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

Thermodynamic optimization tools for power tracking in a multistage concentrated solar power Rankine plant

Abstract: The object of the study is to present a method of thermodynamic optimization of power generating plants, in a mode that consolidates and simplifies the analysis of data on heat-work interaction of the plant components. The optimization scheme identifies the technical and process parameters that can improve the thermodynamic performance of the plant with respect to an objective variable, and further, the required thermodynamic measures necessary to improve the operating condition of the plant. Simple but effective tools are used to evaluate the optimal and suboptimal power generating capacities vis-à-vis the fundamental variables—namely, the thermodynamic quantity ratio (TQR) and the power-energy quantity ratio (PQR)—without routing optimization procedures. Beyond the optimal value of the objective variable, the power generation capacity of the plant is affected. The determination of the optimal value of the objective variable can also be approached by computerization; for fixed prescriptions of the boiler, superheater, and turbine parameters, variables such as boiler pressure and temperature can be optimally selected. DOI: 10.1061/(ASCE)EY.1943-7897.0000367. © 2016 American Society of Civil Engineers

An experimental investigation of the performance of sequentially connected evacuated tubes using concentrated solar power

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.Heated air has many applications including space heating, cooking, absorption refrigeration, curing of industrial products and drying of foodstuffs. Typically air heated using solar irradiance is achieved in a collector which incorporates absorber plates enclosed with a transparent surface to retain heat in the collector. The temperature of air heated in such collectors is limited to some 80 °C. An experimental investigation was carried out in which ambient air was passed through three sequentially connected evacuated tubes, each fitted with parabolic concentrator with a reflectance of 97%. Tests were carried out on 1 September when the maximum elevation of the sun was 56.7° corresponding to a required tilt angle at solar noon of 33.3°. The rig was set at a tilt angle of 30° and an azimuth angle of -12°. The effects of the irradiance angle of incidence on the outlet temperature of the air from the three tubes were evident with the maximum temperatures occurring at solar noon when the outlet temperatures of the air from the first tube was 151.2°C, from the second 221.0 °C, and from the third 250.1 °C. The flow rate of air was 0.00223 kg/s. Using a reflector cross sectional area of 0.51m² per tube the efficiencies of the tubes at solar noon based on the normal component of irradiance into the parabolic reflectors were for the first second and third tubes 42%, 24%, and 12% respectively with an overall efficiency of 28%. The results indicated that heating air to elevated temperatures using concentrated solar power evacuated tubes is feasible but it will be necessary to redesign the system to reduce the excessive energy loss to the atmosphere. This energy loss was found to be directly proportional to the temperature difference between the mean temperature of the air in a tube and atmospheric temperature.cf201

Constant strain rate compression of bovine cortical bone on the Split-Hopkinson Pressure Bar

Cortical bone is a visco-elastic material which implies that strain rate will affect its response. Although the Split-Hopkinson Pressure Bar is an accepted technique for determining the dynamic compressive properties of cortical bone it has been shown that the strain rate of compression does not remain constant throughout the duration of a classical experiment with a uniform striker. This raises concerns as to the measurement of smeared responses. This paper presents a shaped striker technique whereby the incident pulse can be shaped to attain a constant strain rate experiment for bovine bone. Shaped strikers offer benefits such as reusability and increased test repeatability. A comparison of the stress–strain–strain rate responses attained through classical and constant strain rate experiments shows that the shape of the stress–strain curves from conventional experiments is adversely affected in the portion where the strain rate varies. The dynamic response corridors for the two tests are similar, however the ultimate properties are affected. It is concluded that the strain rate history should be presented with dynamic stress–strain responses since the instantaneous strain rate is a likely contributor to potential constitutive models.http://www.elsevier.com/locate/msechb2016Mechanical and Aeronautical Engineerin

A study on the response of single and double circular plates subjected to localised blast loading

The response of single and double layered steel plates to localised air-blast loading was examined. Two configurations, both comprising fully clamped circular plates with a 200 mm exposed diameter, were considered: 4mm thick single and (2+2) mm double layered plates. The localised air-blast loading was applied by centrally detonating discs of PE4 plastic explosive. Similar failure modes were evident in the single and double plate configurations, namely, Mode I (large inelastic deformation) and Mode II (capping failure along with deformation) responses. The double plates exhibited larger midpoint deflections than the single plates, and partial tearing of the front plate in the double plates was observed at a lower impulse than in the single plates. However, complete capping of both plates in the double plate configuration occurred at the same charge mass as for the single plates, implying that both configurations offer equivalent protection from capping failure as a result of this type of localised blast loading. A metallographic study of the deformed and torn plate regions did not reveal any phase transformation in the steel. It was also found that the 2 mm thick plates exhibited larger increases in grain size than the 4 mm thick plates

