The Experts below are selected from a list of 247419 Experts worldwide ranked by ideXlab platform

Mandar Chaitanya Kulkarni - One of the best experts on this subject based on the ideXlab platform.

  • mechanics of light weight proppants a Discrete Approach
    Composites Science and Technology, 2012
    Co-Authors: Mandar Chaitanya Kulkarni
    Abstract:

    Abstract The computational and experimental assessment of light-weight proppants are undertaken to identify their effectiveness and efficiency to replace sand enlisted in hydraulic fracturing treatments in oil or gas well operations. A mixture of ground-nut-shells, aluminum or ceramic particles are shown to reduce the viscosity of the fracturing fluid while increasing its resistance to compression. Herein explicit dynamic finite element method is implemented to study quasi-static compression of a proppant pack where each granule (particle) is modeled individually. Various mixtures of hard and soft particles are investigated as a function of shape, size and inter-particle friction. The particle interactions clearly illustrate changes in pore space as a function of pressure, mixture composition and friction. The pressure vs displacement response of a proppant pack reflects strong dependence on mixture composition and initial particle configuration and has been compared with the test data. Friction leads to higher porosity by limiting particle rearrangement. Models reveal that softer rock with a mixture of hard and soft particles inhibit flowback but may decrease the pack permeability.

Udi Wieder - One of the best experts on this subject based on the ideXlab platform.

  • novel architectures for p2p applications the continuous Discrete Approach
    ACM Transactions on Algorithms, 2007
    Co-Authors: Moni Naor, Udi Wieder
    Abstract:

    We propose a new Approach for constructing P2P networks based on a dynamic decomposition of a continuous space into cells corresponding to servers. We demonstrate the power of this Approach by suggesting two new P2P architectures and various algorithms for them. The first serves as a DHT (distributed hash table) and the other is a dynamic expander network. The DHT network, which we call Distance Halving, allows logarithmic routing and load while preserving constant degrees. It offers an optimal tradeoff between degree and path length in the sense that degree d guarantees a path length of O(logdn). Another advantage over previous constructions is its relative simplicity. A major new contribution of this construction is a dynamic caching technique that maintains low load and storage, even under the occurrence of hot spots. Our second construction builds a network that is guaranteed to be an expander. The resulting topologies are simple to maintain and implement. Their simplicity makes it easy to modify and add protocols. A small variation yields a DHT which is robust against random Byzantine faults. Finally we show that, using our Approach, it is possible to construct any family of constant degree graphs in a dynamic environment, though with worse parameters. Therefore, we expect that more distributed data structures could be designed and implemented in a dynamic environment.

  • novel architectures for p2p applications the continuous Discrete Approach
    ACM Symposium on Parallel Algorithms and Architectures, 2003
    Co-Authors: Moni Naor, Udi Wieder
    Abstract:

    We propose a new Approach for constructing P2P networks based on a dynamic decomposition of a continuous space into cells corresponding to processors. We demonstrate the power of these design rules by suggesting two new architectures, one for DHT (Distributed Hash Table) and the other for dynamic expander networks. The DHT network, which we call Distance Halving allows logarithmic routing and load, while preserving constant degrees. It offers an optimal tradeoff between the degree and the dilation in the sense that degree d guarantees a dilation of O(log dn). Another advantage over previous constructions is its relative simplicity. A major new contribution of this construction is a dynamic caching technique that maintains low load and storage even under the occurrence of hot spots. Our second construction builds a network that is guaranteed to be an expander. The resulting topologies are simple to maintain and implement. Their simplicity makes it easy to modify and add protocols. A small variation yields a DHT which is robust against random faults. Finally we show that, using our Approach, it is possible to construct any family of constant degree graphs in a dynamic environment, though with worst parameters. Therefore we expect that more distributed data structures could be designed and implemented in a dynamic environment.

Moni Naor - One of the best experts on this subject based on the ideXlab platform.

  • novel architectures for p2p applications the continuous Discrete Approach
    ACM Transactions on Algorithms, 2007
    Co-Authors: Moni Naor, Udi Wieder
    Abstract:

    We propose a new Approach for constructing P2P networks based on a dynamic decomposition of a continuous space into cells corresponding to servers. We demonstrate the power of this Approach by suggesting two new P2P architectures and various algorithms for them. The first serves as a DHT (distributed hash table) and the other is a dynamic expander network. The DHT network, which we call Distance Halving, allows logarithmic routing and load while preserving constant degrees. It offers an optimal tradeoff between degree and path length in the sense that degree d guarantees a path length of O(logdn). Another advantage over previous constructions is its relative simplicity. A major new contribution of this construction is a dynamic caching technique that maintains low load and storage, even under the occurrence of hot spots. Our second construction builds a network that is guaranteed to be an expander. The resulting topologies are simple to maintain and implement. Their simplicity makes it easy to modify and add protocols. A small variation yields a DHT which is robust against random Byzantine faults. Finally we show that, using our Approach, it is possible to construct any family of constant degree graphs in a dynamic environment, though with worse parameters. Therefore, we expect that more distributed data structures could be designed and implemented in a dynamic environment.

