Hydromechanical Theory Research Articles

Three-dimensional hydro-mechanical coupling numerical simulation of shield-driven cross-river twin tunnels: A case study

With the rapid development of urban underground space, the construction of shield-driven cross-river twin tunnels is increasing, and the complex hydro-mechanical coupling effects and twin-tunnel interactions bring huge construction risks to such projects, which have attracted more and more attention. This study aims to understand the excavation effects induced by shield driving of cross-river twin tunnels through numerical simulation. A refined three-dimensional numerical model based on the fully coupled hydro-mechanical theory is established. The model considers the main components of the slurry pressure balance shield (SPBS) machine, including support force, jacking thrust, grouting pressure, shield-rock interaction and lining-grouting interaction, as well as the detailed construction process. The purpose is to examine the excavation effects during construction, including rock deformation around tunnels, the change in pore pressure, and the response of the lining. The results show the influence range of twin-tunnel excavation on rock deformation and pore pressure, as well as the modes of lining response. In addition, this study also systematically investigates the effects of water level fluctuation and burial depth on twin-tunnel excavation. The results indicate that the increase of water level or burial depth will enhance the excavation effects and strengthen the twin-tunnel interactions. These results provide useful insights for estimating the construction impact range and degree of twin tunnels, and serve as basic references for the design of cross-river twin tunnels.

Modeling of liquid-solid hydrodynamic water wave energy harvesting system based on triboelectric nanogenerator

Wave energy collector (WEC) based on triboelectric nanogenerator (TENG) (W-TENG) is excellent candidate in complex marine environments. However, the improvement of energy conversion efficiency and understanding of motion mechanisms of W-TENG were limited due to the lack of theoretical basis. Here, based on the theory of hydromechanics, an energy conversion model is proposed to unveil the energy conversion mechanism and interaction mechanism between W-TENG (solid) and water wave (liquid) during the wave energy harvesting process. An inverted pendulum-typed multilayer triboelectric nanogenerator (IPM-TENG) is developed to capture water wave energy in weak wave environment (wave height: 2–13 cm, wave frequency: 0.5–1.25 Hz). Guided by the theoretical model and hydrodynamic experiments, the structural parameters and output performance of the device are further optimized. Most importantly, the available energy conversion efficiency of the optimized device is up to 14.5%. Furthermore, the optimized IPM-TENG can serve as a console for the ‘on demand’ release of pesticides to promote the development of self-powered smart agriculture. This work can not only provide guidance for the design and energy conversion efficiency improvement of future blue energy harvesting devices, but also accelerate the commercial rollout and practical application of W-TENG.

Development and verification of coupled hydro-mechanical analysis for rainfall-induced shallow landslides

To improve the performance of rainfall-based shallow landslide warning systems, a coupled hydro-mechanical analysis framework that integrates mechanical slope analysis and hydraulic infiltration is proposed. The limit equilibrium approach for infinite slopes of unsaturated soil is coupled with 1D infiltration analysis to evaluate the transient stability of the soil mass. A hybrid testing process that combines the calculations of stress and hydraulic boundaries near the sliding surface and an element testing system capable of simulating both the stress and hydraulic states on the element boundaries was developed to verify the coupled hydro-mechanical theory. The element-level modeling reveals that the proposed coupled hydro-mechanical analysis is adequate to predict the sliding depth and time of shallow landslides. Furthermore, a time-dependent warning framework based on subsurface moisture content measurements is proposed as an alternative to rainfall-based approaches for early warning of shallow landslides.

Wave-Energy Dissipation: Seaweeds and Marine Plants Are Ecosystem Engineers

Ocean waves deliver an immense amount of energy to coasts around the planet, powering high-velocity flows that interact with nearshore marine plants and animals. Although some of these interactions are beneficial, it is often advantageous for subtidal and intertidal ecological communities if wave-induced water velocities can be reduced by safely dissipating wave energy. This function is often fulfilled by seaweeds and marine plants, which thereby act as ecosystem engineers, modifying the environment to the benefit of the community. Recent advances in hydro-mechanical theory help to explain the mechanisms by which vegetation dissipates wave energy, highlighting the role that organisms’ tendency to bend in flow—their structural flexibility—plays in their ability to engineer wave-induced flows. Here, I review these theories and their application to salt marsh plants, seagrasses, mangroves, and seaweeds, focusing on the ways that marine vegetation serves a foundational role in community function.

