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An investigation of IsoTruss structures in bending and torsion was conducted. A model was developed in ANSYS APDL where bay length and longitudinal member to helical member cross-sectional area ratio could be varied while holding the diameter constant. The model was validated using previously reported values from analytical models and empirical data. The model was used to make predictions of a specific geometry that was manufactured, tested and compared against the model. 12 specimens were built and tested. In flexure, empirical data had a percent error with respect to the model ranging from 10.9 to 65.4% with one outlier at 94.1%. In torsion, the empirical data had a percent error with respect to the model ranging from 0.4 to 34%. The test data exhibited similar trends compared to the model. An IsoTruss structure built to maximize torsional rigidity should have a diameter and bay length such that its helical angle is between 55 and 60 degrees. The inclusion of longitudinal members has a negligible impact on rigidity. Flexural rigidity is maximized with longitudinal members and with a minimal helical angle, placing helical members more in the direction of the longitudinal members. In order to minimize flexural rigidity, the longitudinal members should be removed from the design and the helical member angle should be maximized up to 80 degrees.

The eight-node solid-shell finite element models have been developed for the analysis of laminated composite pate/shell structures with piezoelectric actuators and sensors. To resolve the locking problems of the solid-shell elements in laminated materials and improve accuracy, the assumed natural strain method and hybrid stress method are employed. The nonlinear electric potential distribution in piezoelectric layer is described by introducing internal electric potential. The developed finite element models, especially, electric potential node model, have the advantages of simpler modeling and can obtain same effect that exact solution described. / Singapore-MIT Alliance (SMA)

Mini unmanned Air Vehicles (UAV) have high significance among other UAV&#039 / s, in different categories, due to their ease of production, flexibility of maintenance, decrease in weight due to the elimination of landing gear system and simplicity of use. They are usually built to meet &#039 / hand launching&#039 / and &#039 / belly landing&#039 / criteria in order to have easy flight and easy landing features. Due to the hand take-off and belly landing features there is no need to have a runway and this feature is a very significant advantage in operational use. In an operation, belly landing mini UAV&#039 / s may encounter tough landing areas like gravel, concrete or hard soil. Such landing areas may create landing loads which are impulsive in character. The effect of the landing loads on the airframe of the mini unmanned air vehicle must be completely understood and the mini UAV be designed accordingly in order not to damage the mini UAV during belly landing. Typical impact speeds during belly landing is relatively low (&lt / 10 m/s) and in general belly landing phenomenon can be treated as low velocity impact. The purpose of this study is to analyze the impact loads on the composite substructures of a mini UAV due to the belly landing. &#039 / G&uuml / vent&uuml / rk&#039 / Mini UAV which is designed and built in METU Aerospace Engineering Department, is used as the analysis platform. This study is limited to the calculation of stresses and deformation that is caused by the low velocity impact forces encountered during belly landing. The main purpose of this work is to help the designer in making design decisions for a mini UAV that is tolerable to low velocity impact loads. Initial part of the thesis includes analytical treatment of low velocity impact phenomenon. In the simplified analytical approach the loading is assumed as quasistatic and comparisons of such a simplified method of analysis is made with explicit finite element solutions on isotropic and composite plate structures to investigate the applicability of simplified analytical method of analysis. Belly landing analyses of the mini UAV are done by MSC.Dytran, which is an explicit finite element solver. Model building and post processing are done via MSC.Patran. Stress and deformation response of the mini UAV is investigated by performing low velocity impact analysis using sub-structure built-up approach.

This thesis deals with design of an eddy current transducer which enables non-destructive inspection of composite aircraft structures primarily carbon fiber reinforced plastic (CFRP) in areas of manufacture and maintenance. The design of the transducer is based on analytical-experimental approach and its electrical and mechanical parameters were optimized to ensure a good signal to noise ratio at the six composite samples. These samples contain artificial discontinuities in the form of various types of defects. These defects are simulating the various types of damage created in the aircraft structure, especially delamination or thickness changes of composite materials. The experimental measurements, data collection and non-destructive evaluation were performed during the period. The result of this work is functional eddy current probe, which is reliably able to detect some damage of the carbon composite structures to the depth of 3,9 mm.

