Félix García-Carballeira

Applying RCM in large scale systems: a case study with railway networks

Abstract In 2000, the European Union founded a project named ‘RAIL: Reliability centered maintenance approach for the infrastructure and logistics of railway operation’ aimed to study the application of Reliability centered maintenance (RCM) techniques to the railway infrastructure. In this paper, we present the results obtained into the RAIL project, including a RCM methodology adapted to large infrastructure networks and a RCM toolkit to perform the RCM analysis, including cost aspects and maintenance planning guidance. This paper addresses the problem of applying RCM to large scale railway infrastructure networks to achieve an efficient and effective maintenance concept. Railways use nowadays very traditional preventive maintenance (PM) techniques, relying mostly on ‘blind’ periodic inspection and the ‘know-how’ of maintenance staff. RCM was seen as a promising technique from the beginning of the RAIL project because of several factors. First, technical insights obtained were better than the existing, so that several maintenance processes could be revised and adjusted. Second, the interdisciplinary approach used to make the analysis was very enriching and very encouraging for maintenance staff consulted. Third, using the RCM structured approach allowed to achieve well-documented analysis and clear decision diagrams. Our methodology includes some new features to overcome the problems of RCM observed in other projects. As a whole, our methodology and Computerized Maintenance Management Systems have produced two short-term benefits: reduction of time and paperwork because databases and tools are accessible through Internet, and creation of a permanent, accurate, and better collection of information. It will also have some long-term benefits: better PM will increase equipment life and will help to reduce corrective maintenance costs; Production will increase as unscheduled downtime decreases; purchase costs of parts and materials will be reduced; more effective and up-to-date record of inventory/stores reports; and better knowledge of the systems to help the company to chose those systems with the best LCC. The results have been corroborated with the application of our methodology to signal equipment in several railway network sections, as shown in this paper. Because of the successful conclusion of the project, the Spanish railway company (RENFE) and the German railway company (DB A.G.), not only decided to adopt RCM to enhance PM, but they have started a large project to implement Total Preventive Maintenance relying on the implantation of the RCM methodology.

Branch replication scheme: A new model for data replication in large scale data grids

Data replication is a practical and effective method to achieve efficient and fault-tolerant data access in grids. Traditionally, data replication schemes maintain an entire replica in each site where a file is replicated, providing a read-only model. These solutions require huge storage resources to store the whole set of replicas and do not allow efficient data modification to avoid the consistency problem. In this paper we propose a new replication method, called the Branch Replication Scheme (BRS), that provides three main advantages over traditional approaches: optimizing storage usage, by creating subreplicas; increasing data access performance, by applying parallel I/O techniques; and providing the possibility to modify the replicas, by maintaining consistency among updates in an efficient way. An analytical model of the replication scheme, naming system, and replica updating scheme are formally described in the paper. Using this model, operations such as reading, writing, or updating a replica are analyzed. Simulation results demonstrate the feasibility of BRS, as they show that the new replication algorithm increases data access performance, compared with popular replication schemes such as hierarchical and server-directed replication, which are commonly used in current data grids.

The Design of the Expand Parallel File System

This article describes an implementation of MPI-IO using a new parallel file system, called Expand (Expandable Parallel File System), which is based on NFS servers. Expand combines multiple NFS servers to create a distributed partition where files are striped. Expand requires no changes to the NFS server and uses RPC operations to provide parallel access to the same file. Expand is also independent of the clients, because all operations are implemented using RPC and NFS protocols. Using this system, we can join heterogeneous servers (Linux, Solaris, Windows 2000, etc.) to provide a parallel and distributed partition. The article describes the design, implementation and evaluation of Expand with MPI-IO. This evaluation has been made in Linux clusters and compares Expand and PVFS.

An ontology-driven decision support system for high-performance and cost-optimized design of complex railway portal frames

Highlights? We model the design process of complex railway electrification structures. ? We provide ontology and rules to model railway engineers knowledge. ? Increasing automation will increase infrastructure quality and will reduce design and construction costs. ? Our tool reduces design time from days to minutes, getting optimized structures compliant with railway normative. Electrification structures design for railway systems is a crucial and complex process, since it compounds plenty of infrastructure elements, design decisions, and calculation conditions. In this paper, an ontology-driven decision support system for designing complex railway portal frames is presented and developed. A knowledge-rules database has been also developed relying on experts knowledge and complying with railway standards. Our system outperforms the current portal frames design methods by decreasing construction time and costs. As a result, an intelligent computer-aided design tool is provided, thus facilitating the task of seeking for the optimal portal frame, which is geometrically and structurally feasible, and cost-effective.

New stream caching schemas for multimedia systems

In this paper a new multimedia caching strategy is proposed that includes several optimizations to the state of the art. This algorithm takes its roots from the interval caching algorithms but it evolves towards a more adaptive approaching that could obtain a better performance for variable bit-rate streams and serving media stored on multiple disks following different distributions. All of this without loosing competitiveness for constant bit-rate streams on a single disk. All this efforts are oriented towards the consecution of MUPIC (multi policy integrated cache), a cache architecture designed to fit the requirements of an integrated storage system that meet the requirements of deterministic applications, multimedia systems, and traditional best-effort applications altogether.

