On the coupling of CFD and CSD methodologies for modeling blast-structure interactions

This paper describes applications of a coupled Computational Fluid Dynamics (CFD) and Computational Structural Dynamics (CSD) methodology to the simulation of blast waves generated by bare explosive charges in a test facility with rigid and deformable walls. The coupled algorithm combines FEFLO98 (CFD) and MARS3D (CSD) via an embedded approach, where the CSD objects float through the CFD domain. This combination enables an easier and more accurate prediction of structural deformation, cracking and failure under blast loading. Several experiments were conducted to characterize blast load and structural response as a function of charge size, weapon ignition point (nose or tail) and orientation (horizontal or vertical). The numerical simulations helped in understanding the experimental results, some of which were not intuitively understood. Good agreement between the experimental results and the numerical predictions were demonstrated for pressure data, blast loading and the corresponding structural response. Keywords: blast-structure interaction, coupled CFD and CSD, blast wave evolution, structural response to blast loading

Coupling of discrete particle model with embedded mesh flow solver

This chapter describes a unique coupling between a discrete particle model and an embedded mesh flow solver, with the focus on solving blast loadings on reinforced concrete structures. The development of a discrete particle method (DPM) model is more complex and time-consuming than the mesh generation of a typical finite element method (FEM) analysis. The DPM process is a bootstrapping process, where the discrete particle solver is used in the development of the model. Two methods are commonly used for creating particle models: “fill and expand” (F+E), and the "depositional" methods. There have been numerous successes in coupling the finite element-based structural models to the finite-element fluid-flow solver (FEFLO). Two methods for solving the coupled fluid/structure interaction problem are: the body-conforming and the embedded grid methods. In the body-conforming method, the external faces of the structure are used to define the fluid domain. In the embedded method, the structure is placed inside a larger flow region with special treatment of the fluid elements close to the structural surfaces

Convergence study for the discrete particle method

The Discrete Particle Method (DPM) is a numerical technique in the class of the discrete element methods for the modeling of cementitious material in the pre- and post-failure regimes. Because the DPM is not based on continuum mechanics, the conventional convergence properties of Galerkin based methods, such as the finite element method, are not expected to apply. This chapter presents the results of a study to assess the convergence properties of the DPM for elastic problems. The DPM belongs to the general class of methods denoted as discrete element methods. The benchmark problem is based on the vibrations of a concrete beam free in space. Axial oscillations are used to adjust DPM model parameters, bending oscillations are used to test convergence characteristics. Results show that the DPM solution converges to the equivalent converged finite element solution

Utilisation of PID controller in explicit solver

In this paper the implementation of a proportional-integral-derivative (PID) controller is presented to drive the loading of structures within the framework of explicit solver. Such approach is especially necessary for the system in which the initiation of damage results in the snap-back, i.e., the initiation of damage causes a reduced system deformation (in certain points) with a reduced load. The PID controller is utilised within the framework of MARS software and several examples are provided to demonstrate the capability of current implementation

Recent development of a coupled CFD/CSD methodology using an embedded approach

A new algorithm for modeling the response of structures to severe airblast and fragment loading, including the modeling of large plastic deformations, structural failure and break-up, is described in this paper. The coupled Computational Fluid Dynamics (CFD) and Computational Structural Dynamics (CSD) methodologies required to describe these phenomena include the FEFL098 flow solver and DYNA3D structural solver. The original coupling between the two domains was based on the so-called “glued-mesh” approach, where the CFD and CSD interfaces match. Recent failure of this approach to model severe structural deformation, as well as crack propagation in steel and concrete, led us to the development and use of the “embedded-mesh” approach. Here, the CSD objects float through the CFD domain. While each approach has its own advantages, limitations and deficiencies, the embedded approach was proven to be superior for the problems modeled here. Critical applications of both approaches are described, including weapon detonation and fragmentation, airblast interaction with a reinforced concrete wall, and fragment/airblast interaction with a steel wall. The final applications model the interaction of an external airblast with a generic steel ship hull and a generic multi-chamber steel tower

Large-scale fluid-structure interaction simulations

Combining computational-science disciplines, such as in fluid-structure interaction simulations, introduces a number of problems. The authors offer a convenient and cost-effective approach for coupling computational fluid dynamics (CFD) and computational structural dynamics (CSD) codes without rewriting them. With the advancement of numerical techniques and the advent, first, of affordable 3D graphics workstations and scalable compute servers, and, more recently, PCs with sufficiently large memory and 3D graphics cards, public-domain and commercial software for each of the computational core disciplines has matured rapidly and received wide acceptance in the design and analysis process. Most of these packages are now at the threshold mesh generation pre-processor. This has prompted the development of the next logical step: multidisciplinary links of codes, a trend that is clearly documented by the growing number of publications and software releases in this area. In this paper, we concentrate on fluid-structure and fluid-structure-thermal interaction, in which changes of geometry due to fluid pressure, shear, and heat loads considerably affect the flowfield, changing die loads in turn. Problems in this category include: steady-state aerodynamics of wings under cruise conditions; aeroelasticity of vibrating - that is, elastic - structures such as flutter and buzz (aeroplanes and turbines), galloping (cables and bridges), and maneuvering and control (missiles and drones); weak and nonlinear structures, such as wetted membranes (parachutes and tents) and biological tissues (hearts and blood vessels); and strong and nonlinear structures, such as shock-structure interaction (command and control centers, military vehicles) and hypersonic flight vehicles

Review of the current practices in blast-resistant analysis and design of concrete structures

© The Author(s) 2016.In contemporary society, industrialization and rising of terrorism threats highlight the necessity and importance of structural protection against accidental and intentionally malicious blast loads. Consequences of these extreme loading events are known to be catastrophic, involving personnel injuries and fatalities, economic loss and immeasurable social disruption. These impacts are generated not only from direct explosion effects, that is, blast overpressure and primary or secondary fragments, but also from the indirect effects such as structural collapse. The latter one is known to be more critical leading to massive losses. It is therefore imperative to enlighten our structural engineers and policy regulators when designing modern structures. Towards a better protection of concrete structures, efforts have been devoted to understanding properties of construction materials and responses of structures subjected to blast loads. Reliable blast resistance design requires a comprehensive knowledge of blast loading characteristics, dynamic material properties and dynamic response predictions of structures. This article presents a state-of- The- Art review of the current blast-resistant design and analysis of concrete structures subjected to blast loads. The blast load estimation, design considerations and approaches, dynamic material properties at high strain rate, testing methods and numerical simulation tools and methods are considered and reviewed. Discussions on the accuracies and advantages of these current approaches and suggestions on possible improvements are also made