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1
Miller, James Thomas Ph D. Massachusetts Institute of Technology. „Mechanical behavior of elastic rods under constraint“. Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/88280.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 213-223).
We present the results of an experimental investigation of the mechanics of thin elastic rods under a variety of loading conditions. Four scenarios are explored, with increasing complexity: i) the shape of a naturally curved rod suspended under self-weight, ii) the buckling and post-buckling behavior of a rod compressed inside a cylindrical constraint, iii) the mechanical instabilities arising when a rod is progressively injected into a horizontal cylinder, and iv) strategies for mitigation of these instabilities by dynamic excitation of the constraint. First, we consider the role of natural curvature in determining the shape of a hanging elastic rod suspended under its own weight. We categorize three distinct configurations: planar hooks, localized helices, and global helices. Experimental results are contrasted with simulations and theory and the phase diagram of the system is rationalized. Secondly, in what we call the classic case experiment, we study the buckling and post-buckling behavior of a rod compressed inside a cylindrical constraint. Under imposed displacement, the initially straight rod buckles into a sinusoidal mode and eventually undergoes a secondary instability into a helical configuration. The critical buckling loads are quantified and found to depend strongly on the aspect ratio of the rod to pipe diameter. Thirdly, we inject a thin elastic rod into a horizontal cylinder under imposed velocity in the real case experiment. Friction between the rod and constraining pipe causes an increasing axial load with continued injection. Consecutive buckling transitions lead to straight, sinusoidal, and helical configurations in a spatially heterogeneous distribution. We quantify critical lengths and loads for the onset of the helical instability. The geometric parameters of the system strongly affect the buckling and post-buckling behavior. Finally, we explore active strategies for delaying the onset of helical buckling in the real case. Distributed vertical vibration is applied to the cylindrical constraint, which destabilizes frictional contacts between the rod and pipe. Injection speed, peak acceleration of vibration, and vibration frequency are all found to affect the postponement of helical initiation. The process is rationalized and design
by James T. Miller.
Ph. D.
2
Serrano, David. „Constraint management in conceptual design“. Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14689.
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3
Hermus, James Russell. „Human physical interaction with a circular constraint“. Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118670.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 113-119).
Despite large feedback delays, and many degrees of freedom, humans are incredibly dexterous and excel at physical interaction with complex objects. In this work we developed an upper limb crank turning experiment to study the human controller used to manage physical interaction. Subjects turned a crank with and without visual feedback, in two directions (clockwise and counterclockwise), and in three speed conditions (slow (0.075 rev/s), medium (0.5 rev/s), and fast (2 rev/s)). We made several predictions about the dependent measures including: mean speed, standard deviation of speed, coefficient of variation of speed, mean normal force, and standard deviation of normal force. We hypothesized that subjects should perform the best at slow speeds where the effect of feedback delays, inertial dynamics, and muscle noise decrease. Notably, subjects became more variable at slow speeds, and exerted significant nonzero normal force in the slow condition. At slow speeds, increased speed variability and compressive normal forces cannot be explained by biomechanics - suggesting they result from neural control. Next, the zero-force trajectory was computed. The zero-force trajectory allows for the peripheral biomechanics to be 'subtracted' to 'reveal' the underlying neural commands, expressed in terms of motion. We detected a coincidence of curvature and velocity extrema in the zero-force trajectory. Furthermore, this observation was robust to changes in impedance parameters. This finding is exciting. Even though the hand was confined to a circular path, when the peripheral biomechanics were subtracted, the same velocity curvature relationship seen in unconstrained movements was revealed. Lastly, the increased variability at slow speeds was present in the zero force trajectory. This indicates that the increased variability at slow speeds is a result of neural control, not biomechanics; this finding is consistent with previous research in unconstrained motion.
National Science Foundation National Robotics Initiative Grant No. 1637824
by James Russell Hermus.
S.M.
4
Karstensen, Annette Degn. „Constraint estimation schemes in fracture mechanics“. Thesis, University of Glasgow, 1996. http://theses.gla.ac.uk/7228/.
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Elastic-plastic crack tip constraint has been estimated for the common planar crack geometries. These include single edge cracked bars in tension and bending, centre cracked panels, and double edge cracked bars. The description of the stress field has been modified from a one parameter characterisation, based on K or J, to include a second term. The second parameter is a non-singular term, described either in terms of an elastic T-stress or a Q field. The limits of one and two parameter characterisation are discussed for single edge bars in tension and bending and for centre cracked panels. For the single edge geometries the two parameter characterisation was found to extend the characterisation well beyond the one parameter approach. For the centre cracked panels the two parameter characterisation in terms of a J-Q approach was found to be more accurate than a J-T approach at high levels of deformation. For the single edge cracked bending and tension geometries the second parameter Q is divided into two components named QT and QP. QT is an elastic term which depends on the elastic T stress and is independent of the distance from the crack tip. The second component, QP, arises from global bending on the uncracked ligament. This is a distance dependent term which depends on the level of deformation and can either be expressed as a function of the load normalised by the limit load or as a function of the plastic component of the J-integral. For single edge bend bars the constraint estimation provides a basis for a method of predicting fracture toughness using local failure approach, where the failure criterion is expressed in terms of the stress level ahead of the crack tip. Finally the constraint of mixed mode problem has been analysed and compared with that of pure Mode I problems.
5
Agrawal, Rajiv. „A Constraint Management Approach for Optimal Design of Mechanical Systems“. Connect to resource, 1991. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1225216291.
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6
Forest, Craig Richard 1978. „X-ray telescope foil optics : assembly, metrology, and constraint“. Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/89385.
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7
Dias, Carlson Rachel (Rachel A. ). „Precision constraint of deformable bodies for medical imaging applications“. Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103465.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 102-104).
