This dissertation focuses on studying membrane air dehumidification for a membrane moisture exchanger in a membrane heat pump system. The study has two parts: an optimization of membrane moisture exchanger for air dehumidification in the macroscale, and diffusion of water vapor in polymer nanocomposites membrane for humid air dehumidification in the nanoscale. In the first part of the research, the mass transport of water vapor molecules through hydrophilic silica nanochannel chains in hydrophobic polyurethane matrix was studied by simulations and experiments for different membrane moisture exchanger design configurations. The mass transport across the polymer nanocomposite membrane occurs with the diffusion of moist air water vapor molecules in the membrane moisture exchanger in a membrane heat pump air conditioning system for air dehumidification purposes. The hydrophobic polyurethane matrix containing the hydrophilic silica nanochannel chains membrane is responsible for transporting water vapor molecules from the feed side to the permeate side of the membrane without allowing air molecules to pass through.In the second part of the research, diffusion analysis of the polymer nanocomposite membrane were performed in the nanoscale for the polymer nanocomposite membrane. The diffusion phenomena through the polymer, the polymer nanocomposite without modifying the silica surfaces, and the polymer nanocomposite with two different silica modified surfaces were studied in order to obtain the highest water vapor removal through the membrane. Different membrane moisture exchanger configurations for optimal water vapor removal were compared to get the desired membrane moisture exchanger design using the finite element method (FEM) with the COMSOL Multiphysics software package. The prediction of mass transport through different membrane configurations can be done by obtaining the mass flux value for each configuration. An experimental setup of one membrane moisture exchanger design was introduced to verify the simulation results. Also, for different membrane structures, permeability was measured according to the ASTM E-96 method. The prediction of water vapor diffusion through the polymer nanocomposite was studied by molecular dynamics simulation with the MAPS 4.3 and LAMMPS software packages. As a new nanocomposite material used in air dehumidification application, water vapor diffusivity through Silica-Polyurethane nanocomposite membranes was measured by the random movement of water vapor molecules through the formed nanochannels in the nanocomposite. For the diffusivity value, the Einstein's relationship was employed for the movement of each single water vapor molecule during the simulation time for all suggested membranes. The results of the proposed research will contribute to enhancing the energy efficiency of air conditioning systems by choosing the membrane moisture exchanger configuration which maximizes water vapor removal while, at the same time, enhancing the silica surfaces with the desired surface modifier that will maximize diffusion through the membrane itself.

<p>There are significant problems during construction to establish an adequate foundation for fills and/or subgrade for pavements when the natural ground has low-bearing soils. Geosynthetics such as geogrids, geotextiles and/or geocells could provide an alternative, less costly in time and money, to establish an adequate foundation for the fill and/or subgrade. There is extensive evidence in the literature and on DOTs practices about the suitability of using geotextiles in pavements as separators. Previous studies have also shown that the use of geogrids in flexible pavements as a reinforcing mechanism could decrease the thickness of the base layer and/or increase the life of the pavement. In this study, analyses of selected pavement designs using Pavement ME, while considering geogrid-enhanced base or subgrade resilient modulus values, showed that geogrid-reinforcement, when placed at the interface between subgrade and base, did not produce significant benefits, as only a modest increase in pavement life was predicted. In addition, parametric finite element analyses were carried out to investigate the potential benefits of placing a geogrid at the base of a fill over a localized weak foundation zone. The analyses showed that the use of geogrids is beneficial only when: (a) the stiffness of the weak foundation soil is about an order of magnitude smaller than the rest of the foundation soil; and (b) the horizontal extent of the weak foundation soil is at least 30% of the base of the embankment foundation. The largest decrease in differential settlements at the surface of the fill, resulting from geogrid-reinforcement, was less than 20% and, therefore, it is unlikely that the sole use of geogrids would be sufficient to mitigate differential settlements. Based on previous studies, a geocell mattress, which is a three-dimensional geosynthetic filled with different types of materials, could act as a stiff platform at the base of an embankment and bridge over weak zones in the foundation. However, given the limited experience on the use of geocells, further research is required to demonstrate that geocells can be effectively used instead of other reinforcement methods.</p>

