In the context of damage tolerance for aeronautical structures, substantial research has focused on simulating skin-stiffener separation in stiffened composite panels. This separation is marked by unstable crack growth at the skin-stiffener interface, which can lead to structural collapse in the post-buckled regime. Recent post-buckling tests on thermoplastic butt-joint single stiffener panels indicate the development of delamination within the skin before crack propagation occurs at the skin-stiffener interface. This delamination is likely triggered by the crack extension process prior to the buckling tests, where the skin was subjected to out-of-plane loads away from the stiffener, promoting the extension of the artificial crack at the interface. It has been hypothesized that this delamination results from crack migration from the skin-stiffener interface into the ply interfaces within the skin. Crack migration, which involves complex interactions between delamination and matrix cracks, is crucial for improving numerical models. For accurate prediction, these models must capture both matrix crack and delamination interactions.

Cohesive zone models, in conjunction with the eXtended Finite Element Method (XFEM) and cohesive elements (CE), have been employed in literature to model the interaction between matrix cracks and delamination. While previous approaches often enrich cohesive elements using user subroutines, this thesis aims to leverage ABAQUS's built-in methods to model crack migration. A series of migration test simulations were conducted to evaluate the combined XFEM and CE approach. The LaRC05 failure criterion in ABAQUS was applied to initiate inclined matrix cracks within the plies, while delamination was modeled with standard 8-node linear cohesive elements. A three-dimensional mesoscale model of the test specimen was developed to simulate the migration test. The LaRC05 criterion successfully captured the orientation changes in matrix cracks due to changes in shear stress, consistent with experimental results. However, the predicted migration distance was 2-3 times greater than observed experimentally. A parametric study revealed that lower matrix strength and fracture energy facilitated migration, although increasing these parameters did not result in a consistent delay in migration, with discrepancies arising at higher values. Despite this, the methodology demonstrated the ability to predict crack migration tendencies and is considered suitable for structural-level applications.

Simulations of the butt-joint thermoplastic skin-stiffener panel under bending were also performed using a global-local modeling approach. The 19-ply skin was meshed with shell elements, while the local model explicitly represented the outer two plies (45/-45) with solid elements and the remaining 17 plies with shell elements. Three modeling approaches were explored: (i) damage only at the skin-stiffener interface, (ii) damage at both the skin-stiffener and ply interfaces (global-local model), and (iii) matrix cracks combined with delamination at both interfaces (global-local model). The first two approaches predicted mode I crack extension at the skin-stiffener interface, with no interlaminar damage in the second approach. However, the third approach using XFEM-CE predicted significant matrix cracking in the outer ply beneath the filler material, which further initiated delamination at the 45/-45 interface. This method successfully predicted delamination migration in the stiffened panel, demonstrating its capability to capture complex damage interactions at the structural level.

Pushing the envelope of aerospace structures requires the complete exploitation of their potential in terms of load-carrying capacity per unit weight for both economic and ecological reasons: the two most important being the reduction of fuel consumption and greenhouse gas emissions. A key approach involves allowing structures like stiffened panels to function within the post-buckling range domain while in service. To do so, the finite element approach allows a broad design space for researching the post-buckling behaviour of such structures.

Accurately representing post-buckling behaviour in finite element models requires accounting for geometric and loading imperfections. The present study explores their effects on the post-buckling behaviour of a composite L-stiffened panel. A finite element model is created and validated based on an experimental case. This is then further modified to incorporate imperfections. Geometric imperfections are modelled using linear eigenvalue modes, while loading imperfections are introduced via a rigid loading plate making contact at an angle.

The research showed that both first and higher eigenmode combinations for geometric imperfections influence post-buckling behaviour. Their shape and amplitude impact the transition into post-buckling and their ultimate loads. Similar behaviour was also observed for loading imperfections. Additionally, their configuration also showed an offset in axial displacement results. These insights emphasise the need for precise imperfection modelling to promote safer and more efficient post-buckling design of aerospace structures.

