Pressure Fluctuations in Natural Gas Networks caused by Gas-Electric Coupling

The development of hydraulic fracturing technology has dramatically increased the supply and lowered the cost of natural gas in the United States, driving an expansion of natural gas-fired generation capacity in several electrical inter-connections. Gas-fired generators have the capability to ramp quickly and are often utilized by grid operators to balance intermittency caused by wind generation. The time-varying output of these generators results in time-varying natural gas consumption rates that impact the pressure and line-pack of the gas network. As gas system operators assume nearly constant gas consumption when estimating pipeline transfer capacity and for planning operations, such fluctuations are a source of risk to their system. Here, we develop a new method to assess this risk. We consider a model of gas networks with consumption modeled through two components: forecasted consumption and small spatio-temporarily varying consumption due to the gas-fired generators being used to balance wind. While the forecasted consumption is globally balanced over longer time scales, the fluctuating consumption causes pressure fluctuations in the gas system to grow diffusively in time with a diffusion rate sensitive to the steady but spatially-inhomogeneous forecasted distribution of mass flow. To motivate our approach, we analyze the effect of fluctuating gas consumption on a model of the Transco gas pipeline that extends from the Gulf of Mexico to the Northeast of the United States.Comment: 10 pages, 7 figure

Towards the modeling of mucus draining from human lung: role of airways deformation on air-mucus interaction

Chest physiotherapy is an empirical technique used to help secretions to get out of the lung whenever stagnation occurs. Although commonly used, little is known about the inner mechanisms of chest physiotherapy and controversies about its use are coming out regularly. Thus, a scientific validation of chest physiotherapy is needed to evaluate its effects on secretions. We setup a quasi-static numerical model of chest physiotherapy based on thorax and lung physiology and on their respective biophysics. We modeled the lung with an idealized deformable symmetric bifurcating tree. Bronchi and their inner fluids mechanics are assumed axisymmetric. Static data from the literature is used to build a model for the lung's mechanics. Secretions motion is the consequence of the shear constraints apply by the air flow. The input of the model is the pressure on the chest wall at each time, and the output is the bronchi geometry and air and secretions properties. In the limit of our model, we mimicked manual and mechanical chest physiotherapy techniques. We show that for secretions to move, air flow has to be high enough to overcome secretion resistance to motion. Moreover, the higher the pressure or the quicker it is applied, the higher is the air flow and thus the mobilization of secretions. However, pressures too high are efficient up to a point where airways compressions prevents air flow to increases any further. Generally, the first effects of manipulations is a decrease of the airway tree hydrodynamic resistance, thus improving ventilation even if secretions do not get out of the lungs. Also, some secretions might be pushed deeper into the lungs; this effect is stronger for high pressures and for mechanical chest physiotherapy. Finally, we propose and tested two adimensional numbers that depend on lung properties and that allow to measure the efficiency and comfort of a manipulation

Design and implementation of MIMO-long term evolution-advanced to support larger bandwidth

The migration of mobile communication technologies are divided into four generations. Long Term Evolution (LTE) is called LTE rel-8, the evolution of LTE led to new technology referred to as LTE-Advanced, is the true fourth generation (4G) evolution step, with the first release of LTE (rel-8) which was labeled as “3.9G”. LTE-Advanced is a mobile broadband access technology founded as a response to the need for the improvement to support the increasing demand for high data rates. The standard for LTE-A is a milestone in the development of Third Generation Partnership Project (3GPP) technologies. Carrier Aggregation is one of the most distinct features of LTE�Advanced that makes the bandwidth extension of up to 100 MHz thus the theoretical peak data rate of LTE-A may be even up to 1 Gbps. This proposed system presents new LTE-Advanced depending on carrier aggregation to obtain better performance of the system. The new design of LTE-Advanced offers higher peak data rates than even the initial LTE-A; while the spectrum efficiency has been amended; As a result, the aggregated LTE-A will support 120 MHz instead of 100 MHz in order to obtain higher peak data rate access up to 4 Gbps. The system was applied with 8x8 Multiple Input Multiple Output (MIMO) using different modulation techniques: QPSK, 16 QAM, and 64 QAM. From the simulation results, it is clear that proposed LTE-Advanced with 64 QAM has high values of throughput in case of depending code rate equals to 5/6 with 8x8 MIMO

