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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.
121

Application of a Two-Level Targeter for Low-Thrust Spacecraft Trajectories

Collin E. York (5930948) 16 January 2019 (has links)
<div>Applications of electric propulsion to spaceflight in multi-body environments require a targeting algorithm to produce suitable trajectories on the ground and on board spacecraft. The two-level targeter with low thrust (TLT-LT) provides a framework to implement differential corrections in computationally-limited autonomous spacecraft applications as well as the larger design space of pre-mission planning. Extending existing two-level corrections algorithms, applications of the TLT-LT to spacecraft with a range of propulsive capabilities, from nearly-impulsive to low-thrust, are explored. The process of determining partial derivatives is generalized, allowing reduced logical complexity and increased flexibility in designing sequences of thrusting and ballistic segments. Various implementation strategies are explored to enforce constraints on time and other design variables as well as to improve convergence behavior through the use of dynamical systems theory and attenuation factors. The TLT-LT is applied to both nearly-impulsive and low-thrust spacecraft applications in the circular restricted three-body problem to demonstrate the flexibility of the framework to correct trajectories across the spectrum of thrust magnitude. Finally, parameter continuation is employed to extend a family of trajectories from a solution with nearly-impulsive thrust events to the low-thrust regime, and the characteristics of this transition are investigated.</div>
122

Thrust Vector Control of Multi-Body Systems Subject to Constraints

Nguyen, Tâm Willy 11 December 2018 (has links) (PDF)
This dissertation focuses on the constrained control of multi-body systems which are actuated by vectorized thrusters. A general control framework is proposed to stabilize the task configuration while ensuring constraints satisfaction at all times. For this purpose, the equations of motion of the system are derived using the Euler-Lagrange method. It is seen that under some reasonable conditions, the system dynamics are decoupled. This property is exploited in a cascade control scheme to stabilize the points of equilibrium of the system. The control scheme is composed of an inner loop, tasked to control the attitude of the vectorized thrusters, and an outer loop which is tasked to stabilize the task configuration of the system to a desired configuration. To prove stability, input-to-state stability and small gain arguments are used. All stability properties are derived in the absence of constraints, and are shown to be local. The main result of this analysis is that the proposed control scheme can be directly applied under the assumption that a suitable mapping between the generalized force and the real inputs of the system is designed. This thesis proposes to enforce constraints by augmenting the control scheme with two types of Reference Governor units: the Scalar Reference Governor, and the Explicit Reference Governor. This dissertation presents two case studies which inspired the main generalization of this thesis: (i) the control of an unmanned aerial and ground vehicle manipulating an object, and (ii) the control of a tethered quadrotor. Two further case studies are discussed afterwards to show that the generalized control framework can be directly applied when a suitable mapping is designed. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished
123

Structural Geology of Eastern Part of Dairy Ridge Quadrangle and Western Part of Meachum Ridge Quadrangle, Utah

