Single Line Model Research Articles

A novel formulation of low voltage distribution network equivalents for reliability analysis

Reliability analysis of large power networks requires accurate aggregate models of low voltage (LV) networks to allow for reasonable calculation complexity and to prevent long computational times. However, commonly used lumped load models neglect the differences in spatial distribution of demand, type of phase-connection of served customers and implemented protection system components (e.g., single-pole vs three-pole). This paper proposes a novel use of state enumeration (SE) and Monte Carlo simulation (MCS) techniques to formulate more accurate LV network reliability equivalents. The combined SE and MCS method is illustrated using a generic suburban LV test network, which is realistically represented by a reduced number of system states. This approach allows for a much faster and more accurate reliability assessments, where further reduction of system states results in a single-component equivalent reliability model with the same unavailability as the original LV network. Both mean values and probability distributions of standard reliability indices are calculated, where errors associated with the use of single-line models, as opposed to more detailed three-phase models, are quantified.

Dual-energy computed tomography imaging with megavoltage and kilovoltage X-ray spectra.

Single-energy computed tomography (CT) often suffers from poor contrast yet remains critical for effective radiotherapy treatment. Modern therapy systems are often equipped with both megavoltage (MV) and kilovoltage (kV) X-ray sources and thus already possess hardware for dual-energy (DE) CT. There is unexplored potential for enhanced image contrast using MV-kV DE-CT in radiotherapy contexts. A single-line integral toy model was designed for computing basis material signal-to-noise ratio (SNR) using estimation theory. Five dose-matched spectra (3kV, 2 MV) and three variables were considered: spectral combination, spectral dose allocation, and object material composition. The single-line model was extended to a simulated CT acquisition of an anthropomorphic phantom with and without a metal implant. Basis material sinograms were computed and synthesized into virtual monoenergetic images (VMIs). MV-kV and kV-kV VMIs were compared with single-energy images. The 80kV-140kV pair typically yielded the best SNRs, but for bone thicknesses , the detunedMV-80kV pair surpassed it. Peak MV-kV SNR was achieved with dose allocated to the MV spectrum. In CT simulations of the pelvis with a steel implant, MV-kV VMIs yielded a higher contrast-to-noise ratio (CNR) than single-energy CT and kV-kV DE-CT. Without steel, the MV-kV VMIs produced higher contrast but lower CNR than single-energy CT. This work analyzes MV-kV DE-CT imaging and assesses its potential advantages. The technique may be used for metal artifact correction and generation of VMIs with higher native contrast than single-energy CT. Improved denoising is generally necessary for greater CNR without metal.

New beam-based models for fire-induced buckling analysis of class 4 steel columns

Steel cross-sections with thin walls are vulnerable to fire-induced buckling instability, which reduces their load-bearing capacity. Eurocode 3 design provisions have been found inadequate, leading to alternative methods such as effective design strategies and advanced structural models built mostly with shell FE, which can be complex. For Class 4 steel beam-columns subjected to fire conditions, beam-type modelling to predict the Flexural-Torsional Buckling (FTB) strength has been proposed as an alternative approach, but it has not yielded satisfactory results for large compressive load eccentricities. This paper presents two new low computational cost modelling strategies based on Timoshenko's beam FE to address this issue: the Single beam-column Model (SbcM) and the Cruciform beam-column Model (CbcM). The first consists of a single line of beam FE, while the second uses a grid of beam FE for more flexibility. Both strategies effectively simulate the FTB behaviour in Class 4 steel beam-column during a fire, offering quicker computations compared to shell models. Still, the single-line model is favoured for its simplicity, making it more efficient in analysing complex fire engineering problems.

Pre-Emphasis Pulse Design for Reducing Bit-Line Access Time in NAND Flash Memory

This paper describes pre-emphasis (PE) pulses to reduce bit-line (BL) access time in NAND flash memory. Optimum PE pulse widths and resultant minimum BL delay times are investigated, where the BL delay is determined by the sense current at the input terminal of a sensing circuit in contrast with the word-line (WL) delay that is determined by the WL voltage at the gate of a selected memory cell. Two BL models are used, namely, a single-line model (SLM) for the shielded BL read operation and a three-line model (TLM) for the all-BL read operation. Under the condition that the sense current delay is defined by the time when the sense current becomes stable between 110% and 90% of the cell current and the BL voltage delay is defined by the time when the BL voltage at the selected cell reaches a window between 110% and 90%, SPICE simulation results show that the sensed current delay and the BL voltage delay are reduced by 43% and 36% in the case of SLM and by 16% and 28% in the case of TLM, respectively. Thus, the key results are the following: (1) PE pulses are effective to reduce the sense current delay time for BL access, as well as the BL voltage delay time for both SLM and TLM; (2) the sensitivity of the PE pulse on the delay time is much larger for the sensed current delay than the BL voltage delay due to the absence of filtering with the RC delay element in BL delay; and (3) address-dependent PE pulse control can reduce the sense current delay significantly, especially for access to cells closely located to the sensing circuit.

