Fluid-solid Coupling Numerical Simulation Research Articles

Numerical Simulation Analysis of Debris Filtration in the Bottom Nozzle

According to the IAEA report, debris fretting is the second largest factor causing fuel rod cladding rupture and causing fuel rod failure, accounting for 11%. As the first structural component for fluid entering the fuel assembly, the bottom nozzle has the function of filtering debris entering the core area, effectively reducing the possibility of debris entering the fuel area causing fretting. Currently, there is no suitable numerical simulation method for calculating it. Therefore, based on the coupling method of discrete element method and computational fluid dynamics, considering the stress and contact models of typical debris in the complex flow field near the bottom nozzle under different structures, this study established the fluid solid coupling numerical simulation method between the solid debris and the flow field near the bottom nozzle. Compared with the test results, the error is less than 10%, which verifies the correctness and reliability of this method, And based on this method, typical debris filtering behavior analysis was conducted. The numerical simulation method studied in this article provides support for the design and optimization of the filtration structure of the fuel assembly's bottom nozzle for debris filtration efficiency.

Effect of Vibration Conditions on the Seed Suction Performance of an Air-Suction Precision Seeder for Small Seeds

The air-suction precision seeder for small seeds is a planting machine, characterized by precision, high efficiency, and ease of operation, that uses air suction technology to sow small grain seeds at set intervals and depths into the soil. However, the forced vibration, enhanced by the increase in the operating speed, affects the seeding accuracy of the seeder and limits the seeding efficiency. To study the influence of vibration conditions on the seed suction performance of the air-suction precision seeder, we developed a computational fluid dynamics–discrete element coupling method to construct a bidirectional fluid–solid coupling numerical simulation model of the seed suction process under vibration conditions. Within the range of operating speeds from 0.6 km/h to 8 km/h, we quantitatively studied the population movement under different vibration frequencies, vibration amplitudes, negative pressure values, and seeding disc speeds and verified the simulation model and its analysis results through bench tests. The numerical results show that the interaction between the vibration frequency, vibration amplitude, and negative pressure value has the most significant impact on the single-seed rate. In addition, via variance analysis and response surface analysis, the optimal range of negative pressure values for achieving high single-seed rates under different vibration frequencies (4~10 Hz), vibration amplitudes (3~7.5 mm), and seeding disc speeds (4~50 rpm) was determined. The results indicate that, rather than the higher the negative pressure value, the higher the seed suction rate, the optimal negative pressure value for achieving a high seed suction rate varies with the specific vibration frequencies and amplitudes.

Fluid-solid coupling numerical simulation of the effects of different doses of verapamil on cancellous bone in type 2 diabetic rats

BackgroundThe purpose of this study was to investigate the effects of four different doses of verapamil on the mechanical behaviors of solid and the characteristics of fluid flow in cancellous bone of distal femur of type 2 diabetes rats under dynamic external load.MethodsBased on the micro-CT images, the finite element models of cancellous bones and fluids at distal femurs of rats in control group, diabetes group, treatment groups VER 4, VER 12, VER 24, and VER 48 (verapamil doses of 4, 12, 24, and 48 mg/kg/day, respectively) were constructed. A sinusoidal time-varying displacement load with an amplitude of 0.8 μm and a period of 1s was applied to the upper surface of the solid region. Then, fluid-solid coupling numerical simulation method was used to analyze the magnitudes and distributions of von Mises stress, flow velocity, and fluid shear stress of cancellous bone models in each group.ResultsThe results for mean values of von Mises stress, flow velocity and FSS (t = 0.25s) were as follows: their values in control group were lower than those in diabetes group; the three parameters varied with the dose of verapamil; in the four treatment groups, the values of VER 48 group were the lowest, they were the closest to control group, and they were smaller than diabetes group. Among the four treatment groups, VER 48 group had the highest proportion of the nodes with FSS = 1-3 Pa on the surface of cancellous bone, and more areas in VER 48 group were subjected to fluid shear stress of 1-3 Pa for more than half of the time.ConclusionIt could be seen that among the four treatment groups, osteoblasts on the cancellous bone surface in the highest dose group (VER 48 group) were more easily activated by mechanical loading, and the treatment effect was the best. This study might help in understanding the mechanism of verapamil’s effect on the bone of type 2 diabetes mellitus, and provide theoretical guidance for the selection of verapamil dose in the clinical treatment of type 2 diabetes mellitus.

