Showing papers on "Deformation (meteorology) published in 2010"

Discrete and continuum analysis of localised deformation in sand using X-ray mu CT and volumetric digital image correlation

Abstract: The objective of this work was to observe and quantify the onset and evolution of localised deformation processes in sand with grain-scale resolution. The key element of the proposed approach is combining state-of-the-art X-ray micro tomography imaging with three-dimensional volumetric digital image correlation techniques. This allows not only the grain-scale details of a deforming sand specimen to be viewed, but also, and more importantly, the evolving three-dimensional displacement and strain fields throughout loading to be assessed. X-ray imaging and digital image correlation have been in the past applied individually to study sand deformation, but the combination of these two methods to study the kinematics of shear band formation at the grain scale is the first novel aspect of this work. Moreover, the authors have developed a completely original grain-scale volumetric digital image correlation method that permits the characterisation of the full kinematics (i.e. three-dimensional displacements and rotations) of all the individual sand grains in a specimen. The results obtained using the discrete volumetric digital image correlation confirm the importance of grain rotations associated with strain localisation.

Theory of dielectric elastomers capable of giant deformation of actuation.

Abstract: The deformation of a dielectric induced by voltage is limited by electrical breakdown if the dielectric is stiff, and by electromechanical instability if the dielectric is compliant. The interplay of the two modes of instability is analyzed for a dielectric elastomer, which is compliant at a small stretch, but stiffens steeply. The theory is illustrated with recent experiments of interpenetrating networks, and with a model of swollen elastomers. The theory predicts that, for an elastomer with a stress-stretch curve of a desirable form, the voltage can induce giant deformation.

Discrete plasticity in sub-10-nm-sized gold crystals

Abstract: Although deformation processes in submicron-sized metallic crystals are well documented, the direct observation of deformation mechanisms in crystals with dimensions below the sub-10-nm range is currently lacking. Here, through in situ high-resolution transmission electron microscopy (HRTEM) observations, we show that (1) in sharp contrast to what happens in bulk materials, in which plasticity is mediated by dislocation emission from Frank-Read sources and multiplication, partial dislocations emitted from free surfaces dominate the deformation of gold (Au) nanocrystals; (2) the crystallographic orientation (Schmid factor) is not the only factor in determining the deformation mechanism of nanometre-sized Au; and (3) the Au nanocrystal exhibits a phase transformation from a face-centered cubic to a body-centered tetragonal structure after failure. These findings provide direct experimental evidence for the vast amount of theoretical modelling on the deformation mechanisms of nanomaterials that have appeared in recent years.

Sampling Moiré Method for Accurate Small Deformation Distribution Measurement

Abstract: In this paper, a novel accurate deformation distribution measurement technique by using sampling moire method is proposed. The basic principle and an experimental result of a steel beam in symmetric three-point bending are reported. In this method, the measurement area of a target is attached with an adhesive tape of a known pitch grating firstly. An ordinary CCD camera is installed on a fixed point to record the image during deformation. The captured image is analyzed by performing easy image processing, i.e., thinning-out and linear interpolation, to obtain the multiple phase-shifted moire patterns. Then, the phase distribution of the moire pattern can be calculated using phase-shifting method. Finally, the deformation distribution is calculated by the grating pitch times the phase difference of before deformation and after deformation. The experimental results in symmetric three-point bending test show that the displacement of the steel beam at loading point agree well with those obtained by an accurate displacement sensor. The average error of displacement measurement is less than 4 μm when 2 mm grating pitch is used, and it corresponds to 1/500 of the grating pitch accuracy. This indicates that noncontact deformation distribution measurement is possible by simple and easy procedure with high accuracy, high speed, and low cost for the structural evaluation of infrastructures.

Adsorption-induced deformation of mesoporous solids.

