Large civil infrastructure systems all over the world have become an integral part of our civilization. The inspection and maintenance of these structures for public safety is a difficult task. The assessment of integrity of such huge structures due to local damages is even more difficult to deal with. The conventional inspections are performed manually, generally by visual examination and sometimes by more advanced techniques like ultrasonic, electromagnetic and fiber optic techniques. These inspections involve human interventions, depend on individual inspector's experience, and are time consuming. Such inspection methods may not be very useful for real time health assessment of a structure in service and as a result are not very helpful in preventing any disastrous situation through early warning. Therefore, it is very important to look for a comprehensive strategy of global integrity monitoring infused with information about local damages in the structure. For local damage assessment the current state of the health monitoring technology lacks a generalized and definitive approach to the identification and localization of damage. In past decades several signal processing tools have been used for solving different health monitoring problems but the commutability of the tools between different problems has been restricted. Fundamental reasons for this shortcoming have never been investigated in detail. In this dissertation an investigation has been carried out employing almost all promising feature extraction tools on a representative problem - a plate with rivet holes. The problem considered has radial cracks around rivet holes in a joint panel of a steel truss bridge. Such defects are very difficult to detect. Although well established, Lamb wave based nondestructive evaluation techniques are revisited and new tools are developed to address this issue. Simulation of the scattered ultrasonic wave field is carried out using the finite element method. This ultrasonic wave field is further analyzed to evaluate the integrity of the structure using various feature extraction (FE) techniques. Joint time-frequency-energy representation is obtained from ultrasonic signals recorded at various locations on the plate (joint panel) and used to extract damage sensitive features. Those features were then used to formulate a new Damage Parameter (DP) for better visualization of the crack. Results are shown to demonstrate the comparative effectiveness of these techniques. It is concluded that any particular FE technique cannot detect all possible sizes and orientations of the crack. It is suggested that the statistical occurrence and pattern of the crack must be visualized through a few selective FE techniques in a sequence. Modeling of the wave scattering phenomenon by conventional numerical techniques such as finite element method requires very fine mesh at high frequencies necessitating heavy computational power. Distributed point source method (DPSM) which is a recently developed semi-analytical technique, is applied to model the scattering of ultrasonic wave field on representative problem geometries and the results are used to diagnose structural damages. DPSM is a newly developed robust mesh-free technique for simulating ultrasonic, electrostatic and electromagnetic field problems. In most of the previous studies the DPSM technique has been applied to model two dimensional surface geometries and relatively simple three dimensional scatterer geometries. It has been very difficult to perform the wave scattering analysis for very complex three-dimensional geometries. This technique has been extended to model wave scattering in an arbitrary geometry. The simulation has been carried out with and without the presence of cracks near the rivet holes.

<p>The overall aim of this thesis was to discuss kinematics and muscle function changes due to foot and ankle injury or deformity. The first study aims to characterize gait patterns of subjects with a common lower limb injury, ankle fractures. Using three-dimensional movement analysis with a modified multi-segment foot model, the inter-segment foot kinematics was determined during gait in 18 subjects one year after surgically treated ankle fractures. Gait data were compared to an age- and gender-matched control group and the correlations between functional ankle score and gait parameters were determined. It was observed that even with fairly good clinical results, restricted range of motion at and around the injured area, and less adducted forefoot were found in the injured limb. The second study aims to quantify the effect of subtalar inversion/eversion on the dynamic function of the main ankle dorsi/plantarflexors: gastrocnemius, soleus and tibialis anterior. Induced acceleration analysis was used to compute muscle-induced joint angular and body center of mass accelerations. A three-dimensional subject specific linkage model was configured by gait data and driven by 1 Newton of individual muscle force. The excessive subtalar inversion or eversion was modified by offsetting up to ±20˚ from the normal subtalar angle while other configurations remain unaltered. We confirmed that in the normal gait, muscles generally acted as their anatomical definitions and muscles can create motion in joints, even not spanned by the muscles. The plantarflexors play important roles in body support and forward progression. Excessive subtalar eversion had negative effect on ankle plantarflexion, which may induce a less plantarflexed ankle, less extended knee and more flexed hip after initial contact. This thesis focused on gait kinematics and muscle functions in the foot and ankle area employing both experimental gait and computational simulations. The findings can be regarded as references for evaluating of future patients and for dynamic muscle functions during gait.</p>