Fluid-solid coupling numerical simulation of entire rat caudal vertebrae under dynamic loading

Trabeculae bone undergoes directional growth along the applied force under physiological loading. The growth of bone structure relies on the coordinated interplay among osteocytes, osteoblasts, and osteoclasts. Under normal circumstances, bone remodeling maintains a state of equilibrium. Excessive bone formation can lead to osteosclerosis, while excessive bone resorption can result in osteoporosis and osteonecrosis. The investigation of the structural characteristics of trabeculae and the mechanotransduction between bone cells plays a vital role in the treatment of bone-related diseases. In this study, a fluid-solid coupling model of the entire vertebral bone was established based on micro-CT images obtained from rat tail vertebrae subjected to tensile loading experiments. The flow characteristics of bone marrow and the mechanical response of osteocytes in different regions under physiological loading were investigated. The results revealed a U-shaped distribution of wall fluid shear stress (FSS) along the longitudinal axis in trabecular bone, with higher FSS regions exhibiting greater mechanical stimulation on osteocytes. These findings elucidate a positive correlation between the mechanical microenvironment among osteocytes, osteoblasts, and osteoclasts, providing potential strategies for the prevention and treatment of bone diseases.

Numerical simulation of hydraulic fracture propagation under energy supplement conditions

After the long-term production, due to the influence of low-pressure and low-stress fields in the near-well area, the reversion and propagation of new fractures after temporary plugging is short. It is difficult for the new fracture to extend to the remaining oil enrichment areas on both sides of the primary fractures, resulting in a low increase in the bandwidth of the fracture group after repeated fracturing, which affects the reservoir utilization. In the early stage of repeated fracturing, a large amount of pre-fracturing fluid is injected to supplement the energy of the fractures and rapidly increase the pore pressure in the local range, weakening rock strength and change the pore structure. In addition, the combination of energy replenishment and reservoir stimulation, coupled reconstruction of the seepage field and stress field, promotes the effective propagation of new fractures. However, in the process of increasing formation energy, the propagation law of hydraulic fractures and natural fractures is not clear. In this paper, the model of tight sandstone reservoir in the HQ block of Ordos Basin was established with the finite element software ABAQUS, based on the effective stress principle and the theoretical method of fluid-solid coupling numerical simulation. The propagation of a single hydraulic fracture and the interaction between hydraulic fracture and natural fracture under the condition of energy increase was investigated to better guide the field operation. The results show that for every 1 MPa pressure increase in a single hydraulic fracture, the fracture length increases by 0.62 m and the maximum fracture width decreases by 0.09 mm. When the formation energy increases by 6 MPa, the time for the hydraulic fracture to reach the intersection point with the natural fracture is shortened by 10 %, and the length of the natural fracture is 2.16 times compared with the case of 3 MPa energy increase.

Study on Fluid–Solid Coupling Numerical Simulation and Early Warning of Weathered Granite Landslides Induced by Extreme Rainfall

Rainfall is the main factor inducing landslides. Clarifying rainfall-induced landslides’ mechanisms and establishing adequate warning and prevention measures are crucial for regional disaster prevention and sustainable development. The weathering degree of fully weathered granite slopes is high, and the engineering mechanics property is poor, so it is easy to lose stability under extreme rainfall conditions. In this paper, the Fanling fully weathered granite landslide in Laoshan Scenic Spot in eastern China is taken as the research object, and the fluid–solid coupling landslide numerical model is established using ABAQUS 2022. The numerical simulation is carried out under five different rainfall intensity and time conditions, and the seepage field response, deformation response, and stability of the slope are analyzed. The research results indicate that (1) the fully weathered granite landslide in Fanling is a thrust-type landslide, and the response of horizontal deformation is greater than that of vertical deformation. (2) Compared with a long-term small rainstorm, a short-term heavy rainstorm is more harmful, and the slope is more prone to instability and damage. (3) The established unstable and under-stable rainfall warning curves for fully weathered granite landslides can provide a reference for the warning and prevention of similar regional landslides.