An ageing elasto-viscoplastic model for ceramics

This work has been achieved in the framework of the PLEIADES project, financially supported by CEA (Commissariat à l’Énergie Atomique et aux Énergies Alternatives), EDF (Électricité de France) and AREVA.A model reproducing strain softening behavior in ceramic materials is proposed, base on a critical treatment of previous mechanical experimental results on uranium dioxide. The main hypothesis is that the strain softening phenomenon is related to an ageing process, where some point defects move towards the dislocations and modify their velocity. This is different from most of models used up to now, as they were based on the hypothesis that only the initial lack of dislocations was responsible of the strain softening behavior. A model is first developed in a simple 1D framework. Evolution of the mechanical behavior with strain rate and temperature is well reproduced by this model. Then, the 1D model is extended to a 3D mechanical model, and mechanical compressive tests on UO2 pellets are simulated. The 3D model well reproduces the observed asymmetrical shape of the compressed pellet if one considers that the material is not initially perfectly homogeneous, which highlights the importance of accounting for spatial heteregeneity of materials in models

Wavelet-based Adaptive Techniques Applied to Turbulent Hypersonic Scramjet Intake Flows

The simulation of hypersonic flows is computationally demanding due to large gradients of the flow variables caused by strong shock waves and thick boundary or shear layers. The resolution of those gradients imposes the use of extremely small cells in the respective regions. Taking turbulence into account intensives the variation in scales even more. Furthermore, hypersonic flows have been shown to be extremely grid sensitive. For the simulation of three-dimensional configurations of engineering applications, this results in a huge amount of cells and prohibitive computational time. Therefore, modern adaptive techniques can provide a gain with respect to computational costs and accuracy, allowing the generation of locally highly resolved flow regions where they are needed and retaining an otherwise smooth distribution. An h-adaptive technique based on wavelets is employed for the solution of hypersonic flows. The compressible Reynolds averaged Navier-Stokes equations are solved using a differential Reynolds stress turbulence model, well suited to predict shock-wave-boundary-layer interactions in high enthalpy flows. Two test cases are considered: a compression corner and a scramjet intake. The compression corner is a classical test case in hypersonic flow investigations because it poses a shock-wave-turbulent-boundary-layer interaction problem. The adaptive procedure is applied to a two-dimensional confguration as validation. The scramjet intake is firstly computed in two dimensions. Subsequently a three-dimensional geometry is considered. Both test cases are validated with experimental data and compared to non-adaptive computations. The results show that the use of an adaptive technique for hypersonic turbulent flows at high enthalpy conditions can strongly improve the performance in terms of memory and CPU time while at the same time maintaining the required accuracy of the results.Comment: 26 pages, 29 Figures, submitted to AIAA Journa

Spatio-temporal evolution of the nonresonant instability in shock precursors of young supernova remnants

A nonresonant cosmic-ray-current-driven instability may operate in the shock precursors of young supernova remnants and be responsible for magnetic-field amplification, plasma heating and turbulence. Earlier simulations demonstrated magnetic-field amplification, and in kinetic studies a reduction of the relative drift between cosmic rays and thermal plasma was observed as backreaction. However, all published simulations used periodic boundary conditions, which do not account for mass conservation in decelerating flows and only allow the temporal development to be studied. Here we report results of fully kinetic Particle-In-Cell simulations with open boundaries that permit inflow of plasma on one side of the simulation box and outflow at the other end, hence allowing an investigation of both the temporal and the spatial development of the instability. Magnetic-field amplification proceeds as in studies with periodic boundaries and, observed here for the first time, the reduction of relative drifts causes the formation of a shock-like compression structure at which a fraction of the plasma ions are reflected. Turbulent electric field generated by the nonresonant instability inelastically scatters cosmic rays, modifying and anisotropizing their energy distribution. Spatial CR scattering is compatible with Bohm diffusion. Electromagnetic turbulence leads to significant nonadiabatic heating of the background plasma maintaining bulk equipartition between ions and electrons. The highest temperatures are reached at sites of large-amplitude electrostatic fields. Ion spectra show supra-thermal tails resulting from stochastic scattering in the turbulent electric field. Together, these modifications in the plasma flow will affect the properties of the shock and particle acceleration there.Comment: Accepted for publication in MNRAS. 16 pages, 15 figure

Specialized turbomolecular pumping stage for RF ion thrusters

This paper proposes the application of a highly specialized Turbomolecular Vacuum Pump (TMP) device as a subsystem for electrostatic RF ion thrusters, using D. Fearn’s Dual-Stage 4-Grid design as a cutting-edge example. The TMP turbine’s rotor impulse is transmitted via collisions to neutral gas atoms en route to their ionization, with the goal of producing an anisotropic ion flux that is directed at the extracting screen grid. Operating regimes of such thruster design are hypothesized, and electromagnetic complexities of realization of this concept are identified