Fiber-reinforced composite (FRC) marine propellers potentially outperform metallic propellers in terms of efficiency and underwater radiated noise (URN) by hydro-elastic tailoring of the blades. Several methods can assess the extent of these potentials. Research shows that embedded sensing methods can be used in dynamic measurements of composites. This thesis studies a full-scale application of a network of embedded piezoelectric sensors in an FRC marine propeller blade. The study prefers using piezoelectric sensors because of their ability to operate in a relatively wide frequency range. The focus of the thesis starts with designing the full-scale network of embedded piezoelectric sensors. Since no literature includes this application on FRC blades, this study holds a pioneering role in embedding piezoelectric sensors in an FRC marine propeller blade. Detailed analysis of material dimensions - including sensors, wiring, and fiber plies - leads to a successful sensor network design. Considerations regarding the location of 24 sensors included both the in-plane and the in-depth position within the FRC laminate. Fabrication of an FRC blade has been done using a resin transfer moulding (RTM) process. For the first time, an FRC marine propeller blade is embedded with piezoelectric sensors. Demoulding of the blade caused damage to some of the sensor wires. An amount of 54% of the embedded sensors survived the process with full connectivity. The performance of the intact sensors after fabrication is assessed. These sensors are exposed to free vibration tests of the FRC blade. An excitation is imposed on the blade with an impact hammer. A data acquisition (DAQ) system is used to capture the responses of the embedded piezo-sensors. The frequency response functions (FRFs) of multiple locations on the blade are computed. These FRFs provide more insight into the dynamic behavior of the blade. A frequency range of 1-1000Hz is used in the modal analysis. The first five natural frequencies are found between 240Hz and 840Hz. Natural frequencies measured by the embedded piezo-sensors and surface-mounted strain gauges differ up until 25% from natural frequencies computed by a finite element model (FEM) of the blade. The mode shape of the blade at the natural frequencies is computed for by the FEM and embedded piezo-sensors. Some difference in mode shapes is demonstrated between measurements computed by FEM and those measured by the embedded piezo-sensors and surface-mounted strain gauges. The piezo-sensors and strain gauges are in agreement regarding the measured natural frequencies. Therefore, it is expected that discrepancies exist between the physical blade and FEM. Several points for improvement of the results have been found. The study provides the first-time feasibility of dynamic measurements from embedded piezo-sensors in an FRC marine propeller blade. Additionally, a framework for reconstructing the full-field vibration response is provided, which can provide more accurate results when the agreement between piezo-sensor and FEM measurements has improved.

Wind energy is a growing industry, and in an effort to reduce costs and increase turbine efficiency, rotor blades are becoming increasingly large in size. To facilitate this effort, the SmartBlades2 research project has designed, built, and tested a set of prototype research blades. As part of the SmartBlades2 project, high sensor density modal testing has been conducted on the research blades. The analysis of the modal tests showed good agreement of the global vibration modes with the finite element model predictions. However, the test analysis also identified low frequency vibration modes, referred to as breathing modes, which were not predicted by the finite element models. These vibration modes were found on all of the blades and are characterised by out-of-plane trailing edge panel motion. The objective of this thesis is to identify and predict the aforementioned breathing modes using finite element analysis. To achieve this, three model characteristics are analysed to determine their influence on the breathing mode prediction, namely, model topology, shell element configuration, and material properties. To characterise the affect of model topology, a cut section from the SmartBlades2 prototype blade is modelled with shell elements and continuum element glue joints. To validate the blade section model, a modal test is conducted which identifies breathing modes analogous to the full blade. Various topology features are investigated with the focus on the shell glue joints and spar web joints of the blade section. The analysis shows that while these changes significantly effect the mode shapes and frequencies, none of them predict the experimentally identified breathing modes. To investigate the source of this discrepancy, the modal behaviour of a sample plate structure with the same materials is used to remove the variability of topology. The effects of shell element size and configuration are analysed with mutual comparisons. The analysis shows that higher fidelity element configurations offer no advantage over linear shell elements for prediction of modal behaviour, while the element size shows higher sensitivity. Furthermore, the effects of material properties are examined using the sample plate, subject to modal and flexural tests. It is found that the specified properties are stiffer than measured, and new predictions of the properties are made which better fit the plates experimental results. Finally, the topology, element, and material investigations are then applied to an improved finite element model of the complete blade and correlated with the experimental modal tests. It is found that the improved blade model has closer correlation with the experimental modal tests for global modes, however is unable to predict the identified breathing modes for the blade. It is hypothesised that cause of this may relate to the connection of the spar web with the glue flanges.

