Physical Network Parameters Research Articles

A Novel Approach to Model a Gas Network

The continuous uninterrupted supply of Natural Gas (NG) is crucial to today’s economy, with issues in key infrastructure, e.g., Baumgarten hub in Austria in 2017, highlighting the importance of the NG infrastructure for the supply of primary energy. The balancing of gas supply from a wide range of sources with various end users can be challenging due to the unique and different behaviours of the end users, which in some cases span across a continent. Further complicating the management of the NG network is its role in supporting the electrical network. The fast response times of NG power plants and the potential to store energy in the network play a key role in adding flexibility across other energy systems. Traditionally, modelling the NG network relies on nonlinear pipe flow equations that incorporate the demand (load), flow rate, and physical network parameters including topography and NG properties. It is crucial that the simulations produce accurate results quickly. This paper seeks to provide a novel method to solve gas flow equations through a network under steady-state conditions. Firstly, the model is reformulated into non-linear matrix equations, then the equations separated into their linear and nonlinear components, and thirdly, the non-linear system is solved approximately by providing a linear system with similar solutions to the non-linear one. The non-linear equations of the NG transport system include the main variables and characteristics of a gas network, focusing on pressure drop in the gas network. Two simplified models, both of the Irish gas network (1. A gas network with 13 nodes, 2. A gas network with 109 nodes) are used as a case study for comparison of the solutions. Results are generated by using the novel method, and they are compared to the outputs of two numerical methods, the Newton–Raphson solution using MATLAB and SAINT, a commercial software that is used for the simulation of the gas network and electrical grids.

Co-Optimizing Allocation of Nyquist Superchannels and Physical Impairments Aware Placement of Regenerators in Elastic WDM Networks

Within the frame of the WDM networks, this paper articulates and validates the benefits of elastic spectral efficiency relying upon Nyquist superchannel, assuming static or incremental traffic and optimization of the superchannel filling ratio by means of electronic intermediate traffic grooming. This assessment is reported in terms of total accepted network capacity, average number of transponders per Gb/s transmitted, and mean number of regenerators traversed per Gb/s transported. This analysis points out why these two latter parameters differ when using adaptive bit rate interfaces. It also investigates how these outcomes depend on: (i) restriction about the regeneration, (ii) forward error correction coding, (iii) practical constraints on the spectral alignment of the subcarriers within the superchannels, and (iv) uncertain knowledge of the physical network parameters. This study highlights under which conditions the elasticity of the subcarrier modulation scheme effectively complements flexible subcarrier spacing. It proposes a particular placement of regenerators keeping substantial gain of network capacity even in the case of incremental traffic that may challenge profitable allocation of elastic superchannel.

Capacity of Wireless Ad Hoc Networks with Opportunistic Collaborative Communications

Optimal multihop routing in ad hoc networks requires the exchange of control messages at the MAC and network layer in order to set up the (centralized) optimization problem. Distributed opportunistic space-time collaboration (OST) is a valid alternative that avoids this drawback by enabling opportunistic cooperation with the source at the physical layer. In this paper, the performance of OST is investigated. It is shown analytically that opportunistic collaboration outperforms (centralized) optimal multihop in case spatial reuse (i.e., the simultaneous transmission of more than one data stream) is not allowed by the transmission protocol. Conversely, in case spatial reuse is possible, the relative performance between the two protocols has to be studied case by case in terms of the corresponding capacity regions, given the topology and the physical parameters of network at hand. Simulation results confirm that opportunistic collaborative communication is a promising paradigm for wireless ad hoc networks that deserves further investigation.

Simulation of the Harmful Consequences of Self-Similar Network Traffic

For a long time, the area of network traffic research has lacked adequate traffic measurements. During the past years, large amounts of network traffic measurements have become available, collected in the Web and high-speed networks. Measurements of real traffic indicate that burstiness is present on a wide range of time scales and show evidence of self-similarity and long-range dependency. Many traditional models originating in conventional voice networks either assumed that the underlying time series are short-range dependent or do not focus on the various, interrelated network components affected by bursty traffic. In order to provide explanations for empirically observed phenomena, such as burstiness in terms of physical network parameters, we need to develop models that can allow for the details of the complex architecture of today's networks and can analyze the interrelated network parameters that ultimately determine the performance and operation of a network. In the paper, we investigate the harmful consequences of burstiness on various network components using a model implemented by a discrete event simulation methodology. The methodology based on a modified version of the M/Pareto model can measure network performance parameters, such as the momentary utilization of links, response time, and the queuing performance of interconnected switches and routers along the traffic paths. Our paper intends to narrow the gap between existing, well-known theoretical results and their applicability in everyday, practical network analysis and modeling. Our methodology can help network designers and engineers, the ultimate users of traffic modeling, understand the dynamic nature of network traffic and assist them to design, monitor, and control complex, high-speed networks in everyday practice.

A new degree of freedom in ATM network dimensioning: optimizing the logical configuration

A mathematical model is presented that provides a well-defined formulation of the logical configuration problem of ATM networks (the carriers of future B-ISDN) with the objective of maximizing the total expected network revenue, given the physical network parameters and the traffic requirements of each virtual subnetwork. A two-phase solution procedure is developed in which the decision variables are the logical link capacities that specify the logical decomposition into virtual subnetworks, and the load sharing parameters. The first phase of the solution finds a global optimum in a rougher model. The second phase uses this as an initial point for a gradient-based hill climbing that applies the partial derivatives of the network revenue function obtained in a more refined model.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Thermoelastic properties of plasticized polyvinylchloride

A thermodynamic study was made of the elongation of polyvinylchloride over the concentration range of a didecylphthalate plasticizer of 0 to 70%. It was shown that the reduction of entropy and enthalpy in elongation depends markedly on the concentration of the plasticizer having maximum values in the region of 7–30% and minimum in the region of 60–70%. Results are interpreted on the basis of structural concepts concerning plasticized PVC and calculations of physical network parameters intermolecular bonds.