<p>Converging cylindrical shock waves have been studied experimentally. Numericalcalculations based on the Euler equations and analytical comparisons basedon the approximate theory of geometrical shock dynamics have been made tocomplement the study.Shock waves with circular or polygonal shock front shapes have been createdand focused in a shock tube. With initial Mach numbers ranging from 2 to4, the shock fronts accelerate as they converge. The shocked gas at the centreof convergence attains temperatures high enough to emit radiation which isvisible to the human eye. The strength and duration of the light pulse due toshock implosion depends on the medium. In this study, shock waves convergingin air and argon have been studied. In the latter case, the implosion lightpulse has a duration of roughly 10 μs. This enables non-intrusive spectrometricmeasurements on the gas conditions.Circular shock waves are very sensitive to disturbances which deform theshock front, decreasing repeatability. Shocks consisting of plane sides makingup a symmetrical polygon have a more stable behaviour during focusing,which provides less run-to-run variance in light strength. The radiation fromthe gas at the implosion centre has been studied photometrically and spectrometrically.Polygonal shocks were used to provide better repeatability. Thefull visible spectrum of the light pulse created by a shock wave in argon hasbeen recorded, showing the gas behaving as a blackbody radiator with apparenttemperatures up to 6000 K. This value is interpreted as a modest estimation ofthe temperatures actually achieved at the centre as the light has been collectedfrom an area larger than the bright gas core.As apparent from experimental data real gas effects must be taken intoconsideration for calculations at the implosion focal point. Ideal gas numericaland analytical solutions show temperatures and pressures approaching infinity,which is clearly not physical. Real gas effects due to ionisation of theargon atoms have been considered in the numerical work and its effect on thetemperature has been calculated.The propagation of circular and polygonal have also been experimentallystudied and compared to the self-similar theory and geometrical shock dynamics,showing good agreement.</p>

<p>THIS THESIS EXPLORES novel CAD modeling methods for design reuse and tomation realization. It will be demonstrated that by applying the described methods, CAD models can be utilized as framework integrators in order to generate geometric input for various engineering analysis tools. Multidisciplinary design can as a result be facilitated in early design due to decreased manual model re-definitions. Furthermore, due to the complex dependency between analysis tools, certain product characteristics can only be evaluated by applying a holistic design approach. Therefore, by applying multidisciplinary design, the level of knowledge about the product will increase.</p><p>To simulate and evaluate the properties and behavior of an engineering product during design, the geometry has to be constantly re-estimated. CAD tools can be employed to produce the requested geometry. However simplifications introduced in the geometry, due to incomplete and imprecise knowledge available in early design, result in inaccurate geometries. Thus re-modeling has to occur in a frequent rate in order to achieve sufficiently accurate models. Hence CAD tool are traditionally applied in later stages of design when the geometry of the product is more or less defined and CAD is applied to generate drafting and technical drawings for manufacturing purposes</p><p>It is therefore proposed that geometries for repetitive components are stored in so called high level templates and instantiated in the CAD model parametrically. Upon instantiation, each instance can be modified parametrically. Given the fact that the instantiation process is automated, the deletion and replacement procedures are also automatic, enabling easier model modifications in the design process.</p><p>To estimate the gained advantage when applying the proposed methods, holistic design frameworks are implemented. The frameworks consist of a combination of various engineering tools which are integrated through a user interface. Given that an information flow between the design tools is implemented, many aspects of design is computed and optimized concurrently. Consequently in order to draw general conclusion concerning geometric modeling, two different design applications with dissimilar requirements are studied in this work, namely aircraft and industrial robots.</p>

