Coupling Algorithm Research Articles

Numerical investigation of cavitation-vortex structures around a sphere with boundary data immersion method

The boundary data immersion method (BDIM) coupled with the artificial compressibility method is applied to investigate the interaction of the cavitation-vortex dynamics around a sphere. The convolution of governing equation with a nascent delta kernel is employed to smooth the transition region between the solid and the fluid subdomain. Therefore, the BDIM addresses a key problem with smooth immersion boundary method in representing the discontinuity of the velocity gradient ∂u/∂y at the wall when considering flows with intermediate to high Reynolds numbers. In addition, a pseudo-time derivative of the pressure multiplied by an artificial-compressibility factor is added to the continuity equation. The developed coupling algorithm can accurately capture the unsteady cavitation characteristics, which is consistent with the previous experimental data. Subsequently, the typical vortex identification methods and the turbulent kinetic energy (TKE) transport equation are applied to analyze the interaction between the cavitation dynamics and turbulence vortices structures. A series of turbulent vortices are captured with the cloud cavity shedding. Moreover, it is found that the unsteady cavity topology will promote the generation of TKE.

Cable Steady-State Ampacity Correction Method based on Multi Physical Field Coupling Algorithm

The difference between the single air laying ampacity test value of medium voltage power cable and the system ampacity of three-phase laying and operation is a common problem in the industry. Based on the TICW-2012 standard, the single cable ampacity of medium voltage single core power cable is tested, and the COMSOL basic simulation model is debugged with the measured ampacity value. On the premise of correct single cable basic simulation model, the system ampacity under three-phase operation under different working conditions is calculated, including triangular laying, plane laying, single circuit and double circuit laying, The difference and correction coefficient between the test current carrying capacity and the of single air laying of medium voltage single core power cable are further analysed. Finally, the analytical formula is derived through the cable ampacity equivalent thermal circuit diagram, and the cable samples are theoretically analysed and calculated. According to the ampacity calculation results of single loop triangular laying and plane laying, the correctness of the simulation results is verified. This study provides a reference basis for the current carrying capacity test and correction of medium voltage power cable in the future, and also provides an effective method for the actual operation state analysis of medium voltage power cable.

A self-aligned lithography method based on Fabry-Perot resonator effect

Fabry-Perot (F-P) resonator is widely applied in the field of optics such as micro-ring resonator and photonic crystal, but there are not yet relevant reports about optical imaging. We propose a self-aligned lithography method based on F-P resonator effect and realize self-aligned effect successfully by controlling film stack parameters. The self-aligned structure is composed of Ag/photoresist/Ag film stack and wafer layer which contains SiO2 layer and SiO2/Si gratings. A rapid simulation model based on Rigorous Coupled Wave Analysis algorithm is established to optimize the best parameters of the self-aligned structure. Then rigorous Finite Difference Time Domain model and Finite Element Method model are used to verify the self-aligned effect and the results show that such process has extremely large mask critical dimension (CD) and overlay variation. The mask CD could be tuned more than 50% of structure period while the wafer CD maintains in the range less than 10%, and the maximum mask overlay offset could be ± 25% of half pitch while the wafer pattern center maintains unchanged. All the results show that the proposed method has lots of process robustness and could increase the application area of imaging lithography technology.

An incompressible smoothed particle hydrodynamics‐finite volume method coupling algorithm for interface tracking of two‐phase fluid flows

AbstractTwo‐phase flow involves complex interface evolution process such as the formation, development, pulsation, and rupture of phase interfaces. Numerical simulation is one of the important means to study two‐phase flow. The tracking and reconstruction of phase interface is the focus of two‐phase flow simulation. A two‐phase flow simulation algorithm based on coupled incompressible smoothed particle hydrodynamics (ISPH) method and finite volume method (FVM) is developed in this article. In present ISPH‐FVM coupling algorithm, one phase which has smaller volume is represented by SPH particles, while the other phase is defined on the FVM grids. The coupling of ISPH and FVM is achieved through the transfer and interaction of physical parameters at the overlapping area of the SPH particles and FVM grids. The continuous medium surface force model is also introduced into the ISPH‐FVM coupling algorithm to study the effect of surface tension on the two‐phase flow. Several numerical examples of two‐phase flow are adopted to verify the effectiveness of the ISPH‐FVM coupling method.