Hydrodynamic Analysis-Based Modeling and Experimental Verification of a New Water-Jet Thruster for an Amphibious Spherical Robot.

Thrusters are the bottom actuators of the amphibious spherical robot, and play an important role in the motion control of these robots. To realize accurate motion control, a thrust model for a new water-jet thruster based on hydrodynamic analyses is proposed in this paper. First, the hydrodynamic characteristics of the new thruster were numerically analyzed using computational fluid dynamics (CFD) commercial software CFX. The moving reference frame (MRF) technique was utilized to simulate propeller rotation. In particular, the hydrodynamics of the thruster were studied not only in the axial flow but also in oblique flow. Then, the basic framework of the thrust model was built according to hydromechanics theory. Parameters in the basic framework were identified through the results of the hydrodynamic simulation. Finally, a series of relevant experiments were conducted to verify the accuracy of the thrust model. These proved that the thrust model-based simulation results agreed well with the experimental results. The maximum error between the experimental results and simulation results was only 7%, which indicates that the thrust model is precise enough to be utilized in the motion control of amphibious spherical robots.

A Dynamic Model of Drag Force for Catalytic Micromotors Based on Navier⁻Stokes Equations.

In past decades, considerable advances have been achieved in micro and nanomotors. Particular attention has been given to self-propelled catalytic micromotors, which have been widely used in cell separation, drug delivery, microsurgery, lithography and environmental remediation. Fast moving, long life micromotors appear regularly, however it seems there are no solutions yet that thoroughly clarify the hydrodynamic behavior of catalytic micromotors moving in fluid. Dynamic behavior of this kind of micromotors is mainly determined by the driving force and drag force acting on the micromotors. Based on the hydromechanics theory, a hydrodynamic model is established to predict the drag force for a conical micromotor immersed in the flow field. By using the computational fluid dynamics software Fluent 18.0 (ANSYS), the drag force and the drag coefficient of different conical micromotors are calculated. A mathematical model was proposed to describe the relationship among Reynolds numbers Re, the ratio λ, the semi-cone angle δ and the drag coefficient Cd of the micromotors. This work provides theoretical support and reference for optimizing the design and development of conical micromotors.

Research on air suspension with novel dampers based on glowworm swarm optimization proportional–integral–derivative algorithm

In order to enhance automotive ride performance, permanent magnets and magnetic valves were introduced in magnetorheological dampers and hence permanent magnets and magnetic valves introduced in magnetorheological damper’s air suspension was studied. First, on the basic principle of providing magnetic field by permanent magnets and adjusting damping force by magnetic valves, a novel permanent magnets and magnetic valves introduced in magnetorheological damper was designed. On the basis of equivalent surface current model, magnetic induction intensity activated by permanent magnets in damping channel was calculated, and damping force model was built based on hydromechanics theory. Damping force–displacement experiments and damping force–velocity experiments were carried out, and the theoretical model of permanent magnets and magnetic valves introduced in magnetorheological damper was verified. Then, physical and mathematical models of 4 degree-of-freedom permanent magnets and magnetic valves introduced in magnetorheological damper air suspension model were built. In order to enhance the controlling effects of the studied air suspension, optional moving operation, moving variation operation and operation of step size changing with fluorescein proportionality were introduced into glowworm swarm optimization algorithm, and glowworm swarm optimization proportional–integral–derivative controlling algorithm was designed. Finally, three experiments with input of impact road surface, sine wave road surface, and white noise road surface were carried out, and the experimental results verified that the working performance of permanent magnets and magnetic valves introduced in magnetorheological damper air suspension based on glowworm swarm optimization proportional–integral–derivative controlling algorithm was good.

