1,755 research outputs found

    Evaluating long-duration blast loads on steel columns using computational fluid dynamics

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    Long-duration blasts are typically defined by positive pressure durations exceeding 100ms (Denny & Clubley, 2019; Johns & Clubley, 2016). 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 programs 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-section 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

    A critical review of a computational fluid dynamics (CFD)-based explosion numerical analysis of offshore facilities

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    In oil and gas industries, the explosive hazards receive lots of attention to achieve a safety design of relevant facilities. As a part of the robust design for offshore structures, an explosion risk analysis is normally conducted to examine the potential hazards and the influence of them on structural members in a real explosion situation. Explosion accidents in the oil and gas industries are related to lots of parameters through complex interaction. Hence, lots of research and industrial projects have been carried out to understand physical mechanism of explosion accidents. Computational fluid dynamics-based explosion risk analysis method is frequently used to identify contributing factors and their interactions to understand such accidents. It is an effective method when modelled explosion phenomena including detailed geometrical features. This study presents a detailed review and analysis of Computational Fluid Dynamics-based explosion risk analysis that used in the offshore industries. The underlying issues of this method and current limitation are identified and analysed. This study also reviewed potential preventative measures to eliminate such limitation. Additionally, this study proposes the prospective research topic regarding computational fluid dynamics-based explosion risk analysis

    Coupled modeling for investigation of blast induced traumatic brain injury

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    Modeling of human body biomechanics resulting from blast exposure is very challenging because of the complex geometry and the substantially different materials involved. We have developed anatomy based high-fidelity finite element model (FEM) of the human body and finite volume model (FVM) of air around the human. The FEM model was used to accurately simulate the stress wave propagation in the human body under blast loading. The blast loading was generated by simulating C4 explosions, via a combination of 1-D and 3-D computational fluid dynamics (CFD) formulations. By employing the coupled Eulerian-Lagrangian fluid structure interaction (FSI) approach we obtained the parametric response of the human brain by the blast wave impact. We also developed the methodology to solve the strong interaction between cerebrospinal fluids (CSF) and the surrounding tissue for the closed-head impact. We presented both the arbitrary Lagrangian Eulerian (ALE) method and a new unified approach based on the material point method (MPM) to solve fluid dynamics and solid mechanics simultaneously. The accuracy and efficiency of ALE and MPM solvers for the skull-CSF-brain coupling problem was compared. The presented results suggest that the developed coupled models and techniques could be used to predict human biomechanical responses in blast events, and help design the protection against the blast induced TBI

    High Speed Vehicle Fluid-Structure-Jet Interaction Analysis and Modeling

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    Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143047/1/6.2017-0405.pd

    Prediction of far-field acoustic emissions from cavitation clouds during shock wave lithotripsy for development of a clinical device

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    This study presents the key simulation and decision stage of a multi-disciplinary project to develop a hospital device for monitoring the effectiveness of kidney stone fragmentation by shock wave lithotripsy (SWL). The device analyses, in real time, the pressure fields detected by sensors placed on the patient's torso, fields generated by the interaction of the incident shock wave, cavitation, kidney stone and soft tissue. Earlier free-Lagrange simulations of those interactions were restricted (by limited computational resources) to computational domains within a few centimetres of the stone. Later studies estimated the far-field pressures generated when those interactions involved only single bubbles. This study extends the free-Lagrange method to quantify the bubble–bubble interaction as a function of their separation. This, in turn, allowed identification of the validity of using a model of non-interacting bubbles to obtain estimations of the far-field pressures from 1000 bubbles distributed within the focus of the SWL field. Up to this point in the multi-disciplinary project, the design of the clinical device had been led by the simulations. This study records the decision point when the project's direction had to be led by far more costly clinical trials instead of the relatively inexpensive simulations. <br/

    Numerical study on scaling effects and decoupled network-based simulation of gaseous explosion

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    This research seeks to improve the prediction efficiency of gaseous explosions realized by numerical simulations in a full-scale underground network using a decoupled method. To provide quick predictions of overpressure distribution of methane explosions in underground airway networks, a two-section theory is employed. The explosion space is divided into a driver section and a blast-wave section. Governing equations including conservation of mass, momentum, and energy, together with chemical reaction and turbulence models are solved for the driver and the blast-wave sections using computational fluid dynamics (CFD) solver ANSYS Fluent (3D-based) and Flowmaster (1D-based) respectively. The three dimensional (3D) and one dimensional (1D) numerical analyses are preceded separately (decoupled). In the driver section, the numerical calculation results with three variables (FLSF, HDSF, and concentration) considering the size of explosion space and methane concentration level for the driver section are stored in a database tool Microsoft SQL Server Express aims to generate a methane explosion source database. To validate the selected combustion and turbulent models, a series of lab-scale methane explosion experiments were conducted. In the blast-wave section, the influences of geometric changes are quantified by using 2D Euler equations, whereas the simulation results are used to adjust the 1D network-based modeling. The decoupled method is applied in two case studies and proved capable to predict the pressure distribution of methane explosions that occurs in a complex airway network. --Abstract, page iii

    A Moving Frame Algorithm for High Mach Number Hydrodynamics

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    We present a new approach to Eulerian computational fluid dynamics that is designed to work at high Mach numbers encountered in astrophysical hydrodynamic simulations. The Eulerian fluid conservation equations are solved in an adaptive frame moving with the fluid where Mach numbers are minimized. The moving frame approach uses a velocity decomposition technique to define local kinetic variables while storing the bulk kinetic components in a smoothed background velocity field that is associated with the grid velocity. Gravitationally induced accelerations are added to the grid, thereby minimizing the spurious heating problem encountered in cold gas flows. Separately tracking local and bulk flow components allows thermodynamic variables to be accurately calculated in both subsonic and supersonic regions. A main feature of the algorithm, that is not possible in previous Eulerian implementations, is the ability to resolve shocks and prevent spurious heating where both the preshock and postshock Mach numbers are high. The hybrid algorithm combines the high resolution shock capturing ability of the second-order accurate Eulerian TVD scheme with a low-diffusion Lagrangian advection scheme. We have implemented a cosmological code where the hydrodynamic evolution of the baryons is captured using the moving frame algorithm while the gravitational evolution of the collisionless dark matter is tracked using a particle-mesh N-body algorithm. The MACH code is highly suited for simulating the evolution of the IGM where accurate thermodynamic evolution is needed for studies of the Lyman alpha forest, the Sunyaev-Zeldovich effect, and the X-ray background. Hydrodynamic and cosmological tests are described and results presented. The current code is fast, memory-friendly, and parallelized for shared-memory machines.Comment: 19 pages, 5 figure
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