Time Domain Analysis of 3-D Microwave Film Bulk Acoustic Resonator Based on Electro- Mechanical Coupling Algorithm

Time Domain Analysis of 3-D Microwave Film Bulk Acoustic Resonator Based on Electro- Mechanical Coupling Algorithm

Model-Based Analysis of Myocardial Contraction Patterns in Ischemic Heart Disease

ObjectivesThe objective of the current study is to assess the feasibility of using a left ventricle (LV) model in order to reproduce myocardial strains in the case of ischemic heart disease (IHD). Materials and MethodsThe proposed integrated LV model couples a finite element method (FEM) sub-model of the cardiac electrical activity, representing the propagation of the transmembrane potential through the LV, a FEM sub-model of the cardiac mechanical activity, and a lumped-parameter model of the circulatory system that improves the physiological definition of appropriate boundary conditions. Simulations were compared to myocardial strain data obtained from echocardiography, performed on two healthy subjects and two patients diagnosed with chronic IHD. ResultsResults show the model ability to simulate jointly the hemodynamic variables (Systolic and diastolic pressures respectively equal to 110 and 60 mmHg) and myocardial strain curves during each phase of the cardiac cycle. A close match is observed between minimum strains obtained from simulations and clinical data from healthy subjects and IHD patient, with a root mean square error around 2,81% and 2,63% respectively. The modifications of regional LV systolic strains observed from IHD patients with respect to healthy cases were partially explained by a decrease of regional cardiac stress. ConclusionThis paper provides a description of a new coupling algorithm between FEM and lumped-parameter models. Results are promising for the analysis of cardiac strains in the context of IHD.

Rapid Detection of Carbendazim Residue in Apple Using Surface-Enhanced Raman Scattering and Coupled Chemometric Algorithm.

In order to achieve rapid and precise quantification detection of carbendazim residues, surface-enhanced Raman spectroscopy (SERS) combined with variable selected regression methods were developed. A higher sensitivity and greater density of “hot spots” in three-dimensional (3D) SERS substrates based on silver nanoparticles compound polyacrylonitrile (Ag-NPs @PAN) nanohump arrays were fabricated to capture and amplify the SERS signal of carbendazim. Four Raman spectral variable selection regression models were established and comparatively assessed. The results showed that the bootstrapping soft shrinkage-partial least squares (BOSS-PLS) method achieved the best predictive capacity after variable selection, and the final BOSS-PLS model has the correlation coefficient (RP) of 0.992. Then, this method used to detect the carbendazim residue in apple samples; the recoveries were 86~116%, and relative standard deviation (RSD) is less than 10%. The 3D SERS substrates combined with the BOSS-PLS algorithm can deliver a simple and accurate method for trace detection of carbendazim residues in apples.

LBcuda: A high-performance CUDA port of LBsoft for simulation of colloidal systems

We present LBcuda, a GPU accelerated version of LBsoft, our open-source MPI-based software for the simulation of multi-component colloidal flows. We describe the design principles, the optimization and the resulting performance as compared to the CPU version, using both an average cost GPU and high-end NVidia GPU cards (V100 and the latest A100). The results show a substantial acceleration for the fluid solver reaching up to 200 GLUPS (Giga Lattice Updates Per Second) on a cluster made of 512 A100 NVIDIA cards simulating a grid of eight billion lattice points. These results open attractive prospects for the computational design of new materials based on colloidal particles. Program summaryProgram Title: LBcudaCPC Library link to program files:https://doi.org/10.17632/v6fvmzpcrn.1Developer's repository link:https://github.com/copmat/LBcudaLicensing provisions: 3-Clause BSD LicenseProgramming language: CUDA FortranNature of problem: Hydro-dynamics of colloidal multi-component systems and Pickering emulsions.Solution method: Lattice-Boltzmann method solving the Navier-Stokes equations for the fluid dynamics within an Eulerian description. Particle solver describing colloidal particles within a Lagrangian representation coupled to the fluid solver. The numerical solution of the coupling algorithm includes the back reaction effects for each force terms according to a fluid-particle multi-scale paradigm.