The current generation of commercial aircrafts extensively use composite materials such as Carbon Fibre Reinforced Polymers (CFRP) in both exposed and primary structures. These materials lack through-thickness reinforcement and are hence susceptible to out-of-plane impact damages. Barely visible impact damage caused by low energy impacts poses a unique problem, since delaminations, de-bonding and cracking may be present below the surface layers without any indication of damage on the surface. The focus of this research is on one such scenario, multiple site low energy hail impacts, while the aircraft is on the ground. Taking into account the relevant parameters, a hail impact envelope was established both in terms of the initial kinetic energy and peak impact force. Further, contradictions found in literature over the influence of the compressive strength of hailstones were resolved. These were accomplished with the aid of a state-of-the-art finite element model and experiments in the laboratory. With help from a custom designed and assembled impact force measurement experimental setup a relation was established between impacts carried out with steel impactors and those with simulated hail ice impactors. Based on this relation, predictions are made on which hailstones have the potential to cause damages to CFRP structures.

Predicting the critical buckling load of cylindrical shells with circular cutouts subjected to uniform axial compression is an important part of the structural design in the aerospace industry as buckling significantly reduces the load-carrying capability of the structure. A cutout constitutes a major disruption in the shell geometry, and therefore it should be expected that it has a significant effect on the sustainable buckling load. An analytical solution for estimating the buckling load of isotropic and quasi-isotropic composite cylindrical shells with circular cutouts is developed to assess changes made to the geometry and the material during the preliminary design phase quickly. The Ritz method is employed to minimize the total potential energy of an ideal shell that contains a central opening in order to predict a linear buckling load. Finite element simulations are conducted to verify the accuracy of the analytical solution. In addition, they are used to investigate the evolution of buckling modes, the effects of initial geometric imperfections, as well as the shell failure mode. The nondimensional curvature parameter α can be used to categorize the buckling behavior of cylindrical shells and is a function of the cutout radius, the shell radius, and the shell thickness. A small cutout has virtually no influence on the buckling load compared to a pristine shell and the displacement pattern at buckling is global. The buckling load decreases rapidly for moderately large cutouts where the stability loss is the result of a local buckling mode that immediately leads to global buckling. Cylindrical shells with large cutouts are again relatively insensitive to an increase of the cutout size, but the buckling load is greatly reduced relative to a shell without a cutout. Large openings also feature a stable local buckling mode where substantial lateral prebuckling displacements emerge before the structure buckles globally. While the analytical procedure theoretically should not capture the onset of global buckling independent of local buckling, it follows numerical trends for cutouts of moderate and large size regardless. Therefore, it may be used during preliminary design to estimate the impact of changes made to the shell geometry and material. Local buckling is caused by high compressive stresses next to the cutout and, in some cases, large lateral prebuckling displacements. The detrimental effect of the stress field may be partially relieved in composite cylindrical shells by reducing the amount of axial bending stresses that occur. Hence, the chosen stacking sequence can have a significant influence on the buckling load of shells with moderate and large openings.

The safety of offshore assets such as wind turbines, offshore cranes, and turret mooring systems partly relies on the integrity of heavy-duty bolted joints. These critical connections can be of different dimensions and exposed to monotonic and cyclic loading. Despite being small components of a structure, bolts need to be maintained appropriately to ensure structural safety and reliability. The integrity of bolted joints can be assured by checking for adequate preload. In addition, fatigue failure resulting from preload loss is of primary concern, as it can occur suddenly without any visible changes. Hence, bolts should be re-tightened periodically to ensure sufficient preload. However, in offshore conditions, this countermeasure leads to high maintenance costs while exposing the crew to unfavourable conditions and risks.

This research focuses on the feasibility of condition-based maintenance of bolts using ultrasonic waves. An energy attenuation method has been implemented for this feasibility research. The main objective is to establish a proper methodology and hypotheses for preload detection. Furthermore, along with preload detection, the feasibility of crack detection was investigated. Finally, the proposed methodology and hypotheses were validated by performing experiments and numerical simulations.

