Elastomer seals are used in a variety of industries that require flow isolation. The characterization of the behavior of these seals remains largely unexplored and hence, this study is focused on simulating and validating the axial-compressive behavior of an annular rubber seal constrained concentrically in a pipe. The elastomer material composing the seal, was experimentally characterized for its mechanical, frictional, and viscoelastic properties and modelled using models developed by Yeoh, Thirion, and Prony respectively. A 2D axisymmetric finite-element model was developed using ANSYS 16 and used alongside the material models to simulate an axial load versus displacement curve, a contact pressure distribution, and a pipe hoop strain gradient. The results for quasi-static loading and viscoelastic effects agreed within 7% and 18% of the experimental results, respectively. It was observed that pipe geometry, rubber chemistry, frictional properties, and viscoelastic effects have significant effect on the compressive behavior of the seal. / October 2016

Die Analyse des Standes der Technik zu Simulationsmethoden im Werkzeugentwicklungsprozess zeigt die breiten Bestrebungen ganzheitliche Modelle zur Abbildung der Maschinen- und Werkzeugeigenschaften in der Prozesssimulation zu schaffen um die Werkzeuginbetriebnahme in Zukunft in die virtuelle Welt überführen zu können. Dabei werden die Einflüsse wie die Stößelkippung unter Last, die Durchbiegung der Werkzeugaufspannplatten, die Verformung des Ziehkissens und die elastische Nachgiebigkeit der Werkzeuge separat betrachtet. Es konnte kein Simulationsmodell identifiziert werden, welche alle relevanten Eigenschaften der Werkzeuge und der Maschinen zu einem Gesamtmodell vereint. Zudem fehlten Modellierungsansätze für wesentliche Teilaspekte einer ganzheitlichen Abbildung der Wechselwirkungen von Maschine, Werkzeug und Prozess. Insbesondere ist dabei die systematische Untersuchung zur Abbildung des Pinolentragbildes sowohl örtlich als auch über dem Pressenhub und der versteifende Einfluss der Werkzeugführung zu nennen. Mit der vorliegenden Arbeit konnte ein ganzheitliches FE-Prozessmodell mit den wesentlichen elastischen Eigenschaften der Maschine und der Werkzeuge erstellt werden. Wichtig ist dabei insbesondere die systematische Abbildung relevanter mechanischer Ziehkissenstrukturen als Ersatzmodell und die Integration der tatsächlichen Ziehkissenkraft im Prozessmodell. Bekannte Modellierungsansätze wie z.B. die Abbildung der Kippsteifigkeit des Stößelsystems und die Berücksichtigung der Durchbiegung der Werkzeugaufspannplatten wurden weiterentwickelt und in das Gesamtmodell implementiert. Für jedes Ersatzmodell wurde eine Strategie zur Modellerstellung und zur zweckmäßigen Parametrierung mit dem Ziel eines minimalen Zeit- und Kostenaufwandes vorgeschlagen. Die elastische Modellierung der Werkzeuge wurde mit einer systematischen Vorgehensweise hinterlegt und zeigt bei konsequenter Anwendung signifikant reduzierte Berechnungszeiten. Die Berücksichtigung der Ziehstäbe erfolgt in dieser Arbeit aufgrund der Einschränkungen des verwendeten FE-Solvers als Strukturmodell. Zusätzlich wurde ein Modellierungsansatz vorgestellt, welcher die analytische Berücksichtigung der Ziehstäbe auf elastischen Werkzeugstrukturen ermöglicht. Damit steht jetzt ein Prozessmodell mit den relevanten Maschinen- und Werkzeugeigenschaften zur Verfügung, welches durch eine einfache Parametrierung auf die jeweilige Prozess-Maschinen-Konfiguration angepasst werden kann. Dies ermöglicht eine deutlich genauere Abbildung des Pinolentragbildes, der daraus resultierenden Niederhalterdruckverteilung und damit des Materialeinzuges in die Matrize. Dieses erweiterte Prozessmodell ist damit in der Lage eine virtuelle Inbetriebnahme der Werkzeuge zu unterstützen und in Zukunft eine weitere Verkürzung des Inbetriebnahmeprozesses zu ermöglichen.

