A nonlinear compaction model for fibrous preforms

Based on the mechanics of porous media and physical insight gained from experimental observation, a model for predicting the nonlinear compaction of fibrous preforms in the resin transfer molding process is developed. A key physical constant — namely, preform bulk compressibility — is proposed to establish the relationship between the applied pressure and the preform bulk volume. The preform bulk compressibility is a function of fiber volume fraction and five parameters — the initial fiber volume fraction, the final (maximum attainable) fiber volume fraction, the initial pore volume compressibility, the fiber compressibility, and an empirical index. Results of compaction experiments on plain-woven fabric preforms and unidirectional non-woven materials support the validity of the model. Excellent agreement between theory and experiments has been obtained. The present model provides for fibrous preforms a nonlinear constitutive law whose coefficients can be physically interpreted.     

Switched numerical Shuman filters for shock calculations

Summary When using Shuman's filtering operator in the numerical computation of shock waves, nonlinear instabilities are prevented, but high order accuracy is lost even in smooth regions. In order to preserve second or higher order accuracy in these regions, an automatic switched Shuman filter is constructed. Nonsteady shock calculations in one and two spatial dimensions, demonstrate the usefulness and accuracy of the method, including examples with third and fourth order accurate finite difference schemes.     

A numerical model of light adjustable lens

We model numerically the mechanical effects of UV induced photo-polymerization in elastomeric artificial lens. The elastomer is originated upon cross-linking of a silicone matrix. UV irradiation of one side of the lens polymerizes selectively a photosensitive macromer, causing local variations of its concentration. The subsequent diffusion of macromers from high concentration to low concentration zones modifies the shape of the lens and thus its dioptric power. In vitro experiments on artificial lens showed that the power change is dependent on UV exposure time, irradiation intensity and light pattern. With the aim to define a numerical tool able to predict the dioptric power adjustment as a function of the UV irradiation parameters, we setup a purely mechanic finite element model of the lens, adopting a hyperelastic material model embedded with eigen-deformations. Numerical simulations of axis-symmetric irradiation closely reproduced the experimental results, in terms of both lens geometry and dioptric power, for positive, negative and lock-in corrections.     

A model for predicting uniaxial compression behavior of fused fibrous networks

Fused fibrous networks are increasingly being used for emerging industrial applications ranging from thermal/sound insulation, fluid filtration/separation, and energy conversion to tissue scaffolds. Majority of these applications need a deeper understanding of fused fibrous networks under compression loading. In this research work, a compression model of fused fibrous networks has been proposed by defining two distinct regions displaying the bending of free fiber segments between the fiber-to-fiber contacts followed by the transverse compression of fiber contacts through classical Hertzian contact mechanics approach. The mechanistic models developed in this study, have clearly elucidated the main fiber and structural parameters that control the compression behavior of fused fibrous networks. A comparison has also been made between the theoretical and experimental pressure–strain curves of randomly and preferentially aligned fused fibrous networks.     

A numerical wave tank model for cavitating hydrofoils

In this paper, an iterative boundary element method (IBEM) for both 2-D and 3-D cavitating hydrofoils moving steadily inside a numerical wave tank (NWT) is presented and some extensive numerical results are given. The cavitating hydrofoil part, the free surface part and the wall parts of NWT are solved separately, with the effects of one on the others being accounted for in an iterative manner. The cavitating hydrofoil surface, the free surface, the bottom surface and the side walls are modelled by a low-order potential based panel method using constant strength dipole and source panels. Second-order correction on the free surface in 2-D are included into the calculations by the method of small perturbation expansion both for potential and for wave elevation. The source strengths on the free surface are expressed in terms of perturbation potential by applying first-order (linearized) and second-order free surface conditions. The IBEM is applied to a 2-D (NACA16006 and NACA0012) and a 3-D rectangular cavitating hydrofoil and the effect of number of iterations, the effect of the depth of the hydrofoil from finite bottom and the effect of the walls of NWT, on the results are discussed.     

A numerical model for a wet air-side economiser

Geared dehumidifiers operating at low indoor temperatures can experience condensation in the air-side economiser. In this paper we present a numerical air-side economiser model which accounts for condensation in the hot-side ducting. The economiser model has been integrated with an existing dehumidifier model and the overall model tested under two modes – economiser with smooth ducts and economiser ducts embossed with turbulence inducing ribs. Numerical results from the ribbed duct tests are compared with experimental test data and, in the absence of empirical transfer coefficients for wet, rib-roughened rectangular ducts, enhancement factors have been used to model rib effects. Model results are also presented for a varied number of hot-side economiser ducts and the numerical data show reasonable agreement with experimental data showing that the model is suitable for the design and analysis of geared dehumidifiers operating with plate type economisers.     

