Transient Behavior Research Articles

Interwell interference model of horizontal wells in shale gas reservoirs based on multi-connected boundary element method

Due to the wide application of closely spaced multi-well horizontal pads for developing unconventional gas reservoirs, interference between wells becomes a significant concern. Communication between wells mainly occurs through natural fractures. However, previous studies have found that interwell communication through natural fractures is varied, and non-communication also appears in the mid and late stages of production due to natural fracture closure. This study proposes a boundary element method for coupling multi-connected regions for the first time. Using this method, we coupled multiple flow fields to establish dual-well models with various connectivity conditions of the stimulated reservoir volume (SRV) region. These models also take into consideration of adsorption and desorption mechanism of natural gas as well as the impact of fracturing fluid retention.The study found that when considering the non-communication of SRV regions between multi-well horizontal pads, the transient behavior of the targeted well exhibits a transitional flow stage occurring before the well interference flow stage. In addition, sensitivity analysis shows that the well spacing and production regime, as well as the connectivity conditions of the SRV region, affect the timing of interwell interference. Meanwhile, the productivity of the two wells, reservoir properties, and fracturing operations affect the intensity of interwell interference.

First evidence of white sharks, Carcharodon carcharias, in the tongue of the ocean, central Bahamas

The white shark, Carcharodon carcharias, is an iconic apex predator, playing an important ecological role across its range. Persistent bycatch and overfishing led to white shark declines, but recent studies in the North Western Atlantic (NWA) revealed evidence for regional recovery, and highlighted the importance of Southeastern Florida and the Gulf of Mexico as overwintering grounds for maturing white sharks. However, despite its proximity to Florida and comparably productive habitats, records of white sharks in The Bahamas are extremely rare, with a comprehensive survey of sightings and captures describing only one white shark between 1800 - 2010. Here, we reveal acoustic tracking detections of ten white sharks from 2020 - 2024 along the western edge of the Tongue of the Ocean off Central Andros Island, The Bahamas. White sharks were originally tagged off the coast of the United States and Canada, and detected off Andros Island, The Bahamas from November-May. White sharks were detected along the drop-off zone of the reef at ca. 25 m, exclusively between dusk and dawn, with the number of detections suggesting transient behavior. These findings expand our knowledge of white shark distribution in the NWA, highlighting data gaps in The Bahamas and underlining the importance of collaborative protective measures for species recovery.

Threshold Inverter Quantizer-Based 2-Bit Comparator using Spatial Wavefunction Switched (SWS) FET Inverters: Power Dissipation Analysis

This paper aims to assess the power dissipation of a threshold quantizer (TIQ) 2-bit-based comparator using a SWS-FET-based inverter [1, 2, 4, 5]. Unlike conventional comparators, SWS-based comparator functionalized with TIQ comprises two or more vertically stacked quantum dots or well channels [1-3, 5, 6]. Herein, power dissipation analysis of the simulated circuit is carried out using Cadence by integrating the Berkeley Short-Channel IGFET Model (BSIM) and the analog behavioral model (ABM) [1,3,4,9]. The transient behavior of the inverter circuit is evaluated using 180 nm technology node. Our results demonstrated a significant reduction in power dissipation which overcome the limitation of previous 4-state logic implementations.

Physics-informed neural networks for phase locked loop transient stability assessment

A significant increase in renewable energy production is necessary to achieve the UN’s net-zero emission targets for 2050. Using power-electronic controllers, such as Phase Locked Loops (PLLs), to keep grid-tied renewable resources in synchronism with the grid can cause fast transient behavior during grid faults leading to instability. However, assessing all the probable scenarios is impractical, so determining the stability boundary or region of attraction (ROA) is necessary. However, using EMT simulations or Reduced-order models (ROMs) to accurately determine the ROA is computationally expensive. Alternatively, Machine Learning (ML) models have been proposed as an efficient method to predict stability. However, traditional ML algorithms require large amounts of labeled data for training, which is computationally expensive. This paper proposes a Physics-Informed Neural Network (PINN) architecture that accurately predicts the nonlinear transient dynamics of a inverter with a PLL-based controller under fault with less labeled training data. The proposed PINN algorithm can be incorporated into conventional simulations, accelerating EMT simulations or ROMs by over 100 times. The PINN algorithm’s performance is compared against a ROM and an EMT simulation in PSCAD for the CIGRE benchmark model C4.49, demonstrating its ability to accurately approximate trajectories and ROAs of a inverter with a PLL-based controller under varying grid impedance.

