The high strength/stiffness-to-weight ratio that composite materials exhibit has led to the utilization of composites as alternative to traditional materials in weight-critical applications. However, the highly anisotropic nature of composites renders the strength prediction under complex loading challenging. To efficiently predict the failure of composite structures especially in cases where out-of-plane stresses are dominant, the modeling of damage onset and propagation plays an essential role in accurate strength predictions.Firstly, in this Thesis work the analysis of a composite L-profile, which is loaded such that significant out-of-plane stresses are generated in the curved region, is conducted. However, the inherent heterogeneity at the micro/meso scale is not modeled for the stress analysis.Secondly, in this project the target was to accurately predict the initiation of failure at the ply level, modal based Puck’s matrix failure criteria have been implemented to the failure analysis. Maximum stress failure criteria were however retained to check the possible fiber-based failure which is not directly captured with in Puck’s failure criterion.Thirdly, Cohesive Zone Material Model has also been employed to model the growth of interlaminar damage (delamination). The delamination study is based on the Inter Fibre Fracture crack initiation and doesn’t include other causes like edge effects, voids, manufacturing defects etc.Finally, the attempt to validate the analysis results with the available test results was made. Further development of the existing model and several tests are required to be carried out for material characterization and complete validation of the developed damage model for composite structure.

This is the report of a master thesis in light weight design of a component in a system that harnesses wind power with a kite. The thesis is a degree project in Naval Architecture at KTH with the course code SD271X. The design work is mostly of a structural nature, but systems engineering, and conceptual design is also a major part of thestudy. The first part introduces the problem where the client, SkySails Power GmbH, is looking to design a new control pod for a system that carries 3 times the load as a previous design. The thesis is limited to the design of the load bearing chassis of the pod, but because at the time the other sub systems or components have not yetbeen designed, the study includes concept design of the entire pod system. The flight pattern and load cases of the kite are studied to get the right understanding of the forces that affect the system. The goal is to design achassis that is as affordable, light weight, and as strong as needed for the task.The requirements of the design problem are decided by the master student and the client together after a prestudy was made but they had minor changes further along the design process. It is a real life, organic iterative design process that has a goal from the start to use the opportunity of an outsider to reconsider the design of akey component of the client’s product.The result is a chassis design that is cheaper to produce and weighs less than if the old chassis would be linearly scaled up with the loads. This design has the same concept as the last but with a couple of modifications concerning some attachments to the rest of the system. The requirement of maintaining all previous functionsis achieved. A significant part of the thesis was to determine the boundaries between the areas of where FEM modelling is applicable and where hand calculations estimations are necessary. The results from this work will be used to build a prototype of the chassis, test it in a tensile testing machine, and finally integrate it into theentire system and flown. / I en värld som hotas av klimatförändringar på grund av utsläppen av fossila bränslen i atmosfären, men där människorna som befolkar den har ett stort behov av energi för sin livsstil finns det ett behov av alternativa källor och metoder till att utvinna den. Ett relativt nytt och hållbart sätt till detta är kite-baserad vindkraft. Mananvänder sig av en skärm eller drake, lite som en fallskärm fast i större storlek, som är kopplad med en vajer till en bas-station där vajern rullas upp på en trumma. Skärmen fungerar som en vinge och skapar ett lyft när den flyger i kors-vind och rullar ut vajern på trumman som fungerar samtidigt som en elektrisk generator. Alternativtlåter man skärmen ha ett konstant avstånd och har bas-stationen installerad på ett fartyg och använder lyftet från skärmen till att driva fram fartyget.Ett av företagen som arbetar med att få denna teknik lönsammare än konventionell vindkraft i vissa väder och geografiska lägen är SkySails som gav i uppdrag som examensarbete att utveckla en ny modell av chassit till styrenheten till sitt kite-system. Styrenhetens ligger mellan skärmen och vajern och har som huvudfunktion attstyra draken som görs med en mindre elektrisk motor och ett tandat bälte. Dessutom innehåller styrenheten mycket elektronik och sensorer vilket gör utvecklingen till ett komplext problem. Studentens två huvuduppgifter var göra en konceptuell utvecklingsstudie av hela styrenheten och att utveckla ett chassi, till ett stadie att dengår att tillverka från ritningar, för det mest framgångsrika konceptet. Chassit måste tåla hela skärmens laster och kosta och väga så lite som möjligt.Designprocessen var iterativ med ett systemingenjörsmässigt angreppssätt. Första delen av tiden ägnades åt att studera den befintliga styrenheten och lära sig om hela kite-teknologin. Sedan sattes tydligare och mätbara mål och specifikationer tillsammans med uppdragsgivaren. Därefter började den kreativa fasen och skissa fram bådekonventionella och okonventionella koncept för hela styrenheten. De tre mest lovande koncepten utvärderades mot de tidigare satta kriterierna så kvantifierbart som möjligt och det visade sig att det koncept som hade används var fortfarande det bästa. Sista fasen av arbetet var att sätta gränssnittet för chassit i detta koncept ochdesigna chassit så lätt som möjligt.Resultatet blev ett liknande chassi jämfört med vad det var innan men med en vikt som var lägre än om det förra chassit hade ökat sin vikt lika mycket som lastökningen. Kostnaden för chassitillverkningen gick ner i absoluta termen på grund av byte av material och tillverkningsmetod. Av detta kan man påstå att examensarbetet varframgångsrikt och nådde sina mål. Däremot måste en prototyp tillverkas testas i för att fastställa att modellerna som tog fram designen motsvarar verkligheten. Dessutom måste de andra komponenterna tillverkas i för att hela styrenheten kunna testas så som den är avsedd att användas. Chassit och styrenheten är bara ett steg på vägentill en hållbarare värld men metoderna som användes kan återanvändas.