Kienast, Val A. 01 May 1985 (has links)
A detailed geologic investigation was made of the eastern part of the Dairy Ridge Quadrangle and the western part of the Meachum Ridge Quadrangle, Utah. The area is located in north-central Utah in Rich County. It lies between lat. 41°22'30" N. and lat. 41° 28'50" N. and between long. 111° 21'40" W. and long. 111°25'15" W. The area measures 13.8 km in the north-south direction and 5.5 km in the east-west direction. It is on the eastern side of the Wasatch Range about 20 km west-southwest of Randolph, Utah. Stratigraphic units of Precambrian to Cambrian age crop out in the western part of the area, above the Woodruff thrust fault, and dip west. These include the Precambrian Mutual Formation and the Cambrian Geertsen Canyon Quartzite. Units of Pennsylvanian to Jurassic age crop out in the eastern part of the area below the Woodruff thrust fault. They dip west and are overturned to the east. These units include the following: Pennsylvanian Weber Formation, Permian Grandeur Member of the Park City Formation, Permian Phosphoria Formation, Triassic Thaynes Limestone, Triassic Ankareh Formation, Jurassic Nugget Sandstone, and Jurassic Twin Creek Limestone. The Tertiary Wasatch Formation unconformably overlies all older units in places. The Woodruff thrust fault is the major structural feature of the area. Quartzite of the Precambrian Mutual Formation is thrust eastward over the Pennsylvanian Weber Formation as well as over formations of Permian and Triassic ages. The Woodruff thrust fault strikes about N. 20° E. and dips 18° W. to 33° W. Stratigraphic throw is at least 5,800 m. Probable horizontal displacement is tens of kilometers. The stratigraphic units, under the thrust fault, dip west and are overturned to the east. They form the western limb of a large asymmetrical syncline. The overturned units are cut by a west-dipping high-angle thrust fault. The syncline and the thrust faults were produced by the Sevier orogeny which began in latest Jurassic or earliest Cretaceous time. Deformation may have continued into Paleocene time.
124

Aircraft Simulator / Simulator för flygfarkost

Iskender, Hani January 2005 (has links)
<p>At Saab Bofors Dynamics there are projects running which purpose are to develop simulators for various weapon systems like RBS 70. In order to manage creating real working simulators Saab Bofors Dynamics has to do more research and this final thesis is a part of this process.</p><p>This final thesis has been performed at Saab Bofors Dynamics in the department of modelling and simulation, RTRKM, in Karlskoga. The purpose was to develop a control algorithm which makes it possible for an aircraft to behave real when controlling through a joystick.</p><p>The conclusions show that further improvements are needed before the aircraft behaves entirely by the laws of physics. Among other things it is necessary to decrease the number of delimitations that have been done.</p>
125

Surface and subsurface structures of the western Valley and Ridge in Tennessee and geometry and kinematics that permit reconstruction of the Tennessee salient, southern Appalachians

Whisner, Jennifer Kathleen 01 August 2010 (has links)
The southern and central Appalachian foreland fold-thrust belt comprises a series of orogen -scale curves that extend from Alabama to New York. One of these is the Tennessee salient, a foreland-convex curve that extends from Cartersville, Georgia, to Roanoke, Virginia. Development of a kinematic model for deformation in the salient has been hindered by a paucity of penetrative deformation in this generally low temperature, low volume-loss portion of the orogen. Industry seismic reflection lines provide greater resolution of subsurface geometry of both the basement surface and the overlying fold-thrust belt, confirming some previous interpretations and changing others. A series of cross sections based on the seismic reflection data incorporates the improved understanding of basement geometry, as well as new interpretations of fold-thrust belt structures such as a sub-thrust detachment fold along the western margin of the Valley and Ridge, a smaller detachment fold along the Cumberland Escarpment, and a duplex below the Knoxville sheet in southeastern Tennessee. The cross sections, combined with recently published analyses of calcite twin strain and paleomagnetic data around the salient, provide sufficient data to develop a new palinspastic reconstruction method and to propose a kinematic model for development of the salient. The basis of the reconstruction method is, in areas where the front of the indenter is oriented oblique to transport, the maximum shortening direction and particle displacement paths are also oblique to the bulk transport direction. Cross sections, kinematic indicators, and palinspastic reconstructions suggest that the Tennessee salient is a primary arc formed by a combination of uniform displacement in a single direction and transport-parallel simple shear (plane strain), that most major faults formed initially curved in front of the irregularly shaped Blue Ridge-Inner Piedmont indenter, and that transport in the fold-thrust belt may have occurred by plan view movement on networks of minor faults, which permitted forelandward propagation of the curved faults without significant rotation. Although the technique does not provide a unique solution, the resulting palinspastic restoration is kinematically admissible and geometrically reasonable. So, it may improve palinspastic restorations of facies in basins with no vertical axis rotations and minimal penetrative strain. Attachments are in PDF format and may be opened with Adobe Reader™.
126

