Smoothed Particle Hydrodynamics for Computational Fluid Dynamics

Smoothed particle hydrodynamics (SPH) is a simple and effective numerical method that can be used to solve a variety of challenging problems in computational mechanics. It is a Lagrangian mesh-free method ideal for solving deformation problems. In the SPH method, the state of a system is represented by a set of particles, which possesses individual material properties and interact with each other within a specific range defined as a support domain by a weight function or smoothing function. SPH features flexibility in handling complex flow fields and in including physical effects. In theory, the basic concept of the SPH method is introduced in this paper. Some detailed numerical aspects are discussed including the kernel approximation in continuous form and particle approximation in discrete form, the properties for the smoothing functions and some of the most frequently used ones in the SPH literature, the concept of support and interface domain, SPH formulations for Navier-Stokes equation, time integration, boundary treatment, particle interaction, artificial viscosity, laminar viscosity, shifting algorithm, and so on. In applications, this paper presents an improved SPH method for modeling the diffusion process of a microneedle and using smoothed particle hydrodynamics (SPH) method to simulate the 25% cross-section stenosis blood vessel model and the 75% crosssection stenosis blood vessel model. The obtained numerical results are in close agreement with available theoretical and experimental results in the literature. As an emerging transdermal drug delivery device, microneedles demonstrate some superior potential and advantages over traditional metallic needles-on-syringes in skin injection and vaccine [1]. However, very few research papers are available. This project uses a high order continuous method, the spectral element method (SEM), and a low order discrete method, the Smoothed Particle Hydrodynamics (SPH), to investigate this new drug delivery system. The incompressible Navier-Stokes equations were solved with SEM under appropriate initial and slip boundary conditions for the transport of medicine inside microneedles of rectangular and circular cross-sections. In addition, Darcy-Brinkman equations and a concentration equation were solved with SEM under appropriate initial and boundary conditions for the infiltration of medicine solution through porous media of the dermis tissue once a microneedle enters the skin. Meanwhile, the Lagrangian form of the Navier-Stokes equations were solved with the weighted interpolation approach via numerical integrations without inverting any matrices. Results from the mesh-based SEM and the mesh-free SPH simulations revealed technical details about the processes of delivery of medicine particles through microneedles and diffusion in the skin tissue, and the medicine concentration changes with space and time. The overall effect of medicine delivery under initial concentration and conditions were simulated and the effect of drug delivery were assessed. The formation of thrombus is a complicated process. The existing literature rarely has a model for high-fidelity simulation of the effects and hazards of blood clots on blood flow. In this model, high-fidelity simulations are performed for complex human internal environments. The result of this simulation indicates high pressure area in blood vessel wall which matches the real condition of the vessel experiment

Using the generalized interpolation material point method for fluid-solid interactions induced by surface tension

This thesis is devoted to the development of new, Generalized Interpolation Material Point Method (GIMP)-based algorithms for handling surface tension and contact (wetting) in fluid-solid interaction (FSI) problems at small scales. In these problems, surface tension becomes so dominant that its influence on both fluids and solids must be considered. Since analytical solutions for most engineering problems are usually unavailable, numerical methods are needed to describe and predict complicated time-dependent states in the solid and fluid involved due to surface tension effects. Traditional computational methods for handling fluid-solid interactions may not be effective due to their weakness in solving large-deformation problems and the complicated coupling of two different types of computational frameworks: one for solid, and the other for fluid. On the contrary, GIMP, a mesh-free algorithm for solid mechanics problems, is numerically effective in handling problems involving large deformations and fracture. Here we extend the capability of GIMP to handle fluid dynamics problems with surface tension, and to develop a new contact algorithm to deal with the wetting boundary conditions that include the modeling of contact angle and slip near the triple points where the three phases -- fluid, solid, and vapor -- meet. The error of the new GIMP algorithm for FSI problems at small scales, as verified by various benchmark problems, generally falls within the 5% range. In this thesis, we have successfully extended the capability of GIMP for handling FSI problems under surface tension in a one-solver numerical framework, a unique and innovative approach.Chapter 1. Introduction -- Chapter 2. Using the generalized interpolation material point method for fluid dynamics at low reynolds numbers -- Chapter 3. On the modeling of surface tension and its applications by the generalized interpolation material point method -- Chapter 4. Using the generalized interpolation material point method for fluid-solid interactions induced by surface tension -- Chapter 5. Conclusions