This thesis presents a systematic approach to solving the problem of large deflections in the ZBee vehicle, proposing feasible insert solutions while reducing weight and increasing efficiency were possible.An experimental study was done on the structural deformations of a sample ZBee floor using highly advanced measuring instruments. Based on this background a finite element model was developed which simulates the experiment to a good level of correlation. Modifications were then carried out on the model to examine different factors which affect the stiffness and hence deflections experienced by the driver. Based on a systematic selection of alternative solution an insert analysis was done which gives initial design parameters for a new insert implementation.To improve the manufacturability and hence cost of the Zbee floor, a new floor design with simpler geometry was analyzed and further developed based on the stiffness properties studied on the old chassis. / ZBee är ett trehjuligt fordon utformat för att transportera tre personer inklusive föraren. Det är helt elektriskt och nästan helt byggt med kompositmaterial för att möta behovet av lättvikt och energibesparing.I det här arbetet analyseras och föreslås lösningar för ökad strukturell styvhet och insatslösning i fordonets komposit chassi. En alternativ geometri utformad för att minska komplexiteten och därför förenkla produktionen analyseras också och modifieringar föreslås.Den första steget studerar ett existerande provgolv med hjälp av högspecialiserade mätinstrument. Syftet var att studera deformationerna i strukturen vid en given belastning.Baserat på resultaten från strukturprovningarna utvecklades en finit element modell med motsvarande belastningar och gränsvillkor. Flera iterationer utfördes med varierande material, tjocklekar och struktur modifiering. Resultatet av detta var ett optimalt lösning för ett styvare och lättare fordonschassi.Med hjälp av det befintliga golvet som standard bedömdes alternativa geometrin för styvhet och rekommendationer för en bättre struktur, vilket fortfarande bevarar enkelheten i designen föreslogs.En lokaliserad studie utfördes sedan i framhjuls sektion vilket resulterade i utformningen av en genomförbar insatslösning för fastsättning av kompositstrukturen på framgaffeln och styrsystemet.Slutligen gjordes rekommendationer för ytterligare arbete för att tid och resurser inte kunde möjliggöra fortsatt arbete inom denna exjobb.

This report describes the structural design of a wing for a Vertical Take Off  and Landing drone, in which all the structure will be built by fused deposition modeling of polylactic acid (PLA). To perform this de-sign, the material used is first characterized in different orientations using tensile stress tests, Image Correlation and MATLAB. These properties are then input in a MATLAB program specially developed for this project to obtain the optimum skin and spar thickness in the wing for certain fight conditions. Results are finally verified with a 3D model in CAD and scaled wings in bending tests.

