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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

On improving efficiency of flight using optimization

Jacobsen, Marianne January 2009 (has links)
In this thesis, optimization is used to improve the performance of aircraft. The focus is on operating current generation aircraft more efficiently rather than designing new aircraft. Drag minimization and aircraft trajectory optimization is used to increase efficiency. Optimization methods are implemented and evaluated on different problem formulations. The first part of the thesis presents a drag minimization strategy using multiple control surfaces distributed across the span of an elastic wing. Aeroelasticity is exploited to reduce drag for a wide range of flight conditions. A method to minimize drag during a long distance flight is developed and tested in a wind tunnel environment. The method is based on continuously changing the control surface deflections to obtain a more beneficial load distribution from a drag point of view for the current flight condition. In a second study, the method is extended to include the angle of attack as a variable together with the control surface deflections in the drag minimization algorithm. Extensive wind tunnel testing demonstrates the possibility to reduce drag significantly with the presented method for a wide range of flight conditions. The second topic in the thesis is optimizing the aircraft trajectory. The emissions from the aircraft engine are modeled as smooth functions suitable for optimization using published certification data. These emissions are combined in different environmental indices and used as objective functions in the aircraft trajectory optimization problem. The optimization problem is formulated by discretizing the trajectory in time. The resulting large scale nonlinear optimization problem is solved using a sequential quadratic programming method. The trajectory optimization problem is first studied using a model of the Boeing 737 and the results show that the optimal trajectory depends significantly on the definition of the environmental objective function. A method to treat restricted airspace is also presented and evaluated using a model of the Swedish Air Force trainer SK60. The results show that the method for imposing airspace constraints on the flight path works well, especially when the initial point for the optimization is feasible. / QC 20100720
12

Improving a six-wheeler’sperformance both on- and off-road

Noréus, Olof January 2010 (has links)
In vehicles with electric transmission and independent wheel stations, there is apossibility to control propulsion, steering and suspension individually for eachwheel. This makes it possible to improve mobility in terrain as well as performanceand driving safety on road. This contribution concerns how a six wheeledelectric transmission vehicle should be modelled to enable evaluation of thedynamic behaviour both in terrain and on road. This is made by combiningmodelling of vehicle, transmission and tyre/terrain behaviour.A tyre/terrain model is needed to simulate driving on soft ground. Heretyre/terrain models for simulating driving with both rigid and pneumatic wheelson soft ground have been developed. A method to measure terrain parametersand drawbar pull for a six-wheeled vehicle on sand is proposed, tested andevaluated.To simulate a six wheeled vehicle at the handling limit on road, a vehicle modelwith a brush tyre model is used in order to get physically reasonable simulationresults during high combined slip conditions. Different vehicle configurationsare considered, where front wheel steering is combined with eithersecond axle steering, rear wheel steering or individual wheel torque control.By applying different vehicle slip angles and thereby limiting the DOF of thevehicle model, the vehicle configurations are evaluated during different drivingconditions. The results show that by applying individual torque control to thefront wheel steered vehicle, the performance is improved for all evaluated manoeuvres,and the achievable aligning torque during a rear wheel skid increasessignificantly if the vehicle slip angle is larger than the maximum front wheelsteering angle.To conclude, models of a six-wheeled vehicle with electric transmission andtyre models both for soft and rigid ground have been developed. These modelsform a simulation platform, which makes it possible to evaluate controlstrategies for the electric transmission with the purpose to improve mobility interrain as well as performance and driving safety on road. Some examples ofapplications of the models are included, e.g. improving at-the-limit handlingand pivot turning performance. / QC 20101026
13