Design and Implementation of Crowbar and STATCOM for Enhanced Stability of Grid-Tied Doubly Fed Induction Wind Generators

These days, one of the most used layouts in the wind power industry is a variable-speed doubly-fed induction wind generator (DFIWG). For providing active power (P) and reactive power (Q) control during grid failures, this research examines the DFIWG. The system's transient behavior is examined under normal and abnormal circumstances. Through control of rotor side (RSC) and grid side (GSC) converters, Q assistance for the grid, and power converter stress reduction, the suggested control approach achieves system stability while enabling DFIWG to operate smoothly during grid failures. The DFIWG is exposed to three- and two-phase faults to analyze the machine's performance. The crowbar and STATCOM tools are implemented to enhance the system performance under faults and compared with the base case. The implemented tools successfully suppress rotor and stator overcurrent, over voltage at the DC link (DCL), and power oscillations, as well as supporting the grid voltage understudied cases. The obtained results prove that both STATCOM and crowbar not only enhance the system's effectiveness and performance but also enable the system to achieve the fault ride-through capacity (FRTC). MATLAB/SIMULINK 2017b is used for time-domain computer simulations.

Grounding grid effective area and impulsive impedance considering statistical–probabilistic characteristics of lightning currents

The grounding grid transient behavior is an important substation design criterion. This behavior is determined through interaction with impulsive currents typical of lightning. Based on the technical literature, the behavior in question is determined considering fixed current waves, with median parameters (peak values and front and tail times etc.). Therefore, important statistical–probabilistic characteristics of lightning currents, such as correlations and statistical regressions, are not included. From this perspective, this paper includes research into the sensitivity of impulsive impedance and effective area values of substation grounding grids in relation to the waveform of currents typical of the first return strokes. The results (original) illustrate significant sensitivity of the grids transient behavior in relation to those mentioned statistical–probabilistic characteristics, considering a wide range of resistivities in both current injection points considered in this study.

Thermal analysis by numerical simulations of a multilayered coating applied on a heavy-duty diesel engine piston

A methodology to numerically study the impact of a thin, multi-layer coating applied on the piston crown surface of an internal combustion engine is proposed. It relies on a loose thermal coupling between 3D-RANS simulations of the combustion chamber and 3D conduction simulations of the piston. The approach allows to characterize the transient thermal behavior of the piston, which is crucial to capture the thermal swing effect of the coating, as well as its potential impact on the combustion, heat transfer and engine efficiency. This methodology is used to simulate the impact of a 200-µm, 3-layer coating, applied on the piston crown surface of a single-cylinder, heavy-duty Diesel engine, for one operating point. No gain in terms of efficiency is observed with the coated piston (the decrease in heat losses through the piston surface due to the coating is counter-balanced by an increase in heat losses through the non-coated cylinder head). However, the methodology proves capable of predicting a coherent thermal behavior of the coated piston (decrease in piston body temperature of 5 K, average bowl surface temperature swing amplitude of 60 K, <5 K temperature swing at the interface between the metallic substrate and the coating) and is able to provide insightful information regarding the impact of coating on volumetric efficiency, heat losses, combustion but also on the coating reliability itself, for a reduced computational cost compared to a fully coupled approach. It can then be employed to evaluate the effect of a coating applied not only on the piston but also on the cylinder head, which would certainly have a more significant impact on the engine efficiency.

