Coupling Characteristics Research Articles

The coupling characteristics and influencing factors of the "homestead-cultivated land system" in the Three Gorges Reservoir Region of China: A farmer perspective

Homesteads and cultivated land are crucial elements of the rural territorial system. Their coupling characteristics and changing patterns are essential for understanding the evolution of rural human-land systems and for developing coordinated rural development strategies. This study takes Huilong Village and Pingba Village in the TGRR, employing methods such as GIS spatial analysis, comprehensive index evaluation, coupling coordination degree model, and geographic detector model. The analysis focuses on the coupling characteristics and influencing factors of the “HCS” in these villages and proposes optimization strategies to provide scientific guidance for village planning, selection of high-quality rural development paths, and strategy design. The main findings are as follows: (1) The spatial distribution of homesteads and cultivated land in typical villages exhibits clear traffic directionality. The spatial coupling of the “HCS” demonstrates significant convergent evolution and adjacent distribution characteristics. (2) The utilization coupling of the “HCS” in Huilong Village and Pingba Village is predominantly high, with 98.72% and 94.62% of farmers, respectively, being highly coupled. However, the degree of coupling coordination is mostly barely coordinated. (3) The primary factors influencing the coordinated development of the “HCS” in the study area include the utilization conditions of homestead and cultivated land, labor status, and economic status. These factors can be categorized into four types: labor factor restrictions, nonagricultural development disturbance, agricultural development, and lagging farming conditions. Differentiated development strategies are proposed for each type. This research enhances the understanding of the coupling between homestead land and cultivated land, offering valuable insights for regional village planning, high-quality development path selection, and government decision-making.

Study on Seasonal Permafrost Roadbed Deformation Based on Water–Heat Coupling Characteristics

Study on Seasonal Permafrost Roadbed Deformation Based on Water–Heat Coupling Characteristics

Evaluation Approach and Controller Design Guidelines for Subsequent Commutation Failure in Hybrid Multi-Infeed HVDC System

Due to the difference in output characteristics between the line-commutated converter-based high-voltage direct current (LCC-HVDC) and voltage-source converter-based high-voltage direct current (VSC-HVDC), the hybrid multi-infeed high-voltage direct current (HMIDC) presents complex coupling characteristics. As the AC side is disturbed, the commutation failure (CF) occurring on the LCC side is the main factor threatening the safe operation of the system. In this paper, the simplified equivalent network model of HMIDC is established by analyzing the output characteristics of VSC and LCC. Hereafter, based on the derived model and the control system of LCC-HVDC, the dynamic equations of the extinction angle are deduced. Consequently, by applying the phase portrait method, the causes of CF occurring in the HMIDC system as well as the impacts of control parameters on the transient stability are revealed. Furthermore, the stabilization boundaries for the reference value of the DC voltage are obtained via the above analysis. Finally, the theoretical analysis is verified by the simulations in the PSCAD/EMTDC.

Sensitivity analysis-based quality optimization strategy for multi-correlation parameters in spinning process

To address the problem of quality optimization of multi-correlation parameters in the spinning process, this paper proposes a new method based on a sparrow search algorithm (SSA). Firstly, a generalized regression neural network (GRNN) is used to investigate the impact of the spinning process parameters on yarn quality, and quality forward modeling in the spinning process is established. And based on the coupling and correlation characteristics of spinning process parameters, sensitivity analysis is used to analyze the influence of each spinning process parameter on yarn quality, the correlation spinning process parameters for further analysis. Then a model of quality optimization with spinning process parameters is established, and SSA is used to solve the model of quality optimization with multi-correlation parameters in the spinning process. Finally, the effectiveness of the proposed method was validated through an instance. The results show that the optimal spinning process parameters combination generation of [32.159 5.2 0.8 14.8 24.540 8588.677 21.708] occurs in a configuration with a fitness value of 0.0003. The proposed sensitivity analysis-based quality optimization strategy reveals good performances in terms of both convergence speed and optimization accuracy, which will provide guidance for improving yarn quality.

