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The purpose of this paper is to address the problem of substitution of steel with fiber-reinforced polymer-matrix composite in military-vehicle hull-floors, and identifies and quantifies the associated main benefits and shortcomings.

The problem is investigated using a combined finite-element/discrete-particle computational analysis. Within this analysis, soil (in which a landmine is buried), gaseous detonation products and air are modeled as assemblies of discrete, interacting particles while the hull-floor is treated as a Lagrangian-type continuum structure. Considerable effort has been invested in deriving the discrete-material properties from the available experimental data. Special attention has been given to the derivation of the contact properties since these, in the cases involving discrete particles, contain a majority of the information pertaining to the constitutive response of the associated materials. The potential ramifications associated with the aforementioned material substitution are investigated under a large number of mine-detonation scenarios involving physically realistic ranges of the landmine mass, its depth of burial in the soil, and the soil-surface/floor-plate distances.

The results obtained clearly revealed both the benefits and the shortcomings associated with the examined material substitution, suggesting that they should be properly weighted in each specific case of hull-floor design.

To the authors’ knowledge, the present work is the first public-domain report of the findings concerning the complexity of steel substitution with composite-material in military-vehicle hull-floors.

The recently proposed concept solution for improving blast-survivability of the light tactical military vehicles is critically assessed using combined finite-element/discrete-particle computational methods and tools. The purpose of this paper is to propose a concept that involves the use of side-vent-channels attached to the V-shaped vehicle underbody. Since the solution does not connect the bottom and the roof or pass through the cabin of a light tactical vehicle, this solution is not expected to: first, reduce the available cabin space; second, interfere with the vehicle occupants’ ability to scout the surroundings; and third, compromise the vehicle’s off-road structural durability/reliability. Furthermore, the concept solution attempts to exploit ideas and principles of operation of the so-called “pulse detonation” rocket engines in order to create a downward thrust on the targeted vehicle.

To maximize the downward thrust effects and minimize the extent of vehicle upward movement, standard engineering-optimization methods and tools are employed for the design of side-vent-channels.

The results obtained confirmed the beneficial effects of the side-vent-channels in reducing the blast momentum, although the extent of these effects is relatively small (3-4 percent).

To the authors’ knowledge, the present work is the first public-domain report of the side-vent-channel blast-mitigation concept.

The purpose of this paper is to carry out a design-optimization analysis of the recently proposed side-vent-channel concept/solution for mitigation of the blast loads resulting from a shallow-buried mine detonated underneath a light tactical vehicle. Within this concept/solution, side-vent-channels attached to the V-shaped vehicle underbody are used to promote venting of ejected soil and supersonically expanding gaseous detonation products. This effect generates a downward thrust on the targeted vehicle, helping the vehicle survive mine-detonation-induced impulse loading.

The utility and the blast-mitigation capacity of this concept are investigated computationally using coupled finite-element/discrete-particle computational methods and tools. To maximize the blast-mitigation capacity of the solution (as defined by a tradeoff between the maximum reductions in the detonation-induced total momentum transferred to, and the acceleration acquired by, the target vehicle), the geometry and size of the side-vent-channel solution are optimized.

It is found that by optimizing the shape and size of the side-vent-channels, their ability to mitigate blast can be improved, but the overall blast-mitigation potential of the side-vent-channel solution remains relatively modest.

To the authors’ knowledge, the present work is the first attempt to combine the finite-element/discrete-particle analysis with optimization in order to refine the side-vent-channel blast-mitigation concept.

This paper aims to present a novel scheme for imposing periodic boundary conditions with downscaled macroscopic strain measures of gradient Cosserat continuum on the representative volume element (RVE) of discrete particle assembly in the frame of the second-order computational homogenization methods for granular materials.