Correlation study of biomechanical changes between diabetic eye disease and glaucoma using finite element model of human eye with different iris-lens channel distances.

To find out the effect on the biomechanical response of the eye in the setting of diabetes combined with glaucoma. Five finite element models of the human eyes with various iris-lens channel (ILC) distances (2μm-20μm) were constructed, respectively. The human eye model used for finite element analysis contain all the ocular contents and the optic nerve head. All these models with different ILC distances were used to simulate the effect of pupillary block and abnormal aqueous flow induced by diabetes. And those models were also used for the biomechanical properties study of ocular tissues under the elevated intraocular pressure (IOP), using unidirectional fluid-solid coupling numerical simulation method. For the most severe cases of pupil block (2μm), a significant difference in chamber pressure caused the iris to move forward and had posterior adhesion to the lens. And the strain, stress, and displacement of the whole eyeball were significantly higher than those of the other four cases, while the Optic Nerve Head (ONH) region was the opposite. The promotion of IOP to biomechanical response at both global eye and ONH region was close to the normal eye conditions, or even ease for ILC=2μm. But in the cases of glaucoma with pupil block and high aqueous flow, the biomechanical properties of the whole eyeball were remarkably enhanced for all IOP conditions. Less influence was observed in the ONH region. The promotion of diabetes for glaucoma is not directly on the optic nerve, instead, it indirectly affects the optic nerve by affecting the global eye. Glaucoma combined with diabetes complications may increase the biomechanical damage of IOP to the whole eye.

Numerical Analysis of Instability Mechanism of a High Slope under Excavation Unloading and Rainfall

High slope simulation analysis is an essential means of slope engineering design, construction, and operation management. It is necessary to master slope dynamics, ensure slope safety, analyze slope instability mechanisms, and carry out slope stability early warning and prediction. This paper, aiming at the landslide phenomenon of the high slope on the left bank of a reservoir project, considering the influence of stratum lithology, fault, excavation unloading, rainfall, and water storage, establishes a refined finite element model that reflects the internal structure of the slope. The fluid-solid coupling numerical simulation analysis of the high slope is carried out. Based on this, the failure mechanism of the slope under excavation unloading and heavy rainfall is explained. The application of an engineering example shows that under the combined action of excavation unloading and rainfall infiltration, the in-plane saturation of the structure formed at fault at the trailing edge of the excavation slope surface increases, the pore water pressure increases, and the shear strain concentration area appears at the internal structural surface of the slope. The shear strain concentration area extends along the structural surface to the front and rear edges of the slope, resulting in landslide damage.

Prediction of water source and water volume of underground reservoir in coal mine under multiple aquifers

Abstract The role of coal mine underground reservoirs (CMUR) in ‘guide storage and use’ greatly solves the problem of mine water waste. Replenishment and prediction of reservoir water sources provide an important support for the successful development of key technologies concerning CMUR. To study water replenishment for CMUR, the hydrogeological conditions of the Shendong mining area were investigated as an example. Based on the relationship between the development height of the ‘two belts’ of shallow coal seams and the relative occurrence of location of aquifers, the aquifers are generalized and classified according to occurrences location. Taking Bulianta coal mine as the research background, a discrete element fluid–solid coupling numerical simulation model is constructed to analyze the development characteristics of mining-induced fractures after coal seam mining, and the water replenishment channel of the CMUR is determined. On this basis, analysis is made on the change law of water pressure in the aquifer, aquifuge and coal seam roof under mining action. Taking hydraulic head pressure and water velocity as the judgment basis, prediction and evaluation are made on the water replenishment capacity of CMUR. The research results can provide references for coal mine safety production and mine water protection and utilization.