Multi-fastener single-lap joints in composite structures

Ekh, Johan January 2006 (has links)
This thesis deals with composite joints. Designing such joints is more difficult than metallic joints due to the mechanical properties of composite materials. Composites are anisotropic and have a limited ability of yielding. The low degree of yielding means that stress concentrations are not relieved by plastic deformation, which is important in multi-fastener single-lap joints. The distribution of load between the fasteners may be more uneven than in metallic joints due to that the stress concentrations around the holes are not relieved. Single-lap joints have an eccentric load path which generates a nonuniform bolt-hole contact pressure through the plate thickness. This generates out-of-plane deflection of the joint, termed secondary bending. Such nonuniform contact stress severely limits the strength of the joint. The nonuniform contact stress distribution is affected by several factors, e.g. bolthole clearance and secondary bending. The first part of the work is devoted to investigating secondary bending, and its effect on stresses in the joint. A novel technique to study secondary bending has been developed and used in a parametric study. It is based on the calculation of specimen curvature from out-of-plane deflections measured with an optical technique. It is shown that the specimen curvature is correlated to the conventional definition of secondary bending, which involves strain measurements on both sides of the plate. The two most important parameters affecting specimen curvature was found to be the overlap length and the thickness of the plates. The finite element method was used to study the influence of secondary bending on joint strength. Secondary bending was changed in magnitude by altering the length of the overlap region in a two-fastener specimen. It was found that secondary bending affects the local stress field around the fasteners and that it may change the strength and the mode of failure. The second part is concerned with the load distribution and prediction of joint strength. A detailed finite element model was developed to calculate the load distribution while accounting for bolt-hole clearances, bolt clamp-up, secondary bending and friction. An experimental programme was conducted in order to validate the finite element model by means of instrumented fasteners. Good agreement between simulations and experiments was achieved and it was found that bolt-hole clearance is the most important factor in terms of load distribution between the fasteners. Sensitivity to this parameter was found to be large, implying that temperature changes could affect the load distribution if member plates with different thermal expansion properties are used. Calculating the load distribution in structures with a large number of fasteners is in general not feasible with detailed finite element models based on continuum elements. A simplified, computationally effective model of a multi-fastener, singlelap joint has been developed by means of structural finite elements. The model accounts for bolt-hole clearances, bolt clamp-up, secondary bending and friction. Comparisons with the detailed finite element model and experiments validated the accuracy of the simplified model. A parametric study was conducted where it was found that an increased stiffness mismatch between the plates generates a more uneven load distribution, while reducing the length of the overlap region has the opposite effect. Increasing the stiffness of a fastener shifts some of the load from the nearest fasteners to that particular fastener. An idealized optimization study was conducted in order to minimize bearing stresses in the joint with restrictions on the increase of joint weight and net-section stresses. Maximum bearing stress was reduced from 220 MPa to 120 MPa while both weight and net-section stresses decreased. A procedure to predict bearing strength based on the results from the simplified model was developed. It was established by an experimental programme that fiber micro-buckling is the initial failure mode. The stress state in the laminate was determined through force and moment equilibrium, based on output from the finite element model. An existing criterion was used to predict the fiber microbuckling, and thus the initial failure. Predictions were compared with experiments which validated the method. The small computational cost required by the procedure suggests that the method is applicable on large scale structures and suitable to use in conjunction with iterative schemes such as optimization and statistical investigations. / QC 20110121
14

Effects of Mach cruise number on conventional civil jet aircraft sizing

Bergman, Niklas January 2009 (has links)
This thesis work was executed at Swift Engineering Incorporated located in San Clemente, California during spring in 2009. Placement supervisor from Swift was Mark Page and advisor and examiner from the Division of future products at Mälardalen University, Sweden was Gustaf Enebog. The objective with this thesis work was to examine the effects of fitness ratio, lift over drag, lift coefficient at cruise, winglet span, wing sweep angle, wing aspect ratio, wing area and weights with respect to Mach number for a conventional business jet capable of 18 passengers. The cruise speed study range from Mach 0.88 to 0.99. The Excel based conceptual design tool Jetsizer 2008c was used to make four models with similar configuration and mission but with different cruise Mach numbers. A new Jetsizer module was then created to handle a modification process where the models are optimized for their speed and configuration. The result in this report gives guidelines for the needed values when creating an initial CFD model for this type of airplane.
15