The proposed scheme is based on the generalized Hill’s lemma of gradient Cosserat continuum and the incremental non-linear constitutive relation condensed to the peripheral particles of the RVE of discrete particle assembly. The generalized Hill’s lemma conducts to downscale the macroscopic strain or stress measures and to impose the periodic boundary conditions on the RVE boundary so that the Hill-Mandel energy equivalence condition is ensured. Because of the incremental non-linear constitutive relation condensed to the peripheral particles of the RVE, the periodic boundary displacement and traction constraints together with the downscaled macroscopic strains and strain gradients, micro-rotations and curvatures are imposed in the point-wise sense without the need of introducing the Lagrange multipliers for enforcing the periodic boundary displacement and traction constraints in a weak sense.

Numerical results demonstrate that the applicability and effectiveness of the proposed scheme in imposing the periodic boundary conditions on the RVE. The results of the RVE subjected to the periodic boundary conditions together with the displacement boundary conditions in the second-order computational homogenization for granular materials provide the desired estimations, which lie between the upper and the lower bounds provided by the displacement and the traction boundary conditions imposed on the RVE respectively.

Each grain in the particulate system under consideration is assumed to be rigid and circular.

The proposed scheme for imposing periodic boundary conditions on the RVE can be adopted solely for estimating the effective mechanical properties of granular materials and/or integrated into the frame of the second-order computational homogenization method with a nested finite element method-discrete element method solution procedure for granular materials. It will tend to provide, at least theoretically, more reasonable results for effective material properties and solutions of a macroscopic boundary value problem simulated by the computational homogenization method.

This paper presents a novel scheme for imposing periodic boundary conditions with downscaled macroscopic strain measures of gradient Cosserat continuum on the RVE of discrete particle assembly for granular materials without need of introducing Lagrange multipliers for enforcing periodic boundary conditions in a weak (integration) sense.

The purpose of this paper is computer-aided engineering analysis of the recently proposed side-vent-channel concept for mitigation of the blast-loads resulting from a shallow-buried mine detonated underneath a light tactical vehicle. The concept involves the use of side-vent-channels attached to the V-shaped vehicle underbody, and was motivated by the concepts and principles of operation of the so-called “pulse detonation” rocket engines. By proper shaping of the V-hull and side-vent-channels, venting of supersonically expanding gaseous detonation products is promoted in order to generate a downward thrust on the targeted vehicle.

The utility and the blast-mitigation capacity of this concept were examined in the prior work using computational methods and tools which suffered from some deficiencies related to the proper representation of the mine, soil, and vehicle materials, as well as air/gaseous detonation products. In the present work, an attempt is made to remove some of these deficiencies, and to carry out a bi-objective engineering-optimization analysis of the V-hull and side-vent-channel shape and size for maximum reduction of the momentum transferred to and the maximum acceleration acquired by the targeted vehicle.

Due to the conflicting nature of the two objectives, a set of the Pareto designs was identified, which provide the optimal levels of the trade-off between the two objectives.

To the authors’ knowledge, the present work is the first public-domain report of the side-vent-channel blast-mitigation concept.

In the high-speed trains (HSTs) production process, assembly sequence planning (ASP) problems is an extremely core issue. ASP problems influence the economic cost, amount of workers and the working time in the assembly process, seriously. In the design process of HSTs, the assembly sequence is usually given by experience, and the correctness of the assembly sequence is difficult to guarantee by experience and low effectiveness. The ASP based on improved discrete particle swarm optimization (IDPSO) algorithm was proposed to address these issues.

In view of the local convergence problem with basic DPSO in ASP, this paper presents an IDPSO, in which a chosen strategy of global optimal particle is introduced in, to solve the ASP problems in the assembly process of HSTs operation panel. The geometric feasibility, the assembly stability, and the number of assembly orientation changes of the assembly are chosen to be the optimization objective. Furthermore, the influences of the population size, the weight coefficient, and the learning factors to the stability and efficiency of IDPSO algorithm were discussed.

The results show that the IDPSO algorithm can obtain the global optimum efficiently, which is proved to be a more useful method for solving ASP problems than basic DPSO. The IDPSO approach could reduce the working time and economic cost of ASP problems in HSTs significantly.

The method may save the economic cost, reduce the amount of workers and save the time in the assembly process of HSTs. And also may change the method of ASP in design and manufacturing process, and make the production process in HSTs more efficiently.

