This study investigated the effect of chord deformation on the unsteady aerodynamic mechanisms found in hovering flapping flight at a Reynolds number of Re = 2002. This was done in order to get a better understanding of the physics involved in flapping flight, which in turn could lead to improved Micro Aerial Vehicle (MAV) designs. A three-dimensional numerical study was performed using an immersed boundary method (IBM) with the discrete forcing approach. The solver was first validated against an experiment by Kim and Gharib (2011).

The GMRES algorithm has been discussed to solve the linear system Ax = b for application in a flow solver. Besides the conventional GMRES algorithm, several approaches are discussed which supposedly reduce the computational costs of the method, and reduce the number of iterations needed to satisfy the convergence criteria. GMRES is one of the most popular methods for solving non-symmetric systems. The method is robust, i.e. the solution of the least squares problem always exists. GMRES does have full recurrences since the basis of the Krylov subspace needs to be stored completely. Also, orthogonalisation of new basis vectors becomes increasingly more expensive when the iterations proceed. GMRES minimizes the residual norm, as a result the residual norm decreases monotonically and the convergence is smooth.

This thesis introduces a higher-order numerical method for elliptic boundary value problems. The discretization method belongs to the class of mimetic discretizations, which translate as many of properties of the continuous problem to the discrete system, aiming to improve accuracy and reliability. The novelty lies in the application of B-splines as basis functions in a dual grid approach. B-splines or basis splines are piecewise polynomials with a certain degree of continuity between the polynomial pieces. Therefore, splines offer an attractive compromise between piecewise linear functions, commonly seen in finite element analysis, and the Lagrange polynomials from spectral element methods.

The application of Computational Fluid Dynamics to model and simulate flows around flexible and moving objects has grown in the last decades fueled by new technological challenges in particular in the aerospace engineering field because of the introduction of highly deformable materials and complex moving systems. Existing body-fitted mesh methods such as the Arbitrary Lagrangian Eulerian (ALE) approach have been proposed to simulate the flow around moving and deforming structures but their applicability is limited because of the issues arising in deforming the computational grid constrained to the moving/deforming structure. This thesis focuses on the verification, and validation of an Embedded Boundary method (developed at Stanford University by Prof. Farhat research group) for the solution of fluidstructure interaction problems involving large and complex structural motions and deformations. The Embedded Boundary method works on non-body fitted grids, by using a tracking algorithm is able to impose the effects of an ’immersed’ moving and deforming surface mesh on the fixed Eulerian fluid mesh. For this reason this method is gaining popularity because it simplify a number of issues ranging from codes coupling (fluid-structure solvers) to formulating and implementing algorithms for applications that involve very large and complex motions-deformations and for which ALE algorithms are unfeasible.

The field of remote sensing and information gathering is being revolutionized by the recent developments in Micro Air Vehicles, MAVs. The need for maneuverability and flight in confined spaces has directed the focus of research towards flapping flight. Biological flapping flyers exhibit all the characteristics that are desired by MAVs. Biological flyers are able to hover, make rapid changes in their attitude, and navigate through very narrow spaces. For the purpose of this Master thesis the hawkmoth was used as a starting point and source of inspiration. First and foremost the hawkmoth is a fairly large insect, with a wingspan of roughly 10 cm. The larger scale of the insect will translate to an easier design in terms of the scalability of structural and electronic components. Furthermore, the hawkmoth displays consistent and simple kinematics.

With the increasing interest for renewable energy resources in the last couple of decades, the possible benefits of flow control is brought under more and more attention. Boundary layer suction (or blowing) is one type of control that has proven its applicability in various fields. Being able to predict these effects on the boundary layer and airfoil properties can save both money and time in early design stages. At the moment, this prediction is still unsatisfactory and not well validated. This is especially true for turbulent boundary layers with suction. For this reason, the main objective is to provide new ways to model boundary layer suction on airfoils by using different computational techniques. Next to this, the results should be compared with other design tools as well as with analytical and experimental data for validation.

Modelling of fluid-structure interactions (FSI) plays a key role in many engineering applications. However, due to the interaction between fluid and structure the computational cost related to high fidelity models (especially for strongly coupled systems) limits the direct use of current FSI simulation techniques in industry. Since a thorough knowledge of FSI phenomena is very important in design processes, efficient simulation techniques that combine low cost with high accuracy need to be developed. To this end, the use of the space mapping optimization technique as coupling approach for partitioned FSI simulations is investigated.

