bluuebunny/crossref_metadata_2025 huggingface dataset:
An IPINP model for the assessment of filter allocation and replacement strategies in a hydraulic contamination control system under uncertainty
Authors: Nie S L , Li Y P , Shi X Y , Huang G H , Hu B
Published: December 2008

An interval-parameter integer non-linear programming (IPINP) model is developed for the assessment of filter allocation and replacement strategies in a hydraulic contamination control system under uncertainty. The IPINP can handle uncertainties expressed as interval values that exist in the left- and right-hand sides of constraints as well as in the objective function. A piecewise linearization approach is proposed to solve the IPINP model, which has advantages in identifying global optimum and is associated with low computational efforts for an uncertain non-linear programme. The developed method has been applied to a case of planning filter allocation and replacement strategies under uncertainty for a fluid power system (FPS) with a single circuit. Three different contaminant ingression/generation rates are examined based on several filter-installation scenarios. The combination of low-costing suction and return filters exhibits excellent contaminant resistibility along with the optimum replacement periods of filter elements and operation costs under the low and medium contaminant ingression/generation level. The solutions can be used for generating a range of decision alternatives and thus help the decision-makers to identify desired filter allocation and replacement plan with a minimized operation cost and a minimized system-failure risk for FPS.
Convective cooling of tandem heated squares in a channel
Authors: Farhadi M , Sedighi K , Madani M M
Published: December 2008

This article elaborates on the numerical simulation of forced convective incompressi-ble flow in a horizontal plane channel and heat transfer over two isothermal tandem square cylinders. Finite-volume method was applied to discretize the momentum and energy equations. This study details the effects of S/ H (gap between two squares), Reynolds number, and blockage ratio on the characteristics of flow field and heat transfer. The blockage ratios and Reynolds numbers were chosen between 12.5 to 50 per cent and 100≤ Re≤300, respectively. Results are presented in the form of time-averaged streamlines, instantaneous contours of temperature and vorticity, and some characteristics of fluid flow and heat transfer such as time-averaged of the local and total Nusselt number, drag coefficient, and Strouhal number. The present results show that the gap spacing between squares at high blockage ratios does not have an obvious effect on heat transfer. On the other hand, this parameter plays a main role on the drag coefficient at a high value ( S/ H=4), which is because of the formation of the vortex cores in gap spacing and downstream of the second square. The heat transfer rate of the second square increases with the increase of S/ H. Increasing the blockage ratio has a negative effect on convective heat transfer of the second square. With the vortex shedding in the gap spacing, the drag coefficient and the Nusselt number both increase in the second square in comparison to the first square.
Robust optimization based on a polynomial expansion of chaos constructed with integration point rules
Authors: Wei D L , Cui Z S , Chen J
Published: December 2008

Robust optimization is a probabilistic approach to engineering design under uncertainty. The main idea is to select designs insensitive to changes in given parameters. Robust optimization using numerical simulations for black-box problems has received increasing interest. However, when the simulation programmes are computationally expensive, robust optimization is difficult to implement due to the intensive computational demand of uncertainty propagation. Based on polynomial chaos expansion (PCE), an efficient robust optimization method is presented. The PCE is constructed with points of monomial cubature rules (MCRs) to approximate the original model. As the number of points of MCRs is small and all of the points are sampled, the robust optimization procedure is computationally efficient and stable. Two engineering design problems are employed to demonstrate the availability of the proposed method.
Structural damage detection using combined finite-element and model Lamb wave propagation parameters
Authors: Ratnam C , Ben B S , Ben B A
Published: December 2008

This article presents a combined finite-element and model Lamb wave propagation parameters method for structural health monitoring. Modal analysis allows identifying the mode conversions induced by the defects. A simulation combining a planar, lossless finite-element analysis with Lamb wave propagation parameter is proposed. This analysis is performed on two aluminium bars in both undamaged and damaged states, where the two damaged states are: (a) one having a circular hole and (b) the other having a cut partway through the bar, perpendicular to the long axis of the bar. The Lamb wave propagation parameters are calibrated by using the ultrasonic pulse generator test set-up. The natural frequencies for the theoretical, finite element and experimental results are compared, and close agreement is found between the frequencies obtained experimentally and computationally.
A preliminary numerical study of a swirling jet behind a circular disc
Authors: Toh H T , Huang R F , Chern M J
Published: December 2008

