Numerical Simulation Method Research Articles

Melnikov analysis of Type I subharmonic orbits in quadruple-well coupled SD oscillators

Abstract When appropriate parameters are selected, coupled SD oscillators can exhibit bistability, tristability, and even quadrastability. The presence of multiple potential wells introduces rich dynamical characteristics into these multi-stable systems. As a result, global dynamical analysis of quad-stable systems, particularly the study of sub-harmonic orbits, has garnered significant attention in recent years. This paper aims to investigate subharmonic motion in the quad-stable system of coupled SD oscillators and to establish a theoretical framework for Melnikov analysis of Type I subharmonic orbits. Based on the derived Melnikov function, the existence of Type I subharmonic orbits is verified. Finally, numerical simulation methods are employed to validate the proposed approach by plotting phase portrait, the time history diagram t − x and spectrum diagram.

Study on progressive collapse of overall structure based on numerical simulation method and prediction of structural collapse

This study investigated the structural progressive collapse using finite element (FE) and theoretical methods. Firstly, an FE model was established based on the component method and layered shell element method. The reliability of modeling approaches was evaluated by comparing them with the previous experimental tests by the author. The NIST building was taken as an example to investigate the structural collapse behavior and the failure modes after different component failure scenarios including single column, double columns, multiple columns, and horizontal components based on the alternative path method. The results indicated that the failure of gravity columns and joints more easily triggered the progressive collapse of the structure. After the failure of double moment-resisting frame columns, the structure still demonstrated considerable robustness. The impact of floor fragments played a controlling role in the process of collapse propagation. A method for achieving rapid collapse of structures was proposed based on the structural collapse characteristics. The study found that a demolition strategy based on gravity columns can facilitate the rapid collapse of structures. After comparing the different simplified modeling methods, it was revealed that the 2D models underestimated the anti-collapse performance of structures compared to the 3D models. Under the same scenarios, the predicted structural collapse response of the 2D model was several times greater than that of the 3D model (up to 7 times). Meanwhile, the structural collapse occurred earlier in the 2D model. The anti-collapse performance of structures adopting different design codes also was compared. It was revealed that GSA 2016 has put forward requirements for higher collapse resistance of buildings. In this study, a new calculation method was proposed, namely the Collapse Probability Prediction Method Based on the Randomness of Structural Load (CPPM-RSL). In the CPPM-RSL, load reliability theory was employed to ensure that the structural collapse resistance design fell within the realm of structural engineering theory. Meanwhile, the CPPM-RSL offered greater engineering interpretability compared to previous methods. Additionally, a new simplified mechanical model was proposed to predict the collapse resistance of structures. The new simplified model did not depend on the computational results obtained from the finite element method (FEM) unlike the existing model. At the same time, the simplified method also exhibited high reliability as revealed by comparisons with the FEM. To solve highly nonlinear problems, machine learning (ML) algorithms were established to predict the anti-collapse performance and the collapse probability of structures based on the proposed theoretical model. Meanwhile, the applicability and performance of the multiple ML algorithms in estimating the structural collapse behavior were compared and evaluated. The results indicated that the LightGBM model exhibited stronger robustness and predictive ability.

Numerical simulation of the dual-loop different velocity air curtain system in the operating room

The problem of cross-infection between patients and surgeons in the operating room had been widely concerned by the international community. The purpose of this study had been to explore the potential of a Dual-loop Different Velocity Air Curtain System (DDVACS) being applied in the operating room to reduce cross-infection. In this study, the performance of the system was studied using the computational fluid dynamics (CFD) numerical simulation method, with the operating conditions of different air supply velocities inside and outside being set. The RNG k-ε model, Discrete Phase Model (DPM), and Species Transport model were used to simulate the air distribution, particle diffusion, and virus diffusion. The main research results showed that, when the DDVACS was operated at an inner air supply velocity of 0.24 m/s and an outer air supply velocity of 0.45 m/s, the virus concentration in the surgical area had decreased by 89%, the particulate matter concentration in the surgical area had decreased by 78.08%, but the deposition of particulate matter had increased by 21.62%. This study concluded that DDVACS had been found to effectively reduce the concentration of cross-infection. Finally, the velocity difference between the inner and outer sides was controlled within 2 times. This setting had been arranged to make the DDVACS work better. This study's contribution was to further verify the application of the DDVACS in operating rooms, providing a new perspective and empirical support for related fields and possessing certain practical application value.

