Dissertations / Theses on the topic 'Computational fluid dynamics; Naval architecture'

This thesis focuses on the numerical simulation of yacht sails using both computational fluid dynamics (CFD) and fluid structure interaction (FSI) modelling. The modelling of yacht sails using RANS based CFD and the SST turbulence model is justified with validation against wind tunnel studies (Collie, 2005; Wilkinson, 1983). The CFD method is found to perform well, with the ability to predict flow separation, velocity and pressure profiles satisfactorily. This work is extended to look into multiple sail interaction and the impact of the mast upon performance. A FSI solution is proposed next, coupling viscous RANS based CFD and a structural code capable of modelling anistropic laminate sails (RELAX, 2009). The aim of this FSI solution is to offer the ability to investigate sails' performance and flying shapes more accurately than with current methods. The FSI solution is validated with the comparison to flying shapes of offwind sails from a bespoke wind tunnel experiment carried out at the University of Nottingham. The method predicted offwind flying shapes to a greater level of accuracy than previous methods. Finally the CFD and FSI solution described here above is showcased and used to model a full scale Volvo Open 70 racing yacht, including multiple offwind laminate sails, mast, hull, deck and twisted wind profile. The model is used to demonstrate the potential of viscous CFD and FSI to predict performance and aid in the design of high performance sails and yachts. The method predicted flying shapes and performance through a range of realistic sail trims providing valuable data for crews, naval architects and sail designers.

Increasing interest in renewable energy sources for electricity production complying with stricter environmental policies has greatly contributed to further optimisation of existing devices and the development of novel renewable energy generation systems. The research and development of these advanced systems is tightly bound to the use of reliable design methods, which enable accurate and efficient design. Reynolds-averaged Navier-Stokes Computational Fluid Dynamics is one of the design methods that may be used to accurately analyse complex flows past current and forthcoming renewable energy fluid machinery such as wind turbines and oscillating wings for marine power generation. The use of this simulation technology offers a deeper insight into the complex flow physics of renewable energy machines than the lower-fidelity methods widely used in industry. The complex flows past these devices, which are characterised by highly unsteady and, often, predominantly periodic behaviour, can significantly affect power production and structural loads. Therefore, such flows need to be accurately predicted. The research work presented in this thesis deals with the development of a novel, accurate, scalable, massively parallel CFD research code COSA for general fluid-based renewable energy applications. The research work also demonstrates the capabilities of newly developed solvers of COSA by investigating complex three-dimensional unsteady periodic flows past oscillating wings and horizontal-axis wind turbines. Oscillating wings for the extraction of energy from an oncoming water or air stream, feature highly unsteady hydrodynamics. The flow past oscillating wings may feature dynamic stall and leading edge vortex shedding, and is significantly three-dimensional due to finite-wing effects. Detailed understanding of these phenomena is essential for maximising the power generation efficiency. Most of the knowledge on oscillating wing hydrodynamics is based on two-dimensional low-Reynolds number computational fluid dynamics studies and experimental testing. However, real installations are expected to feature Reynolds numbers of the order of 1 million and strong finite-wing-induced losses. This research investigates the impact of finite wing effects on the hydrodynamics of a realistic aspect ratio 10 oscillating wing device in a stream with Reynolds number of 1.5 million, for two high-energy extraction operating regimes. The benefits of using endplates in order to reduce finite-wing-induced losses are also analyzed. Three-dimensional time-accurate Reynolds-averaged Navier-Stokes simulations using Menter's shear stress transport turbulence model and a 30-million-cell grid are performed. Detailed comparative hydrodynamic analyses of the finite and infinite wings highlight that the power generation efficiency of the finite wing with sharp tips for the considered high energy-extraction regimes decreases by up to 20 %, whereas the maximum power drop is 15 % at most when using the endplates. Horizontal-axis wind turbines may experience strong unsteady periodic flow regimes, such as those associated with the yawed wind condition. Reynolds-averaged Navier-Stokes CFD has been demonstrated to predict horizontal-axis wind turbine unsteady flows with accuracy suitable for reliable turbine design. The major drawback of conventional Reynolds-averaged Navier-Stokes CFD is its high computational cost. A time-step-independent time-domain simulation of horizontal-axis wind turbine periodic flows requires long runtimes, as several rotor revolutions have to be simulated before the periodic state is achieved. Runtimes can be significantly reduced by using the frequency-domain harmonic balance method for solving the unsteady Reynolds-averaged Navier-Stokes equations. This research has demonstrated that this promising technology can be efficiently used for the analyses of complex three-dimensional horizontal-axis wind turbine periodic flows, and has a vast potential for rapid wind turbine design. The three-dimensional simulations of the periodic flow past the blade of the NREL 5-MW baseline horizontal-axis wind turbine in yawed wind have been selected for the demonstration of the effectiveness of the developed technology. The comparative assessment is based on thorough parametric time-domain and harmonic balance analyses. Presented results highlight that horizontal-axis wind turbine periodic flows can be computed by the harmonic balance solver about fifty times more rapidly than by the conventional time-domain analysis, with accuracy comparable to that of the time-domain solver.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Architecture, 2002.