The lighter an object is the easier it is to send into space. This principle is what drives the never ending hunt for lighter structures in the space industry. One way to reduce weight is to replace existing materials with lighter ones. Polymer matrix composites are such materials, as their density is lower than both steel and aluminium. The company RUAG Space produces a payload separating system that operates by clamping the payload using a clamp band to the rocket and releasing the payload by releasing the tension in the band. The current band is made in aluminium but RUAG seeks to build them using carbon fiber reinforced epoxy instead. Earlier projects have shown that carbon fiber fulfills the basic requirements, but has insufficient bearing strength to handle the loads at the bolted joints to the release mechanism. Research suggests that making the individual layers of carbon fiber thinner will increase the bearing strength and so in this project test specimen have been manufactured using thick and thin carbon fiber layers. These specimen were then subjected to bearing loads and the response was observed. The result showed that the ultimate bearing strength only increased a small amount with thin plies, but the onset of damage came at 47% higher stress levels compared to thick plies, suggesting a more brittle behavior. Since the onset of damage is the most important factor for RUAG the use of thin plies produced very positive results and could be a viable solution to increase the bearing strength in the clamp band. / Inom rymdindustrin är vikten på olika komponenter en väldigt viktig egenskap, i och med att det är lättare att skjuta upp en lätt produkt i rymden än en tung. På grund av detta finns det en konstantsträvan inom industrin att bygga lättare uppskjutningsriggar. Ett sätt att minska vikten är att använda lättare konstruktionsmaterial. Polymera fiberkompositer är sådana material, de har mekaniska egenskaper som är ungefär lika bra som hos metaller, men har lägre densitet. RUAG Space tillverkar ett klampförband som håller fast nyttolasten vid det sista raketsteget under en uppskjutning. Detta band är tillverkat i aluminium, men det finns intresse av att tillverka det i kolfiberförstärkt epoxy. Tidigare projekt har visat att kolfiberepoxy uppfyller de globala kraven på styrka och styvhet, men att hålkantsstyrkan är otillräcklig vid de skruvförband som finns i släppmekanismen. Forskning tyder på att hålkantsstyrkan kan ökas för kompositmaterial om de individuella lagren i laminatet görs tunnare. I det här projektet tillverkades laminat av tunna och tjocka kolfiberskikt. Av dessa laminat tillverkades provstavar som sedan blev utsatta för hålkantslast. Resultatet från dessa tester visade att provstavarna med tunna skikt kunde utsättas för 47% högre last än de med tjocka skikt innan skada började uppstå. Med detta resultat drogs slutsatsen att kolfiber med tunna skikt är en möjlig ersättare till aluminium i klampförbandet.

Two different numerical tools were considered, the first one is a seakeeping method developed by KTH Ship Dynamics Research Program. It utilizes strip theory and Lewis forms and is further addressed as SMS. The second one, Nemoh is an open source code utilizing three-dimensional panel method for calculating first order hydrodynamic coefficients in the frequency domain.A comprehensive revision of Nemoh and SMS has been performed on behalf of the KTH Ship Dynamics Research Program. The background to the revision was the high interest in accurately capturing a ships dynamic response. The aim was to explore the prospect of making use of the open source code Nemoh for modelling of added mass and damping in terms of modelling, computational efforts and ship motion prediction improvements. Further, the thesis includes a well-described method on how to operate and pre-process data for Nemoh together with a validation study including results from commercial software´s and experimental studies. An approach with the aim to capture the speed-dependency of the hydrodynamic coefficients together with further potential development of Nemoh is addressed.The validation of Nemoh is showing diverse result. For two cases, the Response Amplitude in Heave is insufficiently modelled. In consequence it’s stated that further studies are required in order to establish whether it’s the case of inadequate input from the authors’ side or lack of robustness in Nemoh that is the cause. The approach to capture speed effects in the hydrodynamic coefficients is proven to be fairly accurate and is considered to be of further use for future development of Nemoh.With respect to identified computational efforts, it’s concluded that Nemoh requires much more computational time than SMS while the accuracy of result is lower. No major improvements may therefore be achieved by substituting or implementing parts of Nemoh into SMS. Nemoh is however of use for the KTH Ship Dynamics Research Program and of other users of Lewis Method when establishing whether a hull-geometry is considered to be “too” unconventional for a two-parameter mapping technique or not. The capability to calculate the RAO in surge is also of interest for KTH Ship Dynamics Research Program since it’s not a feature in SMS.

This Master Thesis is about the assessment of the seakeeping performance of different ships subjected to hull parametric variations. The latest version of the potential flow CFD software Shipflow in combination with a CAD platform (CAESES) have been used to carry out the evaluations. Two ships are studied: a simple one that can be mathematically defined, the Wigley hull, and the KVLCC2, a realistic oil tanker. The software is validated, comparing it to experimental results and other CFD solvers, showing a good agreement with the rest of the data; the mesh dependence studies also show only small variations between the used meshes and finer ones. Then, first the performance in calm water is evaluated for both ships by looking at the wave resistance. With the results of the original hulls as a reference, they are parametrically modified in different ways and evaluated as well to see which trends lead to an improved resistance. With the parametrization applied in the Wigley hull big changes can be appreciated, as the variation in wave resistance due to different parametric modifications ranges between -6% and 14%. For the KVLCC2, two different parametrizations are tested. The first one, focusing mainly on the bulb, produces changes that are generally smaller than for the Wigley hull, especially the ones due to bulb modifications; and the negative effects over the wave resistance due to variations affecting the general shape of the hull are larger than the positive effects. The second parametrization mimics the one used for the Wigley hull, focusing on the general forebody: the results obtained with this approach are very similar to the ones of the Wigley hull, also reaching wave resistance reductions of about a 6%. After that, the evaluation is moved to the ships in regular head waves, where the added resistance due to waves is studied; in a range of wavelengths going from 30% to a 200% of the length of the ship for the Wigley hull, while the study of the KVLCC2 is focused around the wavelength where the resistance is higher, at a 120% of the ship’s length and extending to 100% and 140%. Here the differences of the effect a same parametric variation has over the resistance in calm water and waves are assessed. The results of the Wigley hull show many interesting facts: some of the parametrically modified designs that performed worse in calm water have a consistent better behaviour at the wavelengths analysed; while the best designs in calm water exhibit both large positive and negative added resistance variations depending on the wavelength observed. The first KVLCC2 parametrization approach presents again smaller deviations in resistance, frequently even minor than in calm water; despite that, most of the parametric variations that worked well in calm water display also a reduction of added resistance in waves. On the other hand, the results obtained with the second parametrization of the KVLCC2 show the same trends and behaviour as for the Wigley hull.

