Nonhomogeneous Properties Research Articles

Numerical Study of Standing Wave-Induced Seabed Residual Response with the Non-homogeneous Soil Property

ABSTRACT Sui, T.; Zhang, C.; Zheng, J.; Guo, Y., and Xie, M., 2018. Numerical study of standing wave-induced residual response with the non-homogenous soil property. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 921–925. Coconut Creek (Florida), ISSN 0749-0208. Coastal seabed soil is usually non-homogeneous vertically. Seabed instability may take place under dynamic wave loading which may lead to the marine landslides. Most of the existing models have been limited to the soil oscillatory mechanism for a sandy seabed with relatively large permeability, which neglects the residual mechanism in a silt seabed with poor drainage condition. In this study, based on the Fully-dynamic (FD) seabed model, the numerical invesitgation for standing wave induced non-homogeneous seabed residual response is proposed. The present model is validated based on the flume tests in...

Integrated simulation of continuous-scale and discrete-scale radiative transfer in metal foams

A novel integrated simulation of radiative transfer in metal foams is presented. It integrates the continuous-scale simulation with the direct discrete-scale simulation in a single computational domain. It relies on the coupling of the real discrete-scale foam geometry with the equivalent continuous-scale medium through a specially defined scale-coupled zone. This zone holds continuous but nonhomogeneous volumetric radiative properties. The scale-coupled approach is compared to the traditional continuous-scale approach using volumetric radiative properties in the equivalent participating medium and to the direct discrete-scale approach employing the real 3D foam geometry obtained by computed tomography. All the analyses are based on geometrical optics. The Monte Carlo ray-tracing procedure is used for computations of the absorbed radiative fluxes and the apparent radiative behaviors of metal foams. The results obtained by the three approaches are in tenable agreement. The scale-coupled approach is fully validated in calculating the apparent radiative behaviors of metal foams composed of very absorbing to very reflective struts and that composed of very rough to very smooth struts. This new approach leads to a reduction in computational time by approximately one order of magnitude compared to the direct discrete-scale approach. Meanwhile, it can offer information on the local geometry-dependent feature and at the same time the equivalent feature in an integrated simulation. This new approach is promising to combine the advantages of the continuous-scale approach (rapid calculations) and direct discrete-scale approach (accurate prediction of local radiative quantities).

LINKED SIMULATION-OPTIMIZATION MODEL FOR OPTIMUM HYDRAULIC DESIGN OF WATER RETAINING STRUCTURES CONSTRUCTED ON PERMEABLE SOILS

Hydraulic Water Retaining Structures (HWRS), such as dams, weirs and regulators are important projects and necessary for water management. Seepage analysis under HWRS substantially influences the design of HWRS. One of the biggest challenges in design of HWRS is to determine the accurate seepage characteristics with complex flow conditions, and simultaneously to find the optimum design considering safety and cost. Therefore, this study concentrates on developing a linked simulation-optimization (S-O) model for non-homogenous anisotropic soil properties. This is achieved via linking the numerical seepage simulation (Geo-Studio/SEEPW) with the Genetic Algorithm (GA) evolutionary optimization solver. Since, a direct linking of numerical model with optimization model is computationally expensive and time consuming, accurate surrogate models are integrated instead of a numerical simulation model within the S-O model. A Support vector machine (SVM) based surrogate model is linked with the optimization model to achieve the optimum hydraulic design of HWRS. The seepage characteristics of optimum design obtained by S-O are evaluated by comparing these with the numerical seepage modeling (SEEPW) solutions. The comparison, in general, shows good agreements. Accordingly, the S-O methodology is potentially applicable for providing safe, efficient and economical design of HWRS constructed on a complex seepage flow domain.

Design And Fabrication Of Fatigue Test Rig And Preliminary Investigation On Flax Composite Beam

Reinforced polymer laminates are used increasingly as structural parts in automobile, aircraft and navel industries due to their excellent mechanical characteristics for relatively low density when compared to the conventional materials and therefore much information on mechanical properties are necessary. Composite materials behaviour subjected to fatigue load is very complex due to its non-homogeneous and anisotropic properties. So it is very important to understand the fatigue behaviour of FRP laminates to extend its usage for various applications in the current industries. Main objective of the project is to understand the fatigue behaviour of the composite laminates when it is subjected to fully reversed bending fatigue cycle. In this case it is very important to develop a specific test setup and approach to perform fatigue test avoid the utilization of expensive test methods available in the market. So a fatigue test rig was designed and developed for this project. Fatigue behaviour of composite laminates was studied in terms of stiffness degradation by performing experimental static deflection test on the test specimen before and after subjecting it to the fatigue load.