The purpose of this work is to learn how the performance of a constraint system that interfaces with nonlinear elastic materials such as biological tissue can be predicted by a model. The direct application of this work is the determination of the feasibility of restraining awake and anesthetized mice skulls to submicron levels of movement for biological imaging applications without direct attachment to the skull. A device capable of restricting mouse skull movement to less than a micron in every direction without requiring the rigid attachment of a fixture to the skull would enable studies of bone marrow activity that are not currently possible. No existing work has attempted to determine the performance limits of a constraint system interfacing with nonlinear elastic material. This thesis introduces a model for determining the constraint system performance, and demonstrates how material properties may be tested to determine their relative significance and inclusion in the system model. The theoretical model is applied to the case of an awake mouse to demonstrate that a tissue-interfacing constraint system can only limit movement to hundreds of microns and is not capable of achieving the desired submicron level performance. For the case of an anesthetized mouse, the designed device is tested and achieves the desired sub-micron performance in all three axes for improved imaging capabilities in anesthetized mice.
by Rachel Dias Carlson.
S.M.
8
Anderson, Sterling J. Ph D. Massachusetts Institute of Technology. „Constraint-based navigation for safe, shared control of ground vehicles“. Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/79314.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 138-147).
Human error in machine operation is common and costly. This thesis introduces, develops, and experimentally demonstrates a new paradigm for shared-adaptive control of human-machine systems that mitigates the effects of human error without removing humans from the control loop. Motivated by observed human proclivity toward navigation in fields of safe travel rather than along specific trajectories, the planning and control framework developed in this thesis is rooted in the design and enforcement of constraints rather than the more traditional use of reference paths. Two constraint-planning methods are introduced. The first uses a constrained Delaunay triangulation of the environment to identify, cumulatively evaluate, and succinctly circumscribe the paths belonging to a particular homotopy with a set of semi autonomously enforceable constraints on the vehicle's position. The second identifies a desired homotopy by planning - and then laterally expanding - the optimal path that traverses it. Simulated results show both of these constraint-planning methods capable of improving the performance of one or multiple agents traversing an environment with obstacles. A method for predicting the threat posed to the vehicle given the current driver action, present state of the environment, and modeled vehicle dynamics is also presented. This threat assessment method, and the shared control approach it facilitates, are shown in simulation to prevent constraint violation or vehicular loss of control with minimal control intervention. Visual and haptic driver feedback mechanisms facilitated by this constraint-based control and threat-based intervention are also introduced. Finally, a large-scale, repeated measures study is presented to evaluate this control framework's effect on the performance, confidence, and cognitive workload of 20 drivers teleoperating an unmanned ground vehicle through an outdoor obstacle course. In 1,200 trials, the constraint-based framework developed in this thesis is shown to increase vehicle velocity by 26% while reducing the occurrence of collisions by 78%, improving driver reaction time to a secondary task by 8.7%, and increasing overall user confidence and sense of control by 44% and 12%, respectively. These performance improvements were realized with the autonomous controller usurping less than 43% of available vehicle control authority, on average.
by Sterling J. Anderson.
Ph.D.
9
Mulcahy, Connor Gordon. „Rotation of a slender rod injected into a cylindrical constraint“. Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103460.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 59-61).
We investigate the buckling of a slender elastic rod injected into a cylindrical constraint while undergoing axial rotation. Particular focus is given to extension of the helical buckling length. This problem is of particular application to coiled tubing operations in the oil and gas industry where helical buckling and eventual lockup occur, thereby preventing complete access to horizontal oil wells. Our approach focuses on using desktop experiments to perform a precise exploration of the parameters affecting buckling. We examine two separate modes of axial rotation: continuous rotation and oscillatory rotation. In each case, we demonstrate potential for significant increases in helical buckling length by a factor of as much as 5 within the parameter space studied and develop an understanding of the underlying mechanisms at play. In the case of continuous rotation, we compare our experimental results to theoretical predictions motivated by this work. The extensions in helical buckling length observed here suggest significant application to the problem of helical buckling in coiled tubing operations.
by Connor Gordon Mulcahy.
S.M.
10
Rusli, Leonard Priyatna. „Design and analysis of mechanical assembly via kinematic screw theory“. Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1218042368.
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11
Terfas, Osama Abdulhamid. „Quantification of constraint in three-dimensional fracture mechanics“. Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/2119/.
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Abstract The role of crack tip constraint in three dimensional fracture mechanics has been investigated under elastic-plastic conditions using finite element techniques. Out-of-plane constraint loss has been identified by comparing the mean stress of the three dimensional cracked body with a reference plane strain configuration. This has allowed the quantification of constraint loss due to thickness. This is important for fitness-for-service procedures where the use of standard thick deeply cracked samples inherently leads to conservative assessments. The proximity to plane–strain conditions was investigated, as well as the J-integral along the crack fronts of typical fracture mechanics specimens. It was shown that deep cracks (a/w=0.5) were significantly affected by out-of-plane constraint loss, while the effect was smaller for shallow cracks (a/w=0.1) when in-plane effects were dominant, where a is the crack length and w is the width of the specimen. The out-of-plane effect was confirmed experimentally with a series of fracture mechanics tests on thin and thick deeply cracked fracture mechanics samples. Computational and experimental studies showed that geometries with B/w=0.2 maintained high constraint conditions at the centre plane and exhibited a low fracture toughness, where B is the thickness of the specimen. As such they can be used to measure the plane strain fracture toughness (JIc) as long as the thickness and the ligament exceed 20J/σ0. The increased slope of the resistance JR curve and enhanced fracture toughness were correlated to the loss of out-of-plane constraint that developed in thinner samples (B/w=0.1). A procedure to incorporate the effects of out-of-plane constraint in the R6 failure assessment diagram was proposed. A procedure was developed to determine ductile crack growth of semi-elliptical surface cracks in flat plates. The procedure used the J-a resistance curve developed from standard high and low constraint geometries in conjunction with an analysis of the crack tip stress field using finite element modelling. This allowed the evolution of crack shape under ductile tearing to be modelled. The majority of the work was devoted to the study of surface breaking semi-elliptical cracks subject to bending, uniaxial tension or biaxial loading. Both the mean stress and J-integral were geometry and load dependent, and were non-uniformly distributed around the crack front. Crack growth was dependent on the level of crack tip constraint, and the original crack shape was generally not retained after ductile tearing. In bending the crack growth was suppressed in the thickness direction and the crack extended significantly sub-surface in a stable manner so that the crack adopted a boat shape. In tension the crack extended through the thickness and this was accompanied with extensive growth in the angular range 45ْ-70ْ. In biaxial loading higher constraint levels were observed, however the overall trend of crack growth was similar to uniaxial tension. Finally, the results from the finite element modelling and the crack growth procedure were verified with experimental data. Excellent agreement in the crack shape patterns was observed between the test data and the crack growth models.