Abstract: The Derjaguin−Broekhoff−de Boer theory of capillary condensation is employed to describe deformation of mesoporous solids in the course of adsorption−desorption hysteretic cycles. We suggest a thermodynamic model, which relates the mechanical stress induced by the adsorbed phase to the adsorption isotherm. Analytical expressions are derived for the dependence of the solvation pressure on the vapor pressure. The proposed method provides a description of nonmonotonic hysteretic deformation during capillary condensation without invoking any adjustable parameters. The method is showcased drawing on the examples of literature experimental data on adsorption deformation of porous glass and SBA-15 silica.

Internal solitary waves: propagation, deformation and disintegration

Abstract: . In coastal seas and straits, the interaction of barotropic tidal currents with the continental shelf, seamounts or sills is often observed to generate large-amplitude, horizontally propagating internal solitary waves. Typically these waves occur in regions of variable bottom topography, with the consequence that they are often modeled by nonlinear evolution equations of the Korteweg-de Vries type with variable coefficients. We shall review how these models are used to describe the propagation, deformation and disintegration of internal solitary waves as they propagate over the continental shelf and slope.

A Study of Injection-Induced Mechanical Deformation At the In Salah CO2 Storage Project

Abstract: The In Salah project (a joint venture of BP, Statoil and Sonatrach) includes a CO 2 sequestration effort that has successfully injected millions of tons of CO 2 into a deep saline formation close to a producing gas field in Algeria. We have performed detailed simulations of the hydromechanical response in the vicinity of the KB-502 CO 2 injection well specifically because the morphology of the observed surface deformation differed from that above the other injectors at the field. We have simulated the mm-scale uplift of the overburden associated with the injection and compared the results with observed ground surface deformation measured by InSAR. By solely including conducting and bounding faults in the model we achieve better agreement with the magnitude of the observed net uplift at the ground surface, but not the shape of the uplift pattern. However, by further including flow into a hypothetical vertical extension of a fault, our simulations better match the morphology of the surface deformation. Our results indicate that the best fit is obtained through a combination of reservoir and fault pressurization, rather than either alone. However, our analysis required assumptions regarding the mechanical properties of the faults and the overburden. These results demonstrate that InSAR provides a powerful tool for gaining insight into the fate of fluid in the subsurface, but also highlight the need for detailed, accurate static geomodels.

Internal solitary waves: propagation, deformation and disintegration

Abstract: In coastal seas and straits, the interaction of barotropic tidal currents with the continental shelf, seamounts or sills is often observed to generate large- amplitude, horizontally propagating internal solitary waves. Typically these waves occur in regions of variable bottom topography, with the consequence that they are often modeled by nonlinear evolution equations of the Korteweg- de Vries type with variable coefficients. We shall review how these models are used to describe the propagation, deformation and disintegration of internal solitary waves as they propagate over the continental shelf and slope.

Non-invasive 3D analysis of local soil deformation under mechanical and hydraulic stresses by μCT and digital image correlation

Abstract: Soil deformation is a perpetual process in the pedosphere where besides physicochemical stresses primarily alternating hydraulic and mechanical stresses continuously re-arrange the configuration of solid particles. In this study we present a local strain analysis and changes in soil structure resulting from hydraulic and mechanical stresses based on X-ray microtomography data. Digital image reconstructions were used to quantify local structural pore space characteristics and local soil deformation by 3D morphological and correlation analysis of grayscale tomograms. Swelling and shrinkage resulted in a complex heterogeneous soil structure which proofed to be very stable when mechanical loads were applied. The mechanism of soil deformation for both structure formation by internal hydraulic stresses and structure degradation by external mechanical stresses were in both cases controlled by pre-existing (micro)-structures. Especially during wetting such structures served as a nucleus for subsequent structure evolution. The results demonstrate the potential of more detailed non-invasive micromechanical analysis of soil deformation processes which could improve the conceptual understanding of the physical behavior of soil systems.

