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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.
481

En kvalitativ undersökning om infärgning ur matematiklärarens perspektiv. : Är infärgning den ultimata lösningen för ett G i matematik A för fordonselever?

Krutholm, Tommy January 2008 (has links)
<p>In this study the reader will learn how to work with student adaptation as a method for students to easier study and learn mathematics at a vocational school focusing on vehicle maintenance. This secondary school is located in the southern part of Sweden. Four math teachers who teach at this program use in-depth interview when it comes into explaining what they mean regarding adaptation and its role in teaching this students and helping them pass the course. This is very much a topic of today and has been so for some time. We hear about reports which reveals alarmingly low levels of know light which continue to drop especially at vocational programs in particular in mathematic. The math teachers describe specific obstacles and circumstances which in their experiences will limit their teaching options and alternatives and therefore will also limit the adaptation and its role. One may say in general that adaptation not necessarily is a method with an obvious template to follow so many various players will have to be involved in the teaching. This holds true with regards to all various aspects of learning. The student is here by enabled to see and experience the full picture of the program and the subject in question. No matter what the subject is, focus will always be the goal of the program and the students’ future careers. There are questions as to whether there may be conflicts of interest between the various actors involved in the learning process.</p><p>.</p>
482

Conceptual modeling architecture and implementation of object-oriented simulation for automated guided vehicle (AGV) systems

Wang, I-Chien 09 June 1995 (has links)
Traditional simulation languages and simulators do not fully support the need to design, modify, and extend simulation models of manufacturing systems, especially, material handling systems. Since AGV systems, one type of automated material handling systems, require complicated control logic, flexible job routings, and frequent layout modifications and extensions to correspond to production requirements, the time consumption and efforts to achieve the above tasks in traditional paradigms are significant. However, such difficulties can be overcome by the use of object-oriented simulation. This research develops an object-oriented modeling architecture for the simulation of AGV (automated guided vehicle) systems by extending Beaumariage's object-oriented modeling environment (1990) which is originally designed for the simulation of job shop type manufacturing systems. For this extension, several classes required to comprise an AGV system are created into the original environment which include AGV, limited size queue, control point, track segment, machine cell, AGV system control classes, and so on. This architecture provides a flexible environment that enables the modeling of traditional and tandem AGV system layouts. A best-first search approach, one artificial intelligence search algorithm, is employed to direct AGVs to determine the shortest path from all possible travel paths. The computerized modeling system with this conceptual architecture is easy to use, especially compared with traditional simulation tools. In addition, the extended object-oriented architecture used for the simulation of AGV systems is program independent and may be implemented in any object-oriented language. The prototype system implemented as a portion of this research is performed in Smalltalk/V. Two case examples are presented for verification and validation. / Graduation date: 1996
483

Knowledge Extraction from Logged Truck Data using Unsupervised Learning Methods

Grubinger, Thomas January 2008 (has links)
<p>The goal was to extract knowledge from data that is logged by the electronic system of</p><p>every Volvo truck. This allowed the evaluation of large populations of trucks without requiring additional measuring devices and facilities.</p><p>An evaluation cycle, similar to the knowledge discovery from databases model, was</p><p>developed and applied to extract knowledge from data. The focus was on extracting</p><p>information in the logged data that is related to the class labels of different populations,</p><p>but also supported knowledge extraction inherent from the given classes. The methods</p><p>used come from the field of unsupervised learning, a sub-field of machine learning and</p><p>include the methods self-organizing maps, multi-dimensional scaling and fuzzy c-means</p><p>clustering.</p><p>The developed evaluation cycle was exemplied by the evaluation of three data-sets.</p><p>Two data-sets were arranged from populations of trucks differing by their operating</p><p>environment regarding road condition or gross combination weight. The results showed</p><p>that there is relevant information in the logged data that describes these differences</p><p>in the operating environment. A third data-set consisted of populations with different</p><p>engine configurations, causing the two groups of trucks being unequally powerful.</p><p>Using the knowledge extracted in this task, engines that were sold in one of the two</p><p>configurations and were modified later, could be detected.</p><p>Information in the logged data that describes the vehicle's operating environment,</p><p>allows to detect trucks that are operated differently of their intended use. Initial experiments</p><p>to find such vehicles were conducted and recommendations for an automated</p><p>application were given.</p>
484