12
Hopkins, Jonathan B. (Jonathan Brigham). „Design of parallel flexure systems via Freedom and Constraint Topologies (FACT)“. Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39879.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 391-393).
The aim of this thesis was to generate the knowledge required to represent the possible freedom topologies (motions of a mechanism) and the possible constraint topologies (flexural elements that guide the mechanism) in a form that designers can use to design parallel flexure systems. The framework that links these topologies enables designers to create three-dimensional, multi-axis flexure systems by using "Freedom and Constraint Topologies" (FACT). FACT embodies every possible design solution for parallel flexure systems. This information enables designers to consider every possible design and then select the design that is best suited for a specific application. FACT was created to improve the design processes for small-scale flexure systems and precision machines. For instance, there is a need to create multi-axis nanopositioners for emerging three-dimensional nano-scale research/manufacturing.
(cont.) Through this work the following contributions were made: (1) twenty six unique matching pairs of freedom and constraint spaces were identified; (2) it was proven that these spaces embody all possible solutions; (3) a design process was created to guide a designer from design requirements, to freedom spaces, to constraint spaces, to mechanism designs; (4) a sub-process was created to guide designers in the selection of redundant constraints that help satisfy stiffness and symmetry requirements without altering the mechanism's kinematics; (5) mathematical expressions were created to represent the freedom and constraint spaces in a form that enables computers to identify and manipulate them. In this thesis, three case studies are provided to demonstrate the FACT design process for mechanisms of varying complexity: (1) a compliant spherical ball joint, (2) a compliant probe for a five axis STM, and (3) a compliant rotary flexure are designed. The second case study demonstrates the sub-process for selecting redundant constraints.
by Jonathan Brigham Hopkins.
S.M.
13
Mendieta, Juan Pablo. „The design of an educational tool for visualizing freedom and constraint topologies“. Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45326.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (leaf 29).
The purpose of this thesis project was to figure out how to make a parametric CAD model of a cylindroid, hyperboloid and a hyperbolic paraboloid. These models will help designers better visualize and understand flexure motion and constraint topologies. The models needed to include the lines that form the ruled surface of each shape. It was difficult to model these lines. The equations that represent the shapes define the position of the points on the surface, not the lines of the ruled surface. I had to figure out how to model each line such that the shape's geometric parameters were satisfied and the surface would still be ruled. Using the equations and specific points on the surface, I developed a method to make the parametric CAD models of each shape with the lines on the ruled surface. With this approach, anyone with basic SolidWorks skills can model these shapes to meet their preferences, whether it is a matter of size, resolution of lines or curvature. These shapes will be displayed and handled at conferences to give flexure designers a better physical intuition of the complex geometric entities that make up the essential building blocks of the FACT design process. These geometric shapes were solid modeled with the intention of 3-D printing them.
by Juan Pablo Mendieta.
S.B.
14
Homann, Bradley S. (Bradley Scott). „A constraint-based system for the design and evaluation of precision machine tools“. Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/43569.
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15
Sedore, Blake William Clark. „Assembly lead time reduction in a semiconductor capital equipment plant through constraint based scheduling“. Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/93851.
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Thesis: M. Eng. in Manufacturing, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (page 80).
The assembly protocols for a semiconductor capital equipment machine were analyzed for potential lead time reduction. The objective of this study was to determine the minimum assembly lead time for the machine based on the constraints of design, space, and labor availability. An assembly requires the completion of a set of procedures that each contains assembly tasks. Precedence relationships between tasks indicate for each procedure what other tasks must be completed before it can start. Each procedure was assumed to have constant resource requirements throughout its duration. The Critical Path Method (CPM) was used to identify 13 procedures on the critical path, based on design and space constraints. A preliminary build schedule was developed that prioritized critical path procedures. A trial of this build schedule achieved an assembly lead time of 39 hours, resulting in a 70% reduction from the current average of 5.5 days. This trial was also accomplished with 76% of the average labor hours for assembly. A production build schedule with a lead time of 43 hours was developed based on the trial results. This schedule allows for production rates of up to 5 machines per week to be achieved with the current shift structure of the company, without the incurrence of overtime. A critical path drag analysis identified critical procedures with the highest potential for lead time reduction. The highest drag of a critical path item was 260 minutes, accounting for 10% of the assembly lead time.
by Blake William Clark Sedore.
M. Eng. in Manufacturing
16
Sridhar, Natarajan. „Constraint Management Techniques for The Design of Large-Scale and Complex Mechanical Systems /“. The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487932351059941.
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17
Hopkins, Jonathan B. (Jonathan Brigham). „Design of flexure-based motion stages for mechatronic systems via Freedom, Actuation and Constraint Topologies (FACT)“. Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62511.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 191-195).
The aim of this thesis is to generate the knowledge required to (i) synthesize serial flexure systems and (ii) optimally place actuators using a comprehensive library of geometric shapes called freedom, actuation, and constraint spaces. These geometric shapes guide designers through the creative process of concept generation without compromising engineering rigor. Each shape rapidly conveys the mathematics of screw theory, projective geometry, and constraint-based design by visually depicting regions where constraints and actuators may be placed for synthesizing optimal flexure concepts. In this way, designers may consider every flexure concept that satisfies the desired functional requirements before selecting the final design. FACT was created to improve the design processes for small-scale flexure systems and precision machines. For instance, there is a need to create multi-axis nanopositioners for emerging three-dimensional nano-scale research/manufacturing. Through this work the following contributions were made: (1) the fifty freedom and constraint space types were found that may be used to synthesize both parallel and serial flexure concepts, (2) intermediate freedom spaces were created that help designers stack conjugated flexure elements to avoid or utilize underconstraint, (3) a twist-wrench stiffness matrix was created to model the elastomechanic behavior of flexure systems, (4) the twenty-six actuation spaces were found that help guide designers in placing actuators that minimize motion errors, and (5) a theory was created that determines the force and displacement actuator outputs for accessing a desired DOF once actuators have been placed. A serially conjugated lead screw flexure was designed using the FACT design process and a parallel flexure system was built to validate the theory of actuation described in this thesis.
by Jonathan Brigham Hopkins.
