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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

Design Guidelines for the use of Curbs and Curb/Guardrail Combinations Along High-Speed Roadways

Plaxico, Chuck Aldon 18 December 2002 (has links)
"The potential hazard of using curbs on high-speed roadways has been a concern for highway designers for almost half a century. Curbs extend 75-200 mm above the road surface for appreciable distances and are located very near the edge of the traveled way, thus, they constitute a continuous hazard for motorist. Curbs are sometimes used in combination with guardrails or other roadside safety barriers. Full-scale crash testing has demonstrated that inadequate design and placement of these systems can result in vehicles vaulting, underriding or rupturing a strong-post guardrail system though the mechanisms for these failures are not well understood. For these reasons, the use of curbs has generally been discouraged on high-speed roadways. Curbs are often essential, however, because of restricted right-of-way, drainage considerations, access control, delineation and other curb functions. Thus, there is a need for nationally recognized guidelines for the design and use of curbs. The primary purpose of this study was to develop design guidelines for the use of curbs and curb-barrier combinations on roadways with operating speeds greater than 60 km/hr. The research presented herein identifies common types of curbs that can be used safely and effectively on high-speed roadways and also identifies the proper combination and placement of curbs and barriers that will allow the traffic barriers to safely contain and redirect an impacting vehicle. Finite element models of curbs and curb-guardrail systems were developed, and the finite element program, LS-DYNA, was used to investigate the event of a vehicle traversing several curb types. Finite element analysis was also used in the analysis of a vehicle impacting a number of curb-guardrail combinations. The results obtained from these analyses were synthesized with the results of previous studies, which involved full-scale crash testing, computer simulation, and other methods. The combined information was then used to develop a set of guidelines for using curbs and curb-barrier combinations on high-speed roadways."
12

Desempenho de defensas rodoviárias sujeitas ao impacto de automóveis. / Performance of road restraint systems subjected to automobiles impact.

Neves, Renato Ramirez Viana 01 February 2013 (has links)
As defensas rodoviárias têm a finalidade de redirecionar com segurança um veículo fora de controle de uma colisão frontal ou trajetória mais perigosa. Secundariamente, a absorção de energia através da deformação do sistema de contenção ou outro método de dissipação da energia de impacto é ressaltado como um benefício em prol da segurança dos ocupantes. Considerando as premissas anteriores e os índices de severidade ao ocupante ASI, THIV e PHD, os desempenhos de uma defensa metálica e outras defensas de concreto são então classificados. Além disso, investiga-se o mecanismo de falha das conexões parafusadas e a sua influência no resultado do impacto de um automóvel leve contra uma defensa metálica. Importância é dada à modelagem do comportamento do material da defensa metálica sob baixas e altas taxas de deformação. Dessa forma, a necessidade de avaliar as propriedades dinâmicas do material motivou o projeto e construção de uma Barra de Hopkinson para testes de tração e compressão até 5000s-1. Adicionalmente, um modelo analítico simplificado da defensa metálica sob ação de uma força estática foi equacionado para validar um modelo em elementos finitos. Um estudo paramétrico da falha da conexão parafusada foi levantado através de diversas simulações estáticas e também do impacto de um veículo leve em uma defensa metálica de acordo com a norma EN 1317. Os resultados das simulações de impacto utilizando um modelo de veículo leve e diferentes sistemas de contenção foram comparados em função dos índices de severidade ao ocupante, indicando que a defensa metálica é mais segura do que uma defensa de concreto com perfil New Jersey ou vertical. / The main function of a road guardrail is to redirect an out of control vehicle avoiding a frontal collision or a dangerous veering off the road trajectory. Secondarily, the energy absorption measured by barrier deformation or any other energy dissipation method is beneficial to the car occupant safety. Considering the previous tasks and some severity occupant index like ASI, THIV and PHD, the performance of a guardrail and other concrete barriers are classified. Besides, it is investigated the fail mechanism of bolted connections and its influence on the guardrail impact result of an automobile. Special attention was taken into the material behavior modeling under low and high strain rates. Thereby, the need of accessing dynamic material properties motivated the design and manufacture of a Hopkinson Bar set-up for tension and compression tests up to 5000s-1. In addition, a simplified analytical model of a guardrail subjected to a static force was settled in order to validate a guardrail finite element model. A parametric study of the bolted connection failure was performed through several impact simulations of a light car model and a guardrail according to EN 1317 standard. The impact simulation results using a light vehicle car model and different barriers types were compared through the occupant severity index showing that the guardrail is a safer system than concrete barrier with New Jersey or vertical profile.
13

