The memristor has long been presented as the fourth fundamental circuit element alongside the resistor, the capacitor, and the inductor. As the future of computing heads toward neuromorphic circuits, ...there has been a renewed interest in the modeling and simulation of memristors which have emerged as promising key components in the design of these systems. Despite such critical applications, very few models have been presented in the literature that allow for the automated and flexible integration of memristors in different simulators. In this article, three different models of the memristor are presented using the modified nodal analysis (MNA) formulation technique. Each stamp is tested and compared with a theoretical model of the memristor. Simulations are also performed on a memristor-based active high-pass filter circuit to demonstrate the accuracy of the model.
Petrolün yaygın biçimde enerji kaynağı olarak kullanımı iklim değişikliği, çevre ve atmosfer kirlenmesi, canlı varlıkların yaşam koşullarının yok olması gibi bir takım olumsuz gelişmeleri ...doğurmuştur. Bu olumsuz gelişmelerin önüne geçilebilmesi için güneş enerjisi, nükleer enerji ve jeotermal enerji gibi temiz ve tükenmez enerjilerin kullanımının yaygınlaştırılması gerekmektedir. Bu enerjilerin kullanımının yaygınlaştırılabilmesi için her türlü ısıyı mekanik enerjiye dönüştürebilen bir makinenin geliştirilmesi gerekmektedir. Bu amaçla geliştirilmeye çalışılan makinelerden birisi de Stirling motorlarıdır. Stirling motorları hâlihazırda endüstriyel boyutta kullanılan bir makine olmamakla birlikte, üzerinde en çok araştırma yapılan enerji dönüşüm makinelerinden birisidir. Bu araştırmada, krank kaydırma esasına göre çalışan alfa tipi bir Stirling motorunun termodinamik performansı; iş akışkanı olan Helyumun kütlesi, silindirlerin uzunluğu, krank kaydırmanın miktarı, silindirlerin rölatif konumu, biyellerin uzunlukları ve ısıtıcı sıcaklığına bağlı olarak incelenmiştir. Yapılan incelemede kullanılan matematik model; kinematik ilişkiler, termodinamiğin birinci kanunu, ideal gazların hal denklemi, kütlenin korunumu yasası ve Schmidt formülünden oluşmaktadır. Helyum kütlesi 3,5 g, ısıtıcı sıcaklığı 800 K, silindir tepesi ile krank merkezi arasındaki uzaklık 328,5 mm, biyel uzunluğu 171 mm ve krank kaçıklığı 40 mm olarak atandığında; iş 223 J, ortalama basınç 24,9 bar, motor gücü 3,55 kW ve ısıl verim %52 olarak belirlenmiştir.
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In this first time effort, we developed a multiscale coupled electromechanical model capable of computing the piezoresistive properties of carbon nanotube (CNT)-reinforced composites. ...Monte-Carlo based algorithm was used to generate representative volume elements (RVEs) randomly filled with CNTs surrounded by the polymer matrix. The coupling between the applied mechanical load and the resulting electrical response was treated in a sequential manner in two steps. Firstly, a three-dimensional finite element model of the RVE was developed to determine the structural response of the nanocomposite system under different loading conditions. The results of the finite element model were then used to update the locations of the CNTs in the deformed RVE. Secondly, an electrical model based on the modified nodal analysis technique was developed to calculate the corresponding electrical conductivity of the nanocomposite. The developed model was successfully used to determine the piezoresistive behavior of CNT-epoxy composite under tension, compression, and shear loads. The results show that the composite gauge factor can reach up to 3.95 and is sensitive to the loading direction and CNT volume fraction. The predictions of the current model are in good agreement with the experimental findings of earlier studies, verifying its validity.