Effect of the Deformation Temperature on the Shape‐Memory Behavior of Epoxy Networks

Abstract: The impact of the deformation conditions, specifically the temperature, on the shape-memory behavior and characteristics of epoxy SMPs is studied. By simply varying the temperature during deformation (i.e., the programming step of the SM effect), the ultimate strain of the formulated epoxy was improved three- to fivefold, thereby providing for an increased range of reachable deformation strains during SM thermo-mechanical cycling. This research unveils newly developed epoxy-based SMPs with improved deformability range and high strength with intrinsically good thermal and chemical stability.

Heterogeneous dynamics during deformation of a polymer glass

Abstract: The origins of molecular mobility in polymer glasses, particularly under deformation, are not well understood. A concerted experimental and computational approach is adopted to examine the segmental motion of a polymeric glass undergoing creep and constant strain rate deformations. Through a combination of molecular dynamics simulations and optical photobleaching experiments we are able to directly probe how dynamic heterogeneity evolves during deformation. Two distinct regimes emerge from our analysis; early in the deformation, the dynamics of the glass are strongly heterogeneous, as evidenced by the spectrum of relaxation times measured experimentally and the participation ratio of the atomic non-affine displacements measured computationally. After the onset of flow, the dynamics become significantly more homogeneous, and the participation ratio increases considerably.

Impact of a compound droplet on a flat surface: A model for single cell epitaxy.

Abstract: The impact and spreading of a compound viscous droplet on a flat surface are studied computationally using a front-tracking method as a model for the single cell epitaxy. This is a technology developed to create two-dimensional and three-dimensional tissue constructs cell by cell by printing cell-encapsulating droplets precisely on a substrate using an existing ink-jet printing method. The success of cell printing mainly depends on the cell viability during the printing process, which requires a deeper understanding of the impact dynamics of encapsulated cells onto a solid surface. The present study is a first step in developing a model for deposition of cell-encapsulating droplets. The inner droplet representing the cell, the encapsulating droplet, and the ambient fluid are all assumed to be Newtonian. Simulations are performed for a range of dimensionless parameters to probe the deformation and rate of deformation of the encapsulated cell, which are both hypothesized to be related to cell damage. The deformation of the inner droplet consistently increases: as the Reynolds number increases; as the diameter ratio of the encapsulating droplet to the cell decreases; as the ratio of surface tensions of the air-solution interface to the solution-cell interface increases; as the viscosity ratio of the cell to encapsulating droplet decreases; or as the equilibrium contact angle decreases. It is observed that maximum deformation for a range of Weber numbers has (at least) one local minimum at We=2. Thereafter, the effects of cell deformation on viability are estimated by employing a correlation based on the experimental data of compression of cells between parallel plates. These results provide insight into achieving optimal parameter ranges for maximal cell viability during cell printing.

Mesoscale simulation of the high-temperature austenitizing and dynamic recrystallization by coupling a cellular automaton with a topology deformation technique

Abstract: This paper reports on work in developing a cellular automaton (CA) model coupling with a topology deformation technique to simulate the microstructural evolution of 30Cr2Ni4MoV rotor steel during the high-temperature austenitizing and dynamic recrystallization (DRX). The state transition rules for simulating the normal grain growth was established based on the curvature-driven mechanism, thermodynamic driving mechanism and established based on the curvature-driven mechanism, thermodynamic driving mechanism and the lowest energy principle. To describe the compression effect on the topology of grain deformation more accurately, the update topology deformation model was proposed in which a cellular coordinate system and a material coordinate system were established separately. The cellular coordinate system remains unchangeable, but the material coordinate system and the corresponding grain boundary shape will change with deformation in the update topology deformation model. The effects of a wide range of thermomechanical parameters (e.g., temperature and strain rate) on the DRX kinetics and mean grain size were investigated. It was found that increasing the temperature and/or decreasing the strain rate can reduce the incubation period, and decreasing the temperature and/or increasing the strain rate can refine the DRX grain size. The simulation results are validated by comparing the experimental results.