Includes bibliographical references (p. 128-133).
Current design of building indoor environment comprises macroscopIC approaches, such as CONT AM multizone airflow analysis tool, and microscopic approaches that apply Computational Fluid Dynamics (CFD). Each has certain advantages and shortfalls in terms of indoor airflow simulation. A coupling approach that combines multizone airflow analysis and detailed CFD airflow modeling would provide complementary information of a building and make results more accurate for practical design. The present study attempted to integrate such building simulation tools in order to better represent the complexity of the real world. The overall objective of this study was to couple an in-house CFD program, MIT-CFD, with a multizone airflow analysis program, CONT AM. Three coupling strategies were introduced. The virtual coupling makes use of the CFD simulation results in a large scale to provide boundary conditions for CONT AM. The quasi-dynamic strategy assumes that CFD can produce a "true" flow pattern and the CONTAM results should be changed accordingly. The dynamic coupling realizes an active two-way interaction between CFD and CONTAM through a bisection search procedure designed by the author that forces the airflow rates from the two models to converge. Various case studies were conducted to validate the coupling strategies. Preliminary results show that all three coupling schemes can result in more reliable airflow patterns. Further investigations are needed to improve the coupling procedures and to apply to more generalized and complex real-world cases.
by Yang Gao.
S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Architecture, 2003.
Includes bibliographical references (p. 237-246).
Building energy simulation (ES) and computational fluid dynamics (CFD) can play important roles in building design by providing essential information to help design energy-efficient, thermally comfortable and healthy buildings. However, separate applications of ES and CFD usually cannot give an accurate prediction of building thermal and airflow behaviors due to the partial modeling of the problem. An integration of ES and CFD can eliminate many of the assumptions used in ES and CFD because of the complementary nature of ES and CFD results. This thesis studies the fundamentals, implementation and application of ES and CFD coupling, significantly advancing the knowledge and experience in this area. The study has been focused on the iterative coupling of individual ES and CFD programs, which shows good potential of providing reasonable results with acceptable computing costs. The research first analyzes the principles and challenges of ES and CFD program coupling. To bridge three major discontinuities in time-scale, spatial resolution and computing speed between ES and CFD programs, special coupling strategies have been developed. Particularly, the staged coupling strategies proposed can effectively reduce computing time while preserving the accuracy and details of the computed results. The study discusses the solution characteristics of iterative coupling simulation. Through theoretical analysis and numerical experiments, the research verifies the solution existence and uniqueness of a coupled simulation. The investigation concludes that a converged and stable simulation can be achieved with four different data coupling methods. The study has further developed an improved iteration and control algorithm for the coupled simulation. An integrated program, E+MIT-CFD, has been developed by coupling a new- generation ES program (E+) with a newly-developed ready-to-plug-in CFD solver (MIT- CFD). All the coupling methods and strategies proposed have been implemented in this program. The program has been well validated with various experimental facilities. The comparison of numerical solutions with experimental data reveals the advantages of the integrated simulation over the separate ES and CFD applications. The study further demonstrates the performance and capabilities of the coupled program through practical
(cont.) through practical design projects. Finally, sensitivity analysis of the coupling simulation to building characteristics and coupling strategies has been performed, based on which general guidelines are established for appropriate usage of the coupling simulation.
by Zhiqiang Zhai.
