Dynamics of trains and train-like articulated systems travelling in confined fluid—Part 2: Wave propagation and flow-excited vibration

Wave propagation and response of a train of flexibly interconnected rigid cars travelling in a confined cylindrical “tunnel” subjected to fluid dynamic forces are studied theoretically. For the wave propagation analysis, an infinite-length train represented by a lumped-parameter Timoshenko-beam (LTB) model is employed. The train response is simulated using a travelling sinusoidal aerodynamic force that mimics the features obtained during running experiments on real trains. In addition, the response of the system is examined when the velocity of the force approaches the minimum phase velocity of a travelling wave in the train. The principal aim of this study is to investigate the effect of aerodynamic forces on the dynamics of a high-speed train running in a tunnel, or more generally of a train-like system travelling in a coaxial cylindrical tube. The results of this study show that: (a) when aerodynamic forces act on a train, the frequency bands of the dispersion relation of wave propagation shift, and thus no classical normal modes (standing wave solutions) exist in the system; (b) the wavelength of the travelling sinusoidal force controls the phase differences between cars in the train; and (c) the response of the train can be considerably amplified when the speed of the travelling force coincides with the minimum phase velocity of travelling waves in the train.     

Study on steerability of articulated tracked vehicles — Part 1. Theoretical and experimental analysis

This paper presents theoretical and experimental analysis of steering performance of articulated tracked vehicles on level ground. A mathematical model for predicting the steerability of articulated units has been developed and computerized for numerical application. The accuracy of the analog has been verified by scale model tests.From the results of the simulation and scale model tests it was found that steerability was significantly improved and required sprocket torques for steering and track slippage were considerably decreased in articulated tracked vehicles when compared with a single and coupled tracked vehicles.     

Modelling techniques for fluid–solid coupling dynamics of bundle tubes vibrating and colliding in fluids

Nonlinear vibrations that occur in such bundle structures caused collisions between tubes and cross flows of the surrounding fluid. This paper presents modeling techniques for simulating the FSI dynamics of bundle tubes vibrating and colliding in fluids. A typical configuration of a three-dimensional tube bundles submerged in fluid of a cylindrical container is studied. Coupling conditions of displacement, velocity and forces are considered on the fluid-structure coupling interfaces. Contacts boundary between tubes and topological domain changes of the fluid are also considered on the fluid-structure coupling interface. Modeling techniques and algorithm are then established for flow-induced vibrations of the tubes, and collisions between tubes in fluids. The examples are presented to demonstrate the effectiveness of the proposed techniques. It has confirmed that our code produces the correct physics of the FSI problem, and capable of revealing the complex nonlinear mechanism with solid-solid contacts together with fluid-solid interactions.     

Heat transfer and fluid dynamics of air–water two-phase flow in micro-channels

Heat transfer, pressure drop, and void fraction were simultaneously measured for upward heated air–water non-boiling two-phase flow in 0.51 mm ID tube to investigate thermo–hydro dynamic characteristics of two-phase flow in micro-channels. At low liquid superficial velocity j_l frictional pressure drop agreed with Mishima–Hibiki’s correlation, whereas agreed with Chisholm–Laird’s correlation at relatively high j_l. Void fraction was lower than the homogeneous model and conventional empirical correlations. To interpret the decrease of void fraction with decrease of tube diameter, a relation among the void fraction, pressure gradient and tube diameter was derived. Heat transfer coefficient fairly agreed with the data for 1.03 and 2.01 mm ID tubes when j_l was relatively high. But it became lower than that for larger diameter tubes when j_l was low. Analogy between heat transfer and frictional pressure drop was proved to hold roughly for the two-phase flow in micro-channel. But satisfactory relation was not obtained under the condition of low liquid superficial velocity.     

Pore-Scale Imaging and Modelling of Reactive Flow in Evolving Porous Media: Tracking the Dynamics of the Fluid–Rock Interface

Transport in Porous Media - Fluid–mineral and fluid–rock interfaces are key parameters controlling the reactivity and fate of fluids in reservoir rocks and aquifers. The interface...     

Biaxial crushing of honeycombs: —Part 1: Experiments

The in-plane compression and crushing of honeycombs is known to be closely related to the crushing behavior of the broader class of space filling cellular solids. Previously, the authors conducted an extensive study of uniaxial crushing of a polycarbonate honeycomb with circular cells. In this paper the same honeycomb is crushed biaxially. The crushing was performed in a custom testing facility between rigid platens which can be moved independently in two orthogonal directions. The facility allows testing at various biaxiality ratios and volume reductions as high as 95%. The facility was used to conduct several series of biaxial crushing experiments on nearly square honeycomb specimens (18×21 cells) . In each experiment we recorded the true stress–displacement responses in the x- and y-directions as well as full field views of the deformation using a video camera. Biaxial crushing is quite complex and the prevalent mechanisms of collapse depend on the biaxiality ratio (γ) . As is the case in uniaxial crushing, the onset of collapse involves localized instabilities, however, the extent of localized deformation varies with γ. The energy absorption capacity of the material depends on γ. The highest energy is required when the specimen is crushed at the same rates in the two directions.     