The experimental and numerical results verify the proposed methodology by showing an increasing trend in the energy and the power of the transmitted ultrasonic wave for increasing preload. Also, the feasibility of crack detection using the same setup has been positively evaluated.

The obtained results suggest that the ultrasonic waves can be employed to monitor bolts for condition-based maintenance. Additionally, a number of relevant research activities are recommended based on this study.

Due to an exponential growth in the number of shipments of Unmanned Aerial Systems (UAS), the amount of these devices operating in the sky has increased remarkably over the last few years. This led to an increasing number of proximity incidents with manned aircraft. Since these devices share certain airspace with rotorcraft, the question arises how much damage a helicopter could sustain after an impact with a UAS. Within this thesis, a risk assessment was completed initially to determine which collision in terms of type of UAS and helicopter impact location poses the highest risk to the operator of the helicopter. Subsequently a validated model of a DJI Phantom III was developed and impacted onto a rotorcraft windshield in explicit Finite Element software. The sustained damage was compared with a simulated bird strike event to determine whether the prevailing certification requirements would suffice to guarantee safety of the crew.

Type IV composite pressure vessels (CPVs) are used commercially for the gaseous storage of hydrogen in fuel cell electric vehicles (FCEVs). However, their economic implementation requires material optimization and a reliable prediction of the vessel strength. In this regard, their burst when loaded under internal pressure is impacted by the combined effect of the stacking sequence design and the variability of mechanical properties resulting from the manufacturing process. This work shows a framework for analysis that accounts for some of these manufacturing-induced characteristics in the mechanical response, namely the relation between the vessel stacking sequence, its final geometry, and the material properties. Furthermore, vessel burst pressures are alternatively estimated from the failure criteria evaluation in constitutively elastic analyses and the modeling of damage progression. Predictions are reasonably accurate when the collapse occurs in the cylinder (+2.2 %), although a more considerable discrepancy exists with experimental results when vessels fail in the dome transition region (+12.3 %).

Strain rate, how fast a material is strained, is known to have an effect on the behaviour of metals. Being able to measure the effect of strain rate in a material provides more reliable material data as input for material models. Strain rates up to 10 per second can be tested using a (fast) hydraulic testing machine. Strain rates upwards from 500 per second can be tested using a Split-Hopkinson bar, but for the strain rates in between no such standard method is available. The goal of this thesis is to provide a design guide for a reliable experiment that measures the effect of strain rate, in the range 10-100 per second, on the tensile stress-strain curve of a metal. The test method proposed in this thesis consists of two parts. The first part is a test using a universal testing machine to determine material behaviour at low strain rates of 0.001-10 per second. A regular dogbone specimen with a longer grip section is used for the UTM tests, which provides the material data to design specimens for the second part. The second part is an impact test where a drophead impacts a specimen, causing it to strain. The specimens are U-shaped strips with a dogbone at either side to test material behaviour at higher strain rates of 10-100 per second. For both tests, strains are recorded in the grip and gauge sections by means of a DIC system. The main advantages of the proposed test method are (i) that no sensors are required in the drophead as the load is extracted from strain measurements in the linear elastic grip section, while the gauge section is allowed to deform plastically and (ii) by using DIC, unobtrusive measurements are taken of the strain field in the recorded area. Two analytical models have been developed, one for the universal testing machine tests and one for the impact tests. The analytical models for the UTM tests and the impact tests have been compared to a finite element model of the same specimen. When plastic strain in the gauge section becomes the most dominant component of the strain, both analytical and FE strain curves show good agreement. Numerical simulations of the impact test have been done by means of an explicit, dynamic, non-linear impact simulation using finite element analysis. A parametric study has been done using the FE model to determine the effect of drophead mass, impact velocity and specimen dimensions on the strain rate in the gauge section and the measurement accuracy. Based on the results of this study, a guideline is presented for performing the experiment. In conclusion, a novel test method and corresponding guideline to determine the stress-strain curve of metals at intermediate strain rates in the range of 10-100 per second has been presented and demonstrated by means of numerical simulations. As a future step, a set of experiments should be performed to prove the validity of the proposed test method.

