Dept. of Aerospace Engineering
http://hdl.handle.net/2142/14799
Wed, 13 Nov 2019 20:38:56 GMT2019-11-13T20:38:56ZSimultaneous three-dimensional printing and frontal polymerization of dicyclopentadiene resin
http://hdl.handle.net/2142/105277
Simultaneous three-dimensional printing and frontal polymerization of dicyclopentadiene resin
Aw, Jia En
Three-dimensional (3D) printing has widespread uses across many industries due to its versatility and capabilities. However, freeform fabrication of thermoset polymers remains a technical challenge. This thesis combines 3D printing with frontal polymerization (FP) — a method to rapidly cure resin — for curing filaments in tandem with the printing process. A partially cured dicyclopentadiene (DCPD) resin was developed into a printing ink. Critical rheological characteristics were identified, and DCPD inks of varying incubation times were screened to find the most suitable properties. Results of the rheological study indicate that 90 minutes of incubation time resulted in optimum print behavior. Problems associated with FP were effectively tackled through temperature control across the printing setup. In situ infrared images showed an exothermic reaction front propagating during the print process, giving evidence of in situ polymerization. The optimized technique produced one-dimensional, two-dimensional and 3D freeform prints with excellent fidelity. A self-equilibrating behavior was identified in the reaction front, such that the front autonomously tune its speed to the programmed print speed. This phenomenon autonomously controls the viscoelastic bridge length, Lb, and inevitably curbs deformations to achieve high print fidelity.
3D printing; thermoset; frontal polymerization; direct ink writing; advanced manufacturing
Fri, 26 Apr 2019 00:00:00 GMThttp://hdl.handle.net/2142/1052772019-04-26T00:00:00ZAw, Jia EnModeling real world phenomena using molecular dynamics and continuum simulations
http://hdl.handle.net/2142/105245
Modeling real world phenomena using molecular dynamics and continuum simulations
Rayabharam, Archith
In the first part of this work, MD trajectory simulations of ice-like argon and amorphous silica aggregates have been performed on the HOPG and crystalline quartz surface. The ice-like argon aggregate showed tendency to deform and fragment upon contact with the surface while the more rigid amorphous SiO 2 aggregate retained its structure and gained rotational energy upon contact with the smoother HOPG surface and got accommodated or stuck when incident on the rougher quartz surface. It was observed that the final total kinetic energy retained by the aggregates decreased as the incident velocity was increased. Fragmentation was observed only from the ice-like argon aggregates. The time of emission of the fragmented Ar atoms was shorter when the ice-like argon was incident on the quartz surface compared to that obtained when the aggregate was incident on the HOPG surface. Also, more number of Ar atoms were emitted when the aggregate was incident on the quartz surface compared to that from the HOPG surface. It was observed that the sticking probability of ice-like argon aggregate is higher than that of the amorphous SiO 2 aggregate when incident on the HOPG surface. The sticking probability of SiO 2 is significantly higher than that of the ice-like argon aggregate at 1.5 km/s on the quartz surface. Dr. Levin was the supervisor for this portion of the thesis only.
In the second part of this work, two types of experimental systems have been modeled, with an aim to replicate the results of experiments and study the dynamics of the respective systems in a more detailed manner. Firstly, continuum simulations have been performed to understand a recently developed method which can potentially reduce the time required to diagnose a bacterial infection by weeks. Secondly, molecular dynamics and ab-initio molecular dynamics simulations have been performed to validate molecular-sieving of organic molecules like cyclohexane and n-hexane through carbon nanotubes. This can potentially lead to a process which can separate liquids which are otherwise very hard to separate.
Molecular Dynamics; particle-surface interactions
Tue, 23 Apr 2019 00:00:00 GMThttp://hdl.handle.net/2142/1052452019-04-23T00:00:00ZRayabharam, ArchithFrom micro-CT TO A NURBS-based interface-enriched generalized finite element method
http://hdl.handle.net/2142/104980
From micro-CT TO A NURBS-based interface-enriched generalized finite element method
Dang, Qi
In the solid mechanic community, the finite element method is widely used to simulate the mechanical or thermal response of materials and structures. In most cases, conforming meshes are used to discretize the simulated geometry. However, this traditional method is not efficient in the analysis of complex microstructures, since the shape of most microstructures is quite irregular. Creating a conforming mesh with good element quality requires a tremendous amount of time and effort. Furthermore, conventional meshing techniques typically yield a large number of elements, thereby increasing the computational cost of the analysis.