Numerical Simulation of Temporal and Spatial Evolution of Stress Field in Unconsolidated Sandstone Oil Reservoir

Casing damage in the process of oilfield development is a serious problem, which is affected by geological structure, production technology and many other factors. To prevent casing damage, it is necessary to master the space-time evolution law of reservoir in-situ stress field, to provide support for casing damage prevention. Based on the perseage-stress coupling theory, taking the actual reservoir block as the research object, the change law of the in-situ stress field in unconsolidated sandstone reservoir is obtained through the fluid-solid coupling numerical simulation of the reservoir, and the internal correlation between the stress field and casing damage is analysed. The research results provide theoretical guidance for the formulation of casing damage prevention measures in the research block.

Analysis of Characteristics of Damping Valve Based on High-Order Discrete Scheme

In this paper, based on the high-order discrete scheme, a two-way fluid-solid coupling numerical simulation is for the damping valve plate. According to the discrete method, the governing equations of fluid structure coupling of damping valve plate are studied, including the basic conservation laws; Meanwhile, it analyzes the discretization of the control equation, including the discretization method and the high-order discretization format when the finite volume method is adopted. And based on this discrete format, a numerical simulation was performed on the damping valve, the oil flow condition is analyzed, and the velocity of the throttling hole at different time points and the throttling pressure are analyzed.

EXPERIMENTAL STUDY AND SIMULATION OF UPVC-FRP COMPOSITE FLOATING SYSTEMS FOR PHOTOVOLTAIC POWER STATIONS ON THE WATER SURFACE

Considering the defects and shortcomings of traditional plastic floating systems such as low strength, poor durability and easy to sink, we present a new composite floating system for floating photovoltaic power stations. In the system, the composite floating tube is made of UPVC plastic tubes wrapped with glass fiber reinforced resin matrix composite (FRP) from outside. The manufacturing and installation process were introduced in detail. The mechanical properties of the materials as well as the flat compression and bending properties were experimentally investigated. The composite floating system was optimized by considering its mechanical properties and economy. Furthermore, the hydrodynamic characteristics of the floating system caused by wind, wave and flow were studied based on a fluid-solid coupling numerical simulation method. The results showed that the composite floating system can resist wind, wave and flow safely and reliably. The study provides reference to the choice of the water environment for the selection of applicable composite floating systems.

New insights into the delayed initiation of a debris flow in southwest China

On 6 July 2020, 3 h 40 min after rainfall stopped, a delayed debris-flow disaster occurred due to colluvium deposits in a hollow region (CDH) in the Chenghuangmiao Gully, Sichuan Province, China, resulting in 4 deaths and 27 injuries. This study explores the initiation process of the delayed debris flow and the cause for the delay. Field investigations, catchment geometry interpretation, laboratory tests, theoretical calculations, and fluid–solid coupling numerical simulation were performed to obtain landslide parameters and understand the mechanisms of the event. Results show that (1) the event was a giant low-frequency viscous debris flow. (2) It was initiated by the delayed landslide process under the influence of back-end confluence. (3) The debris-flow discharge in the main gully increased over 19.5 min. (4) The seepage process inside the CDH continued for 3 h 20 min after the rainfall stopped before the pore pressure and reduction in strength were sufficient to initiate the debris flow. This research provides new insights on delayed debris-flow disasters and can be a reference for improving disaster management systems, especially monitoring and early warning systems, thereby avoiding future casualties.