A new certification approach for bonded primary Fiber Metal Laminate (FML) structures is investigated: using bolts as Disbond Arrest Features (DAF)s to contain the growth of bond line damages so that they can be found and repaired by inspection before becoming critical. By fatigue testing with coupon specimens and model analysis, it has been demonstrated that reducing the Mode I Strain Energy Release Rate (SERR) is the main driver for arrest. The peak stress associated with a disbond front can initiate adherend fatigue cracks during slow growth. The effect of adherend fatigue cracks on the arrest of disbond growth could not be determined and must be investigated in future work. In the process, a novel quasi-analytical disbond growth model has been developed and validated. An algorithm is developed and verified that utilizes the strain field measured by Digital Image Correlation (DIC) to locate the disbonded region.

This paper is a representation of the research that has been performed with regards of the weight estimation of the Flying V and its conventional reference aircraft. The goal is to establish the feasibility of the Flying V as a structural concept. In order to do this a structural model of the Flying V has been created, as well as the design and structural model of a conventional reference aircraft. This paper will cover every step required to design and analyze both models, while at the same time making sure that both models can be compared to each other. By implementing a chain of 6 software packages both models started at parametric conceptual design and were developed to the point where they have been analyzed using the finite element method to obtain the (FEM) structural mass. Chapter 2 gives an overview of the entire process. Both the set-up of the thesis and its process flow are discussed here, as well as a detailed goal statement. In Chapter 3 the design mission was established. In addition, the design requirements are mentioned as well. Both the requirements and mission are the same for both aircraft. Chapter 4 describes conceptual design of the reference aircraft. Herein the used assumptions were stated and explained, and the resulting graphical and parametric model was shared. Chapter 5 does the same for the Flying V. Chapter 6 explains how the graphical models were appended in order to obtain a full three dimensional model, ready for the analysis. It was explained how ZORRO-X was applied to do this, and manual corrections were discussed as well. The loading of the models is described in Chapter 7, it describes how ODILILA was implemented to obtain the different aerodynamic loads. Ground loads and mass distributions were obtained in this chapter as well. From this, the initial C.G. ranges were established. Load cases were build up by combining aero, mass and ground loads. In total 22 load cases were used during the sizing optimization. The FEM optimization was initiated in Chapter 8. This was done by mapping the aforementioned loads and setting the design criteria and constraints. Finally, the results are summarized in Chapter 9. The results include the analysis of critical load cases, critical design constraint, thicknesses and displacements of both the Flying V and the reference aircraft. It was found that while the Flying V still has some structural problems at the kink and nose-fuselage intersection, the overall FEM mass of the Flying V is still lighter than that of the conventional reference aircraft. It is expected that the proposed solutions for the structural problems will not influence the mass to such an extent that this is no longer the case. Therefore, the conclusion, stated in Chapter 10, is that the Flying V is indeed a viable structural concept. Based on current results it is expected that after further development proposed in Chapter 11, the Flying V might even prove not only viable but even desirable compared to conventional aircraft.

A buckling analysis and imperfection sensitivity study of scaled launch-vehicle cylindrical shells have been executed. The emphasis is on scaled cylindrical shells due to the expensive nature of full scale launch-vehicle cylindrical shells and the size constraints of experimental testing equipment. The work as presented in this thesis is part of a framework of a collaboration with NASA Langley. The main objective was to investigate if a scaling method, which is developed as part of this afore mentioned collaboration, results in representative scaled cylindrical composite shells. These scaled cylindrical composite shells will be validated by experimental tests at NASA Langley. The scaling of structures can be a challenging process, as a scaled model which shows full scale representative behaviour is difficult to design due to constraints such as manufacturability. The buckling of cylindrical shells is considered to be a structural problem which is yet to be fully understood. The cylindrical shells show a high imperfection sensitivity, but the exact influence of imperfections caused by different manufacturing processes is a source of uncertainty. The thesis will focus on two scaled cylindrical shells which resulted from the scaling method, next to the full scale CTA 8.1 cylindrical shell they are based on. The CTA 8.1 is a sandwich cylindrical shell with a honeycomb core which is designed to be representative for a launch-vehicle structure. The first scaled cylindrical shell consists of a solid laminate and the second scaled cylindrical shell consists of a sandwich with foam core. A scaled solid laminate cylindrical shell is of interest, as the core thickness of a scaled sandwich cylindrical shell can become too thin to manufacture...