The three-dimensional flow fields behind a circular disc produced by an annular swirling jet alone and by an annular swirling jet with a central jet issuing from the disc centre are studied by solving the three-dimensional incompressible Navier—Stokes equations numerically using the solution algorithm of Hirt et al. ( Los Alamos Scientific Lab. Rept. LA-5852 (1970)). The swirl number and the Reynolds number based on the disc diameter and the volumetric mean axial velocity of the annular swirling jet are S=0.194 and Re=656, respectively. The convective and diffusive terms in the governing equations are discretized using the second-order central difference scheme. The resulting discretized equations are advanced in time using the second-order Runge—Kutta scheme. The simulation shows that the flow field behind the circular disc exhibit periodic oscillating behaviour, with the second case having a higher frequency due to the presence of the central jet. The mechanism responsible for this oscillating behaviour is identified and discussed. An analysis of the mean velocity fields in the mid-plane shows the existence of a stagnation point on the axis of symmetry in the first case and two saddle points off the axis of symmetry in the second case.
A posteriori error estimate improvement in mesh adaptation for computer fluid dynamics applications
Authors: Remaki L , Habashi W G
Published: December 2008

The objective of this work is to study, in a first part, the impact of mesh adaptation on computational estimates of lift and drag coefficients. The convergence of these quantities with successive adaptation is demonstrated by comparing with experimental results. As a second part, optimization of relevant adaptation parameters to accelerate the convergence is investigated. A combination of adaptation variables is proposed to better capture some physical features that are poorly represented when a single variable is used. On the other hand, a new error metric is derived from both Hessian and gradient that are used separately in the framework of mesh adaptation in general. The impact of the proposed improvements is demonstrated through test cases.
Decomposition of forced turbulent jet flows
Authors: Erdil A , Ertunc H M , Yilmaz T
Published: December 2008

In many cases, turbulence is superimposed on an unsteady organized motion of a mean flow. Indeed, large ranges of scales are involved in these flows, and it is important to investigate their characteristics and interactions. Thus, the time—frequency decomposition provided by the wavelet analysis appears an efficient tool that complements the classical approach and the Fourier transform. In this study, the wavelet decomposition (WD) method has been applied to the forced turbulent jet flows. The obtained results of the WD are compared with those of the other most common techniques such as proper orthogonal decomposition and phase averaging. In addition, the spectrogram of the signals has been presented for a visual representation of the frequency contents. It is shown that the WD is a successful tool to decompose the forced turbulent jet flows into its components for various axial distances, Re numbers, and forcing frequencies.
A study of laser welding modes with varying beam energy levels
Authors: Buvanashekaran G , Shanmugam Siva N , Sankaranarayanasamy K , Sabarikanth R
Published: December 2008

The energy of a laser beam is generally calculated based on the laser power and its processing speed. In this work, the laser welding modes such as conduction, conduction—penetration, and keyhole welding of thickness 1.6, 2, and 2.5 mm AISI304 stainless steel sheets, respectively, are studied at different beam energy levels. A series of bead-on-plate trials are conducted using a 500 W continuous wave Nd:YAG laser source to study the beam—material interaction and the influence of laser power and welding speed on the formation of weld pool. In addition to the experimental study, a three-dimensional finite-element model is developed to analyse the transient heat flow and to predict the formation of the weld pool. The correlation among the parameters including laser power, welding speed, beam incident angle, and the characteristic geometry of weld pool are established. Temperature-dependent thermal properties of AISI304 stainless steel, the effect of latent heat of fusion, and the convective and radiative aspects of boundary conditions are considered in the model. The heat input to the developed model is assumed to be a three-dimensional conical Gaussian heat source. Finite-element simulations are carried out by using finite-element code, SYSWELD, and FORTRAN subroutines available within the code are used to obtain the numerical results. The result of the numerical analysis provides the shape of the molten pool with different beam energy levels, which is then compared with the results obtained through experimentation. It is observed that the results obtained from finite-element simulation and the experimental trials are in good agreement.
Crack tip stress intensity factors for a crack emanating from a semi-infinite notch with application to the avoidance of fatigue in complete contacts
Authors: Philipps A G , Karuppanan S , Banerjee N , Hills D A
Published: December 2008

Crack tip stress intensity factors are found for the problem of a short crack adjacent to the apex of a notch, and lying perpendicular to one of the notch faces. Loading is represented by the two Williams eigensolutions, the ratio between which provides a reference length scale and permits a comprehensive display of the solution. The results are applied to the problem of a crack starting from the edge of a notionally adhered complete contact, and conditions for the avoidance of crack development are found.
Computational parametric analysis of rotating surface flow
Authors: Kaptan Y , Ecder A , Atalik K
Published: December 2008

