Experimental response of an optical sensor used to determine the moment of blast by sensing the flash of the explosion

The Council for Scientific and Industrial Research (CSIR) conducts research into the effect of underwater explosions on maritime structures and equipment. One of the parameters that are required to be measured to a large degree of accuracy is the shock wave velocity in close proximity (10 - 120 charge radii) of the explosion, without having to revert to the streak photography method. This distance is in the region where the near field crosses over to the far field, and it would be expected that the distance-time curve would not be linear. The streak photography method produces accuracy in the very near field of the explosion, but is not recommended for accurate measurements at distances beyond 20 charge radii. We investigated the response of an optical sensor constructed to measure the light flash of an underwater blast to determine the moment of explosion. By measurement of the time taken between this moment and the time when the shock wave reaches the pressure sensors, accurate measurements of the distance-time history (and hence shock wave velocity) could be calculated. Twelve general purpose phototransistors were used in a parallel configuration to enhance the sensitivity of the sensor. These transistors were connected directly to a conditioning amplifier which formed the interface between the transistors and the data acquisition equipment. The results that were obtained confirmed that the light intensity of the flash of the explosion increased to a maximum within several microseconds. Measurements of the average velocity of the shock wave propagation, based on the flash measurement as a marker, correlated to within 0.1%, meaning that this method of marking the moment of explosion to within several microseconds had been successful. This method can therefore be used in similar underwater blast measurement applications when a measurement marker of the moment of explosion is required

Perforated Plates as Passive Mitigation Systems

This paper presents the results of tests on fully-clamped circular plates subjected to blastloading directed down a tube. Four series of tests were performed. In one set of experiments,the blast wave was allowed to progress unhindered down the tube to impinge upon the plate,and in the other tests, perforated plates were placed in the path of the blast wave to hinderprogression down the tube, disrupting the blast and absorbing some of the kinetic energy.Results of the tests indicate that the perforated plates can be used as a form of passive mitigation

Experimental measurement of specific impulse distribution and transient deformation of plates subjected to near-field explosive blasts

The shock wave generated from a high explosive detonation can cause significant damage to any objects that it encounters, particularly those objects located close to the source of the explosion. Understanding blast wave development and accurately quantifying its effect on structural systems remains a considerable challenge to the scientific community. This paper presents a comprehensive experimental study into the loading acting on, and subsequent deformation of, targets subjected to near-field explosive detonations. Two experimental test series were conducted at the University of Sheffield (UoS), UK, and the University of Cape Town (UCT), South Africa, where blast load distributions using Hopkinson pressure bars and dynamic target deflections using digital image correlation were measured respectively. It is shown through conservation of momentum and Hopkinson-Cranz scaling that initial plate velocity profiles are directly proportional to the imparted impulse distribution, and that spatial variations in loading as a result of surface instabilities in the expanding detonation product cloud are significant enough to influence the transient displacement profile of a blast loaded plate

Development of a new assessment tool for cervical myelopathy using hand-tracking sensor: Part 1: validity and reliability

Purpose To assess the reliability and validity of a hand motion sensor, Leap Motion Controller (LMC), in the 15-s hand grip-and-release test, as compared against human inspection of an external digital camera recording. Methods Fifty healthy participants were asked to fully grip-and-release their dominant hand as rapidly as possible for two trials with a 10-min rest in-between, while wearing a non-metal wrist splint. Each test lasted for 15 s, and a digital camera was used to film the anterolateral side of the hand on the first test. Three assessors counted the frequency of grip-and-release (G-R) cycles independently and in a blinded fashion. The average mean of the three was compared with that measured by LMC using the Bland–Altman method. Test–retest reliability was examined by comparing the two 15-s tests. Results The mean number of G-R cycles recorded was: 47.8 ± 6.4 (test 1, video observer); 47.7 ± 6.5 (test 1, LMC); and 50.2 ± 6.5 (test 2, LMC). Bland–Altman indicated good agreement, with a low bias (0.15 cycles) and narrow limits of agreement. The ICC showed high inter-rater agreement and the coefficient of repeatability for the number of cycles was ±5.393, with a mean bias of 3.63. Conclusions LMC appears to be valid and reliable in the 15-s grip-and-release test. This serves as a first step towards the development of an objective myelopathy assessment device and platform for the assessment of neuromotor hand function in general. Further assessment in a clinical setting and to gauge healthy benchmark values is warranted

Automated imaging to track the 3D motion of particles

ABSTRACT--An automated 3D tracking technique for studying the motion of particles deep within the tumbling ball charge of an experimental grinding mill is described. The use of a Biplanar angioscope for the accurate location of objects moving in three dimensions is a novel application of this X-ray equipment. The X-ray beam used to produce the image data was parameterized using an accurately measured control frame. Preliminary experiments were conducted on a Perspex mill with a length and diameter of 140 mm. The digitally acquired X-ray images of the tumbling mill were processed using a fully automated imaging technique. The final 3D coordinates of the tracked particle trajectories are accurate to within 0.40 mm. This indicates that the technique is robust and thus capable of providing accurate verification data for the numerical modeling of the tumbling motion in mills