Fiber-reinforcedplastic (FRP) is an upcoming material in the construction industry due tocharacteristic material properties such as its high resistance to corrosion andhigh strength to density ratio. Also, it is often claimed that structures fromFRP have lower life-cycle costs and eco burden compared to constructions madefrom steel, concrete, or wood; this can be attributed to the low amount ofrequired maintenance and longer life span of FRP. Therefore, FRP seems a verysuitable material in the harsh environments where hydraulic structures residecompared to conventional materials.

No actual commercial jetties, besidessmall pedestrian jetties, are yet constructed from FRP: knowledge regarding thepotential financial savings or the environmental impact of such jetties are notwell known. Also, specific consequences of constructing a jetty from FRP areunknown, as well the ability of FRP jetties to maintain their structuralcapabilities over their entire life-time. Therefore, this thesis investigatesthe feasibility of FRP jetties and judges whether FRP jetties are betteralternatives than jetties constructed fromtraditional materials. In the scope of this thesis, the research is narrowed down to comparing FRP withreinforce concrete (RC).

The main design challenge of FRP incivil engineering related structures is coping with the relatively lowstiffness of FRP, as this presumably determines the dimensions of thestructural elements and restrictions of the structure as a whole. Governingstructural safety criteria in steel and concrete are more often strengthrelated. The research rests on a case study of an RC jetty, which provides boundaryconditions and a program of requirements. An FRP jetty is designed whichcomplies with the structural criteria. These criteria were both extracted fromthe case study and provided by the CUR96, a Dutch design guideline for FRP incivil engineering practice. Most structural elements are designed from scratch:laminates are designed for the flanges and webs in a composite calculator namedeLamX2. The finite element method (FEM) software program SCIA Engineer is usedfor the structural analysis. One dimensional structural elements were firstvalidated before utilizing them in the FEM model. The pile properties anddimensions are based on contemporary literature and commercially availableproducts. The driveability of the FRP piles is researched by means of Wave EquationAnalysis of Piles (WEAP), for which the program AllwavePDP is utilized.Furthermore, sustainability aspects of both jetties are researched by means ofa Life Cycle Assessment (LCA). The LCA determines how much equivalentgreenhouse gases are expelled over the life-time of the jetties for a set ofimpact categories. These results are normalized by calculating the respectiveshadow costs for each impact category; this makes the total environmentalimpact of the structures comparable. The financial feasibility is the lastinvestigated topic; under various scenarios, life-cycle costs of both jettiesare investigated. The scenarios contained different variables such as estimatesof FRP raw material costs or assumed share of maintenance costs; end-of-lifecosts were not included in the analysis.

The structural analysis of the FRPjetty indicated that both Serviceability Limit State (SLS) criteria and UltimateLimit State criteria (ULS) determine the dimensions of the structural elementsand the jetty design in general. The most crucial parts are partially embeddedFRP piles, which are prone to buckling. Initially, the FRP piles in thedetailed design were to be installed to a depth of 13 meter below ground level,but the results from the WEAP indicated that the piles refused duringinstallation before reaching this level. An analysis indicated that drivingshorter piles to a depth of 8 meter is possible: at this depth, the piles donot refuse and have accumulated sufficient bearing capacity by shaft frictionto support the superstructure. The eco burden of the FRP jetty was foundsignificantly higher compared to the RC jetty: in the base case LCA, therelative difference is 365 percent higher for the FRP variant. After asensitivity analysis, the relative difference is still 59 percent higher when comparingthe best-case scenario of the FRP jetty with the worst-case scenario of the RCjetty. The RC jetty also performed better than the FRP jetty regardinglife-cycle costs in various considered scenarios. The relative difference inlife-cycle costs for the most favorable scenario of the FRP jetty is still 28 %higher compared to the life-cycle costs of the RC jetty.