Investigation on the milling performance of titanium alloy thin-walled part with air jet assistance

Cutter back-off and vibration are easily generated when machining of titanium alloy thin-walled parts due to its low rigidity, which has become the bottleneck for processing titanium alloy thin-walled parts. In order to investigate whether the impact force of air jet can reduce the part deformation and the vibration during machining process or not, experiments of milling Ti6Al4V alloy thin-walled part with and without air jet assistance were conducted. Vibration acceleration signals and cutting force signals in the milling process under the same cutting parameters are analyzed and compared. Also, vibration acceleration signals in frequency domain obtained by Fast Fourier Transform (FFT) are analyzed and compared. Furthermore, the impact force produced by air jet acting on the thin-walled part was collected separately before milling experiments and calculated according to the theory of hydromechanics to investigate its supporting effect. Finally, the experiment results show that air jet assistance can improve cutting stability and reduce cutting force, leading to better surface quality and reduced part deformation.

Electromagnetic-fluid-thermal field calculation and analysis of a permanent magnet linear motor

The temperature analysis of permanent magnet linear motor (PMLM) is related to their optimization design, which is important in improving a motor's efficiency and working capacity. However, a typical dilemma exists in computational accuracy, computing time and practicability of a 3-Dimentional (3-D) Electromagnetic-fluid-thermal (EM-FT) field. The purpose of this paper is to reduce the computing time of this coupled field on the premise of guaranteeing computational accuracy, thus improving its practicability. Through interpolation and fitting of a polynomial, the average wind velocities and heat transfer convection coefficients of different external surfaces of the PMLM are obtained, separating the fluid field from the coupled calculation. Based on the basic theory of electromagnetic calculation, hydromechanics, heat and mass transfer, a simplified 3-D flow model is built without considering the inner structure of the mover. Because of the nonlinear characteristics of the electromagnetic and fluid field, a 3-D electromagnetic-simplified fluid-thermal coupled model is built, and the coils steady-state temperature and distribution characteristics are stated. The results are verified by the experiment. The 3-D electromagnetic-simplified fluid-thermal coupled model makes it possible to predict the thermal performance for the PMLM rapidly and accurately.

Numerical Simulation on the Effect of Vehicle Movement on Pollutant Dispersion in Urban Street

Combined processes of ambient crosswind and vehicle-induced turbulence have a very significant effect on the distribution of pollutants emitted by vehicles in street canyon. So the purpose of this study is to analyze the process of pollutants dispersion when moving vehicles pass the urban streets based on the basic theory of hydromechanics. The air flow and pollutants dispersion in a street canyon in the presence of a moving vehicle by a dynamic mesh approach using computational fluid dynamics (CFD) is investigated. The standard k-epsilon model and enhanced wall functions are employed to establish airflow field, and species transport model and the tracer gas technique are combined to simulate pollutants dispersion. The simulation results are compared with the published experimental data of mean velocity and turbulence for the validation. Then on the base of this validation, we further explore the effect of vehicle speed and the vehicle driving lanes. This study is a good understanding of the mechanism of vehicle-induced pollutants dispersion within the urban street canyon. Thanks to the different piston effect formed by moving vehicle in different lanes, the concentration on the leeward side in the descending order are L1, No vehicle, L4, L3, L2. Meanwhile, the concentration of pollutant behind the vehicle on the leeward side decreases with increasing vehicle moving speed. Higher moving speed could lead to a reduction of concentration on the windward side.

Numerical Simulation of 3D Temperature Field and Fluid Field for Induction Generator Based on Fluid-Solid Coupled Model

通过对3 MW感应发电机的部分结构进行简化，建立了发电机定子和转子的三维温度场和流体场的流固耦合模型，并根据流体力学基本理论，采用有限体积法在Fluent仿真软件平台上对电机的温度场及流体场进行了仿真计算。所提出的仿真计算方法不仅为电机温度场的研究和分析提供一定的参考作用，也为电机结构优化和通风设计提供了理论依据。 By simplifying the structure of the 3 MW induction generator, the fluid-solid coupled model of 3D temperature field and fluid field for stator and rotor is built; the numerical simulation of temperature field and fluid field distribution for stator and rotor is done by using the finite volume method on Fluent simulation software platform based on hydromechanics theory. The proposed method can not only provide certain reference for studying temperature field of the generator, but also provide a theory gist for structure optimization and ventilation design of the generator.