Implementation of UAV design into CAD

Boman, David January 2011 (has links)
SAMMANFATTNING Detta arbete har gått ut på att i CAD implementera en UAV-design av Enebog, Designen har förmedlats av handledaren via möten och mail. Ett ”levande” dokument skapades och har sedan uppdaterats från båda sidor genom projektets fortlöpande. Dimensioner och mått har diskuterats samt hur det ska implementeras i CAD. UAV’n är uppbyggd som en ”assembly” i CAD, med tillhörande modeller och ”sub-assemblies”. Modellerna är designade i Solid Works standard-arbetsbänk och ihopsatta i assemblyn med så kallade ”mates”. Tyngdpunkt och massa har beräknats i Solid Works för flygplanets olika delar. Datat har exporterats till Excel för att kunna presenteras. Resultatet är 7 stycken 2D ritningar kopplade till en 3D modell. Flygplanet har en spännvidd på 2,7 meter och en vingarea på 0,91m2. Den totala längden dimensionerades till 1,87 meter och den totala massan kalkylerades till 8,68 kg, som också är flygplanets ”take off weight”. Flygplanet är designat för att byggas med två olika komposit material: kolfiber/epoxy och glasfiber/epoxy. I ritningsunderlaget genererares tre-plans vyer med måttsättning, detaljvyer på till exempel nos-poden i den främre delen av flygplanet samt en sprängskiss med innehållsförteckning. / ABSTRACT This work has been focused on implementing, into CAD (Solid Works), a UAV-design by Enebog. The design has been given to the author on meetings and mail. A “living” document with design parameters was updated from both sides continuously throughout the project. The measurements/dimensions of the aircraft were discussed as well as how to implement in CAD. All updates were also continuously updated in the document. The UAV is built up as an assembly in CAD, with sub-assemblies and parts. The parts are designed with the standard work bench in Solid Works and mated together to form an aircraft. Center of gravity and mass properties of the parts were calculated in Solid Works and exported to Excel for the purpose of presenting the data. The result is 7 2D drawings attached to a 3D model. The aircraft has a wing span of 2,7 meters (8,68 ft), with a corresponding wing area of 0,91 m2 (9,8 ft2). The total length is dimensioned to 1,87 m (6,14 ft) and the total mass is calculated to 8,68 kg (19,14 lbs), which is also the aircrafts takeoff weight. The aircraft is designed to be built with two composite materials; carbon fiber/epoxy and glass fiber/epoxy. In the drawing material plan views with dimensions of the aircraft, detail views of e.g. the nose pod in the front part of the aircraft, an exploded view with a corresponding build of material-table was generated.
16

