Coupling Method Research Articles

Coupled nodal integral-immersed boundary method (NI-IBM) for simulating convection-diffusion physics

The Nodal Integral Method (NIM), which is a coarse grid numerical method, works quite efficiently on orthogonal grids. However, there are many challenges to the implementation of this method in the complex shaped domains due to its intricate discretization process. In contrast, the Immersed Boundary Method (IBM) offers the advantage of implementing boundary conditions in an arbitrarily shaped domain using rectilinear, non-conformal body grids. This work presents the NIM, coupled with the IBM methodology, to solve convection-diffusion physics in complex shaped domains. IBM is utilized to enforce the boundary effect on the non-body-conformal Cartesian grid, while the NIM serves as a numerical technique to discretize the governing equations. The study describes the detailed implementation of coupled NI-IBM (Nodal Integral-Immersed Boundary Method) for convection-diffusion physics. The validation and verification of the NI-IBM methodology is done through the comparison of the numerical results with analytical solutions of the diffusion and convection-diffusion test cases. Results demonstrate that the scheme maintains its accuracy in the coarse grid structure as well as second-order accurate. Furthermore, the numerical results produced by NI-IBM are at par or more accurate with respect to the NIM based schemes for arbitrarily shaped domains and the FV-IBM (Finite Volume-Immersed Boundary Method) method for the convection-diffusion physics. The results also indicate that even with coarse grids and higher convection, the NI-IBM method preserves its nature to produce reasonably accurate numerical results.

Investigation on the responses of geotechnical materials to unloading and seepage based on the CFD-DEM coupling method

The unloading issue is prevalent in underground engineering and significantly affects construction safety and the operation of surrounding facilities, while research regarding it is still relatively scarce. A novel CFD-DEM coupling method with dynamic fluid meshes is proposed to reproduce the unloading effect and reveal its micro-scale mechanisms. It adopts uniformly distributed point sets to generate/update fluid meshes and solves with a proposed numerical mapping method. The one-dimensional linear unloading modeling method is further established. The numerically obtained excess pore pressure and rebound deformation under the one-way drained condition are compared with the analytical solutions. The coupling method demonstrates considerable reliability in forecasting the pore pressure response and its advantage for predicting rebound deformation is revealed. The evolutions of the fluid velocity field, particle displacement field, and pore pressure distribution profile are described. The influences of fluid compressibility, unloading rate, unloading volume and initial pore pressure on the unloading characteristics are carefully investigated. The results indicate that the pore pressure is obviously influenced by the selected factors. However, the impact of unloading volume on the final rebound deformation is most significant. Finally, influences of frictionless walls, two-way drained conditions, buoyancy and fluid viscosity on the unloading response are further discussed.

Comparative study of multiple statistical damage mechanics models for rock behaviors under high temperature

Under the influence of external factors such as high temperature, chemical corrosion, and loading-unloading cycles, micro-cracks and pores may develop within rock structures. Continuum damage mechanics (CDM) characterizes these micro-defects arising within rocks, investigating the physico-mechanical behaviors of rocks in damaged states. This study, grounded in the theoretical framework of CDM and utilizing the Mohr-Coulomb failure criterion, integrates different probability distributions and damage coupling methods to develop three statistical damage models. The investigation primarily explores the effects of strength criteria, probability functions, and damage coupling mechanisms on the statistical damage models. In addressing the complex interplay between rock micro-defects and external stressors such as high temperatures and chemical corrosion, this study leverages the principles of CDM within the Mohr-Coulomb criterion framework. It advances the field by developing three innovative statistical damage models, enriched by diverse probability distributions and damage coupling methods. The research delineates the substantial impact of strength criteria, probability functions, and damage coupling mechanisms on the behavior of these models. Notably, it achieves a synthesis of theoretical constructs and experimental validation, demonstrating the models' capacity to reflect the nuanced behaviors of damaged rock accurately. Furthermore, this investigation contributes a methodological blueprint for statistical damage model construction, underscoring the critical selection of strength criteria and probability distributions. These efforts fortify the theoretical underpinnings necessary for the enhanced engineering application of statistics-driven damage analysis.

