A weak shock theory is developed which allows for dense gas effects when the fundamental derivative of gas dynarnics, Γ , becomes small and possibly negative. The nonclassical behavior in these negative Γ regions has potential applications in turbomachinery design. The weak shock development results in a Burgers equation which is then solved numerically using the well-known MacCormack scheme. The results include the demonstration of many non-classical results such as expansion shocks, compression fans, shock-splitting and shock-fan combinations. Results are shown which could help improve turbine efficiency. / M.S.

A criterion using rigid-body modes to verify the conservation of mass inertias is presented. Conservation of rod element mass guarantees convergence to the exact eigensolutions of a rod. Conservation of beam element mass guarantees convergence to the exact eigensolutions of a Bernoulli-Euler beam without rotatory inertia. Conservation of element mass and rotatory inertia guarantees convergence to the exact solutions of a Bernoulli-Euler beam with rotatory inertia. Conservation of mass moment of inertia is not a requirement for convergence, but is important for a beam mass matrix with respect to their accuracy and consistency with various boundary conditions. Based on this criterion, a concept for the formulation of a non-consistent mass matrix is presented. The concept unifies the formulation of various kinds of rod and beam mass matrices, and facilitates the generation of new mass matrices for optimization. To gain more physical insight into the formulation, the shape functions for the non-consistent mass matrices are also introduced. Four examples are considered. The first two examples are used to find the optimized mass matrices for rods and beams and to study their eigensolution errors. The optimized mass matrices minimize the root mean square errors of natural frequencies over a specified range of modes. The results of using a rod optimized mass matrix show that the root mean square error of natural frequencies for the first half of total extractable modes is reduced from 5%, obtained from using the consistent-mass and the lumped-mass matrices, to 1%. The results also show that if equally spaced elements are used for a rod, all the eigenvectors are exact. However, if unequal-length elements are used, both the frequency errors and eigenvector errors increase, and the upper half of total extractable modes are not reliable. The results of using a beam optimized mass matrix show that the root mean square error of natural frequencies is reduced from 0.16%, obtained from using a consistent-mass matrix, to 0.10%. The upper half of the total modes are not reliable. The remaining two examples are used to study the performances of all rod and beam mass matrices (consistent-mass, lumped-mass, and higher-order mass matrices) on a portal arch. According to the results, the higher-order mass matrix generates the most accurate eigensolutions. The use of the higher-order mass matrix in place of the consistent-mass matrix is recommended. The block-diagonal lumped-mass matrix performs better than the diagonal lumped-mass matrices at free ends of a structure. The eigensolution errors for all the mass matrices start to increase significantly after the first one third of the total modes. Finally, a technique for finding the modal reduction mass matrices is proposed. Fully populated modal reduction mass matrices for a rod are successfully extracted. This type of models generate exact natural frequencies and mode shapes for all the extractable modes of a rod problem. Further investigation of this technique is recommended. / Ph. D.

A basic experimental study of the aerodynamic breakup of a viscoelastic non-Newtonian liquid injected into a supersonic stream was conducted. All test runs were made either at a free stream Mach number of 2.4 and a total pressure of 4.1 atm or a Mach number of 4.0 and a total pressure of 10.9 atm. The air flow had a total temperature of 300 K, and the injectant was always at room temperature. The injectant used for the majority of the test runs was diethylmalonate thickened with polymethyl-methacrylate, which has the characteristics of being viscoelastic. A limited number of test runs were made with glycerin in order to make a comparison between the behavior of Newtonian and viscoelastic non-Newtonian fluids. Several areas concerning the disintegration of the viscoelastic non-Newtonian fluid were investigated, including the effects of free stream Mach number, injection velocity, jet diameter, twin in-line jets, injection angle, and injector shape. Spark Shadowgraphs of 1.2 microsecond duration and high speed movies were obtained to qualitatively appraise the breakup behavior. The breakup of the jet was found to be a function of free stream Mach number and jet diameter, injection angle, and frontal area. It also was observed that the breakup behavior of the viscoelastic non-Newtonian fluid is remarkably different from that of (Newtonian) glycerin. The time scales for breakup are substantially increased regarding the dissemination of the viscoelastic liquid as compared to the Newtonian glycerin. Furthermore, penetration of the viscoelastic non-Newtonian fluid was observed to be on the order of 50% less than that measured for glycerin at comparable injection conditions. / Master of Science