Non-contact optical system, computer-accessible medium and method for measuring at least one mechanical property of tissue using coherent speckle techniques(s)

Abstract: Exemplary embodiments of apparatus and method for determining at least one material property of an anatomical structure can be provided. According to one exemplary embodiment, it is possible to apply at least one first coherent radiation to at least one portion of the anatomical structure, and receive at least one second coherent radiation from such portion(s). The first and second coherent radiations can be associated with one another. In addition, it is possible to determine the material property based on the second coherent radiation(s). Such determination can be performed without (i) any portion of an apparatus performing the procedure causing an induction of at least one mechanical deformation on or in the anatomical structure, and/or (ii) any mechanical deformation on or in the anatomical structure.

Flapping Wing Structural Deformation and Thrust Correlation Study with Flexible Membrane Wings

Abstract: This experimental study investigates the relationship between flapping wing structure and the production of aerodynamic forces for micro air vehicle hovering flight by measuring full-field structural deformation and thrust generation. Results from four flexible micromembrane wings with different skeletal reinforcement demonstrate that wing compliance is crucial in thrust production: only certain modes of passive aeroelastic deformation allow the wing to effectively produce thrust. The experimental setup consists of a flapping mechanism with a single-degree-of- freedom rotary actuation up to 45 Hz at 70 deg stoke amplitude and with power measurement, a force and torque sensor that measures the lift and thrust, and a digital image correlation system that consists of four cameras capable of capturing the complete stroke kinematics and structural deformation. Several technical challenges related to the experimental testing of microflapping wings are resolved in this study: primarily, flapping wings less than 3 in. in length produce loads and deformations that are difficult to measure in an accurate and nonintrusive manner. Furthermore, the synchronization of the load measurement system, the vision-based wing deformation measurement system, and the flapping mechanism is demonstrated. Intensive data analyses are performed to extract useful information from the measurements in both air and vacuum.

Patient-specific non-linear finite element modelling for predicting soft organ deformation in real-time: application to non-rigid neuroimage registration.

Abstract: Long computation times of non-linear (i.e. accounting for geometric and material non-linearity) biomechanical models have been regarded as one of the key factors preventing application of such models in predicting organ deformation for image-guided surgery. This contribution presents real-time patient-specific computation of the deformation field within the brain for six cases of brain shift induced by craniotomy (i.e. surgical opening of the skull) using specialised non-linear finite element procedures implemented on a graphics processing unit (GPU). In contrast to commercial finite element codes that rely on an updated Lagrangian formulation and implicit integration in time domain for steady state solutions, our procedures utilise the total Lagrangian formulation with explicit time stepping and dynamic relaxation. We used patient-specific finite element meshes consisting of hexahedral and non-locking tetrahedral elements, together with realistic material properties for the brain tissue and appropriate contact conditions at the boundaries. The loading was defined by prescribing deformations on the brain surface under the craniotomy. Application of the computed deformation fields to register (i.e. align) the preoperative and intraoperative images indicated that the models very accurately predict the intraoperative deformations within the brain. For each case, computing the brain deformation field took less than 4 s using an NVIDIA Tesla C870 GPU, which is two orders of magnitude reduction in computation time in comparison to our previous study in which the brain deformation was predicted using a commercial finite element solver executed on a personal computer.

Excitations in the deformed D1D5 CFT

Abstract: We perform some simple computations for the first order deformation of the D1D5 CFT off its orbifold point. It had been shown earlier that under this deformation the vacuum state changes to a squeezed state (with the further action of a supercharge). We now start with states containing one or two initial quanta and write down the corresponding states obtained under the action of deformation operator. The result is relevant to the evolution of an initial excitation in the CFT dual to the near extremal D1D5 black hole: when a left and a right moving excitation collide in the CFT, the deformation operator spreads their energy over a larger number of quanta, thus evolving the state towards the infrared.