F$$_3$$ORNITS : a flexible variable step size non-iterative co-simulation method handling subsystems with hybrid advanced capabilities

This paper introduces the F $$_3$$ ORNITS non-iterative co-simulation algorithm in which F $$_3$$ stands for the 3 flexible aspects of the method: flexible polynomial order representation of coupling variables, flexible time-stepper applying variable co-simulation step size rules on subsystems allowing it, and flexible scheduler orchestrating the meeting times among the subsystems and capable of asynchronousness when subsystems’ constraints require it. The motivation of the F $$_3$$ ORNITS method is to accept any kind of co-simulation model as far as they represent circuits (0D models, such as ODE or DAE), including any kind of subsystem (open circuits), regardless on their available capabilities. Indeed, one of the major problems in industry is that the subsystems usually have constraints or lack of advanced capabilities making it impossible to implement most of the advanced co-simulation algorithms on them. The method makes it possible to preserve the dynamics of the coupling constraints when necessary as well as to avoid breaking $$C^1$$ smoothness at communication times, and also to adapt the co-simulation step size in a way that is robust both to zero-crossing variables (contrary to classical relative error-based criteria) and to jumps. Five test cases are presented to illustrate the robustness of the F $$_3$$ ORNITS method as well as its higher accuracy than the non-iterative Jacobi coupling algorithm (the most commonly used method in industry) for a smaller number of co-simulation steps.

Multiscale analysis of tunnel surrounding rock disturbance: A PFC3D-FLAC3D coupling algorithm with the overlapping domain method

Under the condition of high in-situ stress, the instantaneous excavation disturbs surrounding rocks, which shows different internal mechanisms on the different scales. At present, there still lacks numerical simulation algorithms for multiscale analysis in this field. A PFC3D-FLAC3D coupling algorithm with the overlapping domain method (ODM) was proposed. ODM can optimize the problem of energy reflection between different coupling domains and improve the accuracy of calculation. ODM was verified to a certain extent, including the velocity transmission and the mechanical deformation of models. In addition, the coupling algorithm with ODM was applied to the tunnel excavation under the assumption of the Kastner formula and the Songhua–Changchun diversion tunnel in China. In the tunnel excavation simulation, the simulation results showed that the coupling algorithm can characterize the stress distribution of surrounding rocks on the macro-scale, and reveal the phenomena of crack initiation propagation and large deformation on the micro-scale. By comparing with the empirical formula and the engineering data, it can be found that the coupling algorithm accurately and effectively realized the multiscale simulation of rocks disturbance. This research have some reference value for the multiscale investigation, which is the disturbance of surrounding rock caused by tunnelling.

IFOSMONDI Co-simulation Algorithm with Jacobian-Free Methods in PETSc

Co-simulation is a widely used solution to enable global simulation of a modular system via the composition of black-boxed simulators. Among co-simulation methods, the IFOSMONDI implicit iterative algorithm, previously introduced by the authors, enables us to solve the non-linear coupling function while keeping the smoothness of interfaces without introducing a delay. Moreover, it automatically adapts the size of the steps between data exchanges among the subsystems according to the difficulty of solving the coupling constraint. The latter was solved by a fixed-point algorithm, whereas this paper introduces the Jacobian-Free Methods version. Most implementations of Newton-like methods require a jacobian matrix which, except in the Zero-Order-Hold case, can be difficult to compute in the co-simulation context. As IFOSMONDI coupling algorithm uses Hermite interpolation for smoothness enhancement, we propose hereafter a new formulation of the non-linear coupling function including both the values and the time-derivatives of the coupling variables. This formulation is well designed for solving the coupling through jacobian-free Newton-type methods. Consequently, successive function evaluations consist in multiple simulations of the systems on a co-simulation time-step using rollback. The orchestrator-workers structure of the algorithm enables us to combine the PETSc framework on the orchestrator side for the non-linear Newton-type solvers with the parallel integrations of the systems on the workers’ side thanks to MPI processes. Different non-linear methods will be compared to one another and to the original fixed-point implementation on a newly proposed 2-system academic test case with direct feedthrough on both sides. An industrial model will also be considered to investigate the performance of the method.