For a long time, the development of component-based systems has been a crucial part of real-time software development required for embedded and automotive domains. However, most of the existing tools used in these fields are not only proprietary, but also expensive and not research-friendly. Open-source tools in this domain are so far quite limited in terms of the features supported, especially, code generation. In this thesis, we demonstrate how we can improve the development of real-time and concurrent systems by the introduction of component-based modelling into Umple, an open-source modelling tool. Our work enables component-based modelling to be performed both textually and visually, as is the case with other Umple features. We introduce a number of major features into Umple. First, we introduce support for real-time C++ code generation. This includes supporting all Umple features, such as class diagrams, associations, state machines, and attributes. In order to achieve this, we also introduce Umple Template Language (Umple-TL), which helps Umple developers to use Umple itself to emit text using easy-to-use constructs, such that the text emitted can be in different target languages such Java and C++. Umple-TL provides additional capabilities relying on Umple being a model-oriented and object-oriented language. Umple-TL has become the technology for all code generation in Umple, not just our real-time C++ generators. Umple-TL also plays a vital role easing writing component descriptions Second, we support concurrency, which is crucial for the underlying architecture of composite structure. We have to avoid relying on any third-party libraries in order to make sure that the code generated will be deployable on embedded devices, which are limited and do not provide a lot of options. The concurrency pattern we follow extends the active object pattern aiming to enhance communication among active objects. Concurrency development in general, even if a programming language used is not real-time, is not easy. Hence, we simplify active object concepts, such as future, promise, and delay, using new Umple keywords. We also add composite structure support to Umple, we believe that our syntax and language constructs are comprehensive, and do not require a wide knowledge of modelling and UML concepts. Additionally, we introduce a novel protocol-free approach that dynamically extracts communication protocols from ports, bindings, and active objects as a way to simplify development, and to lead to concise and optimized code generation. We demonstrate the effectiveness of our work using cases studies, in which we implement Umple models using our new composite structure and concurrency constructs. We show that the amount of code required to specify complex concepts is reduced, and the generated systems are effective.

This thesis deals with design of an eddy current transducer which enables non-destructive inspection of composite aircraft structures primarily carbon fiber reinforced plastic (CFRP) in areas of manufacture and maintenance. The design of the transducer is based on analytical-experimental approach and its electrical and mechanical parameters were optimized to ensure a good signal to noise ratio at the six composite samples. These samples contain artificial discontinuities in the form of various types of defects. These defects are simulating the various types of damage created in the aircraft structure, especially delamination or thickness changes of composite materials. The experimental measurements, data collection and non-destructive evaluation were performed during the period. The result of this work is functional eddy current probe, which is reliably able to detect some damage of the carbon composite structures to the depth of 3,9 mm.

The aim of the offered thesis is an analysis of usage of uncommon concrete matrix and its contribution to steel-concrete composites structures. It especially refers to the area of internal supports, where usually acts negative bending moments. These statical systems are very often used for bridge structures, or even for building constructions. Nowdays, the static infuence of concrete at the area of negative moment is neglected. Only the steel part of cross section and steel reinforcement are included to the static action. This work is focused on the usage of tensile strength of uncommon concrete. The improvement of tensile strength of cement matrix is due to glass fiber reinforcement acting as scattered reinforcing. The introduction is focused on common approach of design of the structures mentioned above. Next, there is a part which describes possibilites of using fibre reinforcing until nowdays.

