The flow conditions in a low attenuation electromagnetic shock tube are discussed and compared with those in pressure driven shock tubes and conventional electromagnetic shock tubes. The low attenuation electromagnetic shock tube differs from the conventional electromagnetic shock tube in that it incorporates a diaphragm separating the high pressure driver section from the low pressure expansion section. It was shown that the shock tube gives a plane shock front and a region of shock heated gas separated from the driver gas by a non-plane contact surface. The electrical conductivity of shock heated argon was measured for shock speeds of from Mach 8 to Mach 35, and downstream pressures of from 0.01 to 2.0 mm Hg, and was found to agree with theory at the higher downstream pressures but to fall below the theoretical values at the low pressures. The low values of conductivity were attributed to a non-attainment of equilibrium behind the shock front due to the greater relative importance of electron diffusion at low densities. The shock heated gas was used as the working fluid in two magnetohydrodynamic power generators. In the first the internal resistance of the generator was measured as a function of electrode area and generator current. It was concluded that at high currents a cathode spot was formed, and the measured resistances were related to a theory of cathode spot conduction. In the second generator some effects of the non-scalar conductivity of the plasma at high magnetic fields were investigated. It was shown that the values of Hall voltages in a magnetohydrodynamic generator agree with theory, and can be used to obtain an estimate of the electron density in the plasma. The reduction of the generator current by Hall currents was measured. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This thesis is concerned with a theoretical and experimental investigation of Alfvén waves in an ionized medium, and magnetic interaction effects between a moving plasma and a magnetic coil external to the plasma. Methods for generating Alfvén disturbances for varying conditions of gas density and magnetic fields are considered and various means for measuring any effects that may be produced. It will be seen that for propagation of m.h.d. waves, extremely strong coupling between the plasma and field is necessary with consequent necessary high fields and Alfvén speeds. The effect of an axial magnetic field modifying the shock speed in the plasma is investigated and also the effect of the field on incident and reflected shock speeds by placing a plain obstruction in the shock tube which blocks the plasma flow. A further study of magnetic interaction effects between a moving plasma and a localized radial field was undertaken with the desire of correlating mechanical momentum transfer with varying conditions of applied field and gas pressures in the plasma (hence conductivity, density, and shock speed variations). Mechanical and electrical measurements of momentum transfer are compared with theory, and it will be seen that the mechanical method offers a fairly reliable means of measurement. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The propagation of a shock wave into a general inhomo-geneous flow field is studied. The equations for the shock velocity through such a region are developed in a general manner. A consequence of these equations is the development of the shock wave as a probe into unknown flow fields. The shock velocity is measured and the initial parameters ahead of the shock are calculated. The unique advantage of the shock probe is that it does not perturb the gas ahead of the front. An experimental application is described in which the shock probe is used to analyze the unknown flow field created by a constricted arc light source. The flow field is subsequently identified as a radiation front at the Chapman-Jouguet point. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The present study examined the following two hypotheses: (a) shock which has been associated with food will reduce responding less than shock which has not been associated with food: (b) response-contingent shock will reduce responding more than response-noncontingent shock. Response rates and the number of reinforcements received in Punishment training, and response rates in Punishment-Extinction training were examined for the following five groups: (a) shock and pellet for the same response (Pun-Rft Group): (b) shock and food for different responses (Pun Group): (c) response-noncontingent shock delivered automatically as response-contingent food becomes available for the next response (Shock-SD Group): (d) response-noncontingent shock delivered automatically independent of the availability of reinforcement (NC-Shock Group): (e) no shock (Control Group). The results indicated that (a) response-contingent and response-noncontingent shock reduced responding equally in Punishment training, and that (b) following Punishment-training, response-contingent shock reduced responding in Punishment-Extinction training whereas response-noncontingent shock had no effect on rate of responding in Punishment-Extinction training. The results also indicated that shock which had been associated with food had the same overall effect on response rates as shock which had not been associated with food. The relevance of these results to the discriminative and conditioned reinforcing functions of shock was discussed. / Arts, Faculty of / Psychology, Department of / Graduate

