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

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

A review of blast loading in the urban environment

Urban blasts have become a significant concern in recent years. Whilst free-field blasts are well understood, the introduction of an urban setting (or any complex geometry) gives rise to multiple blast wave interactions and unique flow complexities, significantly increasing the difficulty of loading predictions. This review identifies commonly agreed-upon concepts or behaviours that are utilised to describe urban shock wave propagation, such as channelling and shielding, in conjunction with exploring urban characterisation metrics that aim to predict the effects on global blast loading for an urban blast. Likewise, discrepancies and contradictions are highlighted to promote key areas that require further work and clarification. Multiple numerical modelling programmes are acknowledged to showcase their ability to act as a means of validation and a preliminary testing tool. The findings contained within this review aim to inform future research decisions and topics better

Mitigation of Moving Shocks in an Expanding Duct

Inviscid flow theory governs the bulk motion of a gas at some distance away from the walls (i.e. outside the boundary layer). That is to say, there are no viscous forces in the bulk flow, which is modeled using the Euler equations. The Euler equations are simply the Navier-Stokes equations with zero viscosity terms. An ideal inviscid fluid, when brought into contact with a surface or wall, would naturally slip right past it since the fluid has no viscosity. In real life, however, a thin boundary layer forms between the wall or surface and the bulk flow. Shock wave boundary layer theory governs this flow. That boundary layer naturally starts as laminar, but grows in thickness over the length of the boundary until it either separates (due to an adverse pressure gradient) or becomes turbulent. Generally, a turbulent boundary layer is thicker (or reaches further into the bulk flow) than a laminar boundary layer. The flow is regime is even more complicated when moving supersonically, where shocks and boundary layer interact to cause even greater turbulence and unsteadiness. For most engineering applications involving supersonic flow, a turbulence and unsteadiness is undesirable. However, for the application of presented herein it was postulated that the turbulence and unsteadiness would help mitigate the propagation of a blast/shock wave traveling in an expanding duct or laser beam tube. It was also postulated that small wall obstructions in the flow could enhance those effects to the point of mitigating the impulsive forces of the blast/shock wave on a thin laser focusing optic. Three questions were asked and answered: 1. Will the blast/shock wave generated from fusion burn propagate from the target chamber to the final optic? Yes, it will. 2. If the blast/shock wave does propagate to the final optic, is it strong enough to damage the final optic? Yes, it does. 3. If the advancing blast/shock wave is strong enough to damage to final optic, what types of mitigation strategies can be deployed to lessen or eliminate the impacts of the blast/shock wave on the final optic? Yes, they can. By purposely tripping the boundary layer using small wall obstructions in a short section of beam tube, the turbulent boundary layer may grow in thickness to point where it reaches far enough into the bulk flow to cause the bulk to flow to lose it\u27s parallel streamlined looking profile. The turbulent boundary layer may also reach far enough into the bulk flow that it sees the turbulent boundary layer from the opposite side of the wall, thus really knocking the bulk flow out of its streamlined pattern. Upon exiting the short section of beam tube, this turbulent and unsteady flow is not directly in-line with an opening to a longer beam tube section, and therefore does not supersonically jet across but enters the longer section of diverging beam tube subsonically and naturally slows

Toroidal Imploding Detonation Wave Initiator for Pulse Detonation Engines

Imploding toroidal detonation waves were used to initiate detonations in propane–air and ethylene–air mixtures inside of a tube. The imploding wave was generated by an initiator consisting of an array of channels filled with acetylene–oxygen gas and ignited with a single spark. The initiator was designed as a low-drag initiator tube for use with pulse detonation engines. To detonate hydrocarbon–air mixtures, the initiator was overfilled so that some acetylene oxygen spilled into the tube. The overfill amount required to detonate propane air was less than 2% of the volume of the 1-m-long, 76-mm-diam tube. The energy necessary to create an implosion strong enough to detonate propane–air mixtures was estimated to be 13% more than that used by a typical initiator tube, although the initiator was also estimated to use less oxygen. Images and pressure traces show a regular, repeatable imploding wave that generates focal pressures in excess of 6 times the Chapman–Jouguet pressure.Atheoretical analysis of the imploding toroidal wave performed using Whitham’s method was found to agree well with experimental data and showed that, unlike imploding cylindrical and spherical geometries, imploding toroids initially experience a period of diffraction before wave focusing occurs. A nonreacting numerical simulation was used to assist in the interpretation of the experimental data

