Three-dimensional Physical Model Research Articles

Characteristics and Safety of CO2 for the Fire Prevention Technology with Gob-Side Entry Retaining in Goaf.

The mining technology of gob-side entry retaining without a coal pillar is gradually becoming a mature and increasingly important mining technology. As it maintains the roadway near goaf, the air leakage should be greater than a U-type ventilation system in goaf, so it is prone to cause coal spontaneous combustion problems. CO2 is an inert gas, and it is usually used to prevent spontaneous combustion and extinguish coal fire. However, there is a lack of research on characteristics and safety of CO2 for the mining technology of gob-side entry retaining without the coal pillar. In this paper, the indexes of influencing factors were proposed on gas, pipelines, and mining technical parameters. Using a three-dimensional physical model of coal stope, the gas migration law of CO2, the relationship between gas injection rate and the oxidation zone area, and the safety of the CO2 inerting technology were analyzed. The results indicate that the O2 concentration is diluted between the working face and the injection port, especially in the air intake side. Furthermore, the CO2 injection rate is an important parameter to the fire prevention and extinguishing technology. When the gas injection rate ranges from 240 to 720 m3/h, the oxidation zone area varies from 7380 to 14 760 m2, and the gas injection rate grows exponentially with the area of the oxidation zone. Moreover, the redundant CO2 gas flows to the retaining roadway, and it reduces the O2 concentration, resulting in asphyxia accidents of miners. The research results are helpful to balance the relationship between inert gas injection and production safety and provide guidance for the practical application of the inert gas fire prevention technology.

Research on the verification method of flyback high-frequency transformer (FHFT) based on field-circuit coupling model

In view of the current status of research on verification of the correctness and effectiveness of FHFT design, a field-circuit coupling based FHFT design verification method is proposed in this paper. This paper proposes a FHFT design verification method based on field-circuit coupling. The steps of FHFT verification using field-circuit coupling method are elaborated in detail. A three-dimensional physical model of FHFT based on AP method is established. The calculation of FHFT flux density and the verifying of transformer output waveform are completed by using the field-circuit coupling method of alternating iteration of non-linear magnetic field solution and circuit. On the basis of completing the flux density calculation, the field circuit coupling method is used to verify the output waveform of the transformer. It is found that the output waveform of FHFT is not an ideal square wave, but has some distortion, which is caused by neglecting the leakage inductance of transformer in the design process. This shows that the influence of transformer leakage inductance is very important and should be paid attention to.

Physical Simulation Experimental Technology and Mechanism of Water Invasion in Fractured-Porous Gas Reservoir: A Review

In the development process for a fractured-porous gas reservoir with developed fracture and active water, edge water or bottom water easily bursts rapidly along the fracture to the production well, and the reservoir matrix will absorb water, reducing the gas percolation channel and increasing the gas phase percolation resistance of the reservoir matrix, therefor reducing the stable production capacity and recovery efficiency of the gas reservoir. For this reason, this paper investigates physical simulation experimental technology and mechanisms as reported by both domestic and foreign scholars regarding water invasion in fractured-porous gas reservoirs. In this paper, it is considered that the future trend and focus of water invasion experiments will be to establish a more realistic three-dimensional physical model on the basis of fine geological description, combined with gas reservoir well pattern deployment and production characteristics, and to fully consider the difference between horizontal and vertical water invasion along the reservoir side; at the same time, dynamic parameters such as model pressure field and water saturation field can be obtained in real time. Based on this understanding of the water invasion mechanism of fractured-porous gas reservoirs, we propose the next research direction and the development countermeasures such as water controls, drainage, and dissolved water seals and water locks to combat water invasion in reservoirs, along with the injection of gas to replenish formation energy, etc., so as to slow down and control the influence of water invasion.

Research on influence factors of corona onset characteristics of AC grading rings based on three‐dimensional calculation physical model

In order to obtain the influence laws and mechanisms of size parameters (ring diameter and pipe diameter) of the grading ring and environmental parameters (atmospheric pressure, temperature, and humidity) on corona onset characteristics of a grading ring, a three-dimensional (3-D) calculation physical model of corona onset considering the influence of size parameters of the grading ring and environmental parameters is established by proposing an area factor of a photon absorption function suitable for the grading ring. Combined with the thickness of ionised layer and the effective ionisation coefficient, the influence mechanisms of size parameters of the grading ring and environmental parameters on corona onset characteristics are given. The calculation results show that with the increase of the pipe diameter and ring diameter, the corona onset voltage increases gradually and the corona onset field intensity decreases gradually. The increase of the effective ionisation coefficient leads to the expansion of ionisation region, which leads to the decrease of corona onset voltage with the decrease of atmospheric pressure and the increase of temperature. The enhancement of capacity for collisional ionisation in the region with the high field intensity leads to the decrease of corona onset voltage with the increase of humidity.