Multi-fastener single-lap joints in composite structures

Ekh, Johan January 2006 (has links)
<p>This thesis deals with composite joints. Designing such joints is more difficult than metallic joints due to the mechanical properties of composite materials. Composites are anisotropic and have a limited ability of yielding. The low degree of yielding means that stress concentrations are not relieved by plastic deformation, which is important in multi-fastener single-lap joints. The distribution of load between the fasteners may be more uneven than in metallic joints due to that the stress concentrations around the holes are not relieved. Single-lap joints have an eccentric load path which generates a nonuniform bolt-hole contact pressure through the plate thickness. This generates out-of-plane deflection of the joint, termed secondary bending.</p><p>Such nonuniform contact stress severely limits the strength of the joint. The nonuniform contact stress distribution is affected by several factors, e.g. bolthole clearance and secondary bending. The first part of the work is devoted to investigating secondary bending, and its effect on stresses in the joint. A novel technique to study secondary bending has been developed and used in a parametric study. It is based on the calculation of specimen curvature from out-of-plane deflections measured with an optical technique. It is shown that the specimen curvature is correlated to the conventional definition of secondary bending, which involves strain measurements on both sides of the plate. The two most important parameters affecting specimen curvature was found to be the overlap length and the thickness of the plates. The finite element method was used to study the influence of secondary bending on joint strength. Secondary bending was changed in magnitude by altering the length of the overlap region in a two-fastener specimen. It was found that secondary bending affects the local stress field around the fasteners and that it may change the strength and the mode of failure.</p><p>The second part is concerned with the load distribution and prediction of joint strength. A detailed finite element model was developed to calculate the load distribution while accounting for bolt-hole clearances, bolt clamp-up, secondary bending and friction. An experimental programme was conducted in order to validate the finite element model by means of instrumented fasteners. Good agreement between simulations and experiments was achieved and it was found that bolt-hole clearance is the most important factor in terms of load distribution between the fasteners. Sensitivity to this parameter was found to be large, implying that temperature changes could affect the load distribution if member plates with different thermal expansion properties are used.</p><p>Calculating the load distribution in structures with a large number of fasteners is in general not feasible with detailed finite element models based on continuum elements. A simplified, computationally effective model of a multi-fastener, singlelap joint has been developed by means of structural finite elements. The model accounts for bolt-hole clearances, bolt clamp-up, secondary bending and friction. Comparisons with the detailed finite element model and experiments validated the accuracy of the simplified model. A parametric study was conducted where it was found that an increased stiffness mismatch between the plates generates a more uneven load distribution, while reducing the length of the overlap region has the opposite effect. Increasing the stiffness of a fastener shifts some of the load from the nearest fasteners to that particular fastener. An idealized optimization study was conducted in order to minimize bearing stresses in the joint with restrictions on the increase of joint weight and net-section stresses. Maximum bearing stress was reduced from 220 MPa to 120 MPa while both weight and net-section stresses decreased.</p><p>A procedure to predict bearing strength based on the results from the simplified model was developed. It was established by an experimental programme that fiber micro-buckling is the initial failure mode. The stress state in the laminate was determined through force and moment equilibrium, based on output from the finite element model. An existing criterion was used to predict the fiber microbuckling, and thus the initial failure. Predictions were compared with experiments which validated the method. The small computational cost required by the procedure suggests that the method is applicable on large scale structures and suitable to use in conjunction with iterative schemes such as optimization and statistical investigations.</p>
17

Aspects of autonomous corner modules as an enabler for new vehicle chassis solutions

Jonasson, Mats January 2006 (has links)
<p>This thesis adopts a novel approach to propelling and controlling the dynamics of a vehicle by using autonomous corner modules (ACM). This configuration is characterised by vehicle controlled functions and distributed actuation and offers active and individual control of steering, camber, propulsion/braking and vertical load.</p><p>Algorithms which control vehicles with ACMs from a state-space trajectory description are reviewed and further developed. This principle involves force allocation, where forces to each tyre are distributed within their limitations. One force allocation procedure proposed and used is based on a constrained, linear, least-square optimisation, where cost functions are used to favour solutions directed to specific attributes.</p><p>The ACM configuration reduces tyre force constraints, due to lessen estrictions in wheel kinematics compared to conventional vehicles. Thus, the tyres can generate forces considerably differently, which in turn, enables a new motion pattern. This is used to control vehicle slip and vehicle yaw independently. The ACM shows one important potential; the extraordinary ability to ensure vehicle stability. This is feasible firstly due to closed-loop control of a large number of available actuators and secondly due to better use of adhesion potential. The ability to ensure vehicle stability was demonstrated by creating actuator faults.</p><p>This thesis also offers an insight in ACM actuators and their interaction, as a result of the force allocation procedure.</p>
18