Fluid flow simulation with an [formula omitted]-accelerated Boundary-Domain Integral Method

The development of new numerical methods for fluid flow simulations is challenging but such tools may help to understand flow problems better. Here, the Boundary-Domain Integral Method is applied to simulate laminar fluid flow governed by a dimensionless velocity–vorticity formulation of the Navier–Stokes equation. The Reynolds number is chosen in all examples small enough to ensure laminar flow conditions. The false transient approach is utilised to improve stability.As all boundary element methods, the Boundary-Domain Integral Method has a quadratic complexity. Here, the H2-methodology is applied to obtain an almost linear complexity. This acceleration technique is not only applied to the boundary only part but more important to the domain related part of the formulation. The application of the H2-methodology does not allow to use the rigid body method to determine the singular integrals and the integral free term as done until now. It is shown how to apply the technique of Guigiani and Gigante to handle the strongly singular integrals in this application. Further, a parametric study shows the influence of the introduced approximation parameters. For this purpose the example of a lid driven cavity is utilised. The second example demonstrates the performance of the proposed method by simulating the Hagen–Poiseuille flow in a pipe. The third example considers the flow around a rigid cylinder to show the behaviour of the method for an unstructured grid. All examples show that the proposed method results in an almost linear complexity as the mathematical analysis promisses.

The influence of time steps and turbulence model in numerical predicting total resistance on Japan Bulk Carrier with and without pre-duct

Abstract As a numerical fluid dynamic simulation method, Computational Fluid Dynamic (CFD) must guarantee the accuracy of the simulation results carried out, where the accuracy of the simulation results depends on: numerical method, grid generation, mesh independence, grid type, turbulence model, etc. This paper explains the influence of turbulence model and time step on the resistance prediction results of the Japan Bulk Carrier (JBC) ships, with CFD simulations using the ANSYS CFX software package. The model is simulated with several turbulence models including: k-Epsilon (k-ε), k-Omega (k-ω) and Shear Stress Transport k-ω (SST k-ω), apart from that the turbulence model is simulated in several time steps. From the results of the CFD modelling carried out, the influence of the turbulence model and time step on the accuracy of predicting ship resistance from the JBC ship was analysed, by comparing the CFD modelling results with experimental results from National Maritime Research Institute (NMRI). In general, the turbulence model and time step influence modelling and mesh selection, the correct time step provides accurate and convergent modelling results.

Investigation of unsteady characteristics in a counter-rotating compressor based on unsteady numerical simulation and mode decomposition methods

Investigation of unsteady characteristics in a counter-rotating compressor based on unsteady numerical simulation and mode decomposition methods

Boundary element simulations of dynamic wetting with a mesoscale contact line model

It is known that numerical simulations of moving contact lines are challenging owing to the fact that multiple scales are inherently involved. In this paper, we propose an efficient boundary element method for numerical simulations of dynamic wetting/dewetting. The flow domain is truncated in a mesoscopic scale, where boundary conditions resulted from a wedge flow and the asymptotic theory of the intermediate region are imposed. This procedure avoids the high resolution near the contact line in full-scale simulations and hence significantly reduces the computational cost. Numerical tests for dip coating problem show that the meniscus profiles and slopes produced by the proposed method agree well with high-resolution full-scale simulations as well as the local asymptotic theory.

A numerical simulation research on fish adaption behavior based on deep reinforcement learning and fluid–structure coupling: The refuge–predation behaviors of intelligent fish under varying environmental pressure

The study of fish swimming behavior and locomotion mechanisms holds substantial scientific and engineering significance. With the rapid progression of artificial intelligence, the integration of artificial intelligence with high-precision numerical simulation methods presents a novel and highly efficient tool for investigating fish behavior. In this paper, we proposed a fish perception model that more closely reflects natural logic. By introducing the individual vision and partially visibility model, a physics-based visual system that mirrored the sensory capabilities of live fish was developed. Furthermore, through the construction of a flow vision using conventional neural networks, we enhanced the intelligent fish's ability to detect unsteady hydrodynamic parameters via numerical lateral line. The validity of the new model was demonstrated through experiments, which the intelligent fish hunts complex moving targets in unsteady flow. Finally, we applied the model to study the refuge/predation behaviors of coral reef fish under varying unsteady flow pressures. The results indicated that swimming capabilities significantly impact fish survival strategies in high flow velocity, highly unsteady hydrodynamic environments, shaping distinct evolutionary decision-making traits. These insights may help to understand the niche competition mechanisms of fish in different flow conditions.