The flow due to rotating surfaces in a cylindrical enclosure is commonly used in many applications such as rheometry, electronic cooling, and turbomachinery, and has drawn scientists’ attention for many years. The main objective of this study is to solve the problem with a robust and efficient code. It is achieved by using the ‘Portable, Extensible Toolkit for Scientific computation’ (PETSc), which is a computational tool for the parallel solution of scientific problems. By keeping the Newton's method as the non-linear solver, different linear solvers, preconditioning techniques, and numbers of processors are tested for the performance. In addition to computational parameters such as the performance of the linear solver, performance of the preconditioner, parallel performance, and grid dependence, the effects of some physical parameters such as the Reynolds number, aspect ratio, and altering of the rotating surface are investigated. The results indicate that the core of the circulation moves towards the stationary boundaries and the boundary layers become thinner with the increasing Reynolds number. Furthermore, decreasing the aspect ratio makes diffusion harder and lowers the maximum velocities. Some of the results are compared with data in the literature.
On the non-linear phenomena due to source loading in rotor—motor systems
Authors: Samantaray A K
Published: December 2008

The effects of source loading of the drive motor due to rotating material damping induced self-excited asynchronous whirl and unbalance induced synchronous whirl on the overall steady-state behaviour of a rotor—motor system are studied in this article. The formulation is based on finding the existence of a plausible conservative state of the system where the orbital energies are conserved. This method is very simple and, at the same time, it is physically meaningful. The analysis reveals some interesting non-linear phenomena in non-ideal rotor—motor systems. A bond graph model is used to represent the system dynamics. The analytically obtained whirl characteristics are validated through numerical studies.
Design and analysis of a novel six-degrees-of-freedom precision positioning table
Authors: Fung R-F , Fan C-T , Lin W-C
Published: December 2008

The purpose of this study is to design and analyse a novel six-degrees-of-freedom (DOF) precision positioning table, which is assembled by two different kinds of three-DOF precision positioning tables: a plane-type three-DOF ( X, Y, θ z) precision positioning table and a cylinder-type three-DOF (θ x, θ y, Z) one, and each table is driven by three piezoelectric actuators (PAs). In this paper, the Bouc—Wen model is employed to describe the hysteretic phenomenon of the PAs. The transfer matrices with cross-coupling terms between the output displacements and input voltages are derived from the dynamic equations in the steady-state conditions. In order to obtain the best transfer matrix, experimental measurements of the whole six-DOF table are compared with those from the two individual three-DOF precision positioning tables. Finally, the transfer matrices with better performance for the two three-DOF tables and the novel six-DOF table are obtained.
Forced convection and nucleate boiling on a small flat heater in a rectangular duct: Experiments with two working fluids, a 50–50 ethylene glycol—water mixture, and water
Authors: Lee H S , O'Neill A T
Published: December 2008

The heat transfer characteristics for two working fluids, a 50–50 ethylene glycol—water mixture and water, on a small flat heater in a rectangular flow channel were examined for operating conditions in typical internal combustion engines. A particular effort was made to present robust heat transfer data without the constraints of the cross-section of the channel in the regions of forced convection and nucleate boiling, including the onsets of nucleate boiling. The effects of velocity, pressure, and subcooling were discussed using both boiling curves and visual observations.
Parallel hybrid electric system energy optimization control with automated mechanical transmission
Authors: Wang F , Mao X-J , Zhuo B , Zhong H , Ma Z-L
Published: December 2008

Energy optimization control for a parallel hybrid electric system with automated mechanical transmission (AMT) can be divided into two steps in this paper. First, the AMT shift is not optimized and the optimal torque distribution strategy is proposed to minimize the powertrain equivalent specific fuel consumption by considering the power conversion efficiency, which distributes the vehicle single torque request into separate torque requests for the internal combustion engine (ICE) and the electric motor (EM). The distribution results are expressed in a table format and can be found from the simple process of looking up the table using the vehicle torque request, the ICE speed, and the battery state of charge (SOC). Then, the AMT shift control is suggested to maximize the powertrain system efficiency and optimizes the speed as the basis for the above-mentioned torque distribution, in which the ICE efficiency, the EM efficiency, and the battery efficiency are all explicitly taken into account. The AMT optimal shift control law and the EM optimal torque are essentially look-up-table-based control according to the ICE power, the EM power, the vehicle velocity, and the battery SOC after offline calculations. Simulation results reveal that potential fuel economy improvement has been achieved by using the energy optimization control.
Theoretical analysis of the natural frequency of a geared system under the influence of a variable mesh stiffness
Authors: Han Q-K , Wang J-J , Li Q-H
Published: December 2008

Owing to the change in the number of contact tooth pairs, the mesh stiffness is periodically time varying, which leads to additional time-variant coefficients in the corresponding governing equations of a geared dynamic system. The natural frequency of such a system differs distinctly from that of a time-invariant system. However, it has not gained sufficient attention in geared dynamic analysis, and the natural frequency of a geared system is usually assumed to be the average frequency obtained using the time-average mesh stiffness. Whether it is reasonable to obtain the natural frequency of a geared system in this way should be analysed seriously. Thus, the natural frequency of parametric vibration for a spur-gear-pair system will be researched using the Floquet theory in this paper. The influences of the periodically time-varying mesh stiffness parameters (including the mesh frequency and the contact ratio) on the natural frequency will be discussed in detail. Contrasts between the natural frequency and the average frequency for the system in the stable and unstable regions will be processed and the scope of application for taking the average frequency as a substitution for the natural frequency of a geared system will then be presented.
Modelling and optimizing two- and four-stroke hybrid pneumatic engines
Authors: Dönitz C , Vasile I , Onder C H , Guzzella L
Published: December 2008