Due to the poorer performance of theFRP jetty regarding the life-cycle costs and environmental burden, it isconcluded that FRP jetties, for the time being, are not better alternativesthan RC jetties. Regarding the type of jetty, the conclusion can begeneralized. The jetty is designed for the turnover of liquid bulk; imposed loadsare generally lower than loads on Ro-Ro, solid bulk, or container transfer jetties.It therefore seems unlikely that FRP does seem to be a better alternative forthose cases. Regarding the material choice, the conclusion cannot begeneralized. The FRP jetty was compared to an RC jetty. Jetties made from steelor wood are likely more vulnerable to degradation in harsh conditions. Thedurability properties of FRP might be more beneficial to the assessment of FRP jettiesin these cases. Certain future developments might affect the conclusion.Innovation in manufacturing techniques and an increase of market demand for FRPcould lower the price. Besides, biodegradable FRP materials are being developedwhich potentially may reduce the environmental burden of FRP.

 Keywords: FRP, composite design,hydraulic structures, jetty, pile driving, LCA, life-cycle costs

The main purpose of this project was the creation of a tool, based on the research performed by Scheldbergen [25] and Roscher [24], capable of performing Finite Element Analysis (FEA) on a Horizontal Axis Wind Turbine (HAWT) blade and minimize its weight by altering the various thicknesses locally, always satisfying a number of structural constraints. The first goal was the development of a geometry creation algorithm based on a Non Uniform Rational Basis Splines (NURBS) algorithm developed by Ferede [14], with a more complex spanwise/chordwise discretization technique in order to more accurately design a discretized HAWT blade. The second goal was the alteration of the material creation algorithm developed by Scheldbergen [25], so that different stacks at various blade locations can be assigned. Moreover, the aerodynamic loads generation algorithm of Scheldbergen [25] was modified to apply for different airfoils along the blade span. Also, Blade Element Momentum (BEM) theory was used for the calculation of the aerodynamic loads and the software XFOIL was used for the aerodynamic analysis of the airfoils (pressure distribution on the airfoil at corresponding angles of attack and Re numbers). An initial HAWT blade design was created, matching the SANDIA 5 MW wind turbine blade [23] geometry and materials. Furthermore, the apwise/edgewise stiffness, moments of inertia, mass and mode shapes were also validated. Additionally, the SANDIA blade was analyzed in DNV GL Bladed in order to validate the aerodynamic loads on the blade. Following, the tool was designed to process the geometry, the materials and the gravitational/ centrifugal/aerodynamic loads of the blade and translate them to an input for the FEA software MSC Nastran for Linear Static Analysis (SOL 101), Buckling Analysis (SOL 105) and Modal Analysis (SOL 103). The post processing algorithm of Scheldbergen [25] was modified to apply for a HAWT (instead of a VAWT), transforming the results of the FEA analysis into optimization constraints (ultimate load, buckling, tip deflection and fatigue). The final part of the algorithm involved the minimization of the blade's mass by altering the thickness at various locations, using the MATLAB function fmincon. Concluding, a case study of a smart rotor blade equipped with trailing edge ap (TRF) was examined. A _ 2 flap was used at 90-100% of the chord and 78-98% of the span. Two kinds of optimization were performed for the HAWT and smart rotor scenarios; one that included ultimate stress, tip deflection and fatigue constraints (UL-TD-FA) and one that also included buckling constraints (UL-BU-TD-FA). It was found that the buckling constraint was the limiting factor of the optimization and the fatigue constraint was the least dominant. The initial design of the smart rotor blade showed a 16.5% decrease of the maximum fatigue damage and a 2% decrease in the maximum stress. The optimized smart rotor blade mass was 0.5 % lower in the UL-TD-FA scenario and 2.5% in the UL-BU-TD-FA scenario compared to the HAWT blade. The tool created is capable of creating a flexible and fairly accurate representation of a HAWT and smart rotor blade. It also provides the ability to structurally analyze the blade under the most significant structural criteria and minimize the blade's weight under specific loading conditions. The tool constitutes a good starting point for more detailed structural analysis of smart rotors and more complex structural optimization of HAWT and smart rotor blades.