This article presents the findings of an exploratory study of teacher leadership roles in a metropolitan K-8 school district. These findings suggest that the development and performance of these roles are mediated by the organizational contexts in which they are established. They thus suggest that teacher leadership should be approached as an issue of organizational development rather than solely as an issue of individual empowerment.
Long-duration blasts are typically defined by positive pressure durations exceeding 100 ms. Such blasts can generate dynamic pressures (blast winds) capable of exerting damaging drag loads on comparatively slender structural components such as columns. With limited drag coefficient availability for specific structural geometries, Computational Fluid Dynamics (CFD) can be the only satisfactory approach for analysing blast loading on user-specified, finite geometries. The ability to analyse long-duration blasts with commercially available CFD programmes is still not confidently offered, with no prior studies examining the accuracy of modelling interaction with relatively much smaller, finite geometries. This paper presents a comparative investigation between numerical and experimental results to assess the predictive capacity of inviscid Eulerian CFD as a method for calculating long-duration blast drag loading on finite cross-sectional geometries. Full-scale long-duration blast experiments successfully measured surface pressure-time histories on a steel I-section column aligned at four orientations. Calculated pressure-time histories on exposed geometry surfaces demonstrated good agreement although reduced accuracy and under-prediction occurred on shielded surfaces manifesting as overestimated net loading. This study provides new understanding and awareness of the numerical capability and limitations of using CFD to calculate long-duration blast loads on intricate geometries.
Blast injuries remain a serious threat to defence and civilian populations around the world. 'Primary' blast injuries (PBIs) are caused by direct blast wave interaction with the human body, particularly affecting air-containing organs. Despite development of blast injury criteria since the 1960s, work to define blast loading conditions for safety limits, protective design and injury research has received relatively little attention. With a continued experimental focus on PBI mechanisms and idealised blast assumptions, meaningful test outcomes rely on appropriate simulated conditions. This paper critically evaluates existing predictive criteria for PBIs (grouped into those affecting the auditory system, pulmonary injuries and brain trauma) as a function of incident blast wave parameters, assuming idealised air blast scenarios. Analysis of the multi-injury criteria reveals new insights and understanding. It showed that blast conditions of relevance to realistic explosive threats are limited and they should be an important consideration in the design of clinical trials simulating blast injury. Zones of relevance for PBI research are proposed to guide experimental designs and compare future data. This work will prove valuable to blast protection engineers and clinical researchers seeking to determine blast loading conditions for safety limits, protective design requirements and injury investigations.
IntroductionThere is little systematic tracking or detailed analysis of investments in research and development for blast injury to support decision-making around research future funding.MethodsThis study examined global investments into blast injury-related research from public and philanthropic funders across 2000–2019. Research databases were searched using keywords, and open data were extracted from funder websites. Data collected included study title, abstract, award amount, funder and year. Individual awards were categorised to compare amounts invested into different blast injuries, the scientific approaches taken and analysis of research investment into blast traumatic brain injury (TBI).ResultsA total of 806 awards were identified into blast injury-related research globally, equating to US$902.1 million (m, £565.9m GBP). There was a general increase in year-on-year investment between 2003 and 2009 followed by a consistent decline in annual funding since 2010. Pre-clinical research received $671.3 m (74.4%) of investment. Brain-related injury research received $427.7 m (47.4%), orthopaedic injury $138.6 m (15.4%), eye injury $63.7 m (7.0%) and ear injury $60.5m (6.7%). Blast TBI research received a total investment of $384.3 m, representing 42.6% of all blast injury-related research. The U.S. Department of Defense funded $719.3 m (80%).ConclusionsInvestment data suggest that blast TBI research has received greater funding than other blast injury health areas. The funding pattern observed can be seen as reactive, driven by the response to the War on Terror, the rising profile of blast TBI and congressionally mandated research.
Blast injuries remain a serious threat to defence and civilian populations around the world. ‘Primary’ blast injuries (PBIs) are caused by direct blast wave interaction with the human body, particularly affecting air-containing organs. Despite development of blast injury criteria since the 1960s, work to define blast loading conditions for safety limits, protective design and injury research has received relatively little attention. With a continued experimental focus on PBI mechanisms and idealised blast assumptions, meaningful test outcomes rely on appropriate simulated conditions. This paper critically evaluates existing predictive criteria for PBIs (grouped into those affecting the auditory system, pulmonary injuries and brain trauma) as a function of incident blast wave parameters, assuming idealised air blast scenarios. Analysis of the multi-injury criteria reveals new insights and understanding. It showed that blast conditions of relevance to realistic explosive threats are limited and they should be an important consideration in the design of clinical trials simulating blast injury. Zones of relevance for PBI research are proposed to guide experimental designs and compare future data. This work will prove valuable to blast protection engineers and clinical researchers seeking to determine blast loading conditions for safety limits, protective design requirements and injury investigations.
Blast Engineering research group, Faculty of Engineering and the Environment, university of Southampton, uK. ABStrACt typically defined by positive pressure durations over 100ms, long-duration blasts can generate dynamic pressures (blast winds) capable of exerting damaging drag loads on slender structural elements such as columns. With limited availability of appropriate drag coefficients for specific structural geometries or different section orientations, Computational Fluid Dynamics (CFD) can provide a valuable tool for calculating blast interaction and loading on user-specified geometries. Commercially available CFD programs or 'hydrocodes' with shock wave modelling capabilities remain based on solving the inviscid Euler equations. the ability to analyse long-duration blasts is still not confidently offered however, with no prior studies examining the accuracy of modelling interaction with relatively much smaller, finite geometries. this remains particularly challenging due to large wavelengths and time durations inherent to long-duration blasts, usually limited by impractical solution domains and computing resource. this paper presents a comparative investigation between numerical simulations and experimental results to assess the predictive capability of Eulerian CFD as a tool for calculating long-duration blast drag loading on an intricate I-section geometry from different angles of incidence. Calculated pressure-time histories on exposed geometry surfaces demonstrated good agreement although reduced accuracy and under-prediction occurred for shielded surfaces manifesting as overestimated net translational loading. Numerical discrepancies were attributed to the inviscid Euler equations underpinning the CFD solver, limiting accuracy when resolving complex aerodynamic flows at bluff I-section orientations. results of this study provide new understanding and awareness of the numerical capability and limitations of using CFD to calculate long-duration blast loads on intricate geometries.
Explosions increasingly occur in densely populated, urban locations. Primary blast injuries (PBIs), caused by exposure to blast wave overpressure, can be predicted using injury criteria, although many are based on idealised loading scenarios that do not necessarily reflect real life situations. At present, there is limited understanding of how, and to what extent, blast-structure interaction influences injury risk, and the suitability of injury criteria that assume idealised loading. This work employed computational fluid dynamics to investigate the influence of blast interaction effects such as shielding and channelling on blast load characteristics and predicted PBIs. The validated modelling showed that blast interaction with common urban features like walls and corners resulted in complex waveforms featuring multiple peaks and less clearly defined durations, and that these alter potential injury risk maps. For example, blast shielding due to corners reduced peak overpressures by 43%–60% at locations behind the corner. However, when the urban layout included a corner and a wall structure, higher pressures and impulse due to channelling were observed. The channelling significantly increased the injury risk at the exposed location and reduced the shielding effects behind the corner. In these cases, the application and interpretation of existing injury criteria had several limitations and reduced reliability. This demonstrates that structural-blast interaction from common urban layouts has a significant effect on PBI risk. Specific challenges and further work to develop understanding and reliability of injury prediction for urban blast scenarios are discussed.
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