Geological Evolution of the Supracrustal Palaeoproterozoic Hamrånge Group: A Svecofennian Case Study

Ogenhall, Erik January 2010 (has links)
The work presented in this thesis utilizes several geological methods to investigate the origin and evolution of the supracrustal rocks in the Palaeoproterozoic Hamrånge Group (HG) in the south-central Swedish Svecofennian. The first paper is based on whole-rock geochemistry to show the plate tectonic setting of volcanic rocks within the HG. This indicates that the environment was probably an oceanic volcanic arc. Geochronology, used in paper two, shows that the volcanism was active at 1888±6 Ma and that the sediments forming the stratigraphically overlying quartzite were deposited after 1855±10 Ma, with provenance ages overlapping both the volcanic rocks and the 1.86-1.84 Ga continental margin Ljusdal granitoids. In the third paper, thermobarometry was applied to samples from the HG, the migmatitic Ockelbo sub-domain to the south, and the 1.81 Ga Hagsta Gneiss Zone (HGZ) that separate these two units. The results show distinct differences in the metamorphic conditions that have affected the HG and the Ockelbo sub-domain, supporting previous interpretations that the HGZ is an important crustal structure, possibly a terrane or domain boundary. Paper four deals with the structural geology of the Hamrånge area. The study shows that the volcanic rocks and the underlying mica schist have been subjected to three deformation episodes (D1-D3), while the uppermost quartzite was most likely only affected by D2 and D3. While structures related to D1 are rarely seen, D2 resulted in a penetrative foliation, strong lineations and NW-vergent folding and thrusting. D3 is a result of a N-S compression that formed regional E-W folds and steep, ca. NW-SE shear zones, e.g. the HGZ. The results presented in this thesis, integrated with previously published data, outline a model for the geological evolution of the Hamrånge area: At 1.89 Ga a volcanic arc formed that subsequently collided with a continental margin resulting in the first deformation episode, D1, and probably a metamorphic event. This was possibly followed by an extensional period, after 1855±10 Ma, forming a basin that accumulated sediments later to form the quartzite stratigraphically on top of the volcanic rocks. The second deformation episode, D2, formed a fold-thrust belt when the supracrustal HG was thrusted to the NW, on top of the 1.86-1-84 Ga Ljusdal Domain. Flattening and a second metamorphic period followed this thickening of the crust. The last ductile deformation, D3, caused by regional tectonic forces, resulted in F3-folds that matured into ca. 1.8 Ga large-scale, steep shear zones transecting the Fennoscandian Shield.
127

The Ten Stone Ranges Structural Complex of the central Mackenzie Mountains fold-and-thrust belt: a structural analysis with implications on the Plateau Fault and regional detachment level