Numerical simulation modeling of middle ear-eustachian tube ventilation based on Chinese digital visual human body

Objective: To establish a three-dimensional model of middle ear-eustachian tube based on Chinese digital visual human dataset, and the deformation and pressure changes of the middle ear-eustachian tube system after eustachian tube opening are simulated by computer numerical simulation. Methods: The first female Chinese Digital Visual Human data was adopted. The images were imported by Amira image processing software, and the images were segmented by Geomagic software to form a three-dimensional model of middle ear-eustachian tube system, including eustachian tube, tympanum, tympanic membrane, auditory ossicles, and mastoid air cells system. The 3D model was imported into Hypermesh software for meshing and analysis. The structural mechanics calculation was carried out by Abaqus, and gas flow was simulated by Xflow. The tissue deformation and middle ear pressure changes during eustachian tube opening were numerically simulated by fluid-solid coupling algorithm. Several pressure monitoring points including tympanum, mastoid, tympanic isthmus, and external auditory canal were set up in the model, and the pressure changes of each monitoring point were recorded and compared. Results: In this study, a three-dimensional model of middle ear-eustachian tube and a numerical simulation model of middle ear ventilation were established, including eustachian tube, tympanum, mastoid air cells, tympanic membrane, and auditory ossicles. The dynamic changes of the model after ventilation could be divided into five stages according to the pressure. In addition, the pressure changes of tympanum and tympanic isthmus were basically synchronous, and the pressure changes of mastoid air cells system were later than that of tympanum and tympanic isthmus, which verified the pressure buffering effect of mastoid. The extracted pressure curve of the external auditory canal was basically consistent with that of tympanometry in terms of value and trend, which verified the effectiveness of the model. Conclusions: The numerical simulation model of middle ear-eustachian tube ventilation established in this paper can simulate the tissue deformation and middle ear pressure changes after eustachian tube opening, and its accuracy and effectiveness are also verified. This not only lays a foundation for further research, but also provides a new research method for the study of middle ear ventilation.

FLUID–STRUCTURE COUPLING SIMULATION OF EXPLOSIVE FLOW FIELD IN HETEROGENEOUS POROUS MEDIA BASED ON FRACTAL THEORY

In this paper, through finite difference and finite element coupling algorithms with structured grid, the fluid–structure coupling problems of the pressure of the fluid as well as stress and strain of the heterogeneous porous medium under the initial pressure of MPa magnitude are calculated, respectively. The porous medium is a cavity cylinder with fractal characteristics. The parameters of porosity, elastic modulus and Poisson’s ratio of porous media with different fractal dimensions ([Formula: see text], 2.4 and 2.5) are obtained by theoretical calculation. Through theoretical derivation, the amplitude of WM function is expressed by the fractal parameter porosity, which can predict the uneven characteristics caused by the nonuniformity of pore size distribution after explosion. The results show that with the increase of fractal dimensions, the porosity increases, and both the elastic modulus and the Poisson’s ratio decrease. The Poisson’s ratio has a linear relationship with porosity, which is well consistent with the modified formula in the literature. Under the same initial pressure, the stress and strain values of the material without fractal characteristics are much larger than those of the material with fractal feature which has an obvious fluctuation by extracting the average values. It indicates that the fractal porous media with rough surface can effectively reduce the pressure wave peak at the wall surface, and reduce the size of the stress and strain concentrations to prevent the vibration of the cylinder. As expected, if the initial pressure increases with an equal fractal dimension, the stress and strain values of the fluid–structure coupling will increase too. When the initial pressure is equal, the peak value of pressure in wall decreases gradually with the increase of fractal dimension, and the stress and strain values also decrease.