Today a lot of attention is paid to the development of environmental friendly technologies. In the aircraft industry, emissions need to be reduced as well. Fuel can be saved by ensuring that the flow over the wings of the aircraft is completely or partly laminar. A laminar boundary layer creates less skin friction drag than a turbulent boundary layer. It is however more prone to separation. Nevertheless, at the cruise speeds of transport aircraft a laminar boundary layer can be beneficial (because of the small angle of attack). At these speeds a shock wave can however be present on the airfoil at off-design conditions. This shock wave can cause a local separation of the boundary layer, if the pressure gradient is however not too strong, the flow will reattach after the shock and hence the drag of the aircraft will be reduced. During flight disturbances in the flow can set the aircraft into motion. This motion can be damped or amplified. The boundary between these types of motion is called the flutter boundary. This boundary is an important constraint of the flight envelope of aircraft. The influence of boundary layer transition on the flutter behaviour of transonic aircraft has not been investigated yet, therefore a first step has been taken in this thesis. The objective of this thesis is to: Investigate the influence of laminar to turbulent boundary layer transition on the flutter boundary and damping characteristics of a supercritical laminar airfoil (the CAST-10 airfoil) in transonic flow using numerical simulations. In order to do so numerical simulations are performed with the CAST-10 airfoil with two RANS codes: the DLR TAU code and the ANSYS CFX code. The DLR TAU code uses the eN-method for transition prediction, whereas CFX uses the γ − Re_ transition model. Steady and unsteady flow simulations have been performed with both codes. The steady flow simulations are used to initialise the unsteady flow simulations. In these unsteady flow simulations, the airfoil is forced to perform a sinusoidal pitching or plunging motion. The response of the airfoil to these applied motions serves as input to a flutter program, which uses the k-method to compute the flutter boundary. Simulations with both free and fixed transition are carried out. In case of fixed transition, transition was fixed at the leading edge of the airfoil.

The research done on bat flight has increased the knowledge about bat flight and the corresponding aerodynamic phenomena in great extent. In the mid seventies and eighties, the first kinematic studies by Norberg (1976a,b) and Aldridge (1986, 1987) were performed with the use of high speed cameras and made it possible to analyze the kinematics of bat flight in great detail. These studies were first performed in _ight corridors, later followed by measurements in windtunnels (Busse von, 2011). This made it possible to measure over a range of flight speeds, which shows a gradual change in kinematics when _ight speed is increased. Aerodynamic measurements were the next step in bat flight research and gave a better insight in the vortex structure of bat _ight both onwing (Muijres et al., 2008) and in the wake (Hedenstrom et al., 2007, 2009; Johansson et al., 2008).

In the on-going search for improvements in high lift device performance, the field of flow separation control has seen explosive growth in recent years. This is due to a continuously improved understanding of fluid mechanics, the development in experimental and computational techniques and the variety of flow control mechanisms existing today. These multiple mechanisms can be differentiated into active and passive flow control techniques. In this research two passive flow separation control methods are tested on their ability to postpone flow separation on an airfoil with trailing edge flap model of the Extra EA-400. The two methods are the application of vortex generators on the airfoil and the positioning of vortex producing cylinders in the slot of the airfoil flap system.

It is investigated if a Multi Point Inflow Performance Relationship (MIPR) using Uncer- tainty Quantification (UQ) can lead to a step change in completion design. The MIPR model consists of several Kuchuk IPR models coupled with a wellbore network, and is verified against a discretized model. It is found that the assumption of artificial no-flow boundaries for this model is limiting, which leads to an overprediction of the distributed productivity index. A calibration using Markov Chain Monte Carlo (MCMC) is pre- formed, which incorporates both epistemic and aleatory model parameters. In addition, a more efficient ‘partitioned MCMC’ is investigated, which shows promising results. The UQ MIPR model can predict the change in productivity index due to a uniform com- pletion skin profile, and can give an indication of results for a non-uniform change in completion skin. In conjunction with a discretized model, a MIPR model can lead to a step change in completion by providing information to a production technologists earlier on in field development.

In this master thesis, the numerical investigation of an upper airway in a patient suffering from stridor is investigated using a fluid-structure-acoustic interaction simulation in OpenFOAMR . The geometry of an upper airway model is very difficult, leading to various cross sections and a large spectrum of ow phenomena. Many ow forms were discovered during the analysis, such as ow separation, ow attachment, laminar ow, transitional ow and turbulent ow. Next, there is a large difference in geometry per patient, especially with respect to the age. Neonates and adults have different upper airway's, making a comparison very difficult. Also, taking into account the various possible causes of stridor, detection methods are scarce and mostly unsuccessful. There are too many variables and there is too much variation in a detection model in order to accurately predict the noise. This thesis is an attempt to create one numerical detection method, allowing to change one variable each time a simulation is run.