Continuous improvements are an integral part for the development of everyday life. These improvements do not only ascertain financial gain but also lessening the environmental impact. The purpose of this study is to gain a deeper understanding of the design process and the decisions required to achieve an optimal design with respect to weight reduction, while retaining the required strength. The study will also investigate the choice of material. This will be done through material and design studies, along with strength calculations of the product in question. The conclusion from this study is that it is possible to save a certain percentage of the material used, while keeping the strength, form, fit and function intact. The material study provided with a recommendation of the zinc alloy ZA-8. It is an alloy with a good combination of great strength, low density and price.

"The recent years have seen the innovative system integration of a great many actuator technologies, such as point force actuators for space vehicle applications and the use of single fire actuators; such as pyrocharges to guide a free falling bomb to it’s target. The inherent limitations of these developments, such as nonlinear behavior under extreme environments and/or prolonged/repeated usage leading to a relaxation time component between firing of actuators and inherent system power limitations, have resulted in greater need for sophisticated control algorithms that allow for optimal switching between various actuators in any given embedded configuration so as to achieve the best possible performance of the system. The objective of this investigation is to offer a proof of concept experimental verification of a real time control algorithm, which switches between online piezoelectric actuators, employed for vibration control in an aluminum beam with fixed boundary conditions. In this investigation at a given interval of time, only one actuator is activated and the rest are kept dormant. The reason is to demonstrate the better vibration alleviation characteristics realized in switching between actuators depending on the state of the system, over the use of a single actuator that is always in fire mode. This effect is particularly pronounced in controlling systems affected by spatiotemporal disturbances. The algorithm can be easily adapted for various design configurations or system requirements. The optimality of switching is with respect to the minimal cost of an LQR performance index that corresponds to each actuator. Computer simulations with repeatable disturbance profiles, revealed that this algorithm offered better performance over the non-switched case. Performance measures employed were the time varying total energy norm of the dynamic system and position traces at any particular location on the beam. This algorithm was incorporated on a dSPACE rapid prototyping platform along with suitable hardware. Experimental and simulation results are discussed. "

Tunnelling in urban areas causes short-term and long-term ground movements under existing buildings. Finite element analysis provides a useful option for assessing the likely extent of damage induced in these buildings. Although finite element analysis is suggested to be used in the later phases of the building damage assessment procedures employed in practice, only the effect of short-term ground movements is typically considered and there are no detailed guidelines on the specification and complexity of the modelling. This thesis addresses the tunnel-soil-building interaction problem and the effect of long-term consolidation, as well as demonstrating the application of 3D finite element analysis with appropriate simplifications for practical assessment purposes. Finite element models are developed to quantify the effect of shallow tunnelling on an example masonry building founded on strip footings, considering both single- and twin-tunnel scenarios in a typical London soil profile. Total stress and effective stress analyses are adopted with specific modelling procedures to focus on the short-term and long-term response respectively. The analyses use a non-linear model for the masonry, and allow slippage and gapping at the soil-footing interface. Two advanced constitutive models for the soil (the extended Mohr-Coulomb model and the modified two-surface kinematic hardening model) are implemented with customized stress update schemes. The finite element results present the interaction between the soil and the building by comparing with the greenfield ground response. The horizontal coupling between the foundation and the ground is shown to be relatively weak. The dominant deformation mode of the building varies with the tunnel configuration (i.e. single or twin tunnels) and the tunnel eccentricity. Strain localization is found around the explicitly modelled window and door openings. The long-term consolidation is sensitive to the permeability of the tunnel lining. The building response to long-term ground movements is further affected by the tunnel-tunnel interaction in the case of twin-tunnel configuration. Performing 3D analysis of a single facade and foundation provides useful damage predictions, without the need to model a complete building. The proposed result processing methods such as characteristic strain and damage bar chart are practical tools for assessment. The study highlights some limitations of the elastic beam assessment method, which is often adopted in the early phase of the damage assessment process.