Three-dimensional calculation physical model for corona onset characteristics of AC grading rings

Corona discharge on the surface of power transmission and transformation fittings becomes increasingly serious with increasing voltage levels, especially for many grading rings in transformer substations. With the enhancement of people’s environmental awareness, the environmental protection administration requires noise and electromagnetic environment at transformer substations shall meet relevant standards. In order to suppress corona discharge on the surface of a grading ring, it is necessary to study its corona onset characteristics. Considering the basic physical process of the corona discharge, in this study, the electric field intensity is first calculated at any point in the space around the grading ring through ring charge simulation. Then, based on the theory of secondary electron emission, criteria for calculating the onset voltage of negative corona of the grading ring are derived, leading to an area factor of a photon absorption function suitable for the grading ring. In this way, a three-dimensional (3D) calculation physical model of the corona onset suitable for the grading ring is developed. This study calculates the corona onset voltage and field intensity of the grading ring under the typical working conditions by using the proposed 3D calculation physical model of the corona onset. The calculation results are compared with test results of the corona onset voltage and field intensity of grading rings in an outdoor 750 kV transformer substation in an ultrahigh voltage (UHV) alternating current (AC) test base. Furthermore, the simulation results of the area factor of the photon absorption function, electron collision coefficient, electron adsorption coefficient, and effective ionization coefficient in the 3D calculation physical model are obtained. In this way, the accuracy of the 3D calculation physical model of the corona onset proposed in this paper is verified. The research results can provide a theoretical basis for the corona prevention design of grading rings in extra high voltage/UHV AC power transmission and transformation projects.

An Experimental Study of a Nailed Soil Slope: Effects of Surcharge Loading and Nails Characteristics

The earth nailing system is a ground improvement technique used to stabilize earth slopes. The behavior of the earth nailing system is dependent on soil and nailing characteristics, such as the spacing between nails, the orientation, length, and method of installation of nails, soil properties, slope height and angle, and surcharge loading, among others. In the present study, a three-dimensional physical model was built to simulate a soil nailed slope with a model scale of 1:10 with various soil nail characteristics. The simulated models consist of Perspex strips as facing and steel bars as a reinforcing system to stabilize the soil slope. Sand beds in the model were formed, using a sand raining system. The performance of nailed soil slope models under three important nails characteristics, i.e., length, spacing and orientation, with varying surcharge loading were studied. It was observed that there is a reduction in the lateral movement of slope and footing settlements with an increase in length. It was found that the slope face horizontal pressure is non-linear with different nail characteristics. The increase in length and inclination of the soil nails decreased the vertical, horizontal stress and footing settlement, while the increase in spacing of the nails increased the vertical and horizontal stress behind the soil mass.

Effect of Meander Structure on Magnetoimpedance Characteristics in FeNi/Cu/FeNi Films

The three-dimensional physical models for FeNi/Cu/FeNi films with two different types of structures which are linear and meander are developed. The relationship between the impedance of the films and the applied magnetic field or excitation frequency is obtained and the influence of geometric parameters and structures of the films on the giant magnetoimpedance (GMI) effect is analyzed. The result shows that the GMI effect in the film with a horizontal meander structure appears to be much stronger compared with that in a linear structure. The negative mutual inductance of the meander FeNi/Cu/FeNi films reduces the total inductance and decreases frequency response. Meanwhile, the GMI effect and the negative mutual inductance are enhanced by increasing the number of turns or decreasing the space width between each segment. Based on these effects, the FeNi/Cu/FeNi film with a vertical meander structure is proposed and simulated, which reflects the design of the meander structure in the thickness direction. The distance between each segment is reduced to 500 nm. The GMI effect and the negative mutual inductance are greatly enhanced (the maximum value of the GMI ratio increases from 207% to 1247% when the excitation frequency changes from 50MHz to 300MHz). Furthermore, the spatial resolution of the film is further improved. The results obtained could be useful both for a better understanding of the GMI effect of the FeNi/Cu/FeNi film with a meander structure and for providing a choice for the device preparation of highly sensitive magnetic sensors.

