The role of evacuation and fire modelling in the development of safer air travel

Computer based mathematical models describing the aircraft evacuation process and aircraft fire have a role to play in the design and development of safer aircraft, in the implementaion of safer and more rigorous certification criteria and in post mortuum accident investigation. As the cost and risk involved in performing large-scale fire/evacuation experiments for the next generation 'Very Large Aircraft' (VLA) are expected to be high, the development and use of these modelling tools may become essential if these aircraft are to prove a viable reality. By describing the present capabililties and limitations of the EXODUS evacuation model and associated fire models, this paper will examine the future development and data requirements of these models.

Computer modelling of human behaviour in aircraft fire accidents

The mathematical simulation of the evacuation process has a wide and largely untapped scope of application within the aircraft industry. The function of the mathematical model is to provide insight into complex behaviour by allowing designers, legislators, and investigators to ask ‘what if’ questions. Such a model, EXODUS, is currently under development, and this paper describes its evolution and potential applications. EXODUS is an egress model designed to simulate the evacuation of large numbers of individuals from an enclosure, such as an aircraft. The model tracks the trajectory of each individual as they make their way out of the enclosure or are overcome by fire hazards, such as heat and toxic gases. The software is expert system-based, the progressive motion and behaviour of each individual being determined by a set of heuristics or rules. EXODUS comprises five core interacting components: (i) the Movement Submodel — controls the physical movement of individual passengers from their current position to the most suitable neighbouring location; (ii) the Behaviour Submodel — determines an individual's response to the current prevailing situation; (iii) the Passenger Submodel — describes an individual as a collection of 22 defining attributes and variables; (iv) the Hazard Submodel — controls the atmospheric and physical environment; and (v) the Toxicity Submodel — determines the effects on an individual exposed to the fire products, heat, and narcotic gases through the Fractional Effective Dose calculations. These components are briefly described and their capabilities and limitations are demonstrated through comparison with experimental data and several hypothetical evacuation scenarios.

Thermal, mechanical and optical modelling of VCSEL packaging

Hybrid OECB (Opto-Electrical Circuit Boards) are expected to make a significant impact in the telecomm switches arena within the next five years, creating optical backplanes with high speed point-to-point optical interconnects. OECB's incorporate short range optical interconnects, and are based on VCSEL (Vertical Cavity Surface Emitting Diode) and PD (Photo Diode) pairs, connected to each other via embedded waveguides in the OECB. The VCSEL device is flip-chip assembled onto an organic substrate with embedded optical waveguides. The performance of the VCSEL device is governed by the thermal, mechanical and optical characteristics of this assembly. During operation, the VCSEL device will heat up and the thermal change together with the CTE mismatch in the materials, will result in potential misalignment between the VCSEL apertures and the waveguide openings in the substrate. Any degree of misalignment will affect the optical performance of the package. This paper will present results from a highly coupled modelling analysis involving thermal, mechanical and optical models. The paper will also present results from an optimisation analysis based on Design of Experiments (DOE).

Computer modelling of the reliability of flip chips with metal column bumping

Recently, research has been carried out to test a novel bumping method which omits the under bump metallurgy forming process by bonding copper columns directly onto the Al pads of the silicon dies. This bumping method could be adopted to simplify the flip chip manufacturing process, increase the productivity and achieve a higher I/O count. This paper describes an investigation of the solder joint reliability of flip-chips based on this new bumping process. Computer modelling methods are used to predict the shape of solder joints and response of flip chips to thermal cyclic loading. The accumulated plastic strain energy at the comer solder joints is used as the damage indicator. Models with a range of design parameters have been compared for their reliability. The parameters that have been investigated are the copper column height, radius and solder volume. The ranking of the relative importance of these parameters is given. For most of the results presented in the paper, the solder material has been assumed to be the lead-free 96.5Sn3.5Ag alloy but some results for 60Sn40Pb solder joints have also been presented.

[Review] M. Feistauer, J. Felcman, I. Straskbraba, Mathematical and Computational Methods for Compressible Flow, Oxford Science Publication, Oxford, ISBN 0198505884, 2004 (535pp.)

The growth of computer power allows the solution of complex problems related to compressible flow, which is an important class of problems in modern day CFD. Over the last 15 years or so, many review works on CFD have been published. This book concerns both mathematical and numerical methods for compressible flow. In particular, it provides a clear cut introduction as well as in depth treatment of modern numerical methods in CFD. This book is organised in two parts. The first part consists of Chapters 1 and 2, and is mainly devoted to theoretical discussions and results. Chapter 1 concerns fundamental physical concepts and theoretical results in gas dynamics. Chapter 2 describes the basic mathematical theory of compressible flow using the inviscid Euler equations and the viscous Navier–Stokes equations. Existence and uniqueness results are also included. The second part consists of modern numerical methods for the Euler and Navier–Stokes equations. Chapter 3 is devoted entirely to the finite volume method for the numerical solution of the Euler equations and covers fundamental concepts such as order of numerical schemes, stability and high-order schemes. The finite volume method is illustrated for 1-D as well as multidimensional Euler equations. Chapter 4 covers the theory of the finite element method and its application to compressible flow. A section is devoted to the combined finite volume–finite element method, and its background theory is also included. Throughout the book numerous examples have been included to demonstrate the numerical methods. The book provides a good insight into the numerical schemes, theoretical analysis, and validation of test problems. It is a very useful reference for applied mathematicians, numerical analysts, and practice engineers. It is also an important reference for postgraduate researchers in the field of scientific computing and CFD.

