Fire structural modelling of fibre–polymer laminates protected with an intumescent coating

This paper presents a new modelling approach to analyse the fire structural response of fibre–polymer laminates protected with an intumescent surface coating. The model is designed to predict the temperature, decomposition, softening and failure of laminates with an intumescent coating in fire. The modelling involves a three-stage analytical approach: (i) thermal-chemical analysis of the intumescent coating, (ii) thermal-chemical analysis of heat transfer through the laminate substrate (beneath the intumescent coating), and (iii) thermal-mechanical analysis of the softening and failure of the laminate under tension or compression loading. Fire structural tests were performed on a woven glass/vinyl ester laminate coated with an organic intumescent material to validate the modelling approach. It is shown the model can predict with good accuracy the temperature distribution and swelling of the intumescent coating with increasing exposure time to a constant heat flux. The model can approximate the temperature, softening and failure of the laminate substrate.     

Thermal–mechanical modelling of laminates with fire protection coating

This paper presents a modelling approach to analyse the protection provided by passive and intumescent surface coatings on glass fibre reinforced laminate substrates exposed to fire. The modelling involves a multi-stage analytical approach: (i) thermal analysis of heat transfer from the fire through the surface insulation coating, which includes decomposition and expansion in the case of an intumescent material; (ii) thermal–chemical analysis of heat transfer through the fibreglass laminate substrate (beneath the fire protective coating), including decomposition of the polymer matrix; and (iii) thermal–mechanical analysis of softening and failure of the laminate under in-plane tension or compression loading. The modelling approach is validated using experimental temperature and strength data from fire structural tests performed on woven glass–vinyl ester laminates insulated with passive (ceramic fibre mat) or organic intumescent surface coatings.     

Stabilized space–time computation of wind-turbine rotor aerodynamics

We show how we use the Deforming-Spatial-Domain/Stabilized Space–Time (DSD/SST) formulation for accurate 3D computation of the aerodynamics of a wind-turbine rotor. As the test case, we use the NREL 5MW offshore baseline wind-turbine rotor. This class of computational problems are rather challenging, because they involve large Reynolds numbers and rotating turbulent flows, and computing the correct torque requires an accurate and meticulous numerical approach. We compute the problem with both the original version of the DSD/SST formulation and a recently introduced version with an advanced turbulence model. The DSD/SST formulation with the advanced turbulence model is a space–time version of the residual-based variational multiscale method. We compare our results to those reported recently, which were obtained with the residual-based variational multiscale Arbitrary Lagrangian–Eulerian method using NURBS for spatial discretization and which we take as the reference solution. While the original DSD/SST formulation yields torque values not far from the reference solution, the DSD/SST formulation with the variational multiscale turbulence model yields torque values very close to the reference solution.     

Dynamic observations of deformation in an ultrafine-grained Al–Mg alloy with bimodal grain structure

The tensile properties and deformation response of an ultrafine-grained (UFG) Al–Mg alloy with bimodal grain structure were investigated using a micro-straining unit and a strain mapping technique. Atomized Al 5083 powder was ball-milled in liquid N₂ to obtain a nanocrystalline (NC) structure, then blended with 50 wt.% unmilled coarse-grained (CG) powder, and consolidated to produce a bimodal grain structure. The blended powder was hot vacuum degassed to remove residual contaminants, consolidated by cold isostatic pressing (CIP), and then quasi-isostatic (QI) forged twice. The resultant material consisted of a UFG matrix and CG regions. The dynamic response during tensile deformation was observed using a light microscope, and the surface displacements were mapped and visualized using a digital image correlation (DIC) technique. The DIC results showed inhomogeneous strain between the UFG and CG regions after yielding, and the strain was localized primarily in the CG regions. Strain hardening in the CG regions accompanied the localization and was confirmed by variations in Vickers hardness.     