Markovian lifting and asymptotic log-Harnack inequality for stochastic Volterra integral equations

We introduce a new framework of Markovian lifts of stochastic Volterra integral equations (SVIEs for short) with completely monotone kernels. We define the state space of the Markovian lift as a separable Hilbert space which incorporates the singularity or regularity of the kernel into the definition. We show that the solution of an SVIE is represented by the solution of a lifted stochastic evolution equation (SEE for short) defined on the Hilbert space and prove the existence, uniqueness and Markov property of the solution of the lifted SEE. Furthermore, we establish an asymptotic log-Harnack inequality and some consequent properties for the Markov semigroup associated with the Markovian lift via the asymptotic coupling method.

Experimental study on flow field and performance of bionic-wavy leading edge in an axial compressor with positive bowed blades

To enhance the aerodynamic performance of compressors in advanced aeroengines, a compound flow control method combining positively bowed blades and bionic-wavy leading edges is proposed for improving the aerodynamic performance of compressor cascades with controlled diffusion airfoils. This study verified the effectiveness of the compound control method through low-speed wind tunnel experiments using five-hole probe measurements and surface oil-flow visualization techniques. Additionally, the flow field structure was analyzed, and vortex models were established to thoroughly discuss the mechanism of the compound flow control method. The results show that within the incidence angle range of 0°–4° studied in this paper, the composite control method achieved significantly effective control, with a maximum reduction in overall total pressure loss of 25.8% compared to straight blade cascades. Three vortex models were established. The positive bowed blade cascade induced a complex vortex structure in the concentrated shedding vortex region, increasing losses in the concentrated shedding vortex (CSV) region but reducing profile losses. The coupled method further reduced profile losses and optimized the flow field in the CSV region. This study not only validates the feasibility of the compound method but also provides guidance for applying flow control methods to bowed blade cascades.

An Innovative and Efficient Implementation of Matrix-Free Newton Krylov Method for Neutronics/Thermal-hydraulics Coupling Simulation

The core physical behavior of reactors is essentially the result of multi-physical fields coupling feedback. High-fidelity neutronics/thermal-hydraulics (N/TH) analysis can simulate and predict nuclear reactor core phenomena realistically, providing advanced and reliable technical means during the design and safety analysis of nuclear reactor. In this work, an efficient and robustness coupling method using power density as the coupling parameter, Matrix-Free Newton Krylov (MFNK) method, is successfully developed and innovatively implemented in HNET for high-fidelity N/TH coupling simulation. To enhance the efficiency and stability, the multi-level generalized equivalence theory-based CMFD (ML-gCMFD) iterative acceleration method and ML-gCMFD coupling acceleration method are proposed. In addition, the nonlinear preconditioning and hybrid perturbation size formula are implemented to further improve the convergence. Finally, to evaluate the numerical accuracy, convergence, efficiency and stability of MFNK method, a series of representative problems, including a three-dimensional (3D) single fuel pin problem, VERA Benchmark Problem 6, and VERA Benchmark Problem 7, are analyzed by comparing with the current N/TH coupling methods. Numerical results indicate that MFNK method can obtain strong stability, high convergence performance, and relatively high computational efficiency while ensuring high accuracy. It demonstrates that MFNK method has significant performance advantages and potential for high-fidelity N/TH coupling simulation.

Numerical Study of Skipping Motion of Blended-Wing–Body Aircraft Ditching on Calm/Wavy Water

The blended-wing–body (BWB) is hoped to be the main configuration of next-generation transport aircraft. However, its large flat belly may cause a violent skipping motion during the ditching on water. In this paper, the skipping motions of a BWB aircraft ditching on calm and wavy water are numerically investigated. The finite volume method with the volume-of-fluid approach is employed to solve the unsteady Reynolds-averaged Navier–Stokes equations. A coupled method between global moving mesh and overset mesh is proposed to avoid a large background domain and improve the prediction accuracy of the free surface, and its accuracy is well validated by predicting the motions of a skipping stone, the hydrodynamic load and pressure on a flat plate in high-speed ditching, and the fifth-order Stokes wave in a dynamic wave tank. At the beginning of every surfing stage, the flat belly of BWB aircraft impacts heavily on the water surface at a smaller pitch angle and larger speed, resulting in the local vertical overload peak, which is much larger than the peak in the porpoising motion. The wavy water surface intensifies the heave and pitch motions and increases the risk of the cockpit diving into the water.