Being a widely used structure, composite shells have been studied for a long time. The features of small thickness, heterogeneity, and anisotropy of composite shells have created many challenges for analyzing them. A number of theories have been developed for modeling composite shells, while they are either not practical for engineering use, or rely on assumptions that do not always hold. Consequently, a better theory is needed, especially for the application on challenging problems such as shells involving thermoelasticity, viscoelasticity, or viscoplasticity.<br><br>In this dissertation, a shell theory based on mechanics of structure genome (MSG), a unified theory for multiscale constitutive modeling, is developed. This theory is capable of handling fully anisotropy and complex heterogeneity, and because the derivation follows principle of minimum information loss (PMIL) and using the variational asymptotic method (VAM), high accuracy can be achieved. Both a linear version and a nonlinear version using Euler method combined with Newton-Raphson method are presented. This MSG-based shell theory is used for analyzing the curing process of composites, deployable structures made with thin-ply high strain composite (TP-HSC), and material nonlinear shell behaviors.<br><br>When using the MSG-based shell theory to simulate the curing process of composites, the formulation is written in an analytical form, with the effect of temperature change and degree of cure (DOC) included. In addition to an equivalent classical shell theory, a higher order model with the correction from initial geometry and transverse shear deformation is presented in the form of the Reissner-Mindlin model. Examples show that MSG-based shell theory can accurately capture the deformation caused by temperature change and cure shrinkage, while errors exist when recovering three-dimensional (3D) strain field. Besides, the influence of varying transverse shear stiffness needs to be further studied.<br><br>In order to analyze TP-HSC deployable structures, linear viscoelasticity behavior of composite shells is modeled. Then, column bending test (CBT), an experiment for testing the bending stiffness of thin panels under large bending deformation, is simulated with both quasi-elastic (QE) and direct integration (DI) implementation of viscoelastic shell properties. Comparisons of the test and analysis results show that the model is capable of predicting most of the measured trends. Residual curvature measured in the tests, but not predicted by the present model, suggests that viscoplasticity should be considered. A demonstrative study also shows the potential of material model calibration using the virtual CBT developed in this work. A deployable boom structure is also analyzed. The complete process of flattening, coiling, stowage, deployment and recovery is simulated with the viscoelastic shell model. Results show that major residual deformation happens in the hoop direction.<br><br>A nonlinear version of the MSG-based general purpose constitutive modeling code SwiftComp is developed. The nonlinear solving algorithm based on the combined Euler-Newton method is implemented into SwiftComp. For the convenience of implementing a nonlinear material model, the capability of using user material is also added. A viscoelastic material model and a continuum damage model is tested and shows excellent match when compared with Abaqus results with solid elements and UMAT. Further validation of the nonlinear SwiftComp is done with a nonlinear viscoelastic-viscoplastic model. The high computational cost is emphasized with a preliminary study with surrogate model.

No description available.

By applying the finite element approach to the design and analysis of the impact diffusion helmet, many helmet configurations were able to be analyzed. Initially it was important to determine what design variables had an influence on the impact reducing abilities of the helmet design. The helmet was run through a series of Abaqus simulations that determined that a design with two oval shaped channels running along the length of the helmet was best. Next, these options were optimized to generate the helmet that produced the greatest impact reduction. The optimization simulations determined that a helmet that pushed the channels as far from the impact zone as possible reported the lowest acceleration. This indicated that removing the channels from play was most advantageous from an impact reduction perspective. Finally, a 3-D printed experimental helmet was impact tested and compared to a 3-D printed control helmet. The experimental helmet brought the channels back into the impact zone in order to judge if they had a physical effect on the acceleration. Both the simulations and the subsequent physical testing indicated that the Impact Diffusion Helmet design has a negative influence on the concussion reducing properties of a football helmet.

Syntactic foams are hollow particles-filled lightweight composites that are widely used in areas that require high strength while maintaining low weight and density. These foams are highly tailorable materials whose properties can be altered during the manufacturing process by changing various parameters like matrix and microballoon material type, size, distribution, as well as the volume fraction and wall thickness of microballoons. Therefore, understanding the effect of these parameter changes in the behavior of syntactic foams is very important to manufacture the foam for different applications. In the present study, syntactic foams of various volume fractions of microballoons were fabricated and different mechanical testing was conducted to study their elastic and viscoelastic behavior. Moreover, density, void content, and microstructure of the syntactic foam with varying volume fractions of microballoons were also studied to better characterize these foams. Results show that changes in the volume fraction of the microballoons had a significant impact on the elastic and viscoelastic behavior of the foams. The introduction of the microballoons into the epoxy resin decreased the density of the epoxy resin by up to 43.36% and at the same time increasing the specific modulus by up to 21.059%. In addition, representative 3D models of these syntactic foams were also developed to further study the elastic behavior of these materials which were found to be in good agreement with the experimental results. These findings will help in designing and optimizing the material properties of the syntactic foam required for different applications.