A chosen strategy of global optimal particle is presented, which can overcome the local convergence problem with basic DPSO for solving ASP problems.

Safety improvement and pollutant reduction in many practical combustion systems and especially in aero-gas turbine engines require an adequate understanding of flame ignition and stabilization mechanisms. Improved software and hardware have opened up greater possibilities for translating basic knowledge and the results of experiments into better designs. The present study deals with the large eddy simulation (LES) of an ignition sequence in a conical shaped bluff-body stabilized burner involving a turbulent non-premixed flame. The purpose of this paper is to investigate the impact of spark location on ignition success. Particular attention is paid to the ease of handling of the numerical tool, the computational cost and the accuracy of the results.

The discrete particle ignition kernel (DPIK) model is used to capture the ignition kernel dynamics in its early stage of growth after the breakdown period. The ignition model is coupled with two combustion models based on the mixture fraction-progress variable formulation. An infinitely fast chemistry assumption is first done, and the turbulent fluctuations of the progress variable are captured with a bimodal probability density function (PDF) in the line of the Bray–Moss–Libby (BML) model. Thereafter, a finite rate chemistry assumption is considered through the flamelet-generated manifold (FGM) method. In these two assumptions, the classical beta-PDF is used to model the temporal fluctuations of the mixture fraction in the turbulent flow. To model subgrid scale stresses and residual scalars fluxes, the wall-adapting local eddy (WALE) and the eddy diffusivity models are, respectively, used under the low-Mach number assumption.

Numerical results of velocity and mixing fields, as well as the ignition sequences, are validated through a comparison with their experimental counterparts. It is found that by coupling the DPIK model with each of the two combustion models implemented in a LES-based solver, the ignition event is reasonably predicted with further improvements provided by the finite rate chemistry assumption. Finally, the spark locations most likely to lead to a complete ignition of the burner are found to be around the shear layer delimiting the central recirculation zone, owing to the presence of a mixture within flammability limits.

Some discrepancies are found in the radial profiles of the radial velocity and consequently in those of the mixture fraction, owing to a mismatch of the radial velocity at the inlet section of the computational domain. Also, unlike FGM methods, the BML model predicts the overall ignition earlier than suggested by the experiment; this may be related to the overestimation of the reaction rate, especially in the zones such as flame holder wakes which feature high strain rate due to fuel-air mixing.

This work is adding a contribution for ignition modeling, which is a crucial issue in various combustion systems and especially in aircraft engines. The exclusive use of a commercial computational fluid dynamics (CFD) code widely used by combustion system manufacturers allows a direct application of this simulation approach to other configurations while keeping computing costs at an affordable level.

This study provides a robust and simple way to address some ignition issues in various spark ignition-based engines, namely, the optimization of engines ignition with affordable computational costs. Based on the promising results obtained in the current work, it would be relevant to extend this simulation approach to spray combustion that is required for aircraft engines because of storage volume constraints. From this standpoint, the simulation approach formulated in the present work is useful to engineers interested in optimizing the engines ignition at the design stage.

A least‐squares finite element analysis of viscous fluid flow together with a trajectory integration technique for tracers is formulated and provides a mechanism for investigating mixing. Tracer integration is carried out using an improved Heun predictor‐corrector. Results from our supporting numerical studies on the CRAY and Connection Machine (CM) closely resemble the patterns of mixing observed in experiments. A “box‐counting” scheme and other measures to characterize the level of mixing are developed and investigated. This measure is utilized in numerical experiments to determine an optimal forcing frequency for mixing by periodic boundary motion in a rectangular enclosure. Some details concerning the numerical schemes and vector‐parallel implementation are also included.

This paper aims to present a design methodology to enable product design for ease of assembly. It is corroborated by means of a case study. The methodology is based on standard time data. This enables quick computation of assembly time as well as comparing different design options for ease of assembly.