This work examines a novel concept and design of simultaneous energy harvesting and vibration control on the same host structure. The motivating application is a multifunctional composite sandwich wing spar for a small Unmanned Aerial Vehicle (UAV) with the goal of providing self-contained gust alleviation. The basic idea is that the wing itself is able to harvest energy from the ambient vibrations along with available sunlight during normal flight. If the wing experiences any strong wind gust, it will sense the increased vibration levels and provide vibration control to maintain its stability. This work holds promise for improving performance of small UAVs in wind gusts. The proposed multifunctional wing spar integrates a flexible solar cell array, flexible piezoelectric wafers, a thin film battery and an electronic module into a composite sandwich structure. The basic design factors are discussed for a beam-like multifunctional wing spar with load-bearing energy harvesting, strain sensing and self-controlling functions. Three-point bending tests are performed on the composite sandwich structure for bending strength analysis and bending stiffness prediction under a given safety factor. Additional design factors such as the configuration, location and actuation type of each piezoelectric transducer are investigated for optimal power generation. The equivalent electromechanical representations of a multifunctional wing spar is derived theoretically, simulated numerically and validated experimentally. Special attention is given to the development of a reduced energy control (REC) law, aiming to minimize the actuation energy and the dissipated heat. The REC law integrates a nonlinear switching algorithm with a positive strain feedback controller, and is represented by a positive feedback operation amplifier (op-amp) and a voltage buffer op-amp for each mode. Experimental results exhibit that the use of nonlinear REC law requires 67.3 % less power than a conventional nonlinear controller to have the same settling time under free vibrations. Nonlinearity in the electromechanical coupling coefficient of the piezoelectric transducer is also observed, arising from the piezoelectric hysteresis in the constitutive equations coupling the strain field and the electric field. If a constant and voltage-independent electromechanical coupling coefficient is assumed, this nonlinearity results in considerable discrepancies between experimental measurements and simulation results. The voltage-dependent coupling coefficient function is identified experimentally, and a real time adaptive control algorithm is developed to account for the nonlinear coupling behavior, allowing for more accurate numerical simulations. Experimental validations build upon recent advances in harvester, sensor and actuator technology that have resulted in thin, light-weight multilayered composite sandwich wing spars. These multifunctional wing spars are designed and validated to able to alleviate wind gust of small UAVs using the harvested energy. Experimental results are presented for cantilever wing spars with micro-fiber composite transducers controlled by reduced energy controllers with a focus on two vibration modes. A reduction of 11dB and 7dB is obtained for the first and the second mode using the harvested ambient energy. This work demonstrates the use of reduced energy control laws for solving gust alleviation problems in small UAVs, provides the experimental verification details, and focuses on applications to autonomous light-weight aerospace systems. / Ph. D.

Efficient electromagnetic solvers based on surface integral equations (SIEs) are developed for the analysis of scattering from large-scale and complex composite structures that consist of piecewise homogeneous magnetodielectric and perfect electrically/magnetically conducting (PEC/PMC) regions. First, a multiple-grid extension of the adaptive integral method (AIM) is presented for multi-region problems. The proposed method accelerates the iterative method-of-moments solution of the pertinent SIEs by employing multiple auxiliary Cartesian grids: If the structure of interest is composed of K homogeneous regions, it introduces K different auxiliary grids. It uses the k^{th} auxiliary grid first to determine near-zones for the basis functions and then to execute AIM projection/anterpolation, propagation, interpolation, and near-zone pre-correction stages in the k^{th} region. Thus, the AIM stages are executed a total of K times using different grids and different groups of basis functions. The proposed multiple-grid AIM scheme requires a total of O(N^{nz,near}+sum({N_k}^Clog{N_k}^C)) operations per iteration, where N^{nz,near} denotes the total number of near-zone interactions in all regions and {N_k}^C denotes the number of nodes of the k^{th} Cartesian grid. Numerical results validate the method’s accuracy and reduced complexity for large-scale canonical structures with large numbers of regions (up to 10^6 degrees of freedom and 10^3 regions). Then, a Green function modification approach and a scheme of Hankel- to Teoplitz-matrix conversions are efficiently incorporated to the multiple-grid AIM method to account for a PEC/PMC plane. Theoretical analysis and numerical examples show that, compared to a brute-force imaging scheme, the Green function modification approach reduces the simulation time and memory requirement by a factor of (almost) two or larger if the structure of interest is terminated on or resides above the plane, respectively. In addition, the SIEs are extended to cover structures composed of metamaterial regions, PEC regions, and PEC-material junctions. Moreover, recently introduced well-conditioned SIEs are adopted to achieve faster iterative solver convergence. Comprehensive numerical tests are performed to evaluate the accuracy, computational complexity, and convergence of the novel formulation which is shown to significantly reduce the number of iterations and the overall computational work. Lastly, the efficiency and capabilities of the proposed solvers are demonstrated by solving complex scattering problems, specifically those pertinent to analysis of wave propagation in natural forested environments, the design of metamaterials, and the application of metamaterials to radar cross section reduction. / text