Stable construction and analysis of MDD modular networks based on multi-center EEG data

BackgroundThe modular structure can reflect the activity pattern of the brain, and exploring it may help us understand the pathogenesis of major depressive disorder (MDD). However, little is known about how to build a stable modular structure in MDD patients and how modules are separated and integrated. MethodWe used four independent resting state Electroencephalography (EEG) datasets. Different coupling methods, window lengths, and optimized community detection algorithms were used to find a reliable and robust modular structure, and the module differences of MDD were analyzed from the perspectives of global module attributes and local topology in multiple frequency bands. ResultsThe combination of the Phase Lag Index (PLI) and the Louvain algorithm can achieve better results and can achieve stability at smaller window lengths. Compared with Healthy Controls (HC), MDD had higher Modularity (Q) values and the number of modules in low-frequency bands. In addition, MDD showed significant structural changes in the frontal and parietal-occipital lobes, which were confirmed by further correlation analysis. ConclusionOur results provided a reliable validation of the modular structure construction method in MDD patients and contributed strong evidence for the changes in emotional cognition and visual system function in MDD patients from a new perspective. These results would afford valuable insights for further exploration of the pathogenesis of MDD.

On a method of constructing a biaxial multitype conservative chaotic system and an image encryption scheme

On the basis of single axis coupling for constructing conservative chaos, a method for constructing a biaxial multitype conservative chaotic system is proposed. The method constructs more types of chaotic systems with a wider range of traversal. When coupling the Eulerian subbody biaxially, it is discovered that the structural matrix is able to exhibit two different multistates, namely, 0 and the opposite state, 0 and the same state, and depending on the location of the introduced adjustable parameter, the constructed chaotic equations also exhibit multiple types. When the structure matrix exhibits 0 and opposite state, the chaotic equations exhibit three types, which are opposite, one-parameter, and two-parameter types; and when the structure matrix is 0 and the same state, the chaotic equations exhibit the same type, one-parameter, and two-parameter types. The relationship of each pair of adjustable parameters satisfies the structure matrix antisymmetry, which leads to many types of Hamiltonian conservative chaotic systems that can transition between quasi-periodic, hyperchaotic, and chaotic states, all of which pass the NIST test, increasing the diversity of chaotic system choices in image encryption. The chaotic system is applied in image encryption, using Hadamard product matrix permutation, index permutation and four-dimensional pixel diffusion algorithms, and finally generates the ciphertext image. The method of biaxial coupling can construct six different types of chaotic systems, after image encryption, the average value of information entropy reaches 7.9994, the correlation coefficient is close to 0, the NPCR and UACI are close to the ideal values of 99.61 % and 33.46 %, the algorithm can effectively resist the statistical attack, the robustness attack and the differential attack, and the results demonstrate that the algorithm has better security performance.

Multi-objective optimization design of a sewage pump based on non-dominated sorting genetic algorithm III

Accumulation of sanitary refuse, such as flexible cloth-like structures or the so-called rags, inflows through sewage pumps are prone to tangling, ultimately leading to clogging and wear. To prevent this, the ability of sewage pumps to handle wet wipes, rags, and similar flexible materials is a key feature that must be considered as the pumps are designed. Therefore, this paper proposed a multi-objective optimization strategy based on the fluid–structure interaction simulation, Support Vector Regression (SVR), and non-dominated sorting genetic algorithm III (NSGA-III). First, the values of the optimization objectives were obtained by a Coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) approach. Then, SVR was utilized to establish an approximate model between the design variables and the optimization objectives. The NSGA-III was applied to search the Pareto front. Finally, the improved impeller model was selected by adopting technique for order preference by similarity to an ideal solution (TOPSIS) with entropy weight. The results show that the multi-objective optimization method is suitable for the optimization design of sewage pumps. Comparing the numerical calculations of the original pump and the optimized pump, the results show that the optimized head and efficiency increased by 9.7% and 7.13%, respectively. The optimized pump improves the passage rate of the rag and effectively improves the clogging behavior. The wear amount of the optimized pump is significantly reduced by 32.54%.