Harmonic Sequence Component Model-Based Small-Signal Stability Analysis in Synchronous Machines during Asymmetrical Faults

Power systems are complex and often subject to faults, requiring accurate mathematical models for a thorough analysis. Traditional time-domain models are employed to evaluate the dynamic response of power system elements during transmission system faults. However, only the positive sequence components are considered for unbalanced faults, so the small-signal stability analysis is no longer accurate when assuming balanced conditions for asymmetrical faults. The dynamic phasor approach extends traditional models by representing synchronous machines with harmonic sequence components, making it suitable for an unbalanced condition analysis and revealing dynamic couplings not evident in conventional methods. By modeling electrical and mechanical equations with harmonic sequence components, the study implements an eigenvalue sensitivity analysis and participation factor analysis to identify the variable with significant participation in the critical modes and consequently in the dynamic response of synchronous machines during asymmetric faults, thereby control strategies can be proposed to improve system stability. The article validates the dynamic phasor model through simulations of a single-phase short circuit, demonstrating its accuracy and effectiveness in representing the transient and dynamic behavior of synchronous machines, and correctly identifies the harmonic sequence component with significant participation in the critical modes identified by the eigenvalue sensitivity to the rotor angular velocity and rotor angle.

Steady and transient state behavior of a gasification process under fixed-bed downdraft configuration

Gasification is a thermochemical process that has gained significant interest in the field of biomass energy conversion. Despite the level of technological maturity of the process, the dynamic variation of the process as a result of changes in both the properties of the gasifying agent and biomass has not been analysed in sufficient depth. Therefore, the present study characterizes the process dynamically as a function of step-type changes in rice husk biomass moisture content and gasifying airflow. To identify stability conditions and the range for inducing disturbances, steady-state tests were carried out using a 32-factorial design. The experimental results demonstrate that within the tested range of airflow, the gasification process operates in the oxygen-limited zone. Despite increasing the airflow from 20 to 40 standard liters per minute (SLPM) and driving the reaction towards the combustion zone, the high temperatures achieved resulted in the gas reaching a peak Lower Heating Value (LHV) of 2.6 MJ/Nm3 and a gas power of 2.6 kW, with a Cold Gas Efficiency (CGE) of 62%. In contrast, the effect of biomass moisture content was negligible due to the thermal inertia of the reactor and the natural variation of the process. Dynamic evaluation revealed that the oxidation temperature and gas concentration were the variables that took the longest to return to stability after air disturbances. It took approximately 1200 s for the hydrogen (H2) concentration to stabilize, while the gas power required about 300 s. No clear results were observed regarding the impact of the dynamic disturbance in moisture content, which varied between 12.3% w.t and 21.5% w.t.

A discharge plasma regulation method with spike current for electrical discharge machining

Improving material removal rate (MRR) has been one of the most important issues in electrical discharge machining (EDM). A major factor which hinders the improvement of MRR in EDM is the relatively low expulsion ratio of molten material. During a discharge process, a large portion of molten material cannot be expelled sufficiently from the molten pool but re-solidifies, ultimately resulting in a low machining efficiency. In this study, aiming at enhancing the expulsion ratio of molten material in EDM, a discharge plasma regulation method with a spike current is proposed. A novel discharge pulse shape, with a spike current aligned at pulse turn-off stage, is adopted. The transient behaviors of the discharge plasma when a spike current engaged are captured using a high-speed camera, and the morphologies of the corresponding discharge craters are also analyzed. A particle-in-cell with Monte Carlo collision simulation method is used to analyze the changes in particle state inside the plasma. It is found that the spike current applied at the stage when the plasma contracts to a smaller diameter is more conducive to facilitating molten material expulsion. The results of consecutive-pulse machining experiments verify that the proposed discharge plasma regulation method can increase MRR by at least 25.89 % for stainless steel.