Ph.D.
18
McDermott, Ryan A. „Enhanced reach of a rod injected into a cylindrical constraint by on-off injection and rotation“. Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100883.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 42-43).
Using a desktop scale analog for the injection of a thin rod into a horizontal pipe to service wellbores in the oil industry, we perform an experimental investigation of the effect of rotating a thin rod as it undergoes on-off injection into a cylindrical constraint. When a thin rod is injected into a cylindrical constraint, the force required to continue injection increases over time, thus causing stresses to build inside the rod. These stresses eventually lead to buckling configurations, which can be described as sinusoidal and helical. If the stress in the rod continues to increase while in a helical configuration, the rod will reach a "lock-up" state, where the rod can no longer progress through the cylinder. To perform experiments, a custom manufactured elastic rod is injected into a borosilicate tube. A rotating apparatus was designed and constructed to rotate the rod at the injection site, allowing rotation to propagate through the entire rod, thus causing the length until lock-up to increase. This enhanced reach is directly proportional to rotation speed and radius of the rod, and inversely proportional to injection speed. Initial experiments examined the effect of rotation speed on the release time, which is the time required for a rod in a helical configuration to release into a straight configuration while experiencing rotation. The relationship between rotation speed and release time is exponential, with slower rotation speeds having a large release time and faster rotation speeds reaching an asymptote. The relationship between helical initiation length and release time is linear, but release times vary significantly for the same helical initiation lengths. On-off injection consisted of using a stepper motor to inject the rod with a square wave function that had a 50% duty cycle. The lock up length and helical initiation length were examined for different square wave periods. On-off injection with rotation can enhance the rod's reach by at least 175% as compared to the only rotation condition. This is evidence that on-off injection can significantly enhance the reach of rods injected into cylindrical constraints.
by Ryan A. McDermott.
S.B.
19
Rothwell, Glynn. „Fracture toughness determination using constraint enhanced sub-sized specimens“. Thesis, Liverpool John Moores University, 2003. http://researchonline.ljmu.ac.uk/4971/.
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20
Valdés, R. José Leoncio 1973. „Constraint analysis and throughput improvement at an automotive assembly plant“. Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/84349.
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Thesis (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; in conjunction with the Leaders for Manufacturing Program at MIT, 2003.Includes bibliographical references (leaves 93-94).
by José Leoncio Valdés R.
S.M.
M.B.A.
21
Davies, Christopher Michael. „Study on the dynamic response of a printed circuit board focusing on constraint clearances“. Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1213368683.
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22
Strimling, Jonathan M. (Jonathan Mark). „A constraint based optimization of manufacturing and sales in the copper tubing industry“. Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/41396.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1996, and Thesis (M.S.)--Massachusetts Institute of Technology, Sloan School of Management, 1996.Includes bibliographical references (p. 81-82).
by Jonathan M. Strimling.
M.S.
23
Du, Lucy W. „Design of a constraint device for compliant bodies using quasi-conformal contact surfaces as applied to mouse imaging“. Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104291.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 99-101).
The purpose of this work is the modeling and prototyping of quasi-conformal constraint contacts and the investigation of their positioning ability for compliant bodies, specifically for the holding of mice in optical imaging setups. The direct application of this work is the restraint of laboratory mice for biological imaging of micron- and submicron-scale biological structures. No existing research has measured the shear stiffness of mouse facial tissue or modeled the effect of quasi-conformal contact constraints on nonlinear materials. The constraint devices and techniques currently available for mice have limitations that have prevented further exploration of their biological structures. The theoretical model, design rationale, and testing results of a prototype device utilizing quasi-conformal constraints are presented in this thesis. This device is capable of restraining anesthetized mice to sub-micron movement in all axes of translation, without additional surgery or discomfort to the mouse. With the findings presented in this thesis, the design of further optimized devices can be made-both for anesthetized and awake mice-enabling further studies in bone marrow and neural activity that are currently impossible. This could ultimately lead to breakthroughs in stem cell and neurobiological research.
by Lucy W. Du.
S.M.
24
Prakash, Sunil. „Modeling the Constraint Effects on Fracture Toughness of Materials“. University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1259271280.
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25
Charpentier, Erik L. „Applying constraint-based theory to a complex aerospace manufacturing process“. Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99017.
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Thesis: M.B.A., Massachusetts Institute of Technology, Sloan School of Management, 2015. In conjunction with the Leaders for Global Operations Program at MIT.Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. In conjunction with the Leaders for Global Operations Program at MIT.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 56-57).
A new airplane model is quickly ramping up in production rates, and in order to achieve the organizational targets and commitments, Flow Days, Unit Hours and Cycle Times must be reduced throughout the entire supply chain. The Continuous Improvement Group (CIG) is an initiative supporting these improvements by applying the Theory of Constraints to identify improvement opportunities and lead teams to implement solutions and make the improvements. This thesis details the approach of using historical manufacturing data to identify focus areas for analysis and a methodology for analyzing a specific manufacturing process. This analysis and the improvement opportunities identified for several processes in the Final Assembly of the new plane are discussed, as well as the efforts implement solutions to these opportunities. Finally, this thesis also describes the mindsets and organizational characteristics that are necessary in order to make large efficiency improvements in a complex manufacturing process.
by Erik L. Charpentier.
M.B.A.
S.M.
26
Dias, Carlson Rachel (Rachel A. ). „Design of an individual vertex actuator and its use in understanding the effect of constraint location on Miura-Ori folding behavior“. Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92668.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (page 37).
The Miura-Ori fold is an origami pattern that can translate from a flat sheet to a compact folded state with a single degree of freedom. Currently little is understood about the relationship between the physical properties of the miura-ori lattice and its folding behavior. The objective of this thesis was to design an actuation setup to quantify the effect of individual vertex actuation and constraint on the adherence of folding behavior to an idealized model. The setup constrains specific vertices to the x/y plane while actuating other vertices along their ideal paths as specified by the idealized geometric model. The minimum number of constraints needed to drive a unit cell miura ori pattern into the folded state was found to be two, adjacent to the center actuator. This rule was also found to be applicable to larger lattice sizes. In addition, the adherence of each node path to the predicted ideal path was found to improve as the number of constraints increased. Several improvements to the setup that would enable further exploration of miura-ori behavior are suggested.
by Rachel Dias Carlson.