MD-80 Engine Change Kit

Nogueira, Tiago, Twofik, Twana January 2007 (has links)
Den här rapporten ämnar svara på frågan om och med hur mycket tröskelvärdena av alla inkommande komponenter, tillhörande ett MD-80 Engine change kit, kan höjas med och vilka kostnadsbesparingar en sådan höjning kan medföra. Undersökningen har föranletts av företaget SAS Components vilja att få reda på om en optimering av tröskelvärden kan leda till en minskning av kasserade komponenter hos dem. / This report’s aim is to verify if it is possible, and if so, by how much SAS Component could increase the threshold values of all incoming components belonging to an MD-80 Engine Change Kit. How would this raise in the components threshold lower SAS Component’s expenses?
19

Experimentell motståndsanalys av kåpkonfigurationer på Scaniamodells busstak

Karlsson, Robert January 2008 (has links)
Sammanfattning Dagens stigande bränslepriser gör det alltmer viktigt för tillverkare samt brukare av fordon, att fokusera på detaljer som kan minimera drivmedelåtgången. Scania linjetrafikbussar är utrustade med ett antal olika konfigurationer av kåpor som figurerar på bussarnas tak. Projektet har således innefattat att undersöka dessa ur ett aerodynamisk perspektiv i Mälardalens högskolas låghastighetsvindtunnel, förlagt vid Hässlö i Västerås. Resultaten som uppnåddes är att motståndskofficienten kan reduceras från CD=0,46 till CD=0,41 genom att omplacera orginalkåporna på andra positioner över taket. CD =0,39 erhålls genom att bruka de aerodynamiskt modifierade kåporna. Det skapar en vinst på 55-60 000 kr för orginalkåporna och motsvarande en vinst på 75-80 000 kr för de modifierade kåporna, räknat under bussens livslängd och en drivmedelkostnad på 8 kr/l. Beräkningarna är snålt tilltagna för att ej ge ett överskattat värde, utan är mer ett resultat i underkant. I bilagorna figurerar även andra värden som ger än mer större vinst i kronor Resultat uppnås då man tenderar minimera det återcirkulerande och energialstrande flöde som skapas inledningsvis på bussens tak under dess färd.
20

On Generic Road Vehicle Motion Modelling and Control

Andreasson, Johan January 2006 (has links)
With the increased amount of on-board electric power driven by the ongoing hybridization, new ways to realize vehicles are likely to occur. This thesis outlines a future direction of vehicle motion control based on the assumptions that: 1) future vehicle development will face an increased amount of available actuators for vehicle propulsion and control that will open up for an increased variety of possible configurations, 2) the onboard computational power will continue to increase and allow higher demands on active safety and drivability that will require a tighter interaction between sensors and actuators, 3) the trend towards more individualized vehicles on common platforms with shorter time-to-market require design approaches that allow engineering knowledge to be transferred conveniently from one generation to the next. A methodology to facilitate the selection of vehicle configurations and the design of the corresponding vehicle motion controllers is presented. This includes a method to classify and map configurations and control strategies onto their possible influence on the vehicle's motion. Further, a structured way of implementing and managing vehicle and subsystem models that are easy to reconfigure and reuse is suggested and realised in the developed VehicleDynamics Library. In addition, generic ways to evaluate vehicle configurations, especially the use of the adhesion potential to identify safety margin and expected limit behaviour are presented. Special attention is given to how the characteristics of a vehicle configuration can be expressed so that it can be used in vehicle motion control design. A controller structure that enables a generic approach to this is introduced and within this structure, two methods for control allocation are proposed, via tyre forces and directly. The first method uses a developed mapping of available actuators as constraints onto the achievable tyre forces and inverse tyre models to calculate the actuator inputs. The second method allocates the actuator inputs directly for an adapted problem that is linearized around the current operating point. It is shown that the methods are applicable to a variety of different vehicle configurations without redesign. Therefore, the same controller can manage a variety of vehicle configurations and there is no need to recognize and treat each different situation separately. Finally, a road map on how to continue this research towards a possible industry implementation is given. Also suggestions on more detailed improvements for modelling and vehicle motion control are provided. / QC 20100629

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