EVALUATION OF THE USE OF RADIATIVE COOLING TECHNOLOGY TO SUPPORT THE AIR CONDITIONING SYSTEM OF A DATA CENTRE

Data centre space cooling systems consume a lot of energy and will increase over the years. Therefore, it is necessary to propose new refrigeration strategies. Radiative cooling (RC) production is a renewable alternative solution with a promising future. In this work, the energy modelling of the air conditioning system of a data centre coupled to a RC emitter is carried out to explore the benefits of this technology. The system consists of a water chiller connected to a cooling coil through which air is circulated for distribution in the data centre room. The simulations were carried out for a typical summer week in Barcelona. The RC production was carried out during the night, and this power was used during the day and was implemented directly in the energy balance of the data centre room, considering emission surfaces of 80 and 60% of the total building roof, reducing the water chiller energy consumption by 13 and 10% respectively. In the transient behaviour of the temperature in the data centre room, when the RC was used to reduce the peak cooling load, a reduction of the temperatures was observed approaching to the design setpoint, therefore, the IT equipment was not affected.

Relaxation dynamics in the alternating XY chain following a quantum quench

We investigate the relaxation dynamics of the fermion two-point correlation function Cmn(t)=〈ψ(t)∣cm†cn∣ψ(t)〉 in the XY chain with alternating nearest-neighbor hopping interaction after a quench. We find that the deviation δ C mn (t) = C mn (t) − C mn (∞) decays with time following the power law behavior t −μ , where the exponent μ depends on whether the quench is to the commensurate phase (μ = 1) or incommensurate phase ( μ=12 ). This decay of δ C mn (t) arises from the transient behavior of the double-excited quasiparticle occupations and the transitions between different excitation spectra. Furthermore, we find that the steady value C mn (∞) only involves the average fermion occupation numbers (i.e. the average excited single particle) over the time-evolved state, which are different from the ground state expectation values. We also observe nonanalytic singularities in the steady value C mn (∞) for the quench to the critical points of the quantum phase transitions (QPTs), suggesting its potential use as a signature of QPTs.

Numerical investigation of the transient fluid flow and heat transfer behavior in self-driven natural circulation cooling loop

An innovative open natural circulation system is proposed in this work, which utilizes the difference of the heat flux loaded on different parts of the pipe to form a self-circulation flow of working fluid. Via CFD simulation established by embedding self-programmed code into commercial software, the transient performance of a three-dimensional natural circulation loop is studied. The results indicate that: applying uniform heat flux on the wall of the loop, the fluid flow state successively experiences three stages, i.e., liquid expansion, partial circulation, and phase change, and finally a vapor plunger blocks the pipe, leading to local heat transfer deterioration and temperature increase; applying non-uniform heat flux, the fluid can be driven to form self-circulation flow, which can not only cool the structure via convection, but also prevent bubbles from accumulating, stabilizing the maximum temperature of the system around the boiling point; further for the loop with a more complex configuration, the self-circulation can be also started but with different start modes. Therefore, the new natural circulation system can achieve effective and adaptive cooling according to the external thermal environment, avoid fluctuation and vapor block phenomenon caused by violent phase change, and reduce the driving equipment and control unit. This work provides a reference for the design of the natural circulation system applied in a non-uniform heating environment. Through transient numerical simulation of the start-up stage, the fluid flow, phase change, and heat transfer characteristics in the natural circulation loop are studied, and the start mode and mechanism are analyzed.

Transient behavior of oxide fuels with controlled microstructure and Cr2O3 additive

Microstructure and Cr2O3 doping profoundly impact the thermal-mechanical properties and fracture of oxides fuels. It is a challenge to study the transient behavior of nuclear fuels under loss-of-coolant-event (LOCA). In this study, the crack behavior of UO2 pellets with controlled grain structure and Cr2O3 doping was tested with rapid power ramping (300−900 °C per min) mimicking a prototypical LOCA heating profile. Dense micron-sized UO2 pellets display well-maintained integrity without cracking with the ramping up to 1500 °C at a heating rate of 8 °C per second. Fracture occurs in both pure and Cr2O3-doped dense nano-sized UO2 pellets. The Cr2O3 doped oxide fuel pellet with a larger grain size (~ 22.2 μm) displays the best performance under LOCA testing due to its highest thermal conductivity under high temperature. FEA calculations suggest a temperature gradient across the fuel pellet during transient testing, resulting in residual stress and cracking, which can be correlated with their thermal-mechanical properties.