Cutting force and hole quality analysis in micro-drilling of CFRP

ABSTRACTMicro-drilling in carbon fiber reinforced plastic (CFRP) composite material is challenging because this material machining is difficult due to anisotropic, abrasive and non-homogeneous properties and also downscaling of cutting process parameters affect the cutting forces and micro-drilled hole quality extensively. In this work, experimental results based statistical analysis is applied to investigate feed and cutting speed effect on cutting force components and hole quality. Analysis of variance based regression equation is used to predict cutting forces and hole quality and their trend are described by response surface methodology. Results show that roundness error and delamination factor have similar trends to those of radial forces and thrust force, respectively. Non-linear trends of cutting forces and hole quality errors are observed during downscaling of the micro-drill feed value. Optimization results show that cutting forces and hole quality errors are minimum at a feed value which is almost equal to the tool edge radius rather than at the lowest feed value. Therefore, the presented results clearly show the influences of size effects on cutting forces and hole quality parameters in micro-drilling of CFRP composite material.

Safe Tissue Manipulation in Retinal Microsurgery via Motorized Instruments with Force Sensing.

Retinal microsurgery involves careful manipulation of delicate tissues by applying very small amount of forces most of which lie below the tactile sensory threshold of the surgeons. Membrane peeling is a common task in this domain, where application of excessive peeling forces can easily lead to serious complications, hence needs to be avoided. To quantify tool-tissue interaction forces during retinal microsurgery, various force-sensing tools were developed based on fiber Bragg grating sensors, yet the most beneficial way of using the acquired force information is currently unknown. In this study, using a motorized force-sensing micro-forceps tool, we develop an assistive method that enhances safety during membrane peeling by automatically opening the forceps and releasing the tissue based on the detected peeling forces. Through peeling experiments using bandages, we demonstrate that our method can effectively maintain the peeling force at a safe level even in case of non-homogeneous adhesion properties of the membrane.

Analysis of pullout load capacity of suction caissons in clay by a three-dimensional displacement approach

ABSTRACTA study was made to present analytical solutions of pullout load capacity for a suction caisson subjected to inclined tension in clay. The inclined tension on the skirt of the suction caisson is transformed into an equivalent system comprised of the vertical, horizontal, and moment load applied on the center of the lid. The vertical and horizontal stiffness coefficients along the skirt of the suction caisson in clay are presented by three-dimensional elastic solutions considering the nonhomogeneous and nonlinear property of clay. The vertical, horizontal, and rocking stiffness coefficient of the suction caisson on the base are presented considering the solutions of a hollow rigid cylindrical punch acting on the surface of clay. The envelopes of the horizontal and vertical ultimate load capacity for clay are presented. The yield, pullout, and failure for clay are taken into consideration. The effects of load inclination, loading depth, and aspect ratio on the pullout load capacity are shown. Behavior of the suction caisson in clay up to failure is investigated using the relationship between tensile load and displacement and that between depth, vertical, and horizontal pressure.

Electrospun nanofibres to mimic natural hierarchical structure of tissues: application in musculoskeletal regeneration.

Biomimetic scaffolds mimicking the natural hierarchical structure of tissues have recently attracted the interest of researchers and provide a promising strategy to resemble the nonhomogeneous property of tissues. This review provides an overview of the various hierarchical length scales in the native tissues of the musculoskeletal system. It further focuses on electrospinning as a technique to mimic the tissue structures with specific emphasis on bone. The effect of cellular alignment, infiltration, vascularisation, and differentiation in these nanostructures has also been discussed. An outline of the various additive manufacturing techniques in combination with electrospinning has been elaborated. The review concludes with the challenges and future directions to understand the intricacies of bottom-up approach to engineer the systems at a macroscale. Copyright © 2016 John Wiley & Sons, Ltd.