Design of Multifunctional Body Panels for Conflicting Structural and Acoustic Requirements in Automotive Applications

Cameron, Christopher John January 2011 (has links)
Over the past century, the automobile has become an integral part of society, with vastincreases in safety, refinement, and complexity, but most unfortunately in mass. Thetrend of increasing mass cannot be maintained in the face of increasingly stringentregulations on fuel consumption and emissions.The body of work within this thesis exists to help the vehicle industry to take a stepforward in producing vehicles for the future in a sustainable manner in terms of botheconomic and ecological costs. In particular, the fundamentally conflicting requirementsof low weight and high stiffness in a structure which should have good acousticperformance is addressed.An iterative five step design method based on the concepts of multifunctionality andmultidisciplinary engineering is proposed to address the problem, and explained witha case study.In the first step of the process, the necessary functional requirements of the systemare evaluated. Focus is placed on the overall system behavior and diverted from subproblems.For the case study presented, the functional requirements included: structuralstiffness for various loading scenarios, mass efficiency, acoustic absorption, vibrationaldamping, protecting from the elements, durability of the external surfaces,and elements of styling.In the second step of the process, the performance requirements of the system wereestablished. This involved a thorough literature survey to establish the state of theart, a rigorous testing program, and an assessment of numerical models and tools toevaluate the performance metrics.In the third step of the process, a concept to fulfil requirements is proposed. Here, amulti-layered, multi-functional panel using composite materials, and polymer foamswith varying structural and acoustic properties was proposed.In the fourth step of the process, a method of refinement of the concept is proposed.Numerical tools and parameterized models were used to optimize the three dimensionaltopology of the panel,material properties, and dimensions of the layers in a stepwisemanner to simultaneously address the structural and acoustic performance.In the fifth and final step of the process, the final result and effectiveness of the methodused to achieve it is examined. Both the tools used and the final result in itself shouldbe examined. In the case study the process is repeated several times with increasingdegrees of complexity and success in achieving the overall design objectives.In addition to the design method, the concept of a multifunctional body panel is definedand developed and a considerable body of knowledge and understanding is presented.Variations in core topology, materials used, stacking sequence of layers, effects ofperforations, and air gaps within the structure are examined and their effects on performanceare explored and discussed. The concept shows promise in reducing vehicleweight while maintaining the structural and acoustic performance necessary in the contextof sustainable vehicle development. / QC 20110311
485

Modelling for Fuel Optimal Control of a Variable Compression Engine

Nilsson, Ylva January 2007 (has links)
Variable compression engines are a mean to meet the demand on lower fuel consumption. A high compression ratio results in high engine efficiency, but also increases the knock tendency. On conventional engines with fixed compression ratio, knock is avoided by retarding the ignition angle. The variable compression engine offers an extra dimension in knock control, since both ignition angle and compression ratio can be adjusted. The central question is thus for what combination of compression ratio and ignition angle the maximum efficiency is achieved, considering the set of compression ratios and ignition angles that give a sufficiently low knock intensity. Four knock detection methods are proposed, compared and evaluated with respect to robustness for noise and choices of parameter values. Three of the knock detectors are categorised as on-line, and are designed for giving feedback about knock occurrence to the engine control unit. The methods can determine both whether or not knock is present and the crank angle at knock onset. A study of the relationship between knock oscillation properties and knock-onset is performed. It is concluded that the logarithm of the normalised knock energy depends almost linearly on the rate of knock occurrence. A new formulation of multi-zone engine models is presented. The formulation makes it easy to increase or decrease the number of zones during the simulation. One of many possible applications is the investigation of engine efficiency. An analysis of experimental data shows how the engine efficiency changes with compression ratio and ignition angle. An engine torque model is developed and validated, from which the optimal choice of compression ratio and ignition angle can be calculated with high accuracy.
486

Design, Development And Flight Control Of Sapthami - A Fixed Wing Micro Air Vehicle