Water-Coal Ratio Control Strategy of Ultra Supercritical Unit Based on Neural Network Inverse Model

Since the boiler water-coal ratio control system is a complex system with the characteristics of non-linearity and strong coupling, water-coal ratio control is one of the most difficult problems in the coal-fired power generation process control engineering, whose control strategy is of great importance. While, in order to achieve the control of water-coal ratio effectively during the coal-fired power generation process, the neural network inverse system scheme is proposed for the control of the water-coal ratio of ultra-supercritical units. Firstly, the model for the water-coal ratio system of an ultra-supercritical unit is presented in allusion to the characteristics of the water-coal ratio control system. Then the concept of the neural network based inverse system, the principle and method of the design of the neural network inverse controller are discussed. Finally, the control scheme is verified by establishing neural network inverse system on MATLAB toolbox. The experimental results show that the neural network based inverse system models has better control effect in terms of anti-interference ability, stability time than that of PID control system.

Seepage-stress coupling characteristics of initial damaged glass fiber reinforced concrete under different loading conditions

Different loading methods induce variations in the macroscopic performance of the specimens. In this investigation, experiments were conducted on glass fiber reinforced concrete subjected to varying degrees of damage. Initially, axial compression loading and unloading were performed, followed by continuous axial compression loading. The study elucidates the evolution of permeability and strength characteristics of specimens under these two loading regimes. The experimental results delineate the trend of permeability and its corresponding strength attributes under complex stress paths. It was observed that during the axial compression loading and unloading phases, the permeability of the specimens follows a negative exponential function. As axial pressure increases, internal pores within the specimens were compacted, leading to a reduction in seepage pathways and a significant decline in permeability. At different stages of axial compression (0–5 MPa, 5–15 MPa, 15–25 MPa), the rate of permeability reduction diminishes progressively, with minimal change observed in the high-stress stage. During the unloading phase, due to incomplete recovery of plastic deformation, permeability shows only a limited increase, with the maximum recovery rate being less than 40 %. During the initial phase of continuous axial compression loading, the permeability first diminishes, subsequently entering an elastic stage where it stabilizes. However, upon reaching the point of instability failure due to crack propagation, permeability increases sharply. Additionally, as the number of freeze-thaw cycles rises, the degree of internal damage within the specimen escalates, manifesting as an increase in both pore size and quantity. Notably, the initial permeability and peak strength exhibited opposing trends: after 40 freeze-thaw cycles, initial permeability increased by 36 %, while peak strength decreased by 22 %.

Intelligent modeling of combined heat and power unit under full operating conditions via improved crossformer and precise sparrow search algorithm

The flexible operation capability of combined heat and power (CHP) unit under full operating conditions must be promoted to suppress the power grid fluctuation in large-scale integration of renewable energy. However, obtaining CHP unit model under large-scale variable loads and deep peak shaving is extremely challenging. To this end, an intelligent modeling method incorporating improved crossformer and precise sparrow search algorithm is designed to provide reference for flexible controller design. Firstly, to address the strong time dependence of CHP unit boiler-turbine coupling process, a bidirectional gated recurrent unit is employed as the position encoding to extract the hidden temporal feature. Secondly, a novel encoder structure with multi-receptive field convolution module is designed to enhance the local feature extraction capability of the network, which is conducive to the analysis of multivariable coupling characteristics of CHP unit. On this basis, a precise sparrow search algorithm with stronger search ability is formed by combining Tent chaotic mapping, osprey optimization algorithm, Cauchy mutation and quantum behavior, which provides support for the dynamic characteristics analysis of CHP unit. The time dependence, local feature information and optimal parameter settings are fully considered in the comprehensive modeling scheme, which results in an accurate identification model for CHP unit under full operating conditions. Finally, the effectiveness of the proposed method is verified based on the actual operating data of a 350 MW CHP unit. The accuracy of established model is greater than 99.4 %, which can well reflect the nonlinear characteristics of the unit. Therefore, the built model can be used for controller design and simulation analysis.

A systematic method of long-sequence prediction of natural gas supply in IES based on spatio-temporal causal network of multi-energy

Natural gas plays an important role in the energy peak-shaving process of Integrated Energy Systems (IES). Accurate prediction of natural gas supply over longer time scales is one of the most important conditions to ensure the stability and security of IES energy supply. However, as the sequence length of the predicted time series increases, it becomes more difficult to extract valid dependencies from the data. At the same time, there are complex spatio-temporal coupling characteristics of various energy resources in the IES, which makes the construction of long sequence prediction models for natural gas supply very difficult. To solve this problem, we propose a systematic method for long-sequence prediction with natural gas supply in IES based on spatio-temporal causal network of multi-energy. First, the proposed approach uses a causal analysis algorithm to represent the complex coupled spatio-temporal relationships of multiple energy resources in an IES. Then, the natural gas time-series are decomposed through the Variational Modal Decomposition (VMD), to reveal its inherent trend and cyclical characteristics. Finally, the long-sequence prediction model is proposed by fusing the attention mechanism into Graph Convolutional Neural Network (GCN). Attentional mechanisms are introduced to obtain important long-term dependencies in the long sequence prediction process. We use a integrated energy dataset from Spain to test the validity and superiority of the method. The results show that the proposed model in this paper improves the Root Mean Square Error (RMSE) by at least 9.5% and reduces the Mean Absolute Error (MAE) by at least 14.5% compared to several baseline models.