This study is evaluating Solid-Acoustic Finite Element modelling as a method for calculating structural vibration response in water. When designing for example vehicles, it is important to avoid vibrational resonance in any part of the structure, as this causes additional noise and reduced lifespan. It is known that vibration response can be affected by the surrounding medium, i.e. water for marine applications.Previous studies show that this effect is both material and geometry dependant why it is hard to apply standardised design rules. An alternative approach is direct calculation using full Fluid Structure Interaction (FSI) by Computational Fluid Dynamics (CFD) and Finite Element Methods (FEM) which is a powerful but slow and computationally costly method.Therefore, there exists a need for a faster and more efficient calculation method to predict how structures subjected to dynamic loads will respond when submerged in water. By modelling water as an acoustic medium, viscous effects are neglected and calculation time can be drastically reduced. Such an approximation is a linearization of the problem and can be suitable when all deformations are assumed to be small and there are no other nonlinear effects present.This study consists of experimental tests where vibrational response was measured for rod shaped test specimens which were suspended in a water filled test rig and excited using an electrodynamic shaker. A Solid-Acoustic Finite Element model of the same experiment was created, and the test and simulation results were compared. The numerical results were shown to agree well with experiments up to 450 Hz. Above 450 Hz differences occur which is probably due to a simplified rig geometry in the numerical model.

Products are increasingly judged by their acoustic performance; and during the last decades, sound quality in general has gained a lot of attention, both from academia and companies. An obstacle in the evaluation of the sound quality is that jury testing is time consuming and require human resources. In an attempt to overcome these limitations, neural networks have been applied in this work with the objective to find a relation between human acoustic perception and a quantity possible to physically measure. For this purpose, 30 of 170 sound samples of interior aircraft noise have been subjectively assessed  during jury testing with 40 participators. With extracted psychoacoustic features from the sound samples and the obtained results from the jury testing, a shallow neural network (SNN) with one hidden layer is trained and tested. The prediction performance of the SNN is compared with another alternative method - multiple linear regression. The evaluation of the remaining un-assessed sound samples is predicted by the trained SNN and implemented in the deep learning neural networks, such as Convolutional Neural Network (CNN) and Recurrent Neural Network (RNN).

One of the main issues of cast-iron block brake material is high noise. Nowadays, train operators tend to change the brake block material from cast-iron to composite material. However, composite block brake materials are likely to produce more wear than cast-iron block brakes, degrading the dynamic behavior of the vehicle on the track. Therefore, comparison of the dynamic behavior and the maintenance cost of each block brake material of the train has been performed. The dynamic behavior is analyzed using GENSYS software and the maintenance cost analysis is done by using the Universal Cost Model developed in the EU project Roll2Rail. The iron ore train that operates in Malmbanan has been used as the simulation model. One-wheel profile before changing the block brake material before 2010 and two-wheel profiles after changing the block brake material after 2010 have been used for simulation. Certain radii, cant, vehicle speeds and wheel-rail friction coefficients has been taken into consideration in the simulations. After that, the wheel and track maintenance costs have been taken into consideration for analyzing the Universal Cost Model. The simulation results show that the wheel profiles after changing the block brake material possess higher risk of RCF than wheel profile before changing the brake block material. The UCM calculation show that the wheel profile after changing brake material leads to higher track maintenance costs, 9.3% higher for new1 and 2.8% higher for new2 wheel profiles, compared to the worn wheel profile before changing brake material. Moreover, The UCM calculation show that the wheel profile after changing brake material leads to higher wheel maintenance costs, 1.04% higher for new1 and 4.3% higher for new2 wheel profiles, compared to the worn wheel profile before changing brake material. The total of maintenance cost also shows that the wheel profile after changing brake material leads to higher maintenance costs, around 2-4%, compared to the worn profile before changing brake material.