Component design that is easy to assemble is likely to take less time and vice versa. Assembly time is a function of product design attributes such as geometric shape, weight, center of gravity, type of material, number of fasteners and types of fasteners. The methodology uses standard data to achieve its objective. Numeric scores are developed for each design feature based on the aforementioned design attributes. This enables not only computation of assembly time for a brand new product but also comparison of two or more alternative design configurations from the point of view of ease of assembly.

The value of the system is corroborated by means of case studies of actual product designs. It is demonstrated that changing any of the underlying design attributes (such as type of fastener used, number of fasteners used, material of the component and component shape) is likely to result in changing the amount of time taken to assemble the product. The scoring system facilitates the quick computation of assembly time

The amount of time to assemble a product before the product is ever designed is facilitated by this system. Assembly time is a direct function of product design attributes. Process time is calculated using standard data, specifically, the Methods Time Measurement (MTM) system. This is accomplished by converting design features into time measurement units (TMUs). Assembly cost can then be easily computed by using assembly time as the basis. The computation of assembly time and cost is important inasmuch as its role in influencing productivity. This is of obvious value not only to the designer but the company as a whole.

This study aims to deal with the large eddy simulation (LES) of an ignition sequence and the resulting steady combustion in a swirl-stabilized liquid-fueled combustor. Particular attention is paid to the ease of handling the numerical tool, the accuracy of the results and the reasonable computational cost involved. The primary aim of the study is to appraise the ability of the newly developed computational fluid dynamics (CFD) methodology to retrieve the spark-based flame kernel initiation, its propagation until the full ignition of the combustion chamber, the flame stabilization and the combustion processes governing the steady combustion regime.

The CFD model consists of an LES-based spray module coupled to a subgrid-scale ignition model to capture the flame kernel initiation and the early stage of the flame kernel growth, and a combustion model based on the mixture fraction-progress variable formulation in the line of the flamelet generated manifold (FGM) method to retrieve the subsequent flame propagation and combustion properties. The LES-spray module is based on an Eulerian-Lagrangian approach and includes a fully two-way coupling at each time step to account for the interactions between the liquid and the gaseous phases. The Wall-Adapting Local Eddy-viscosity (WALE) model is used for the flow field while the eddy diffusivity model is used for the scalar fluxes. The fuel is liquid kerosene, injected in the form of a polydisperse spray of droplets. The spray dynamics are tracked using the Lagrangian procedure, and the phase transition of droplets is calculated using a non-equilibrium evaporation model. The oxidation mechanism of the Jet A-1 surrogate is described through a reduced reaction mechanism derived from a detailed mechanism using a species sensitivity method.

By comparing the numerical results with a set of published data for a swirl-stabilized spray flame, the proposed CFD methodology is found capable of capturing the whole spark-based ignition sequence in a liquid-fueled combustion chamber and the main flame characteristics in the steady combustion regime with reasonable computing costs.

The proposed CFD methodology simulates the whole ignition sequence, namely, the flame kernel initiation, its propagation to fully ignite the combustion chamber, and the global flame stabilization. Due to the lack of experimental ignition data on this liquid-fueled configuration, the ability of the proposed CFD methodology to accurately predict ignition timing was not quantitatively assessed. It would, therefore, be interesting to apply this CFD methodology to other configurations that have experimental ignition data, to quantitatively assess its ability to predict the ignition timing and the flame characteristics during the ignition sequence. Such further investigations will not only provide further validation of the proposed methodology but also will potentially identify its shortfalls for better improvement.

This CFD methodology is developed by customizing a commercial CFD code widely used in the industry. It is, therefore, directly applicable to practical configurations, and provides not only a relatively straightforward approach to predict an ignition sequence in liquid-fueled combustion chambers but also a robust way to predict the flame characteristics in the steady combustion regime as significant improvements are noticed on the prediction of slow species.

The incorporation of the subgrid ignition model paired with a combustion model based on tabulated chemistry allows reducing computational costs involved in the simulation of the ignition phase. The incorporation of the FGM-based tabulated chemistry provides a drastic reduction of computing resources with reasonable accuracy. The CFD methodology is developed using the platform of a commercial CFD code widely used in the industry for relatively straightforward applicability.