A study of capacity demands for heat pumps intermittent heating of China’s residences

Heat pump heating is one of the most promising solutions for transitioning residential heating in China’s cold regions, as well as hot summer and cold winter regions from centralized, continuous heating to decentralized, intermittent heating, promoting low-carbon transformation. However, the fundamental issue of the actual capacity requirements for heat pumps in intermittent heating has not yet been addressed. In view of this, this study developed a numerical model that considers the dynamic coupling characteristics between the heat pump and the building environment. Using the model, the worst startup conditions for heat pumps in intermittent heating, actual heat pump capacity demands, and the differences in capacity compared to continuous heating mode for residential buildings in 230 Chinese cities are analyzed. The findings revealed an exponential relationship between intermittent heating capacity demands and time constraints, as well as a linear relationship with heating temperature. Specifically, the impact of the set temperature on capacity demands in cold regions and hot summer and cold winter regions is 22.8 W/(m2·°C) and 32 W/(m2·°C), respectively. These findings provide insights into the planning and design of future intermittent heating renovation projects in China.

Study on the coupling characteristics of laser-TIG hybrid heat source with different offsets

Study on the coupling characteristics of laser-TIG hybrid heat source with different offsets

A portable photoacoustic microscopy and ultrasound system for rectal cancer imaging

Photoacoustic microscopy offers functional information regarding tissue vasculature while ultrasound characterizes tissue structure. Combining these two modalities provides novel clinical applications including response assessment among rectal cancer patients undergoing therapy. We have previously demonstrated the capabilities of a co-registered photoacoustic and ultrasound device in vivo, but multiple challenges limited broad adoption. In this paper, we report significant improvements in an acoustic resolution photoacoustic microscopy and ultrasound (ARPAM/US) system characterized by simulation and phantom study, focusing on resolution, optical coupling, and signal characteristics. In turn, higher in-probe optical coupling efficiency, higher signal-to-noise ratio, higher data throughput, and better stability with minimal maintenance requirements were all accomplished. We applied the system to 19 ex vivo resected colorectal cancer samples and found significantly different signals between normal, cancer, and post-treatment tumor tissues. Finally, we report initial results of the first in vivo imaging study.

Fracture Evolution during CO2 Fracturing in Unconventional Formations: A Simulation Study Using the Phase Field Method

With the introduction of China’s “dual carbon” goals, CO2 is increasingly valued as a resource and is being utilized in unconventional oil and gas development. Its application in fracturing operations shows promising prospects, enabling efficient extraction of oil and gas while facilitating carbon sequestration. The process of reservoir stimulation using CO2 fracturing is complex, involving coupled phenomena such as temperature variations, fluid behavior, and rock mechanics. Currently, numerous scholars have conducted fracturing experiments to explore the mechanisms of supercritical CO2 (SC-CO2)-induced fractures in relatively deep formations. However, there is relatively limited numerical simulation research on the coupling processes involved in CO2 fracturing. Some simulation studies have simplified reservoir and operational parameters, indicating a need for further exploration into the multi-field coupling mechanisms of CO2 fracturing. In this study, a coupled thermo-hydro-mechanical fracturing model considering the CO2 properties and heat transfer characteristics was developed using the phase field method. The multi-field coupling characteristics of hydraulic fracturing with water and SC-CO2 are compared, and the effects of different geological parameters (such as in situ stress) and engineering parameters (such as the injection rate) on fracturing performance in tight reservoirs were investigated. The simulation results validate the conclusion that CO2, especially in its supercritical state, effectively reduces reservoir breakdown pressures and induces relatively complex fractures compared with water fracturing. During CO2 injection, heat transfer between the fluid and rock creates a thermal transition zone near the wellbore, beyond which the reservoir temperature remains relatively unchanged. Larger temperature differentials between the injected CO2 fluid and the formation result in more complicated fracture patterns due to thermal stress effects. With a CO2 injection, the displacement field of the formation deviated asymmetrically and changed abruptly when the fracture formed. As the in situ stress difference increased, the morphology of the SC-CO2-induced fractures tended to become simpler, and conversely, the fracture presented a complicated distribution. Furthermore, with an increasing injection rate of CO2, the fractures exhibited a greater width and extended over longer distances, which are more conducive to reservoir volumetric enhancement. The findings of this study validate the authenticity of previous experimental results, and it analyzed fracture evolution through the multi-field coupling process of CO2 fracturing, thereby enhancing theoretical understanding and laying a foundational basis for the application of this technology.