Evaluation of pullout load capacity of suction caissons in sand using a three-dimensional displacement approach

ABSTRACTAn investigation was conducted to obtain analytical solutions for the pullout behavior of a suction caisson undergoing inclined loads in sand. The inclined load is transformed into an equivalent load system in which the vertical, horizontal, and moment loads are applied on the center of the lid of the suction caisson. The vertical and lateral stiffness coefficients along the skirt of the suction caisson in sands are presented using the new three-dimensional elastic solutions taking into account the nonhomogeneous and nonlinear properties of the sand. The vertical, lateral, and rocking stiffness coefficients on the base of the suction caisson are presented considering the solutions of a hollow rigid cylindrical punch acting on the surface of a soil. The yield, pullout, and failure for sands with the nonhomogeneous and nonlinear characteristics are taken into consideration. The effects of the load inclination, the loading depth, and the aspect ratio on the pullout load capacity of the suction caisson are presented. Behaviour of the suction caisson in sand prior to failure is clarified from the relationship between tensile load, displacement, and rotation and that between depth, vertical pressure, and lateral pressure.

Pore surface grafting of porous low-k dielectrics by selective polymers

Polymer grafting of pore sidewalls is studied as a protecting agent against processing damage. Polymethyl-methacrylate (PMMA), an improved polystyrene (PS-pro), and a tailored plasma damage management polymer (PDM) are considered as potential candidates. PMMA and PS-pro show nonhomogeneous grafting properties, while PDM coat the pore sidewalls uniformly through the bulk of the porous low-k film. A k ∼ 2.2 porous spin-on glass is used as a vehicle for processing damage study. Approximately one monolayer is grafted on the pore walls, leading to a k-value increase up to Δk ∼ 0.2. Using grafted PDM, the porous low-k chemical stability in 0.5% diluted hydrofluoric acid is significantly improved. Concerning plasma damage, at constant etch depth methyl depletion is decreased, mainly in capacitive coupled plasma discharge showing high polymerizing character, leading to similar damage depth as found for a reference organo-silicate glass 2.7 low-k. However, moisture uptake is not improved, leading to significant drift in the dielectric constant.

Elucidating the DEP phenomena using a volumetric polarization approach with consideration of the electric double layer.

Dielectrophoretic (DEP) phenomena have been explored to great success for various applications like particle sorting and separation. To elucidate the underlying mechanism and quantify the DEP force experienced by particles, the point-dipole and Maxwell Stress Tensor (MST) methods are commonly used. However, both methods exhibit their own limitations. For example, the point-dipole method is unable to fully capture the essence of particle-particle interactions and the MST method is not suitable for particles of non-homogeneous property. Moreover, both methods fare poorly when it comes to explaining DEP phenomena such as the dependence of crossover frequency on medium conductivity. To address these limitations, the authors have developed a new method, termed volumetric-integration method, with the aid of computational implementation, to reexamine the DEP phenomena, elucidate the governing mechanism, and quantify the DEP force. The effect of an electric double layer (EDL) on particles' crossover behavior is dealt with through consideration of the EDL structure along with surface ionic/molecular adsorption, unlike in other methods, where the EDL is accounted for through simply assigning a surface conductance value to the particles. For validation, by comparing with literature experimental data, the authors show that the new method can quantify the DEP force on not only homogeneous particles but also non-homogeneous ones, and predict particle-particle interactions fairly accurately. Moreover, the authors also show that the predicted dependence of crossover frequency on medium conductivity and particle size agrees very well with experimental measurements.

Elastic deformations driven by non-uniform lubrication flows

The ability to create dynamic deformations of micron-sized structures is relevant to a wide variety of applications such as adaptable optics, soft robotics and reconfigurable microfluidic devices. In this work, we examine non-uniform lubrication flow as a mechanism to create complex deformation fields in an elastic plate. We consider a Kirchhoff–Love elasticity model for the plate and Hele-Shaw flow in a narrow gap between the plate and a parallel rigid surface. Based on linearization of the Reynolds equation, we obtain a governing equation which relates elastic deformations to gradients in non-homogeneous physical properties of the fluid (e.g. body forces, viscosity and slip velocity). We then focus on a specific case of non-uniform Helmholtz–Smoluchowski electro-osmotic slip velocity, and provide a method for determining the zeta-potential distribution necessary to generate arbitrary static and quasi-static deformations of the elastic plate. Extending the problem to time-dependent solutions, we analyse transient effects on asymptotically static solutions, and finally provide a closed form solution for a Green’s function for time periodic actuations.

