Numerical simulation techniques for the efficient and accurate treatment of local fluidic transport processes together with chemical reactions

This work describes a numerical framework developed for the efficient and accurate simulation of microfluidic applications related to two leading ex-periments of the DFG SPP 1740 research initiative, namely the ‘Superfocus Mi-cromixer’ and the ‘Taylor bubble flow’. Both of these basic experiments are con-sidered in a reactive framework using the SPP 1740 specific chemical reaction systems. A description of the utilized numerical components related to special meshing techniques, discretization methods and decoupling solver strategies is provided and its particular implementation is performed in the open-source CFD package FeatFlow [19]. A demonstration of the developed simulation tool is based on already defined validation cases and on suitable examples being re-sponsible for the determination of the related convergence properties (in the range of targeted process parameter values) of the developed numerical frame-work. The subsequent studies give an insight into a parameter estimation method with the aim of determination of unknown reaction-kinetic parameter values by the help of experimentally measured data

Design of three dimensional isotropic microstructures for maximized stiffness and conductivity

The level-set method of topology optimization is used to design isotropic two-phase periodic multifunctional composites in three dimensions. One phase is stiff and insulating whereas the other is conductive and mechanically compliant. The optimization objective is to maximize a linear combination of the effective bulk modulus and conductivity of the composite. Composites with the Schwartz primitive and diamond minimal surfaces as the phase interface have been shown to have maximal bulk modulus and conductivity. Since these composites are not elastically isotropic their stiffness under uniaxial loading varies with the direction of the load. An isotropic composite is presented with similar conductivity which is at least 23% stiffer under uniaxial loading than the Schwartz structures when loaded uniaxially along their weakest direction. Other new near-optimal isotropic composites are presented, proving the capablities of the level-set method for microstructure design.Comment: 25 pages, 11 figures, to be submitted to International Journal of Solids and Structure

Preliminary finite element modeling of a piezoelectric actuated marine propulsion fin

New technologies surrounding composite materials and autonomous underwater vehicle (AUV) design have led to numerous studies involving the marine propulsion for these AUVs. AUVs traditionally are classified as highly efficient, payload capable, and can be utilized as reconnaissance or surveillance vehicles. Undullatory and oscillatory propulsion devices have been conceived to replace the present propulsion technologies, of propellers, with highly maneuverable, efficient, and quiet propulsion systems. Undullatory and oscillatory propulsion has been around for centuries employed by aquatic life, but only recently have the mini-technologies been available to present such propulsion devices economically and with enough materials research as to mimic biologic life on the same scale. Piezoelectric properties coupled with a thin plate allow for actuation properties, similar to bimetallic metals. Applying two piezoelectrics to the fixed end of a cantilevered beam or plate, on opposite sides, and actuating them with an opposite phase shift in electrical voltage potential results in transverse motion of the beam from the orthogonal plane to the vertical axis of the piezoelectric device. Coupling this property to a particular fiber orientation, composite thin plate, significantly increases the actuation properties. In addition, placing more than two piezoelectrics along the length of the thin composite plate gives the potential to increase actuation properties and change the motion from oscillatory to undullatory. These motions can again be increased by utilizing the natural vibration modes of the thin composite plate with piezoelectrics near resonance actuation. The current research is involved with modeling a piezoelectric actuated marine propulsion fin using the Galerkin finite element technique. An experimental proof of concept was developed to compare results. Using fluid-structure interaction (FSI) methods, it is proposed that the fluid and structure programs are resolved within one program. This is in contrast to traditional attempts at FSI problems that utilize a computational fluid dynamics (CFD) solver transferring load data between a structural dynamics/finite element (FE) program

Development of Imaging Paradigms for Drug Distribution and Fate in the Eye

Aging-associated vision loss is increasingly prevalent in our population and intravitreal injections are commonly used to administer ocular drugs to the posterior segment of the eye. This work aims to visualize and predict the delivery of ocular drugs by combining micro- computed tomography (micro-CT) imaging and computational fluid dynamics (CFD) modeling. Intravitreal injections were administered into ex vivo porcine eyes and imaged for an extended period of time to track the progression of the injected drug mimic. Non-invasive imaging allowed for precise determination of contrast agent concentration, flow patterns and fate. A computational model was developed that provided quantitative agreement with the concentration values found in the experimental study and allowed for easy manipulation of parameters. The ability to accurately model drug transport following an intravitreal injection provides vital information to better understand the specific concentration and time frame for the drug to reach the target sit

Fluid–structure interaction simulations of a wind gust impacting on the blades of a large horizontal axis wind turbine

The effect of a wind gust impacting on the blades of a large horizontal-axis wind turbine is analyzed by means of high-fidelity fluid-structure interaction (FSI) simulations. The employed FSI model consisted of a computational fluid dynamics (CFD) model reproducing the velocity stratification of the atmospheric boundary layer (ABL) and a computational structural mechanics (CSM) model loyally reproducing the composite materials of each blade. Two different gust shapes were simulated, and for each of them, two different amplitudes were analyzed. The gusts were chosen to impact the blade when it pointed upwards and was attacked by the highest wind velocity due to the presence of the ABL. The loads and the performance of the impacted blade were studied in detail, analyzing the effect of the different gust shapes and intensities. Also, the deflections of the blade were evaluated and followed during the blade's rotation. The flow patterns over the blade were monitored in order to assess the occurrence and impact of flow separation over the monitored quantities