Compact device for the generation of toroidal spatiotemporal optical vortices

Due to the unique spatiotemporal coupling characteristics in phase, spatiotemporal optical vortices have attracted extensive attention. Toroidal vortices, as high-dimensional spatiotemporal optical vortices, have become a research hotspot in recent years due to their unique topological structures. In this paper, we propose an asymmetric grating structure for the generation of optical toroidal vortices in a compact way. A cylindrical vector wave packet is transformed by the structure into a transmitted toroidal vortex pulse. Such a compact toroidal vortex generator may find applications in optical topology and high-dimensional optical communications.

Study on Multi-Span Tension Coupling Relationship of Gravure Printed Electronic Equipment

To improve the performance of the tension control system in gravure printed electronic equipment, it is necessary to study the tension system model of gravure-printing electronic equipment. This paper focuses on the coupling characteristics of multi-span tension systems. Firstly, based on the single-span tension model, the mathematical model of the printing tension subsystem is established and simplified into a general multi-span tension coupling model. Then, using the relationship between the inputs and outputs of the system, the coupling model is simulated using MATLAB/Simulink and verified through experiments on the gravure printed electronic platform. Finally, the coupling relationship and influence laws among multi-physical quantities of the system are analyzed. The research results show that changes in the input web tension of the multi-span system will affect the steady-state tension values of all subsequent spans. Moreover, the speed change in a roller in the multi-span system will not only affect the steady-state tension value of its own span, but also cause transient tension fluctuations in all subsequent spans. The findings of this paper provide an important theoretical basis for the research of the tension system in gravure printed electronic equipment, contributing to the enhancement of printed electronic product quality.

Enhanced integrated energy system planning through unified model coupling multiple energy and carbon emission flows

Integrated energy system plays a crucial role in achieving low carbon emissions while supplying multiple loads. As the energy Internet continues to evolve, integrated energy system, acting as a cell-level prosumer, exhibits intricate coupling characteristics between multiple energy flows and carbon flows. This paper presents a flexible planning method based on a unified energy-carbon coupled operation model. It can realize blank-paper planning under multiple energy-carbon flow constraints, that is, jointly optimize equipment configuration and capacity size from scratch. The proposed method combines clustering algorithms and Latin hypercube sampling to generate the operational scenarios for renewable resources and energy loads, enhancing the representativeness and reliability of planning solutions. The results demonstrate that the proposed method can effectively meet the requirements of electricity, cooling and heat loads under different seasonal scenarios. Furthermore, it elucidates the corresponding carbon emission distribution across distinct energy flows of the planned system. Compared with the conventional fixed equipment connected planning method, the more flexible blank-paper planning method can achieve annual economic cost savings of about 7.5 % and reduce annual carbon emissions by 6.7 %.

Flexible BTO piezoelectric generator fabricated by hydrothermal method with the assistance of lignocellulose and carbon nanomaterials

It is of great significance to develop piezoelectric composites with mechanical flexibility and high electromechanical coupling characteristics for the collection and conversion of mechanical energy. In this work, a barium titanate (BTO) based piezoelectric composite was prepared by hydrothermal synthesis and high-temperature carbonization with the assistance of cellulose nanofibers (CNF), graphene oxide (GO) and carboxylated carbon nanotubes (C-CNT). C-CNT, GO and CNF can provide growth sites for BTO, but compared with C-CNT, CNF and GO have stronger interaction with BTO, which can improve the compatibility between BTO and CNF/polyvinylidene fluoride (PVDF) matrix. The tensile strength of the composite membrane prepared by GO-CNF-BTO treated at 1100 °C can reach 23.36 ± 8.30 MPa. After further hot pressing and polarization treatment, its longitudinal piezoelectric coefficient (d33) reaches 9.8 ± 2.6 pC·N−1. Correspondingly, the open-circuit voltage (VOC) and short-circuit current (ISC) increases to 11.64 V and 824 nA, respectively. In addition, the assembled piezoelectric generator (PEG) can charge for small commercial capacitors, as well as light small bulbs and electronic screens. It also has good piezoelectric output stability and sensing performance, which can effectively convert the mechanical energy from human motion into electrical energy. This work provides a reference for the performance improvement of flexible piezoelectric devices.