Suppressing impact intensity of cavitation collapse by micro-protrusions on the cylinder surface

Under specific cavitating flow conditions, the collapse of cavitation structures near the bluff body surface can trigger intense pressure pulsations, resulting in severe vibration and noise. To effectively control the damage caused by the collapse of cavitation structures, this study investigates the cavitation flow field around a cylinder using a compressible numerical simulation method based on implicit large eddy simulation. This work is the first to examine the cavitation control effects of placing micro-protrusions on the surface of a cylinder. The results show that the wall-attached cavitation collapse near the separation point on the cylinder surface is the main cause of induced vibrations and noise. The height and location of the micro-protrusions are key factors in controlling the wall-attached cavitation in the cylinder's shear layer. It is recommended to position the protrusions approximately 5° upstream of the separation point, with the protrusion height entering at least the logarithmic region of the boundary layer. Appropriately placed micro-protrusions can block the reverse flow, reducing the cavitation volume involved in the collapse and the overall collapse intensity, thereby diminishing the load impact on the cylinder surface.

Analysis of hydrodynamic performance and acoustic characteristics of loop propellers

To improve the efficiency and stealthiness of marine operations of autonomous underwater vehicles (AUVs), 12 loop propellers with different structural parameters are selected as research subjects. The Reynolds-averaged Navier–Stokes equations method is used to simulate the flow field result around the loop propellers and is combined with detached eddy simulation and the acoustic analogy method for hydrodynamic analysis and noise prediction. The influence of three structural parameters, namely the number of propeller blades, the thickness of propeller blades, and the pitch of propeller blades, on the hydrodynamic and noise performance of the propeller is investigated, and the loop propeller structure with the optimal hydrodynamic and noise performance is selected. The research results indicate that increasing the number of propeller blades and increasing the pitch of the loop propeller can significantly improve the thrust and torque of the propeller and effectively reduce the noise. However, increasing the thickness of the propeller blades can also increase the thrust and torque of the propeller, but it will sacrifice the noise performance of the loop propeller to a certain extent. The sensitivity of the noise performance with respect to the blade thickness is significantly higher than that of the two parameters of blade number and pitch. To verify the accuracy of the hydrodynamic and noise performance simulation results, this study conducted hydrodynamic and noise performance tests on the preferred loop propeller structure in the towing pool and anechoic pool and successfully verifies the reliability of the numerical simulation method used in this study for the prediction of the propeller performance by comparing the test data with the simulation results. This study provides theoretical support for the design optimization of loop propellers and helps to promote the design of high-efficiency and low-noise propellers in complex marine environments.

Flow field and performance analysis of downhole pipe string in single-well injection-production technology

High water content is a critical issue that must be urgently addressed in the current oilfield development, and the single-well injection-production technology (SWIPT) is an effective approach for achieving economical extraction in high-water-content oilfields. To meet the 5.5-inch casing size requirements, further improve SWIPT performance, and minimize the impact of pump pressurization on the subsequent oil–water separation process, dual-pump suction-SWIPT is proposed and an axial-flow cyclone separation pipe string is designed. A theoretical fluid–solid interaction (FSI) model of the downhole pipe string (DHPS) applicable to SWIPT is established through vibration testing and data analysis. Based on the new FSI model-corrected numerical simulation method, single-factor experiments are performed to analyze the medium transport process and oil–water separation performance within the flow field under structural vibration disturbances. The results indicate that the separation of fluid media within the single-well injection-production DHPS is not significantly affected by structural interference. The simulation results closely matched the experimental data, with the average error of the axial velocity at different test points being within 0.041 m/s. In the transport pipe regions, minor variations in the velocity and pressure fields are observed under vibration conditions. Under an inlet flow rate of 4 m3/h, split ratio of 30%, and oil volume fraction of 1%, the optimal separation efficiency of 97.26% is achieved. This study provides new insights for the development and application of SWIPT.

Investigation of the effects of alumina particle phase transition on internal flow field and engine performance in solid rocket motors

This study integrates theoretical modeling with numerical simulation methods to establish a comprehensive phase change dynamics model. The model encompasses critical stages of the phase change process, including undercooling, nucleation, solidification, and crystal phase transformation. We also utilize the latest drag coefficient model and heat transfer model in the two-phase flow field. Through numerical simulation, we delve into the impact of the phase change process of monodisperse particles on the flow field characteristics within a nozzle, extending our investigation to polydisperse particles phase change process. Furthermore, we systematically analyze the specific effects of variations in particle size distribution and particle loading on nozzle performance. In our simulation results, the most significant specific impulse enhancement was achieved under conditions of d43 = 2.63 μm and 20% particle loading, resulting in a specific impulse increase in approximately 0.53% compared to scenarios neglecting phase change. This work provides a solid theoretical foundation for accurately evaluating engine performance through numerical simulation.