Design and Topology Optimisation of Tissue Scaffolds

Tissue restoration by tissue scaffolding is an emerging technique with many potential applications. While it is well-known that the structural properties of tissue scaffolds play a critical role in cell regrowth, it is usually unclear how optimal tissue regeneration can be achieved. This thesis hereby presents a computational investigation of tissue scaffold design and optimisation. This study proposes an isosurface-based characterisation and optimisation technique for the design of microscopic architecture, and a porosity-based approach for the design of macroscopic structure. The goal of this study is to physically define the optimal tissue scaffold construct, and to establish any link between cell viability and scaffold architecture. Single-objective and multi-objective topology optimisation was conducted at both microscopic and macroscopic scales to determine the ideal scaffold design. A high quality isosurface modelling technique was formulated and automated to define the microstructure in stereolithography format. Periodic structures with maximised permeability, and theoretically maximum diffusivity and bulk modulus were found using a modified level set method. Microstructures with specific effective diffusivity were also created by means of inverse homogenisation. Cell viability simulation was subsequently conducted to show that the optimised microstructures offered a more viable environment than those with random microstructure. The cell proliferation outcome in terms of cell number and survival rate was also improved through the optimisation of the macroscopic porosity profile. Additionally artificial vascular systems were created and optimised to enhance diffusive nutrient transport. The formation of vasculature in the optimisation process suggests that natural vascular systems acquire their fractal shapes through self-optimisation

Design and Topology Optimisation of Tissue Scaffolds

Tissue restoration by tissue scaffolding is an emerging technique with many potential applications. While it is well-known that the structural properties of tissue scaffolds play a critical role in cell regrowth, it is usually unclear how optimal tissue regeneration can be achieved. This thesis hereby presents a computational investigation of tissue scaffold design and optimisation. This study proposes an isosurface-based characterisation and optimisation technique for the design of microscopic architecture, and a porosity-based approach for the design of macroscopic structure. The goal of this study is to physically define the optimal tissue scaffold construct, and to establish any link between cell viability and scaffold architecture. Single-objective and multi-objective topology optimisation was conducted at both microscopic and macroscopic scales to determine the ideal scaffold design. A high quality isosurface modelling technique was formulated and automated to define the microstructure in stereolithography format. Periodic structures with maximised permeability, and theoretically maximum diffusivity and bulk modulus were found using a modified level set method. Microstructures with specific effective diffusivity were also created by means of inverse homogenisation. Cell viability simulation was subsequently conducted to show that the optimised microstructures offered a more viable environment than those with random microstructure. The cell proliferation outcome in terms of cell number and survival rate was also improved through the optimisation of the macroscopic porosity profile. Additionally artificial vascular systems were created and optimised to enhance diffusive nutrient transport. The formation of vasculature in the optimisation process suggests that natural vascular systems acquire their fractal shapes through self-optimisation

Modeling Acoustic Microfluidic Phenomena in Unconventional Geometries

In this work, the performance of a piezoelectrically-actuated ultrasonic droplet generator is analyzed by modeling the harmonic response of a two-dimensional representation of the device cross-section. Observed vibrational and acoustic resonances provide insight into optimal design conditions to achieve efficient, robust droplet ejection. Numerical simulations highlight the importance of the coupled electrical and mechanical behavior of the resonator assembly and show that elastic modes can effectively amplify or dampen acoustic modes within the fluid chamber. Experimentally-validated modeling results guide development of an optimization strategy to further improve device performance. In addition, the standing acoustic field that is the focus of the harmonic response model is incorporated into a custom simulation of the acoustophoretic migration of microparticles. Particles achieve terminal distributions at pressure nodes in the quiescent fluid, exhibiting remarkable agreement with experimental observations. The migratory speed of microparticles in a simple rectangular fluid chamber geometry has been shown to be inversely proportional to the square of the particle radius. Here, this relationship is confirmed for particle migration in more complex acoustic microfluidic geometries

Smart Material Wing Morphing for Unmanned Aerial Vehicles.

Morphing, or geometric adaptation to off-design conditions, has been considered in aircraft design since the Wright Brothers’ first powered flight. Decades later, smooth, bio-mimetic shape variation for control over aerodynamic forces still remains elusive. Unmanned Aerial Vehicles are prime targets for morphing implementation as they must adapt to large changes in flight conditions associated with locally varying wind or large changes in mass associated with payload delivery. The Spanwise Morphing Trailing Edge (SMTE) concept is developed to locally vary the trailing edge camber of a wing or control surface, functioning as a modular replacement for conventional ailerons without altering the wing’s spar box. The SMTE design was realized utilizing alternating active sections of Macro Fiber Composites (MFCs) driving internal elastomeric compliant mechanisms and passive sections of anisotropic, elastomeric skin with tailorable stiffness, produced by additive manufacturing. Experimental investigations of the modular design via a new scaling methodology for reduced-span test articles revealed that increased use of more MFCs within the active section did not increase aerodynamic performance due to asymmetric voltage constraints. The comparative mass and aerodynamic gains for the SMTE concept are evaluated for a representative finite wing as compared with a conventional, articulated flap wing. Informed by a simplistic system model and measured control derivatives, experimental investigations identified a reduction in the adaptive drag penalty up to 20% at off-design conditions. To investigate the potential for augmented aeroelastic performance and actuation range, a hybrid multiple-smart material morphing concept, the Synergistic Smart Morphing Aileron (SSMA), is introduced. The SSMA leverages the properties of two different smart material actuators to achieve performance exceeding that of the constituent materials. Utilizing the relatively higher work density and phase transformation of Shape-Memory Alloys combined with the larger bandwidth and conformal bending of MFCs, the resultant design is demonstrated to achieve the desired goals while providing additional control authority at stall and for unsteady conditions through synergistic use of reflex actuation. These advances highlight and motivate new morphing structures for the growing field of UAVs in which adaptation involves advanced compliance tailoring of complex geometry with synergistic actuation of embedded, smart materials.PhDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111533/1/alexmp_1.pd