Hybrid pneumatic engines, which are designed to follow the downsizing and supercharging paradigm, offer a fuel-saving potential that is almost equal to that of hybrid electric powertrains while inducing much lower additional mass and cost penalties. This paper presents a systematic optimization of the operation of such an engine system. Both two-stroke and four-stroke modes are analysed. The optimized valve and throttle actuation laws for all modes and operating areas lead to generic maps that are independent of the engine size. So far, the pneumatic hybridization of internal combustion engines was thought to require two-stroke operation. This paper presents a novel hybrid pneumatic engine configuration that entails fixed camshafts for both intake and exhaust valves while utilizing variable valve actuation for one charge valve per cylinder only. This configuration is operated entirely in four-stroke modes. Such a configuration requires a careful optimization of its operating strategy to achieve its fuel economy potential. Compared with a full two-stroke operation, only small efficiency losses result from using four-stroke modes with these new operating strategies. Initial measurement results with such an engine system are presented in this paper to confirm the validity of the principles of operation.
Influence of a shock absorber model on vehicle dynamic simulation
Authors: Calvo J A , López-Boada B , Román J L San , Gauchía A
Published: December 2008

The dynamic simulation of mechanical systems is an essential tool in vehicle design. This work analyses the influence of a shock absorber model on a vehicle's dynamic behaviour by means of a simulation-based model. The real behaviour of a European medium-range car shock absorber has been obtained by means of a test rig. From the damper's real behaviour, three mathematical models were generated, increasing the complexity. An existing full vehicle simulation application (CarSim™) was used for this particular study. The vehicle's behaviour was analysed for typical driving manoeuvres taking into account lateral, vertical, and longitudinal forces and was compared with the results obtained with the different shock absorber models developed. As a result of this paper, it was demonstrated that, in order to obtain results with an acceptable level of accuracy, it is not necessary to rely on extremely complex shock absorber models.
Performance testing of gasketed flange joint under combined loading
Authors: Abid M
Published: December 2008

This technical note presents joint strength and sealing capability of a gasketed flange joint using extensive experimental studies with different load combinations. Actual joint load capacity is determined under both the design and proof test pressure with maximum additional external loading (axial and bending) that can be applied for safe joint performance. In addition, application of combined load is also discussed in the light of equivalent pressure approach.
Optimal gain-scheduled flight control system design using a new fuzzy clustering algorithm
Authors: Roshanian J , Hashemi S V , Mehrabian A R
Published: December 2008

This article presents an analytical framework for the design of autopilots using fuzzy systems. A new fuzzy clustering method is presented in this article, which is used to model a non-linear flight vehicle using a set of linear models. It is shown that the proposed fuzzy clustering technique produces lower estimation errors compared with other fuzzy clustering techniques; it means that the modelling error using the technique introduced is lower than other clustering methods. The membership functions and rule sets, which are obtained by fuzzy clustering, are then applied to a set of linear time-invariant optimal state-feedback controllers, obtained for each rule, towards extraction of the global non-linear controller matching closely with the dynamic properties and changes in the plant. The stability of the fuzzy model and the fuzzy system is established by the Lyapunov-based linear matrix inequality analysis. Simulation studies are reported to demonstrate the merits of the fuzzy set-based modelling and control approach in handling the demanding non-linear modelling and control task.
Novel chevron nozzle concepts for jet noise reduction
Authors: Tide P S , Srinivasan K
Published: December 2008

Chevron nozzles are known to be excellent attenuators of jet noise. Conventional chevron nozzles use triangular serrations at the trailing edge of the nozzle. This article proposes two novel chevron concepts and evaluates their noise reduction performance. The new chevron concepts proposed are protrusions with a sinusoidal profile and chevrons with asymmetry. These nozzles are compared against the symmetric chevron nozzle with triangular profile and a baseline circular nozzle without chevrons. The results indicate that the sinusoidal profile chevron nozzle shows better noise reduction at higher pressure ratios for all emission angles. At lower pressure ratios, the acoustic benefit is marginal due to reduced turbulent mixing of jet by low-strength vortices. Shadowgraph images of the asymmetric chevron nozzle shows bevelling due to the relieving effect in the direction of the longer chevron lobes, which reduces noise in the opposite side. This asymmetry of the noise sources and the acoustic field could be advantageously exploited in the implementations of chevron nozzles for aircraft.
Fault tolerant flight control system design using a multiple model adaptive controller
Authors: Jung B , Kim Y , Ha C
Published: December 2008

