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As an effective carbon utilization technology, the injection of N2/CO2 mixtures into coal seams has significant potential for improving coalbed methane recovery. Considering the technical barrier that injection of pure CO2 decreases the well injectivity index and pure N2 injection leads to the rapid methane recovery, a method of injecting N2‐enriched gas mixtures with a constant component is proposed. In this study, a thermo‐hydro‐mechanical (THM) coupling numerical model for enhanced coalbed methane (CBM) recovery by injecting N2/CO2 mixtures is established. This model includes complex interactions of coal deformation, competitive adsorption, ternary gas seepage, and heat transfer. The THM coupling model is first validated, and then applied to investigate the evolution of mixed gas concentrations, reservoir permeability, reservoir temperature, CH4 production, and N2/CO2 storage during N2/CO2 enhanced CBM recovery. The results show that the displacement radius and concentration of the mixed gas in the coal seam increased with gas injection pressure increase. The concentration of CH4 gradually decreased with time, and the early decline is faster than the later stage. The sweep of the N2 flow accelerates CH4 desorption and migration, promoting a reduction in reservoir temperature near the production well. Reservoir permeability evolution results from the combined effects of ternary gases (CH4, CO2, N2) competitive adsorption, gas pressure, and geostress on the coal seam within the THM fields. At the methane natural depletion stage (within 250 days), the permeability of coal reservoir first decreases and then increases. With the arrival of the N2/CO2 mixture, the permeability decreases dramatically. From the perspective of cumulative CH4 production, the optimal composition is dominated by the synergistic effect of maximizing breakthrough time and minimizing coal matrix swelling. For 30% CO2‐70% N2, the CH4 recovery ratio reached 71.76%, representing an increase of 16.67% compared to natural depletion. To reveal the coupling mechanism of ternary gases (CH4, CO2, N2) in the coal reservoir during CBM recovery, a thermo‐hydro‐mechanical (THM) coupling model of ternary gases was established, including the competitive adsorption of ternary gases, free gas diffusion and seepage, as well as nonisothermal heat transfer and coal deformation. Gas production and storage of different mixed gas injection cases were compared to optimize the composition of injected gas mixture.

The quality and efficiency of coalbed methane (CBM) drainage are critical for the safe production of coal mining enterprises in China. Air leakage should be prevented during CBM drainage because it can reduce drainage concentration and induce produce accidents such as coal seam spontaneous combustion. However, existing theoretical models for CBM drainage do not consider the air leakage effect. This study sets up a gas-solid coupling theoretical model in which the air leakage effect is taken into account as well as gas diffusion and gas seepage. The influencing factors on the drainage quality of CBM were analyzed using numerical simulation. The results show that the CBM drainage quality linearly improves with the increase of drainage negative pressure, while increasing initial CBM pressure can linearly enhance drainage quality at the early drainage stage. The CBM drainage quality exponentially increases with Langmuir content and exponentially decreases with Langmuir pressure. With the increase of coal's initial permeability, CBM drainage quality exponentially increases at the early drainage stage but exponentially decreases at the middle and late drainage stages. The new theoretical model effectively depicts the drop in CBM drainage quality and the increase of air leakage during the entire drainage process.

Coalbed methane (CBM) is the very important unconventional energy resource. Enhancing extraction is the main method to improve the utilization of CBM and prevent coal mine gas disasters. To reveal the laws of gas migration during the underground gas extraction, the paper established the solid‐gas coupling model, regarding coal as the homogeneous elastic medium with dual pore‐fracture structure and dual permeability and considering the gas dynamic diffusion coefficient. Then, the regulations of gas migration in the in‐seam borehole were simulated by the COMSOL Multiphysics software and verified via the field trials of gas extraction. The results revealed that the permeability increased with time due to the coupling of matrix shrinkage and volume compression of coal, in which the matrix shrinkage played a leading role. The gas seepage velocity at the observation points can be divided into three stages: the rapid rise stage, the stable decline stage, and the stable and invariant stage. The gas extraction rate continued decreasing with time and finally tended to a fixed value. In the coal seam #4 of Zhongxing coal mine, the measured flow rates of three in‐seam drilling holes were in good agreement with the simulation results, which verified the correctness of the theoretical coupling model. A solid‐gas coupling model of coal containing methane with dual porosity/dual permeability was established. The distribution of matrix gas pressure, fracture permeability, and seepage velocity were obtained. The dual‐porosity/dual‐permeability model was verified by experimental results of CBM extraction.