S.B.
27
Sleath, Leslie C. „The dimensional variation analysis of complex mechanical systems“. Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/13996.
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Dimensional variation analysis (DVA) is a computer based simulation process used to identify potential assembly process issues due the effects of component part and assembly variation during manufacture. The sponsoring company has over a number of years developed a DVA process to simulate the variation behaviour of a wide range of static mechanical systems. This project considers whether the current DVA process used by the sponsoring company is suitable for the simulation of complex kinematic systems. The project, which consists of three case studies, identifies several issues that became apparent with the current DVA process when applied to three types of complex kinematic systems. The project goes on to develop solutions to the issues raised in the case studies in the form of new or enhanced methods of information acquisition, simulation modelling and the interpretation and presentation of the simulation output Development of these methods has enabled the sponsoring company to expand the range of system types that can be successfully simulated and significantly enhances the information flow between the DVA process and the wider product development process.
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Hammond, Alisha M. „Establishing A Quantitative Foundation for Exactly Constrained Design“. BYU ScholarsArchive, 2003. https://scholarsarchive.byu.edu/etd/115.
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Exactly constrained (EC) design is a robust design method which can be used for mechanical assemblies. It entails using the minimum number of constraints to eliminate all desired motion. While found by some engineers in industry to have many benefits (including robust assembly, no binding or play, ease of assembly, and the ability to tolerate the wear of parts), EC designs remain somewhat unrecognized by academia. One reason for this minimal exposure may be the lack of a quantitative foundation for such designs. This thesis describes the history and current background for EC designs, and it also begins to develop a quantitative foundation for EC design based on several mathematical methods. EC designs can be analyzed quite simply by understanding that they are statically determinate. Because of this, the equations of equilibrium can be used to validate the rules and the nesting force window that have been defined by Blanding [1999]. In addition, a generalized method using the equations of equilibrium has been developed in this thesis to analyze an EC design based on the locations of the constraints and to find the nesting force window. The direct linearization method (DLM) is another mathematical method used to quantify information in an EC design. While EC designs provide many advantages, some EC assemblies may be "better" than others. A quantitative measure of goodness is developed in this thesis using the DLM. The goodness value assigned to each design through this process can either be used to make a decision on an individual design, or it can be used to compare similar EC designs. Finally, the robust nature of EC design is examined using a Monte Carlo simulation. In general, the results show that EC designs have a higher rate of assembly than similar designs that are over-constrained. They are more robust. In addition, EC designs have lower assembly error than the similarly over-constrained assemblies.
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Leach, Austin M. „A NEW CONSTRAINT BASED FRACTURE PREDICTION METHODOLOGY FOR DUCTILE MATERIALS CONTAINING SURFACE CRACKS [FLAWS]“. Master's thesis, Mississippi State : Mississippi State University, 2004. http://library.msstate.edu/etd/show.asp?etd=etd-07122004-155332.
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Granfeldt, Hans. „The use of mechanical circulatory support and passive ventricular constraint in patients with acute and chronic heart failure“. Doctoral thesis, Linköpings universitet, Thoraxkirurgi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-56424.
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Many patients are diagnosed as having chronic heart failure (CHF) and apart from the fact that daily activities are impaired, they are great consumers of health care, and the prognosis is poor. The distinction between acute heart failure (AHF) and CHF may be difficult and is more a question of time rather than severity. The “gold standard” treatment for end‐stage heart failure is heart transplantation. Due to organ shortage this is reserved for selected patients only. Since the introduction of mechanical circulatory support (MCS) more and more patients with progressive CHF have been bridged‐to‐heart‐transplantation. There are MCS systems available for both short‐ and long‐term support. Newer concepts such as ventricular constraint to prevent ventricular remodelling are on the way. We have investigated short‐ (ImpellaTM) and long‐term (HeartMateTM I and II) MCS and ventricular constraint (CorCapTM CSD) as treatment concepts for all forms of heart failure, the aims being: bridge‐to‐decision, bridge‐to‐transplant and extended therapy, called “destination therapy” (DT). Methods and results: In Paper I, the use of HM‐ITM pulsatile MCS in bridge‐to‐transplantation patients in Sweden was retrospectively investigated regarding outcome and risk factors for mortality and morbidity. Fifty‐nine patients were treated between 1993 and 2002. The dominating diagnosis was dilated cardiomyopathy in 61%. Median support time was 99.5 days. 18.6% died before transplantation. Four patients needed RV assist due to right ventricular failure. Haemorrhage was an issue. Six patients (10%) suffered a cerebrovascular thromboembolic lesion. 15% developed driveline infection. 45% of the MCS patients were discharged home while on pump treatment. Massive blood transfusion was a predictor for mortality and morbidity, p<0.001. In Paper II the second generation long‐term MCS, the continuous axial flow pump HM‐IITM, was prospectively evaluated for mortality and morbidity. Eleven patients, from 2005 until 2008, were consecutively included at our institution. One patient received the pump for DT. The median pump time was 155 days. Survival to transplantation was 81.8%. Ten patients could be discharged home before transplantation after a median time of 65 days. Paper III investigated the Swedish experience and outcome of short‐term axial flow MCS, the ImpellaTM, in patients with AHF. Fifty patients were collected between 2003 and 2007 and divided into two groups: 1. Surgical group (n=33) with cardiogenic shock after cardiac surgery; and 2. Non‐surgical group (n=17), patients with AHF due to acute coronary syndromes with cardiogenic shock (53%) and myocarditis (29%). The 1‐year survival was 36% and 70%, respectively. 52% were reoperated because of bleeding. Predictors for survival at 30 days were preoperatively placed IABP (p=0.01), postoperatively cardiac output at 12 hours and Cardiac Power Output at 6 and 12 hours. In Paper IV we evaluated the use and long term outcome of ventricular constraint CorCapTM CSD. Since 2003, 26 consecutive patients with chronic progressive heart failure were operated with CSD via sternotomy (n=25) or left mini‐thoracotomy (n=1). Seven patients were operated with CorCapTM only. Nineteen patients had concomitant cardiac surgery. There were three early and three late deaths. The remaining cohort (n=18) was investigated in a cross‐sectional study regarding QoL with SF‐36. There was no difference in QoL measured with SF‐36 after a mean 3‐years follow up period, when compared to an age‐ and sex‐matched control group from the general population. The one‐year survival was 86%, and after three years 76%. Echocardiographic dimensions had improved significantly after three years. Conclusion: In our unit, a non‐transplanting medium‐sized cardiothoracic department, short‐ and long‐term MCS (ImpellaTM resp. HMTM) in patients with acute or chronic HF have been used with good results. The use of ventricular constraint early in the course of the disease is a good adjunct to other treatment options in progressive chronic HF patients.