MacDonald, Justin January 2009 (has links)
The Cordilleran Orogen affected majority of the western margin of ancient continental North America in the Cretaceous, which is well recorded in the Foreland Belt. The Mackenzie Mountains fold-and-thrust belt is located primarily in the westernmost Northwest Territories and easternmost Yukon Territory in northern Canada. The mountains are often described as the northern extension of the Rocky Mountains to the south which are one of the world’s best examples of a thin-skinned fold-and-thrust belt. Within the Mackenzie Mountains, Neo-Proterozoic through Cretaceous sedimentary rocks record the Laramide aged deformation, with a range of structures that vary in size and complexity. Previous mapping by the Geological Survey of Canada produced a series of reconnaissance maps that are still in use today, many of which are available in only black and white. This study is focused on a part of the 1:250 000 scale NTS 106A Mount Eduni map sheet from Geological Survey of Canada reconnaissance mapping in 1974. The study involved re-mapping a large panel at 1:50 000 scale to better understand the structural geometry, regional shortening and the depth of the underlying detachment level. Through systematic geologic mapping and structural analyses, this study presents a balanced regional cross-section, numerous serial cross-sections and a detailed geologic map of the study area, the Ten Stone Ranges Structural Complex. The serial cross-sections were used to define the geometry of the Cache Lake Fold, a large fault-bend-fold system that involves a folded thrust fault and complicated subsurface geometry. In addition to this, the sections confirmed that the TSRSC is a transfer zone whereby a series of thrust faults and décollement folds are responsible for much of the displacement and shortening in the Mount Eduni map sheet. The balanced regional cross-section was constructed across a number of key structural elements, in particular the Plateau Fault, a regional structure with a > 250 kilometer strike length and the subject of much debate as to its geometry. In addition to this structure, the cross-section transects the Cache Lake Fold and the Shattered Range Anticline, a regional box shaped anticline that was used for a “depth to detachment” calculation. By examining the regional detachment level estimated from the balanced cross-section and calculating the detachment depth using the Shattered Range Anticline the detachment depth was found to be – 11.3 kilometers below the current erosional level. This study is the first structural analyses of the Mount Eduni map sheet, particularly the Ten Stone Ranges Structural Complex, and has resulted in an estimate of the detachment depth for the area, a shortening estimate of > 7 kilometers across the 50 kilometer line of section and a displacement estimate for the Plateau Thrust of > 20 kilometers.
128

Aircraft Simulator / Simulator för flygfarkost

Iskender, Hani January 2005 (has links)
At Saab Bofors Dynamics there are projects running which purpose are to develop simulators for various weapon systems like RBS 70. In order to manage creating real working simulators Saab Bofors Dynamics has to do more research and this final thesis is a part of this process. This final thesis has been performed at Saab Bofors Dynamics in the department of modelling and simulation, RTRKM, in Karlskoga. The purpose was to develop a control algorithm which makes it possible for an aircraft to behave real when controlling through a joystick. The conclusions show that further improvements are needed before the aircraft behaves entirely by the laws of physics. Among other things it is necessary to decrease the number of delimitations that have been done.
129

The Ten Stone Ranges Structural Complex of the central Mackenzie Mountains fold-and-thrust belt: a structural analysis with implications on the Plateau Fault and regional detachment level

MacDonald, Justin January 2009 (has links)
The Cordilleran Orogen affected majority of the western margin of ancient continental North America in the Cretaceous, which is well recorded in the Foreland Belt. The Mackenzie Mountains fold-and-thrust belt is located primarily in the westernmost Northwest Territories and easternmost Yukon Territory in northern Canada. The mountains are often described as the northern extension of the Rocky Mountains to the south which are one of the world’s best examples of a thin-skinned fold-and-thrust belt. Within the Mackenzie Mountains, Neo-Proterozoic through Cretaceous sedimentary rocks record the Laramide aged deformation, with a range of structures that vary in size and complexity. Previous mapping by the Geological Survey of Canada produced a series of reconnaissance maps that are still in use today, many of which are available in only black and white. This study is focused on a part of the 1:250 000 scale NTS 106A Mount Eduni map sheet from Geological Survey of Canada reconnaissance mapping in 1974. The study involved re-mapping a large panel at 1:50 000 scale to better understand the structural geometry, regional shortening and the depth of the underlying detachment level. Through systematic geologic mapping and structural analyses, this study presents a balanced regional cross-section, numerous serial cross-sections and a detailed geologic map of the study area, the Ten Stone Ranges Structural Complex. The serial cross-sections were used to define the geometry of the Cache Lake Fold, a large fault-bend-fold system that involves a folded thrust fault and complicated subsurface geometry. In addition to this, the sections confirmed that the TSRSC is a transfer zone whereby a series of thrust faults and décollement folds are responsible for much of the displacement and shortening in the Mount Eduni map sheet. The balanced regional cross-section was constructed across a number of key structural elements, in particular the Plateau Fault, a regional structure with a > 250 kilometer strike length and the subject of much debate as to its geometry. In addition to this structure, the cross-section transects the Cache Lake Fold and the Shattered Range Anticline, a regional box shaped anticline that was used for a “depth to detachment” calculation. By examining the regional detachment level estimated from the balanced cross-section and calculating the detachment depth using the Shattered Range Anticline the detachment depth was found to be – 11.3 kilometers below the current erosional level. This study is the first structural analyses of the Mount Eduni map sheet, particularly the Ten Stone Ranges Structural Complex, and has resulted in an estimate of the detachment depth for the area, a shortening estimate of > 7 kilometers across the 50 kilometer line of section and a displacement estimate for the Plateau Thrust of > 20 kilometers.
130