In this work, a structured non-conforming mesh generation process is proposed and demonstrated for the analysis of heterogeneous materials with complex microstructures using a NURBS-based Interface-enriched Generalized Finite Element Method (NIGFEM) developed in Prof. Geubelle’s group over the past few years. The NIGFEM relies on structured meshes that do not conform to the material interfaces, and uses NURBS (Non-Uniform Rational B-Spline)-based enrichments of the finite element approximation in the elements intersected by the material interfaces. These enrichments capture the key features of the solution along the material interfaces (e.g., C0 or C-1 continuity) and provide a very accurate description of the interface geometrical features.
The proposed meshing method uses an octree structure to subdivide the computational domain iteratively. At each iteration, the topology relation between nodes, edges, and surfaces within the subdivided elements are calculated and classified into different types. A set of hierarchical mesh refinement rules are defined to continuously divide the element if they meet specific criteria. To accurately capture the material interfaces that falls inside the structured mesh grid, NURBS are used as basis functions to capture the boundary geometry shape. This hierarchical NURBS-based structured mesh can largely reduce the number of elements without sacrificing the accuracy of discretization. The method is particularly attractive for the computational analysis of real microstructures captured through X-ray tomography, as the micro-CT images are converted into a set of NURBS representations of the material interfaces using a set of steps also described in this thesis.
NURBS; NIGFEM; Computational Geometry
Thu, 28 Mar 2019 00:00:00 GMThttp://hdl.handle.net/2142/1049802019-03-28T00:00:00ZDang, QiA new method for projection based model reduction of linear inequality constrained systems
http://hdl.handle.net/2142/104952
A new method for projection based model reduction of linear inequality constrained systems
Turner, Jason Eric
Computational modeling research centers around developing ever better representations of physics. The objective of model reduction specialists is to take that high fidelity understanding and compress it into a Reduced Order Model (ROM) capable of replicating the physical accuracy of the more complicated model with a significantly reduced computational cost. A current challenge in reduced order modeling is the presence of linear inequality constraints in optimization problems. Constrained optimization problems arise in design, contact modeling, financial engineering and other subfields of mathematical modeling. As such, there is a strong motivation to leverage the repeatability of ROMs to rapidly address these engineering challenges. Inherent to the problem of con- strained optimization is feasibility of solutions, and while all FOMs are expected to comply perfectly with their constraints, that property is not necessarily preserved in their corresponding ROMs. The problem is then two fold. First the issue of the constraint must be addressed, and second the resulting ROM must obey the constraints. This thesis develops a method, in a projection-based framework, capable of reducing the linear inequality constraints while preserving a strong degree of feasibility. The proposed method is successfully applied to the reduction of the one-dimensional, constrained Poisson Equation with varied parameters.
Constrained Optimization; Model Reduction; POD; Generalized Coordinate Bounding
Fri, 26 Apr 2019 00:00:00 GMThttp://hdl.handle.net/2142/1049522019-04-26T00:00:00ZTurner, Jason EricModel order reduction in the frequency domain via spectral proper orthogonal decomposition
http://hdl.handle.net/2142/104953
Model order reduction in the frequency domain via spectral proper orthogonal decomposition
Lin, Cong
In this thesis, we introduce a novel model order reduction framework for harmonically and randomly forced dynamical systems. Specifically, we emphasize the usage of spectral proper orthogonal decomposition (SPOD), recently revived by Towne et. al. (2018), which results in sets of orthogonal modes, each oscillating at a single frequency, that are said to optimally represent coherent-structures evolving in space and time. However, reduced-order models (ROMs) using SPOD modes have not yet been developed. Hence, in this study we investigate the potential of a novel approach utilizing SPOD modes to construct the lower-dimensional subspace for ROMs. Upon the discrete-time Fourier-transform (DFT) of the governing ordinary differential equation (ODE) system, an orthogonal projection onto the SPOD modes is performed, analogous to Proper Orthogonal Decomposition (POD) Galerkin ROMs, but compressing the system at each discrete frequency within the frequency domain. The ROM is solved at each frequency and after the inverse DFT of the spectral solution matrix we obtain the entire solution for a given timespan at once, with no time integration necessary. This new approach is illustrated using the example PDE of steady passive scalar transport in an inhomogenous, time-invariant flow field. Finally, we compare the performance of our ROM with the standard POD-Galerkin ROM in terms of accuracy and computational speedup.
