• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.6
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• pp.552-559
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• 2009

The effect of porosity on the crack propagation is studied by using the cohesive zone model. Standard mode I fracture test were done by using compact tension specimens with various porosities. Load-load line displacement curves and ${\delta}_5$-crack resistance curves for various porosities were obtained from experiments. The cohesive zone model proposed by Xu and Needleman was employed to describe the crack propagation in porous media, and the Gurson model is used for constitutive relation of porous materials. These models were implemented into user subroutines of a finite element program ABAQUS. The fracture mode changes from ductile fracture to brittle fracture as the porosity increases. Numerical calculations agree well with experimental results.

• Journal of Mechanical Science and Technology
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• v.19 no.11
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• pp.2025-2031
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• 2005

Eshelby type micro mechanics model with a newly developed piezoelectric Eshelby tensor is proposed for predicting the effective electroelastic properties of the piezoelectric composite. The model is applied for piezoelectric solids containing both porosities and metal inhomogeneities. The effective electroelastic moduli of the composites such as stiffness, piezoelectric constants, and dielectric constants are predicted by the present model, which are extensively compared with the existing experimental results from the literatures. The validity of Eshelby type model for predicting the effective properties of the composite is thoroughly examined. It can be concluded from this study that a new mechanism is needed to compute correctly the dielectric constants among the effective properties of the composites.

• Journal of Wind Energy
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• v.4 no.1
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• pp.68-74
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• 2013

Offshore wind farm is being increased since there are much trouble to develop onshore wind farm. But in the offshore, wind turbine wake does not dissipate less than onshore wind turbine because of low turbulence level. Thus this remained wake interacted to other wind turbine. This interaction reduces energy production in wind farm and have a bad influence on fatigue load of wind turbine. In this research, CFD model was constructed to analyze wake effect in offshore wind farm. A method that wind turbine rotor region was modelled in porous media was devised to reduce computation load and validated by comparison with Horns Rev measurement. Then wake interaction between two wind turbine was analyzed by devised porous model.

• International Journal of High-Rise Buildings
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• v.11 no.4
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• pp.265-276
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• 2022

Double-Skin Facades (DSF) on tall buildings are becoming increasingly common in urban environments due to their ability to provide architectural merit, passive design, acoustic control and even improved structural efficiency. This study aims to understand the effects of porous DSF on the aerodynamic characteristics of tall buildings using wind tunnel tests. High Frequency Force Balance and pressure tests were performed on the CAARC standard tall building model with a variable porous DSF on the windward face. The introduction of a porous DSF did not adversely affect the overall mean forces and moments experienced by the building, with few differences compared to the standard tall building model. There was also minimal variation between the results for the three porosities tested: 50%, 65% and 80%. The presence of a full-height porous DSF was shown to effectively reduce the mean and fluctuating wind pressure on the side face of the building by about 10%, and a porous DSF over the lower half height of the building was almost as effective. This indicates that the porous DSF could be used to reduce the design load on cladding and fixtures on the side faces of tall buildings, where most damage to facades typically occurs.

• Biomaterials and Biomechanics in Bioengineering
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• v.3 no.1
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• pp.1-14
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• 2016

Well-ordered porous materials are very promising in orthopedics since they allow tailoring the mechanical properties. Finite element (FE) analysis is commonly used to evaluate the mechanical behavior of well-ordered porous materials. However, FE results generally differ importantly from experimental data. In the present article, three types of manufacturing irregularities were characterized on an additive manufactured porous titanium sample having a simple cubic unit-cell: strut diameter variation, strut inclination and fractured struts. These were included in a beam FE model. Results were compared with experimental data in terms of the apparent elastic modulus (Eap) and apparent yield strength (SY,ap). The combination of manufacturing irregularities that yielded the closest results to experimental data was determined. The idealized FE model resulted in an Eap one order of magnitude larger than experimental data and a SY,ap almost twice the experimental values. The strut inclination and fractured struts showed the strongest effects on Eap and SY,ap, respectively. Combining the three manufacturing irregularities produced the closest results to experimental data. The model also performed well when applied to samples having different structural dimensions. We recommend including the three proposed manufacturing irregularities in the FE models to predict the mechanical behavior of such porous structures.