Satak, Neha 12 1900 (has links)
Two micro air vehicles, namely Sapthami and Sapthami-flyer, are developed in this thesis. Their total weight is less than 200grams each. They fit inside a 30cm and 32cm sphere respectively and carry the commercially available Kestrel autopilot hardware. The vehicles have an endurance of around 20-30 minutes. The stall speed of Sapthami is around 7m/s and that of Sapthami-flyer is around 5m/s as found by nonlinear modeling. The low stall speed makes it possible for them to be launched by hand. This enhances their portability as they do not require any launching equipment. The vehicle installed with Kestrel autopilot system is capable of many modes of operations. It is capable of fully autonomous flight with the aid of a variety of sensors like the GPS unit, heading sensor, 2-axis magnetometer, 3-axis accelerometer and 3-axis gyros. The vehicle carrying the Kestrel autopilot hardware is capable of autonomous and semi-autonomous flights after installation and tuning of feedback loops. Sapthami, is a tailless flying wing with an inverse zimmermann profile. A flying wing is a preferred configuration for the MAV as it maximizes the lifting area for a given size constraint. For a maximum size constraint of 30cm and aspect ratio around 1, the vehicle operates at Reynolds number between 100,000 to 250,000, at flight velocity 7 m/s to 15 m/s. The Inverse Zimmerman profile has a higher lift coefficient, CL, in comparison to the other planforms such as rectangular, elliptical and Zimmermann, for aspect ratio 1 to 1.25 and tested at Reynolds number of 100,000. The configuration of Sapthami is clean as there is no fuselage and all the components like autopilot hardware and battery are housed inside the wing. A thick reflex Martin Hepperle (MH) airfoil MH18 is chosen which gives sufficient space to place the components. This airfoil is specially used for tailless configurations due to its negative camber at the trailing edge. This negative camber helps in reducing the negative pitching moment of the wing, since no separate horizontal tail is available on a tailless aircraft to compensate for it. The vehicle is fabricated using the blue foam, having a density of 30kg/m3 . The wing is fabricated by CNC machining after which slots are cut manually to embed the electronics. The vehicle is found to have stable flying characteristics. Limited flight trials are done for Sapthami. It takes large time to fabricate the vehicle due to limited availability of CNC machining facility. Therefore, a new tailless, wing-fuselage configuration, which can be fabricated with balsa wood, is designed. Sapthami-flyer is the second vehicle designed in this thesis. Its wing span is slightly more than Sapthami. Since it is a wing-fuselage configuration, therefore there is no need for a thick airfoil. Mark drela’s AG airfoils are found to have better lift than MH airfoils for the inverse Zimmerman profile. The thickness of the airfoils is reduced to 1% so that the wing can be made by a 1.5mm thick balsa sheet to reduce weight. The inverse Zimmermann profile wing with the AG09 airfoil is found to have best lift-to-drag ratio when compared to AG36, MH45 and MH18. The analysis is done using commercially available AVL software. AG09 with 1% thickness is used in the final configuration. This configuration has better short period damping than Sapthami. It also has slower modes of operation than Sapthami. The operating modes of most of the MAVs, including Sapthami and Sapthami-flyer, are lowly damped but fast. This makes it difficult for the pilot to fly the vehicle. To improve the flying qualities of the vehicle artificial stabilization is required. The feedback is implemented on the Kestrel autopilot hardware. It allows only PID based feedback structures to be implemented, hence gives no choice to the designer to implement higher order control. The digital integrator and differentiator implementation for feedback are non-ideal. This further reduces the effectiveness of control. The problem is dealt with by incorporating the additional dynamics introduced by these implementation while formulating the control problem. Further the modeling of the micro air vehicle is done by using vortex lattice simulation based softwares. The fidelity of the obtained dynamics is low. Therefore, there is high uncertainty in the plant model. The controller also needs to reject the wind gust disturbances which are of the order of the flight speed of the vehicle. All the above stated requirements from the control design can be best addressed by a robust control design. Sapthami-flyer uses aileron and elevator for control. There is no rudder in the configuration in order to reduce weight. In the longitudinal dynamics, pitch rate and pitch error feedback to elevator are used to increase the short period and phugoid damping respectively. In the lateral dynamics, a combination of roll rate, yaw rate and roll error feedback is given to aileron to improve the dutch roll damping and stabilize the spiral mode. The feedback loops for both longitudinal and lateral dynamics are multi-output single input design problems, therefore simultaneous tuning of loops is beneficial. The PID control is designed by first converting the actual plant to a static output feedback equivalent plant. The dynamics introduced by non-ideal differentiator and integrator implementation on the autopilot hardware are incorporated in the open loop static output feedback formulation. The robust pole placement for the SOF plant is done by using the modified iterative matrix inequality algorithm developed in this thesis. It is capable of multi-loop, multi-objective feedback design for SOF plants. The algorithm finds the optimal solution by simultaneously putting constraints on the H2 performance, pole placement, gain and phase margin of the closed loop system. The pole placement is done to minimize the real part of largest eigenvalue. A single controller is designed at a suit-able operating point and constraints are put on the gain and phase margin of the closed loop plant at other operating points. The designed controller is tested in flight on board Sapthami-flyer. The vehicle is also capable of tracking commanded pitch and roll attitude with the help of pitch error, roller or feedbacks. This is shown in the flight when the pilot leaves the RC stick and the vehicle tracks the desired attitude. The vehicle has shown improved flying characteristics in the closed loop mode.
487