Phase-Amplitude Coupling in Theta and Beta Bands: A Potential Electrophysiological Marker for Obstructive Sleep Apnea.

Phase-amplitude coupling (PAC) between the phase of low-frequency signals and the amplitude of high-frequency activities plays many physiological roles and is involved in the pathological processed of various neurological disorders. However, how low-frequency and high-frequency neural oscillations or information synchronization activities change under chronic central hypoxia in OSA patients and whether these changes are closely associated with OSA remains largely unexplored. This study arm to elucidate the long-term consequences of OSA-related oxygen deprivation on central nervous system function. : We screened 521 patients who were clinically suspected of having OSA at our neurology and sleep centers. Through polysomnography (PSG) and other clinical examinations, 103 patients were ultimately included in the study and classified into mild, moderate, and severe OSA groups based on the severity of hypoxia determined by PSG. We utilized the phase-amplitude coupling (PAC) method to analyze the modulation index (MI) trends between different frequency bands during NREM (N1/N2/N3), REM, and wakefulness stages in OSA patients with varying severity levels. We also examined the correlation between the MI index and OSA hypoxia indices. Apart from reduced N2 sleep duration and increased microarousal index, the sleep architecture remained largely unchanged among OSA patients with varying severity levels. Compared to the mild OSA group, patients with moderate and severe OSA exhibited higher MI values of PAC in the low-frequency theta phase and high-frequency beta amplitude in the frontal and occipital regions during N1 sleep and wakefulness. No significant differences in the MI of phase-amplitude coupling were observed during N2/3 and REM sleep. Moreover, the MI of phase-amplitude coupling in theta and beta bands positively correlated with hypoxia-related indices, including the apnea-hypopnea index (AHI) and oxygenation desaturation index (ODI), and the percentage of oxygen saturation below 90% (SaO2<90%). OSA patients demonstrated increased MI values of theta phase and beta amplitude in the frontal and occipital regions during N1 sleep and wakefulness. This suggests that cortical coupling is prevalent and exhibits sleep-stage-specific patterns in OSA. Theta-beta PAC during N1 and wakefulness was positively correlated with hypoxia-related indices, suggesting a potential relationship between these neural oscillations and OSA severity. The present study provides new insights into the relationship between neural oscillations and respiratory hypoxia in OSA patients.

Numerical Analysis on Fractured Roadway Stability Based on the FDM–DFN Coupling Method

Numerical Analysis on Fractured Roadway Stability Based on the FDM–DFN Coupling Method

A coupling method for CRUD mass calculation based on Eulerian-Eulerian two-fluid model

Abstract The corrosion products occur in the pressure boundary in the pressurized water reactor primary loop which is known as CRUD. CRUD could increase the risks of crud induced power shift and crud induced localized corrosion. The mechanism of CRUD production depends on nucleate boiling. Eulerian-Eulerian two-fluid model has been currently proved as effective means to understand flow boiling character. In this research, the input data of thermo-hydraulic parameter is obtained by CFD method. The CRUD mass has been calculated based on thermo-hydraulic and chemical coupled model. The main calculation code in this article is FLUENT and CAMPSIS. The calculation results show that the CRUD does most likely occur the 3rd grid mixing vanes from the top of the fuel rod. The maximum CRUD mass is closer to the position of onset of nucleate boiling.

Parameter characterization of the PBM-DEM method in numerical simulation of shallow buried mine explosions

Abstract To investigate the impact of various parameters on the numerical simulation of shallow buried mine explosions through the particle explosion method and discrete element method, this paper adopts a coupled method of particle blast method and discrete element method, namely the PBM-DEM method, to simulate the response of AL-6XN stainless steel plate under shallow buried mine explosions. This article first combines the experimental results of Børvik to validate the precision of the PBM-DEM approach. Then, the influence of particle quantity, interaction parameters between sand particles, and interaction parameters between sand particles and plate on the outcomes of the numerical simulations are analyzed. The analysis reveals that as the quantity of explosive particles rises, the central displacement and maximum kinetic energy of the plate escalate. In contrast, these values decrease as the number of sand particles increases. The interaction parameters between sand particles have almost no effect on the numerical simulation results. The damping and stiffness parameters between the sand particles and the plate have a pronounced effect on the numerical simulation results, and the center displacement and peak kinetic energy of the plate rise as the damping and stiffness parameters between the sand particles and the plate increase.