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Vaidya, Rohan. „Optimum Support Structure Generation for Additive Manufacturing using Unit Cell Structures and Support Removal Constraint“. University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1490354059543447.
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Guo, Jiajie. „Effects of joint constraints on deformation of multi-body compliant mechanisms“. Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/45971.
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Motivated by the interests to understand bio-structure deformation and exploit their advantages to create bio-inspired systems for engineering applications, a curvature-based model for analyzing compliant mechanisms capable of large deformation in a three dimensional space has been developed. Unlike methods (such as finite element) that formulate problems based on displacements and/or rotational angles, superposition holds for curvatures in the case of finite rotation but not for rotational angles; thus the curvature-based formulation presents an advantage in presenting nonlinear geometries. Along with a generalized constraint that relaxes traditional boundary constraints (such as fixed, pinned or sliding constraint) on compliant mechanisms, the method of deriving the compliant members in the same global referenced frame is presented. The attractive features of the method, which greatly simplifies the models and improves the computation efficiency of multi-body system deformation where compliant beams play an important role, have been experimentally validated. To demonstrate the applicability of this proposed method to a broad spectrum of applications, three practical examples are given; the first example verifies the generalized constraint by analyzing the multi-axis rotation motion within a natural human knee joint and investigates the human-exoskeleton interactions through dynamic analysis. The second example studies a deformable bio-structure by incorporating the generalized joint constraint into the curvature-based model for automated poultry meat processing. The last example designs a bio-inspired robot with a compliant mechanism to serve as a flexonic mobile node for ferromagnetic structure health monitoring. The analytical models have been employed (with experimental validation) to investigate the effects of different joint constraints on the mechanism deformations. It is expected that the proposed method will find a broad range of applications involving compliant mechanisms.
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Wang, Lyang Suan. „Automating Parametric Redesign of Structural Thin-Walled Frames Based On Topology Optimized Structure“. The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu156618342438725.
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Salem, Adel I. „Weight and Cost Multi-Objective Optimization of Hybrid Composite Sandwich Structures“. University of Dayton / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1478637482819839.
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To, Curtis Sai-Hay. „Closed-Loop Control and Variable Constraint Mechanisms of a Hybrid Neuroprosthesis to Restore Gait after Spinal Cord Injury“. Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1269809553.
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Tong, Yuxuan. „Four-bar Linkage Synthesis for a Combination of Motion and Path-point Generation“. University of Dayton / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1366643444.
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Wu, Fei. „Parallel computational methods for constrained mechanical systems“. Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/282561.
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Two methods suitable for parallel computation in the study of mechanical systems with holonomic and nonholonomic constraints are presented: one is an explicit solution based on generalized inverse algebra; the second solves problems of this class through the direct application of Gauss' principle of least constraint and genetic algorithms. Algorithms for both methods are presented for sequential and parallel implementations. The method using generalized inverses is able to solve problems that involve redundant, degenerate and intermittent constraints, and can identify inconsistent constraint sets. It also allows a single program to perform pure kinematic and dynamic analyses. Its computational cost is among the lowest in comparison with other methods. In addition, constraint violation control methods are investigated to improve integration accuracy and further reduce computational cost. Constrained dynamics problems are also solved using optimization methods by applying Gauss' principle directly. An objective function that incorporates constraints is derived using a symmetric scheme, which is implemented using genetic algorithms in a parallel computing environment. It is shown that this method is capable of solving the same cases of constraints as the former method. Examples and numerical experiments demonstrating the applications of the two methods to constrained multiparticle and multibody systems are presented.
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Aidanpää, Jan-Olov. „Dynamics of some vibro-impacting systems with amplitude constraints“. Doctoral thesis, Luleå tekniska universitet, Material- och solidmekanik, 1995. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-16841.
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This thesis concerns the dynamics of some vibro-impacting systems with fixed or moving amplitude constraints. It is based on and includes five papers, marked A to E. Simple models of three different vibro-impacting systems with applications in the fields of impact hammers, granular flow and disk brakes in vehicles are analysed. A 2-DOF (two-degree-of-freedom) model of a threshold-limited impact hammer is studied (Paper A). The stability of a class of periodic motions is analysed. For some parameter values these periodic motions are found to be qualitatively similar to the ones observed for a corresponding 1-DOF system. At other parameter combinations, however, new kinds of periodic or chaotic motions can be observed. For low damping, phenomena resembling antiresonance for linear systems can also be observed. Granular shear flows show a transitional behaviour in the rapid flow regime as the shear speed or the concentration of the grains is varied. The motion can, for example, change from smooth and orderly to erratic and turbulent. Some aspects of this transitional behaviour in granular shear flow are studied numerically, analytically and experimentally (Papers B, C and D). Simple vibro-impacting models are suggested to get some analytical insight into the dynamics of shear layers. Results from a 1-DOF model show that for high forcing frequencies, which correspond to high shear speeds, periodic as well as chaotic motions can exist, whereas, for low forcing frequencies the vibrations are completely damped out to a stationary state (Paper B). Stability of this stationary state is studied analytically (Paper C), and experimentally (Paper D), where the motions of granular particles in a transparent shear cell are followed by using video techniques. For low shear speeds a single shear layer adjacent to the bottom boundary of the shear cell is observed. As the shear speed is increased, a transition to a random like state involving many layers is found to occur. In order to understand the phenomenon of squeal in disk brakes, a 3-DOF model is suggested to simulate the dynamics of a brake pad. The region of contact between the brake pad and the disk is described by using a coefficient of friction and distributed stiffness. The brake pad is allowed to have adjustable support locations and possibilities of impacts with its surroundings. The equilibrium state of the pad is determined by using a static analysis. The assumption is that the instability of this stationary state is a possible explanation of squeal, therefore, the stability is analysed in detail. Examples of different kinds of pad motions are presented. A rich variety of motions are found to exist including periodic, seemingly chaotic, stationary behaviour in slip, vibrations with full contact with the disk, stick-slip and impacts.Godkänd; 1995; 20070426 (ysko)
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Pasquotti, Maura. „Topics on Optimization Strategies for Constrained Mechanical Systems“. Doctoral thesis, Università degli studi di Padova, 2008. http://hdl.handle.net/11577/3425582.