A new method for surge arrester placement in high‐voltage substations considering environmental effects

AbstractConventional approaches for determining the optimal locations of surge arresters (SAs) can result in an unnecessary increase in the number of these devices in high‐voltage substations. This study presents an effective technique for determining the optimal locations of SAs. The lightning back flashover (BF) and switching over‐voltages are predicted with the accurate modeling of the transient behavior of all elements of high‐voltage substations and transmission lines, considering the effect of environmental conditions. Also, the proposed limiting parameter Monte Carlo (MC‐LP) method is utilized to correctly select the probability distribution of the possible strokes for predicting the insulation risk (IR) of a transformer based on transient over‐voltage on the transformer end. Therefore, the most appropriate location to install an SA can be determined with a minimum number of calculations using the structural data of the substation, lines connected to it, and the transformer. Simulations are based on experimental results, and the number of calculations significantly decreases using the proposed algorithm. Simulations of the sample network and implementation of the proposed algorithm with MATLAB and EMTP‐RV prove the efficiency of the proposed method for optimum SA placement.

Parameter identification and uncertainty propagation of hydrogel coupled diffusion-deformation using POD-based reduced-order modeling

AbstractThis study explores reduced-order modeling for analyzing time-dependent diffusion-deformation of hydrogels. The full-order model describing hydrogel transient behavior consists of a coupled system of partial differential equations in which the chemical potential and displacements are coupled. This system is formulated in a monolithic fashion and solved using the finite element method. We employ proper orthogonal decomposition as a model order reduction approach. The reduced-order model performance is tested through a benchmark problem on hydrogel swelling and a case study simulating co-axial printing. Then, we embed the reduced-order model into an optimization loop to efficiently identify the coupled problem’s material parameters using full-field data. Finally, a study is conducted on the uncertainty propagation of the material parameter.

RPV top and bottom break SBLOCA with passive emergency core cooling system using ATLAS test facility

A SBLOCA test, named as C2.1 in the frame of the OECD/NEA ATLAS3 project, using a passive emergency core cooling system (PECCS) was performed by Korea Atomic Energy Research Institute (KAERI). In the test, two simultaneous 2-inch equivalent breaks occurred at top and bottom nozzles of the reactor pressure vessel of ATLAS test facility. The main purpose of the test is to investigate thermal hydraulic transient behavior in a reactor coolant system (RCS) during a SBLOCA scenario and to evaluate the effectiveness of PECCS. From the observation on thermal hydraulic phenomena during the test, the test period was divided into three characteristic phases such as pressure plateau, safety injection, and clad temperature re-increase phases. Continuous inventory loss of the primary loop through two break nozzles led to a primary system pressure decrease and a clad temperature increase. Even though high-pressure safety injection tanks (HPSITs) were actuated in an early stage of the pressure plateau phase, safety injection from HPSITs, however, were not actually injected. Safety injection flows from the HPSITs and SITs were practically injected to the downcomer only after the opening of automatic depressurization valves (ADVs). With a continuous decrease of a primary system pressure, low-pressure (LP) injection was started. However, LP injection could not change the increasing trend of the clad temperatures. Post-test calculations were performed using MARS-KS 1.4, and calculation results were compared with those of the test.

Interrogation of Oxidative Pulsed Methods for the Stabilization of Copper Electrodes for CO2 Electrolysis.