Desempenho de defensas rodoviárias sujeitas ao impacto de automóveis. / Performance of road restraint systems subjected to automobiles impact.

Renato Ramirez Viana Neves 01 February 2013 (has links)
As defensas rodoviárias têm a finalidade de redirecionar com segurança um veículo fora de controle de uma colisão frontal ou trajetória mais perigosa. Secundariamente, a absorção de energia através da deformação do sistema de contenção ou outro método de dissipação da energia de impacto é ressaltado como um benefício em prol da segurança dos ocupantes. Considerando as premissas anteriores e os índices de severidade ao ocupante ASI, THIV e PHD, os desempenhos de uma defensa metálica e outras defensas de concreto são então classificados. Além disso, investiga-se o mecanismo de falha das conexões parafusadas e a sua influência no resultado do impacto de um automóvel leve contra uma defensa metálica. Importância é dada à modelagem do comportamento do material da defensa metálica sob baixas e altas taxas de deformação. Dessa forma, a necessidade de avaliar as propriedades dinâmicas do material motivou o projeto e construção de uma Barra de Hopkinson para testes de tração e compressão até 5000s-1. Adicionalmente, um modelo analítico simplificado da defensa metálica sob ação de uma força estática foi equacionado para validar um modelo em elementos finitos. Um estudo paramétrico da falha da conexão parafusada foi levantado através de diversas simulações estáticas e também do impacto de um veículo leve em uma defensa metálica de acordo com a norma EN 1317. Os resultados das simulações de impacto utilizando um modelo de veículo leve e diferentes sistemas de contenção foram comparados em função dos índices de severidade ao ocupante, indicando que a defensa metálica é mais segura do que uma defensa de concreto com perfil New Jersey ou vertical. / The main function of a road guardrail is to redirect an out of control vehicle avoiding a frontal collision or a dangerous veering off the road trajectory. Secondarily, the energy absorption measured by barrier deformation or any other energy dissipation method is beneficial to the car occupant safety. Considering the previous tasks and some severity occupant index like ASI, THIV and PHD, the performance of a guardrail and other concrete barriers are classified. Besides, it is investigated the fail mechanism of bolted connections and its influence on the guardrail impact result of an automobile. Special attention was taken into the material behavior modeling under low and high strain rates. Thereby, the need of accessing dynamic material properties motivated the design and manufacture of a Hopkinson Bar set-up for tension and compression tests up to 5000s-1. In addition, a simplified analytical model of a guardrail subjected to a static force was settled in order to validate a guardrail finite element model. A parametric study of the bolted connection failure was performed through several impact simulations of a light car model and a guardrail according to EN 1317 standard. The impact simulation results using a light vehicle car model and different barriers types were compared through the occupant severity index showing that the guardrail is a safer system than concrete barrier with New Jersey or vertical profile.
14