This article presents a fault tolerant flight control system using multiple model adaptive control (MMAC). To apply this method to the aircraft, model reference adaptive control is extended to a linear discrete-time multiple-input multiple-output system. Multiple models can be determined by various flight conditions with respect to possible aircraft fault situations. In this article, the damages of control effectors are considered as aircraft faults. The aerodynamic coefficients of fault model are derived by a damaged control surface area. In the MMAC, how to select a proper fault model and how to switch into the selected model are significant issues. The conventional mode switching method, however, has a tendency to make the system fluctuate because of frequent mode switching, and therefore may deteriorate the performance of the aircraft. In this study, the modified adaptive mode switching scheme and new decision logic are proposed to improve the adaptiveness in the transient state dynamics of system. Numerical simulations are performed for a linear discrete-time aircraft model to validate the effectiveness of the proposed method.
Influence of blade tip cutting on axial compressor aerodynamic performance
Authors: Lu J L , Chu W , Zhang H
Published: December 2008

The purpose of this article is to numerically investigate the function of blade tip cutting on axial flow compressors. The subject of this article is a subsonic compressor stage built and tested by Northwest Polytechnic University. The effect of cutting material from the blade pressure side is first analysed as an isolated rotor, and then in the environment of a stage with a downstream stator. The tool used for simulation is commercial computational fluid dynamics package of NUMECA. The numerical results show the possibility of increasing the rotor/stage pressure ratio and improve rotor efficiency by finding the right cut. The most significant effect of blade tip cutting is that it redistributes the load along blade span. When the adjusted load shape now fits with the downstream stator, the advantage of blade tip cut can be magnified; on the contrary, if the shape is not compatible with the downstream load, then the configuration that favours the performance of the rotor may deteriorate than that of the stage. This study also indicates that the blade tip cutting technique is rather case-dependent and that the performance of the cut blade is very sensitive to the shape of blade leading edge. Positive effect will only be significant when the cut is tailored to benefit both the local rotor flow field and the downstream flow field.
Exponential stability of anti-periodic solutions for neural networks with multiple discrete and distributed delays
Authors: Liu X , Cao J
Published: December 2008

In this paper, the anti-periodic solutions are considered for generalized neural networks with multiple discrete delays and distributed delays. Several new sufficient conditions are established for ensuring the existence and exponential stability of anti-periodic solutions based on the Lyapunov method and M-matrix theory. It is shown that, by means of the techniques developed, the analysis of stability for anti-periodic solutions is different from the familiar periodic ones. The obtained results generalize and improve the earlier works. Two numerical examples are given to illustrate the effectiveness of the proposed theories.
Automatic collision avoidance of ships
Authors: Xue Y , Lee B S , Han D
Published: December 2008

One of the key elements in automatic simulation of ship manoeuvring in confined waterways is route finding and collision avoidance. This paper presents a new practical method of automatic trajectory planning and collision avoidance based on an artificial potential field and speed vector. Collision prevention regulations and international navigational rules have been incorporated into the algorithm. The algorithm is fairly straightforward and simple to implement, but has been shown to be effective in finding safe paths for all ships concerned in complex situations. The method has been applied to some typical test cases and the results are very encouraging.
Common-cause failure analysis in event assessment
Authors: Rasmuson D M , Kelly D L
Published: December 2008

This paper reviews the basic concepts of modelling common-cause failures (CCFs) in reliability and risk studies and then applies these concepts to the treatment of CCF in event assessment. The cases of a failed component (with and without shared CCF potential) and a component being unavailable due to preventive maintenance or testing are addressed. The treatment of two related failure modes (e.g. failure to start and failure to run) is a new feature of this paper, as is the treatment of asymmetry within a common-cause component group.
Reasoning in reliability-centred maintenance based on a Dempster—Shafer approach
Authors: Rakowsky U K , Gocht U
Published: December 2008

This approach to modelling of uncertainties in reliability-centred maintenance (RCM) is a continuation of the probabilistic and the fuzzy RCM. The evidence measures, belief and plausibility, are applied to express the uncertainties of experts in reasoning and to give weighted recommendations during the RCM process. Brief introductions to RCM and to the Dempster—Shafer theory are given. Finally, the Dempster—Shafer approach to RCM (DS-RCM) is applied to a fire detection and extinguishing system.
Maintenance policy for a deteriorating system evolving in a stressful environment
Authors: Deloux E , Castanier B , Bérenguer C
Published: December 2008