Modelling wave-induced 3D non-homogeneous seabed response

Marine seabed is often composed of non-homogeneous soil in various directions, where its response to dynamic wave loading shows much difference from the case of homogeneous soil. Most existing numerical models for wave-induced non-homogeneous seabed response have been limited to vertically layered seabed. In this study, a new model is developed to simulate wave-induced seabed response considering non-homogeneous soil properties in three dimensions. The present model (1) directly solves the original fully dynamic governing equations for the overall equilibrium of soil, the equilibrium of pore fluid flow and the mass balance of porous seabed, (2) allows non-uniform distribution of eight soil parameters in the three-dimensional space, and (3) retains all the spatial derivative terms of soil parameters to fully represent the three-dimensional non-homogeneous seabed behavior. The model well reproduces the existing experimental data, numerical solution and field observation. Two preliminary model tests are performed to investigate the effects of horizontally non-homogeneous soil property on the local seabed response, and the three-dimensional non-homogeneous seabed response around a mono-pile. It is found that the presence of coarser soil will reduce the liquefaction depth of the adjacent finer soil. This impact is more pronounced for larger wave period, wave height, soil permeability, saturation degree, and smaller water depth. The seabed response around a mono-pile can be considerably modified if the soil sorting due to long-time lateral rocking of mono-pile is taken into account, which decreases the liquefaction depth in the vicinity of the mono-pile.

A Review of Backup Mechanism for Reducing Delamination when Drilling Composite Laminates

Over the past decades, composite materials have been increasingly utilized in various industries because of their superior mechanical properties and resistance to corrosion. Drilling is essential to produce precise holes when load-carrying structures are produced using composites. Because of the non-homogeneous and anisotropic property of composite laminates, delamination often occurs at the point where the drill exits, which affects reliability and safety. Some studies present a suppressed mechanism to prevent delamination when drilling composite laminates. The experimental results demonstrate delamination is significantly reduced by various suppressed mechanisms and greater feed rates produce the same level of delamination. The use of special drill geometries and backup has been demonstrated to be more advantageous than the use of adapted feed controls. The basis for the future development of a suppression mechanism for drilling composite laminates is determined.

Thermal post-buckling behavior of imperfect temperature-dependent sandwich FGM plates resting on Pasternak elastic foundation

In this paper, post-buckling behavior of sandwich plates with functionally graded (FG) face sheets under uniform temperature rise loading is examined based on both sinusoidal shear deformation theory and stress function. It is supposed that the sandwich plate is in contact with an elastic foundation during deformation, which acts in both compression and tension. Thermo-elastic non-homogeneous properties of FG layers change smoothly by the variation of power law within the thickness, and temperature dependency of material constituents is considered in the formulation. In the present development, Von Karman nonlinearity and initial geometrical imperfection of sandwich plate are also taken into account. By employing Galerkin method, analytical solutions of thermal buckling and postbuckling equilibrium paths for simply supported plates are determined. Numerical examples presented in the present study discuss the effects of gradient index, sandwich plate geometry, geometrical imperfection, temperature dependency, and the elastic foundation parameters.

Bond mechanism and bond strength of GFRP bars to concrete: A review

Abstract Glass fiber-reinforced polymer (GFRP) reinforcements are taken as an alternative solution for the deterioration of civil infrastructures. GFRP bars have received increasing attention due to low cost compared to carbon fiber-reinforced polymer (CFRP) bars. Bond characteristic of GFRP bars in concrete is the most critical parameter for implementation of the material to the corrosion-free concrete structures. Unlike steel reinforcement, GFRP materials behave anisotropic, non-homogeneous and linear elastic properties, which may result in different force transfer mechanism between reinforcement and concrete. With the purpose of covering the most valuable contributions regarding bond mechanism in the past work, a comprehensive review focusing on the failure mode and bond strength is carried out in this paper. A database consisted of 682 pullout-test specimens was created to observe the factors affecting bond behavior. Basic relationship between bond strength/slip and factors was analyzed accordingly. In addition, the development of bond degradation under environmental conditions, such as freezing-thawing cycling, wet-dry cycling, alkaline solutions and high temperature was presented thereafter. These environmental influences need to be further investigated.