Impacts analysis for inverse integrated assessments of climate change

Füssel, Hans-Martin January 2003 (has links)
Diese Dissertation beschreibt die Entwicklung und Anwendung des Klimawirkungsmoduls des ICLIPS-Modells, eines integrierten Modells des Klimawandels ('Integrated Assessment'-Modell). Vorangestellt ist eine Diskussion des gesellschaftspolitischen Kontexts, in dem modellbasiertes 'Integrated Assessment' stattfindet, aus der wichtige Anforderungen an die Spezifikation des Klimawirkungsmoduls abgeleitet werden. <br /> <br /> Das 'Integrated Assessment' des Klimawandels umfasst eine weiten Bereich von Aktivitäten zur wissenschaftsbasierten Unterstützung klimapolitischer Entscheidungen. Hierbei wird eine Vielzahl von Ansätzen verfolgt, um politikrelevante Informationen über die erwarteten Auswirkungen des Klimawandels zu berücksichtigen. Wichtige Herausforderungen in diesem Bereich sind die große Bandbreite der relevanten räumlichen und zeitlichen Skalen, die multifaktorielle Verursachung vieler 'Klimafolgen', erhebliche wissenschaftliche Unsicherheiten sowie die Mehrdeutigkeit unvermeidlicher Werturteile. Die Entwicklung eines hierarchischen Konzeptmodells erlaubt die Strukturierung der verschiedenen Ansätze sowie die Darstellung eines mehrstufigen Entwicklungsprozesses, der sich in der Praxis und der zu Grunde liegenden Theorie von Studien zur Vulnerabilität hinsichtlich des Klimawandels wiederspiegelt. <br /> <br /> 'Integrated Assessment'-Modelle des Klimawandels sind wissenschaftliche Werkzeuge, welche eine vereinfachte Beschreibung des gekoppelten Mensch-Klima-Systems enthalten. Die wichtigsten entscheidungstheoretischen Ansätze im Bereich des modellbasierten 'Integrated Assessment' werden im Hinblick auf ihre Fähigkeit zur adäquaten Darstellung klimapolitischer Entscheidungsprobleme bewertet. Dabei stellt der 'Leitplankenansatz' eine 'inverse' Herangehensweise zur Unterstützung klimapolitischer Entscheidungen dar, bei der versucht wird, die Gesamtheit der klimapolitischen Strategien zu bestimmen, die mit einer Reihe von zuvor normativ bestimmten Mindestkriterien (den sogenannten 'Leitplanken') verträglich sind. Dieser Ansatz verbindet bis zu einem gewissen Grad die wissenschaftliche Strenge und Objektivität simulationsbasierter Ansätze mit der Fähigkeit von Optimierungsansätzen, die Gesamtheit aller Entscheidungsoptionen zu berücksichtigen. Das ICLIPS-Modell ist das erste 'Integrated Assessment'-Modell des Klimawandels, welches den Leitplankenansatz implementiert. <br /> <br /> Die Darstellung von Klimafolgen ist eine wichtige Herausforderung für 'Integrated Assessment'-Modelle des Klimawandels. Eine Betrachtung bestehender 'Integrated Assessment'-Modelle offenbart große Unterschiede in der Berücksichtigung verschiedener vom Klimawandel betroffenen Sektoren, in der Wahl des bzw. der Indikatoren zur Darstellung von Klimafolgen, in der Berücksichtigung nicht-klimatischer Entwicklungen einschließlich gezielter Anpassungsmaßnahmen an den Klimawandel, in der Behandlung von Unsicherheiten und in der Berücksichtigung von 'singulären' Ereignissen. 'Integrated Assessment'-Modelle, die auf einem Inversansatz beruhen, stellen besondere Anforderungen an die Darstellung von Klimafolgen. Einerseits muss der Detaillierungsgrad hinreichend sein, um Leitplanken für Klimafolgen sinnvoll definieren zu können; andererseits muss die Darstellung effizient genug sein, um die Gesamtheit der möglichen klimapolitischen Strategien erkunden zu können. Großräumige Singularitäten können häufig durch vereinfachte dynamische Modelle abgebildet werden. Diese Methode ist jedoch weniger geeignet für reguläre Klimafolgen, bei denen die Bestimmung relevanter Ergebnisse in der Regel die Berücksichtigung der Heterogenität von klimatischen, naturräumlichen und sozialen Faktoren auf der lokalen oder regionalen Ebene erfordert. <br /> <br /> Klimawirkungsfunktionen stellen sich als die geeignetste Darstellung regulärer Klimafolgen im ICLIPS-Modell heraus. Eine Klimawirkungsfunktion beschreibt in aggregierter Form die Reaktion eines klimasensitiven Systems, wie sie von einem geographisch expliziten Klimawirkungsmodell für eine repräsentative Teilmenge möglicher zukünftiger Entwicklungen simuliert wurde. Die in dieser Arbeit vorgestellten Klimawirkungsfunktionen nutzen die globale Mitteltemperatur sowie die atmosphärische CO2-Konzentration als Prädiktoren für global und regional aggregierte Auswirkungen des Klimawandels auf natürliche Ökosysteme, die landwirtschaftliche Produktion und die Wasserverfügbarkeit. Die Anwendung einer 'Musterskalierungstechnik' ermöglicht hierbei die Berücksichtigung der regionalen und saisonalen Muster des Klimaänderungssignals aus allgemeinen Zirkulationsmodellen, ohne die Effizienz