Computer modeling approach for multilayer interlocked woven structures

Abstract This study aimed to simulate the geometric modeling of the multilayer interlocked woven structures in three dimensions (3D) using computer aided design (CAD). The simulation of yarn was composed of fibers assembled together for presenting the structures. Two and three layers for multilayer interlocked woven structures were simulated with a filament assemble model and compared with yarn path of single line model. The result showed that the new model developed was more realistic than the previous works. The strength of these models is required as an input to many computational methods such as simulation the tensile/bending properties of fabrics structure or composite parts, forecasting the fiber volume fraction of fabrics.

Urban Rail Transit Running Hierarchized Simulation based on Timed Discrete Petri and Matlab under the Background of Industry 4.0

This paper, taking Changchun rail transit as an example, proposes a new method to simulate its running that is hierarchized simulation using timed discrete Petri and Simulink/Stateflow. Firstly, this paper uses the timed discrete Petri nets to build Changchun rail transit line 1-4 running model. And then, based on the timed discrete Petri nets model above, this paper also studies hierarchized simulation model by the tool of Simulink/Stateflow, which consists of two layers: the bottom layer is a single line model, and the top layer is a whole line model. In order to realize the rail transit running visualization, the tool of Matlab/App Designer is employed to design monitoring interface for Changchun rail transit line 1-4. This method is scalable and popularized.

Strategies for transit fleet design considering peak and off-peak periods using the single-line model

Transit demand and traffic conditions present relevant differences between peak and off-peak periods - e.g. flows, trip lengths, congestion - raising a relevant strategic design choice regarding the potential use of vehicles with different sizes. Here we first revisit the optimal design using a single-line, single-fleet model, showing that buses should always run full at the peak but not always at the off-peak. Then we develop a two-fleet strategy (with different vehicle sizes) where one fleet operates the whole day and the other during the peak period only. This strategy includes holding during the peak (in order to avoid bunching) by imposing equal cycle times for both fleets. The two-fleet operation has slightly lower total costs than one-fleet, but exhibits very different effects on users’ and on operators’ costs across periods. A sensitivity analysis reveals the role played by various elements and shows that results are robust. Optimal one and two-fleet designs are both better than optimizing each period independently, revealing economies of time scope.

DC corona characteristics derived from corona cage tests and simulations

This study presents experimental and simulation studies on DC corona characteristics to investigate the behavior of high voltage direct current transmission (HVDC) lines. Experimental studies are performed using an indoor corona cage and various conductor configurations, which are the scaled models of the prospective HVDC line in Turkey. Following the preliminary tests with single line models of aluminum rods and stranded conductors, DC corona inception voltages (CIVs) of prospective bundled conductor configurations are measured by using a daylight UV corona camera and a high-sensitive micro ammeter. Measurements include three different sub-conductor spacing both for the positive and for the negative DC voltages. Corona currents are measured for the voltages above the CIV levels. Experimental studies are varied by complementary simulations using a FEM based software, COMSOL Multyphysics. Following the development of 3D models of the corona cage and the prospective conductor configurations, electric field distribution along the conductor surfaces are determined. CIV measurements and simulation results are used to compute the corona inception electric field strengths of the aforementioned configurations. Radio interference voltages and audible noise levels of the configurations are finally calculated at a constant test voltage using the empirical formulations and the field simulation results. The results are discussed at the end to guide the design of intended HVDC line in Turkey.

Estimation of the Transmission Line Parameters Using a Grid Model

The parameters of an equivalent circuit of power transmission lines in the UNPG single-line model are estimated from synchrophasor measurements of nodal voltages and currents. Systematic and random errors in PMU measurements that lead to errors in the estimates of the transmission line parameters are considered.

Probing the circumgalactic medium at high-redshift using composite BOSS spectra of strong Lyman α forest absorbers

We present composite spectra constructed from a sample of 242,150 Lyman-alpha (Lya) forest absorbers at redshifts 2.4<z<3.1 identified in quasar spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) as part of Data Release 9 of the Sloan Digital Sky Survey III. We select forest absorbers by their flux in bins 138 km/s wide (approximately the size of the BOSS resolution element). We split these absorbers into five samples spanning the range of flux -0.05 < F<0.45. Tests on a smaller sample of high-resolution spectra show that our three strongest absorption bins would probe circumgalactic regions (projected separation < 300 proper kpc and |Delta v| < 300km/s) in about 60% of cases for very high signal-to-noise ratio. Within this subset, weakening Lya absorption is associated with decreasing purity of circumgalactic selection once BOSS noise is included. Our weaker two Lya absorption samples are dominated by the intergalactic medium. We present composite spectra of these samples and a catalogue of measured absorption features from HI and 13 metal ionization species, all of which we make available to the community. We compare measurements of seven Lyman series transitions in our composite spectra to single line models and obtain further constraints from their associated excess Lyman limit opacity. This analysis provides results consistent with column densities over the range 14.4 <~ Log (N_HI) <~ 16.45. We compare our measurements of metal absorption to a variety of simple single-line, single-phase models for a preliminary interpretation. Our results imply clumping on scales down to ~30 pc and near-solar metallicities in the circumgalactic samples, while high-ionization metal absorption consistent with typical IGM densities and metallicities is visible in all samples.