A tractable genotype–phenotype map modelling the self-assembly of protein quaternary structure

The mapping between biological genotypes and phenotypes is central to the study of biological evolution. Here, we introduce a rich, intuitive and biologically realistic genotype–phenotype (GP) map that serves as a model of self-assembling biological structures, such as protein complexes, and remains computationally and analytically tractable. Our GP map arises naturally from the self-assembly of polyomino structures on a two-dimensional lattice and exhibits a number of properties: redundancy (genotypes vastly outnumber phenotypes), phenotype bias (genotypic redundancy varies greatly between phenotypes), genotype component disconnectivity (phenotypes consist of disconnected mutational networks) and shape space covering (most phenotypes can be reached in a small number of mutations). We also show that the mutational robustness of phenotypes scales very roughly logarithmically with phenotype redundancy and is positively correlated with phenotypic evolvability. Although our GP map describes the assembly of disconnected objects, it shares many properties with other popular GP maps for connected units, such as models for RNA secondary structure or the hydrophobic-polar (HP) lattice model for protein tertiary structure. The remarkable fact that these important properties similarly emerge from such different models suggests the possibility that universal features underlie a much wider class of biologically realistic GP maps.     

A Newton multigrid framework for optimal control of fluid–structure interactions

Optimization and Engineering - In this paper we consider optimal control of nonlinear time-dependent fluid structure interactions. To determine a time-dependent control variable a BFGS algorithm is...     

Blast response simulation of an elastic structure: Evaluation of the fluid–structure interaction effect

Blast pressure wave interaction with an elastic structure is investigated using a numerical analysis approach, which considers fluid–structure interaction (FSI) within an Arbitrary Lagrange Euler (ALE) framework. Approximate numerical procedures for solving the Riemann problem associated with the shock are implemented within the Godunov finite volume scheme for the fluid domain. The structural displacement predicted by ignoring FSI is larger than the corresponding displacement considering FSI. The influence of the structural and blast pressure wave parameters on the importance of FSI is studied using an analysis of variables. Two non-dimensional parameters corresponding to the ratios of blast duration to the time period of the structure and the velocity of the structure to the particle velocity of the incident blast pressure wave are identified. It is shown that for a given blast pressure wave, the error in the maximum displacement predicted by ignoring FSI effect during structural motion is directly proportional to the ratio of the structure velocity to the particle velocity of the incident blast pressure wave. There is a continuous exchange of energy between the structure and air during the structural motion, which is significant when the structural velocity is significant compared to the particle velocity of incident blast pressure wave. FSI effect become insignificant when the ratio of velocities starts approaching zero.     

Space–time VMS computation of wind-turbine rotor and tower aerodynamics

We present the space–time variational multiscale (ST-VMS) computation of wind-turbine rotor and tower aerodynamics. The rotor geometry is that of the NREL 5MW offshore baseline wind turbine. We compute with a given wind speed and a specified rotor speed. The computation is challenging because of the large Reynolds numbers and rotating turbulent flows, and computing the correct torque requires an accurate and meticulous numerical approach. The presence of the tower increases the computational challenge because of the fast, rotational relative motion between the rotor and tower. The ST-VMS method is the residual-based VMS version of the Deforming-Spatial-Domain/Stabilized ST (DSD/SST) method, and is also called “DSD/SST-VMST” method (i.e., the version with the VMS turbulence model). In calculating the stabilization parameters embedded in the method, we are using a new element length definition for the diffusion-dominated limit. The DSD/SST method, which was introduced as a general-purpose moving-mesh method for computation of flows with moving interfaces, requires a mesh update method. Mesh update typically consists of moving the mesh for as long as possible and remeshing as needed. In the computations reported here, NURBS basis functions are used for the temporal representation of the rotor motion, enabling us to represent the circular paths associated with that motion exactly and specify a constant angular velocity corresponding to the invariant speeds along those paths. In addition, temporal NURBS basis functions are used in representation of the motion and deformation of the volume meshes computed and also in remeshing. We name this “ST/NURBS Mesh Update Method (STNMUM).” The STNMUM increases computational efficiency in terms of computer time and storage, and computational flexibility in terms of being able to change the time-step size of the computation. We use layers of thin elements near the blade surfaces, which undergo rigid-body motion with the rotor. We compare the results from computations with and without tower, and we also compare using NURBS and linear finite element basis functions in temporal representation of the mesh motion.     