A Vortex-Lattice Method (VLM) has been developed for the analysis of three-dimensional lifting bodies undergoing arbitrary motions. So far, the present method has been applied to thin surfaces in translational motion. Several cases were tested, such as rectangular, delta, sweptback and trapezoidal planforms. Emphasis has been placed on the comparison of the results with available experimental data. Consequently, many of the strengths and limitations of the technique were made apparent. Good agreement has been obtained for the aerodynamic coefficients, with a relatively coarse discretization of the surface. Results are valid as long as there is no separation or vortex breakdown. However, accurate pressure distribution calculations need at least three or four times the number of panels used for aerodynamic coefficients calculations. The method gives a qualitative description of the wake configuration, but unrealistically high velocities are induced near the vortex elements. Work is underway to extend the technique to more general types of bodies and maneuvers. / Master of Science

The topological dynamics of continuous and noncontinuous dynamical systems are investigated. Various definitions of chaos are studied, as well as notions of stability. Results are obtained on asymptotically stable sets and the perturbation stability of such sets. The primary focus is on the traditional point sets of topological dynamics, including the chain recurrent set, omega-limit sets and attractors. The basic setting is that of a continuous function on a compact metric space, sometimes with additional properties on the space. The investigation includes results on the dynamical properties of typical continuous functions in the sense of Baire category. Results are also developed concerning dynamical systems involving quasi-continuous functions. An invariance property for the omega-limit sets of such functions is given. Omega-limit sets are characterized for Riemann integrable derivatives and derivatiyes which are continuous almost everywhere. Techniques used in the investigation and formulation of results include finding theorems which relate the rather disparate notions of dynamical properties and generalized continuity. In addition to dynamical systems, numerous other applications of generalized continuity are imoestigated. Techniques used include application of the Baire Category Theorem and the notion of semi-closure. For example, results are formulated concerning functions determined by dense sets, including separately continuous functions, thus generalizing the classical result for continuous functions on dense subsets of the domain. The uniform boundedness theorem is extended to functions which are not necessarily continuous, including various derivatives. The closed graph theorem is strictly generalized in two separate ways, and applications are presented using these generalizations. An invariance property of separately continuous functions is given. Cluster sets are studied in connection with separate continuity, and various results are presented concerning locally bounded functions.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering / It has been said that experimental modal analysis (EMA) "grew to prominence because the engineering community was incapable of properly analyzing the dynamics of commercially significant structures" [24]. The advent of powerful theoretical methods, such as the Finite Element Method (FEM) has not, however, resulted in the demise of EMA. In fact both FEM and EMA have undergone rapid growth and the merging of the two into an effective design and diagnostic tool has had a major impact on the engineering community's approach to dynamics related problems. In this study, the term dual has no mathematical connotations and is used to describe the complementary use of the techniques of EMA and FEM. The mining industry, worldwide, has experienced dynamics related problems in the operation of conveyances in vertical shafts. A study undertaken in South Africa investigated the behaviour of shaft steelwork and skips, resulting in a set of design guidelines for future shaft steelwork designs. This work only investigated the dynamic behaviour of skips. In this project, the ABAQUS and MODEL SOLUTION FEM codes were used to construct models of a. mine cage. An impact modal test was carried ant on the cage, using a GenRad 2515 CAT system, An impact hammer, suitable for exciting large structures, and a strain gauge force transducer were designed and built for the purpose of the test. The natural frequencies and mode shapes obtained from both FEM and EMA are compared by means of the modal assurance criterion (MAC). The test data is used to tune the model to produce accurate results. The model Could then be used (with minimal further test work) for predicting the response of the structure to dynamic loading or the effects of structural modifications. / Andrew Chakane 2020

