Predicting toxic gas concentrations resulting from enclosure fires using local equivalence ratio concept linked to fire field models

A practical CFD method is presented in this study to predict the generation of toxic gases in enclosure fires. The model makes use of local combustion conditions to determine the yield of carbon monoxide, carbon dioxide, hydrocarbon, soot and oxygen. The local conditions used in the determination of these species are the local equivalence ratio (LER) and the local temperature. The heat released from combustion is calculated using the volumetric heat source model or the eddy dissipation model (EDM). The model is then used to simulate a range of reduced-scale and full-scale fire experiments. The model predictions for most of the predicted species are then shown to be in good agreement with the test results

Liquid metal induction heating modelling for cold crucible applications

The time dependent numerical model of cold crucible melting is based on the coupled electromagnetic, temperature and turbulent velocity field calculation accounting for the magnetically confined liquid metal shape continuous change. The model is applied to investigate the process energy efficiency dependence on the critical choice of AC power supply frequency and an optional addition of a DC magnetic field. Test cases of the metal load up to 50 kg are considered. The behaviour of the numerical model at high AC frequencies is instructively validated by the use of the electromagnetic analytical solution for a sphere and temperature measurements in a commercial size cold crucible furnace

The impact of the passenger response time distribution on ship evacuation performance

The International Maritime Organisation (IMO) has adopted the use of computer simulation to assist in the assessment of the assembly time for passenger ships. A key parameter required for this analysis and specified as part of the IMO guidelines is the passenger response time distribution. It is demonstrated in this paper that the IMO specified response time distribution assumes an unrealistic mathematical form. This unrealistic mathematical form can lead to serious congestion issues being overlooked in the evacuation analysis and lead to incorrect conclusions concerning the suitability of vessel design. In light of these results, it is vital that IMO undertake research to generate passenger response time data suitable for use in evacuation analysis of passenger ships. Until this type of data becomes readily available, it is strongly recommended that rather than continuing to use the artificial and unrepresentative form of the response time distribution, IMO should adopt plausible and more realistic response time data derived from land based applications. © 2005: Royal Institution of Naval Architects.

"System in package technology" - design for manufacture challenges

Purpose – To present key challenges associated with the evolution of system-in-package technologies and present technical work in reliability modeling and embedded test that contributes to these challenges. Design/methodology/approach – Key challenges have been identified from the electronics and integrated MEMS industrial sectors. Solutions to optimising the reliability of a typical assembly process and reducing the cost of production test have been studied through simulation and modelling studies based on technology data released by NXP and in collaboration with EDA tool vendors Coventor and Flomerics. Findings – Characterised models that deliver special and material dependent reliability data that can be used to optimize robustness of SiP assemblies together with results that indicate relative contributions of various structural variables. An initial analytical model for solder ball reliability and a solution for embedding a low cost test for a capacitive RF-MEMS switch identified as an SiP component presenting a key test challenge. Research limitations/implications – Results will contribute to the further development of NXP wafer level system-in-package technology. Limitations are that feedback on the implementation of recommendations and the physical characterisation of the embedded test solution. Originality/value – Both the methodology and associated studies on the structural reliability of an industrial SiP technology are unique. The analytical model for solder ball life is new as is the embedded test solution for the RF-MEMS switch.

A study of modelling approaches for rail vehicle collision behaviour

A rigid wall model has been used widely in the numerical simulation of rail vehicle impacts. Finite element impact modelling of rail vehicles is generally based on a half-width and full-length or half-length structure, depending on the symmetry. The structure and components of rail vehicles are normally designed to cope with proof loading to ensure adequate ride performance. In this paper, the authors present a study of a rail vehicle with driving cab focused on improving the modelling approach and exploring the intrinsic structural weaknesses to enhance its crashworthiness. The underpinning research used finite element analysis and compared the behaviour of the rail vehicle in different impact scenarios. It was found that the simulation of a rigid wall impact can mask structural weaknesses; that even a completely symmetrical impact may lead to an asymmetrical result; that downward bending is an intrinsic weakness of conventional rail vehicles and that a rigid part of the vehicle structure, such as the body bolster, may cause uncoordinated deformation and shear fracture between the vehicle sections. These findings have significance for impact simulation, the full-scale testing of rail vehicles and rail vehicle design in general.