The impact of a financial constraint on the spatial structure of public transport services

Using a single line model, it has been shown recently that the presence of a stringent financial constraint induces a less than optimal bus frequency and larger than optimal bus size. This occurs because the constraint induces a reduction of the importance of users’ costs (their time); in the extreme, users’ costs disappear from the design problem. In this paper we show that such a constraint also has an impact on the spatial structure of transit lines. This is done departing from the single line model using an illustrative urban network that could be served either with direct services (no transfers) or with corridors (transfers are needed). First, the optimal structure of lines is investigated along with frequencies and vehicle sizes when the full costs for users and operators are minimized (unconstrained case); the optimal lines structure is shown to depend upon the patronage level, the values of time and the cost of providing bus capacity. Then the same problem is solved for the extreme case of a stringent financial constraint, in which case users’ costs have relatively little or no effect in determining the solution; in this case the preferred outcome would be direct services under all circumstances, with lower frequencies and larger bus sizes. The impact of the financial constraint on the spatial structure of transit lines is shown to be caused by the reduction in cycle time under direct services; the introduction of users’ costs in the objective function makes waiting times reverse this result under some circumstances.

Optimal compensating scheme for limiting secondary arc current of 1000-kV UHV short parallel lines

The optimal single line compensating model is presented and analysed for short 1000-kV UHV parallel lines, to limit secondary arc current and recovery voltage. According to this study, for perfectly transposed 1000-kV lines shorter than 183 km, 750-kV parallel lines shorter than 280 km and 500-kV parallel lines shorter than 500 km, the secondary arc current can be compensated in single line model, and hence achieving the successful selective pole reclosing. Simulations on real time digital simulator (RTDS) have been carried out to evaluate the compensation scheme proposed in this study.

Probabilistic Modeling and Simulation of Transmission Line Temperatures Under Fluctuating Power Flows

Increasing shares of fluctuating renewable energy sources induce higher and higher power flow variability at the transmission level. The question arises as to what extent existing networks can absorb additional fluctuating power injection without exceeding thermal limits. At the same time, the resulting power flow characteristics call for revisiting classical approaches to line temperature prediction. This paper presents a probabilistic modeling and simulation methodology for estimating the occurrence of critical line temperatures in the presence of fluctuating power flows. Cumbersome integration of the dynamic thermal equations at each Monte Carlo simulation trial is sped up by a specific algorithm that makes use of a variance reduction technique adapted from the telecommunications field. The substantial reduction in computational time allows estimations closer to real time, relevant to short-term operational assessments. A case study performed on a single line model provides fundamental insights into the probability of hitting critical line temperatures under given power flow fluctuations. A transmission system application shows how the proposed method can be used for a fast, yet accurate operational assessment.

A Decoupling Technique for Efficient Timing Analysis of VLSI Interconnects With Dynamic Circuit Switching

In today's high-speed/high-density very large scale integrated (VLSI) circuit designs with coupled interconnect lines, signal transients are strongly correlated with the input switching patterns. Signal-delay variations due to the input-switching patterns may be more than /spl plusmn/50% of the delay of an isolated single line. Thus, blind static timing-analysis techniques without consideration of the detailed switching effects may not be accurate enough to meet tight timing margins for today's deep submicron (DSM)-based VLSI circuits. In this paper, the signal-transient responses of multicoupled interconnect lines due to various input-switching patterns are analyzed in terms of the effective capacitances and effective inductances. Thereby, the critical delay line of multicoupled interconnect lines is decoupled into an effective single-isolated line. With the proposed novel decoupling technique for multicoupled interconnect lines, the accurate dynamic delay of strongly coupled interconnect lines can be readily determined with physical layout information. For example, in switching patterns, the paper shows that the signal delays calculated by using the effective single-line models have excellent agreement with SPICE simulations using the generic coupled interconnect circuit models. That is, the accuracy for both RC-dominant lines and RLC lines is within 10% error (but often within 5% error). Thus, without any significant modification of existing IC computer-aided design frameworks, the technique can be directly as well as usefully employed for accurate timing verification of DSM-based VLSI designs.