A numerical model for real-time simulation of ship-ice interaction

A ship advancing in level ice will introduce several failure processes to the ice sheet, such as localised crushing and breaking due to bending stresses. The resulting ice fragments will interact with each other, with water and with the hull of the ship. They may rotate, collide, or slide along ship's hull, and eventually they will be cleared away. The situation is different in a broken ice field, i.e., large ice floes may behave similar to level ice while smaller floes will mostly be pushed aside, rotated or submerged. Modelling of such a complex system is very demanding and often computationally expensive which would typically hinder the chances for real-time simulations. This kind of simulations can be very useful for training personnel for Arctic offshore operations and procedures, for analysing the efficiency of various ice management concepts and as a part of the onboard support systems for station keeping. The challenge of meeting the real-time criterion is overcome in the present paper. The paper describes a numerical model to simulate the process of ship-ice interaction in real-time. New analytical closed form solutions are established and used to represent the ice breaking process. PhysX is used for the first time to solve the equations of rigid body motions in 6 degrees of freedom for all ice floes in the calculation domain. The results of the simulator are validated against experimental data from model-scale and full-scale tests. The validation tests exhibited a satisfactory agreement between the model calculations and experimental measurements.     

A novel numerical model of debonding of FRP-plated concrete beam

Accurate modeling is required to estimate the debonding in a plated fiber-reinforced polymer (FRP) concrete beam. In the present investigation, a numerical method is developed to model a crack in the FRP–concrete interface. An initial notch is located at the mid-span of the concrete beam. A modified crack closure integral method is implemented to model Mode-I fracture in the concrete. In the present research, a special interface element is formulated to simulate and to predict the distribution of interfacial shear stresses by using drilling degrees of freedom in the nodes of interface elements. Cohesive forces in the nodes of interface elements are formulated by finite element methods. A crack propagation criterion is presented to evaluate when the crack grows in FRP–concrete interface. If the principal stress in the node at the tip of an interface element reaches the maximum shear stress along the FRP–concrete interface, debonding happens. The model is robust, accurate, independent of mesh size, and it is able to model the crack growth in the concrete and debonding of the FRP–concrete interface, simultaneously. The model presented in this study showed acceptable similarity to previous research data.     

A numerical simulation model for plate-type, roll-bond evaporators

This study presents a first-principles mathematical model developed to investigate the thermal behavior of a plate-type, roll-bond evaporator. The refrigerated cabinet was also taken into account in order to supply the proper boundary conditions to the evaporator model. The mathematical model was based on the mass, momentum and energy conservation principles applied to each of the following domains: (i) refrigerant flow through the evaporator channels; (ii) heat diffusion in the evaporator plate; and (iii) heat transmission to the refrigerated cabinet. Empirical correlations were also required to estimate the shear stresses, and the internal and external heat transfer rates. The governing partial differential equations were discretized through the finite-volume approach and the resulting set of algebraic equations was solved by successive iterations. Validation of the model against experimental steady-state data showed a reasonable level of agreement: the cabinet air temperature and the evaporator cooling capacity were predicted within error bands of ±1.5 °C and ±6%, respectively.     

Omnidirectional and multiple-channeled high-quality filters of photonic heterostructures containing single-negative materials

The design and application of omnidirectional and multiple-channeled filters with high-quality (high-Q) factors applied by using photonic heterostructures containing single-negative materials is demonstrated. Through adjusting the period number of the heterostructures, the number of the resonance modes can be controlled, and the resonance modes are then insensitive to the incident angle. With perfect transmission, controllable mode, and omnidirectional channel, this structure opens a promising way to fabricate omnidirectional and multiple-channeled filters for future dense wavelength division multiplexing applications. The effect of the losses of single-negative materials on the filters is also considered.     

A numerical model for the cyclic deterioration of railway tracks

An elasto‐plastic material model is proposed that can be used to simulate the cyclic deterioration of railway tracks. The model describes the envelope of the irreversible, plastic material response generated during a cyclic loading process, thereby distinguishing the mechanisms of frictional sliding and volumetric compaction. The reversible response is represented by a pressure‐dependent, hypo‐elastic material law. After the numerical integration of the model is specified, the model is calibrated on laboratory experiments and employed in a finite‐element case study of the long‐term settlement behaviour of a railway track. The main features of the model are illustrated by comparing the computed response with the response obtained by in situ track measurements. Copyright © 2003 John Wiley & Sons, Ltd.     