Stress–phase-transformation interactions – basic principles,modelling, and calculation of internal stresses

Abstract

The two main effects of stress on phase transformation, kinetics modification and transformation plasticity, are reviewed for both diffusional and non-diffusional transformations. Results for these interactions during the pearlitic and martensitic transformation of steels under uniaxial tensile stress are analysed from a metallurgical point of view. These results are used to produce a model for a triaxial stress state, and in a finite element program for calculating internal stresses during quenching. Transformation plasticity is introduced in the calculation of internal stresses as an additional strain related to the stress state and to the progress of transformation, and the kinetics of martensitic transformation are also related to the stress state. The calculated results show that these phenomena have important consequences on the stress and plastic strain histories during quenching.

MST/9     

Fused deposition modelling with ABS–graphene nanocomposites

For the first time, graphene nanoplatelets (xGnP) were incorporated at 4 wt% in acrylonitrile–butadiene–styrene (ABS) filaments obtained by a solvent-free process consisting of melt compounding and extrusion. Nanocomposite filaments were then used to feed a fused deposition modelling (FDM) machine to obtain specimens with various build orientations. The elastic modulus and dynamic storage moduli of 3D printed parts along three different build orientations were increased by the presence of xGnP in the ABS matrix. At the same time, a decrease in both stress and strain at break was observed when xGnP is added to ABS. Moreover, a higher thermal stability was induced on 3D printed parts by xGnP, as indicated by a reduction in both coefficient of linear thermal expansion and creep compliance. A comparison between 3D printed and compression moulded parts highlighted the importance of the orientation effects induced by the fused deposition modelling process.     

Wall shear stress calculations in space–time finite element computation of arterial fluid–structure interactions

The stabilized space–time fluid–structure interaction (SSTFSI) technique was applied to arterial FSI problems soon after its development by the Team for Advanced Flow Simulation and Modeling. The SSTFSI technique is based on the Deforming-Spatial-Domain/Stabilized Space–Time (DSD/SST) formulation and is supplemented with a number of special techniques developed for arterial FSI. The special techniques developed in the recent past include a recipe for pre-FSI computations that improve the convergence of the FSI computations, using an estimated zero-pressure arterial geometry, Sequentially Coupled Arterial FSI technique, using layers of refined fluid mechanics mesh near the arterial walls, and a special mapping technique for specifying the velocity profile at inflow boundaries with non-circular shape. In this paper we introduce some additional special techniques, related to the projection of fluid–structure interface stresses, calculation of the wall shear stress (WSS), and calculation of the oscillatory shear index. In the test computations reported here, we focus on WSS calculations in FSI modeling of a patient-specific middle cerebral artery segment with aneurysm. Two different structural mechanics meshes and three different fluid mechanics meshes are tested to investigate the influence of mesh refinement on the WSS calculations.     

Numerical-performance studies for the stabilized space–time computation of wind-turbine rotor aerodynamics

We present our numerical-performance studies for 3D wind-turbine rotor aerodynamics computation with the deforming-spatial-domain/stabilized space–time (DSD/SST) formulation. The computation is challenging because of the large Reynolds numbers and rotating turbulent flows, and computing the correct torque requires an accurate and meticulous numerical approach. As the test case, we use the NREL 5MW offshore baseline wind-turbine rotor. We compute the problem with both the original version of the DSD/SST formulation and the version with an advanced turbulence model. The DSD/SST formulation with the turbulence model is a recently-introduced space–time version of the residual-based variational multiscale method. We include in our comparison as reference solution the results obtained with the residual-based variational multiscale Arbitrary Lagrangian–Eulerian method using NURBS for spatial discretization. We test different levels of mesh refinement and different definitions for the stabilization parameter embedded in the “least squares on incompressibility constraint” stabilization. We compare the torque values obtained.     

Fluid–structure interaction modeling of clusters of spacecraft parachutes with modified geometric porosity