Computer modelling analysis of the globtop's effects on aluminium wirebond reliability

In power electronics modules, heavy aluminium wires, i.e. wire diameters greater than 100 microns, are bonded to the active semiconductor devices and conductor metallization to form electric circuits of the power electronic module. Due to the high currents that may flow through these wires, a single connection usually contains several wires and thus, a large number of wires are used in a power electronics module. Under normal operation or test condition, a significant amount of stresses and strains induced in the wire and bonding interfaces, resulting in failure over time. In this paper, computer modelling techniques are used to analyse the effect of globtop design on the reliability of aluminium wirebonds under cyclic thermal-mechanical loading conditions. The results will show the sensitivity of the reliability of the wirebonds to the changes in the geometry and the material properties of the wirebond globtop.

Modelling the fluid dynamics and coupled phenomena in arc weld pools

A 3D model of melt pool created by a moving arc type heat sources has been developed. The model solves the equations of turbulent fluid flow, heat transfer and electromagnetic field to demonstrate the flow behaviour phase-change in the pool. The coupled effects of buoyancy, capillary (Marangoni) and electromagnetic (Lorentz) forces are included within an unstructured finite volume mesh environment. The movement of the welding arc along the workpiece is accomplished via a moving co-ordinator system. Additionally a method enabling movement of the weld pool surface by fluid convection is presented whereby the mesh in the liquid region is allowed to move through a free surface. The surface grid lines move to restore equilibrium at the end of each computational time step and interior grid points then adjust following the solution of a Laplace equation.

Using mathematical models to predict the development of aircraft cabin fires

Computer based mathematical models describing aircraft fire have a role to play in the design and development of safer aircraft, in the implementation of safer and more rigorous certification criteria and in post mortuum accident investigation. As the cost involved in performing large-scale fire experiments for the next generation 'Ultra High Capacity Aircraft' (UHCA) are expected to be prohibitively high, the development and use of these modelling tools may become essential if these aircraft are to prove a safe and viable reality. By describing the present capabilities and limitations of aircraft fire models, this paper will examine the future development of these models in the areas of large scale applications through parallel computing, combustion modelling and extinguishment modelling.

Modelling induction melting energy savings

Electromagnetic processing of liquid metals involves dynamic change of the fluid volume interfacing with a melting solid material, gas or vacuum, and possibly a different liquid. Electromagnetic field and the associated force field are strongly coupled to the free surface dynamics and the heat-mass transfer. We present practical modelling examples of the flow and heat transfer using an accurate pseudo-spectral code and the k-omega turbulence model suitable for complex and transitional flows with free surfaces. The 'cold crucible' melting is modelled dynamically including the melting front gradual propagation and the magnetically confined free surrounding interface. Intermittent contact with the water-cooled segmented wall and the radiation heat losses are parts of the complex problem.

Principles and Practice of Fire Modelling: A Collection of Lecture Notes for a Short Course

Once the preserve of university academics and research laboratories with high-powered and expensive computers, the power of sophisticated mathematical fire models has now arrived on the desk top of the fire safety engineer. It is a revolution made possible by parallel advances in PC technology and fire modelling software. But while the tools have proliferated, there has not been a corresponding transfer of knowledge and understanding of the discipline from expert to general user. It is a serious shortfall of which the lack of suitable engineering courses dealing with the subject is symptomatic, if not the cause. The computational vehicles to run the models and an understanding of fire dynamics are not enough to exploit these sophisticated tools. Too often, they become 'black boxes' producing magic answers in exciting three-dimensional colour graphics and client-satisfying 'virtual reality' imagery. As well as a fundamental understanding of the physics and chemistry of fire, the fire safety engineer must have at least a rudimentary understanding of the theoretical basis supporting fire models to appreciate their limitations and capabilities. The five day short course, "Principles and Practice of Fire Modelling" run by the University of Greenwich attempt to bridge the divide between the expert and the general user, providing them with the expertise they need to understand the results of mathematical fire modelling. The course and associated text book, "Mathematical Modelling of Fire Phenomena" are aimed at students and professionals with a wide and varied background, they offer a friendly guide through the unfamiliar terrain of mathematical modelling. These concepts and techniques are introduced and demonstrated in seminars. Those attending also gain experience in using the methods during "hands-on" tutorial and workshop sessions. On completion of this short course, those participating should: - be familiar with the concept of zone and field modelling; - be familiar with zone and field model assumptions; - have an understanding of the capabilities and limitations of modelling software packages for zone and field modelling; - be able to select and use the most appropriate mathematical software and demonstrate their use in compartment fire applications; and - be able to interpret model predictions. The result is that the fire safety engineer is empowered to realise the full value of mathematical models to help in the prediction of fire development, and to determine the consequences of fire under a variety of conditions. This in turn enables him or her to design and implement safety measures which can potentially control, or at the very least reduce the impact of fire.