Asthma, rhinitis, and asthma-related symptoms in relation to vehicle exhaust using different exposure metrics

Modig, Lars January 2009 (has links)
Air pollution is a well known public health problem that involves both long-term and acute effects. An outcome associated with traffic-related air pollution is respiratory illness. Many studies have described the relationship between asthmatic symptoms and traffic-related air pollution; however, few have investigated the potential of air pollution to cause asthma itself, especially among adults. The overall aim of this thesis was to study the relationship between vehicle exhaust levels at home and the prevalence of self-reported annoyance and asthmatic symptoms, and the incidence of asthma and rhinitis. These relationships were evaluated using different indicators of exposure with a high spatial resolution. Three different data sets were used for the four papers included in this thesis. The first paper (paper I) is based on a questionnaire that was sent to a random selection of the adult population within three Swedish cities (Gothenburg, Uppsala, and Umeå) as part of the Swedish Environmental Protection Agency’s health-related environmental monitoring. The aim was to study the degree of self-reported annoyance and the prevalence of asthmatic symptoms in relation to the levels of vehicle exhaust outside the home. The level of exposure was described using modeled levels of nitrogen dioxide (NO2) as the exposure indicator. The second paper (paper II) is based on new asthma cases identified within the Obstructive Lung disease In Northern Sweden (OLIN) study, each with a matched referent. The aim of this study was to analyze if new cases of asthma had higher levels of vehicle exhaust outside the home compared to the population controls. Exposure was assessed using both measured levels of NO2 outside each home, and by summarizing the amount of traffic within a 200 metre buffer surrounding each participant’s home. Papers III and IV were based on the Respiratory Health in Northern Europe (RHINE) Cohort, a prospective cohort of adults included in 1990 and followed up with in 1999. The proportion of new cases of asthma (papers III and IV) and rhinitis (paper IV) were identified based on the answers from the initial and follow-up questionnaires. In paper III, exposure was assessed by using meteorological dispersion models to calculate the levels of NO2 outside each home as an indicator of the levels of vehicle exhaust. As an alternative indicator, the distance from each participant’s home to the nearest major road was calculated using geographical information system (GIS) tools. The exposure assessment in paper IV was also based on meteorological dispersion models, but expressed the levels of vehicle exhaust as particle mass concentration. The results show that the levels of vehicle exhaust outside the home are significantly correlated with the degree of self-reported annoyance and the prevalence of asthmatic symptoms, and also with the risk of developing asthma, but not rhinitis, among adults. The odds ratio (OR) for high annoyance to vehicle exhaust and reporting asthmatic symptoms was 1.14 (95% Confidence Interval, CI 1.11-1.18) and 1.04 (95% CI 1.01-1.07) per 1 µg/m3 increase in the NO2 level outside the home, respectively. Paper II showed there was a non-significant tendency for increased risk of developing asthma among those living with high levels of vehicle exhaust outside their home. This finding was then supported by papers III and IV, showing a significant relationship between the onset of asthma and the mean (winter) levels of NO2 outside the home (OR=1.46, 95% CI 1.07-1.99 per 10 µg/m3) and the levels of vehicle exhaust particles outside the home. In paper III, living close to a major road was significantly related to the risk of developing asthma. No significant results were shown between vehicle exhaust and rhinitis. In conclusion, vehicle exhaust outside the home is associated with the prevalence of annoyance and asthmatic symptoms, and with the risk of developing asthma, but not rhinitis, among adults.
488

