The method of Continuum Sensitivity Analysis (CSA) with Spatial Gradient Reconstruction (SGR) is presented for calculating the sensitivity of fluid, structural, and coupled fluid-structure (aeroelastic) response with respect to shape design parameters. One of the novelties of this work is the derivation of local CSA with SGR for obtaining flow derivatives using finite volume formulation and its nonintrusive implementation (i.e. without accessing the analysis source code). Examples of a NACA0012 airfoil and a lid-driven cavity highlight the effect of the accuracy of the sensitivity boundary conditions on the flow derivatives. It is shown that the spatial gradients of flow velocities, calculated using SGR, contribute significantly to the sensitivity transpiration boundary condition and affect the accuracy of flow derivatives. The effect of using an inconsistent flow solution and Jacobian matrix during the nonintrusive sensitivity analysis is also studied. Another novel contribution is derivation of a hybrid adjoint formulation of CSA, which enables efficient calculation of design derivatives of a few performance functions with respect to many design variables. This method is demonstrated with applications to 1-D, 2-D and 3-D structural problems. The hybrid adjoint CSA method computes the same values for shape derivatives as direct CSA. Therefore accuracy and convergence properties are the same as for the direct local CSA. Finally, we demonstrate implementation of CSA for computing aeroelastic response shape derivatives. We derive the sensitivity equations for the structural and fluid systems, identify the sources of the coupling between the structural and fluid derivatives, and implement CSA nonintrusively to obtain the aeroelastic response derivatives. Particularly for the example of a flexible airfoil, the interface that separates the fluid and structural domains is chosen to be flexible. This leads to coupling terms in the sensitivity analysis which are highlighted. The integration of the geometric sensitivity with the aeroelastic response for obtaining shape derivatives using CSA is demonstrated. / Ph. D. / Many natural and man-made systems exhibit behavior which is a combination of the structural elastic response, such as bending or twisting, and aerodynamic or fluid response, such as pressure; for example, flow of blood in arteries, flapping of a bird’s wings, fluttering of a flag, and flight of a hot-air balloon. Such a coupled fluid-structure response is defined as aeroelastic response. Flight of an aircraft through turbulent weather is another example of an aeroelastic response. In this work, a novel method is proposed for calculating the sensitivity of an aircraft’s aeroelastic response to changes in the shape of the aircraft. These sensitivities are numbers that indicate how sensitive the aircraft’s responses are to changes in the shape of the aircraft. Such sensitivities are essential for aircraft design. The method presented in this work is called Continuum Sensitivity Analysis (CSA). The main goal is to accurately and efficiently calculate the sensitivities which are used by optimization tools to compute the best aircraft shape that suits the customers needs. The key advantages of CSA, as compared to the other methods, are that it is more efficient and it can be used effectively with commercially available (nonintrusive) tools. A unique contribution is that the proposed method can be used to calculate sensitivities with respect to a few or many shape design variables, without much effort. Integration of structural and fluid sensitivities is carried out first by applying CSA individually for structural and fluid systems, followed by connecting these together to obtain the coupled aeroelastic sensitivity. We present the first application of local formulation of CSA for nonintrusive implementation of high-fidelity aeroelastic sensitivities. The following challenging tasks are tackled in this research: (a) deriving the sensitivity equations and boundary conditions, (b) developing and linking computer codes written in different languages (C++, MATLAB, FORTRAN) for solving these equations, and (c) implementing CSA using commercially available tools such as NASTRAN, FLUENT, and SU2. CSA can improve the design process of complex aircraft and spacecraft. Owing to its modularity, CSA is also applicable to multidisciplinary areas such as biomedical, automotive, ocean engineering, space science, etc.

Shape optimization is an important step in many design processes. With the growing use of Computer Aided Engineering in the design chain, it has become very important to develop robust and efficient shape optimization algorithms. The field of Computer Aided Optimal Shape Design has grown substantially over the recent past. In the early days of its development, the method based on small shape perturbation to probe the parameter space and identify an optimal shape was routinely used. This method is nothing but an educated trial and error method. A key development in the pursuit of good shape optimization algorithms has been the advent of the adjoint method to compute the shape sensitivities more formally and efficiently. While undoubtedly, very attractive, this method relies on very sophisticated and advanced mathematical tools which are an impediment to its wider use in the engineering community. It that spirit, it is the purpose of this thesis to propose a new shape optimization algorithm based on more intuitive engineering principles and numerical procedures. In this thesis, the new shape optimization procedure which is proposed is based on the generation of a body-fitted mesh. This process maps the physical domain into a regular computational domain. Based on simple arguments relating to the use of the chain rule in the mapped domain, it is shown that an explicit expression for the shape sensitivity can be derived. This enables the computation of the shape sensitivity in one single solve, a performance analogous to the adjoint method, the current state-of-the art. The discretization is based on the Finite Difference method, a method chosen for its simplicity and ease of implementation. This algorithm is applied to the Laplace equation in the context of heat transfer problems and potential flows. The applicability of the proposed algorithm is demonstrated on a number of benchmark problems which clearly confirm the validity of the sensitivity analysis, the most important aspect of any shape optimization problem. This thesis also explores the relative merits of different minimization algorithms and proposes a technique to “fix” meshes when inverted element arises as part of the optimization process. While the problems treated are still elementary when compared to complex multiphysics engineering problems, the new methodology presented in this thesis could apply in principle to arbitrary Partial Differential Equations.