Reduced Order Modeling of Deformable Tire-Soil Interaction With Proper Orthogonal Decomposition

AbstractIn this study, model order reduction of high-fidelity off-road mobility models is explored to address the computational intensity of nonlinear finite element deformable tire–soil interaction models. To this end, a model order reduction procedure for the tire–soil interaction model is developed with the proper orthogonal decomposition (POD), and it is integrated into the off-road mobility simulation framework, leveraging high-performance computing. The POD is, however, limited in that the modes are dependent on snapshot data collected during the running of a full order model, limiting the modes to being accurate only for the specific scenario from which they were collected. Due to this limitation, a method of mode adaptation through interpolation on a tangent space of the Grassmann manifold is investigated to allow modes to be predicted for cases in which a full order model has not been run. It is demonstrated by several numerical examples that the POD modes are effective at retaining predictive accuracy while reducing computational time. The results show that adapted POD modes are more capable of characterizing the behavior of the model than modes produced at a different value of the simulation parameter. The POD-based reduced order modeling approach is further extended to the full vehicle simulation on deformable terrain through the co-simulation coupling algorithm by leveraging the high-performance computing technique.

Two-way coupling model for wave-induced oscillatory soil response around marine structures

Considerable efforts have been devoted to the topic of wave–seabed interactions in the last two decades because of growing offshore activities. The existing studies have based on one-way coupling approach. In this study, a new two-way coupling algorithm is proposed to overcome the contradiction at the fluid–sediment interface between physical process and the existing theoretical models. The numerical results indicates that the seabed responses obtained by the two-way coupling model are slightly lower than that of the one-way coupling model. However, the two-way coupling model significantly affects the Shields number that would further affect the scour process. Parametric analysis indicates that larger wave height, current velocity and soil permeability and smaller water depth, shear modulus and saturation degree would increase the difference of two coupling algorithms. Meanwhile, the difference between two coupling algorithms is significant around the mono-pile and dumbbell cofferdam, compared with the case without a structure.

Numerical investigation on flow-induced vibration and heat transfer of fuel rods in a small pitch-diameter ratio (P/D) channel

The Korea Atomic Energy Research Institute developed a dual-cooled annular fuel rod bundle structure to enhance the core power of the nuclear reactor and improve its heat transfer efficiency. The structure also reduced the pitch-diameter ratio (P/D) of the channel. In this study, a four-subchannel model is taken as the research object, and the Reynolds stress model (RSM) is applied to calculate the flow-solid-thermal tri-physical field coupling for a typical bare rod beam channel. The accuracy of the numerical calculation method used in this study was first verified by comparing it with the experimental data in the literature. Then, the channel flow field under different P/D conditions was simulated, and the formation conditions and influencing factors of the vortex-street structure were studied. Axial flow-induced vibrations of a cylindrical structure in a channel were investigated using a weak coupling algorithm. Finally, the influence of the vortex-street structure on the heat transfer efficiency of the fluid in the channel is discussed. The results show that the anisotropy-based RSM turbulence model can accurately capture the vortex-street structure in small P/D channels. When P/D < 1.050, a stable vortex-street structure appeared in the channel, which led to the stable micro-amplitude vibration of the cylindrical structure in the channel. The presence of the vortex-street structure significantly improves the heat transfer efficiency of the fluid in the channel.

Vibration response and failure modes analysis of the temporary support structure under blasting excavation of tunnels

The blasting impact poses a serious threat to the safety of temporary support structures in tunnel blasting construction, such as a temporary middle wall. Thus, this study investigated and explored these problems. First, the dynamic response results of the temporary middle wall after the explosion were studied according to the field monitoring data. Subsequently, the damage characteristics of the temporary middle wall near the blasting source were investigated on field, and the development stages of the failure evolution were summarized. Furthermore, combined with the explicit finite element software LS-DYNA, the fluid–solid coupling algorithm was used to simulate the vibration response and the failure modes of the temporary middle wall under the condition of different charge weight and blasting distances. According to the field investigation, the closest blasting holes away from the temporary middle wall had a much more significant impact on its damage than other holes. The failure reason of the sprayed concrete of the supporting structure is caused by the excess high peak tension or compression stress. The failure process of supporting structure can be divided into four development stages with the reduced distance away from the blasting source: the appearance of the cracks, the cracks interconnect to form large X-shaped cracks, structural bending-shear coupling failure, and instability failure. The displacement values of the steel arch in the temporary middle wall continuously exceed 7 cm, 20 cm, 28 cm, and 34 cm, respectively, corresponding to the above four failure stages. The relation function containing the blasting tensile stress (BTS) parameter is obtained through dimensional analysis, which can be directly used to design and the damage evaluated of temporary support structures subjected to blasting at close range.