Novel Particle Model for the Prediction of Stability and Episodic Collapse of Coastal Cliffs and Levees

This thesis investigates the WCSPH model by considering fluid entry and exit, and integrates the WCSPH method into a new, novel, particle-based Bluff Morphology Model (BMM). Using the BMM, this thesis investigates the stability, collapse and equilibrium position of soft coastal bluffs (cliffs). Fluid and floating object interaction using a novel adaptation of the WCSPH method is investigated by incorporating a floating object model. In particular, this thesis examines the water impact, hydrodynamic forces, fluid motions, and movement of objects in the conventional case studies of object entry and exit from still water. A two-dimensional wedge drop analysis was examined, and the hydrodynamic forces show acceptable agreement with published experimental and numerical results. Simulations for water entry and exit of a buoyant and neutral density cylinder compares well with the previous experimental, numerical and empirical studies. These results provide a good foundation to evaluate the accuracy and stability of WCSPH for modelling complex flows, and therefore offers a platform for the use of WCSPH in a Bluff Morphology Model. The BMM combines a multiple wedge displacement method with an adapted Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) method. At first the wedge method is applied to compute the stability of the bluff. Once the critical failure mechanism of the bluff slope has been identified, if the Factor of Safety for the mechanism is less than 1, the adapted WCSPH method is used to predict the failure movement and residual shape of the slope. The model is validated against benchmark test cases of bluff stability for purely frictional, purely cohesive, and mixed strength bluff materials including 2D static water tables. The model predictions give a good correlation with the expected values, with medium resolution models producing errors of typically less than 2.0%. In addition, the prediction of lateral movement of a surveyed cliff and the dynamic collapse of a vertical bluff are computed, and compare well with published literature. This model is further extended to then investigate the effect of two dimensional seepage on the stability and collapse of soil slopes and levees. To incorporate the seepage in the model, Darcy’s Law is applied to the interactions among neighbouring soil particles and ghost particles are introduced along the enclosed soil boundary to ensure that no fluid crosses the boundary. The contribution of partially saturated soils and matric suction, as well as the change in hydraulic conductivity due to seepage, are predicted well by this model. The predicted time evolution of slope stability and seepage induced collapse are in reasonable agreement with the experimental results for homogeneous frictional sand and multiple layered cohesive soils. Rapid drawdown over a sand soil is also investigated, and the location and time of the levee collapse occurrence are captured well. A toe erosion model is incorporated within the numerical model, and the location and quantity of erosion caused by lateral seepage is well predicted. The interplay of erosion, seepage and slope instability is examined

Free Liquid Drag−out from a Liquid Bath Using SPH

The liquid drag−out (LDO) coating process is a key process in metallic−coated strip production in continuous galvanising lines. The liquid is dragged−out by the strip when the strip pulls up from a bath. The liquid in the process is commonly liquid zinc. The LDO physical understanding is important to control the liquid film thickness, coated strip smoothness and production efficiency. The thesis aimed to understand free LDO fundamentals by developing a numerical tool to simulate the free LDO process. The LDO fundamentals (meniscus, stagnation point, re-circulation flow, boundary layer thickness) analysis are important, as the film is influenced by the fundamentals. A graphical processing unit (GPU) enables a Smoothed Particle Hydrodynamics (SPH) tool is to be developed using MATLAB. The SPH tool is validated against the numerical cases: lid−driven cavity, a hydrostatic tank under gravity and a droplet spreading on a solid surface. The inter−particle interaction (IIF) technique is used in modelling the surface tension and adhesion. Non−periodic inlet and outlet boundaries are present in LDO problem. Mirror buffer technique with SPH is implemented in the outlet to model the gradient−free Neumann boundary. Also, to conserve the domain mass over time, a novel approach is introduced to return the domain leaving particle immediately to the domain at the next time step