This paper deals with the maintenance optimization of a system subject to a stressful environment. The system deterioration behaviour can be modified by the environment; the degradation mode can change due to the random evolution of the stressful environment. Reciprocally, the environment conditions can be influenced by the system state and as a consequence, a change in the environment can be an indicator of the system state. This paper describes a condition-based maintenance decision framework to tackle the potential variations in the system deterioration, and especially in the deterioration rate, and the new information on the system state given by the evolution of the environmental variables.
Single-objective deterministic versus multi-objective stochastic water network design: Practical considerations for the water industry
Authors: Filion Y R
Published: December 2008

The strategy in single-objective deterministic water network design is to size and locate components to minimize capital cost and meet future peak demands at or above a minimum pressure. Increasingly, practitioners are turning to multi-objective stochastic design to balance the minimum-cost objective with hydraulic performance objectives. The aim of the current paper is to review single-objective deterministic and multi-objective stochastic network design and discuss practical considerations concerning their advantages and disadvantages of relevance to water industry professionals and practitioners. Key differences in data and computational requirements, comprehensiveness of analysis, and decision flexibility between the two approaches are illustrated with a complex, hypothetical network example. A Monte-Carlo simulation program was used to solve the multi-objective stochastic problem and generate a set of Pareto or near-Pareto solutions with pipe cost ranging between $9.3 and $17.4 million and hydraulic robustness ranging between 65.8 and 96.4 per cent. Results indicated a non-linear relationship between pipe cost and robustness typical of many systems and that a large premium must be paid to achieve marginal improvements in robustness beyond a value of 90 per cent. The MCS program was run for 30.6 h to test the hypothetical network against a broad range of demands to ensure a high level of hydraulic robustness. The Pareto curve allows the decision maker the opportunity to quickly assess trade-offs between pipe cost and robustness.
System reliability and safety assessment using non-parametric flowgraph models
Authors: Collins D H , Huzurbazar A V
Published: December 2008

Multi-state Markov models are widely used for prediction in reliability, safety, and risk analysis. Systems typically pass through different states between correct, reliable operation and failure, as a result of external events or internal ageing, and Markov models provide an effective compromise between realism and mathematical tractability. Statistical flowgraphs analyse these models using transforms of the transition time distributions between states, which are combined and inverted to obtain quantities of interest for the entire model. This paper presents an approach to flowgraphs using empirical transforms based on historical or testing data, with no assumption of parametric probability models for transition times. The non-parametric method is illustrated with an application to predicting cumulative earthquake damage to structures.
On the odd Weibull distribution
Authors: Jiang H , Xie M , Tang L C
Published: December 2008

Based on the idea of evaluating the distribution of the ‘odds of death’ of a lifetime variable, the odd Weibull distribution proposed by Cooray has recently been shown to be useful for testing the goodness of fit of the Weibull and inverse Weibull distributions. The model is also very versatile in modelling lifetime data in that its failure rate function can be increasing, decreasing, constant, bathtub shaped, and unimodal. In this paper, a detailed parametric characterization of the statistical properties of this distribution is carried out. The shapes of the Weibull probability plot with different model parameters are presented and the graphic parameter estimation steps are iterated. Burn-in and useful period-related issues of the bathtub-shaped failure rate curve are discussed. An application example is shown to illustrate the parameter estimation procedure and the superior fit of the model for some real data to the two-parameter Weibull distribution and some other three-parameter Weibull-related distributions.
Using the peak heat release rate to determine the fire risk level of road tunnels
Authors: Cheong M K , Spearpoint M , Fleischmann C M
Published: December 2008

A wide range of fire incidents can occur in a road tunnel, e.g. a fire in the cargo compartment of a goods vehicle, carelessness due to discarded smoker's materials or loss of vehicle control, and a crash resulting in a multiple -vehicle fire. The number of possible fire scenarios is numerous and so, for design applications, rather than attempting to analyse every possible event using a deterministic approach, a preliminary analysis using a quantitative risk assessment approach should be considered. This paper presents a risk assessment methodology to identify the possible fire scenarios that can occur in a road tunnel in order to specify design fire requirements for smoke control systems. The analysis considers factors such as legislation, vehicle fuel load, traffic mix in the tunnel, vehicle accident rate, and causes of vehicle ignition.
Some disturbing facts about depth-first left-most variable ordering heuristics for binary decision diagrams
Authors: Rauzy A B
Published: December 2008

Binary decision diagrams (BDDs) have proven to be a very efficient tool to assess fault trees. However, the size of the BDD, and therefore the efficiency of the whole methodology, is highly dependent on the choice of variable ordering. The determination of the best variable ordering is intractable. Therefore, heuristics have been designed to select reasonably good variable orderings. The most popular of these heuristics consists in numbering variables by means of a depth-first left-most (DFLM) traversal of the formula, after possibly some rearrangements of the inputs of the gates. In this article, this heuristic is studied in a systematic way. It is shown to be very sensitive to the way the formula is written. A series of experiments shows also that the notion of locality of variables, which was believed to be a key issue in the determination of good orderings, must be handled with care. These facts are quite disturbing and raise questions about the design of good variable ordering heuristics.
Guarded transition systems: A new states/events formalism for reliability studies
Authors: Rauzy A B
Published: December 2008