Nonhomogeneous surface properties of parylene-C film etched by an atmospheric pressure He/O2 micro-plasma jet in ambient air

Surface properties of parylene-C film etched by an atmospheric pressure He/O2 micro-plasma jet in ambient air were investigated. The morphologies and chemical compositions of the etched surface were analyzed by optical microscopy, SEM, EDS, XPS and ATR-FTIR. The microscopy and SEM images showed the etched surface was nonhomogeneous with six discernable ring patterns from the center to the outside domain, which were composed of (I) a central region; (II) an effective etching region, where almost all of the parylene-C film was removed by the plasma jet with only a little residual parylene-C being functionalized with carboxyl groups (CO, OCO−); (III) an inner etching boundary; (IV) a middle etching region, where the film surface was smooth and partially removed; (V) an outer etching boundary, where the surface was decorated with clusters of debris, and (VI) a pristine parylene-C film region. The analysis of the different morphologies and chemical compositions illustrated the different localized etching process in the distinct regions. Besides, the influence of O2 flow rate on the surface properties of the etched parylene-C film was also investigated. Higher volume of O2 tended to weaken the nonhomogeneous characteristics of the etched surface and improve the etched surface quality.

Examination of non-homogeneity and lamination scheme effects on deflections and stresses of laminated composite plates

In this study, a convenient formulation for the bending of laminated composite plates that hold non-homogeneous properties is examined. The constitutive equations of first order shear deformation plate theory are obtained using Hamilton Principle. The effect of non-homogeneity, lamination schemes and aspect ratio on the deflections and stresses is analysed. It is understood from the study that economical and optimum designs for laminated composite plates can be achieved by changing lamination scheme and by considering non-homogeneity response of composite plate.

Thermal buckling behavior of functionally graded plates based on neutral surface

This work concerns with the thermal buckling behavior of Functionally Graded Materials (FGMs) based on neutral surface of structures. Especially, the materials have non-homogeneous properties with varying gradually from one surface to the other. In this regard, the neutral surface of the model is not the same as the mid-plane of structure due to asymmetry of material in the thickness direction, and thus it is necessary to select the neutral surface as the reference plane. Further, the material properties are temperature dependent, the location of the neutral surface depends also on the temperature change. For the crucial discussion, thermal buckling behaviors of FGMs are investigated based on the neutral surface concept. In the formulation, linear theory of plate is adopted based on the first-order shear deformation theory, and the steady state thermal conduction is considered as the one dimensional heat transfer. Numerical results show that the present works have little lower estimation of the buckling temperatures than previous data, and the shift of neutral planes are also observed by considering the static equilibrium of FGMs.

Buckling and Vibration of Functionally Graded Non-uniform Circular Plates Resting on Winkler Foundation

ANALYSIS AND NUMERICAL RESULTS FOR THE AXISYMMETRIC VIBRATIONS OF FUNCTIONALLY GRADED CIRCULAR PLATES SUBJECTED TO UNIFORM IN-PLANE FORCE HAVE BEEN PRESENTED ON THE BASIS OF CLASSICAL PLATE THEORY. THE MECHANICAL PROPERTIES OF THE PLATE MATERIAL ARE ASSUMED TO VARY AS A GENERAL FUNCTION OF THICKNESS PARAMETER. A SEMI-ANALYTICAL APPROACH NAMELY, DIFFERENTIAL TRANSFORM METHOD HAS BEEN EMPLOYED TO SOLVE THE DIFFERENTIAL EQUATION GOVERNING THE MOTION OF SUCH SIMPLY SUPPORTED AND CLAMPED PLATES. THE EFFECT OF VOLUME FRACTION INDEX AND THE IN-PLANE FORCE PARAMETER HAS BEEN STUDIED ON THE FIRST THREE NATURAL FREQUENCIES OF VIBRATION. BY ALLOWING THE FREQUENCY TO APPROACH ZERO, THE CRITICAL BUCKLING LOADS FOR BOTH THE PLATES HAVE BEEN COMPUTED. TWO-DIMENSIONAL MODE SHAPES FOR SPECIFIED PLATES HAVE BEEN PLOTTED. A COMPARISON OF RESULTS HAS BEEN PRESENTED.