  • novel architectures for p2p applications the continuous Discrete Approach
    ACM Symposium on Parallel Algorithms and Architectures, 2003
    Co-Authors: Moni Naor, Udi Wieder
    Abstract:

    We propose a new Approach for constructing P2P networks based on a dynamic decomposition of a continuous space into cells corresponding to processors. We demonstrate the power of these design rules by suggesting two new architectures, one for DHT (Distributed Hash Table) and the other for dynamic expander networks. The DHT network, which we call Distance Halving allows logarithmic routing and load, while preserving constant degrees. It offers an optimal tradeoff between the degree and the dilation in the sense that degree d guarantees a dilation of O(log dn). Another advantage over previous constructions is its relative simplicity. A major new contribution of this construction is a dynamic caching technique that maintains low load and storage even under the occurrence of hot spots. Our second construction builds a network that is guaranteed to be an expander. The resulting topologies are simple to maintain and implement. Their simplicity makes it easy to modify and add protocols. A small variation yields a DHT which is robust against random faults. Finally we show that, using our Approach, it is possible to construct any family of constant degree graphs in a dynamic environment, though with worst parameters. Therefore we expect that more distributed data structures could be designed and implemented in a dynamic environment.

Junye Wang - One of the best experts on this subject based on the ideXlab platform.

  • Discrete Approach for flow field designs of parallel channel configurations in fuel cells
    International Journal of Hydrogen Energy, 2012
    Co-Authors: Junye Wang, Hualin Wang
    Abstract:

    Abstract It is the major challenge to transform a laboratory scale production of fuel cells to an industrial scale one and to meet the requirements of throughput, operating life, low cost, reliability and high efficiency in R&D of fuel cells. Designs of uniform flow distribution are central to upscale fuel cells as well as to tackle critical issues of water, thermal and current management. However, in spite of our growing appreciation of designs of uniform flow distribution, there is little or no practical solution to ensure a uniform flow distribution across channels of a cell and cells of a stack in designs of flow fields. The purpose of this paper was to develop a Discrete Approach to find a design that met requirements of flow distribution uniformity and pressure drop in parallel channel configurations with Z-type arrangement through adjustments of configurations and normalised structural parameters. Variation of the frictional and the momentum coefficients with flow velocities was incorporated into the flow distribution equation to improve modelling accuracy. We also developed procedure, measures and guideline for the designs of flow distribution and pressure drop to bridge knowledge gap between the generalised theory and industrial applications. The results showed that the present Approach could provide the practical guideline to evaluate quantitatively performance of different layout configurations, structures, and flow conditions.

Peña Fernando - One of the best experts on this subject based on the ideXlab platform.

  • Structural assessment of gravity dams by means of a semi-Discrete Approach
    'Scipedia S.L.', 2019
    Co-Authors: Peña Fernando
    Abstract:

    A new numerical model for the structural assessment of gravity dams by means of a semiDiscrete Approach is proposed. Gravity dams are massive structures, which their stability depends on the gravity loads applied into the structure. Mainly, its structural assessment is performed by means of a gravity Approach. However, this Approach is too conservative and mostly does not reflect the real structural behaviour of the dam. In this context, there is the need of models that are simplified enough to allow a simple and fast parametric analyses. The proposed model idealizes the dam as a set of rigid elements, where the damage and the deformation are concentrated in the contact sides between adjacent elements. Thus, the elements are rigid, but the material is considered as deformable. As the proposed model is semi-Discrete, it can detect separation or sliding between elements. However, initial contacts do not change during the analyisis and a relative continuity among elements exists, in order to simplify the computational effort. The effective performance of the proposed model is demonstrated by numerical validation and by comparisons with some numerical models presented in the literature.Peer Reviewe

  • Structural assessment of gravity dams by means of a semi-Discrete Approach
    2019
    Co-Authors: Peña Fernando
    Abstract:

    A new numerical model for the structural assessment of gravity dams by means of a semi-Discrete Approach is proposed. Gravity dams are massive structures, which their stability depends on the gravity loads applied into the structure. Mainly, its structural assessment is performed by means of a gravity Approach. However, this Approach is too conservative and mostly does not reflect the real structural behaviour of the dam. In this context, there is the need of models that are simplified enough to allow a simple and fast parametric analyses. The proposed model idealizes the dam as a set of rigid elements, where the damage and the deformation are concentrated in the contact sides between adjacent elements. Thus, the elements are rigid, but the material is considered as deformable. As the proposed model is semi-Discrete, it can detect separation or sliding between elements. However, initial contacts do not change during the analyisis and a relative continuity among elements exists, in order to simplify the computational effort. The effective performance of the proposed model is demonstrated by numerical validation and by comparisons with some numerical models presented in the literature