Comparison between computational fluid dynamics,fluid–structure interaction and computational structural dynamics predictions of flow-induced wall mechanics in an anatomically realistic cerebral aneurysm model

Haemodynamically induced stress plays an important role in the progression and rupture of cerebral aneurysms. The current work describes computational fluid dynamics (CFD), fluid–structure interaction (FSI) and computational structural dynamics (CSD) simulations in an anatomically realistic model of a carotid artery with two saccular cerebral aneurysms in the ophthalmic region. The model was obtained from three-dimensional (3D) rotational angiographic imaging data. CFD and FSI were studied under a physiologically representative waveform of inflow. The arterial wall was assumed elastic or hyperelastic, as a 3D solid or as a shell depending on the type of modelling used. The flow was assumed to be laminar, non-Newtonian and incompressible. The CFD, FSI and CSD models were solved with the finite elements package ADINA. Predictions of velocity field and wall shear stress (WSS) on the aneurysms made using CFD and FSI were compared. The CSD model of the aneurysms using complete geometry was compared with isolated aneurysm models. Additionally, the effects of hypertensive pressure on CSD aneurysm models are also reported. The vortex structure, WSS, effective stress, strain and displacement of the aneurysm walls showed differences, depending on the type of modelling used.     

A Feature-Based Stochastic Permeability of Shale: Part 1—Validation and Two-Phase Permeability in a Utica Shale Sample

Transport in Porous Media - Estimate of permeability plays a crucial role in flow-based studies of fractured tight-rocks. It is well known that most of the flow through tight-rocks (e.g., shales)...     

On the inelastic behavior of solids — Part 1: Twinning

Recently, Wineman and Rajagopal [1990] “On a Constitutive Theory for Materials Undergoing Microstructural Changes,” Arch. Mech., 42, 53 and Rajagopal and Wineman [1992] “A Constitutive Equation for Nonlinear Solids which Undergo Deformation Induced Microstructural Changes,” Int. J. Plasticity, 8, 385, developed a theory that was particularly well suited to describing the inelastic behavior of polymeric materials. Here, we draw upon their ideas and generalize them to include a much larger class of materials. The versatility and efficacy of the theory are illustrated by studying the problem of twinning within the context of the theory. We find that the predictions of the theory are remarkably close — both qualitatively and quantitatively — with the experimental results of Madhava et al. [1972] “Discontinuous Twinning during Essentially Elastic Compression of Steel at 4.2K,” Phil. Mag., 25(2), 519 and Madhava and Armstrong [1974] “A Constitutive Relation for Deformation Twinning at High Strain Rates,” in Rohde, R.W., Butcher, B.M., Holland, J.R., and Karnes, C.H., eds., Metallurgical Effects at High Strain Rates. Plenum, New York, 1974.     

On the detachment of step-tapered doublers : Part 1—foundations

One-dimensional edge debonding of layerwise step-tapered patches from both flat and cylindrical structures is examined. The problems are approach from a unified point of view, as propagating boundary problems in the calculus of variations, with the models for both flat and curved structures being formulated simultaneously. The effects of a contact zone adjacent to the bonded region are incorporated as is the phenomenon of edge-point contact. The formulation results in a selfconsistent representation of the various intact and debonded segments of the composite structure comprised of a multilayer patch and a base structure. It concurrently yields the conditions which establish the locations of the propagating boundary of the bonded (intact) region, and the propagating boundary of the contact zone. The former condition yields the selfconsistent and physically interpretable expressions for the corresponding energy release rates for debonding. The conditions governing edge-point contact are likewise established. Three types of loading conditions are considered : (i) in-plane/circumferential tension, (ii) three-point transverse loading, and (iii) applied transverse (internal ) pressure. It is shown analytically, within the context of the mathematical models employed for both flat and curved structures, that of the loading types considered the third admits a contact zone for certain common conditions of the supports. Results of numerical simulations, based on analytical solutions, pertaining to the test configurations of flat structures subjected to applied in-plane tension and three-point transverse loading are presented for various taper angles and compared.     

Travelling waves in the transport of reactive solutes through porous media: Adsorption and binary ion exchange — Part 1

We develop a model for solute transport in porous media, which takes into account equilibrium and nonequilibrium multiple-site adsorption. Binary ion exchange is included. Adsorption rate formulations and their isotherms are reviewed and their mathematical properties investigated. This forms the basis of the study of travelling-wave solutions in the second part of the paper.This work was supported by the EC project Filtration and Nonlinear Diffusion Processes (Contract No. SC1-OO19-C(TT)).     

