The objective of this work is to gain insight into the process and development of a method for obtaining optimum design shapes for non-lifting aerodynamic struts while employing an interactive viscous- potential flow model for a range of airfoil reynolds numbers. This was done for axially loaded struts with constant cross-sectional area as well as struts loaded in bending with a fixed cross-sectional moment of inertia. The optimization sought the airfoil shape that resulted in minimum drag. The flow field was obtained by using a panel method that was iteratively coupled to a boundary layer solver. The viscous solver used was to model the boundary layer and was based on the zero-equation, Cebeci- Smith turbulence model. The main flow field was computed using a panel method. The airfoil shape was described using a bezier-PArSEC shape parameterization and optimization of the shape param- eters was obtained using differential evolution. The numerical approach of the flow field solver and the simplicity of the genetic algorithm allowed for these results to be obtained in an acceptable timely manner. This paper will present the results of a number of cases and discuss all of the issues that arose. While one can have confidence in the results, limitations and the need for future work were also exposed. The limitations occurred in this thesis were due to the limitations of the boundary layer flow field solver. This solver did not allow airfoils with significant thickness to be evaluated thus restricting the solution space to thin airfoils. It was observed that future work on dealing with separation modelling needs to be done to allow improved certainty of the optimization.

The importance of micro-shock tubes is growing in line with recent developments of microscale technology for products like micro-heat engines and micro-propulsion systems. The flow dynamics within a micro-shock tube are different from those found in a macro shock tube, and knowledge of these dynamics is not as yet well established, as the flow within these tubes includes extra physics namely rarefaction and complex effects due to viscosity. Studies have recently been made with assumed initial condition of instantaneous diaphragm rupture producing centred shock and expansion waves. However, for a real case, the diaphragm ruptures over a finite time causing a period of partial rupture and this will change the shock characteristics. The work here reports on a series of axisymmetric numerical simulations carried out to calculate the influence of an initial finite-time diaphragm rupture. Rarefaction effects were taken into account by the use of Maxwell’s slip velocity and temperature conditions. Use of an initial finite-time diaphragm rupture boundary condition causes the forming of a non-centred shock wave downstream of the diaphragm, and, the shock propagation distance is considerably reduced by use of the finite-time rupture process.

This paper deals with the economic optimization of high-performance post-tensioned concrete box-girder pedestrian bridges. To this end, a program analyzes and evaluates the structural restrictions following Spanish codes for structural concrete and bridge design loads. This problem includes 33 discrete design variables that define the geometry, the concrete, the reinforcing steel bars and the post-tensioned steel. Various acceptance criteria are proposed to modify a variant of the simulated annealing algorithm with a neighborhood move based on the mutation operator from the genetic algo- rithms (SAMO). An objective methodology based on the extreme value theory is used to determine the number of experimental tests required to provide a solution with user-defined accuracy as compared to a global optimum solution. Results indicate that the local optima found by SAMO2 fits a three- parameter Weibull distribution and improves the cost results for this structural problem. The minimum value obtained by SAMO2 differed just 0.34% compared to the theoretical minimum value so that, from the structural engineering perspective, the divergence was small enough to be accepted. High-strength concrete performance was further studied in a concrete strength parametric study to acquire more evidence-based knowledge on its implications for economic efficiency. Finally, the study showed that high-strength concrete decreases the cost by 4.5% and the amount of concrete by 26%.

Understanding the disturbances introduced by cavitation inside spray nozzles is important, when simulating the spray formation of highly viscous liquids. In this paper, a new model for cavitation-induced primary break-up is proposed, which is able to map the influence of cavitating nozzle flow on spray formation. Detailed experimental and numerical investigations of the viscous nozzle flow have been performed in order to develop an improved primary break-up model [1]. The proposed model describes the transition from the flow inside the nozzle, modelled using a homogeneous equilibrium model (HEM) method, to the first primary droplets modelled using a Eulerian–Lagrangian method. Thus, providing the boundary conditions for the calculation of the secondary break-up and spray formation. The nozzle exit is divided into a definite number of patches. Liquid momentum and vapor volume fraction from each patch are used to initialize the primary droplets. The model has been implemented in the open-source CFD software package OpenFOAM and validation has been done using high-speed shadow graphic imaging. The simulated spray tip penetration and spray cone angle at the near-nozzle region show a good agreement with the experiment results.