POD; SPOD; reduced-order modeling; reduced-order model; DMD;
Fri, 26 Apr 2019 00:00:00 GMThttp://hdl.handle.net/2142/1049532019-04-26T00:00:00ZLin, CongDirect simulation of the fluid-structure interaction of a compliant panel in a hypersonic compression ramp flow
http://hdl.handle.net/2142/104947
Direct simulation of the fluid-structure interaction of a compliant panel in a hypersonic compression ramp flow
Sullivan, Bryson
Sustained flight at hypersonic speeds presents a challenge to robust vehicle design and control. An extreme aerothermal environment acting on geometrically-thin, multifunctional structures can result in significant static and dynamic structural deformations of the vehicle and its subcomponents. In particular, for a control surface-motivated scenario, the adverse pressure gradient generated by a compression ramp can produce a large region of subsonic, separated flow with the potential to degrade accurate estimation of surface loading by traditional hypersonic aerodynamic methods such as piston theory. The present work details high-fidelity, coupled fluid-thermal-structure interaction (FTSI) simulations of laminar, unsteady 2D flow at Mach 6.04 over a 35-degree compression ramp with an embedded compliant panel. Surface-pressure loading generated by the corner shock wave boundary layer Interaction (SWBLI) is compared between compliant and non-compliant compression ramp configurations, and SWBLI-excited response of the compliant panel is demonstrated. An analytical model based on Rayleigh's method is introduced which, given the maximum amplitude of vibration, predicts the nonlinear frequency of a compliant panel to within an average error of 8.3% over several orders of magnitude in flexural rigidity. Maximum observed heat transfer rates to the panel were diminished for the compliant panel cases relative to the rigid case, believed to be caused by a break-up in structure of the oscillating shear layer due to the motion of the panel. Reduced-order models, such as shock expansion/ local piston theory (SE/LPT), are computed for each panel and were found to perform well with a modification to account the influence of the corner separation region. Reynolds analogy for estimating heat flux was found to work reasonably well for the rigid case, but lost accuracy when applied to the thinnest panels and largest deflections.
hypersonic, compression ramp, fluid-structure interaction, aerothermoelastic, aeroelasticity, piston theory
Fri, 26 Apr 2019 00:00:00 GMThttp://hdl.handle.net/2142/1049472019-04-26T00:00:00ZSullivan, BrysonDevelopment and evaluation of a dynamically scaled testbed aircraft for a visual inertial odometry dataset
http://hdl.handle.net/2142/104948
Development and evaluation of a dynamically scaled testbed aircraft for a visual inertial odometry dataset
Figueroa, Felipe
In this thesis we describe the design, manufacturing, and testing of a dynamically scaled aircraft, which is a scaled model of a general aviation vehicle that dynamically behaves in a similar manner as the full-scale aircraft. This scaled model (Cirrus SR22T) is to serve as a testbed for both Distributed Electric Propulsion (DEP) aircraft research and for Visual Inertial Odometry (VIO) research. The aircraft is used as a baseline to compare with the DEP aircraft, to draw conclusion regarding the effect of changing to a DEP configuration, and to provide a way to measure the effect that a DEP configuration would have on a full-scale aircraft. The aircraft is also used to collect data from various onboard sensors to provide a data set for the VIO research community to use.
Distributed Electric Propulsion, DEP, Dynamically Scaled, UAV, Visual Inertia Odometry, VIO, Dataset, Model, System Identification, Parameter Estimation
Fri, 26 Apr 2019 00:00:00 GMThttp://hdl.handle.net/2142/1049482019-04-26T00:00:00ZFigueroa, FelipeSpacecraft trajectory tracking and parameter estimation in the presence of a splitting contact binary asteroid
http://hdl.handle.net/2142/104940
Spacecraft trajectory tracking and parameter estimation in the presence of a splitting contact binary asteroid
Silva, Tiago Marrs
Increasing interest in asteroid mining and in-situ resource utilization will lead to an increase in asteroid surface operations. The composition of asteroids is often unknown and potentially unstable, many of which are bound together predominantly by gravitational forces. Surface operations such as mining may significantly alter the asteroid’s structure or, in the case of contact binary asteroids, cause the asteroid to split. Conditions on the evolution of the contact binary system after splitting are derived. Observability issues causing inconclusive results in the previous work were addressed here by identifying an observable set of constant parameters which describes the splitting system. The coupled problem of estimating unknown parameters of a newly-formed binary system and controlling a spacecraft’s trajectory in the system’s vicinity is investigated. An indirect adaptive control scheme is utilized to simultaneously and accurately meet both objectives. Finally, a simpler control scheme, based only on 2-body dynamics is derived to show significant improvement in performance when using the proposed adaptive control scheme over using the simple 2-body controller. For larger contact binary asteroids, the adaptive control scheme has shown up to a 20% reduction in control cost over the 2-body controller.