Investigation of Pulse Detonation Engines; Theory, Design and Analysis

Detonation and constant volume combustion has been known to the scientific community for some time but only recently has active research been done into its applications. Detonation based engines have received much attention in the last two decades because of its simple design and potential benefits to the aerospace industry. It is then the goal of this study to provide a background into detonation theory and application and establish the basis for future detonation based research at Embry-Riddle Aeronautical University. In this paper we will discuss the experimental aspects of building, testing, and analysis of a pulsed detonation tube including the development of a pulsed detonation testbed and analysis via computational fluid dynamics

Arbitrary Lagrangian-Eulerian form of flowfield dependent variation (ALE-FDV) method for moving boundary problems

Flowfield Dependent Variation (FDV) method is a mixed explicit-implicit numerical scheme that was originally developed to solve complex flow problems through the use of so-called implicitness parameters. These parameters determine the implicitness of FDV method by evaluating local gradients of physical flow parameters, hence vary across the computational domain. The method has been used successfully in solving wide range of flow problems. However it has only been applied to problems where the objects or obstacles are static relative to the flow. Since FDV method has been proved to be able to solve many complex flow problems, there is a need to extend FDV method into the application of moving boundary problems where an object experiences motion and deformation in the flow. With the main objective to develop a robust numerical scheme that is applicable for wide range of flow problems involving moving boundaries, in this study, FDV method was combined with a body interpolation technique called Arbitrary Lagrangian-Eulerian (ALE) method. The ALE method is a technique that combines Lagrangian and Eulerian descriptions of a continuum in one numerical scheme, which then enables a computational mesh to follow the moving structures in an arbitrary movement while the fluid is still seen in a Eulerian manner. The new scheme, which is named as ALE-FDV method, is formulated using finite volume method in order to give flexibility in dealing with complicated geometries and freedom of choice of either structured or unstructured mesh. The method is found to be conditionally stable because its stability is dependent on the FDV parameters. The formulation yields a sparse matrix that can be solved by using any iterative algorithm. Several benchmark stationary and moving body problems in one, two and three-dimensional inviscid and viscous flows have been selected to validate the method. Good agreement with available experimental and numerical results from the published literature has been obtained. This shows that the ALE-FDV has great potential for solving a wide range of complex flow problems involving moving bodies

Lagrangian ADER-WENO Finite Volume Schemes on Unstructured Triangular Meshes Based On Genuinely Multidimensional HLL Riemann Solvers

In this paper we use the genuinely multidimensional HLL Riemann solvers recently developed by Balsara et al. to construct a new class of computationally efficient high order Lagrangian ADER-WENO one-step ALE finite volume schemes on unstructured triangular meshes. A nonlinear WENO reconstruction operator allows the algorithm to achieve high order of accuracy in space, while high order of accuracy in time is obtained by the use of an ADER time-stepping technique based on a local space-time Galerkin predictor. The multidimensional HLL and HLLC Riemann solvers operate at each vertex of the grid, considering the entire Voronoi neighborhood of each node and allows for larger time steps than conventional one-dimensional Riemann solvers. The results produced by the multidimensional Riemann solver are then used twice in our one-step ALE algorithm: first, as a node solver that assigns a unique velocity vector to each vertex, in order to preserve the continuity of the computational mesh; second, as a building block for genuinely multidimensional numerical flux evaluation that allows the scheme to run with larger time steps compared to conventional finite volume schemes that use classical one-dimensional Riemann solvers in normal direction. A rezoning step may be necessary in order to overcome element overlapping or crossing-over. We apply the method presented in this article to two systems of hyperbolic conservation laws, namely the Euler equations of compressible gas dynamics and the equations of ideal classical magneto-hydrodynamics (MHD). Convergence studies up to fourth order of accuracy in space and time have been carried out. Several numerical test problems have been solved to validate the new approach

