Holographic flow visualization

Holographic visualization techniques are presented of the vortex wake of a lifting wing. The motions of tracer particles in vortical flows are described along with the development of a liquid-drop tracer generator. An analysis is presented of the motion of particles of arbitrary density and size in solid body and potential vortex flows

Application of a ruby laser to high-speed photography

Multiple pulsing of a ruby laser has been achieved and incorporated into a high-speed camera. The pulsing is accomplished by means of cavity Q spoiling techniques utilizing a Kerr cell. a rotating mirror camera is used with the laser acting as a stroboscopic light source to record the events. Framing rates of over a million frames per second with exposure times of less than 30 nsec are easily obtainable. This in conjunction with the highly intense monochromatic, cohere and collimated nature of the laser light makes the high-speed laser camera desirable in many areas of research

Additional Exploratory Photoelastic Studies in Stress Wave Propagation

In a previous report to the sponsor, the design and description of a high speed framing camera was presented along with several film strips representing the results of a series of qualitative investigations of dynamic stress wave phenomena. These studies included crack propagation, layered media, compressed bars and beams, and cross sections of rocket heads. As part of a continuing study in these and related fields, a final report is submitted covering (1) exploratory experimental studies of shock wave propagation initiated by explosive caps and by nitrogen shock wave impingement, and (2) theoretical studies of a series of dynamic stress wave problems carried out in conjunction with the overall problem

Torsional Magnetoelastic Waves in a Circular Cylinder

In this paper the effect of an electromagnetic field on the propagation of a pure torsional elastic wave in a conducting circular cylinder is investigated. The general field equations and boundary conditions are linearized and the equations of motion for an infinitely long circular rod are obtained for the particular electromagnetic field configurations considered. The torsional motion of a solid rod in a steady axial magnetic field with and without a steady electric field is considered. In the first case it is found that a pure torsional mode will not propagate. In the second case a pure torsional mode will propagate and its frequency equation is obtained. The results for a perfect conductor are compared to a real material. The torsional motion of a hollow rod in a steady tangential magnetic field with and without a steady axial electric field is considered. Without the electric field the equations are completely uncoupled and the solution is the standard elastic one. The electric field introduces coupling via the induced magnetic field. The equations of motion are obtained, however the actual solutions are not obtained due to the mathematical complexity involved

Measuring spatial pressure distribution from explosives buried in dry Leighton Buzzard sand

Direct measurement of the intense loading produced by the detonation of a buried explosive is an extremely difficult task. Historically, high-fidelity measurement techniques have not been sufficiently robust to capture the extremely high pressures associated with such events, and researchers have relied on ‘global’ measurements such as the average loading acting over a particular area of interest. Recently, a large-scale experimental approach to the direct measurement of the spatial and temporal variation in loading resulting from an explosive event has been developed, which utilises Hopkinson pressure bars (HPBs) inserted through holes in a large target plate such that their faces lie flush with the loaded face. This article presents results from ten experiments conducted at 1/4 scale, using 17 HPBs to measure the spatial pressure distribution from explosives buried in dry Leighton Buzzard sand, a commonly available sand used in many geotechnical applications. Localised pressure measurements are used in conjunction with high speed video to provide a detailed examination of the physical processes occurring at the loaded face, as well allowing quantification of these effects. Example pressure–time and impulse–time traces are provided in full to allow researchers to use this data for validation of numerical modelling approaches

Assessing cement injection behaviour in cancellous bone: an in vitro study using flow models.

Understanding the cement injection behaviour during vertebroplasty and accurately predicting the cement placement within the vertebral body is extremely challenging. As there is no standardized methodology, we propose a novel method using reproducible and pathologically representative flow models to study the influence of cement properties on injection behaviour. The models, confined between an upper glass window and a lower aluminium plate, were filled with bone marrow substitute and then injected (4, 6 and 8 min after cement mixing) with commercially available bone cements (SimplexP, Opacity+, OsteopalV and Parallax) at a constant flow rate (3 mL/min). A load cell was used to measure the force applied on the syringe plunger and calculate the peak pressure. A camera was used to monitor the cement flow during injection and calculate the following parameters when the cement had reached the boundary of the models: the time to reach the boundary, the filled area and the roundness. The peak pressure was comparable to that reported during clinical vertebroplasty and showed a similar increase with injection time. The study highlighted the influence of cement formulations and model structure on the injection behaviour and showed that cements with similar composition/particle size had similar flow behaviour, while the introduction of defects reduced the time to reach the boundary, the filled area and the roundness. The proposed method provides a novel tool for quick, robust differentiation between various cement formulations through the visualization and quantitative analysis of the cement spreading at various time intervals

Balloon kyphoplasty in the treatment of metastatic disease of the spine: a 2-year prospective evaluation

There is currently little data on the longer term efficacy and safety of balloon kyphoplasty (BKP) in patients with metastatic vertebral compression fractures (VCFs). To prospectively assess the long-term efficacy and safety of BKP in treating thoracic and lumbar spinal metastatic fractures that result in pain or instability. Sixty-five patients (37 men, mean age: 66 years) underwent 99 BKP procedures. Patient-related outcomes of pain visual analogue scale (VAS) and Oswestry Disability Index were assessed pre- and post-operatively and after 3, 6, 12 and 24 months. Correction of vertebral height and kyphotic deformity were assessed by radiographic measurements. Mean pain VAS and Oswestry Disability Index significantly improved from pre- to post-treatment (P < 0.0001), this improvement being sustained up to 24-month follow up. A gain in height restoration and a reduction of the post-operative kyphotic angle were seen post-operatively and at 3 months although these radiographic outcomes returned to pre-operative levels at 12 months. BKP was associated with a rate of cement leakage and incidence vertebral fracture of 12 and 8%, respectively. No symptomatic cement leaks or serious adverse events were seen during the 24 months of follow up. BKP is a minimally invasive procedure that provides immediate and long-term pain relief and improvement in functional ability in selected patients with metastatic VCFs. The procedure appears to have good long-term safety