Advancing the Contour Method to Characterise Residual Stress in Polymer Composites

The manufacturing route for polymer composites inevitably introduces residual stress. It entails cooling from high cure temperature to room temperature accompanied by constrained shrinkage. The constraints arise from the micro-scale contraction between the fibre and matrix, as well as the macro-scale contraction between adjacent plies with varying fibre orientations inducing strain dissimilarities. The resulting residual stresses are directly associated with dimensional stability such as warpage, shape distortion and the structural integrity of composite structures (e.g. matrix cracking, reduced fibre-matrix bondage and delamination toughness). The composite structures may need to be pre-loaded to get the desired assembly tolerances, creating additional internal stresses and reducing overall performance. Therefore, knowledge and accurate characterisation of residual stress is imperative for optimising the design and structural integrity of polymer composites. Analytical and numerical methods have been developed to predict residual stresses in polymer composites, but these procedures are computationally expensive and require cure and temperature dependent physio-chemo-rheological properties. Experimental methods offer an alternative solution for developing a quantitative understanding of the sign, magnitude and distribution of residual stresses. They are essential for validation of predictive methods. However, the characterization of bulk residual stress in polymer composites remains a challenge as there is currently no experimental approach available for this purpose. The present study investigates the viability of using the Contour Method for measuring 2-dimensional residual stress in polymer composites. Traditionally, the method has been solely applied to metallic structures. The challenge to address is to expand its applications to non-metallic structures through identifying suitable methods for cutting the material. In this work, the feasibility of five different cutting techniques such as wire EDM, abrasive waterjet machine, diamond wire machine, milling machine with end mill and slit saw tools for contour analysis is explored. The results of contour cutting on asymmetric and symmetric epoxy Carbon Fibre Reinforced Polymer (CFRP) cross ply laminates are presented and discussed. The created cut surfaces are carefully interrogated using optical microscopy, scanning electron microscopy, and high-resolution surface topological scanning methods. The quality of contour cuts and the corresponding optimal conditions were evaluated based on three surface features criteria, such as cutting artefacts, subsurface damage and surface roughness coefficient. The deformations observed on the cut surface created by the diamond wire method, as a consequence of the relief of residual stress, clearly demonstrate the ply orientations in both asymmetric and symmetric samples. Therefore, among the five cutting techniques evaluated, the cut quality of the diamond wire machine was found to be sufficiently good for measuring deformation resulting from residual stress relaxation. The diamond wire cutting technique is evaluated by means of a thermal mapping device to ensure that the cutting temperature remains below the glass transition temperature, which is determined using Differential Scanning Calorimetry. The measured out of plane displacement data obtained from the optimum cutting process were then processed using the standard approach for contour measurement. The investigation of data analysis parameters along with the provision of guidelines to assist practitioners of the contour method measurement in selecting an appropriate surface measurement density, mask size for smoothing the deformation data, finite element mesh size for contour method data collection and analysis are reviewed. In addition, a correlation has also been discussed between the minimum resolvable residual stress length scale and the size of constituents and surface roughness induced by the diamond wire cutting process. Finally, residual stresses through the thickness of asymmetric and symmetric samples measured by the Contour Method using diamond wire cutting are presented. The results are validated against measurements using the slitting method. In compliment, they are also compared to Classical Laminate Theory based analytical results and thermally simulated residual stress in ABAQUS and the limitations are addressed. The research marks the first instance of implementing the method on epoxy CFRP composites and showcases the capability of the contour method in determining bulk residual stress distribution across the thickness of cross-ply laminates