• Steel and Composite Structures
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• v.45 no.3
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• pp.409-423
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• 2022

Nowadays, there is a high demand for great structural implementation and multifunctionality with excellent mechanical properties. The porous structures reinforced by graphene platelets (GPLs) having valuable properties, such as heat resistance, lightweight, and excellent energy absorption, have been considerably used in different engineering implementations. However, stiffness of porous structures reduces significantly, due to the internal cavities, by adding GPLs into porous medium, effective mechanical properties of the porous structure considerably enhance. This paper is relating to vibration analysis of fluidconveying cantilever porous graphene platelet reinforced (GPLR) pipe with fractional viscoelastic model resting on foundations. A dynamical model of cantilever porous GPLR pipes conveying fluid and resting on a foundation is proposed, and the vibration, natural frequencies and primary resonant of such a system are explored. The pipe body is considered to be composed of GPLR viscoelastic polymeric pipe with porosity in which Halpin-Tsai scheme in conjunction with the fractional viscoelastic model is used to govern the construction relation of nanocomposite pipe. Three different porosity distributions through the pipe thickness are introduced. The harmonic concentrated force is also applied to the pipe and the excitation frequency is close to the first natural frequency. The governing equation for transverse motions of the pipe is derived by the Hamilton principle and then discretized by the Galerkin procedure. In order to obtain the frequency-response equation, the differential equation is solved with the assumption of small displacement, damping coefficient, and excitation amplitude by the multiple scale method. A parametric sensitivity analysis is carried out to reveal the influence of different parameters, such as nanocomposite pipe properties, fluid velocity and nonlinear viscoelastic foundation coefficients, on the primary resonance and linear natural frequency. Results indicate that the GPLs weight fraction porosity coefficient, fractional derivative order and the retardation time have substantial influences on the dynamic response of the system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.1
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• pp.21-28
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• 2016

A typical heat exchanger, found in many industrial sites, is made up of a large number of unitary cells, which causes difficulties when carrying out full-scale three-dimensional numerical simulations of the heat exchanger to analyze the aero-thermal performance. In the present study, a three-dimensional numerical study using a porous media model was carried out to evaluate the performance of the heat exchanger modelled in two different ways : full-scale and simplified. The pressure drop in the air side and gas side along with the overall heat transfer rate were calculated using a porous media model and the results were then compared to results obtained with a one-dimensional flow network model. The comparison between the results for two different geometries obtained using a porous media model and a one-dimensional flow network model shows good agreement between the simplified geometry and the one-dimensional flow network model. The full-scale geometry shows reasonable differences caused by the geometry such as sudden expansion and contraction.

• Geomechanics and Engineering
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• v.23 no.3
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• pp.217-225
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• 2020

In this paper, the thermoelastic interactions in a two-dimension porous body are studied. This problem is solved by using the Green and Lindsay (GL) generalized thermoelasticity model under fractional time derivative. The derived approaches are estimated. with numeral results which are applied to the porous mediums in simplifying geometrical. The bounding plane surface of the present half-space continuum is subjected to a pulse heat flux. We use the Laplace-Fourier transforms methods with the eigenvalues approach to solve the problem. The numerical solutions for the field functions are obtained numerically using the numerical Laplace inversion technique. The effects of the fractional parameter and the thermal relaxation times on the temperature field, the displacement field, the change in volume fraction field of voids distribution and the stress fields have been calculated and displayed graphically and the obtained results are discussed.

• Journal of Mechanical Science and Technology
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• v.17 no.10
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• pp.1583-1596
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• 2003

A study of forced convection in a circular pipe with a partially filled porous medium was numerically investigated. The Brinkman-Forchheimer extension of the Darcy model was used to analyze the and temperature distribution in the porous medium. Our study includes two types of porous layer configurations: (1) a layer attached at the tube wall extending inward towards the centerline and (2) a layer at the centerline extending outward. The effect of several parameters, such as Darcy number, effective viscosity, effective thermal conductivity, and inertia parameter, as well as the effect of geometric parameters, were investigated.

• Korean Chemical Engineering Research
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• v.53 no.6
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• pp.814-817
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• 2015

A new ionic mass transfer correlation is derived for the fluid-saturated, horizontal porous layer. Darcy-Forchheimer model is used to explain characteristics of fluid motion. Based on the microscales of turbulence a backbone mass transfer relation is derived as a function of the Darcy-Rayleigh number, $Ra_D$ and the porous medium Schmidt number, $Sc_p$. For the Darcy's limit of $Sc_p{\gg}Ra_D$, the Sherwood number, Sh is a function of $Ra_D$ only. However, for the region of high $Ra_D$, Sh can be related with $Ra_DSc_p$. Based on the present backbone equation and the electrochemical mass transfer experiments which are electro plating or electroless plating, the new ionic mass transfer correlation is suggested in the porous media.