Multiphysics modeling and its application to the casting process

A modeling strategy is presented to solve the governing equations of fluid flow, temperature (with solidification), and stress in an integrated manner. These equations are discretized using finite volume methods on unstructured grids, which provide the capability to represent complex domains. Both the cell-centered and vertex-based forms of the finite volume discretization procedure are explained, and the overall integrated solution procedure using these techniques with suitable solvers is detailed. Two industrial processes, based on the casting of metals, are used to demonstrate the capabilities of the resultant modeling framework. This manufacturing process requires a high degree of coupling between the governing physical equations to accurately predict potential defects. Comparisons between model predictions and experimental observations are given.

Surface physics at the nano-scale via scanning probe microscopy and molecular dynamics simulations

Probe-based scanning microscopes, such as the STM and the AFM, are used to obtain the topographical and electronic structure maps of material surfaces, and to modify their morphologies on nanoscopic scales. They have generated new areas of research in condensed matter physics and materials science. We will review some examples from the fields of experimental nano-mechanics, nano-electronics and nano-magnetism. These now form the basis of the emerging field of Nano-technology. A parallel development has been brought about in the field of Computational Nano-science, using quantum-mechanical techniques and computer-based numerical modelling, such as the Molecular Dynamics (MD) simulation method. We will report on the simulation of nucleation and growth of nano-phase films on supporting substrates. Furthermore, a theoretical modelling of the formation of STM images of metallic clusters on metallic substrates will also be discussed within the non-equilibrium Keldysh Green function method to study the effects of coherent tunnelling through different atomic orbitals in a tip-sample geometry.

Modelling the performance of lead-Free solder interconnects for copper bumped flip-chip devices

Traditionally, before flip chips can be assembled the dies have to be attached with solder bumps. This process involves the deposition of metal layers on the Al pads on the dies and this is called the under bump metallurgy (UBM). In an alternative process, however, Copper (Cu) columns can be used to replace solder bumps and the UBM process may be omitted altogether. After the bumping process, the bumped dies can be assembled on to the printed circuit board (PCB) by using either solder or conductive adhesives. In this work, the reliability issues of flip chips with Cu column bumped dies have been studied. The flip chip lifetime associated with the solder fatigue failure has been modeled for a range of geometric parameters. The relative importance of these parameters is given and solder volume has been identified as the most important design parameter for long-term reliability. Another important problem that has been studied in this work is the dissolution of protection metals on the pad and Cu column in the reflow process. For small solder joints the amount of Cu which dissolves into the molten solder after the protection layers have worn out may significantly affect solder joint properties.

Predicting the relationship between reliability and geometric parameters of cu column bumped flip-chips

Cu column bumping is a novel flip chip packaging technique that allows Cu columns to be bonded directly with the dies. It has eliminated the under-bump-metallurgy (UBM) fonnation step of the traditional flip chip manufacturing process. This bumping technique has the potential benefits of simplifying the flip chip manufacturing process, increasing productivity and the UO counts. In this paper, a study of reliability of Cu column bumped flip chips will be presented. Computer modelling methods have been used to predict the shape of solder joints and the response of flip chips to cyclic thermal-mechanical loading. The accumulated plastic strain energy at the corner solder joints has been used as an indicator of the solder joint reliability. Models with a wide range of design parameters have been compared for their reliability. The design parameters that have been investigated are the copper column height and radius, PCB pad radius, solder volume and Cu column wetting height. The relative importance ranking of these parameters has been obtained. The Lead-free solder material 96.5Sn3.5Ag has been used in this modelling work.

Modelling the wave soldering process

Compuational fluid dynamics (CFD) is used to help understand the gas flow characteristics in the wave soldering process. CFD has the ability to calculate (1) heal transfer, (2) fluid dynamics, and (3) oxygen concentration throughout the wave soldering machine. Understanding the impact of fluid dynamics on oxygen concentration is important as excessive oxygen at the solder bath can lead to high dross contents and hence poor solder joint quality on the printed circuit board. This paper describes the CFD modelling approach and illustrates its capability for a machine which has nitrogen injectors near the solder bath. Different magnitiutes of nitrogen flow rates are investigated and it is demonstrated how these effect the oxygen concentration at the bath surface.