Vibration induced High Cycle Fatigue (HCF) is a major consideration in designing gas turbines. Indeed, the Gas Turbine manufacturer must demonstrate that the vibration level of the turbomachinery blading is acceptably low, usually by using an engine strain gauge test. If the test shows unacceptable vibration levels then a redesign is required which adds cost and time to the engine development programme. It is highly desirable, therefore to develop a capability which can predict the vibration level of the blade to ensure that it will be robust. The High-Pressure Turbine is of particular interest because of the harshness of the environment in which it operates (high mechanical speed and high air temperatures and pressures) so friction dampers are routinely introduced to control the vibration level. The friction dampers can introduce a degree of non-linearity into the structure which affects not only the vibration amplitude, but also the resonant frequency. The resonant frequency, amplitude, damper behaviour and aerodynamic forcing are all inter-related such that they must be considered as a single system. This thesis describes the development of two new approaches to predict the vibration behaviour of a High-Pressure Turbine blade including the effect of friction dampers. The first utilises existing prediction tools for modelling of the fluid, the structure and the friction behaviour, but uses a novel method for coupling the various aspects together. This approach is based on modelling an ‘engine acceleration’ across a wide speed range and prescribing the variation of all the relevant parameters with shaft speed. For example, both the excitation force on the blade and the centrifugal load of the damper vary strongly with rotor speed so these effects must be included in the analysis. The second approach extends the first approach by using a new iterative ‘resonance tracking’ methodology in which the aerodynamic boundary conditions are adjusted based on the shaft speed at resonance until convergence is reached. Both methodologies calculate the resonant frequency, amplitude and operating condition of each mode of interest as an output of the analysis. The engine acceleration methodology has been investigated in detail and has been validated against several High-Pressure Turbine cases. It has been found to be reliable: the amplitude predictions were in broad agreement with the available engine strain gauge results and the frequency shift introduced by the damper was in very good agreement. The methodology captures some important features of the physical system such as (a) the amplitude dependence of the damper, (b) the sudden drop in frequency when approaching the second flap resonance because the damper starts to slide, and (c) the effect of the damper on the ratio between stress and tip displacement. One rather surprising result was that in certain cases, where the forcing level was low, the damper increased the blade response because it moved the resonance to a higher shaft speed where the forcing level was larger. The main advantage of the method is its speed, which allows optimisation of key parameters within design timescales. The resonance tracking methodology has been compared directly with the engine acceleration approach on one of the test cases and it produced very similar results. Convergence was achieved quickly, in two or three iterations for the chosen test case, mainly because the blade surface pressure distribution was consistent across a broad speed range. The method showed that the first torsion resonance was more sensitive to aerodynamic conditions than the second flap mode, and may offer an explanation for the scatter seen in engine test results. The approach offers the advantage that it is more generally applicable, because it can deal with cases where the pressure distribution is sensitive to shaft speed, but it can only converge to a single mode and requires significantly more computational effort. The methodologies have been used to explore vibration reduction strategies such as wake shaping, damper optimisation and defining acceptance limits for the orientation of the single crystal material used in turbine manufacture. Overall these provided almost an order of magnitude reduction in blade response. / QC 20100824

Engine research and development is to a large extent driven by the quest of lowering exhaust emissions and fuel consumption. The combination of low emissions and low fuel consumption is not the simultaneous characteristic of the world’s primary engine concepts, the diesel and the spark-ignited (SI) engine. However, such a concept do exist, it is commonly called Homogeneous Charge Compression Ignition (HCCI). The HCCI combustion concept is when a premixed air and fuel mixture is ignited by the heat of compression. The operation is unthrottled, like the diesel engine, which is advantageous for its efficiency. The premixed air / fuel mixture preclude soot formation, like the SI engine. An exclusive feature of HCCI combustion is extremely low NOX production due to low-temperature combustion. The mixture preparation of the typical gasoline HCCI engine is similar to the SI engine, via port-injection, which results in a well homogenized mixture. Port injection of diesel fuel is however very difficult since the environment is too cold for the fuel to vaporise. A better alternative is therefore direct-injection. However, injection must occur in a way where a homogeneous mixture is formed, while contact of the liquid fuel with cold walls is avoided. There are many approaches to direct-injected mixture formation. This thesis focuses on exploring the concept of impinging sprays; its characteristics and its impact on combustion and emissions. The work comprises unique information regarding impinging sprays, as well as results regarding engine performance. It is concluded that impinging sprays are well suited for early direct-injection. / QC 20100824