CFD modeling and analysis of brine spray evaporation system

A spraying evaporation system applied to brine disposal is reported, which is mainly used for disposing the brine with concentration more than 100,000 mg/L. A computational fluid dynamics (CFD) simulation has been carried out to study the brine droplet evaporation and diffusion process in high temperature air flow. A discrete-phase model in spraying evaporation system is developed and a simulation experiment based on the gas–liquid phrase coupling with hydromechanics theory is conducted, respectively. In the present study, this model is further verified by comparing simulated temperature with experimental temperature under the condition of feed rate at 11, 13, and 15 L/h, respectively, hot air flux at 78 m3/h, temperature at 260°C, and compressed air pressure at 0.2 MPa. It should be pointed out that the CFD results are in reasonable agreement with experimentally measured ones. A thorough analysis of the heat- and mass-transfer in controlling steps is conducted based on this model to determine the impacts of key parameters that could contribute to an enhanced spray evaporation system, and finally find out the optimized operating condition. Several operating parameters, including air pressure given by air compressor, temperature and flux of hot air, and feed rate of brine are investigated to examine their effects on the evaporation (E) and the evaporation rate (R). The results show that the optimized operating condition of spraying system is air pressure at 0.3 MPa, hot air temperature at 270°C, hot air flux at 64 m3/h, and brine feed rate at 11 L/h.

CFD modeling and analysis of brine spray evaporation system integrated with solar collector

A spraying evaporation system integrated with a set of parabolic trough solar collector device is applied to brine disposal, which is mainly designed to dispose brine with the concentration more than 100,000mg/L. Computational fluid dynamics (CFD) numerical modeling is applied to simulating the evaporation and diffusion process of brine droplet in high temperature airflow by using a Fluent software. A discrete phase model in spraying evaporation system is developed and a simulation experiment based on the gas–liquid phrase and hydromechanics theory is conducted. This model is verified by comparing simulation temperature with the experimental temperature under the condition of feed rate at 11, 13, and 15L/h, respectively, hot air flux at 66m3/h, temperature at 280°C, and compressed air pressure at 0.2MPa. It should be pointed out that the simulation results showed a great agreement with the measured ones and the relative errors are within 5%. Through CFD simulation of the heat and mass transfer in brine evaporation, the optimum operating condition is determined, namely air pressure at 0.3MPa, hot air temperature at 330°C, and brine feed rate at 14L/h.

Dynamic behaviour of cold rolling mill with unsteady lubrication roll-gap interface during sheet metal forming process

This paper presents the results of developing a vibration model for the rolling mill vertical system with respect to the roll gap under the unsteady lubrication conditions to address the frequently self-excited vibration phenomenon of rolling mill vertical systems. On the basis of rolling theory, hydromechanics theory, lubrication and friction theory, as well as mechanical vibration theory, the interfacial film constrained multiple coupling model consisting of the friction lubrication model of interface, the rolling force model and the motion model of work rolls was applied as the vibration model. The self-excited vibration of the 1,850 cold rolling mill was simulated using MATLAB. The effects of some main parameters on the critical speed and amplitude for vertical vibrations were analysed quantitatively. The results show that the critical speed of the vibration is negatively related to the rolling lubricant viscosity. It was found that the critical speed is positively related to the surface roughness of work roll and strip, the positive damping of rolling mill vertical system. The findings of this research would help related practitioners to control the vibration of rolling mills.

Research on Optimize Scheduling Model and Heuristic Algorithm Based on Capacity Balance

To optimize scheduling pertaining to two production units and many tasks in flexible production, a dynamic scheduling model was proposed considering capacity balance. Each production unit was modeled as a kind of container whose capacity symbolized the container capacity. The capacity was divided as planned and spared parts. Joining spared capacities in two units, the state-to-art dynamic scheduling rules were created according to hydro-mechanical theory. A practical heuristic algorithm was developed for this model. The model was tested as feasible and effective in a case study conducted at an actual business.