der dynamischen Modellkomponenten zu beeinträchtigen. <br /> <br /> Bemühungen zur quantitativen Abschätzung zukünftiger Klimafolgen sehen sich bei der Wahl geeigneter Indikatoren in der Regel einem Zielkonflikt zwischen der Relevanz eines Indikators für Entscheidungsträger und der Zuverlässigkeit, mit der dieser bestimmt werden kann, gegenüber. Eine Reihe von nichtmonetären Indikatoren zur aggregierten Darstellung von Klimafolgen in Klimawirkungsfunktionen wird präsentiert, welche eine Balance zwischen diesen beiden Zielen anstreben und gleichzeitig die Beschränkungen berücksichtigen, die sich aus anderen Komponenten des ICLIPS-Modells ergeben. Klimawirkungsfunktionen werden durch verschiedene Typen von Diagrammen visualisiert, welche jeweils unterschiedliche Perspektiven auf die Ergebnismenge der Klimawirkungssimulationen erlauben.<br /> <br /> Die schiere Anzahl von Klimawirkungsfunktionen verhindert ihre umfassende Darstellung in dieser Arbeit. Ausgewählte Ergebnisse zu Veränderungen in der räumlichen Ausdehnung von Biomen, im landwirtschaftlichen Potential verschiedener Länder und in der Wasserverfügbarkeit in mehreren großen Einzugsgebieten werden diskutiert. Die Gesamtheit der Klimawirkungsfunktionen wird zugänglich gemacht durch das 'ICLIPS Impacts Tool', eine graphische Benutzeroberfläche, die einen bequemen Zugriff auf über 100.000 Klimawirkungsdiagramme ermöglicht. Die technischen Aspekte der Software sowie die zugehörige Datenbasis wird beschrieben. <br /> <br /> Die wichtigste Anwendung von Klimawirkungsfunktionen ist im 'Inversmodus', wo sie genutzt werden, um Leitplanken zur Begrenzung von Klimafolgen in gleichzeitige Randbedingungen für Variablen aus dem optimierenden ICLIPS-Klima-Weltwirtschafts-Modell zu übersetzen. Diese Übersetzung wird ermöglicht durch Algorithmen zur Bestimmung von Mengen erreichbarer Klimazustände ('reachable climate domains') sowie zur parametrisierten Approximation zulässiger Klimafenster ('admissible climate windows'), die aus Klimawirkungsfunktionen abgeleitet werden. Der umfassende Bestand an Klimawirkungsfunktionen zusammen mit diesen Algorithmen ermöglicht es dem integrierten ICLIPS-Modell, in flexibler Weise diejenigen klimapolitischen Strategien zu bestimmen, welche bestimmte in biophysikalischen Einheiten ausgedrückte Begrenzungen von Klimafolgen explizit berücksichtigen. Diese Möglichkeit bietet kein anderes intertemporal optimierendes 'Integrated Assessment'-Modell. Eine Leitplankenanalyse mit dem integrierten ICLIPS-Modell unter Anwendung ausgewählter Klimawirkungsfunktionen für Veränderungen natürlicher Ökosysteme wird beschrieben. In dieser Analyse werden so genannte 'notwendige Emissionskorridore' berechnet, die vorgegebene Beschränkungen hinsichtlich der maximal zulässigen globalen Vegetationsveränderungen und der regionalen Klimaschutzkosten berücksichtigen. Dies geschieht sowohl für eine 'Standardkombination' der drei gewählten Kriterien als auch für deren systematische Variation. <br /> <br /> Eine abschließende Diskussion aktueller Entwicklungen in der 'Integrated Assessment'-Modellierung stellt diese Arbeit mit anderen einschlägigen Bemühungen in Beziehung. / This thesis describes the development and application of the impacts module of the ICLIPS model, a global integrated assessment model of climate change. The presentation of the technical aspects of this model component is preceded by a discussion of the sociopolitical context for model-based integrated assessments, which defines important requirements for the specification of the model.<br /> <br /> Integrated assessment of climate change comprises a broad range of scientific efforts to support the decision-making about objectives and measures for climate policy, whereby many different approaches have been followed to provide policy-relevant information about climate impacts. Major challenges in this context are the large diversity of the relevant spatial and temporal scales, the multifactorial causation of many climate impacts', considerable scientific uncertainties, and the ambiguity associated with unavoidable normative evaluations. A hierarchical framework is presented for structuring climate impact assessments that reflects the evolution of their practice and of the underlying theory.<br /> <br /> Integrated assessment models of climate change (IAMs) are scientific tools that contain simplified representations of the relevant components of the coupled society-climate system. The major decision-analytical frameworks for IAMs are evaluated according to their ability to address important aspects of the pertinent social decision problem. The guardrail approach is presented as an inverse' framework for climate change decision support, which aims to identify the whole set of policy strategies that are compatible with a set of normatively specified constraints (guardrails'). This approach combines, to a certain degree, the scientific rigour and objectivity typical of predictive approaches with the ability to consider virtually all decision options that is at the core of optimization approaches. The ICLIPS model is described as the first IAM that implements the guardrail approach.