Ph.D.

Hypersonic flight at sea-level conditions induces severe thermal loads not seen by any other type of current hypersonic system. Appropriate design of the hypersonic round requires a solid understanding of the thermal environment. Numerous codes were obtained and assessed for their applicability to the problem under study, and outside of the GASP Conjugate Heat Transfer module, Navier-Stokes code from Aerosoft, Inc., no efficient codes are available that can model the aerodynamic heating response for a fully detailed projectile, including all subassemblies, over an entire trajectory. Although the codes obtained were not applicable to a fully detailed thermal soak analyses they were useful in providing insight into ablation effects. These initial trade studies indicated that ablation of up to 1.25 inches could be expected for a Carbon-Carbon nosetip in this flight environment. In order to capture the thermal soak effects a new methodology (BMA) was required. This methodology couples the Sandia aerodynamic heating codes with a full thermal finite element model of the desired projectile, using the finite element code ANSYS from ANSYS, Inc. Since ablation can be treated elsewhere it was not included in the BMA methodology. Various trajectories of quadrant elevations of 0.5, 10, 30, 50, and 80 degrees were analyzed to determine thermal time histories and maximum operating temperatures. All of the trajectories have the same launch condition, Mach 8 sea-level, and therefore will undergo the same initial thermal spike in temperature at the nose-tip of approximately 3,100 K (5600R). Of the five trajectories analyzed the maximum internal temperatures experienced occurred for the 50 degree quadrant elevation trajectory. This trajectory experienced temperatures in excess of 1,000 K (1800R) for more than 80% of its flight time. The BMA methodology was validated by comparisons with experiment and computational fluid solutions with an uncertainty of 10% at a cost savings of over three orders of magnitude.
Ph. D.

Designing buildings to use energy more efficiently can lead to lower energy costs, while maintaining comfort for occupants. Computational fluid dynamics (CFD) can be utilized to visualize and simulate expected flows in buildings and structures. CFD gives architects and designers the ability to calculate the velocity, pressure, and heat transfer within a building. Previous research has not modeled natural ventilation situations that challenge common design rules of thumb used for cross-ventilation and single-sided ventilation. The current study uses a commercial code (FLUENT) to simulate cross-ventilation in simple structures and analyzes the flow patterns and heat transfer in the rooms. In the Casa Giuliana apartment and the Affleck house, this study simulates passive cooling in spaces well-designed for natural ventilation. Heat loads, human models, and electronics are included in the apartment to expand on prior research into natural ventilation in a full-scale building. Two different cases were simulated. The first had a volume flow rate similar to the ambient conditions, while the second had a much lower flow rate that had an ACH of 5, near the minimum recommended value Passive cooling in the Affleck house is simulated and has an unorthodox ventilation method; a window in the floor that opens to an exterior basement is opened along with windows and doors of the main floor to create a pressure difference. In the Affleck house, two different combinations of window and door openings are simulated to model different scenarios. Temperature contours, flow patterns, and the air changes per hour (ACH) are explored to analyze the ventilation of these structures.
Master of Science

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Neste trabalho, foi desenvolvido um simulador numérico baseado no método livre de malhas Smoothed Particle Hydrodynamics (SPH) para a resolução de escoamentos de fluidos newtonianos incompressíveis. Diferentemente da maioria das versões existentes deste método, o código numérico faz uso de uma técnica iterativa na determinação do campo de pressões. Este procedimento emprega a forma diferencial de uma equação de estado para um fluido compressível e a equação da continuidade a fim de que a correção da pressão seja determinada. Uma versão paralelizada do simulador numérico foi implementada usando a linguagem de programação C/C++ e a Compute Unified Device Architecture (CUDA) da NVIDIA Corporation. Foram simulados três problemas, o problema unidimensional do escoamento de Couette e os problemas bidimensionais do escoamento no interior de uma Cavidade (Shear Driven Cavity Problem) e da Quebra de Barragem (Dambreak).