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In the first part of the work we analyze the problem of optimal control of a vehicle along a preassigned trajectory. The vehicle system is studied and simplified in order to obtain a computationally tractable model, which still presents the main characteristics of the real vehicle. The control algorithm, based on MPC techniques, is then explained and its effectiveness is proved through simulation results. The “minimum lap time problem” is afterward considered, which can be considered as an evolution of the trajectory tracking problem; its analysis is presented and is followed by the developed solution, based on pseudospectral methods.
In the second part of the thesis the problem of control of underactuated mechanical systems is discussed. The nonholonomic system classically called “rolling disk” is considered as test case; it is a wheel with punctiform contact surface that can roll on the plane without sliding laterally. Differently from the literature we consider the torque as the unique control input signal. This system is modeled through the Lagrangian formalism and then the control strategy, based on backstepping and receding horizon techniques, is shown and proved to be effective.
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Harker, Shaun Russell. „Classical mechanics with dissipative constraints“. Thesis, Montana State University, 2009. http://etd.lib.montana.edu/etd/2009/harker/HarkerS0809.pdf.
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The aim of this thesis is to consider the mathematical treatment of mechanical systems in the presence of constraints which are energetically dissipative. Constraints may be energetically dissipative due to impacts and friction. In the frictionless setting, we generalize Hamilton's principle of stationary action, central to the Lagrangian formulation of classical mechanics, to reflect optimality conditions in constrained spaces. We show that this generalization leads to the standard measure-theoretic equations for shocks in the presence of unilateral constraints. Previously, these equations were simply postulated; we derive them from a fundamental variational principle. We also present results in the frictional setting. We survey the extensive literature on the subject, which focusses on existence results and numerical schemes known as time- stepping algorithms. We consider a novel model of friction (which is more dissipative than standard Coulomb friction) for which we can give better well-posedness results than what is currently available for the Coulomb theory. To this end, we study multi-valued maps, differential inclusions, and optimization theory. We construct a differential inclusion we call the feedback problem, for which the multi-valued map is the solution set of a convex program. We give existence and uniqueness results regarding this feedback problem. We cast the persistent contact evolution problem of our novel model of friction into the form of a feedback problem to derive an existence result.
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Won, Justin. „The control of constrained and partially constrained arm movements“. Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12621.
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Patten, James McMichael 1977. „Mechanical constraints as common ground between people and computers“. Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/34179.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2006.Includes bibliographical references (p. 143-149).
This thesis presents a new type of human-computer interface based on mechanical constraints that combines some of the tactile feedback and affordances of mechanical systems with the abstract computational power of modern computers. The interface is based on a tabletop interaction surface that can sense and move small objects on top of it. Computation is merged with dynamic physical processes on the tabletop that are exposed to and modified by the user in order to accomplish his or her task. The system places mechanical constraints and mathematical constraints on the same level, allowing users to guide simulations and optimization processes by constraining the motion of physical objects on the interaction surface. The interface provides ample opportunities for improvisation by allowing the user to employ a rich variety of everyday physical objects as interface elements. Subjects in an evaluation were more effective at solving a complex spatial layout problem using this system than with either of two alternative interfaces that did not feature actuation.
James McMichael Patten.
Ph.D.
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Martin, Lucie. „Cοntraintes mécaniques et rigidité de l'envelοppe nucléaire dans le gliοblastοme : implicatiοns dans l'hétérοgénéité et l'agressivité tumοrales“. Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMR090.
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Le glioblastome (GB) est la tumeur cérébrale la plus agressive, sans traitement curatif actuel. La croissance rapide au sein du GB peut être responsable d'un microenvironnement plus rigide alors que l'invasion le long des vaisseaux sanguins en réponse à des facteurs de croissance, peut générer un stress physique sur les cellules en migration. Le but de notre travail est d'évaluer le rôle du stress mécanique induit par des matrices rigides ou par des contraintes physiques aiguës pendant la migration, sur l'intégrité de l’EN, les ruptures potentielles de l'ADN et l'agressivité tumorale. A partir de bases de données publiques, nous avons évalué les niveaux d’expression de gènes de l’EN dans le GB comparativement aux gliomes de bas grade et au tissu cérébral normal. Les niveaux d’expression de certains gènes semblent plutôt associés aux cellules AC- et MES-like ou aux cellules NPC-, OPC- et AC-like. Pour imiter l'élasticité variable entre le cœur et la périphérie tumorales, des lignées de GB de patients et des lignées de GB humains établies ont été cultivées dans des matrices molles et rigides et montrent des capacités de croissance distinctes, que nous avons assignées à des scores d'adaptabilité. Les données RNAseq obtenues à partir de matrices souples et rigides ont montré une altération transcriptomique liée aux gènes de l’EN et donc corrélée au score d'adaptabilité de chaque lignée cellulaire. L'expression génique différentielle entre les conditions souples et rigides affecte plus généralement la traduction, les processus métaboliques et les voies immunitaires. Pour imiter l'impact de la migration cellulaire sous contraintes, les lignées de GB ont été exposées à des contraintes physiques dans des transwells. La migration sous contraintes induit une déstabilisation de la structure nucléaire. Des études protéomiques ont également permis de caractériser les contenus nucléaires et cytoplasmiques après un impact mécanique. Injectées dans le cerveau de souris Nude, les cellules de GB soumises à des contraintes provoquent une réduction de la survie des animaux comparativement aux animaux porteurs de cellules qui n’ont pas migré. En conclusion, nous montrons un lien original entre la contrainte physique, que ce soit dans les matrices ou lors de la migration, et l'agressivité des GB. Nos données fournissent des pistes thérapeutiques originales pour contrer la progression et la récidive des GBGlioblastoma (GB) is the most aggressive brain tumor, with no current curative treatment. Rapid growth within GB may be responsible for a more rigid microenvironment, while invasion along blood vessels in response to growth factors may generate physical stress on migrating cells. The aim of our work was to evaluate the role of mechanical stress induced by rigid matrices or by acute physical constraints during migration, on EN integrity, potential DNA breaks and tumor aggressiveness. Using public available databases, we assessed EN gene expression levels in GB compared with low-grade gliomas and normal brain tissue. The expression levels of certain genes appear to be more closely associated with AC- and MES-like cells, or with NPC-, OPC- and AC-like cells. To mimic the variable elasticity between tumor core and periphery, patient GB cell lines and established human GB lines were grown in soft and rigid matrices and show distinct growth capacities, which we assigned to adaptability scores. RNAseq data obtained from flexible and rigid matrices showed transcriptomic alteration linked to EN genes and therefore correlated with the adaptability score of each cell line. Differential gene expression between soft and rigid conditions globally affects translation, metabolic processes and immune pathways. To mimic the impact of cell migration under constraints, GB cell lines were exposed to physical stress in transwells. Stress migration induced destabilization of the nuclear structure. Proteomic studies were also used to characterize nuclear and cytoplasmic contents after mechanical impact. Injected into the brains of Nude mice, GB cells subjected to stress induced a reduction of animal survival compared to the condition of mice bearing non migrating cells. In conclusion, we show an original link between physical stress, whether in matrices or during migration, and GB aggressiveness. Our data provide original therapeutic avenues to counteract GB progression and recurrence
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Thaller, David Ben. „Treatment of constraints in discrete dynamics“. Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12446.