Indirect Adaptive Control; Spacecraft Trajectory Tracking; Kalman Filter; Parameter Estimation; Contact Binary Asteroids; LQR Control
Fri, 26 Apr 2019 00:00:00 GMThttp://hdl.handle.net/2142/1049402019-04-26T00:00:00ZSilva, Tiago MarrsAssessment of aerocapture-entry trajectories for human Mars exploration
http://hdl.handle.net/2142/104938
Assessment of aerocapture-entry trajectories for human Mars exploration
Zinner, Evan J.
Using aerocapture to insert into an elliptic parking orbit prior to entry, descent, and landing is being explored for human Mars missions. These aerocapture-entry trajectories have advantages over a direct entry, but the advantages come at the cost of additional entry system mass. The goal of this research is to identify the parking orbit which minimizes entry system mass and to compare that to the entry system mass for a direct entry. The impact of a higher efficiency propulsion system, a higher entry velocity, and a reusable thermal protection system on aerocapture-entry system mass requirements is explored. Results indicate that the thermal protection system thickness does not vary significantly with parking orbit selection while shorter period orbits require more propellant for maneuvers. This result is not sensitive to changes in propulsion system efficiency, entry velocity, or heat shield material. Additionally, results show that aerocapture-entry architectures incur a TPS mass penalty up to 27% relative to direct entry, depending on vehicle. In addition, direct entry avoids needing propellant for in-space maneuvers between aerocapture and entry which ranges from 1.5% to 4.5% depending on orbit.
Mars Entry Descent Landing Human Exploration Aerocapture Aerocapture-entry TPS Thermal Protection System Parking Orbit
Fri, 26 Apr 2019 00:00:00 GMThttp://hdl.handle.net/2142/1049382019-04-26T00:00:00ZZinner, Evan J.Optimal lift and drag modulation hypersonic control options for high ballistic coefficient entry vehicles at Mars
http://hdl.handle.net/2142/104926
Optimal lift and drag modulation hypersonic control options for high ballistic coefficient entry vehicles at Mars
Richardson, Nicklaus O.
Future Mars entry, descent, and landing (EDL) missions will require larger mass vehicles and payloads, especially if humans are to land on the surface. Current Mars EDL technology relies heavily on Viking-era supersonic parachutes that are approaching their landed mass limits; however, supersonic retropropulsion (SRP) is a promising replacement for parachutes. Minimizing the propellant mass fraction (PMF) for SRP would enable larger payload masses. Maximizing the terminal descent initiation (TDI) altitude is also an important parameter for parachute deployment systems. The ability of different control methods, lift-only, drag-only, and both lift-and-drag control, to separately maximize TDI altitude and minimize PMF was assessed and compared over a range of entry conditions. Results show optimal control profiles that were always bang-bang with similar profiles for both cost functions. The number of switches that was optimal at a given entry state had a strong, direct relationship to entry flight-path angle with at most two-switches for lift control and at most four switches for drag control. Drag-only control was found to be better than lift-only control at steep entry flight path angles while lift-and-drag control was better than either at shallow entry flight-path angles. Adding drag control to lift-only systems was found to reduce PMF by approximately 40% across ballistic coefficients of 300 kg/m2 to 600 kg/m2 and entry velocities between 5 to 7 km/s. The set of feasible TDI states of each control method was assessed by linking the set of reachable TDI states from the hypersonic flight phase to the set of controllable TDI states from the propulsive descent phase. Increased controllability of lift-and-drag control and larger ballistic coefficients for drag control increases the size of the intersection of these two sets.
Hypersonic control; entry, descent, and landing; optimal control
Fri, 26 Apr 2019 00:00:00 GMThttp://hdl.handle.net/2142/1049262019-04-26T00:00:00ZRichardson, Nicklaus O.