Numerical simulation on metallurgical transport phenomena during DC casting of large-size Mg-Gd-Y alloy billet under various magnetic fields

The manufacture of large-size rare-earth Magnesium alloy billets by direct-chill (DC) casting process is now facing great technical challenges, mainly due to the high cost of casting experiments, and such casting defects like severe cracking, macrosegregation, and non-homogenized solidified structure. Based on the low-cost and high-efficiency numerical simulation method, the present study systematically explores the effects of single pulsed and alternating magnetic fields (PMF and AMF), differential-phase pulsed and alternating magnetic fields (DPMF and DAMF) on DC casting metallurgical transport phenomena of Φ750mm large-size Mg-Gd-Y magnesium alloy billet. The electromagnetic characteristics, flow behavior, and temperature distribution during casting process are clearly visualized. The results demonstrate that traditional DC casting process is optimized by applying magnetic fields. For one thing, pulsed magnetic fields (PMF and DPMF) generate larger and faster changing instantaneous Lorentz forces, which induce huge transient impact and oscillation effects on the melt. For another, alternating magnetic fields (AMF and DAMF) have greater time-average Lorentz forces, which can force the melt to flow continuously and steadily. Additionally, differential-phase magnetic fields (DPMF and DAMF) enhance the melt’s axial flow strength while reducing the small vortex generated at the edges, resulting in improved heat transfer efficiency and uniform temperature field. Among those magnetic fields, DPMF shows dual advantages of transient oscillation and homogenized temperature distribution. Based on the present simulated research, the Φ750mm large-sized rare earth Mg-Gd-Y alloy billet with high-quality and non-cracking has been manufactured during DC casting process under DPMF.

Thermodynamic coupling performance analysis and simulation of aerated oil medium steel-BMC joint surface

In order to study the thermal coupling properties of aerated oil medium steel-basalt mineral composite (BMC) joint surface and establish an accurate and convenient simulation analysis method. The calculation method of the actual contact area ratio weight matrix of the aerated oil medium steel-BMC joint surface was studied. The virtual material theory model of the thermal coupling performance of the aerated oil medium steel-BMC joint surface was established by combining it with the virtual material theory. Based on the virtual material method, the thermodynamic coupling performance of the aerated oil medium steel-BMC joint surface was studied by finite element simulation, and compared with the experiment and numerical simulation methods of fractal theory. The results show that the temperature and strain changes of BMC specimen with virtual material method have a good coincidence with the experimental results, and the relative error is minimal. At the same time, the virtual material simulation model is simple, less computation and higher efficiency. It is proved that the method in this paper has better precision and convenience.

The Effect of Climate Change on Coastal Morphology Changes in Lhokseumawe City Area

Abstract The city of Lhokseumawe in Aceh is mostly located on the coast and is vulnerable to annual tidal waves, causing coastal settlements to sink. The rising sea levels in Indonesia, as observed by the IPCC using the TOPEX/POSEIDEN satellite, have reached 7 mm/year. A study was conducted to assess the impact of tidal waves exacerbated by sea level rise on changes in coastal morphology over 25 and 50 years. The study utilized the Delft3D numerical simulation method with various input data such as Topographic Data, bathymetry, tides, discharge, sediment, and waves. The results of the Delft3D modeling showed that erosion is slightly greater in the 25 and 50-year scenarios, with an average minimum erosion of about 12 m and a maximum erosion and retreat of about 18 m. However, in the 50-year scenario, there were points along the coast where sedimentation occurred, leading to the advancement of the coastline by about 36 m. These dynamic morphological changes in the coastal area of Lhokseumawe highlight the need for a coastal protection plan to address this vulnerability.

Modeling effect of rock shape characteristics on run-out distribution of rockfalls

The aim of this study was to analyze and model the effect of rock shapes on the run-out distribution characteristics of rockfalls. To this end, we conducted a parametric study of rockfall simulations using the discrete element method, which is a numerical simulation method capable of directly representing rock shapes. The results indicated a strong correlation between the sphericity of rocks and the run-out distribution characteristics, expressed by two types of sphericity. Furthermore, we developed a regression model that can predict the run-out distribution using these two sphericities and the parameters of the calculation conditions as the explanatory variables. Although there is some room for improvement in terms of the developed regression model, it was confirmed that the relationship between the sphericity of rocks and the run-out distribution characteristics suggests the potential to enhance efficient rockfall risk assessments through numerical analysis.