Influence of solid particles in liquid tank on sloshing behaviour based on CFD-DEM coupling method

This paper employs multiphase flow theory to investigate the influence of different solid particle densities on the sloshing characteristics within a liquid tank. A numerical model of gas-liquid-solid multiphase flow sloshing motion within the tank was established using the Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) coupling method, simulating the interactive coupling between the two-phase fluid and solid particles. In this context, the gas-liquid two-phase fluid is treated as a continuous phase, described under the Eulerian framework, with the Volume of Fluid (VOF) method applied to capture the gas-liquid interface. Conversely, the solid particles are treated as a discrete phase, described under the Lagrangian framework. The effects of different solid particle densities on the tank sloshing characteristics were analyzed utilizing the STAR-CCM + software platform. Initially, the validity of the CFD-DEM method was confirmed by simulating classical scenarios such as a single spherical particle falling from air into water and the flow dynamics of a gas-liquid-solid three-phase dam break. Subsequently, a numerical simulation of sloshing in a pure water tank was conducted and compared with published experimental results, thereby verifying the feasibility of the numerical method for gas-liquid two-phase sloshing. Following this, a series of simulations were conducted on a pure water tank to validate the effectiveness of the numerical method for gas-liquid two-phase fluid sloshing. Subsequently, solid particles were introduced to the model, and the effect of solid particle densities on sloshing load and response under forced motion was studied. Finally, by comparing and analyzing the sloshing-induced pressure on the tank walls and the amplitude of the free surface motion across different solid particle densities and as well as different excitation frequencies, the sloshing characteristics of the solid-liquid mixed two-phase flow were investigated. The computational results indicate that an increase in solid particle density corresponds to an increase in liquid surface wave amplitude. This suggests that lighter solid particles have a greater damping effect on tank sloshing. It can be inferred that when the density of solid particles is maintained at a constant level, the closer the external excitation frequency is to the natural frequency, the more effective the sloshing suppression effect. This is attributed to the fact that, as sloshing intensifies, fluid velocity increases, resulting in greater damping due to viscosity effects, thereby enhancing the sloshing suppression.

Assessing pre-season workload variation in professional rugby union players by comparing three acute:Chronic workload ratio models based on playing positions

Quantifying the pre-season workload of professional Rugby Union players, in relation to their respective positions not only provides crucial insights into their physical demands and training needs but also underscores the significance of the acute:chronic workload ratio (ACWR) in assessing workload. However, given the diversity in ACWR calculation methods, their applicability requires further exploration. As a result, this study aims to analyze the workload depending on the player's positions and to compare three ACWR calculation methods. Fifty-seven players were categorized into five groups based on their playing positions: tight five (T5), third-row (3R), number nine (N9), center, and third line defense (3L). The coupled and uncoupled rolling averages (RA), as well as the exponentially weighted moving average ACWR method, were employed to compute measures derived from GPS data. Changes throughout the pre-season were assessed using the one-way and two-way analysis of variance. The results revealed that N9 covered significantly greater distances and exhibited higher player load compared to T5 and 3L [p < 0.05, effect size (ES) = 0.16–0.68]. Additionally, 3L players displayed the highest workload across various measures, including counts of accelerations and decelerations (>2.5 m s−2), accelerations (>2.5 m s−2), acceleration distance (>2 m s−2), high-speed running (>15 km h−1), very high-speed running (>21 km h−1, VSHR), sprint running (>25 km h−1, SR) distance. When using coupled RA ACWR method, centers exposed significantly greater values to T5 (p < 0.05, ES = 0.8) and 3R (p < 0.05, ES = 0.83). Moreover, centers exhibited greater (p < 0.05, ES = 0.67–0.91) uncoupled RA ACWR values for VHSR and SR than T5 and 3R. When comparing the three ACWR methods, although significant differences emerged in some specific cases, the ES were all small (0–0.56). In light of these findings, training should be customized to the characteristics of players in different playing positions and the three ACWR calculation methods can be considered as equally effective approaches.