Numerical Analysis of the Water-blocking Performance of a Floor with a Composite Structure under Fluid–solid Coupling

The diversity of geological structure combinations in the coal seam floor makes it difficult to characterize, prevent and control floor water inrush in the Chenghe mining area in the Weibei coalfield, China. Based on a comparative study of the structure of the floor strata and the sedimentary characteristics of the no. 5 coal seam floor in the Chenghe mining area, the floor strata were categorized into four types. Fluid–solid coupling numerical simulation software was used to study floor water-blocking performance. We found that mining failure depth was the shallowest and water-blocking capacity was the best for the “soft-hard-soft” type of floor, followed by two interbeds of soft and hard type floors, while the mining failure depth was the deepest and the water-blocking capacity the worst for the “hard-soft-hard” type of floor. These conclusions were applied to guide the floor grouting reconstruction project at the 22,507 working face in the Dongjiahe coal mine. The “hard-soft-hard” type of floor was transformed into an "interbedded soft and hard" type of floor with a better water-blocking capacity, avoiding blind grouting, reducing grouting costs and the risk of water inrush, and allowing safe mining above the confined aquifer. The research results revealed how floor strata combinations control the water-blocking characteristics of the floor and provides scientific guidance for floor reinforcement and grouting projects.

Analyzing regularity of interpolar air motion and heat dissipation coefficient distribution of a salient pole synchronous generator considering rotary airflow

The extreme attention should be paid to cooling performance of air-cooled synchronous generators in order to ensure that the temperature rise of each part is within the allowable range. It is necessary to know losses distribution, cooling airflow rate distribution laws, heat dissipation coefficient distribution and temperature distribution characteristics. Considering the influence of rotary airflow and yoke ventilation duct structure on air motion, the physical parameters and the motion characteristics of interpolar air were analyzed in three cases. These cases were considered respectively when the rotor was in a rotating or non- rotating state and the yoke ventilation ducts were intake air, and when the rotor was in a rotating state and the yoke ventilation ducts were not intake air. Based on Multi-Reference Frame, the finite volume method was used to solve the fluid-solid coupling numerical simulation of the solving domain. Taking a 250 MW air-cooled hydro-generator as an example, the air velocity of each air cooler was measured and the inlet air velocity of the rotor support was calculated. By calculating the average temperature of the excitation winding in the steady state, the measured value and the simulation result were compared, and the correctness of the calculation method was verified.

Fluid–solid coupling numerical simulation of trabecular bone under cyclic loading in different directions

The structure of a bone tissue is capable of adapting to mechanical loading through the process of bone remodeling, which is regulated by osteoblasts and osteoclasts. Fluid flow within trabecular porosity under cyclic loading is one of the factors stimulating the biological response of osteoblasts and osteoclasts. However, the relation between loading directions and interstitial fluid flow was seldom studied. In the present study, a finite element model based on micro-computed tomographic reconstructions is built by using a mouse femur. Results from the fluid–solid coupling numerical simulation indicate that the loading in different directions generates a distinct distribution of von Mises stress in the bone matrix and a fluid shear stress (FSS) in the bone marrow. The loading along the physiological direction leads to a more uniform distribution of solid stress and produces an FSS level beneficial to the biological response of osteoblasts and osteoclasts compared with those along the non-physiological direction. There was a minimum threshold line of wall FSS with a specific solid stress at the bone surface, suggesting that the wall FSS is mainly induced by the solid strain. These results may offer fundamental data in understanding the mechanical environment around osteoblasts and osteoclasts and the cellular and molecular mechanisms of mechanical loading-induced bone remodeling.

Fluid-solid coupling numerical simulation on ideal porous structure of rat alveolar bone

Fluid shear stress (FSS) caused by interstitial fluid flow within trabecular bone cavities under mechanical loading is the key factor of stimulating biological response of bone cells. Therefore, to investigate the FSS distribution within cancellous bone is important for understanding the transduction process of mechanical forces within alveolar bone and the regulatory mechanism at cell level during tooth development and orthodontics. In the present study, the orthodontic tooth movement experiment on rats was first performed. Finite element model of tooth-periodontal ligament-alveolar bone based on micro computed tomography (micro-CT) images was established and the strain field in alveolar bone was analyzed. An ideal model was constructed mimicking the porous structure of actual rat alveolar bone. Fluid flow in bone was predicted by using fluid-solid coupling numerical simulation. Dynamic occlusal loading with orthodontic tension loading or compression loading was applied on the ideal model. The results showed that FSS on the surface of the trabeculae along occlusal direction was higher than that along perpendicular to occlusal direction, and orthodontic force has little effect on FSS within alveolar bone. This study suggests that the orientation of occlusal loading can be changed clinically by adjusting the shape of occlusal surface, then FSS with different level could be produced on trabecular surface, which further activates the biological response of bone cells and finally regulates the remodeling of alveolar bone.