States/events formalisms, such as Markov graphs or Petri nets, are widely used in reliability engineering studies. They have proved to be a very powerful tool both from conceptual and practical viewpoints. This article introduces a new states/events formalism, the so-called guarded transition system. The guarded transition system generalizes both block diagrams and Petri nets. It also makes it possible to handle looped systems, which no existing formalism is able to handle smoothly. Its use is illustrated by means of examples and several important issues such as composition and graphical representations are discussed. It is shown that current assessment methods for Markov graphs and Petri nets can be improved to a guarded transition system without a significant change of complexity.
Nonparametric predictive inference for system reliability with redundancy allocation
Authors: Coolen-Schrijner P , Coolen F P A , MacPhee I M
Published: December 2008

This paper presents lower and upper probabilities for the reliability of k-out-of- m systems, which include series and parallel systems, and of series systems with independent k i-out-of- m i subsystems, for which optimal redundancy allocation is also presented in case of zero-failure testing. First, attention is restricted to k-out-of- m systems with exchangeable components. The lower and upper probabilities for successful functioning of the system are based on the nonparametric predictive inferential (NPI) approach for Bernoulli data. In this approach, it is assumed that test data are available on the components, and that the future components to be used in the system are exchangeable with these. Thereafter, systems are considered that consist of a series of independent subsystems, with subsystem i a k i-out-of- m i system consisting of exchangeable components. For such systems, an algorithm for optimal redundancy allocation after zero-failure testing is presented. A particularly attractive feature of NPI in reliability, with lower and upper probabilities, is that data containing zero failures can be dealt with in an attractive manner.
Reliability and performance assessment for fuzzy multi-state elements
Authors: Liu Y , Huang H-Z , Levitin G
Published: December 2008

A system consisting of a single multi-state element (MSE) with performance rates and transition intensities presented as fuzzy values is considered. In many cases it is very difficult to evaluate the performance rates and transition intensities of MSEs in a multi-state system with a precise value, because of lack, inaccuracy, or fluctuation of data, especially in continuously degrading elements that are usually simplified to an MSE for computational convenience. Fuzzy theory which is a useful methodology to overcome these deficiencies is used to establish reliability models of an MSE. Given the fuzzy transition intensities and performance rates, the state probabilities of an MSE are also fuzzy values. A fuzzy continuous-time Markov model with finite discrete states is proposed to assess the dynamic reliability corresponding to working time. A fuzzy Markov reward model is also introduced to evaluate the dynamic fuzzy performance. In order to obtain the membership functions of the fuzzy reliability and performance, parametric programming technique is employed according to the extension principle. In this paper, the existing approach for fuzzy MSE availability assessment is modified and extended. An example of a power generator is presented to illustrate the proposed models and algorithms.
Hardware versus lumped cross-monitoring in smart multilane torque-summed electromechanical actuators
Authors: Annaz F Y
Published: December 2008

High integrity in multilane smart electromechanical actuation systems is achieved through hardware redundancy and intelligent monitoring. Hardware redundancy is associated with the inclusion of repeated hardware of key components that are likely to fail. Intelligent monitoring is associated with the inclusion of a fault detection and fault isolation (FDI) system that is capable of correctly detecting, identifying, isolating, and replacing failed components. The main aim of this paper is to address two cross-monitoring techniques (lumped and three-phase) in a single-type torque-summed architecture. In the lumped cross-monitoring technique, all lanes will be represented by their lumped models, while in hardware cross-monitoring, three-phase equivalents will model each motor. The latter is a more accurate representation and allows for more detailed motor and power conditioner failure-related tests. The analysis is based on a four-lane actuation system capable of driving aerodynamic and inertial loads (with two lanes failed) of an aileron control surface similar to that of the Sea Harrier.

The paper will start by giving an overview of the system, by describing:

The paper will then proceed to develop a threshold setting strategy by examining peak lane disparities due to inherent system randomness. The largest failure transient envelopes after failure isolations are then identified for different flight conditions, and their impact on the aircraft response in roll will then be assessed. The paper will conclude by showing that both actuator and aircraft requirements were met despite the use of two different cross-monitoring techniques.
Insights from analysing the Nuclear Regulatory Commission's common-cause failure database
Authors: Rasmuson D M , Mosleh A , Wierman T E
Published: December 2008

This paper summarizes key insights from studies of common-cause failures (CCFs) of emergency diesel generators, motor-operated valves, motor-driven pumps, and circuit breakers from 1980 to 2005. The data studied were derived from the Nuclear Regulatory Commission's CCF database, which is based on US commercial nuclear power plant event data. The insights are the result of an in-depth review of the CCF data. Trends of the annual number of CCF events show that the number of events has been decreasing over time. The insights can help to focus inspection and utility maintenance activities.
Modelling and analysis of risk and reliability for a contingency logistics supply chain
Authors: Miman M , Pohl E
Published: December 2008