A numerical model of ice crushing using a foam analogue

A numerical model for ice crushing has been constructed that takes into account the physical processes identified in many experimental studies. These include the presence and evolution of high-pressure and low-pressure zones, the rapid removal of ice through melting, and the transformation of relatively intact ice (high-pressure zone material) to low-pressure pulverized ice through the creation and shattering of spalls. The model produces cyclic sawtooth load events and pressure distributions that are roughly characteristic of observed ice behavior. The visual and quantitative results suggest that the physical principles incorporated in the model are correct. While still in the early stages of development, with refinements the model has potential for use in simulations of various ice/structure interaction scenarios.     

Direct numerical solution of three-dimensional equations containing elliptic operators

A direct three-dimensional elliptic solver is presented for application in a wide class of numerical methods for solving partial differential equations in physics and engineering. The derived algorithm and FORTRAN code implement Buzbee, Golub and Nielson's proposed extension of Buneman's Cyclic-Reduction Poisson solver to three dimensions. Both a ‘most direct’ cyclic reduction and a revised method (to eliminate roundoff error difficulties) are derived. Tests on an IBM 360/67 computer, using various optional combinations of subroutines, showed significant differences in accuracy and computing time, with the optimum subroutine combination depending on mesh size.     

Simulation of particle collection by model fiber filters

Computer simulations of particle deposition in model fiber filters were conducted. The basic element of the model filters used in the simulation consisted of three identical parallel and equally spaced circular cylinders, with the flow field around the cylinder obtained using the method of Lehner. The deposition process was simulated using the method developed earlier by the present author. The procedure was further modified by including an adhesion mechanism. Both monodispersed and polydispersed aerosols were considered. The results of the simulation agreed with the available experimental data.     

A model predicting carbonation depth of concrete containing silica fume

Silica fume (SF) has been used since long as a mineral admixture to improve durability and produce high strength and high performance concrete. Due to the pozzolanic reaction between calcium hydroxide and silica fume, compared with ordinary Portland cement, the carbonation of concrete containing silica fume is much more complex. In this paper, based on a multi-component concept, a numerical model is built which can predict the carbonation of concrete containing silica fume. The proposed model starts with the mix proportions of concrete and considers both Portland cement hydration reaction and pozzolanic reaction. The amount of hydration products which are susceptible to carbonate, such as calcium hydroxide (CH) and calcium silicate hydrate (CSH), as well as porosity can be obtained as associated results of the proposed model during the hydration period. The influence of water-binder ratio and silica fume content on carbonation is considered. The predicted results agree well with experimental results.     

A numerical model for bird strike of aluminium foam-based sandwich panels

Experimental bird-strike tests have been carried out on double sandwich panels made from AlSi7Mg0.5 aluminium foam core and aluminium AA2024 T3 cover plates. The bird-strike velocity varied from 140 to 190 m/s. The test specimens were instrumented with strain gauges in the impacted area to measure the local strains of the rear sandwich plate. A numerical model of this problem has been developed with the non-linear, finite element program LS-DYNA. A continuum damage-mechanics-based constitutive model was used to describe the behaviour and failure of the aluminium cover plates. The foam core was modelled by a pressure sensitive constitutive model coupled by a failure criterion on maximum volumetric strains. The bird was represented by an idealised geometry and the material model was defined by a linear equation-of-state. A multi-material arbitrary Lagrangian Eulerian (ALE) element formulation was used to represent the motion of the bird, whereas the sandwich panel was described by a Lagrangian reference configuration. A fluid–structure interface ensured proper coupling between the motion of the bird and the solid materials of the sandwich panel. It was found that the model was able to represent failure of both the aluminium cover plates as well as the aluminium foam core.     

On the numerical evaluation of Eshelby's tensor and its application to elastoplastic fibrous composites

A numerical evaluation of Eshelby's S tensor for an ellipsoidal inclusion imbedded in a general anisotropic matrix material is performed. The numerical scheme is valid for any degree of matrix anisotropy and for any aspect ratio of the ellipsoid, including the extreme cases of cracks and cylindrical inclusions. The influence of matrix anisotropy on the evaluation of S is tested extensively for cylindrical inclusions by considering plasticity induced anisotropy in the instantaneous properties of an elastic-plastic matrix material. The Mori-Tanaka averaging method is used to study the influence of the evaluation of S on the prediction of instantaneous effective properties of fibrous composites with elastic fibres and elastic-plastic matrix.