A reusable oxidizer-cooled annular aerospike nozzle was designed for testing on a labscale PMMA-N20[1] hybrid rocket motor at Cal Poly-SLO.[2] The detailed design was based on the results of previous research involving cold-flow testing of annular aerospike nozzles and hot-flow testing of oxidizer-cooled converging-diverging nozzles. In the design, nitrous oxide is routed to the aerospike through a tube that runs up the middle of the combustion chamber. The solid fuel is arranged in an annular configuration, with a solid cylinder of fuel in the center of the combustion chamber and a hollow cylinder of fuel lining the circumference of the combustion chamber. The center fuel grain insulates the coolant from the heat of the combustion chamber. The two-phase mixture of nitrous oxide then is routed through channels that cool the copper surface of the aerospike. The outer copper shell is brazed to a stainless steel core that provides structural rigidity. The gaseous N2O flows from the end of aerospike to provide base bleed, compensating for the necessary truncation of the spike. Sequential and fully-coupled thermal-mechanical finite element models developed in Abaqus CAE were used to analyze the design of the cooled aerospike. The stress and temperature distributions in the aerospike were predicted for a 10-sec burn time of the hybrid rocket motor. [1] PMMA stands for polymethyl methacrylate, a thermoplastic commonly known by the brand name Plexiglas®. N2O is the molecular formula for nitrous oxide. [2] California Polytechnic State University, San Luis Obispo

Composites are now being incorporated into aircraft designs because of their high strength to weight ratio compared to traditional metal materials. Due to the complexity of the material, composite parts are presently being over designed to satisfy static and fatigue requirements. A greater understanding of composite fatigue behavior will allow for even greater weight savings leading to increased fuel economy. A critical part of an aircraft that is subjected to fatigue bending loads are its wings. The forces acting on the wings include its lift distribution, powerplant, and fuel which can be carried in the wing body. When in flight these forces repeatedly cause cyclic displacements which could ultimately lead to failure. It is important to design the wing spars which carry the bending loads, to be fatigue resistant so that damage or expensive inspections could be avoided. Wing models were be made from composite materials with a NACA 0016 airfoil shape, chord length of 9.25”, and a span of 15.25”. The C – channel spars were located at 22% and 72% of the chord. Strain gages on the wing model were used to measure strain at different locations. Static test were conducted on the specimens in order to validate a finite element analysis(FEA) model to be used for simulations. Overall, the strain measurements on the leading edge from two of the wings matched the model within 9% of the simulation results. Additional spar designs were then analyzed to determine the optimal one for static and fatigue bending loads. The wings were fatigue tested under displacement control at a test frequency. A model 8801 servo-hydraulic Instron machine and Wave Matrix software was used to fatigue the wings. After 100,000 cycles the test would be deemed a success and concluded.

No description available.

Knowledge about the dynamic behaviour is a basic condition for a secure operation of modern machine tools. Hence numerical methods predicting the dynamic properties are gaining in importance. Usually for complex and coupled structures, the results of dynamic property calculation are yet insufficient. Therefore Finite Element model updating is a tool to improve the hypothetical factor of the analysis. Within the present thesis Finite Element modelling is performed using the example of the “Scherenkinematik”, a machine tool based on hybrid-kinematics. Initially the results of an Experimental Modal Analysis are evaluated by identifying Modal parameters and deriving possible structural modifications. In the second part of the thesis, the machines Finite Element model is created using the FEA-Software ANSYS. Afterwards the Finite Element model updating is performed by coupling ANSYS and the CAE-Software FEMtools. Therefore two approaches are formulated and tracked. It turns out, that there is no improvement of the analytical and experimental models correlation, neighter with nor without a steady reduction of the search domain needed for mode coupling. It is reasoned, that the characteristics and the results of an Finite Element updating process are affected by the quality of the model at start time and the approach as well as the technique chosen for model updating and parameter modification. Therefore the CAE-Software FEMtools is suitable to only a limited extent for Finite Element updating of strongly coupled mechanical structures as a result of the sensitivity analysis used for parameter modification.