Nodal Analysis Research Articles

MONA—A magnetic oriented nodal analysis for electric circuits

AbstractThe modified nodal analysis (MNA) is probably the most widely used formulation for the modeling and simulation of electric circuits. Its conventional form uses electric node potentials and currents across inductors and voltage sources as unknowns, thus taking an electric viewpoint. In this paper, we propose an alternative magnetic oriented nodal analysis (MONA) for electric circuits, which is based on magnetic node potentials and charges across capacitors and voltage sources as the primary degrees of freedom, thus giving direct access to these quantities. The resulting system has the structure of a generalized gradient system which immediately ensures passivity in the absence of sources. A complete index analysis is presented showing regularity of the magnetic oriented formulation under standard topological conditions on the network interconnection. In comparison to conventional MNA, the differential‐algebraic index of MONA is smaller by one in most cases which facilitates the numerical solution. Some preliminary numerical experiments are presented for illustration of the feasibility and stability of the new approach.

INFLUENCE OF THE SAND PRODUCTION ON THE WELL DRAINAGE AREA

INFLUENCE OF THE SAND PRODUCTION ON THE WELL DRAINAGE AREA

Remote river energy system: an open-source low-maintenance turbine design for remote areas

Axial flow hydro-kinetic turbines convert the kinetic energy of a flowing fluid into electrical energy, and can be designed for deployment in a wide range of locations. As relatively recent technology, these designs are often high in cost, complex and require specialist maintenance and materials. This is not viable for many communities in developing countries, which may subsequently remain reliant on fossil fuels. A remote river energy system has been designed to be built and maintained using minimal equipment, with components that can be readily obtained. A formal design process has been used with design review and feedback stages; design tools included Simulink modelling, finite-element analysis, computational fluid dynamics, nodal analysis and flume testing. A handful of components such as the turbine blades require specialist machining and maintenance. Results demonstrate how an effective water turbine with a 3 kW output can be theoretically produced and maintained without an over-reliance on specialised components and tools, thereby producing a more economically viable water turbine for use in developing countries. Open-source distribution of the design drawings will facilitate application of the design and improvements by other stakeholders. The design study presented is a platform for prototype technology trials to further develop the concept.

Connectomic analysis of Alzheimer's disease using percolation theory.

Alzheimer's disease (AD) is a severe neurodegenerative disorder that affects a growing worldwide elderly population. Identification of brain functional biomarkers is expected to help determine preclinical stages for targeted mechanistic studies and development of therapeutic interventions to deter disease progression. Connectomic analysis, a graph theory-based methodology used in the analysis of brain-derived connectivity matrices was used in conjunction with percolation theory targeted attack model to investigate the network effects of AD-related amyloid deposition. We used matrices derived from resting-state functional magnetic resonance imaging collected on mice with extracellular amyloidosis (TgCRND8 mice, n = 17) and control littermates (n = 17). Global, nodal, spatial, and percolation-based analysis was performed comparing AD and control mice. These data indicate a short-term compensatory response to neurodegeneration in the AD brain via a strongly connected core network with highly vulnerable or disconnected hubs. Targeted attacks demonstrated a greater vulnerability of AD brains to all types of attacks and identified progression models to mimic AD brain functional connectivity through betweenness centrality and collective influence metrics. Furthermore, both spatial analysis and percolation theory identified a key disconnect between the anterior brain of the AD mice to the rest of the brain network.

STAGES NUMBER SENSITIVITY IN ESP DESIGN ON DIRECTIONAL WELL "X" SALAWATI FIELD

An Onshore Well “X” of the JOB Pertamina-Petrochina field is a directional well. This particular well has ESP as the artificial lift to deliver the production fluid to the surface. Due to the “off downhole”, oil production had been suspended since 2012. However recently, the well will be activated and the pump will be modified into the new one. The purpose of this modification is to find the most suitable and effective pump with the optimum number of installed stages on the ESP. This ESP design is started by nodal system analysis which correlates Inflow Performance Relationship (IPR) to Intake Pump Pressure. The calculation using the Pudjo Soekarno equation results in a maximum flow rate in this well is 446,33 BPD. The flow rate is targeted at 65% of the maximum flow rate. Therefore, ESP series 319 NBV 250-500/60 Hz is chosen considering the operating range around 231-416 BPD which in this case is inside the range. The pump will be installed at 8500 ft depth. The number of stages based on calculation is 270 stages capable to lift 300 barrels of fluid per day. This flow rate approximately meets the targeted flow rate, furthermore, the pump will be at 47,9% of its Best Efficiency (BEP) during the operation. With this result, the pump is considered able to operate efficiently and durably.