This thesis aims toward developing strategies in the area of structural optimization and to implement these strategies in design processes. At   GM Powertrain Sweden where powertrains are designed and developed, two designs of a differential housing have been chosen for this thesis. The main tasks have been to perform a topology optimization of a model early in a design process, and a shape optimization on a model late in a design process. In addition the shape optimization strategies have also been applied on a fork shifter. This thesis covers the theory of different optimization strategies in general. The optimization processes are explained in detail and the results from the structural optimization of the differential housings as well as the fork shifter are shown and evaluated. The evaluation of the thesis provides enough arguments to suggest an implementation of the optimization strategies in design processes at GM Powertrain. A Structural Optimization group has great potential of closing the gap between structural designers and structural analysis engineers which in long terms mean that better structures can be developed in less time. To be competitive in the automotive industry these are two of the most important factors for being successful.

<p><p><p>This thesis aims toward developing strategies in the area of structural optimization and to implement these strategies in design processes. At</p><p> </p><em>GM Powertrain Sweden </em>where powertrains are designed and developed, two designs of a differential housing have been chosen for this thesis. The main tasks have been to perform a topology optimization of a model early in a design process, and a shape optimization on a model late in a design process. In addition the shape optimization strategies have also been applied on a fork shifter. This thesis covers the theory of different optimization strategies in general. The optimization processes are explained in detail and the results from the structural optimization of the differential housings as well as the fork shifter are shown and evaluated. The evaluation of the thesis provides enough arguments to suggest an implementation of the optimization strategies in design processes at <em>GM Powertrain</em><p>. A Structural Optimization group has great potential of closing the gap between structural designers and structural analysis engineers which in long terms mean that better structures can be developed in less time. To be competitive in the automotive industry these are two of the most important factors for being successful.</p></p></p>

In 21 century finned surfaces are used in almost all condensers to enhance their heat transfer capabilities. A lot of different models are presented in the literature: on horizontal and vertical finned tubes, inside finned tubes. The validation method of the theoretical models is based on comparison between measurement of average heat transfer coefficient and one calculated by the model. But in this case it is impossible to validate all approaches made in the theory. The presented work aims to understand the real relation between assumptions made in the theory and flow of the condensate film along a fin. Therefore a comprehensive investigation of the film condensation phenomena on curvilinear surfaces has been done. This investigation has been done in the framework of the preparation of “SAFIR” and “EMERALD” space experiments aboard International Space Station. A special attention has been given to clarify some technical and technological problems that could eventually have a positive feedback for industrial applications. The model of the fin shape optimization has been developed. It takes into account surface tension forces and finite heat conductivity of the fin material. Developed model allows to significantly increase the condensate outflow as compared with the case of the optimal isothermal fin shape at the finite heat transfer conductivity. Enhancement coefficient increases with fin heat conductivity decreasing. The experimental and theoretical investigation of film condensation on a disk-shaped fin has been done under groun condition. 3D condensation model at different gravity levels has been developed. This model allows to reveal the area of dominant influence of surface tension forces. First prototype of experimental cell for the space experiments has been developed and tested. The temperature distribution along the curvilinear fin surface has been measured. The measurements of the film thickness at the fin top shows that the film thickness does not equal to zero as was assumed in some previous theoretical models. Developed model is in a good agreement with experimental results. In the ground set-up the measurement techniques as in future space experiments were realized: local temperature measurement of the fin surface, measurement of non-condensable gas mole fraction, optical system for local film thickness measurement and system of average heat transfer coefficient measurement. Experimental results approve the usefulness of these systems. Optical system based on schlieren technique for film surface deformation has been investigated and developed. This system was used for the investigation of shear driven liquid film on the mirror like substrate under microgravity condition. The microgravity condition was simulated during ESA Parabolic Flight Campaign of October-November 2009. The experimental results show the high capabilities of this system. In the framework of the space experiments preparation the analysis of appropriate liquid has been done. Three candidates have been compared: Water, Ethyl alcohol and FC-72. Third liquid has been chosen as applicable liquid for the “SAFIR” and “EMERALD” experiments. The optimal fin shapes and film thickness distribution have been calculated for the working liquid. Using obtained results requirements for space experiments have been prepared.

Increasing environmental concerns and fuel prices motivate the study of alternative, unconventional aircraft configurations. One such example is the blended-wing-body configuration, which has been shown to have several advantages over the conventional tube-and-wing aircraft configuration. In this thesis, a blended-wing-body aircraft is studied and optimized aerodynamically using a high-fidelity Euler-based flow solver, integrated geometry parameterization and mesh movement, adjoint-based gradient evaluation, and a sequential quadratic programming algorithm. Specifically, the aircraft is optimized at transonic conditions to minimize the sum of induced and wave drag. These optimizations are carried out with both fixed and varying airfoil sections. With varying airfoil sections and increased freedom, up to 52% drag reduction relative to the baseline geometry was achieved: at the target lift coefficient of 0.357, a drag coefficient of 0.01313 and an inviscid lift-to-drag ratio of 27.2 were obtained.

Increasing environmental concerns and fuel prices motivate the study of alternative, unconventional aircraft configurations. One such example is the blended-wing-body configuration, which has been shown to have several advantages over the conventional tube-and-wing aircraft configuration. In this thesis, a blended-wing-body aircraft is studied and optimized aerodynamically using a high-fidelity Euler-based flow solver, integrated geometry parameterization and mesh movement, adjoint-based gradient evaluation, and a sequential quadratic programming algorithm. Specifically, the aircraft is optimized at transonic conditions to minimize the sum of induced and wave drag. These optimizations are carried out with both fixed and varying airfoil sections. With varying airfoil sections and increased freedom, up to 52% drag reduction relative to the baseline geometry was achieved: at the target lift coefficient of 0.357, a drag coefficient of 0.01313 and an inviscid lift-to-drag ratio of 27.2 were obtained.

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