Contingency logistic supply chain design and performance are very important for rare events such as natural disasters, terrorist attacks, and other emergency conditions. Although there is ample work on the evaluation of supply chain systems in terms of their profitability and efficiency, there is little work on the effectiveness of the response time of the supply chain, as well as quantitative measures for the robustness of the design and the reliability of the supply chain. Depending on the contingency, the perceived risk may be different for different situations. The level of risk aversion is dependent on the decision maker and the uncertainties associated with the supply and demand for the contingency. In this study the risk associated with shortages due to the uncertainties in supply and demand in the supply chain are modelled using distortion. In addition, a numerical analysis is performed and the sensitivity of the parameters in a contingency logistic supply chain is analysed. Methods to improve the effectiveness of the contingency operation are examined by efficiently allocating available resources, supplies, and time, as well as modelling the decision maker's perception associated with the failure of a particular node. An array of optimization models are formulated and discussed. Each of these models enables a decision maker to examine a variety of trade-offs in a contingency logistics supply chain. For example, one model examines the acquisition of mitigation strategies and the reallocation of resources while taking into consideration the decision maker's risk aversion. The main contribution of this paper is the establishment of an analysis framework for modelling and analysing the risk and reliability of contingency logistic supply chains.
Improved modular reliability analyses of hybrid phased mission systems
Authors: Shrestha A , Xing L
Published: December 2008

Phased mission systems (PMSs) involve a sequence of multiple tasks that must be carried out in consecutive, non-overlapping phases of operation. During each phase, the system is typically subject to different stresses and dependability requirements. Three major factors contribute to the difficulty in analysing PMSs: dynamics in system configuration, failure criteria, and component failure behaviour across different phases; s-dependence across the consecutive phases for a given component; and s-dependence among different components. A phase modular approach that integrates combinatorial solutions to static modules and Markov solutions to dynamic modules as appropriate has been recently proposed to address the above difficulty. Although the modular approach outperforms both the purely combinatorial solutions in modelling power and state-space based methods in computational efficiency, it involves costly path enumeration as well as joint phase module model generation and probability computation. This paper proposes improvements on the phase modular approach that can avoid the aforementioned costly operations and thus facilitate more efficient evaluation of hybrid PMSs. The proposed solutions are verified and illustrated through the analyses of an example phased mission system.
Maintenance modelling and scheduling in fault-tolerant control
Authors: Li H , Zhao Q
Published: December 2008

The present paper studies the modelling and scheduling problem of maintenance strategies in fault-tolerant control systems (FTCSs) using a stochastic modelling method. In FTCSs, the controller reconfigures itself to accommodate the occurrence of critical faults based on the information obtained from a fault detection and identification (FDI) scheme. Discrete semi-Markov chains are constructed to describe the operation of FTCSs with their unique characteristics incorporated. Two different maintenance strategies are discussed: FDI-dependent and FDI-independent periodic strategies, classified based on the use of FDI information in maintenance decision making. For each strategy, methods are presented for calculating the stationary availability and determining the optimal maintenance strategy to achieve the best availability. Two examples are given to demonstrate the proposed methods for both FDI-dependent and -independent cases.
Metal-Catalyzed Reactions of Organoboronic Acids and Esters
Authors: Miyaura Norio
Published: December 2008

Metal-catalyzed B–C and C–C bond-forming reactions of organoboronic acids that have been pursued in the past three decades by our group are summarized in this article. B–C bond-forming reactions for the synthesis of organoboronic acid derivatives include metal-catalyzed addition reactions of pinacolborane or catecholborane (hydroboration), bis(pinacolato)diboron (diboration), and alkylthioboranes (thioboration) to alkenes, alkynes, 1,3-alkadienes, or 1,2-alkadienes (allenes). Other B–C bond-forming reactions include coupling reactions of pinacolborane or bis(pinacolato)diboron for borylation of C–halogen bonds with palladium catalysts and C–H bonds of arenes and alkenes with iridium catalysts. These reactions have provided a convenient new access to aryl-, 1-alkenyl-, allyl-, or benzylboronates. Metal-catalyzed C–C and C–N bond-forming reactions using boronic acid derivatives include synthesis of novel cyclic triolborate salts for palladium- or copper-catalyzed cross-coupling reactions with organic halides or amines, rhodium- or palladium-catalyzed 1,4-addition reactions of arylboronic acids to α,β-unsaturated carbonyl compounds and rhodium-catalyzed addition of aryl- and 1-alkenylboronic acids to aldehydes and imines.