Non-Inferiority Margin and Nodal Analysis of De-Escalated Adjuvant Radiation Therapy (DART) for HPV-Related Oropharyngeal Squamous Cell Carcinoma (OPSCC): A Preplanned Pooled Analysis of MC1273 & MC1675

<h3>Purpose/Objective(s)</h3> We previously reported the results of phase II/III trials (MC1273 & MC1675) evaluating 30-36 Gy of adjuvant radiation therapy for patients with HPV+ OPSCC. Herein we report the results of a pre-planned pooled analysis of MC1273/MC1675 designed to test whether the pooled PFS was statistically non-inferior to the PFS target of NRG HN005. <h3>Materials/Methods</h3> Pts who received DART on MC1675, or pts on MC1273 who fit MC1675 criteria were included in this analysis. All pts underwent margin clearing surgery and neck dissection. Pts with pT4 disease or required >2 attempts to clear margins were excluded. Pts with intermediate risk factors received 30 Gy/1.5 Gy b.i.d. + docetaxel 15 mg/m2 days 1 & 8, while pts with extranodal extension (ENE) simultaneously received 36 Gy/1.8 Gy b.i.d. to ENE+ nodal levels. A pooled analysis was performed on LRC, PFS, and OS using survivorship methodology, including Kaplan-Meier estimation. Pooled 2-yr PFS for the total cohort and subgroups were compared with the PFS non-inferiority margin for HN005 (86.9-92.3%). Cox proportional hazards regression analysis was performed to evaluate the effect of nodal and ENE status on survival outcomes. OS, PFS and LRC were evaluated using Chi-square tests. <h3>Results</h3> Accrual at Mayo Clinic Rochester and Arizona was from 2013 – 2020: MC1273: 72 pts, MC1675/DART: 130 pts, 202 total.) Median follow-up as of 10/21 was 36.6 months. 2 year estimates and 95% CI of OS, LRC, PFS for de-escalated pts can be found in Table 1. The hazard ratios (HR) for ENE status was OS 2.07 (p=0.39); LRC undefined (p=0.99); PFS 3.95 (p=0.015). HR for AJCC 8 pN2 was OS 5.78 (p=0.014), LRC 2.29 (p=0.23), PFS 4.11 (p=0.001). <h3>Conclusion</h3> Pooled PFS for MC1273/1675 (91.1%) was non-inferior to the target PFS for HN005 (92.3%, p = 0.29), and was also significantly above the HN005 acceptable PFS threshold of 86.9% (p=0.043). All ENE/pN subgroups also had PFS significantly above the 86.9% threshold except for the ENE+/pN2 cohort. On multivariate analysis, nodal status was a stronger predictor of OS than ENE. Analyses for extent of ENE and AJCC 7 N stage will be available for the meeting.

Parareal for index two differential algebraic equations

This article proposes modifications of the Parareal algorithm for its application to higher index differential algebraic equations (DAEs). It is based on the idea of applying the algorithm to only the differential components of the equation and the computation of corresponding consistent initial conditions later on. For differential algebraic equations with a special structure as, e.g. given in flux-charge modified nodal analysis, it is shown that the usage of the implicit Euler method as a time integrator suffices for the Parareal algorithm to converge. Both versions of the Parareal method are applied to numerical examples of nonlinear index 2 differential algebraic equations.

A Nodal Analysis Based Monitoring of an Electric Submersible Pump Operation in Multiphase Flow

Electrical submersible pump (ESP) operation is compromised by free gas, resulting in premature pump failure and production losses in new wells. It is essential to detect the onset of abnormal operations. We develop a model that predicts abnormal ESP operation when the free gas level increases in the pump. The model compares operation parameters with the parameters of normal operating ranges; it shuts down the ESP when necessary. We used a Schlumberger PIPESIM software (version 2017.01) to perform nodal analysis technique; we tested the model using the other multiphase correlation model and field case studies (where the gas problem in ESP was reported). We employ a homogenous model to calculate the differential pump pressures at various gas volume fractions. Nodal analysis of the intake and discharge point predicted the commencement of abnormal ESP conditions and the associated parameters (critical gas fraction, minimum operating pump intake pressure, and pump discharge pressure). The model results were similar to other surging correlation models (e.g., Romero, Dunbar, Turpin, Cirilo, and Zhou models); they were also identical to field case studies. We identify three performance stability phases when an ESP is exposed to free gas. These are the normal and abnormal operating ranges, as well as the ESP shutdown condition. Modeling permits careful monitoring of ESP operations that can be compromised by free gas.