Mechatronics development requires the close collaboration of various specialist teams and engineering disciplines. Developers from the different disciplines use domain-specific tools to specify and analyse the system of interest. This leads to different views of the system, each targeting a specific audience, using that audience’s familiar language, and concentrating on that audience’s concerns. Successful system development requires that the views of all developers produced by the different tools are well integrated into a whole, reducing any risks of inconsistencies and conflicts in the design information specified. This thesis discusses techniques of managing and integrating the views from various disciplines, taking better advantage of multidisciplinary, model-based, development. A Model Data Management (MDM) platform that generically manages models from the various domain-specific tools used in development is presented. The platform is viewed as a unification of the management functionalities typically provided by the discipline-specific PDM and SCM systems. The unification is achieved by unifying the kind of objects it manages – models. View integration is considered as an integral functionality of this platform. In demonstrating the platform’s feasibility, a generic version management functionality of models is implemented. In addition, model integration is investigated for the allocation of system functions onto the implementing hardware architecture. The proposed approach promotes the independent development of the views, allowing developers from each discipline to work concurrently, yet ensuring the completeness, correctness and analysis of any inter-view design decisions made. The prototype MDM platform builds on existing technologies from each of the mechanical and software disciplines. The proposed MDM system is built based on a configurable PDM system, given its maturity and ability to manage model contents appropriately. At the same time, the version control functionality borrows ideas from the fine-grained version control algorithms in the software discipline. The platform is argued to be feasible given the move towards model-based development in software engineering, bringing the discipline’s needs closer to those of the hardware discipline. This leads the way for an easier and more effective integrated management platform satisfying the needs of both disciplines using a common set of mechanisms. / QC 20110124

The royal warship Vasa sank on its maiden voyage outside Stockholm and was salvaged more than 300 years later in 1961. Nowadays the vessel lies in its eponymous museum in Stockholm on a dry dock. However, it was determined that the ship cannot handle its own weight in a satisfactory manner with the current support system. Measurements during the past ten years have ascertained that the upper structure components of the hull are slowly deforming, mostly due to creep behavior.   A new support system for the ship needs to be designed in the near future and therefore, the mechanical behavior of its structural members and the stresses they are subjected to have to be determined. Factors that complicate a stress analysis include both inhomogeneity of the oak’s mechanical properties and limited opportunities for experimental testing. Furthermore, contamination, microbial degradation and preservation agents have significantly changed the integrity of the oak.   In this project a section of the Vasa’s bottom structure is studied through Finite Element Analysis in order to determine the stresses and deformations originated by the support system and to have a better understanding of these effects on the ship’s structure. Due to the considerable deterioration of the oak, especially on the external structural members, several assumptions are considered in order to perform analytical calculations to determine appropriate material properties for the FE-Models.    After performing the computational simulations, the obtained results indicate that the bottom structure exhibits sufficient mechanical integrity to endure the stresses generated by the support system. Even by assuming the possibility of several damaged structural connections, only a minor difference of the effects of the reaction forces on the structure members was determined.   The thesis work ends with further conclusions from the performed analysis and suggested future work.

No description available.

<p>Mechatronics development requires the close collaboration of various specialist teams and engineering disciplines. Developers from the different disciplines use domain-specific tools to specify and analyse the system of interest. This leads to different views of the system, each targeting a specific audience, using that audience’s familiar language, and concentrating on that audience’s concerns. Successful system development requires that the views of all developers produced by the different tools are well integrated into a whole, reducing any risks of inconsistencies and conflicts in the design information specified.</p><p>This thesis discusses techniques of managing and integrating the views from various disciplines, taking better advantage of multidisciplinary, model-based, development. A Model Data Management (MDM) platform that generically manages models from the various domain-specific tools used in development is presented. The platform is viewed as a unification of the management functionalities typically provided by the discipline-specific PDM and SCM systems. The unification is achieved by unifying the kind of objects it manages – models. View integration is considered as an integral functionality of this platform.</p><p>In demonstrating the platform’s feasibility, a generic version management functionality of models is implemented. In addition, model integration is investigated for the allocation of system functions onto the implementing hardware architecture. The proposed approach promotes the independent development of the views, allowing developers from each discipline to work concurrently, yet ensuring the completeness, correctness and analysis of any inter-view design decisions made.</p><p>The prototype MDM platform builds on existing technologies from each of the mechanical and software disciplines. The proposed MDM system is built based on a configurable PDM system, given its maturity and ability to manage model contents appropriately. At the same time, the version control functionality borrows ideas from the fine-grained version control algorithms in the software discipline.</p><p>The platform is argued to be feasible given the move towards model-based development in software engineering, bringing the discipline’s needs closer to those of the hardware discipline. This leads the way for an easier and more effective integrated management platform satisfying the needs of both disciplines using a common set of mechanisms.</p>