Velocity-coupled combustion instability is a major issue facing lean combustor design in modern gas turbine applications. In this study, we analyze the complex acoustic field excited by a transverse acoustic mode in an annular combustor. This work is motivated by the need to understand the various velocity disturbance mechanisms present in the flame region during a transverse instability event. Recent simulation and experimental studies have shown that much of the flame response during these transverse instabilities may be due to the longitudinal motion induced by the fluctuating pressure field above the nozzles. This transverse to longitudinal coupling has been discussed in previous work, but in this work it is given a robust acoustic treatment via computational methods in order to verify the mechanisms by which these two motions couple. We will provide an in-depth discussion of this coupling mechanism and propose a parameter, Rz, also referred to as the Impedance Ratio, in order to compare the pressure/velocity relationship at the nozzle outlet to quasi one-dimensional theoretical acoustic approximations. A three-dimensional inviscid simulation was developed to simulate transversely propagating acoustic pressure waves, based on an earlier experiment designed to measure these effects. Modifications to this geometry have been made to account for lack of viscosity in the pure acoustic simulation and are discussed. Results from this study show that transverse acoustic pressure excites significant axial motion in and around the nozzle over a large range of frequencies. Furthermore, the development of Rz offers a defined physical parameter through which to reference this important velocity-coupled instability mechanism. Therefore, this study offers an in-depth and quantifiable understanding of the instability mechanism caused by transversely propagating acoustic waves across a combustor inlet, which can be applied to greatly improve annular combustor design in future low-emissions gas turbine engines.

The current limits of supersonic parachute technology may constrain the ability to safely land future robotic assets on the surface of Mars. This constraint has led to a renewed interest in supersonic inflatable aerodynamic decelerator (IAD) technology, which offers performance advantages over the DGB parachute. Two supersonic IAD designs of interest include the isotensoid and tension cone, named for their respective formative structural theories. Although these concepts have been the subject of various tests and analyses in the 1960s, 1970s, and 2000s, significant work remains to advance supersonic IADs to a technology readiness level that will enable their use on future flight missions. In particular, a review of the literature revealed a deficiency in adequate aerodynamic and aeroelastic data for these two IAD configurations at transonic and subsonic speeds. The first portion of this research amended this deficiency by testing flexible IAD articles at relevant transonic and subsonic conditions. The data obtained from these tests showed that the tension cone has superior drag performance with respect to the isotensoid, but that the isotensoid may demonstrate more favorable aeroelastic qualities than the tension cone. Additionally, despite the best efforts in test article design, there remains ambiguity regarding the accuracy of the observed subscale behavior for flight scale IADs. Due to the expense and complexity of large-scale testing, computational fluid-structure interaction (FSI) analyses will play an increasingly significant role in qualifying flight scale IADs for mission readiness. The second portion of this research involved the verification and validation of finite element analysis (FEA) and computational fluid dynamic (CFD) codes for use within an FSI framework. These verification and validation exercises lend credence to subsequent coupled FSI analyses involving more complex geometries and models. The third portion of this research used this FSI framework to predict the static aeroelastic response of a tension cone IAD in supersonic flow. Computational models were constructed to mimic the wind tunnel test articles and flow conditions. Converged FSI responses computed for the tension cone agreed reasonably well with wind tunnel data when orthotropic material models were used and indicated that current material models may require unrealistic input parameters in order to recover realistic deformations. These FSI analyses are among the first results published that present an extensive comparison between FSI computational models and wind tunnel data for a supersonic IAD.