Using copper (Cu) as an electrocatalyst uniquely produces multicarbon products (C2+-products) during the CO2 reduction reaction (CO2RR). However, the CO2RR stability of Cu is presently 3 orders of magnitude shorter than required for commercial operation. One means of substantially increasing Cu catalyst lifetimes is through periodic oxidative processes, such as cathodic-anodic pulsing. Despite 100-fold improvements, these oxidative methods only delay, but do not circumvent, degradation. Here, we provide an interrogation of chemical and electrochemical Cu oxidative processes to identify the mechanistic processes leading to stable CO2RR through electrochemical and in situ Raman spectroscopy measurements. We first examine chemical oxidation using an open-circuit potential (OCP), identifying that copper oxidation is regulated by the transient behavior of the OCP curve and limited by the rate of the oxygen reduction reaction (ORR). Increasing O2 flux to the cathode subsequently increased ORR rates, both extending lifetimes and reducing "off" times by 3-fold. In a separate approach, the formation of Cu2O is achieved through electrochemical oxidation. Here, we establish the minimum electrode potentials required for fast Cu oxidation (-0.28 V vs Ag/AgCl, 1 M KHCO3) by accounting for transient local pH changes and tracking oxidation charge transfer. Lastly, we performed a stability test resulting in a 20-fold increase in stable ethylene production versus the continuous case, finding that spatial copper migration is slowed but not mitigated by oxidative pulsing approaches alone.

A study of valve-induced water hammer in a woven-jacket fire hose

ABSTRACT The dynamic response of a woven fire hose during valve-induced water hammer events is investigated through a combination of experimental and numerical studies. Unlike conventional polymeric pipes, fire hoses made of synthetic fibres exhibit unique characteristics, transitioning from pliancy to increased rigidity as the pressure within the hose rises. This study explores the transient behaviour of woven fire hoses under variable initial conditions. Experimental studies reveal a direct correlation between the initial piezometric head and the fire hose’s transient response. Numerical simulations employ the viscoelastic Kelvin–Voigt model, proving its suitability for accurately simulating valve-induced hydraulic transients in woven fire hoses. Notably, even a single Kelvin–Voigt element exhibits a relatively good fit with experimental data, accurately reproducing pressure peaks, while the inclusion of two elements enhances the model’s capability, achieving the near-perfect reproduction of pressure oscillations.

A study on the impact of using a subchannel resolution for modeling of large break loss of coolant accidents

The nuclear industry is investigating the feasibility of transitioning from 18- to 24-month fuel cycles because of the positive impact it would have on the operational costs for the current fleet of light-water reactors. A challenge to making this change is the increased risk of fuel fragmentation, relocation, and dispersal (FFRD) due to the known potential for ceramic fuel to pulverize into fine particles at the higher discharge burnups. Previous work has been performed by the Nuclear Energy Advanced Modeling and Simulation program to assess FFRD risk in high-burnup cores using the BISON fuel performance code and a coarse mesh thermal hydraulics (T/H) solution for a loss-of-coolant accident (LOCA) using the TRACE system T/H code. Because of the importance of the T/H solution for FFRD assessment, this study seeks to investigate the impact of using higher-fidelity subchannel techniques for modeling of the LOCA transient. CTF was used to model a subregion of a high-burnup core that was depleted by the Virtual Environment for Reactor Applications (VERA) multiphysics core simulator. Both coarse-mesh and pin-resolved models were created in CTF, and a consistent coarse-mesh TRACE model was also developed to allow for benchmarking the code results. A large-break loss-of-coolant accident (LBLOCA) reflood transient was simulated using these three models, and results were compared. Results showed some consistent differences between the CTF and TRACE coarse models, including a higher peak cladding temperature (PCT) prediction in CTF and later quenching in CTF; however, the transient clad temperature behavior was similar, and these differences are likely due to post-critical heat flux heat transfer modeling differences and minimum film boiling temperature model differences. The pin-resolved results indicate that the PCT in the lumped model is often under-predicted by as much as 70 °C and that PCT occurs at a different location than the high-power pin in the assembly. The lumped model predicts a difference of 10 °C or less between the average and hot pins in the assembly, whereas the pin-resolved model predicts a range of over 100 °C. These results indicate that higher-fidelity T/H results may have an impact on predicted core behavior during LOCA, which may be important to consider when assessing FFRD risk.