Identification of Weak Buses for Optimal Load Shedding Using Differential Evolution

For the sustainability of power supply and operation systems, planners aim to deliver power at an optimum value to consumers, while maintaining stability in the system. The load-shedding approach has proven to be an effective means of achieving the desired stability. This paper presents a nodal analysis to establish critical bus identification in the power grid. A power simulation for load shedding was created using the power system analysis toolbox (PSAT) for identifying and isolating weak buses on the power system. A computational algorithm was developed using differential evolution (DE) for minimizing service interruptions and blackouts, and was tested against the conventional genetic algorithm (GA). The proposed algorithm was implemented on an IEEE 30-bus test system. The simulation results were analyzed before and after the application of DE. It was observed that after the application of DE, load shedding gives an efficient result of 10.6%, 8.7%, and 13.4% improvement at buses 26, 29, and 30, respectively, after being tested using a genetic algorithm (GA), with a result of 10.2%, 7.6% and 13.1% on the same respective buses. This work will further expand the reliability and availability of power systems toward a sustainable, steady power supply that is void of nodal or bus cutoffs.

Modeling and Compensation of IR Drop in Crosspoint Accelerators of Neural Networks

In-memory computing (IMC) has the potential of accelerating data-intensive computing tasks, such as inference and training of neural networks, by the matrix vector multiplication (MVM) in the crosspoint array. As the array size increases, however, a significant problem arises due to the parasitic IR drop at row and column lines. Understanding and compensating IR drop is essential to enable high-density accelerators of MVM. This work presents an analytical model for the IR drop and a numerical algorithm capable of accelerating the nodal analysis of crosspoint arrays up to five orders of magnitude with respect to SPICE analysis. The numerical algorithm is used to study the impact of array size, data density, device/wire resistance, and nonlinearity on the IR drop and the related loss of accuracy in IMC. We also derive two simple compensation schemes and an architectural solution for the mitigation of IR drop that are able to increase the accuracy of neural networks from 59&#x0025; up to 96.6&#x0025;, compared to an ideal accuracy of 97&#x0025;.

Lcapy: symbolic linear circuit analysis with Python.

Lcapy is an open-source Python package for solving linear circuits symbolically. It uses a superposition of DC analysis, AC (phasor) analysis, transient (Laplace) analysis, and noise analysis. Expressions are evaluated using the computer algebra system SymPy. Lcapy can model circuits comprised of combinations of one-port and two-port networks or circuits specified using a netlist with a Spice-like notation. Lcapy can present the system of equations produced from nodal analysis, modified nodal analysis, loop analysis, and state-space analysis. Expressions can be formatted into many representations, parameterized, and transformed to other domains. Dimensional analysis is performed to reduce user errors and to present results with units. Both continuous and discrete signals are supported. Lcapy produces high-quality output. Textbook quality schematics in a number of different formats can be generated from netlists and customized for different conventions. Expressions can be formatted into LaTeX format for inclusion into a document or numerically evaluated and plotted. An overview of the features and capabilities of Lcapy is presented, along with implementation details and performance considerations.

Steady state solution of NFC model with nonlinear load using PEEC

PurposeThe purpose of this paper is to show that the computation of time-periodic signals for coupled antenna-circuit problems can be substantially accelerated by means of the single shooting method. This allows an efficient analysis of nonlinearly loaded coupled loop antennas for near field communication (NFC) applications.Design/methodology/approachFor the modelling of electrically small coupled field-circuit problems, the partial element equivalent circuit (PEEC) method shows to be very efficient. For analysing the circuit-like description of the coupled problem, this paper developed a generalised modified nodal analysis (MNA) and applied it to specific NFC problems.FindingsIt is shown that the periodic steady state (PSS) solution of the resulting differential-algebraic system can be computed very time efficiently by the single shooting method. A speedup of roughly 114 to conventional transient approaches can be achieved.Practical implicationsThe proposed approach appears to be an efficient alternative for the computation of time PSS solutions for nonlinear circuit problems coupled with discretised conductive structures, where the homogeneous solution is not of interest.Originality/valueThe present paper explores the implementation and application of the shooting method for nonlinearly loaded coupled antenna-circuit problems based on the PEEC method and shows the efficiency of this approach.

Production Optimization of an Eruptive Well by Using Nodal Analysis

The objective of this paper is to optimize the eruptive well X-1 of field X so that it achieves an economically profitable production rate in order to be able to increase income. The completion data, pressure-volume-temperature (PVT) data and reservoir data are used to improve the production of the well X-1 by using the nodal analysis and PIPESIM software. Several optimization scenarios are considered by varying: The diameter of the tubing, the wellhead pressure, the diameter of the flow line and the water cut. The main results show that reducing the wellhead pressure from 350 to 100 psia and increasing the flowline diameter from 2.5 to 4 inches improve the production flow rate from 850 to 2030.472 bbl /d. In economic terms, this well gives the payback period after 1 year and 9 months and a net present value (NPV) of 193,546,524 $ after 8 years.