Crop growth models, such as the WOrld FOod STudies (WOFOST) model, mimic the mechanistic processes involved in crop development, growth, and yield production. The accuracy of simulation is decreased in unfavorable low‐temperature settings because these models do not accurately represent crop response processes in low‐temperature stress. Enhancing the WOFOST crop growth model's accuracy in simulating crops' responses to cold temperatures is the aim of this work. Given its vulnerability to low temperatures, the inquiry uses winter wheat in Henan Province as a focal point. It integrates the WHEATGROW wheat phenology model with the Frost model of Lethal Temperature 50 (FROSTOL) inside the framework of the crop growth model. This link aims to improve simulation accuracy and supplement the model's mechanisms, particularly when it comes to the impact of low temperatures on crop development. The study uses Long Short‐Term Memory networks to build a yield model that integrates remote sensing data with information from simulated crop models. Under low temperatures, the leaf area index, total above ground biomass, and total weight of storage organs of the model WWF—which combines FROSTOL and WHEATGROW with WOFOST—show a considerable decline. It was discovered that there is a greater improvement in simulation accuracy of the linked model WWF relative to the WOFOST model in frost years than in normal years, based on a comparison analysis between typical frost years and normal years. To be more precise, the improvement is 8.03% in frost years and 1.98% in regular years. When all is said and done, the coupled model advances our knowledge of how winter wheat is impacted by low temperatures.

The exploitation of groundwater in a riverside water source area is a complex process of conversion of surface water and groundwater. At present, the numerical model for simulating the exploitation of riverside water sources often generalizes rivers to the specified head boundary (CHD) or the river boundary (RIV). The CHD generalizes the river into an infinite supply of water, which is obviously unrealistic for seasonal rivers, and the RIV does not have the function of the river confluence. The above two methods directly affect the calculation accuracy of river water and groundwater conversion amount due to inherent loopholes, so the simulation of the riverside exploitation amount has some errors. This study uses the Streamflow-Routing (SFR) model to generalize the Baima-Jili River. By calculating the stream flow, the upstream, and downstream water levels of the rainy, normal, and dry seasons through the permeability parameter between river water and groundwater (parameters such as riverbed permeability coefficient, riverbed thickness, water depth, and cross-sectional shape), a coupling model of surface water and groundwater is established. In order to verify the accuracy of the SFR model simulation, the CHD and RIV conditions are used to generalize the river, and the simulation results of the three models are compared. The results show that the available groundwater exploitation simulated by the SFR model, the CHD, and the RIV boundary conditions are 27.798 × 106, 35.11 × 106, and 25.76 ×106 m3/a, respectively. The known available groundwater exploitation in the study area is 2,870 × 104 m3/a. Therefore, the SFR simulation results are more realistic, indicating that the SFR model is more suitable for coupling simulation of the surface water and groundwater interaction in riverside water sources of a seasonal river.

Carrier-based unmanned aerial vehicles (UAVs) require precise evaluation methods for their landing and arresting safety due to their high autonomy and demanding reliability requirements. In this paper, an efficient and accurate simulation method is presented for studying the arresting hook engaging arresting cable process. The finite element method and multibody dynamics (FEM-MBD) approach is employed. By establishing a rigid–flexible coupling model encompassing the UAV and arresting gear system, the simulation model for the engagement process is obtained. The model incorporates multiple coordinate systems to effectively capture the relative motion between the rigid and flexible components. The model considers the material properties, arresting gear system characteristics, and UAV state during engagement. Verification is conducted by comparing simulation results with experimental data from a referenced arresting hook rebound. Finally, simulations are performed under different touchdown points and roll angles of the UAV to analyze the stress distribution of the hook, center of gravity variations, and the tire touch and rollover cable response. The proposed rigid–flexible coupling arresting dynamics model in this paper enables the effective analysis of the dynamic behavior during the arresting hook engaging arresting cable process.