To increase aerodynamic performance, the geometric porosity of a ringsail spacecraft parachute canopy is sometimes increased, beyond the “rings” and “sails” with hundreds of “ring gaps” and “sail slits.” This creates extra computational challenges for fluid–structure interaction (FSI) modeling of clusters of such parachutes, beyond those created by the lightness of the canopy structure, geometric complexities of hundreds of gaps and slits, and the contact between the parachutes of the cluster. In FSI computation of parachutes with such “modified geometric porosity,” the flow through the “windows” created by the removal of the panels and the wider gaps created by the removal of the sails cannot be accurately modeled with the Homogenized Modeling of Geometric Porosity (HMGP), which was introduced to deal with the hundreds of gaps and slits. The flow needs to be actually resolved. All these computational challenges need to be addressed simultaneously in FSI modeling of clusters of spacecraft parachutes with modified geometric porosity. The core numerical technology is the Stabilized Space–Time FSI (SSTFSI) technique, and the contact between the parachutes is handled with the Surface-Edge-Node Contact Tracking (SENCT) technique. In the computations reported here, in addition to the SSTFSI and SENCT techniques and HMGP, we use the special techniques we have developed for removing the numerical spinning component of the parachute motion and for restoring the mesh integrity without a remesh. We present results for 2- and 3-parachute clusters with two different payload models.     

Second phase structure effect to the failure of an Al–Si casting

An Al–Si casting (blower pump) failed during pressure test. The material of the casting was aluminum–silicon alloy (BS-LM 9), in solution treated and aged condition. During pressure test the casting failed around 130 bar, while it was designed to sustain a pressure of 160 bar.The failed body was examined with the help of stereo microscope, optical microscope and scanning electron microscope. Fracture started from a sharp edge of a race present at the interior of the body. A granular dull gray fracture surface was observed during unaided visual examination. Fractographic studies showed that the mode of the fracture was transgranular and the material failed in brittle mode. Optical microscopic examination showed a dendritic structure having a continuous network of the secondary phase. A sample taken from the fracture region unveiled the crack propagation along the secondary phase network. It was recommend to use modification process during melting practice to avoid the stress raisers.     

Alfvén wave amplification as a result of nonlinear interaction with a magnetoacoustic wave in an acoustically active conducting medium

It is shown that Alfvén waves propagating parallel and antiparallel to a magnetic field can be generated and amplified in an acoustically active heat-releasing ionized medium. The amplification is due to parametric energy pumping from the unstable magnetoacoustic waves to the Alfvén waves.     

Propagation of detonation wave in hydrogen–air mixture in channels with sound-absorbing surfaces

The possibility of using sound-absorbing surfaces for attenuating the intensity of detonation waves propagating in hydrogen–air mixtures has been experimentally studied in a cylindrical detonation tube open at one end, with an explosive initiated by spark discharge at the closed end. Sound-absorbing elements were made of an acoustic-grade foamed rubber with density of 0.035 g/cm³ containing open pores with an average diameter of 0.5 mm. The degree of attenuation of the detonation wave front velocity was determined as dependent on the volume fraction of hydrogen in the gas mixture.     

Nonreflective absorption of an electromagnetic wave in its incidence on the two-layer system magnetic–metal at an angle

The conditions of nonreflective absorption of an electromagnetic wave in its incidence, at an angle, on a plane layer of absorbing magnetic applied to a metal substrate are found. The dependences of these conditions on the angle of incidence of the wave, the thickness of the layer, and the magnetic properties of the coating material are investigated. The possibility of separating a prescribed polarization component of the incident radiation with the use of the phenomenon of nonreflective wave absorption in the magnetic–metal system is considered.     

LLM and X-FEM based interface modeling of fluid–thin structure interactions on a non-interface-fitted mesh

This paper presents a non-interface-fitted mesh method for fluid–thin structure interactions. The key components are the Lagrangian Lagrange-multiplier (LLM) method and the extended finite element method (X-FEM). The LLM couples fluid and thin structure through the Lagrangian nodes of the structure element. The X-FEM gives flow discontinuity to the fluid elements intersected by the structure element. The combination method is verified through applications to flow with a domain-partitioning boundary and flow-induced flapping of a flexible filament. We discuss how the discontinuities at the interface enhance the simulation results, how the lack of the discontinuities affects the results, and identify some effects of these discontinuity enrichments.     

“Heated layer” effect in interaction of an interplanetary shock wave with a geomagnetic tail

Using the numerical solution as the base the conditions of propagating a prallel MGD shock wave in the presence of a heated layer are analyzed, a new raking regime of interaction not observed with no magnetic field is revealed. A flow steadiness criterion is obtained, and conditions for the onset of a similarity precursor are estimated.Institute of Geosphere Dynamics of RAN, Moscow. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 5, pp. 548–553, May, 1993.