<br /> <br /> The representation of climate impacts is a key concern in any IAM. A review of existing IAMs reveals large differences in the coverage of impact sectors, in the choice of the impact numeraire(s), in the consideration of non-climatic developments, including purposeful adaptation, in the handling of uncertainty, and in the inclusion of singular events. IAMs based on an inverse approach impose specific requirements to the representation of climate impacts. This representation needs to combine a level of detail and reliability that is sufficient for the specification of impact guardrails with the conciseness and efficiency that allows for an exploration of the complete domain of plausible climate protection strategies. Large-scale singular events can often be represented by dynamic reduced-form models. This approach, however, is less appropriate for regular impacts where the determination of policy-relevant results generally needs to consider the heterogeneity of climatic, environmental, and socioeconomic factors at the local or regional scale.<br /> <br /> Climate impact response functions (CIRFs) are identified as the most suitable reduced-form representation of regular climate impacts in the ICLIPS model. A CIRF depicts the aggregated response of a climate-sensitive system or sector as simulated by a spatially explicit sectoral impact model for a representative subset of plausible futures. In the CIRFs presented here, global mean temperature and atmospheric CO2 concentration are used as predictors for global and regional impacts on natural vegetation, agricultural crop production, and water availability. Application of a pattern scaling technique makes it possible to consider the regional and seasonal patterns in the climate anomalies simulated by several general circulation models while ensuring the efficiency of the dynamic model components.<br /> <br /> Efforts to provide quantitative estimates of future climate impacts generally face a trade-off between the relevance of an indicator for stakeholders and the exactness with which it can be determined. A number of non-monetary aggregated impact indicators for the CIRFs is presented, which aim to strike the balance between these two conflicting goals while taking into account additional constraints of the ICLIPS modelling framework. Various types of impact diagrams are used for the visualization of CIRFs, each of which provides a different perspective on the impact result space.<br /> <br /> The sheer number of CIRFs computed for the ICLIPS model precludes their comprehensive presentation in this thesis. Selected results referring to changes in the distribution of biomes in different biogeographical regions, in the agricultural potential of various countries, and in the water availability in selected major catchments are discussed. The full set of CIRFs is accessible via the ICLIPS Impacts Tool, a graphical user interface that provides convenient access to more than 100,000 impact diagrams developed for the ICLIPS model. The technical aspects of the software are described as well as the accompanying database of CIRFs.<br /> <br /> The most important application of CIRFs is in inverse' mode, where they are used to translate impact guardrails into simultaneous constraints for variables from the optimizing ICLIPS climate-economy model. This translation is facilitated by algorithms for the computation of reachable climate domains and for the parameterized approximation of admissible climate windows derived from CIRFs. The comprehensive set of CIRFs, together with these algorithms, enables the ICLIPS model to flexibly explore sets of climate policy strategies that explicitly comply with impact guardrails specified in biophysical units. This feature is not found in any other intertemporally optimizing IAM. A guardrail analysis with the integrated ICLIPS model is described that applies selected CIRFs for ecosystem changes. So-called necessary carbon emission corridors' are determined for a default choice of normative constraints that limit global vegetation impacts as well as regional mitigation costs, and for systematic variations of these constraints.<br /> <br /> A brief discussion of recent developments in integrated assessment modelling of climate change connects the work presented here with related efforts.
15