Yes / This paper argues for the need to reconsider the changing nature of in-work poverty (IWP). In doing so, we present evidence not included in current debates or statistics, of people working in more than one job, yet still experiencing IWP. Using the dynamic theory of poverty and a qualitative approach, we identify various structural constraints that sustain cycles of IWP. This highlights the multi-dimensionalities of poverty, incorporating the temporalities, types and depths of IWP. Our evidence demonstrates how poverty is experienced and individualised and also how it is created and sustained through paid work, rather than being challenged by it.

Indiana University-Purdue University Indianapolis (IUPUI) / Belt-drives are used in many applications such as industrial machines, washing ‎machines, and accessory drives for automobiles and other vehicles. Multibody dynamics/finite ‎element numerical models have become an effective way to predict the dynamic response of ‎belt-drives. In this thesis, a high fidelity numerical model was built using a multibody ‎dynamics/finite element code to simulate a belt-drive. The belt-drive transmits power from a ‎turbine of a Rankin cycle (that uses the exhaust waste heat of the internal combustion engine as ‎heat source) to the crank shaft of the engine. The code uses a time-accurate explicit numerical ‎integration technique to solve the multibody dynamics differential equations. The belt was ‎modeled using three-node beam elements to account for the belt axial and bending ‎stiffness/damping, while the pulleys, shafts and tensioner body were modeled as rigid bodies. ‎The penalty technique was used to model normal contact between the belt and the pulleys. An ‎asperity-based friction model was used to approximate Coulomb friction between the belt and ‎the pulleys. The dynamic response predicted using the model was validated by comparing it to ‎experimental results supplied by Cummins Inc. A parameter sensitivity study was performed to ‎evaluate the change in response due to change in various belt-drive parameters. A fatigue ‎model was developed to predict the belt fatigue life using output from the explicit finite ‎element code including normal and tangential forces between the belt and the pulleys and belt ‎tension. The belt fatigue life was evaluated for alternative belt-drive configurations in order to ‎find the configuration with the longest life.‎

A wildfire of variable intensity occurred in mid-July of 1988 in the Shenandoah National Park and adjacent private lands. This study was established to measure post-fire forest soil and vegetation characteristics in both the mixed pine and mixed oak forest types occurring on Dovel Mountain in the Shenandoah National Park, Virginia. Vegetation and soil results represent one (1989) and two (1990) growing seasons following fire occurrence in the mixed pine forest type, whereas only second year results are reported for the mixed oak forest type. Forest floor and mineral soil parameters differed among burn levels and followed similar trends for both forest types. Forest floor depth and weight were significantly less on low and high burn areas as compared to unburned areas. Low intensity fires removed the Oi-Oe layer while leaving the Oa layer relatively intact. Conversely, high intensity fifes resulted in the consumption of the entire forest floor. Total carbon, nitrogen, and nutrient differences between low and unburned areas for the entire forest floor (Oi-Oe + Oa) were negligible. However, loss of these constituents were much greater following high intensity fifes. Differences in the surface 10 cm of mineral soil were also detected following following high intensity fifes. Differences in the sulface 10 cm of mineral soil were also detected following low and high intensity fires. Mineral soil acidity was lower while exchangeable cation concentrations were higher in burned areas compared to unburned areas. Total carbon and nitrogen levels were higher in low burn areas, whereas total carbon and nitrogen levels were lower on high bum areas. Inorganic nitrogen levels were higher in both low and high burn areas compared to unburned areas. / Master of Science

<p>An investigation of the dynamics governing the growth and development of the space industry with forecasts of the expected state and trajectory of the space industry under various policy tests and scenarios.</p>