The increasingly competitive market is forcing the industry to develop higher-quality products more quickly and less expensively. Engineering analysis, at the same time, plays an important role in helping designers evaluate the performance of the designed product against design requirements. In the context of automated CAD/FEA integration, the domain-dependent engineers different usage views toward product models cause an information gap between CAD and FEA models, which impedes the interoperability among these engineering tools and the automatic transformation from an idealized design model into a solvable FEA model. Especially in highly coupled variable topology multi-body (HCVTMB) problems, this transformation process is usually very labor-intensive and time-consuming. In this dissertation, a knowledge-based FEA modeling method, which consists of three information models and the transformation processes between these models, is presented. An Analysis Building Block (ABB) model represents the idealized analytical concepts in a FEA modeling process. Solution Method Models (SMMs) represent these analytical concepts in a solution technique-specific format. When FEA is used as the solution technique, an SMM consists of a Ready to Mesh Model (RMM) and a Control Information Model (CIM). An RMM is obtained from an ABB through geometry manipulation so that the quality mesh can be automatically generated using FEA tools. CIMs contain information that controls the FEA modeling and solving activities. A Solution Tool Model (STM) represents an analytical model at the tool-specific level to guide the entire FEA modeling process. Two information transformation processes are presented between these information models. A solution method mapping transforms an ABB into an RMM through a complex cell decomposition process and an attribute association process. A solution tool mapping transforms an SMM into an STM by mimicking an engineers selection of FEA modeling operations. Four HCVTMB industrial FEA modeling cases are presented for demonstration and validation. These involve thermo-mechanical analysis scenarios: a simple chip package, a Plastic Ball Grid Array (PBGA), and an Enhanced Ball Grid Array (EBGA), as well as a thermal analysis scenario: another PBGA. Compared to traditional methods, results indicate that this method provides better knowledge capture and decreases the modeling time from days/hours to hours/minutes.

The ultimate goal of this research is to develop a method, from the designers point of view, for using the embodied specialized knowledge of Finite Element Analysis [FEA] software to study the behavior of materials, geometries, and configurations in order to create an iterative design feedback loop that uses structural performance as a primary evaluation criteria and point of departure for generating and refining complex formo-techtonic configurations while ensuring constructability, improved structural performance, and syntactic consistency. Syntactic consistency meaning that there would not be a loss in translation from concept to construct. Instead of the 2-dimensional [planar] manual technology which drove modernist analysis towards the structural hyper-rationality of the trabeated system, this new process should compile and synthesize computational speed, mathematic principles, mechanical knowledge, and material logics within a digital 3-dimensional [spatial] analytical environment in order to realize a new paradigm of constructible spatialized sensuality. The research will focus on the development of interoperability techniques and protocols between advanced parametric CAD systems and advanced structural analysis systems towards the creation of a fluid design + analysis process of creating and engineering complex forms and dynamic systems. Rapid prototyping will be integrated as a secondary feedback and verification loop, and as a precursor to the production of full scale construction machine readable files. In other words, the research focuses on the development of intricately designed, geometrically complex, and materially sophisticated structural skins that can be produced through advanced CAD/CAM techniques.

This dissertation addresses new developments in the constitutive modeling and structural analysis pertaining to rate-independent and rate-dependent irrecoverable inelasticity in Shape Memory Alloys (SMAs). A new model for fully recoverable SMA response is derived that accounts for material behaviors not previously addressed. Rate-independent and rate-dependent irrecoverable deformations (plasticity and viscoplasticity) are then considered. The three phenomenological models are based on continuum thermodynamics where the free energy potentials, evolution equations, and hardening functions are properly chosen. The simultaneous transformation-plastic model considers rate-independent irrecoverable strain generation and uses isotropic and kinematic plastic hardening to capture the interactions between irrecoverable plastic strain and recoverable transformation strain. The combination of theory and implementation is unique in its ability to capture the simultaneous evolution of recoverable transformation strains and irrecoverable plastic strains. The simultaneous transformation-viscoplastic model considers rate-dependent irrecoverable strain generation where the theoretical framework is modfii ed such that the evolution of the viscoplastic strain components are given explicitly. The numerical integration of the constitutive equations is formulated such that objectivity is maintained for SMA structures undergoing moderate strains and large displacements. Experimentally validated analysis results are provided for the fully recoverable model, the simultaneous transformation-plastic yield model, and the transformation-viscoplastic creep model.