Research on Multiphyics bidirectional coupling for small-diameter high-speed submersible permanent magnet synchronous motor

The small-diameter high-speed submersible permanent magnet synchronous motor (SHS-PMSM) is essential equipment for rodless oil and gas extraction in slimhole wells and high-water content oil wells. The SHS-PMSM typically operates for extended periods of time underground in high temperatures. Because of its compact size, the heat is difficult to dissipate, which increases the risk of motor overheating and damage. In order to accurately predict temperature, the method of magnetic-heat-flow multiphysics bidirectional coupling is studied in this paper. A SHS-PMSM with an outer diameter of ø89mm is taken as the object, and its copper loss, friction loss and convective heat transfer coefficient are studied by analytical derivation. The relationship between them and temperature are expressed by functions which can be compiled into User-Defined Functions (UDFs) as variable during the calculation process of finite volume method. Both coupling calculations and experiments are conducted. The temperature calculated by magnetic-heat-flow bidirectional connection is higher than that produced by the conventional method and more in line with experimental results after the results of both simulations and experiments are carried out and compared. The accuracy of the magnetic-heat-flow bidirectional coupling method is verified and the design basis of temperature for SHS-PMSM can be provided.

Electrothermal coupling analysis of submarine cables

ABSTRACT With offshore wind power transmission engineering development, submarine cable laying plays an important role in energy supply. Deep-water heavy-current composite submarine cables generate heat during power transmission, which raises their temperature and impacts energy efficiency and mechanical properties. To address the issue of heat release affecting structural sections during cable operation, a structural temperature field calculation theory is introduced, establishing a method for calculating the temperature field of submarine cables.The IEC standard's equivalent thermal circuit method and COMSOL Multiphysics' electromagnetic, thermal coupling method were employed to assess the current carrying capacity at the insulation temperature. The finite element model's accuracy was confirmed by comparing manufacturer-provided parameters. Additionally, a 3D finite-element model of the cable was created to determine its tensile, bending, and torsional stiffness with and without the electric-heat-force field coupling.

Theoretical approaches to study degradation in Li-ion battery cathodes: Crucial role of exchange and correlation

Abstract Li-ion batteries have become essential in energy storage, with demand rising steadily. Cathodes, crucial for determining capacity and voltage, face challenges like degradation in the form of thermal runaway and battery failure. Understanding these degradation phenomena is vital for developing mitigation strategies. Experimental techniques such as XAS, XPS, PES, UV–Vis, RIXS, NMR, and OEMS are commonly used, but theoretical modelling, particularly atomistic modelling with density-functional theory (DFT), provides key insights into the microscopic electronic behaviours causing degradation. While DFT offers a precise formulation, its approximations in the exchange-correlation functional and its ground-state, 0K limitations necessitate additional methods like ab initio molecular dynamics. Recently, many-body electronic structure methods have been used alongside DFT to better explain electron–electron interactions and temperature effects. This review emphasizes material-specific methods and the importance of electron–electron interactions, highlighting the role of many-body methods in addressing key issues in cathode degradation and future development in electron–phonon coupling methods. Graphical abstract

Leakage detection method based on transient pressure behaviors during pigging process in pipelines

Pipelines are the most common way to transport oil and gas due to its convenience. They are facing many threatens such as leakage, which may cause serious pipeline accidents. This paper proposes a leakage detection method coupled with the transient pressure characteristics to recognize leaks in pipeline. A coupled dynamic mesh method was used to achieve the movement of pigging device. The explicit and implicit coupling method has been developed to simulate transient pressures and leak behaviors. Cases has been conducted through the established experimental pipeline system to validate the proposed leakage detection method. The reasonable agreement between the results from these two methods verify that the proposed leakage detection method is accurate enough to simulate transient pressure behaviors in pipelines during the pigging process. Leak volume and location identification methods have been presented and the calculation accuracy is verified in a reasonable range. The proposed leakage detection method in this paper is a supplement to the field of subsea pipeline detection.