A cloudification methodology for multidimensional analysis: Implementation and application to a railway power simulator

Abstract Many scientific areas make extensive use of computer simulations to study complex real-world processes. These computations are typically very resource-intensive and present scalability issues as experiments get larger even in dedicated clusters, since these are limited by their own hardware resources. Cloud computing raises as an option to move forward into the ideal unlimited scalability by providing virtually infinite resources, yet applications must be adapted to this new paradigm. This process of converting and/or migrating an application and its data in order to make use of cloud computing is sometimes known as cloudifying the application. We propose a generalist cloudification method based in the MapReduce paradigm to migrate scientific simulations into the cloud to provide greater scalability. We analysed its viability by applying it to a real-world railway power consumption simulatior and running the resulting implementation on Hadoop YARN over Amazon EC2. Our tests show that the cloudified application is highly scalable and there is still a large margin to improve the theoretical model and its implementations, and also to extend it to a wider range of simulations. We also propose and evaluate a multidimensional analysis tool based on the cloudified application. It generates, executes and evaluates several experiments in parallel, for the same simulation kernel. The results we obtained indicate that out methodology is suitable for resource intensive simulations and multidimensional analysis, as it improves infrastructure’s utilization, efficiency and scalability when running many complex experiments.

A model to obtain optimal designs of railway overhead knuckle junctions using simulation

Abstract The design of overhead knuckle junctions in railway electrification is a crucial and complex problem. Non-optimal overhead knuckle junction designs cause limitations in train speed and, most important, malfunctions and breakages. Most railway companies have regulations for the design of overhead knuckle junctions. Those regulations have been defined by the experience, but, as far as we know, there are no computerized software tools to help with the task of designing and testing optimal solutions for overhead knuckle junctions. In this paper we present a simulator that allows to look for optimal configurations of overhead knuckle junctions. The simulator starts from a model based on the description of the problem that includes all the significant elements that may affect the design process, in order to find an optimal solution in terms of reliability and safety. The obtained design will be the more reliable to face failures, such as excessive wire and pantograph wears, wrong geometry configurations of the catenary, or electricity supply notches. The simulator also allows to evaluate current designs, so as to prove their possible flaws. This paper describes the simulation algorithm developed, the input data needed to define the experiments, and the achieved results. As the simulator requires heavy computational resources, high productivity parallel issues have been included in the implementation to exploit current multi-core processors. The validation and performance evaluations were made in the paper through the simulation of overhead knuckle junction designs over real switches. Their analysis will show the feasibility and applicability of our simulator.

Implementation and Evaluation of File Write-Back and Prefetching for MPI-IO Over GPFS

In this paper we present the implementation of an open-source MPI-IO interface for the General Parallel File System (GPFS). Our solution includes the design and implementation of GPFS-based write-back and prefetching modules, which have been integrated in ROMIO. A collective file write strategy based on GPFS data-shipping, and a view-based collective I/O mechanism, relying on GPFS mechanisms, are at the core of the novel optimizations proposed in this paper. View-based collective I/O includes a thread-based flushing method implementing a write-back policy for latency hiding, and a prefetching method, based on GPFS hints, to increase small read access performance. Performance evaluations show that our implementation achieves high-performance and hides the latency of file accesses through the combination of view-based collective file accesses, and the overlapping of computation, communication and I/O. This is especially true for collective and small-size access patterns, which are very frequent in parallel scientific applications.

A fault tolerant MPI-IO implementation using the Expand parallel file system

Parallelism in file systems is obtained by using several independent server nodes supporting one or more secondary storage devices. This approach increases the performance and scalability of the system, but a fault in one single node can stop the whole system. To avoid this problem, data must be stored using some kind of redundant technique, so any data stored in a faulty element can be recovered. Fault tolerance can be provided in I/O systems using replication or RAID based schemes. However, most of the current systems apply the same technique for all files in the system. This paper describes the fault tolerance support provided by Expand, a parallel file system based on standard servers. Expand allows to define different fault-tolerant mechanisms at file level. The evaluation compares the performance of Expand with different configurations with PVFS using the FLASH-I/O benchmark.

An adaptive cache coherence protocol specification for parallel input/output systems

Caching has been intensively used in memory and traditional file systems to improve system performance. However, the use of caching in parallel file systems and I/O libraries has been limited to I/O nodes to avoid cache coherence problems. We specify an adaptive cache coherence protocol that is very suitable for parallel file systems and parallel I/O libraries. This model exploits the use of caching, both at processing and I/O nodes, providing performance improvement mechanisms such as aggressive prefetching and delayed-write techniques. The cache coherence problem is solved by using a dynamic scheme of cache coherence protocols with different sizes and shapes of granularity. The proposed model is very appropriate for parallel I/O interfaces, such as MPI-IO. Performance results, obtained on an IBM SP2, are presented to demonstrate the advantages offered by the cache management methods proposed.