode surface.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.396-401
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• 2003

In the present study, preliminary investigation were carried out by analysis of energy system(heat and electricity) based on phosphoric acid fuel-cell of 50 kW for eco-apartment houses. Analysis model were consisted of fuel cell energy system, secondary energy unit and residential building of 5 stories with 20 and 40 households. And the investigation results reviewed under load pattern of heat and electric power of the apartment houses. The results showed mismatch between the needed heat load pattern and output of fuel cell energy system. The mismatch rate were assessed about 10-180% of heat load for apartment houses with season. We found that secondary energy unit are needed in order to supply insufficient heat.

• Transactions of Materials Processing
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• v.33 no.4
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• pp.270-276
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• 2024

In order to improve the performance of the PM (Particulate Matter) filter, the TPMS structure was used as a flow controller to control the flow entering the filter. Among various TPMS structures, a primitive structure that is easy to utilize 3D printing technique was selected and the effect of unit cell size was analyzed. In addition, numerical analysis was performed and swirl ratio was analyzed to confirm changes in filter inlet flow characteristics that affect changes in filter performance. Unit cell size is closely related to filter performance, and both PM collection efficiency and pressure drop increase as unit cell size decreases. Through quality factor (QF) comparison, which comprehensively evaluate collection efficiency and pressure drop, it was confirmed that when the unit cell size is 5 mm, PM collection efficiency increases, but the flow controller actually reduces filter performance. QF values are similar for unit cell sizes of 10 and 20 mm, and it is advantageous to select the unit cell size among these two considering collection efficiency and operating costs. The filter's collection performance increases due to the increase in swirl flow caused by the primitive structure, and the filter's collection efficiency increases due to the swirl flow that increases throughout the flow field as the unit cell size becomes smaller.

• Journal of computational fluids engineering
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• v.14 no.2
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• pp.59-67
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• 2009

An accurate prediction of the bypass flow is of great importance in the VHTR core design concerning the fuel thermal margin. Nevertheless, there has not been much effort in evaluating the amount and the distribution of the core bypass flow. In order to evaluate the behavior and the distribution of the coolant flow, a unit-cell experiment was carried out. Unit-cell is the regular triangular section which is formed by connecting the centers of three hexagonal blocks. Various conditions such as the inlet mass flow rate, block combinations and the size of bypass gap were examined in the experiment. CFD analysis was carried out to analyze detailed characteristics of the flow distribution. Commercial CFD code FLUENT 6.3 was validated by comparing with the experimental results. In addition, SST model and standard k-$\varepsilon$ model were validated. The results of CFD simulation show good agreements with the experimental results. SST model shows better agreement than standard k-$\varepsilon$ model. Results showed that block combinations and the size of the bypass gap have an influence on the bypass flow ratio but the inlet mass flow rate does not.