194,541 research outputs found

    A new technique for steady state and transient analyses of incompressible flow networks

    Get PDF
    A new technique for the calculation of the transient or the steady-state mass flow rate and pressure distribution in incompressible flow networks is presented. Employing the matrix method of network analysis, the nodal continuity and branch momentum equations are solved simultaneously to obtain explicit relations giving the unknown nodal pressures and branch mass flow rates. In this manner, the transient or the steady-state behavior of incompressible flow networks with arbitrary configuration having nodal sources and sinks as well as branch transducers can be determined. In contrast with the conventional steady-state network analysis methods, the new technique can be extended to the unsteady analysis of compressible flow in networks having an arbitrary configuration with heat transfer and phase change. To ascertain the accuracy of the solution, a numerical stability and convergence analysis is performed which provides an estimate for the upper bound of the time for the increment needed for a stable and convergent solution. The new technique can be applied to the treatment of transient problems such as flow coastdown studies resulting from loss of pumping power in nuclear water reactors, hydraulic transients of the cooling system, for large steam power plants as well as the steady-state analysis of water distribution networks. The latter application is demonstrated in this study

    On the Spatial Resolution of Fault Location Techniques Based on Full Fault Transients

    Get PDF
    International audienceThis paper discusses the mechanisms enabling spatial resolution in fault location methods based on full transient signals, as opposed to those only using their early-time portion. This idea is found in recent travelling-wave methods (TWM) and those based on electromagnetic time reversal (EMTR). Their spatial resolution is discussed in terms of the sensitivity of a system resonances to change in the fault position and their coherence bandwidth. It is proven that using the entire transient signal it is possible to bypass the Fourier transform uncertainty principle, which limits the spatial resolution of time-domain reflectometry and standard early-time TWM. Super-resolved fault location is shown to be possible only for resonating systems, enabling high spatial resolution without relying on wide-band data. A detailed theoretical analysis for laterals and numerical results for networks and a three-phase line show that significant differences can be observed for the spatial resolution associated to each resonance, most often resulting in a loss of spatial resolution. The interaction between separate resonant structures, such as laterals in networks and coupled conductors in three-phase lines are shown to be main cause of resolution loss

    From network to phenotype : the dynamic wiring of an Arabidopsis transcriptional network induced by osmotic stress

    Get PDF
    Plants have established different mechanisms to cope with environmental fluctuations and accordingly fine-tune their growth and development through the regulation of complex molecular networks. It is largely unknown how the network architectures change and what the key regulators in stress responses and plant growth are. Here, we investigated a complex, highly interconnected network of 20 Arabidopsis transcription factors (TFs) at the basis of leaf growth inhibition upon mild osmotic stress. We tracked the dynamic behavior of the stress-responsive TFs over time, showing the rapid induction following stress treatment, specifically in growing leaves. The connections between the TFs were uncovered using inducible overexpression lines and were validated with transient expression assays. This study resulted in the identification of a core network, composed of ERF6, ERF8, ERF9, ERF59, and ERF98, which is responsible for most transcriptional connections. The analyses highlight the biological function of this core network in environmental adaptation and its redundancy. Finally, a phenotypic analysis of loss-of-function and gain-of-function lines of the transcription factors established multiple connections between the stress-responsive network and leaf growth

    Sensitivity analysis using Physics-informed neural networks

    Full text link
    The paper's goal is to provide a simple unified approach to perform sensitivity analysis using Physics-informed neural networks (PINN). The main idea lies in adding a new term in the loss function that regularizes the solution in a small neighborhood near the nominal value of the parameter of interest. The added term represents the derivative of the loss function with respect to the parameter of interest. The result of this modification is a solution to the problem along with the derivative of the solution with respect to the parameter of interest (the sensitivity). We call the new technique to perform sensitivity analysis within this context SA-PINN. We show the effectiveness of the technique using 3 examples: the first one is a simple 1D advection-diffusion problem to show the methodology, the second is a 2D Poisson's problem with 9 parameters of interest and the last one is a transient two-phase flow in porous media problem.Comment: 22 pages, 11 figure

    Influence of the line characterization on the transient analysis of nonlinearly loaded lossy transmission lines

    Get PDF
    The analysis of nonlinearly terminated lossy transmission lines is addressed in this paper with a modified version of a method belonging to the class of mixed techniques, which characterize the line in the frequency domain and solve the nonlinear problem in the time domain via a convolution operation. This formulation is based on voltage wave variables defined in the load sections. The physical meaning of such quantities helps to explain the transient scattering process in the line and allows us to discover the importance (so far often overlooked) of the reference impedance used to define the scattering parameters. The complexity of the transient impulse responses, the efficiency of the algorithms, and the precision of the results are shown to be substantially conditioned by the choice of the reference impedance. The optimum value of the reference impedance depends on the amount of line losses. We show that a low-loss line can be effectively described if its characteristic impedance or the characteristic impedance of the associated LC line is chosen as the reference impedance. Based on the physical interpretation of our formulation, we are able to validate the numerical results, and to demonstrate that, despite claimed differences or improvements, the formulations of several mixed methods are fundamentally equivalen

    Transient simulation of lossy multiconductor interconnects

    Get PDF
    The transient simulation of electrically-long low-loss multiconductor interconnects is considered from a practical point of view. The importance of frequency dependent losses in these interconnects is discussed and a simple transmission line characterization procedure allowing for such losses is proposed. The characterization obtained yields simple and efficient interconnect models, that the user can include, without programming, in any simulator accepting differential operator

    The Price of Synchrony: Resistive Losses due to Phase Synchronization in Power Networks

    Full text link
    We investigate the total resistive losses incurred in returning a power network of identical generators to a synchronous state following a transient stability event or in maintaining this state in the presence of persistent stochastic disturbances. We formulate this cost as the input-output H2H^2 norm of a linear dynamical system with distributed disturbances. We derive an expression for the total resistive losses that scales with the size of the network as well as properties of the generators and power lines, but is independent of the network topology. This topologically invariant scaling of what we term the price of synchrony is in contrast to typical power system stability notions like rate of convergence or the region of attraction for rotor-angle stability. Our result indicates that highly connected power networks, whilst desirable for higher phase synchrony, do not offer an advantage in terms of the total resistive power losses needed to achieve this synchrony. Furthermore, if power flow is the mechanism used to achieve synchrony in highly-distributed-generation networks, the cost increases unboundedly with the number of generators.Comment: 7 pages; 2 figure
    • 

    corecore