In this work a numerical simulator was developed based on the mesh-free Smoothed Particle Hydrodynamics (SPH) method to solve incompressible newtonian fluid flows. Unlike most existing versions of this method, the numerical code uses an iterative technique in the pressure field determination. This approach employs a differential state equation for a compressible fluid and the continuity equation to calculate the pressure correction. A parallel version of the numerical code was implemented using the Programming Language C/C++ and Compute Unified Device Architecture (CUDA) from the NVIDIA Corporation. The numerical results were validated and the speed-up evaluated for an one-dimensional Couette flow and two-dimensional Shear Driven Cavity and Dambreak problems.

Os métodos numéricos convencionais, baseados em malhas, têm sido amplamente aplicados na resolução de problemas da Dinâmica dos Fluidos Computacional. Entretanto, em problemas de escoamento de fluidos que envolvem superfícies livres, grandes explosões, grandes deformações, descontinuidades, ondas de choque etc., estes métodos podem apresentar algumas dificuldades práticas quando da resolução destes problemas. Como uma alternativa viável, existem os métodos de partículas livre de malhas. Neste trabalho é feita uma introdução ao método Lagrangeano de partículas, livre de malhas, Smoothed Particle Hydrodynamics (SPH) voltado para a simulação numérica de escoamentos de fluidos newtonianos compressíveis e quase-incompressíveis. Dois códigos numéricos foram desenvolvidos, uma versão serial e outra em paralelo, empregando a linguagem de programação C/C++ e a Compute Unified Device Architecture (CUDA), que possibilita o processamento em paralelo empregando os núcleos das Graphics Processing Units (GPUs) das placas de vídeo da NVIDIA Corporation. Os resultados numéricos foram validados e a eficiência computacional avaliada considerandose a resolução dos problemas unidimensionais Shock Tube e Blast Wave e bidimensional da Cavidade (Shear Driven Cavity Problem).
The conventional mesh-based numerical methods have been widely applied to solving problems in Computational Fluid Dynamics. However, in problems involving fluid flow free surfaces, large explosions, large deformations, discontinuities, shock waves etc. these methods suffer from some inherent difficulties which limit their applications to solving these problems. Meshfree particle methods have emerged as an alternative to the conventional grid-based methods. This work introduces the Smoothed Particle Hydrodynamics (SPH), a meshfree Lagrangian particle method to solve compressible flows. Two numerical codes have been developed, serial and parallel versions, using the Programming Language C/C++ and Compute Unified Device Architecture (CUDA). CUDA is NVIDIAs parallel computing architecture that enables dramatic increasing in computing performance by harnessing the power of the Graphics Processing Units (GPUs). The numerical results were validated and the speedup evaluated for the Shock Tube and Blast Wave one-dimensional problems and Shear Driven Cavity Problem.

NOWADAYS, a number of studies keep on demonstrating the existence of a strong relation between high concentrations of particulate matter (PM) and the prevalence of human morbidity and mortality. Large particles can be filtered in the nose or in the throat, while fine particles (about10 micrometer) can settle in the bronchi and lungs, leading to more serious consequences. According to Karagulian et al. the major sources of urban air pollution are traffic (25%), combustion and agriculture (22%), domestic fuel burning (20%), natural dust (18%) and industrial activities (15%).As a consequence, the detailed study of dispersion phenomena within the urban canopy becomes a target of great interest. To this end, Computational Fluid Dynamics (CFD) can be successfully employed to predict turbulence and dispersion patterns, accounting for a detailed characterization of the pollutant sources, complex obstacles and atmospheric stability classes.Despite being intrinsically different phenomena, turbulence and dispersion are closely related. It is universally accepted that, to reach accurate prediction of the concentration field, it is necessary to properly reproduce the turbulence one. For this reason, the present PhD thesis is split into two main Sections: one focused on turbulence modelling and the subsequent, centered on the dispersion modelling.Thanks to its good compromise between accuracy of results and calculation time, Reynolds-averaged Navier-Stokes (RANS) still represents a valid alternative to more resource-demanding methods. However, focusing on the models’ performance in urban studies, Large Eddy Simulation (LES) generally outperforms RANS results, even if the former is at least one order of magnitude more expensive. Stemming from this consideration, the aim of this work is to propose a variety of approaches meant to solve some of the major limitations linked to standard RANS simulation and to further improve its accuracy in disturbed flow fields, without renouncing to its intrinsic feasibility. The proposed models are suitable for the urban context, being capable of automatically switching from