Analysis of crush behaviours of a rail cab car and structural modifications for improved crashworthiness

In this paper, the authors present a crashworthiness assessment and suggestions for modification of a conventionally designed rail vehicle with a driving cab (cab car). The analytical approach, based on numerical analysis, consisted of two stages. Firstly, the crashworthiness of the cab car was assessed by simulating a collision between the cab car and a rigid wall. Then, after analysing structural weaknesses, the design of the cab car was modified and simulated again in the same scenario. It was found that downward bending is an intrinsic weakness in conventional rail vehicles and that jackknifing is a main form of failures in conventional rail vehicle components. The cab car, as modified by the authors, overcomes the original weaknesses and shows the desired progressive collapse behaviour in simulation. The conclusions have general relevance for other studies but more importantly, point to the need for a rethink of some aspects of rail vehicle design.

An introduction to China's rail transport Part 1: History, present and future of China's railways

In this paper an introduction is given to the history, current situation and future plans of China's railway industry. The history of China's railway is divided into four development phases: the phase in Imperial China, the phase in the Republic of China and the phases before and after the economic rejuvenation of the People's Republic of China. An introduction to the current situation and future plans includes the major projects under construction and development trends of China's railways. The environment of China's railways is also presented. This is the first of two papers on the railway scene in China.

An introduction to China's rail transport Part 2: Urban rail transit systems, highway transport and the reform of China's railways

In this paper, an introduction is provided to some of the components of China's transport system. The authors include the urban rail transit systems, the highway transport systems and its competition for China's railways and the reform of China's railway industry. This is the second of two papers on the situation of rail transport in China.

High electric current density-induced interfacial reactions in micro ball grid array (μBGA) solder joints

The effect of a high electric current density on the interfacial reactions of micro ball grid array solder joints was studied at room temperature and at 150 °C. Four types of phenomena were reported. Along with electromigration-induced interfacial intermetallic compound (IMC) formation, dissolution at the Cu under bump metallization (UBM)/bond pad was also noticed. With a detailed investigation, it was found that the narrow and thin metallization at the component side produced “Joule heating” due to its higher resistance, which in turn was responsible for the rapid dissolution of the Cu UBM/bond pad near to the Cu trace. During an “electromigration test” of a solder joint, the heat generation due to Joule heating and the heat dissipation from the package should be considered carefully. When the heat dissipation fails to compete with the Joule heating, the solder joint melts and molten solder accelerates the interfacial reactions in the solder joint. The presence of a liquid phase was demonstrated from microstructural evidence of solder joints after different current stressing (ranging from 0.3 to 2 A) as well as an in situ observation. Electromigration-induced liquid state diffusion of Cu was found to be responsible for the higher growth rate of the IMC on the anode side.

Effect of 0.5 wt % Cu addition in Sn–3.5% Ag solder on the dissolution rate of Cu metallization

The dissolution of thin film under-bump-metallization (UBM) by molten solder has been one of the most serious processing problems in electronic packaging technology. Due to a higher melting temperature and a greater Sn content, a molten lead-free solder such as eutectic SnAg has a faster dissolution rate of thin film UBM than the eutectic SnPb. The work presented in this paper focuses on the role of 0.5 wt % Cu in the base Sn–3.5%Ag solder to reduce the dissolution of the Cu bond pad in ball grid array applications. We found that after 0.5 wt % Cu addition, the rate of dissolution of Cu in the molten Sn–3.5%Ag solder slows down dramatically. Systematic experimental work was carried out to understand the dissolution behavior of Cu by the molten Sn–3.5%Ag and Sn–3.5%Ag–0.5%Cu solders at 230–250 °C, for different time periods ranging from 1 to 10 min. From the curves of consumed Cu thickness, it was concluded that 0.5 wt % Cu addition actually reduces the concentration gradient at the Cu metallization/molten solder interface which reduces the driving force of dissolution. During the dissolution, excess Cu was found to precipitate out due to heterogeneous nucleation and growth of Cu6Sn5 at the solder melt/oxide interface. In turn, more Cu can be dissolved again. This process continues with time and leads to more dissolution of Cu from the bond pad than the amount expected from the solubility limit, but it occurs at a slower rate for the molten Sn–3.5%Ag–0.5%Cu solder. © 2003 American Institute of Physics.