THE INFLUENCE OF THE PERFORATION DENSITY AND DAMAGED ZONE PERMEABILITY ON A GAS WELL PRODUCTION

The exploitation of wellbore condensate deposits must be carried out in such a way that both water and condensate from the productive layer are not entrained during extraction. That is precisely why the article analyzes the effect of the density of perforations of the productive layer on the amount of extracted gas. The effect of the area affected by the drilling on the produced gas flow is also studied. After 50 years since the first use of the mechanical realization of the perforations of the productive layers of the gas wells, there is little data regarding the influence of the perforation geometry of a gas well, namely the way of communication between the production layer and the borehole, on its production. The aim of this paper is to simulate the operation of the well for different values specific to the drilling mode, highlighting its production. The problem is addressed by nodal analysis. The numerical simulators were used to simulate the flow of the mixture through the layer-well system and respectively through the mixture pipe.

Frequency-Domain Stability Criteria for Converter-Based Power Systems

Frequency-domain stability criteria are developed for converter-based power systems with any number of converters. The converters may be grid following or grid forming, and the grid can be an ac or hybrid ac-dc network. The converters and the network are all modeled in a common (stationary) reference frame based on small-signal sequence immittances. Coupling over frequency and ac-dc coupling are considered in the most general form. For each type of systems, a frequency-domain model is developed first by nodal analysis and then reformulated to fit the form of a feedback loop with open-loop stability guaranteed by practical conditions. System stability is then determined by a Nyquist-like criterion without the need to check open-loop right-half-plane poles. Further simplification of the system models is made possible by a) generalized <inline-formula><tex-math notation="LaTeX">$n$</tex-math></inline-formula>-port equivalent circuits that include both types of coupling, b) equivalence of stability at internal and external nodes, and c) relationship between dynamics at the perturbation and the coupling frequency. Reduction of a system model into separate single-input-single-output models is presented for several special systems along with their practical applications. Quantitative and experimental results are presented to verify the developed theories.

Activation of a non-eruptive well by using gas lift method and step-up of its productivity: sensitivity and economical analysis

This paper aims to design a gas lift that not only activates a non-eruptive well but also and above all, optimises the recovery of hydrocarbons at the surface while using a very less and limited gas quantity per day. The data are reservoir data, fluid data, well architecture properties, and also injection targets. To achieve the objective, it is necessary to carry out a nodal analysis of the non-eruptive well, and design the gas lift system by finding the gas injection pressure in the well, the number of valves, the optimal heights of injection, and the flow rates received by each valve. The evaluation of the system performance, as well as the sensitivity analysis, allows the selection of an optimal production rate. All the simulation operations and the well diagram are carried out with PIPESIM 2017.1. The results obtained show for the continuous injection of gas at 0.73 and 0.23 mmscf/d respectively. For valves 1 and 2 in the well, i.e., 1 mmscf/d for the two valves and using pressure at the head of the well of 100 psia, an optimal flow rate of 262.9 STB/d can be produced and the payback period is one year and two months.

Extending the Frequency Bandwidth of Transient Stability Simulation Using Dynamic Phasors

This paper presents a novel approach to dynamic phasor-based transient stability simulation. The proposed method is based on the modified nodal analysis (MNA) approach to circuit simulation, which is used to construct continuous differential-algebraic equations (DAEs). The proposed method makes use of the stamp technique, which makes it possible to construct a general purpose MNA-based simulator. Stamp-based models for common power system components are derived in this work. A new MNA-based synchronous machine model is presented, which represents machines as nonlinear inductances instead of subtransient equivalents. The resultant continuous DAEs are numerically solved using the general purpose variable step and variable order library IDA. Simulation results from the IEEE 68 bus test system, a real 400 bus power system, and the IEEE 39 bus test system with an embedded HVdc transmission system demonstrate that the proposed method is suitable for large ac networks with power electronic devices. The results demonstrate good agreement between the proposed method and electromagnetic transient (EMT) simulation. The results also demonstrate that the proposed method is fast and scalable with CPU times that are up to 200 times faster than EMT simulation.