Numerical modelling of alongshore variability in waves and wave-driven currents during the morphodynamic change of a laboratory beach

A non-hydrostatic phase-resolving numerical model (SWASH) is used to investigate the wave-driven nearshore hydrodynamics corresponding to new observations from a three-dimensional physical model in a wave basin. In the physical model, waves from a passing storm are simulated by varying the energy and duration of waves generated by a paddle over time and the beach morphology is surveyed in high spatial-resolution using a 3D laser scanner after each segment of the storm. An oblique incident wave angle introduces spatially variability in wave energy along the beach and results in morphologic differences during the storm, with active transport of beach sand by the wave-driven circulation. SWASH is validated using wave and current observations at each stage of the storm, indicating low root-mean-squared errors between model results and wave measurements, where the high-resolution model is able to predict wave shoaling, breaking and generation of the alongshore current. Model-data agreement is not as high for the velocity, suggesting spatial variability in bottom friction and horizontal mixing, and evolution of the bed in the physical model, could explain the differences. The detailed numerical model results indicate that the alongshore current is generated by wave breaking in the nearshore zone, and it increases in speed across a wider surf zone for increasing wave energy during the storm. This is associated with a bottom shear stress that exceeds the critical bed shear stress, with the potential to initiate motion and transport sediment in agreement with the experimental observations.

Three-dimensional physical model experiment of mining-induced deformation and failure characteristics of roof and floor in deep underground coal seams

Underground mining engineering causes complex changes in the three-dimensional stress near the working face of a mine, resulting in deformation and failure of the roof and floor rocks, as well as ground subsidence. To study the stress, deformation, and fracture field characteristics of the roof and floor strata due to mining, an indoor large-scale three-dimensional physical similarity model was developed. A novel method was used to simulate the mining process of coal seams. The results show that coal seam mining disrupted the original stress balance; consequently, a bearing pressure was generated in front of the working face, and a significant pressure relief state appeared in a particular area. The collapsed rock blocks of the overburden strata filled the goaf and played a supporting role, causing the overburden stress to increases again to a value close to the original rock stress. After complete mining, the overburden strata subsided, and the floor strata bulged. With an increasing vertical distance from the working face, the deformation of the rock formation gradually decreased. Evident fractured fields were formed in the surrounding rock of the goaf. In the horizontal section of the overburden rock layer, the cracks were distributed in a “rounded rectangular” shape. As the distance from the coal seam increased, the “rounded rectangular” boundary became smoother; the coverage area decreased; and the degree of crack opening and development in the plane decreased. The fractal dimensions of fractures with different overburden heights and different strike positions are calculated using the fractal geometry theory. We found that as the distance from the excavation face increased, the fractal dimensions of the fractures gradually became stable. In addition, numerical simulation methods were used to verify the correctness of the physical similarity model experiments. The research results can provide important references for the stability of deep underground projects such as coal mining process, tunnel excavation process, nuclear waste storage and other engineering stability.

Research on the Verification Method of Flyback High-Frequency Transformer (FHFT) Based on Field-Circuit Coupling Model

In view of the current status of research on verification of the correctness and effectiveness of FHFT design, a field-circuit coupling based FHFT design verification method is proposed in this paper. This paper proposes a FHFT design verification method based on field-circuit coupling. The steps of FHFT verification using field-circuit coupling method are elaborated in detail. A three-dimensional physical model of FHFT based on AP method is established. The calculation of FHFT flux density and the verifying of transformer output waveform are completed by using the fieldcircuit coupling method of alternating iteration of non-linear magnetic field solution and circuit. On the basis of completing the flux density calculation, the field circuit coupling method is used to verify the output waveform of the transformer. It is found that the output waveform of FHFT is not an ideal square wave, but has some distortion, which is caused by neglecting the leakage inductance of transformer in the design process. This shows that the influence of transformer leakage inductance is very important and should be paid attention to.

Convection heat transfer of supercritical CO2 in a single fracture in enhanced geothermal systems

EGS (Enhanced Geothermal System) is a potential way to utilize geothermal energy efficiently. In present work, a three-dimensional physical model, a single fracture with undulated surface morphology in hot dry rock is constructed. Supercritical CO2 is used as working fluid, and its convection heat transfer characteristics in fracture is numerically investigated. The influence of flow rate, inlet temperature, and reservoir pressure on convection heat transfer are probed. The results indicate that the local convection heat transfer coefficients at upper wall and lower wall of fracture show opposite variation trend at corresponding positions, and it varies with the undulation of surface morphology. In addition, the local convection heat transfer coefficients rise with the decrease of flow rate, the increase of pressure and inlet temperature. Furthermore, the correlation of normalized convection coefficient Nusselt number of supercritical CO2 in fracture is obtained.