Theoretical modeling and analysis of an equipment–shell multiple-transmission-path system with attached liquid-filled pipe

Vibrations generated by mechanical equipment are the main source of radiation noise for ships. In actual systems, there are multiple transmission paths for mechanical vibrations from the equipment to shell. Common paths include vertical support structures, such as vibration isolators, and lateral attachment structures, such as pipes. However, most existing models only consider a single-path scenario. Multi-path systems have more complex modal and vibration transmission characteristics and introduce more complex coupling problems. There is a lack of theoretical modeling and physical analyses of common multiple transmission systems in ships. In this study, a theoretical model of an equipment–shell multiple-transmission-path system with an attached liquid-filled pipe is established as a typical multiple-transmission-path system for ships. In this model, the liquid-filled pipe is solved using a newly proposed traveling-wave method based on Kennard shell theory. Based on the theoretical model, the effects of each type of traveling wave on the pipe on the system modal characteristics, the mechanism behind each path on the system coupling characteristics, the influence of structural parameters on system modal and vibration transmission characteristics, and the proportion of vibration transmitted by the two transmission paths are analyzed. This study provides theoretical insights and guidance for practical vibration and noise reduction engineering.

Mesoscale formation and energy release characteristics of PTFE/Al reactive jet

AbstractIn order to investigate the mechanical formation, the mechanical‐thermo coupling mesoscale mechanism and the corresponding energy release characteristics of PTFE/Al composite material reactive jet, a mesoscale discretization model of PTFE/Al reactive liner with a mass ratio of 73.5 %/26.5 % is developed on the basis of the random delivery principle. The mesoscale numerical simulation is used to perform PTFE/Al reactive jet formation, obtaining the relative distribution characteristics of material, pressure, and temperature. The overpressure experiments for the energy release of reactive jets are conducted. The results show that there is an increasing tendency in the amount of Al particles from the jet's tip to its tail due to the velocity variance between PTFE and Al. The high temperature zones are found to be concentrated on the tip and axis of the jet, with particle deformation, collision and friction in the reactive jet accounting for the temperature rise. Moreover, the Al particle size has a significantly influence on the particle distribution and the mechanical‐thermo coupling behavior in the reactive jet, and the decrease of particle size is beneficial to the chemical reaction among the components of the reactive jet. To be more specifically, under the conditions of Al particle size of 400 μm, 600 μm and 800 μm, the overpressure peaks of reactive jet in 13 L chamber are 3.32 MPa, 2.86 MPa and 2.61 MPa, respectively. The variation of the overpressure with Al particle size obtained by experiment is consistent with the analysis of the mechanical‐thermo coupling characteristics of mesoscale numerical simulation.

Output tracking of coupled stochastic strict-feedback higher-order nonlinear systems under pinning control

This paper focuses on the tracking problem for a class of coupled stochastic strict-feedback higher-order nonlinear systems under pinning control. Compared with existing stochastic nonlinear tracking designs, our approach stands out by simultaneously considering coupling and higher-order characteristics for the first time. By utilizing the backstepping technique and designing virtual controllers, we obtain actual controllers that ensure the closed-loop system has an almost surely unique solution and is bounded in probability. Additionally, the fourth-moment of the output tracking error can be rendered arbitrarily small in the long run. Notably, to address the cost implications of imposing a controller on each node, we employ a pinning control strategy to selectively control a portion of the nodes. Moreover, a global Lyapunov function is derived combining Lyapunov method with graph theory. Eventually, a numerical simulation is shown to verify the theoretical results.

Thermal-mechanical-electrical coupling isogeometric analysis for piezoelectric material structures

To solve the multi-physical coupling characteristics of piezoelectric structures, the thermal-mechanical-electrical coupling isogeometric analysis method (TMEC-IGA) is proposed to explore the structures of piezoelectric materials. Based on the basic equations and boundary conditions of piezoelectric materials, NURBS basis function is introduced to construct displacement and electrical potential functions, and the control equation of TMEC-IGA is derived. Numerical examples show that TMEC-IGA is effective in solving the thermal-mechanical-electro coupling problem of piezoelectric structures, and has broad application prospects in the design, development and performance analysis of piezoelectric devices.