Hybrid Electrical-Submersible-Pump/Gas-Lift Application to Improve Heavy Oil Production: From System Design to Field Optimization

AbstractThe typical challenge encountered in developing heavy-oil reservoirs is inefficient wellbore lifting caused by complex multiphase flows. The literature on modeling of a hybrid artificial-lift (AL) system is relatively sparse and these works typically model the AL system on the basis of individual AL methods. This paper presents a case study of the design and optimization of a hybrid AL system to improve heavy-oil production. We systematically design and model a hybrid electrical-submersible-pump/gas-lift (ESP/GL) system to enhance wellbore lifting and production optimization. We found that the implementation of a hybrid ESP/GL system provides the flexibility to boost production and reduces production downtime. Results from the pilot test show that the production rate in hybrid mode are approximately 30% higher than in ESP-only mode. The power consumption of the hybrid mode is 3% lower in the ESP-only mode. Additionally, the average ESP service life exceeds 6 years which is better than expected in the field development plan. The pump-performance-curve model is built with corrections for density and viscosity owing to the increased water production. We observed a higher pressure drawdown with GL injection at fixed ESP frequency. The GL injection reduces the density of the fluid column above the ESP, resulting in less pressure loss across the pump, less power consumption, and potentially extended service life. The nodal analysis results suggest that the pump capacity can be considerably expanded by manipulating the GL rate instead of increasing the frequency.

Whole-body diffusion-weighted MRI of normal lymph nodes: prospective apparent diffusion coefficient histogram and nodal distribution analysis in a healthy cohort

BackgroundWhole body DWI (WB-DWI) enables the identification of lymph nodes for disease evaluation. However, quantitative data of benign lymph nodes across the body are lacking to allow meaningful comparison of diseased states. We evaluated apparent diffusion coefficient (ADC) histogram parameters of all visible lymph nodes in healthy volunteers on WB-DWI and compared differences in nodal ADC values between anatomical regions.MethodsWB-DWI was performed on a 1.5 T MR system in 20 healthy volunteers (7 female, 13 male, mean age 35 years). The b900 images were evaluated by two radiologists and all visible nodes from the neck to groin areas were segmented and individual nodal median ADC recorded. All segmented nodes in a patient were summated to generate the total nodal volume. Descriptors of the global ADC histogram, derived from individual node median ADCs, including mean, median, skewness and kurtosis were obtained for the global volume and each nodal region per patient. ADC values between nodal regions were compared using one-way ANOVA with Bonferroni post hoc tests and a p-value ≤0.05 was deemed statistically significant.ResultsOne thousand sixty-seven lymph nodes were analyzed. The global mean and median ADC of all lymph nodes were 1.12 ± 0.27 (10− 3 mm2/s) and 1.09 (10− 3 mm2/s). The average median ADC skewness was 0.25 ± 0.02 and average median ADC kurtosis was 0.34 ± 0.04. The ADC values of intrathoracic, portal and retroperitoneal nodes were significantly higher (1.53 × 10− 3, 1.75 × 10− 3 and 1.58 × 10− 3 mm2/s respectively) than in other regions. Intrathoracic, portal and mesenteric nodes were relatively uncommon, accounting for only 3% of the total nodes segmented.ConclusionsThe global mean and median ADC of all lymph nodes were 1.12 ± 0.27 (10− 3 mm2/s) and 1.09 (10− 3 mm2/s). Intrathoracic, portal and retroperitoneal nodes display significantly higher ADCs. Normal intrathoracic, portal and mesenteric nodes are infrequently visualized on WB-DWI of healthy individuals.Trial registrationRoyal Marsden Hospital committee for clinical research registration number 09/H0801/86, 19.10.2009.

Production optimization of a network of multiple wells with each well using a combination of Electrical Submersible Pump and Gas lift

Artificial lift methods such as ESP and GL are commonly used in oil wells around the world, especially in offshore wells. However, these two methods are normally used separately, and this paper therefore aimed to study the possible combination of ESP and GL by analyzing its effects on energy saving using equivalent depth method and on production rate as well as on ESP life cycle using nodal analysis. The paper also performed the production optimization for a network of wells using each well a combination of GL and ESP. The optimization process consists of selecting the appropriate operation frequency for the ESP system and the injection gas lift distributed to each well with the aim of maximizing the total production of the network. In addition, this optimization process was conducted in two cases: unlimited and limited volume of injection gas lift. In case the GL flow is limited, the BST (Binary Search Tree) algorithm was used to determine the suitable gas rates injected into each well to maximize the total network production. The optimization workflow proposed in this study was applied to the field X in Cuu Long basin of Vietnam and was calibrated from the real data of this field. The results demonstrated the advantage of the combination of ESP and GL in energy saving and in application for small diameter wells. In addition, the workflow and source code will allow engineers to replicate the results and to apply this method for future studies in order to determine optimum operating parameters of this hybrid artificial lift to achieve the highest production rate from a network of multiple wells.