With the constant increase in communication requirements in modern society, the number and type of antennas on communication platforms have been increasing at an accelerating rate. This has led to a continuous increase in platform volume and weight, and the electromagnetic environment of antenna operating has increasingly worsened, seriously restricting the further development of communication systems. As a new communication system antenna type, a reconfigurable microstrip antenna can reconstruct operating frequencies, beam directions, etc., by changing the antenna structure to provide the good multifunction characteristics of a single antenna, avoiding the electromagnetic compatibility issues caused by numerous system antennas. At present, most of the research on reconfigurable antennas judges the influence of structural characteristics on electromagnetic characteristics by simulation, which has imposed restrictions on their development and application. Therefore, a reconfigurable antenna with a resonant frequency of 8.66 GHz and 15.26 GHz and a reconfigurable antenna with maximum radiation directions of 36.2° and −36.5° are designed in this paper, and the electromechanical coupling theory of the reconfigurable antennas is studied. The resonance frequency coupling model and the pattern function coupling model considering the structural deformation of a reconfigurable microstrip antenna are established. Within the applicable range of antenna structural parameters, the relative error between the resonance frequency coupling model and the pattern function coupling model is less than 5%, which meets practical engineering application requirements. Finally, the method is shown by experimentation to verify the accuracy and validity of the proposed electromechanical coupling model.

The four-direction performance of a TOSA and power tested with different jumpers are affected by the optical field distribution of the TOSA. In order to improve the optical field distribution of a TOSA, this paper analyzes the factors affecting optical field distribution in the core and cladding of fiber and establishes a 3D defocusing coupling model to improve the uniform distribution of the optical field. The verification between the 2D coupling model and 3D defocusing coupling model shows that four-direction performance with 3D defocusing coupling is less than 1.0 dB, and the difference of power tested with different jumpers is not more than 0.5 dB. The results are better than that of a TOSA with a conventional coupling model, and the reliability and yield of the TOSA are higher. The 3D defocusing coupling model has practical guiding significance and economic value in TOSA production.

Purpose Although the quantitative analysis of electromechanical alternans is important, previous studies have focused on electrical alternans, and there is a lack quantitative analysis of mechanical alternans at the subcellular level according to various basic cycle lengths (BCLs). Therefore, we used the excitation–contraction (E–C) coupling model of human ventricular cells to quantitatively analyze the mechanical alternans of ventricular cells according to various BCLs. Methods To implement E–C coupling, we used calcium transient data, which is the output data of electrical simulation using the electrophysiological model of human ventricular myocytes, as the input data of mechanical simulation using the contractile myofilament dynamics model. Moreover, we applied various loads on ventricular cells for implementation of isotonic and isometric contraction. Results As the BCL was reduced from 1000 to 200 ms at 30 ms increments, mechanical alternans, as well as electrical alternans, were observed. At this time, the myocardial diastolic tension increased, and the contractile ATP consumption rate remained greater than zero even in the resting state. Furthermore, the time of peak tension, equivalent cell length, and contractile ATP consumption rate were all reduced. There are two tendencies that endocardial, mid-myocardial, and epicardial cells have the maximum amplitude of tension and the peak systolic tension begins to appear at a high rate under the isometric condition at a particular BCL. Conclusions We observed mechanical alternans of ventricular myocytes as well as electrical alternans, and identified unstable conditions associated with mechanical alternans. We also determined the amount of BCL given to each ventricular cell to generate stable and high tension state in the case of isometric contraction.

The seismo-ionospheric monitoring technology has been quickly developed in recent years, which provides new ideas and techniques for short-term and imminent earthquake prediction. The multi mechanisms about sphere coupling processes related to earthquakes are reviewed and summarized since this century. Three channels with realized digital model are introduced, including overlapped DC electric field model, acoustic gravity wave and electromagnetic wave propagation model. Compared with the actual observations, the contradiction and deficiency in the models are analyzed. Finally, based on the existing observation systems, the main ideas and research directions in the seismo-ionospheric coupling mechanism in the future are discussed.