Coupled hydro-mechanical effect of a fractured rock mass under high water pressure

To explore the variation of permeability and deformation behaviors of a fractured rock mass in high water pressure, a high pressure permeability test (HPPT), including measuring sensors of pore water pressure and displacement of the rock mass, was designed according to the hydrogeological condition of Heimifeng pumped storage power station. With the assumption of radial water flow pattern in the rock mass during the HPPT, a theoretical formula was presented to estimate the coefficient of permeability of the rock mass using water pressures in injection and measuring boreholes. The variation in permeability of the rock mass with the injected water pressure was studied according to the suggested formula. By fitting the relationship between the coefficient of permeability and the injected water pressure, a mathematical expression was obtained and used in the numerical simulations. For a better understanding of the relationship between the pore water pressure and the displacement of the rock mass, a 3D numerical method based on a coupled hydro-mechanical theory was employed to simulate the response of the rock mass during the test. By comparison of the calculated and measured data of pore water pressure and displacement, the deformation behaviors of the rock mass were analyzed. It is shown that the variation of displacement in the fractured rock mass is caused by water flow passing through it under high water pressure, and the rock deformation during the test could be calculated by using the coupled hydro-mechanical model.

Water Inrush Monitoring of Zhangmatun Mine Grout Curtain and Seepage-Stress-Damage Research

Based on extensive literature review, the state of the art of coupled hydromechanical models and in-situ monitoring for groundwater inrush predictions are summarized in detail, based on which, it is proposed that the key issues for describing the seepage characteristics during groundwater inrush are to calibrate the equations for damage-induced evolution of permeability and of effective stress. Depending on in-situ experiments and numerical simulations, a new academic idea, i.e.“the rock micro seismicity induced by mining processes and water pressure disturbance is in essence the index of groundwater inrush” is put forward based on case studies, coupled hydro-mechanical theory, high-performance computing technology and microseismic monitoring. The authors propose that the tendency for analyzing and predicting the groundwater inrush is to synthetically inverse the inrush pathway formation, strata microseismic precursor and high performance computing results. And relying on the microseismic monitoring events, the groundwater inrush models are calibrated, which could be used to clarify the precursory characteristics and to locate the inrush pathway. This study will lay theoretical basis for establishing the models to predict the groundwater inrush in underground mining. Key words：rock mechanics, groundwater inrush models, calibrating, numerical simulation, microseismic monitoring

Study on the Accessibility Analysis Method of Loop-Pipe-Network with Multi-Gas-Source

This paper carries the study on the accessibility analysis method of loop-pipe-network with multi-gas-source. For the unreasonableness of conventional designing method of loop-pipe-network with multi-gas-source, the accessibility analysis mathematical model is established with relevant theory of graph theory, hydromechanics and linear algebra, and the solution method of the mathematical model of accessibility analysis is set. The accessibility analysis method could achieve the reliability and economy of network.

Numerical Simulation of the Flow Field in Cavitations Nozzle for Impinging Streams Reactor

The pressure distributions in cavitations nozzle of three different structures were studied by Hydromechanics theory, the models and mashes were completed by using Gambit software, for the conditions of the inlet pressure to 20MPa and the outlet pressure to 0.1MPa, the flow field within cavitations nozzles is simulated based on the standard k-ε model and the SIMPLE algorithm with Fluent. The result of numerical simulation is consistent with that of analytical calculation. Simulation results show that the flow has a strong shear effect with the surrounding medium in the diffuser, resulting in significant negative pressure, which is conducive to the formation of cavitations bubbles. The angle nozzle is best selected for impinging streams cavitations reactor on this basis in the paper.

Coupled simulation of wave propagation and water pumping phenomenon in driven concrete piles

The purpose of the paper is to simulate the water pumping phenomenon that may cause damage to driven concrete pile below water. The cracked concrete is modeled as water saturated porous media, where the cracked region is given a high permeability. A FE program based on a coupled hydro-mechanical theory has been developed to perform simulations. The simulations clearly demonstrate the water pumping phenomenon, where water is pressed out from the crack by the compressive wave induced by the pile driving hammer, and then sucked back again by the following tensile wave. Further, the principal tensile stress distribution indicates that further cracking is likely to occur at the surface of the pile around the crack, which is in agreement with the damages seen on piles in reality.