Computational Study on the Biomechanics of Pupil Block Phenomenon

Pupil blocking force (PBF) can indicate the potential risk of pupil block (PB), which is considered as a main pathogenic factor of primary angle-closure glaucoma (PACG). However, the effect of PB on the PBF under different pupil diameters and iris-lens channel (ILC) distance was unknown. Besides, a simple and practical method to assess PBF has not been reported yet. In this study, 21 finite element models of eyes with various pupil diameters (2.4 mm–2.6 mm) and ILC (2 μm–20 μm) were constructed and were conducted to simulate aqueous humor flow by fluid-solid coupling numerical simulation. PBF in each model was calculated based on the numerical simulation results and was fitted using response surface methodology. The results demonstrated that ILC distance had a more significant effect than pupil diameter on PBF. With the decrease of ILC distance, the PBF increased exponentially. When the reduced distance was lower than 5 μm, the PBF exploded quickly, resulting in a high risk of iris bomb. The PBF also varied with pupil diameter, especially under the condition of narrow ILC. Both ILC distance and pupil diameter could explain more than 97% variation in PBF, and a second-order empirical model has been developed to be a good predictor of PBF. Based on the linear relationship between anterior chamber deformation and PBF, a threshold value of PBF was given to guide clinical decisions. This study could be used to investigate PACG pathological correlation and its pathogenesis, so as to provide a reference value for clinical diagnosis of PACG.

Fluid–solid coupling numerical simulation for the performance prediction and valve dynamic analysis of a rotary compressor

To predict the performance of a rotary compressor and study the dynamic coupling characteristics of the valve, a three-dimensional dynamic model of the compressor is constructed in this paper. The model adopts the fluid–solid interaction method and the dynamic grid technique to achieve coupled reed valve motion. Meanwhile, to solve the problem of grid deformation caused by large deformation of the valve plate, a user-defined dynamic grid method is used to realize grid updating in the deformed area based on computational fluid dynamics method and the ideas of spring smoothing method. The model is validated with a cooling capacity error of 6.07% and an indicated power error of 2%. The stress, the displacement, the velocity and the pressure of the valve is analyzed. The flow characteristics and the dynamic characteristics of the valve plate obtained provide a reference for the design of the compressor.

Three-Dimensional Fluid–Solid Coupling Numerical Simulation of Effects of Underlying Karst Cave on Shield Tunnel Through Sand Stratum

This paper is based on the construction project of Wuhan Metro line 6 from Qianjincun Station to Mayinglu Station. In view of the geological condition of overlying sand and underlying limestone, by using FLAC3D5.0 software and considering the fluid–solid coupling effect, the influences of distance between karst cave roof and bedrock surface d, cave diameter D, width w and filling degree ω on the deformation and force of subway tunnel segment after excavation are analyzed. The results show that: (1) The vertical settlements and the axial forces at vault and arch bottom are negatively correlated with d and ω. The axial force at right hance and bending moments at each control point are positively correlated with d and ω. (2) With the increase of D and w, the vertical displacements and axial forces at vault and arch bottom tend to increase. The axial force at right hance and bending moments at each control point have a negative correlation with D and w. (3) Compared with other control points, the axial force and bending moment of arch bottom are the largest and the bending moment of right hance is the smallest. (4) The greater d, the smaller the amplitude of variation of the displacements and internal forces of the segment. The greater D, w and ω, the greater the amplitude of variation of the displacements and internal forces of the segment. The research results can provide guidance for similar engineering.