Three-dimensional numerical research on the effects of lateral pulsating airflow on droplet breakup

A three-dimensional physical and mathematical model of the lateral airflow for droplet breakup was established. Numerical simulation was used to study the impact of the pulsating airflow on the droplet breakup process and analyze the variation in deformation rate under different amplitudes and frequencies. The results show that compared with uniform airflow, pulsating airflow can enhance the effect of droplet breakup, with an optimal droplet crushing effect occurring when the relative amplitude of the pulsating airflow was A = 1 and the Womersley number of the pulsating airflow was 96.6.

Experimental Study on Rock-Support Interaction in Deep Tunnel Under Complex Geological Conditions

Rock-support interaction is one of the most core issues in underground engineering, which is of major interest to supporting structure design, construction safety and cost, as well as environmental protection. In order to study the rock-support interaction in deep tunnel under complex geological conditions, taking Xianglushan Tunnel of Yunnan Water Diversion Project in China as the engineering background, two true three-dimensional physical model tests were conducted. The model test results show: (1) the surrounding rock and support are a pair of opposite and united contradictions, which are both antagonistic and cooperative; (2) the rock-lining interaction and rock-bolt interaction are distinctly different. The lining is a type of outside supporting structure to bear the load from surrounding rock and the bolt is a kind of inside supporting structure to reinforce and protect surrounding rock; (3) the impacts of weak fault on mechanical behavior of surrounding rock and supporting structure are significant. The load bearing effects of surrounding rock and support system exhibit different characteristic depending on the corresponding geological conditions. The results can contribute to the development of construction scheme and optimization of support design, and also provide an ideal data set for the calibration and validation of numerical models to simulate the rock-support interaction.

Numerical simulation for size optimization of refractory support frame in OMB gasifier

The refractory support frame in opposed multi-burner (OMB) gasifier is used to support the refractory bricks. However, excessive thermal stress in OMB gasifier at high temperature will damage it and cause refractory bricks to collapse. The effect of size and structure on the thermal stress of refractory support frame has remained unclear. A three-dimensional physical structure model of industrial refractory support frame was established. The numerical simulation of temperature distribution and thermal behavior with different thickness and length of the support plate was detailedly investigated by the analysis modules of steady-state thermal and static structural through ANSYS. When the temperature of end face of hot-face brick was 1300°C, the outer surface temperature of steel shell was 210.4°C, which matched well with the measured temperature. As the thickness of support plate increased, the equivalent stress at the center of support plate gradually decreased. With increasing the length of support plate, the value and whole saltation of stress were both the smallest at the length of 230 mm. The optimal size of support plate which was beneficial to decrease the stress and prolong the service life of the refractory support frame was obtained. It could be a better guidance for the size optimization of the refractory support frame.

Research instruments on environmental quality applied to small children with Down Syndrome

Abstract Children aged between 4 to 7 years play a minor role in academic studies in Architecture and Urbanism, a situation related to the difficulty of obtaining their opinions, especially those with intellectual disabilities, such as Children with Down Syndrome (CDS). Therefore, little is known about their perception of the built environment. For this to change, instruments should be developed in order to approach these children, which could contribute both to valuing their opinion and supporting the professional practice of architects. This finding led to exploratory, qualitative and interdisciplinary research to create research tools directed to young CDS, and obtain their opinion about the built environment. The study was based on: (a) literature review; (b) expert panels, comprising 10 parents and 28 professionals. Based on this information, three research instruments were prepared: Spatial Qualification Chart, Illustrated Cards and Make-believe in a Three-Dimensional Physical Model. They are tested with eleven CDS. The results showed that: (i) the proposed instruments fit the task; (ii) some care can facilitate the work with this public; (iii) the participating children perceive and qualify the space - which justifies new research endeavors with CDS.