Summary of Supersonic Jet and Rocket Noise

This paper summarizes a two-part special session, “Supersonic Jet and Rocket Noise,” which was held during the 174th Meeting of the Acoustical Society of America in New Orleans, Louisiana. The sessions were cosponsored by the Noise and Physical Acoustics Technical Committees and consisted of talks by government, academic, and industry researchers from institutions in the United States, Japan, France, and India. The sessions described analytical, computational, and experimental approaches to both fundamental and applied problems on model and full-scale jets and rocket exhaust plumes

Development of a Detonation Diffuser

This research includes an investigation of the mechanisms of diffraction and reinitiation that enable a detonation diffuser. It describes a set of geometric parameters necessary to design a diffuser for a given detonable mixture and initial channel height. Predetonators with channel height less than the critical height are ineffective because detonations in small channels decouple into separate shock and combustion fronts when the channel height increases. A detonation diffuser allows the channel height to increase by utilizing the decoupled shock wave to reinitiate detonation. In the diffuser, a detonation initially decouples into separate shock and combustion fronts, and then the decoupled shock front reflects from an oblique surface initiating a secondary detonation that survives the expansion. This research investigated the three regions of a detonation diffuser: the initial diffraction, the reflecting surface, and the second diffraction corner. Schlieren video of two-dimensional diffracting detonations recorded the position of the detonation, decoupled shock front and flame front. Observations of the decoupled shocks reflecting from surfaces showed that a 45° reflecting surface must be placed less than 80 mm downstream of the initial diffraction corner to initiate a secondary detonation in more than 91% of repeated trials. Observations of the interaction of diffracting detonations with multiple obstacles revealed that the best performance (smallest separation, and highest Mach number) occurred when the decoupled shock reflected from four separate obstacles at approximately the same time

Numerical Simulations of Shock and Rarefaction Waves Interacting With Interfaces in Compressible Multiphase Flows

Developing a highly accurate numerical framework to study multiphase mixing in high speed flows containing shear layers, shocks, and strong accelerations is critical to many scientific and engineering endeavors. These flows occur across a wide range of scales: from tiny bubbles in human tissue to massive stars collapsing. The lack of understanding of these flows has impeded the success of many engineering applications, our comprehension of astrophysical and planetary formation processes, and the development of biomedical technologies. Controlling mixing between different fluids is central to achieving fusion energy, where mixing is undesirable, and supersonic combustion, where enhanced mixing is important. Iron, found throughout the universe and a necessary component for life, is dispersed through the mixing processes of a dying star. Non-invasive treatments using ultrasound to induce bubble collapse in tissue are being developed to destroy tumors or deliver genes to specific cells. Laboratory experiments of these flows are challenging because the initial conditions and material properties are difficult to control, modern diagnostics are unable to resolve the flow dynamics and conditions, and experiments of these flows are expensive. Numerical simulations can circumvent these difficulties and, therefore, have become a necessary component of any scientific challenge. Advances in the three fields of numerical methods, high performance computing, and multiphase flow modeling are presented: (i) novel numerical methods to capture accurately the multiphase nature of the problem; (ii) modern high performance computing paradigms to resolve the disparate time and length scales of the physical processes; (iii) new insights and models of the dynamics of multiphase flows, including mixing through hydrodynamic instabilities. These studies have direct applications to engineering and biomedical fields such as fuel injection problems, plasma deposition, cancer treatments, and turbomachinery.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133458/1/marchdf_1.pd