A comprehensive study on the effect of cavitation on injection velocity in diesel nozzles

Results when testing cavitating injection nozzles show a strong reduction in mass flow rate when cavitation appears (the flow is choked), while the momentum flux is reduced to a lesser extent, resulting in an increase in effective injection velocity. So as to better understand the origin of this increase in effective injection velocity, the basic equations for mass and momentum conservation were applied to an injection nozzle in simplified conditions. The study demonstrated that the increase in injection velocity provoked by cavitation is not a direct effect of the latter, but an indirect effect. In fact, the vapor appearance inside the injection hole produces a decrease in the viscosity of the fluid near the wall. This leads to lower momentum flux losses and to a change in the velocity profile, transforming it into a more "top hat" profile type. This change in the profile shape allows explaining why the momentum flux reduction is not so important compared to that of the mass flow rate, thus explaining why the effective injection velocity increases. © 2012 Elsevier Ltd. All rights reserved.The authors thank different members of the CMT-Motores Termicos team of the Universitat Politecnica de Valencia for their contribution to this work: to Jaime Gimeno, for his fruitful comments, and to Xandra Margot, Stavroula Patouna and Gabriela Bra-cho for their help in the CFD calculations. Also they thank the FPU program of the Ministerio de Educacion of Spain for granting the Ph.D. studies of Oscar A. de la Garza (grant AP2008-01913). Open-FOAM and Star-CD are registered trademarks of OpenCFD Ltd. and CD-Adapco, respectively.López, JJ.; Salvador Rubio, FJ.; De La Garza De Leon, O.; Arregle, JJP. (2012). A comprehensive study on the effect of cavitation on injection velocity in diesel nozzles. Energy Conversion and Management. 64:415-423. https://doi.org/10.1016/j.enconman.2012.03.032S4154236

Decompressive cervical laminectomy and lateral mass screw-rod arthrodesis. Surgical analysis and outcome

<p>Abstract</p> <p>Background</p> <p>This study evaluates the outcome and complications of decompressive cervical Laminectomy and lateral mass screw fixation in 110 cases treated for variable cervical spine pathologies that included; degenerative disease, trauma, neoplasms, metabolic-inflammatory disorders and congenital anomalies.</p> <p>Methods</p> <p>A retrospective review of total 785 lateral mass screws were placed in patients ages 16-68 years (40 females and 70 males). All cases were performed with a polyaxial screw-rod construct and screws were placed by using Anderson-Sekhon trajectory. Most patients had 12-14-mm length and 3.5 mm diameter screws placed for subaxial and 28-30 for C1 lateral mass. Screw location was assessed by post operative plain x-ray and computed tomography can (CT), besides that; the facet joint, nerve root foramen and foramen transversarium violation were also appraised.</p> <p>Results</p> <p>No patients experienced neural or vascular injury as a result of screw position. Only one patient needed screw repositioning. Six patients experienced superficial wound infection. Fifteen patients had pain around the shoulder of C5 distribution that subsided over the time. No patients developed screw pullouts or symptomatic adjacent segment disease within the period of follow up.</p> <p>Conclusion</p> <p>decompressive cervical spine laminectomy and Lateral mass screw stabilization is a technique that can be used for a variety of cervical spine pathologies with safety and efficiency.</p

Application of X-ray micro-computed tomography on high-speed cavitating diesel fuel flows

The flow inside a purpose built enlarged single-orifice nozzle replica is quantified using time-averaged X-ray micro-computed tomography (micro-CT) and high-speed shadowgraphy. Results have been obtained at Reynolds and cavitation numbers similar to those of real-size injectors. Good agreement for the cavitation extent inside the orifice is found between the micro-CT and the corresponding temporal mean 2D cavitation image, as captured by the high-speed camera. However, the internal 3D structure of the developing cavitation cloud reveals a hollow vapour cloud ring formed at the hole entrance and extending only at the lower part of the hole due to the asymmetric flow entry. Moreover, the cavitation volume fraction exhibits a significant gradient along the orifice volume. The cavitation number and the needle valve lift seem to be the most influential operating parameters, while the Reynolds number seems to have only small effect for the range of values tested. Overall, the study demonstrates that use of micro-CT can be a reliable tool for cavitation in nozzle orifices operating under nominal steady-state conditions

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