a formulation proper for undisturbed flow fields to one suitable for disturbed areas. For neutral homogeneous atmospheric boundary layer (ABL), a comprehensive approach is adopted, solving the issue of the erroneous stream-wise gradients affecting the turbulent profiles and able to correctly represent the various roughness elements. Around obstacles, more performing closures are employed. The transition between the two treatments is achieved through the definition of a Building Influence Area (BIA). The finalgoal is to offer more affordable alternatives to LES simulations without sacrificing a good grade of accuracy.Focusing on the dispersion modelling framework, there exists a number of parameters which have to be properly specified. In particular, the definition of the turbulent Schmidt number Sct, expressing the ratio of turbulent viscosity to turbulent mass diffusivity, is imperative. Despite its relevance, the literature does not report a clear guideline on the definition of this quantity. Nevertheless, the importance of Sct with respect to dispersion is undoubted and further demonstrated in the works of different authors. For atmospheric boundary layer flows, typical constant values range between 0.2 and 1.3. As a matter of fact, the local variability of Sct is supported by experimental evidence and by direct numerical simulations (DNS). These observations further suggest that the turbulent Schmidt number should be prescribed as a dynamic variable. Following these observations a variable turbulent Schmidt number formulation is proposed in this work. The latter stems from the same hypothesis of the variable formulation developed by Gorlé et al. Moreover, the relevant uncertain model parameters are optimized through uncertainty quantification (UQ). This formulation further increased the accuracy of the predictions, and was successfully verified by Di Bernardino et al. However, the turbulent Schmidt number resulting from this formulation is still intrinsically linked to the turbulence model employed, i.e. to the Cμ coefficient. To overcome this constraint, the nature and the dependencies of Sct were further analyzed through correlation studies and employing principal component analysis (PCA) on data obtained through the proposed ABL RANS model. Subsequently, the same data-driven technique was employed based on the high-fidelity outcomes of a delayed Detached Eddy Simulation (dDES) to derive a generalized turbulentSchmidt number formulation. The latter can be employed within a wide range of turbulence models, without limiting its variability.
Doctorat en Sciences de l'ingénieur et technologie
info:eu-repo/semantics/nonPublished

博士
國立臺北科技大學
設計學院設計博士班
103
Eco-Architecture is a concept of environment and energy sustainability in order to solve the insufficient of global resources, but lacking of effective evaluation method is serious weakness of Eco-Design. How to apply scientific methods and assessment techniques to improve the Eco-Architecture design is major concern to modern designers. At present time, practical simulation tools following with the digital and information technologies development, Performance-oriented Architecture Design is an approach which use of simulation technology to modify design project or built environment. Computational Fluid Dynamics (CFD) technical has becomes an important simulation tool which integrates with the process of architectural design. Many invisible physical factors of environment (such as wind etc.) could be visualized and counted by CFD analysis. The results can use as the basis for the design improvement. As a relative scientific design support method, it runs as a critical role for the development of Eco-Architecture design and the new generation of urban patterns to achieve the concept of sustainable development in future. In this study, researcher studies several cases of famous architectures in the world through CFD turbulence model, and summarized following conclusions: 1.The CFD-based predictions of Tjibaou Culture Center illustrates that the improved design for strengthening the effectiveness of natural ventilation at the normal wind level indicates a significant growth in the volumetric flow rate from 19.24 to 39.34m3/s via an increase of the aeration area in conjunction with minimized obstacles along the flow pathway. 2.The unique form of Guggenheim Museum also causes strong turbulences on the leeward side. The Guggenheim Museum is designed with an irregular fluidic way along the river bank; leading to the positive and negative influences on the physical urban environments reveals by the CFD simulations. 3.We can recognize in depth about the building performance of unique architectural design through the computational simulation analysis. The wind crossing through the building becomes unpredictable due to the round shape of Eryi Lou, particular positions at both ends, the wind velocity to the leeward of Eryi Lou can reach 2.8 m/s. 4.Traditional architectural design has remarkable ingenuity; they could be as great example of reference for ecological architectural design. Performance-Oriented Design concept and CFD simulation will become important tools for architects and designers in the future.