Dissertation (Ph.D.)--Worcester Polytechnic Institute. / Keywords: estimation, radar, asymmetric, inertial, dynamics, rigid body, exo-atmospheric, free body. Includes bibliographical references. (p.150-154)

This thesis discusses the motion of a rigid body about a fixed point subject to a torque arising from internal reaction. Such a body is called self-excited, and its motion is governed by Euler’s dynamical equations. First, in Section 2 we consider the case of a torque vector which is fixed in direction along the largest or smallest principal axis of the body, and has a component in the chosen axis equal to a constant plus a perturbation term that is proportional to the square of the modulus of the spin vector [character omitted] (p,q,r). It is shown that Euler's equations can be integrated in terms of a variable φ, introduced by means of a differential relation. Further quadrature and inversion yield p,q, and r as functions of the time t. Using the method of phase-plane analysis, we show that the spin vector can perform a variety of motions with respect to the body-fixed trihedral. In particular, when the perturbation is zero, we infer from the corresponding phase-plane trajectories that the spin vector can perform asymptotic motions of the first and second kinds and periodic motions about permanent axes lying in the principal plane perpendicular to the torque vector. Some of the results for this case were also obtained by Grammel, using different method. In the general case, when the perturbation is not zero, these motions are preserved. However, a second type of periodic motion exists; it occurs about the principal axis containing the torque vector, the principal axis itself being a direction of stable permanent rotation. In Section 3 we consider the same problem with the torque vector acting along the middle principal axis. Using the methods of the previous Section, we show that [character omitted] can assume periodic motions as well as asymptotic motions of various kinds. The periodic motions established in these two Sections are then computed in Section 4 as power series in a small parameter. Finally, in Section 5 the motion of a symmetric rigid body moving in a viscous medium subject to a time-dependent torque is studied. Its motion is compared with that in a vacuum. We show first that p,q, and r can be expressed in terms of certain integrals. For the special case where the self-excitement is time-independent and fixed in direction within the body, these integrals can be reduced to the generalized sine and cosine integrals. Their values can be computed from asymptotic and power series which are developed in the same Section. The asymptotic behavior of the spin vector is then discussed, yielding qualitative results which are summarized in three theorems. / Science, Faculty of / Mathematics, Department of / Graduate

No description available.

As shared memory platforms continue to grow in core counts, the need for context-aware scheduling continues to grow. Context-aware scheduling takes into account characteristics of the system and application performance when making decisions. Traditionally applications run on a static thread count that is set at compile-time or at job start time, without taking into account the dynamic context of the system, other running applications, and potentially the performance of the application itself. However, many shared memory applications can easily be converted to malleable applications, that is, applications that can run with an arbitrary number of threads and can change thread counts during execution. Many new and intelligent scheduling decisions can be made when applications become context-aware, including expanding to ll an empty system or shrinking to accommodate a more parallelizable job. This thesis describes a prototype system called Resizing for Shared Memory (RSM), which supports OpenMP applications on shared memory platforms. RSM includes a main daemon that records performance information and makes resizing decisions as well as a communication library to allow applications to contact the RSM daemon and enact resizing decisions. Experimental results show that RSM can improve turn-around time and system utilization even using very simple heuristics and resizing policies. / Master of Science

This thesis investigates the torsional performance of steel structures with and without rigid diaphragm constraints through numerical simulations and evaluates the appropriateness of relevant design provisions in current seismic design codes. In the first part of the work, six theme structures with different (1) in-plane stiffness of diaphragm, and (2) horizontal configurations of vertical braced frames were designed and their performance evaluated through both nonlinear static and dynamic analyses. Comparisons of the analytical results between the structures with and without rigid diaphragm constraints indicate that the in-plane rigidity of the diaphragms affects the efficiency of in-plane force transfer mechanisms, resulting in different global ductility and strength demands. Rigid diaphragm structures exhibit higher global strengths as well as higher torsional rotation capacity because of the infinite in-plane stiffness of the diaphragm. Semi-rigid diaphragm structures have higher ductility demands due to the finite in-plane diaphragm stiffness. The inclusion of bi-axial forces in the analyses reduces the structural strength and increases the ductility demands on the peripheral frames. The axial forces in the collectors and chords that make up the diaphragm depend on (1) the sequence of brace buckling and (2) vertical configuration of the braced frames. The results show higher axial forces in collectors in the roof diaphragms, and higher chord axial forces in the third floor diaphragms. The shear connections in the beams that make up both the collectors and chords are susceptible to failure due to the significant increment of axial forces in those members. The conventional beam analogy used in design can severely underestimate the axial forces in chords and collectors when the structures step into the inelastic stage. / Ph. D.