Characteristics of radon transport and optimization of ventilation parameters in large-scale underground cavern

Radon penetrates into the underground caverns through the pores/fissures of the surrounding rock, resulting in high radon concentration area and endangering the health of construction personnel. The on-site monitoring of radon concentration in the underground powerhouse of Tuoba Hydropower Station is conducted in order to study the radon concentration level. The radon transport during the construction period of underground powerhouse under forced ventilation is established by Computational Fluid Dynamics (CFD) numerical simulation method. Furthermore, the distribution characteristics and long-term evolution law of radon concentration in underground powerhouse are revealed, and reasonable ventilation optimization measures are put forward and the results show that: (1) Blasting promotes the increase of radon concentration, while forced ventilation accelerates radon transport. (2) The airflow field along the axis is divided into a vortex distribution zone, a vortex influence zone and stable regions. (3) The radon transport includes both migration and diffusion processes based on forced ventilation. (4) The radon concentration decreases with the increase of height, while exhibits low concentration in the middle and high concentration on both sides at the same height. (5) Compared with forced ventilation, the combined ventilation can improve the ventilation efficiency and shorten the radon transport time. The research results can provide a scientific basis for the safety analysis and evaluation of deep engineering environment.

Real-Time Wind Speed Analysis at Wind-Damaged Tower of a Transmission Line

Affected by the Super Typhoon “Mangkhut,” a total of five base towers of a transmission line in the mountainous area of China collapsed. In this paper, a mathematical model is established based on the Shuttle Radar Topography Mission (SRTM) data near the accident tower. The measured wind speed in the plain area under the mountain is used as the calculation boundary condition. The wind speed at the top of the mountain is calculated by using a numerical simulation method. The design wind speed and calculated wind speed at the tower site are compared, and the influence of wind speed on tower position in this wind disaster accident is analyzed.

Study on the mechanism of flexible deformation affecting the hydrodynamic performance of oscillating hydrofoil

The declining natural environment and rising energy demand have led to increased interest in oscillating hydrofoil structures for their high energy extraction efficiency and environmental benefits. In this study, the numerical simulation method is used to study the mechanism of flexible deformation affecting the hydrodynamic performance of hydrofoil. The results show that the flexible deformation can increase the average power coefficient (CP) by increasing the lift, but it will also aggravate the dynamic stall of the hydrofoil, which has many effects on the hydrodynamic performance of the hydrofoil. Then, the double flexible hydrofoil structure coupled with flexible deformation and dynamic wing-in-ground effect is studied, its hydrodynamic performance is obviously better than other types of hydrofoils. the average power coefficient is 2.51 % higher than that of single flexible hydrofoil and 25.03 % higher than that of double rigid hydrofoil. This shows the superiority of the double flexible hydrofoil structure.

Mathematical model of the system performance mode for simultaneous separate well operation

Relevance. The trend of oil production technology development is related to many relevant topics. One of such actual directions is the technology of simultaneous separate well operation, in particular, including two electric centrifugal pumps and double-sided submersible electric motor. The presence of two formations at the bottomhole implies the selection of the optimal layout, technological parameters of pumps pumping oil. Considering production from two independent formations in the well according to the mentioned technology, there is a high need in selection of correct parameters of installations at the design stage. In the absence of correct selection of technological parameters of units at the design stage, further operation of a well with two independent formations can be economically inexpedient, and in some cases unrealizable, which is due to a number of reasons. First, if the necessary underbalance is not provided for each particular formation, counterflow of fluid may occur and one of the pumps will not participate in the production process. Secondly, when operating an arrangement, which capacity significantly exceeds the capacity (fluid flow from the reservoir) of the well, there is a possibility of pumping failure and, as a consequence, there is a risk of potential failure. In this regard, an extremely urgent task at the moment is to ensure correct selection of technological parameters of electric centrifugal pump units used in simultaneous separate operation of wells with two independent formations. Aim. Development of a mathematical model that allows selecting the optimal technological parameters of the arrangement consisting of two electric centrifugal pumps and a double-sided submersible motor, used for simultaneous separate operation of wells with two independent formations. Methods. Numerical simulation methods for analyzing the operation mode of electric centrifugal pumps in conditions of oil production from two independent reservoirs. Results and conclusions. It was obtained that the developed mathematical model of the system operation mode for simultaneous separate operation of wells allows to estimate the potential of each individual selected pump during oil production (in time dynamics) by analyzing the depression on each individual reservoir, as well as modeling the process taking into account the potential backflow of liquid and supply failure.