En kvalitativ undersökning om infärgning ur matematiklärarens perspektiv. : Är infärgning den ultimata lösningen för ett G i matematik A för fordonselever?

Krutholm, Tommy January 2008 (has links)
In this study the reader will learn how to work with student adaptation as a method for students to easier study and learn mathematics at a vocational school focusing on vehicle maintenance. This secondary school is located in the southern part of Sweden. Four math teachers who teach at this program use in-depth interview when it comes into explaining what they mean regarding adaptation and its role in teaching this students and helping them pass the course. This is very much a topic of today and has been so for some time. We hear about reports which reveals alarmingly low levels of know light which continue to drop especially at vocational programs in particular in mathematic. The math teachers describe specific obstacles and circumstances which in their experiences will limit their teaching options and alternatives and therefore will also limit the adaptation and its role. One may say in general that adaptation not necessarily is a method with an obvious template to follow so many various players will have to be involved in the teaching. This holds true with regards to all various aspects of learning. The student is here by enabled to see and experience the full picture of the program and the subject in question. No matter what the subject is, focus will always be the goal of the program and the students’ future careers. There are questions as to whether there may be conflicts of interest between the various actors involved in the learning process. .
489

Topology-Based Vehicle Systems Modelling

Yam, Edward January 2013 (has links)
The simulation tools that are used to model vehicle systems have not been advancing as quickly as the growth of research and technology surrounding the advancements of vehicle technology itself. A topological vehicle systems modelling package would use Modelica to take advantage of the flexibility and modularity of the language, the inherent multi-domain workspace and analytical accuracy of model equations. This package is defined through the use of SuperBlocks, a generalized model that allows the user to select and parameterize the appropriate sub-system directly within the workspace. This palette of SuperBlocks would be implemented within MapleSim6 to create MapleCar. This provides a customized balance between speed and accuracy after taking advantage of advanced graph-theoretic solutions methods used in MapleSim. MapleCar provides several advantages to a user over conventional tools. The SuperBlocks would ease the required steps to model a full vehicle system by providing clear, simple connections to quickly get a simulation assembled. Next, each SuperBlock is represented by a model that contains a replaceable model, a Modelica function which allows its internal model to be changed through a user-friendly parameter selection. The combination of sub-systems accessible directly through a parameter allows a variety of vehicle systems to be easily assembled, as well as provide a container for future models to be shared and published. A short demonstration of connecting these vehicle SuperBlocks from the MapleCar package is provided using MapleSim6. The generalized vehicle component palette provides a straight-forward, customizable drag-and-drop interface to assist in generating vehicle models for simulation. Conclusions and recommendations are provided at the end.
490

The Rhetoric of Volunteerism: Strategies to Recruit and Retain Volunteers in Nonprofit Organizations

Woods, Terry Bell 04 December 2006 (has links)
This study analyzes the rhetorical strategies of an international public service organization. Drawing upon narrative criticism, volunteer related literatures of the Continental Societies, Inc. were studied in order to gauge their rhetorical efficacy in light of the existing literature on nonprofit organizations and volunteerism. By analyzing the organization’s literatures – their “story” – it was discovered that part of it was missing. In an attempt to fill this void, more effective materials related to volunteer recruitment and retention have been created to exemplify greater narrative fidelity, along with recommended organizational transformations that create a better fit between these “stories” and the truth of them.

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