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Guo, LiYing. „Thermal and mechanical phenomena in nanoscale constrained domains“. [Ames, Iowa : Iowa State University], 2009.
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Caine, Michael E. (Michael Edward). „The design of shape from motion constraints“. Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12331.
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Diel, David D. 1979. „Stochastic constraints for vision-aided inertial navigation“. Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/30317.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (p. 107-110).
This thesis describes a new method to improve inertial navigation using feature-based constraints from one or more video cameras. The proposed method lengthens the period of time during which a human or vehicle can navigate in GPS-deprived environments. Our approach integrates well with existing navigation systems, because we invoke general sensor models that represent a wide range of available hardware. The inertial model includes errors in bias, scale, and random walk. Any camera and tracking algorithm may be used, as long as the visual output can be expressed as ray vectors extending from known locations on the sensor body. A modified linear Kalman filter performs the data fusion. Unlike traditional Simultaneous Localization and Mapping (SLAM/CML), our state vector contains only inertial sensor errors related to position. This choice allows uncertainty to be properly represented by a covariance matrix. We do not augment the state with feature coordinates. Instead, image data contributes stochastic epipolar constraints over a broad baseline in time and space, resulting in improved observability of the IMU error states. The constraints lead to a relative residual and associated relative covariance, defined partly by the state history. Navigation results are presented using high-quality synthetic data and real fisheye imagery.
by David D. Diel.
S.M.
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Bennett, David J. (David James). „The control of human arm movement : models and mechanical constraints“. Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/13588.
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Dai, Siyu S. M. Massachusetts Institute of Technology. „Probabilistic motion planning and optimization incorporating chance constraints“. Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120230.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 201-208).
For high-dimensional robots, motion planning is still a challenging problem, especially for manipulators mounted to underwater vehicles or human support robots where uncertainties and risks of plan failure can have severe impact. However, existing risk-aware planners mostly focus on low-dimensional planning tasks, meanwhile planners that can account for uncertainties and react fast in high degree-of-freedom (DOF) robot planning tasks are lacking. In this thesis, a risk-aware motion planning and execution system called Probabilistic Chekov (p-Chekov) is introduced, which includes a deterministic stage and a risk-aware stage. A systematic set of experiments on existing motion planners as well as p-Chekov is also presented. The deterministic stage of p-Chekov leverages the recent advances in obstacle-aware trajectory optimization to improve the original tube-based-roadmap Chekov planner. Through experiments in 4 common application scenarios with 5000 test cases each, we show that using sampling-based planners alone on high DOF robots can not achieve a high enough reaction speed, whereas the popular trajectory optimizer TrajOpt with naive straight-line seed trajectories has very high collision rate despite its high planning speed. To the best of our knowledge, this is the first work that presents such a systematic and comprehensive evaluation of state-of-the-art motion planners, which are based on a significant amount of experiments. We then combine different stand-alone planners with trajectory optimization. The results show that the deterministic planning part of p-Chekov, which combines a roadmap approach that caches the all pair shortest paths solutions and an online obstacle-aware trajectory optimizer, provides superior performance over other standard sampling-based planners' combinations. Simulation results show that, in typical real-life applications, this "roadmap + TrajOpt" approach takes about 1 s to plan and the failure rate of its solutions is under 1%. The risk-aware stage of p-Chekov accounts for chance constraints through state probability distribution and collision probability estimation. Based on the deterministic Chekov planner, p-Chekov incorporates a linear-quadratic Gaussian motion planning (LQG-MP) approach into robot state probability distribution estimation, applies quadrature-sampling theories to collision risk estimation, and adapts risk allocation approaches for chance constraint satisfaction. It overcomes existing risk-aware planners' limitation in real-time motion planning tasks with high-DOF robots in 3- dimensional non-convex environments. The experimental results in this thesis show that this new risk-aware motion planning and execution system can effectively reduce collision risk and satisfy chance constraints in typical real-world planning scenarios for high-DOF robots. This thesis makes the following three main contributions: (1) a systematic evaluation of several state-of-the-art motion planners in realistic planning scenarios, including popular sampling-based motion planners and trajectory optimization type motion planners, (2) the establishment of a "roadmap + TrajOpt" deterministic motion planning system that shows superior performance in many practical planning tasks in terms of solution feasibility, optimality and reaction time, and (3) the development of a risk-aware motion planning and execution system that can handle high-DOF robotic planning tasks in 3-dimensional non-convex environments.
by Siyu Dai.
S.M.
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Kárason, Steingrímur Páll. „Adaptive control in the presence of input constraints“. Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/118105.
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