Detection threshold (DT) for electric shock under both incentive (IDT; cigarettes) and no-incentive (NIDT) conditions was determined in psychopathic and nonpsychopathic criminals and noncriminal controls (N=14 each group). A modified forced-choice procedure permitted E to vary stimulus intensity from trial to trial in an attempt to counteract boredom or inattentiveness. The use of a constant-current stimulator, a concentric electrode, and monitoring of skin/electrode impedance allowed reasonably precise control over current intensity. There were no differences between groups in NIDT or IDT, a result not consistent with previous findings of relatively high DTs in psychopaths. The result was interpreted in terms of the concept of arousal. An additional result was that IDT was lower than NIDT for all groups. Tolerance level (TL) for shock was also determined in the same groups under both no-incentive (NITL) and incentive (ITL; cigarettes) conditions. Although there was no difference between groups in NITL, psychopaths had a significantly higher ITL than the other groups. The result supported the hypothesis of relatively high stimulus tolerance in psychopaths. An additional result noted was that TL did not correlate with DT, a finding which appears consistent with evidence suggesting that the two parameters have somewhat different response determinants. / Arts, Faculty of / Psychology, Department of / Graduate

The formation and propagation of laser-driven shock waves has been observed by optical shadowgraphy in fused quartz, α-quartz and sodium chloride. Target materials were irradiated with a 0.53 µm , ~ 2.5 ns FWHM laser pulse at intensities ranging between 0.2 — 2 x 10¹³ W/cm², producing peak pressures varying from 0.3 — 3 Mbar at the shock front. Observations in both varieties of quartz reveal transient, high-speed shock propagation followed by deceleration towards a steady asymptotic shock speed. Similar high-speed transients were not seen in sodium chloride. The results in quartz were found to be in significant disagreement with both one-dimensional and two-dimensional hydrodynamic calculations based on equilibrium equations of state. The non-steady shock propagation is interpreted as being due to a relaxation process in the phase transformation of quartz into the high-pressure stishovite phase which occurs at the shock front. The effects of such a relaxation process on the shock dynamics and shock compression process are considered for the case of a direct relaxation from quartz into stishovite, as well as for an indirect relaxation process in which the -transformation of quartz into stishovite is preceded by shock-induced amorphization of the quartz. It is shown that either scenario would result in higher shock speeds and less compressible shock states than those obtained under equilibrium conditions. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Standing shock waves in a supersonic flow field produce density gradients across which an electrical potential is established. If electrodes are mounted upstream and downstream of the standing shock, an electrical current can be extracted. The electrical power output by such a system (called a bow shock generator) has been measured. To produce the supersonic flow an overdriven detonation shock tube, capable of producing Mach 12 shocks in 5 Torr argon, was constructed and used as a short duration supersonic wind tunnel. The open circuit voltage of a single bow shock generator with a 2 cm electrode separation was measured to be 0.95 V, and the maximum power output to 53 mW. By reducing the electrode separation to 1 cm the maximum power output was increased to 90 mW, while the open circuit voltage remained unchanged. It was found that when two bow shock generators are mounted side by side in the flow a parallel connection of their outputs produced a small increase in current. However no increase in output voltage was observed when the generators were connected in series. It was also found that when an oblique shock and its reflection from the wall were connected together in series, the output voltage was less than that of the oblique shock alone. However this was likely due to a short circuit path between the electrodes through the boundary layer. Some of the measurements were inconclusive due to an insufficiently long test time. A preliminary analysis was done on a system in which a set of bow shock generators is used as a topping system for a conventional electrical generation system. It was shown that the bow shock generators must be operated at very low Mach numbers if they are to be efficient in this application. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Shock is one of the environmental tests that a spacecraft must pass before being cleared for launch. Shock testing poses a challenging data acquisition issue and careful selection of equipment is crucial to creating a successful shock test facility. Cal Poly’s CubeSat programs can currently perform all environmental testing other than shock themselves, so a quality shock table would be useful. Previous groups of students had developed a shock table, and this paper details the improvement and characterization of that shock table’s behavior. Several adjustable parameters were tested and documented to discover trends in the shock table’s response to an impact from a pendulum hammer. Then a test meant to mimic an actual shock test was performed. The CubeSat program provided a component to be tested and a requirement to be met. The nominal requirement is proprietary and cannot be given here, and additional stipulations included the test data being within a given tolerance band and at least 50% of the test data having a larger magnitude than the nominal requirement. The requirement needed to be met in all three of the component’s axes. The component was mounted to the shock table and acceleration data was collected and analyzed. A successful test was conducted in one axis, which was the result of impacting the large face of the aluminum shock table plate. The tests in the other two axes, conducted with impacts to the side of the aluminum plate, failed to meet the requirement. A finite element model of the table was developed and correlated to the test data. A new way of attaching the test component to the table was developed that would allow for testing in all three axes to be performed with impacts to the large face of the aluminum plate. A dynamic finite element analysis was performed, and the results indicate that this new attachment method should allow the requirement to be met in all three axes. The shock table is currently fully operational and can be used for testing and teaching purposes. With the implementation of the new attachment method, it is believed that the CubeSat program’s requirements can be met as well.

A thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, Johannesburg, August 2018 / This work details findings of an analytical, numerical and experimental investigation into the physical nature of three-dimensional shock reflection transition. Steady flow shock reflections comprise two types: regular reflection and Mach reflection. Reflection studies have previously been conducted using double-wedge symmetrical test piece configurations. It had been found by previous researchers that the expansion waves resulting from the side edges of the wedges would influence the reflection plane. The three-dimensional nature of real experimental flows gives rise to there generally being a coexistence of regular reflection (at the central portions) and Mach reflection (towards the outer peripheral portions) in between which transition occurs. It is the object of this work to understand three-dimensional transition for flow fields in which edge effects do not influence the reflection plane. Specially modified test piece geometry was developed for this purpose. Experimental tests were required for validation of the numerical models of the flow field. This was achieved by obtaining oblique shadowgraphs with optical orientation in both yaw and roll to assist in visualising the three-dimensional features of the flow field. These were compared with numerically reconstructed images at the same oblique orientations using a novel reconstruction technique. The main objective of this work was to identify the degree of correspondence of the threedimensional transition conditions to those of two-dimensional flows. This was facilitated by means of reducing the three-dimensional analysis to an effective two-dimensional one. It was found that the three-dimensional transition points occur at a higher effective angle than predicted by twodimensional criteria, and tend towards two-dimensional criteria at reduced free-stream Mach numbers and increased model geometrical spreads. Another important aspect of this work was the nature of the intersection line in the vicinity of the transition point, i.e., the point of impingement of the incident wave and its Mach surface on the horizontal symmetry plane in between the test pieces. Here it was found that a cusp exists in the sweep profile of the intersection line at the transition point. This was proved from a theoretical standpoint based on a model developed for the analysis of the flow in the vicinity of transition. Evidence of this from the numerical and experimental results is given as well. Higher geometrical spreads and lower free-stream Mach numbers were found to create flatter intersection line profiles at the horizontal symmetry plane on which the transition points were located further forward towards the apex of this line and which gave rise to greater transverse deflections for the streamlines passing through the regular reflection portions. Further discussion revolves around the nature of the shear and Mach surfaces. The Mach surface heights (representative of the triple line trajectories) are shown to increase monotonically. The shear layer edge trajectory, which originates at the sweep cusp, was found to show considerable transverse divergence but in keeping with the nature and extent of the transition cusp sweep differential, which in some cases was found to be large enough to cause a strong shock solution for the Mach reflection portion. In this case the shear surface edge trajectory diverted from trends seen for other models. The nature of the shear surface as a whole revealed interesting insights into the negative triple configuration of the Mach reflection portions which comprised of convex Mach surfaces. This is in contrast to the geometry obtained for the Mach surface for full Mach reflection numerically studied with a highly-spread geometry. Here, the flat Mach surface was found to increase monotonically towards the periphery in contrast to what was found for flows with edge influences on the Mach surface. It is suggested that this is what precludes complex reflection (central Mach reflection, transitioning to regular reflection further out, with a further transition to Mach reflection at the periphery) from being obtained in such flow fields / MT 2019

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