Reliability study of the electroless Ni–P layer against solder alloy

Copper (Cu) has been widely used in the under bump metallurgy of chip and substrate metallization for chip packaging. However, due to the rapid formation of Cu–Sn intermetallic compound (IMC) at the tin-based solder/Cu interface during solder reaction, the reliability of this type of solder joint is a serious concern. In this work, electroless nickel–phosphorous (Ni–P) layer was deposited on the Cu pad of the flexible substrate as a diffusion barrier between Cu and the solder materials. The deposition was carried out in a commercial acidic sodium hypophosphite bath at 85 °C for different pH values. It was found that for the same deposition time period, higher pH bath composition (mild acidic) yields thicker Ni–P layer with lower phosphorous content. Solder balls having composition 62%Sn–36%Pb–2%Ag were reflowed at 240 °C for 1 to 180 min on three types of electroless Ni–P layers deposited at the pH value of 4, 4.8 and 6, respectively. Thermal stability of the electroless Ni–P barrier layer against the Sn–36%Pb–2%Ag solder reflowed for different time periods was examined by scanning electron microscopy equipped with energy dispersed X-ray. Solder ball shear test was performed in order to find out the relationship between the mechanical strength of solder joints and the characteristics of the electroless Ni–P layer deposited. The layer deposited in the pH 4 acidic bath showed the weak barrier against reflow soldering whereas layer deposited in pH 6 acidic bath showed better barrier against reflow soldering. Mechanical strength of the joints were deteriorated quickly in the layer deposited at pH 4 acidic bath, which was found to be thin and has a high phosphorous content. From the cross-sectional studies and fracture surface analyses, it was found that the appearance of the dark crystalline phosphorous-rich Ni layer weakened the interface and hence lower solder ball shear strength. Ni–Sn IMC formed at the interfaces was found to be more stable at the low phosphorous content (∼14 at.%) layer. Electroless Ni–P deposited at mild acidic bath resulting phosphorous content of around 14 at.% is suggested as the best barrier layer for Sn–36%Pb–2%Ag solder.

Pseudo-spectral solutions for fluid flow and heat transfer in electro-metallurgical applications

The pseudo-spectral solution method offers a flexible and fast alternative to the more usual finite element and volume methods, particularly when the long-time transient behaviour of a system is of interest. The exact solution is obtained at grid collocation points leading to superior accuracy on modest grids. Furthermore, the grid can be freely adapted in time and space to particular flow conditions or geometric variations, especially useful where strongly coupled, time-dependent, multi-physics solutions are investigated. Examples include metallurgical applications involving the interaction of electromagnetic fields and conducting liquids with a free surface. The electromagnetic field determines the instantaneous liquid volume shape, which then affects the electromagnetic field. A general methodology of the pseudo-spectral approach is presented, with several instructive example applications: the aluminium electrolysis MHD problem, induction melting in a cold crucible and the dynamics of AC/DC magnetically levitated droplets. Finally, comparisons with available analytical solutions and to experimental measurements are discussed.

Integrating personnel movement simulation into preliminary ship design

Traditionally, when designing a ship the driving issues are seen to be powering, stability, strength and seakeeping. Issues related to ship operations and evolutions are investigated later in the design process, within the constraint of a fixed layout. This can result in operational inefficiencies and limitations, excessive crew numbers and potentially hazardous situations. University College London and the University of Greenwich are in the final year of a three year EPSRC funded research project to integrate the simulation of personnel movement into early stage ship design. This allows the assessment of onboard operations while the design is still amenable to change. The project brings together the University of Greenwich developed maritimeEXODUS personnel movement simulation software and the SURFCON implementation of the Design Building Block approach to early stage ship design, which originated with the UCL Ship Design Research team. Central to the success of this project is the definition of a suitable series of Naval Combatant Human Performance Metrics which can be used to assess the performance of the design in different operational scenarios. The paper outlines the progress made on deriving the human performance metric from human factors criteria measured in simulations and their incorporation into a Behavioural Matrix for analysis. It describes the production of a series of SURFCON ship designs based on the RN Type 22 Batch 3 frigate, and their analysis using the PARAMARINE and maritimeEXODUS software. Conclusions to date will be presented on the integration of personnel movement simulation into the preliminary ship design process.