Traditionally, geometry has been represented differently in the field of Computer Aided Design (CAD) and Finite Element Analysis (FEA). This means that the CAD geometry, which can be seen as exact, must be converted to an Analysis Suitable Geometry (ASG) for input in a FEA program. A cumbersome and time consuming process, more commonly known as meshing. Furthermore, most engineering analysis techniques use linear or quadratic approximations of the originally exact geometry. Besides the geometry error, these crude geometry approximations can give rise to numerical errors such as spurious oscillations. In order to avoid these problems an integrated approach is necessary which unifies CAD and FEA.

Since the last decade the world energy supply is shifting from fossil- to renewable energy resources. Wind energy is one of the main resources of this new type of energy. However, a lot of work still needs to be done on the e_ciency improvements. This mainly results in increased rotor diameters. These large wind turbines are highly subjected to the vagaries of the atmosphere. Therefore a lot of research is being performed to the inuence of atmospheric conditions on the aerodynamic and structural behavior of wind turbines. Typical atmospheric conditions that are relevant for wind turbine design are gusts, vertical velocity shear, direction change and turbulence. The highly unsteady character of these atmospheric conditions make most of available empirical models inadequate for predicting the ow behavior around wind turbine parts. CFD can be a good alternative. However, wind engineering is a relatively new part in CFD and a lot of investigations still need to be done.

Societies demand for sustainability is one of the main drivers for innovation in the wind energy industry. The increasing size of wind turbines implies increasingly flexible turbine blades. The flexibility of the blades induces the occurrence of fluid-structure interaction (FSI) phenomena. The simulation codes that are used for the design of wind turbines need to be validated with observational data. In the current research a FSI experiment of a wing equipped with a trailing edge flap is performed to provide validation data. Little data is available in literature of free motion FSI experiments. Therefore, a FSI experiment is performed with a freely moving wing equipped with a trailing edge flap.

Although wide range of studies have been performed on the principles of flapping
flight, only recently the influence of flexibility on flapping flight and in particular
the influence of flexibility on the performance of the ’clap-and-peel’ motion have
been performed. In this thesis new methods and higher Reynolds number flows are
used together with experimentally obtained deforming wing shapes of the DelFLy
II to determine the influence of flexibility on the aerodynamics both in single wing
flight and in the ’clap-and-peel’ motion during hovering conditions.

In 2005 the Energy research Centre of the Netherlands (ECN) published its first version of the Offshore Wind Atlas of the Dutch part of the North Sea [3]. This version has been updated and improved using longer time series and another approach for the calculation of the roughness of the sea surface. In contradiction to other Wind Atlases which are based on measurements [28], use is made of data from the Numerical Weather Prediction model Hirlam. Measurements of wind speeds and directions are only used to validate the Wind Atlas. For the Offshore Wind Atlas, the Hirlam data is interpolated where for the vertically interpolation use is made of the Businger-Dyer profiles in combination with the Monin-Obukhov length [3]. One of the required parameters for the interpolation is the surface roughness. For land, it can be assumed constant while for sea it is variable. In the previous version of the Offshore Wind Atlas, the sea surface roughness has been determined using Charnock’s relation [9], where the so-called Charnock parameter is constant. In the new version, the equation of Hsu is introduced which states that the Charnock parameter is variable and dependent on the wave steepness i.e. the wave height divided by the wave length [19]. Assuming that the North Sea is a shallow sea and using the general wave equation, which relates the sea depth and wave length to the phase velocity of the waves, it was found that the wave steepness can be rewritten in a fraction of the wave height over the wave period multiplied by the square root of the sea depth times the gravitational acceleration. These quantities are derived from measured values which are interpolated to the location of interest. Using this approach, it is tried to improve the prediction of the wind speed distributions for a given location and altitude. Using wind measurements at several locations it was found that adding the wave data to the computations show a small improvement in the estimation of the wind speed distribution compared to the previous version of the Offshore Wind Atlas. For each measurement location and method, a two parameter Weibull distribution has been made, after which a comparison was done between the various shape and scale parameters. Generally, the scale parameter was overestimated by both versions of the Offshore Wind Atlas compared to the measurements. The cause of this behavior might be found in the data used to make the Atlas. The shape parameter is well predicted by the new version of the Offshore Wind Atlas due to the use of wave data. The influence of the wave data is found to be larger for lower altitudes than for higher altitudes. Besides Weibull distributions, also maps with average wind speeds are given by the Offshore Wind Atlas which are compared to older maps.

Despite advances in computational power and numerical algorithms, efficiency and stability issues remain in the simulation of very strongly coupled Fluid Structure Interaction problems. These problems are typically solved with partitioned solution techniques. To improve the coupling of these solvers, Quasi-Newton methods are used. The Aitken method calculates an average underrelaxation parameter for the entire interface. The Least-Squares method calculates an underrelaxation matrix as a linear combination of states and residuals of previous iterations. Another method to improve the e_ciency of strongly coupled problems is multi-level acceleration. The computational workload is reduced when iterations are done on a coarser grid.