A. James Clark School of Engineering
http://hdl.handle.net/1903/1654
Sat, 17 Feb 2018 15:37:56 GMT2018-02-17T15:37:56ZSimultaneous Measurements of the Velocity and Vorticity Vector Fields in the Turbulent Near Wake of a Circular Cylinder
http://hdl.handle.net/1903/20486
Simultaneous Measurements of the Velocity and Vorticity Vector Fields in the Turbulent Near Wake of a Circular Cylinder
Nguyen, Phuc Ngoc
Hot-wire measurements of all components of the instantaneous velocity and vorticity vectors in the wake of a circular cylinder are presented. The experiments were performed at x / d = 20 and 30, at ReÎ± = 2000, using a miniature 12-sensor probe for the simultaneous velocity-vorticity measurements and a 4-sensor probe for the velocity-only measurements. A calibration and a data reduction method for multi-sensor hot-wire probes are introduced. The calibration technique is independent of the number of sensors and requires minimal information about probe geometry. The data reduction scheme involves the solution of an overdetermined nonlinear algebraic system of equations in a least-squares sense. The measurements indicate that the Karman vortices are accurately resolved. Statistical characteristics of the velocity aJ1d vorticity fields in this flow, including moments, probability distributions and one-dimensional spectra components are documented for the first time. Conditional analysis of the measurements at x/ d = 30 with respect, to the passage of the Karman vortices are presented. The vortex center and the saddle regions are identified and characterized. The instanteaneous velocity and vorticity signals are decomposed into mean, coherent and incoherent parts using the triple decomposition technique. A significant percentage of the incoherent fluctuations are observed to be phase-locked to the Karman vortices. The enstropy balances are computed for three decomposed parts. The generation of incoherent enstrophy due to incoherent vortex stretching is detected to be the most dominant term and is balanced by the viscous dissipation.
Fri, 01 Jan 1993 00:00:00 GMThttp://hdl.handle.net/1903/204861993-01-01T00:00:00ZAn Investigation of Blast Waves Generated by Constant Velocity Flames
http://hdl.handle.net/1903/20478
An Investigation of Blast Waves Generated by Constant Velocity Flames
Luckritz, Robert Thomas
The relevant flow field parameters associated with the generation and propagation of blast waves from constant velocity flames were systematically studied through numerical integrations of the non-steady equations for mass, momentum, and energy. The flow was assumed to be that of an adiabatic inviscid fluid obeying the ideal gas law and the flame was simulated by a working fluid heat addition model. The flame velocity was varied from infinitely fast (bursting sphere) through velocities characterized by the nearly constant pressure deflagration associated with low Mach number laminar flames. The properties noted included peak pressure, positive impulse, energy distribution, and the blast wave flow field. Results were computed for the case of a methane-air mixture assuming an energy density, q = 8.0, an ambient specific heat ratio, Yo = 1.4 and a specific heat ratio behind the flame, Y4 = 1.2. In the source volume, as the flame velocity decreased to Mach 4.0 the overpressure increased. For flame velocities below Mach 4.0 the overpressure decreased, and approach the acoustic solution originally developed by Taylor. In the far field the overpressure curves for supersonic flame velocities coalesced to a common curve at approximately 70% of Baker's pentolite correlation. Far field overpressures for subsonic flame velocities decreased as the flame velocity decreased. For the flame velocities investigated the near field impulse was greater than the impulse from Baker's pentolite correlation. In the far field the flame generated impulse decreased to 60 to 75% of the pentolite impulse. In cases where the flow was expected to reduce to a self-similar solution and/or show Rayleigh line behavior it did. The calculations showed that the flow field behaved normally where expected, and for flow velocities where steady state behavior is not expected, non-steady behavior was observed.
Sat, 01 Jan 1977 00:00:00 GMThttp://hdl.handle.net/1903/204781977-01-01T00:00:00ZPARAMETRIC STUDY OF SOIL DRYING IN THE FIELD FOR COMPACTION QUALITY ASSURANCE
http://hdl.handle.net/1903/20457
PARAMETRIC STUDY OF SOIL DRYING IN THE FIELD FOR COMPACTION QUALITY ASSURANCE
Afsharikia, Zahra
Moving towards modulus based methods of soil compaction quality assurance using lightweight deflectometers (LWD) requires evaluation of the LWD measured modulus in the field. The resilient modulus of geomaterials is not only influenced by the moisture content (MC) at the time of compaction, but also by the MC at the time of testing, which may be up to few hours after compaction. A parametric study was performed using SoilVisionâ€™s SVFlux analysis package to model the variation of soil moisture profile with depth versus time as a function of environmental factors. Then the drying in a compacted soil layer was modeled and compared to the volumetric water content measurements in an instrumented large-scale test pit. Finally, LWD modulus values in the field were captured immediately and a few hours after compaction to exhibit the variation of modulus with time and to identify if the stiffness gain in geomaterial is significant.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/1903/204572017-01-01T00:00:00ZSeismic Design Optimization of Steel Structures Using Particle Swarm Algorithm
http://hdl.handle.net/1903/20454
Seismic Design Optimization of Steel Structures Using Particle Swarm Algorithm
Middha, Parteek
Earthquakes are one of the most devastating and expensive natural disasters in the world. Economical and earthquake-resistant design remains a challenge for structural engineers. This study explores the optimal design of a seismic force resisting steel frame using a population based stochastic algorithm known as Particle Swarm Optimization (PSO). PSO is able to efficiently explore a complex solution space with many design variables and constraints. PSO is also problem independent and can be built around any approach to earthquake design. As a case study, the seismic design of a three-story moment resisting frame is optimized for the linear static, linear dynamic, and nonlinear static analysis methods. An interface was created between MATLAB and OpenSees to link optimization with a well-known and freely available earthquake engineering software. This application is extended to the performance-based design of structures, in which the optimal design meets the target performance objectives of Immediate Occupancy, Life Safety, and Collapse Prevention under Frequent, Design, and Maximum-considered seismic hazard levels.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/1903/204542017-01-01T00:00:00Z