Determination of the high water mark and its location along a coastline

The High Water Mark (HWM) is an important cadastral boundary that separates land and water. It is also used as a baseline to facilitate coastal hazard management, from which land and infrastructure development is offset to ensure the protection of property from storm surge and sea level rise. However, the location of the HWM is difficult to define accurately due to the ambulatory nature of water and coastal morphology variations. Contemporary research has failed to develop an accurate method for HWM determination because continual changes in tidal levels, together with unimpeded wave runup and the erosion and accretion of shorelines, make it difficult to determine a unique position of the HWM. While traditional surveying techniques are accurate, they selectively record data at a given point in time, and surveying is expensive, not readily repeatable and may not take into account all relevant variables such as erosion and accretion.In this research, a consistent and robust methodology is developed for the determination of the HWM over space and time. The methodology includes two main parts: determination of the HWM by integrating both water and land information, and assessment of HWM indicators in one evaluation system. It takes into account dynamic coastal processes, and the effect of swash or tide probability on the HWM. The methodology is validated using two coastal case study sites in Western Australia. These sites were selected to test the robustness of the methodology in two distinctly different coastal environments

Specifying a hybrid, multiple material CAD system for next-generation prosthetic design

For many years, the biggest issue that causes discomfort and hygiene issues for patients with lower limb amputations have been the interface between body and prosthetic, the socket. Often made of an inflexible, solid polymer that does not allow the residual limb to breathe or perspire and with no consideration for the changes in size and shape of the human body caused by changes in temperature or environment, inflammation, irritation and discomfort often cause reduced usage or outright rejection of the prosthetic by the patient in their day to day lives. To address these issues and move towards a future of improved quality of life for patients who suffer amputations, Loughborough University formed the Next Generation Prosthetics research cluster. This work is one of four multidisciplinary research studies conducted by members of this research cluster, focusing on the area of Computer Aided Design (CAD) for improving the interface with Additive Manufacture (AM) to solve some of the challenges presented with improving prosthetic socket design, with an aim to improve and streamline the process to enable the involvement of clinicians and patients in the design process. The research presented in this thesis is based on three primary studies. The first study involved the conception of a CAD criteria, deciding what features are needed to represent the various properties the future socket outlined by the research cluster needs. These criteria were then used for testing three CAD systems, one each from the Parametric, Non Uniform Rational Basis Spline (NURBS) and Polygon archetypes respectively. The result of these tests led to the creation of a hybrid control workflow, used as the basis for finding improvements. The second study explored emerging CAD solutions, various new systems or plug-ins that had opportunities to improve the control model. These solutions were tested individually in areas where they could improve the workflow, and the successful solutions were added to the hybrid workflow to improve and reduce the workflow further. The final study involved taking the knowledge gained from the literature and the first two studies in order to theorise how an ideal CAD system for producing future prosthetic sockets would work, with considerations for user interface issues as well as background CAD applications. The third study was then used to inform the final deliverable of this research, a software design specification that defines how the system would work. This specification was written as a challenge to the CAD community, hoping to inform and aid future advancements in CAD software. As a final stage of research validation, a number of members of the CAD community were contacted and interviewed about their feelings of the work produced and their feedback was taken in order to inform future research in this area

Micro-mechanical Material Analysis

habilitační práceSimulations in material engineering must consider complex physical phenomena that have a non-linear character and interact with multiple time and space scales. In spite of the intensive development of computational technologies, spatial and temporal simulations penetrating signi cantly di erent scales, starting with the electron structure and visible at the end, can still be realized only very limited. This work is devoted to multi-scale homogenization starting from mathematical formulation and ends up with the construction of a model derived from real data. The rst part introduces a new implementation of periodic boundary conditions in the sense of the Nitsche's method and subsequently tested on complex material structures. The second part introduces the gradient smoothing technique and its use to improve the convergence properties of the nite element method and the accuracy of the estimation of the e ective material properties. The third part is devoted to the e ective reconstruction of brous textile structures from tomographic data including the estimation of morphological parameters

Higher level techniques for the artistic rendering of images and video

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NASA patent abstracts bibliography: A continuing bibliography. Section 1: Abstracts (supplement 40)

Abstracts are provided for 181 patents and patent applications entered into the NASA scientific and technical information system during the period July 1991 through December 1991. Each entry consists of a citation, an abstract, and in most cases, a key illustration selected from the patent or patent application