It is well known in the power system community that frequency is not a global variable during transients. The previously proposed frequency divider (FD) is a valid approach to estimate load bus ...frequencies in large transmission networks wherein the load dynamics are typically ignored. In converter-driven grids, load dynamics may have a significant impact on the local frequency dynamics. This article determines that the FD has low accuracy under such conditions. This paper proposes a centralized dynamic phasor estimator (DPE) to track the frequency of the load buses and additionally estimate the branch current phasors and load bus voltage phasors. The key idea is to formulate the power system state-space model in the dynamic phasor domain such that grid-forming converter (GFC) bus voltage phasors and load power measurements are inputs and the load bus voltage and branch current phasors as states. The dynamic phasor of the GFC bus voltage is calculated by measuring the terminal voltage of the GFC bus and the internal frequency available within the droop-control loop of the GFC. A complex-PLL (C-PLL) is proposed to track the rotation of the load bus voltage phasors to estimate the actual frequency at the load buses. Numerical simulations are carried out on the modified WSCC 9-bus system and the IEEE 39-bus system to demonstrate the effectiveness of the proposed method.
Modular multilevel converters (MMC) are an effective option for the continuously growing demands of voltage-sourced converter-based high-voltage direct-current (VSC-HVDC) transmission. However, ...accurate modeling of MMC with a high level in PSCAD/EMTDC is extremely time-consuming and requires hardware. Based on the Kirchhoff's Law, an equivalent accelerated model for MMC is proposed. The essence of the new model is the partition of one large-scale admittance matrix into substantial small-scale matrices, which is mathematically demonstrated with the nodal analysis method. Finally, the detailed electromagnetic transient simulations are implemented for the comparisons of steady state and transient performances, and the results validate the proposed model.
•Approximated power flow algorithm to radial islanded DC microgrids.•Iterative power flow algorithm to radial islanded DC microgrids.•Iterative power flow algorithm to meshed islanded DC ...microgrids.•Proposed methods have high accuracy and low CPU time.
The main approach used to model uncertainties in microgrid planning is the Probabilistic Power Flow (PPF). However, this technique has a high computational cost due to the need to solve a system of nonlinear equations for different scenarios of microgrid operation. This paper aims to propose low-cost computational power flow algorithms to evaluate nodal voltages in islanded Direct Current (DC) microgrids under uncertainty. An approximated power flow is proposed based on the Admittance Summation Method for radial microgrids. In addition, iterative power flow algorithms, previously developed by the authors for Alternating Current (AC) microgrids, have been adapted for DC microgrids. The proposed iterative and approximated algorithms were combined with Monte Carlo Simulation to obtain a PPF method. The proposed methods were tested and validated in relation to the Newton-Raphson Method in DC radial microgrids with 33 and 906 nodes and in DC meshed microgrids with 33 e 144 nodes. The results showed that the developed methods have good accuracy and obtain considerable saving in the computational cost of the PPF.
This article presents a parallel-in-time adjoint sensitivity analysis which combines a transient adjoint sensitivity analysis with the parareal approach to significantly speed up the simulation. The ...adjoint method is the method of choice to calculate the sensitivities in a many-parameter setting. To obtain sensitivity information that is time-dependent, multiple adjoint problems must be solved. This slows down the simulation wall-clock time and leaves a large optimization potential for the analysis. The parareal is applied to the adjoint solution, significantly speeding up the adjoint solution for every timestep, respectively.
We present a systematic treatment of reciprocity and inter-reciprocity in linear electrical networks, without resorting to the use of Tellegen's theorem. In Part I, we discuss linear time-invariant ...networks. In Part II, we expand the applications of our approach to linear periodically time-varying (LPTV) networks.
Currently, most of the wells in X Oilfield are self-flowing wells. In order to adjust the production system of oil wells in time according to the production requirements of oilfields, it is necessary ...to predict the ceasing–flowing time. Therefore, how to accurately predict the ceasing–flowing time is the main problem faced by the self-flowing well. As the conventional prediction methods only consider the influence of a single variable, the prediction results are not ideal. Combining the production prediction based on the long short-term memory (LSTM) neural network and the inflow and outflow dynamic curves, this study proposes a comprehensive method for predicting the ceasing–flowing time of a flowing well by considering multiple factors. Using the minimum wellhead pressure prediction method, the changes in bottom hole flowing pressure and reservoir pressure are also considered. The practical application results in X Oilfield show that the calculated and predicted results are highly consistent with the actual production data, verifying the reliability of this method. This study can provide a reference for the prediction of oil well ceasing–flowing in other oilfields.