Mathematical and numerical modeling of the non-associated plasticity of soils—Part 1: The boundary value problem

The soil is characterized by the influence of the hydrostatic stress, which leads to a yield surface with a shape of a pyramid for Mohr–Coulomb criteria and a shape of a cone for Drucker–Prager one. These materials are also characterized by a non-associated plasticity where the plastic yielding rule does not follow the normality rule. The usual mechanical models use two independent functions to describe this particular collapse. Unfortunately, this manner broke the model formulation. The purpose of this work is to present a consistent formulation of the non-associated plasticity of soil. The frame of the mathematical analysis is the concept of the implicit standard material. The cornerstone of this new idea is the construction of a single function called the bipotential playing in the same time the roles of the yield surface and the plastic potential. The bipotential concept is then intended to involve the constitutive law, cover the normality rule even for the non-associated soil and the proof of the solution existence. The formulation was initially performed for the case of a regular point out of the cone apex and in present, it is extended to the irregular point located at the apex. The paper presents firstly the implicit standard material method. Then, the methodology to build a full model for the boundary value problem is detailed. Particular expressions and relations are sufficiently explained and discussed. Attention is made to the evolution problem and the variational principles related to the elastic–plastic behavior.     

Wake structures and vortex-induced vibrations of a long flexible cylinder—Part 1: Dynamic response

Results showing the dynamic response of a vertical long flexible cylinder vibrating at low mode numbers are presented in this paper. The model had an external diameter of 16 mm and a total length of 1.5 m giving an aspect ratio of about 94, with Reynolds numbers between 1200 and 12 000. Only the lower 40% of its length was exposed to the water current in the flume and applied top tensions varied from 15 to 110 N giving fundamental natural frequencies in the range from 3.0 to 7.1 Hz. Reduced velocities based on the fundamental natural frequency up to 16 were reached. The mass ratio was 1.8 and the combined mass–damping parameter about 0.05. Cross-flow and in-line amplitudes, x–y trajectories and phase synchronisation, dominant frequencies and modal amplitudes are reported. Cross-flow amplitudes up to 0.7 diameters and in-line amplitudes over 0.2 were observed with dominant frequencies given by a Strouhal number of 0.16.     

Hidden components of 3D-DIC: Triangulation and post-processing—Part 3

Experimental Techniques -     

On the methodologies of stress analysis of composite structures: Part 1: State of the art—phenomenological and physical methodologies

The rapidly increasing technological importance of composite materials and composite structures is leading to the development of new, more advanced models of their actual response to mechanical and thermal loads. This in turn results in the development of new experimental and analytical methods for determination of the mechanical and thermal responses of such structures and materials to various loads. In this respect the reliability and the predictive power of various methods and techniques of stress analysis become very important since all the analytical, experimental and numerical methods used for the determination, prediction and optimization of the actual mechanical responses of composite structures and materials are based on the concepts of strain and stress. Because of the inherently three-dimensional stress and strain states in composite materials and structures and the wide use of viscoelastic polymers as the matrix and some reinforcing fiber materials, a more rigorous type of modelling than had been common in the past is needed of all the involved physical phenomena which influence the strain and stress states at the local and global levels. Also, a more rigorous analysis of practical consequences of the physical and mathematical simplifications is required to assure reliability and accuracy of various methods of stress analysis. The influence of the above-mentioned factors on the reliability and applicability of analytical and experimental procedures is illustrated by examples of actual material responses.Part 2 of this paper presents theories and techniques of three new methods of strain/stress analysis which have been developed on the basis of comprehensive physical models of involved phenomena: the isodyne, strain gradient and thermoelastic effect methods. Presented examples illustrate the efficacy of these methods.     

Investigation of bubble breakup and coalescence in a packed-bed reactor – Part 1: A comparative study of bubble breakup and coalescence models

In a packed-bed reactor a comparative study of bubble breakup and coalescence models has been investigated to study bubble size distributions as a function of the axial location. The bubble size distributions are obtained by solving population balance equations that describe gas–liquid interactions. Each combination of bubble breakup and coalescence models is examined under two inlet flow conditions: (1) predominant bubble breakup flow and (2) predominant bubble coalescence flow. The resulting bubble size distributions, breakup and coalescence rates estimated by individual models, are qualitatively compared to each other. The change of bubble size distributions along the axial direction is also described with medians. The medians resulting from CFD analyses are compared against the experimental data. Since the predictions estimated by CFD analyses with the existing bubble breakup and coalescence models do not agree with the experimental data, a new bubble breakup and coalescence model that takes account of the geometry effects is required to describe gas–liquid interactions in a packed-bed reactor.