Fold-and-thrust belt deformation of the Hongliuhe Group: a Permian tectonic closure record of the Central Asian Orogenic Belt, NW China

Cleven, Nathan January 2011 (has links)
The Early Permian strata of the Hongliuhe Group, NW China, experienced a thin-skinned fold-and-thrust belt style of deformation that recorded the final stages of amalgamation of the Beishan orogenic collage, a part of the Central Asian Orogenic Belt. The Hongliuhe Group was syn-orogenically deposited on an undetermined foreland, with the Mazongshan arc terrane acting as the hinterland. In this study results from detailed mapping combined with a regional analysis elucidate involvement of a northward-dipping subduction system with the collision. Well-preserved fold-and-thrust belt style deformation mapped in the upper stratigraphy of the Hongliuhe Group exhibits dominantly south-southeast verging structure, including shear folding, low-angle thrust ramping, imbrication and duplexing. Restoration of a portion of a mapped outcrop-scale cross-section estimates the accommodation of a minimum of 24% shortening. Lower stratigraphy shows discrete, steeper, north-over-south dip-slip ductile shear zones that bound packages of less deformed Hongliuhe Group strata. Fault displacement is considered to have been prolonged enough to juxtapose basal formations in northerly hangingwalls against upper formations in southerly footwalls. Faulting is closely associated with the creation of large-scale brittle-ductile eye-fold structures that are postulated to be sheath folds. The most examined and mapped structure, 16km wide, is a synclinal structure with axes plunging steeply towards its center. The ellipticity of the exposed bedding traces increases towards the center of the eye-fold, implying a structural relationship with metamorphic shear zones. Except for large-scale folding, the bulk of its strata remain relatively undeformed and have preserved primary soft-sediment deformation structures indicating younging towards the center on both limbs of the synclinal structure. Stratigraphic reconstruction of the Hongliuhe Group that considers the significant faulting shows that the Group's basal conglomerates unconformably overlie a Late-Carboniferous volcanic assemblage. The clast lithotypes of the conglomeratic successions change from polymictic metamorphic rocks at the base to monomictic granitoid clasts mid-section, showing the gradual unroofing sequence of the provenance. The stratigraphic reconstruction shows a general fining upward sequence, transitioning from terrestrial to nearshore marine depositional environments that, and in conjunction with the conglomeratic successions, suggests that the tectonic setting for deposition of the Hongliuhe Group is a foreland basin. Considering the deformation styles reported in this study, the Hongliuhe Group is interpreted to be a foreland fold-and-thrust belt. Stratigraphic reconstruction of the Hongliuhe Group that considers the significant faulting shows that the Group’s basal conglomerates unconformably overlie a Late Carboniferous volcanic assemblage. The clast lithotypes of the conglomeratic successions change from polymictic metamorphic rocks at the base to monomictic granitoid mid-section, showing the gradual unroofing sequence of the provenance. The stratigraphic reconstruction shows a general fining upward sequence through nearshore depositional environments that, and in conjunction with the conglomeratic successions, give interpretation that the tectonic setting for deposition of the Hongliuhe Group is a foreland basin. Considering the deformation styles reported in this study the Hongliuhe Group is interpreted to be a foreland fold-and-thrust belt.

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