Overflows in the ocean occur when dense water flows down a continental slope into less dense ambient water. It is important to study idealized and small-scale models, which allow for confidence and control of parameters. The work presented here is a direct qualitative and quantitative comparison between physical laboratory experiments and lab-scale numerical simulations. Physical parameters are varied, including the Coriolis parameter, the inflow density, and the inflow volumetric flow rate. Laboratory experiments are conducted using a rotating square tank and high-resolution camera mounted on the table in the rotating reference frame. Video results are digitized in order to compare directly to numeri- cal simulations. The MIT General Circulation Model (MITgcm), a three-dimensional ocean model, is used for the direct numerical simulations corresponding to the specific laboratory experiments. It was found that the MITgcm was not a good match to laboratory experiments when physical parameters fell within the high eddy activity regime. However, a more extensive resolution study is needed to understand this fully. The MITgcm simulations did provide a good qualitative and quantitative match to laboratory experiments run in a low eddy activity regime. In all cases, the MITgcm simulations had more eddy activity than the laboratory experiments.

The hydrocarbon leaks from process systems potentially lead to hazardous consequences with regard to human safety, environmental pollution and valuable assets. The hydrocarbon leaks may be gas leaks, liquid leaks or multiphase leaks. The gas leaks have the highest potential of damage due to explosion accidents. both gas and oil leaks can create long-lasting fires threatening personnel safety and structural integrity of process plants and offshore platforms. One common method for limiting the consequences associated with a process emergency is the rapid depressurization or blowdown of pressurized process systems. There is experimental evidence that the assumption of thermodynamic equilibrium is not appropriate during rapid depressurization, since the two phases show an independent temperature evolution. The current work proposes a model for the simulation of the blowdown of vessels containing two-phase (gas–liquid) hydrocarbon fluids, considering partial phase equilibrium between phases. Two phases may be present either already at the beginning of the blowdown process (for instance in gas– liquid separators) or as the liquid is formed from flashing of the vapour due to the cooling induced by pressure decrease. In addition, the transient behaviour of hydrocarbon leaks from pressurized process systems during depressurization is also included in the model providing the inputs for risk assessments. The model is based on a compositional approach, and it takes into account coupled effects of internal heat and mass transfer processes, as well as heat transfer with the vessel wall and the external environ- ment. The vapour liquid equilibria calculations are performed using dynamic link library provided by the comprehensive pressure volume temperature and physical properties package ‘Multiflash’. Numerical simulations show a generally good agreement with experimental measurements.

This paper is concerned with the evaluation of effective material properties of wood. Since both mechanical loading and climatic changes play a crucial role in the prediction of wood response, we consider not only stiffness, but also non-mechanical properties driving the heat and moisture transport and thus indirectly addressing the swelling and shrinkage properties of wood. In this regard, classical micromechanical models as well as numerical simulations based on the Extended Finite Element Method are examined. A special attention is devoted to the influence of microstructural details of the porous phase. To that end, the X-ray computational micro-tomography is adopted when seeking for information beyond the volume fraction of phases that can be identified at various levels of a hierarchical arrangement of wood. A spruce wood is selected as one particular example to compare individual computational approaches.

Not only is the energy efficiency of buildings nowadays becoming more and more important; the legislative requirements, the people’s awareness of the environmental questions and their thermal com- fort expectations are also on a much higher level. all of these issues can be addressed by making the building envelope more thermally resistant. however, with the traditional thermal insulation materials the thickness of thermal insulation layers is already at the viable limits. Therefore, the development of new, more efficient thermal insulation products with a higher thermal resistance is highly promoted. Preliminary research results can be applied to models to develop and confirm the conceptual designs of such new materials. In this paper, an analysis of thermal performance is presented for a novel thermal insulation consisting of graphite polystyrene (gPS) matrix with cavities filled with an insulative gas, and a protective sheath to prevent it from leaking. bearing in mind the suitability for later production, differ- ent configurations of the assembly were considered, regarding the matrix geometry, the type of the gas filling, and the surface emissivity of the cavities. a range of numerical simulations of heat transfer was conducted to determine the efficiency of different designs in reducing the conductive, the convective, and the radiative heat transfer. advantages, limitations and some detailed parameters of the proposed design concepts were determined, which were then used for optimisation. The analysis of the results indicates that the equivalent thermal conductance of a gPS panel can be significantly reduced by the introduction of gas-filled cavities. The reduction is highly dependent on the type of the gas filling (ther- mal conductivity, viscosity, specific heat, etc.), the size of the cavities, and the cavity surface emissivity.