No description available.

Sternal malunion is a complication resulting in displacement of the sternal halves following open heart surgery. Currently, little is known about the effectiveness of alternative fixation systems under physiologically relevant loading scenarios. The goal of this study was to mechanically test several currently marketed sternal fixation devices and compare them to a prototype device in different loading conditions to simulate sitting up or breathing. Each system showed unique differences in cost, failure mode and efficiency; however, no statistical difference in failure load or displacement was observed between the testing groups.

The goal of this thesis is to explore the properties of a certain class of sequences, rigid divisibility sequences, generated by the iteration of certain polynomials whose coefficients are algebraic integers. The main goal is to provide, as far as is possible, a classification and description of those polynomials which generate rigid divisibility sequences.

This report is the documentation for a stiffness formulation to perform rigid diaphragm analysis for wood structures subjected to wind loads. Traditionally, rigid diaphragm analysis has been performed using a vaguely-defined superposition approach; however, this report details a more rational stiffness approach to solving for forces placed on walls resulting from a rigid diaphragm, and its implementation is via a simple spreadsheet application. In addition to the formulation of the spreadsheet, the report contains a User’s Guide and examples of the spreadsheet’s use. The purpose of the spreadsheet is not as a replacement to more sophisticated and comprehensive finite element analysis software, but as a tool to aid designers who practice engineering and may not have access to such software. In general, the application is developed for wood diaphragms as will be noted by references to wood-related codes. However, much of the approach may be used for diaphragms constructed with other materials as well. / text

The service life of rigid sewer pipes is often controlled by joint integrity. Leaking joints can cause ingress of water and develop voids where surrounding soil has eroded. The influence of soil voids on the stability of buried rigid pipes is investigated, considering the effects of void size, void location and void shape. A series of simplified void geometries are defined, and their influence on bending moments in the rigid sewer is studied through finite element analysis. Elastic analysis indicates that the bending moments from expanding voids at the springline will increase slowly, accelerating once the void spans a 45 degree arc, approximately doubling at 90 degrees, and tripling if the loosened backfill is modeled for shear failure. This preliminary study suggests that the growth of erosion voids should be stopped before they reach 45 degrees, but validation through physical testing is necessary. Elastic-plastic finite element analysis is used to calculate the deformation of rigid fractured pipe with different thicknesses, considering both bonded and full-slip interface conditions. The analysis confirms that bonded idealized flexible pipe theory is very effective for calculation of increases in horizontal diameter of the fractured pipe. Furthermore, decreases in vertical diameter can be simply related to increase in horizontal diameter using (1-2t/OD) obtained from fractured pipe kinematics. Both elastic and elastic-plastic finite element analyses used to study the deformations of fractured rigid pipe reveal that contact angle appears to be the dominant factor affecting fractured pipe deformations. Deformation of the damaged rigid pipe increases dramatically with void growth and accelerates when erosion void contacts with the outer surface of the pipe over an arc greater than 45 degrees. Computational analyses examine the behavior of centrifuge model tests which examine soil load transfer to flexible sewer liners after fracture and erosion voids form nearby. The magnitude of deformation changes for finite element models is found to be comparable to observations when voids are formed at springline. However the development patterns are dramatically different as voids located under the invert, and it appears that the laboratory test featured physical characteristics that are not modeled in the analysis. / Thesis (Master, Civil Engineering) -- Queen's University, 2007-09-24 20:33:29.689