Fluid-Structure Interaction Model for Predicting Surgical Result of Total Anomalous Pulmonary Venous Connection and Estimating Pulmonary Venous Properties.

To build a fluid-structure interaction model of pulmonary veins with total anomalous pulmonary venous connection, which can be used to predict the result of surgical treatment and at the same time to estimate the elastic properties of pulmonary veins based on patient-specific data and clinic postoperative results. The fluid-structure interaction (FSI) model was used to simulate the anastomosis on pulmonary veins based on computed tomography angiography data collected from three children with total anomalous pulmonary venous connection (TAPVC), supra-cardiac type. The deformation and the stress of anastomosis, and also the velocity of blood flow were calculated in fluid-structure coupling algorithm. During the simulation the variable boundary conditions were applied, including the thickness of vessel wall and the vessel elasticity for which was selected a range of values. The calculation results were finally compared to postoperative results of same patients and discussed. The corresponding outcomes are given in the conclusions section. The blood flow velocity through the outlet will vary depending on the properties of vessels, including physical properties and thickness of vessel wall. The stress on vessel is lower for smaller values of Young's modulus. The calculated blood flow velocity correlates well with the postoperative results for the Young's modulus of vessels ranging from 0.5 to 1.0 MPa. The FSI model has high potential to predict the result of surgery for TAPVC and to estimate the physical properties of pulmonary vein. This model also has potential to guide the strategy for surgical treatment.

Concurrent interactions between prefrontal cortex and hippocampus during a spatial working memory task.

Spatial working memory (SWM) refers to a short-term system for temporary manipulation of spatial information and requires the cooperation of multiple brain regions. Despite evidence that the hippocampus (HPC) and prefrontal cortex (PFC) are involved in SWM, how the PFC and HPC interact during SWM remains puzzling. In this study, local field potentials (LFPs) were recorded simultaneously from rat ventral HPC and medial PFC during SWM tasks firstly. A cross-frequency coupling algorithm was used to test for functional connectivity in the PFC and HPC. Granger causality (GC) algorithm was used to test for effective connectivity in the PFC and HPC. Finally, concurrent interactions across two brain regions were analyzed based on functional connectivity and effective connectivity. Experimental results show that the LFPs power in the PFC and HPC decreased during the learning period and peaked before the rats' behavioral selection during SWM. Moreover, the LFPs power mainly distributed in theta and gamma that are related to SWM. In relation to the functional connectivity, the effect of activity transmission during SWM in the PFC and HPC is the same; the phase-amplitude coupling (PAC) between gamma in the PFC and theta in the HPC is correlated with the formation of SWM and supports concurrent interactions between the PFC and HPC. In relation to the effective connectivity, the directed activity transmission in the HPC is greater than that in the PFC during SWM, indicating flow of activity from the HPC to the PFC.

Response of 5 MW Floating Wind Turbines to Combined Action of Wind and Rain

For 5 MW floating wind turbines, the load response is significantly affected by wind and rain conditions. In order to reveal the relevant regularity of windblown rain and analyze the load response after being affected by the wind and rain, the rain phase is regarded as a continuous phase to be simulated. The self-compiled solver WARFoam (Wind and Rain Foam) is used to simulate the 5 MW wind turbines under wind and rain conditions. It is based on the Euler multiphase-model theory and the algorithm of unidirectional coupling of wind and rain. In this paper, the results of aerodynamic loads under WAR conditions are compared with the results of using the Lagrange particle-tracking model in order to prove that the Euler multiphase model can accurately calculate rain loads. On the basis of comparative verification, the convergence of the self-compiled solver is verified, which proves that the load-response analysis of the wind turbines under wind and rain conditions is accurate and efficient. The results show that rain has a significant impact on the load response of the wind turbines. Finally, the simulation results obtain the envelope diagram of the influence coefficient of rain-induced loads, which provides a quantitative reference standard for the calculation of the loads under wind and rain conditions.