Research on small-scale sand fracturing and puff technology

Affected by complex fault blocks, sedimentary environment and reservoir physical properties, Jidong Oilfield generally develops small-scale sand bodies, accounting for 24.2% of the produced reserves of medium and low permeability reservoirs. Such sand bodies rely on elastic energy to develop and are difficult to use effectively. In this paper, through the three-dimensional hydraulic physical model experiment and the analysis of the oil layer-dry layer-mudstone mixed sand body, the reasons that affect the model parameters are obtained. The results show that: the length of the high-permeability reservoir area, the length of the intermediate-permeability dry layer area, the rate of change of permeability parameters, the viscosity of the construction fluid, and the construction displacement have an impact on the effect of fracturing enhanced injection energy storage.

Research on the reliability verification and key parameter optimization of numerical simulation of a gas explosion

ABSTRACT Using FLUENT numerical simulation software, combined with pipeline gas explosion test and three-dimensional physical model of full-scale working face, the reliability verification of calculation model and optimization of key parameters were carried out. The results show the following: When the gas filling lengths of the pipeline are 4.0 m, 5.5 m, and 7.0 m, the overpressure peak error obtained by the numerical simulation and experiment is less than 15%, which is within the allowable engineering range. This result verifies the reliability of selecting the LES+ED calculation mode for simulating a gas explosion from an experimental point of view. The calculation results of the gas explosion shock wave attenuation model are very close to the simulation results, and the attenuation trend is the same. The overall degree of agreement is relatively high, which verifies the reliability of selecting the LES+ED calculation model for simulating a gas explosion from the point of view of the theoretical calculation. The influences of key parameters, such as grid size, iteration step length, and ignition temperature on the overpressure peak and explosion time are studied, and the most reasonable grid size, iteration step length, and ignition temperature are determined to be 0.5 m, 0.0005 s and 1600 K. The research results provide important theoretical insight for the numerical simulation of gas explosions.

Experimental investigation on improved vertical sweep efficiency by steam-air injection for heavy oil reservoirs

Steam injection is one of the most widely used technique for heavy oil recovery. There are few laboratory experiments to investigate how to decrease the negative effect of steam override in thick heavy oil reservoirs, thus increasing the vertical sweep efficiency and further improving oil recovery. In this paper, a three-dimensional physical model was introduced to study the sweep efficiency of steam injection and steam/air injection in reservoirs with different rhythms. The mechanisms of improved vertical sweep efficiency by the hybrid injection of steam and air were also analyzed by monitoring the real-time temperature and liquid production of the 3D model. The experimental results indicated that as pure steam was injected, the sweep area mainly located in the upper part of the model. The sweep area decreased from the top to the bottom, and the same to liquid production. The steam override was most serious in negative-rhythm reservoir, followed by the homogeneous and positive-rhythm reservoirs. As steam and air were coinjected, the vertical sweep efficiency of different-type reservoirs was improved to different degrees. The liquid production of in the upper part decreased while that in the lower part increased, among which the liquid production increase at the bottom of negative-rhythm reservoir was most significantly. The investigation of this paper was beneficial to visually recognize steam override by steam injection and provided a guidance to improve the vertical sweep efficiency with the hybrid injection of steam and air in thick heavy oil reservoirs.

Simulation analysis of electromagnetic-temperature field coupling of medium voltage switchgear based on finite element method

In order to study the electric field distribution and temperature distribution of medium-voltage switchgear under normal operating conditions, taking 10kV switchgear as an example. Firstly, a three-dimensional physical model was established based on the solid structure of the switchgear. Secondly, the switchgear was made using the finite element method to simulate and analyze the electromagnetic field and temperature field. Consider various factors that affect the electric field distribution, and obtain the electric field distribution inside the switchgear and the temperature field distribution map on the current-carrying circuit.

Experimental study on the pressure of impulse waves generated by landslides on a bank slope

Impulse waves generated by landslides lead to serious secondary disasters. To investigate the effects of impulse waves on a bank slope, a three-dimensional physical model test was conducted considering multiple factors, such as the width, thickness, and volume of the landslide body, inclination angle of the landslide, and bank slope angle. The results show that the wave did not break upon the first crest. And the waves break and swirl locally when fallback water flowed into the trough. The pressure acting upon the bank slope included pulsating pressure and impact pressure, of which the latter was largely affected by repeated tests, measuring frequencies, and measurement point densities. The existing empirical formulas cannot accurately reflect the wave pressure on the bank slope under the action of landslide-generated impulse waves. The maximum pulsating pressure increased proportionally with width, thickness, volume and inclination angle of the landslide body. This study better restores the interaction process between landslide, impulse waves and bank slope in actual river channels, and provides relevant support for the formulation of water pressure prediction formulas.