Radar Characteristics Study for the Development of Surrogate Roadside Objects

Jun Lin (5931089) 16 January 2020 (has links)
<div>Driving safety is a very important topic in vehicle development. One of the biggest threat of driving safety is road departure. Many vehicle active safety technologies have been developed to warn and mitigate road departure in recent years. In order to evaluate the performance of road departure warning and mitigation technologies, the standard testing environment need to be developed. The testing environment shall be standardized to provide consistent and repeatable features in various locations worldwide and in various seasons. The testing environment should also be safe to the vehicle under test in case the safety features do not function well. Therefore, soft, durable and reusable surrogates of roadside objects need to be used. Meanwhile, all surrogates should have the same representative characteristics of real roadside objects to different automotive sensors (e.g. radar, LIDAR and camera). This thesis describes the study on identifying the radar characteristics of common roadside objects, metal guardrail, grass, and concrete divider, and the development of the required radar characteristics of surrogate objects. The whole process is divided into two steps. The first step is to find the proper methods to measure the radar properties of those three roadside objects. The measurement result of each roadside object will be used as the requirement for making its surrogate. The second step is to create the material for developing the surrogate of each roadside object. In the experimental results demonstrate that all three surrogates satisfy their radar characteristics requirements.</div>
16

Guardrail detection for landmark-based localization

Gumaelius, Nils January 2022 (has links)
A requirement for safe autonomous driving is to have an accurate global localization of the ego vehicle. Methods based on Global Navigation Satellite System (GNSS) are the most common but are not precise enough in areas without good satellite signals. Instead, methods likelandmark-based localization (LBL) can be used. In LBL, sensors onboard the vehicle detectlandmarks near the vehicle. With these detections, the vehicle’s position is deduced by looking up matching landmarks on a high-definition map. Commonly found along roads, stretching for long distances, guardrails are a great landmark that can be used for LBL. In this thesis, two different methods are proposed to detect and vectorize guardrails from vehicle sensor data to enable future map matching for LBL. The first method uses semantically labeled LiDAR data with pre-classified guardrail LiDAR points as input data. The method is based on the DBSCAN clustering algorithm to cluster and filter out false positives from the pre-classified LiDAR points. The second algorithm uses raw LiDAR data as input. The algorithm finds guardrail candidate points by segmenting high-densityareas and matching these with thresholds taken from the geometry of guardrails. Similar to the first method, these are then clustered into guardrail clusters. The clusters are then vectorized into the wanted output of a 2D vector, corresponding to points inside the guardrail with aspecific interval. To evaluate the performance of the proposed algorithms, simulations from real-life data are analyzed in both a quantitative and qualitative way. The qualitative experiments showcase that both methods perform well even in difficult scenarios. Timings of the simulations show that both methods are fast enough to be applicable in real-time use cases. The defined performance measures show that the method using raw LiDAR data is more robust and manages to detect more and longer parts of the guardrails.

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