Effective on-chip inductance modeling for multiple signal lines and application to repeater insertion

/sup A/ new approach to handle inductance effects for multiple signal lines is presented. The worst-case switching pattern is first identified. Then a numerical approach is used to model the effective loop inductance (L/sub eff/) for multiple lines. Based on a look-up table for L/sub eff/, an equivalent single line model can be generated to decouple a specific signal line from the others to perform static timing analysis. Compared to the use of full RLC netlists for multiple lines, this approach greatly improves the computational efficiency and maintains accuracy for timing and signal integrity analysis. We apply these models to repeater insertion in critical paths and find that, for a single line, the RLC model minimizes delay with fewer number of repeaters than RC model. However, for multiple lines, we find that same number of repeaters is inserted for optimal delay according to both the RC and RLC models.

The Hunt for Party Discipline in Congress

We analyze party discipline in the House of Representatives between 1947 and 1998. The effects of party pressures can be represented in a spatial model by allowing each party to have its own cutting line on roll call votes. Adding a second cutting line makes, at best, a marginal improvement over the standard single-line model. Analysis of legislators who switch parties shows, however, that party discipline is manifest in the location of the legislator's ideal point. In contrast to our approach, we find that the Snyder-Groseclose method of estimating the influence of party discipline is biased toward exaggerating party effects.

Scotopic sensitivity during adulthood

Older adults typically exhibit about a half log unit loss in scotopic sensitivity that cannot be attributed to optical factors and retinal disease suggesting a neural origin. Little is understood about the developmental course of this neural deficit as to whether it first appears in late life or gradually emerges during the course of adulthood. To address this developmental issue, scotopic sensitivity was measured in 94 adults ranging in age from the 20s to the 80s. Thresholds were measured at 27 test loci within a 18° radius field. Analogous measurements were made for photopic sensitivity. Fundus photography and a grading scale were used to characterize macular health in subjects over age 49 in order to control for macular disease. Scotopic sensitivity decreased at a rate of 0.08 log units per decade; this decline was better fit by a single line model, not a bilinear model, implying that the impairment does not suddenly emerge in late life but gradually appears over the course of adulthood. Photopic sensitivity also decreased in a linear fashion at a rate of 0.04 log units per decade. Under these test conditions, the rate of scotopic sensitivity decline during adulthood was about double the rate of photopic sensitivity decline.

The Hunt for Party Discipline in Congress

This paper analyzes party discipline in the House of Representatives between 1947 and 1998. The effects of party pressures can be represented in a spatial model by allowing each party to have its own cutting line on roll call votes. Adding a second cutting line makes, at best, a marginal improvement over the standard, single-line model. Analysis of legislators who switch parties shows, however, that party discipline is manifest in the location of the legislator's ideal point. In contrast to our approach, we find that the Snyder-Groseclose method of estimating the influence of party discipline is biased toward exaggerating party effects.

Optimal capacitor placement in distribution networks

This paper deals with the voltage stability problem associated with radial distribution networks. Two load models are studied: the full load flow model (FLFM) and the equivalent generic single-line model (EGSLM). Optimization is then carried out to find the optimal capacitor size that minimizes some costing function, and finally several capacitor placement techniques are studied.

Gain models for source-flow chemical lasers

Four gain models are developed for use in analyzing source-flow chemical laser resonators. The first is a rotational nonequilibrium (RNE) model which traces the evolution of each vibrational-rotational state of the lasing molecule. The second is a less detailed model based on the assumption that each vibrational level is in rotational equilibrium (RE). In the third model, in addition to the rotational equilibrium assumption, the gain is assumed to be the same for all the vibrational transitions. The equations then become identical in form to those describing single-line (SL) lasing from a two-level system. The RE and RNE models solve the chemical kinetics equations for the gain self-consistently with the gasdynamic equations describing the flow field. In the SL model coupling between the gasdynamics and the laser kinetics is eliminated by using the gasdynamics from a simple Fabry–Perot calculation at a representative value of the threshold gain to provide the flow field conditions for the resonator calculation. A fourth gain model investigates the effect of using the gasdynamic calculation from the simpler SL model in a rotational nonequilibrium kinetics model. The objectives of the study are to determine how well the more computationally efficient RE and SL models can reproduce the predictions of the RNE model, and to determine the error introduced by decoupling the solutions to the gasdynamic and laser kinetic equations. The impact of rotational nonequilibrium phenomena on lasing performance is also assessed. Comparisons for the specific case of a HF laser indicate that both the RE and SL models predict output powers and peak-power mode widths which are in good agreement with those predicted by the RNE model over a wide range of values for the resonator gain. Furthermore, the RE model well approximates the power distribution among the vibrational levels, although only the RNE model is capable of providing detailed spectral information. We also find that decoupling the gasdynamic and kinetic equations does not significantly impact the accuracy of the resonator calculation. The utility of the more computationally efficient models in the design of source-flow chemical laser resonators is discussed.