Propagation Law Research Articles

Study of a 2 kN·m Torque Transducer Tested at GUM and PTB, Including Creep Behaviour

Abstract This article presents a study carried out on a 2 kN·m torque transducer at the Central Office of Measures (GUM) and the Physikalisch-Technische Bundesanstalt (PTB). The weighted least squares method was used to generate the linear regression equations for this torque transducer. The Monte Carlo method and the law of uncertainty propagation were used to calculate the expanded uncertainty. In addition, a creep study was carried out at eight measurement points ranging from 200 N·m to 2000 N·m. The investigations showed that the highest readings of the torque transducer, expressed in electrical units as mV/V, occur within the initial few seconds of the test after the removal of the maximum reference torque.

Transient electromagnetic perspective technology in the ultra-long coal mining face

The ultra-long coal mining face has the advantages of high recovery efficiency and low production cost; however, the widening of the coal face poses the difficulty of detecting the hidden geological bodies inside the coal face, and using conventional geophysical methods gives rise to imprecise detection results. Therefore, this paper proposes a transient electromagnetic perspective technology based on the conventional mining transient electromagnetic method. A long rectangular loop is used as the transmitting source in one coal mining tunnel of the coal mining face, and it is received in the opposite coal mining tunnel. This method is characterized by a long detection distance and high construction efficiency. Firstly, the paper used numerical simulation to investigate the spread of the transient electromagnetic field from the long rectangular loop source in both a uniform full-space model and a full-space laminated model. This showed the transient electromagnetic field propagation law and the effect of the coal seam thickness. Then, we analyzed the transient electromagnetic perspective signal characteristics of typical geological structures and gave the all-time apparent resistivity calculation method. Conclusively, the feasibility of this method is ultimately confirmed by the analysis of the measured data. Also, the research results provide a new technological approach to detecting hidden geological structures in the ultra-long coal mining faces.

Uncertainties of Surface Roughness and Tool Wear in Machining of AISI 4140 Alloy Steel

Uncertainty is the probability of statistical dispersion of a quantity from the desired value. Every manufacturing process has some types of uncertainties. In this investigation, individual, combined and expanded uncertainties of surface roughness and tool wear in machining of AISI 4140 alloy steel are quantified and compared. First, the individual and combined uncertainty of two responses namely tool wear, and surface roughness are measured using a deterministic method called the law of propagation of uncertainties (LPUs), and the principal contributors to uncertainties are identified. This method produces uncertainty of surface roughness as 0.1162[Formula: see text][Formula: see text]m and that of tool wear as 7.4036[Formula: see text][Formula: see text]m. It is further observed that cutting speed contributes 77.946% and 57.4853% on overall uncertainties for surface roughness and tool wear respectively. A stochastic method called Monte Carlo simulation (MCS) technique is further employed using 100,000 no. of iterations to compute the uncertainties in surface roughness and tool wear. This method produces uncertainties as 0.0581[Formula: see text][Formula: see text]m and 3.687[Formula: see text][Formula: see text]m in surface roughness and tool wear respectively. The results obtained from the deterministic model (LPU) and the stochastic model (MCS) are compared and it is observed that the MCS method is more reliable and accurate than the LPU method.

A model for simulating PM2.5 concentration in subway systems

Due to adverse effects on health, the PM2.5 of subway systems is increasingly attracting people's attention. Although scholars have conducted many experimental studies on the characteristics of PM2.5 in subway stations, theoretical research on the propagation law of PM2.5 in subway systems is still lacking. In this study, we established a mathematical model for the PM2.5 concentration in the subway system based on the principle of mass conservation, including a PM2.5 generation model for trains operating in tunnels and a network model for calculating the ventilation rate, to simulate the variation of PM2.5 concentration in various areas of the subway system. The model was used to simulate the PM2.5 concentration of a subway line in Nanjing, China and on-site testing was conducted to verify the simulation results, with an error was within 10%. The simulation results quantitatively illustrate the influence of train density and ambient concentrations on PM2.5 variation in the subway system and the comparison with studies in other countries has also verified the applicability. This model could be used based on actual subway lines to simulate the PM2.5 concentration at any time during subway operation, thereby providing effective guidance for improving the environmental air quality of subway stations and optimizing the design of environmental control systems.

Pressure and Flame Propagation Characteristics of Suspended Coal Dust Explosions Induced by Gas Explosions.

In order to explore the pressure and flame propagation characteristics of gas-coal dust composite explosions, a semiclosed pipeline explosion test platform was built. The shock wave overpressure and explosion flame propagation law of different concentrations of suspended coal dust participating in gas explosions were studied in depth through experiments, and the coal dust motion law was simulated and analyzed based on Fluent software. The experimental results show that the peak pressure of gas-coal dust composite explosion is significantly higher than that of single-phase gas explosion, and the pressure peak increase ratio at the pipeline outlet is the highest; as the suspended coal dust concentration increases, the pressure rise rate at point 3 gradually decreases. Under the condition of 600 g/m3 coal dust participating in the explosion, the explosion pressure increase speed reduction ratio is 25.65%, the pressure wave secondary peak decreases, and the fluctuation frequency increases. When the explosion flame front passes through the suspended coal dust area, the flame shape changes from 'v' shape to 'finger' shape and propagates forward. The gas-coal dust composite explosion flame propagation speed shows a secondary acceleration phenomenon, after the flame front passes through the coal dust suspension area. As the coal dust concentration increases, the explosion core area moves away from the flame front. The coal dust cloud moves to the right, showing a concave rectangle; the larger the coal dust concentration, the smaller the moving speed. The experimental results and analysis provide an experimental basis for further exploring the mechanism and dynamic mechanism of gas-coal dust coupling explosion.

Study on load characteristics and structural impact response propagation law of cabin internal explosion

Aiming at the problem that the distribution of explosion load in the cabin and the propagation law of structural impact response was unclear, this paper established the numerical calculation model of explosion in a closed cabin by ALE (Arbitrary Lagrangian Eulerian) method. There was an apparent convergence of shock waves at the cabin's corners, and the pressure relief hole's area and its position significantly affected the peak of quasi-static pressure. The peak acceleration of the deck structure decreased exponentially as the distance from the location of charge increased. Peak acceleration decreased by approximately 50% for each bulkhead crossing. There was a “paper window effect” during the cabin interior explosion on the whole ship. It meant there was a limit to the value for the energy generated by the explosion to be transmitted along the frame structure. When the charge was 150 kg, it reached the limit of the energy transferred by the structure in this paper. The response of the distant structure did not change significantly with the increase in the charge quality. The research revealed the impact response propagation mechanism in the structure and provided a reference for designing protective structures.

Nonlinear stress growth and failure characteristics of gangue-cemented backfill

The stability of a filling body is the main control index of the filling effect, which is significantly affected by the strength and damage characteristics, and its stress increases nonlinearly with damage evolution. In this study, the uniaxial compression test and digital image correlation (DIC) method were used to investigate the stress and damage characteristics of a gangue-cemented backfill, and the stress–strain characteristics and crack propagation laws of the backfill under different curing ages were analyzed. A modified damage model of the gangue-cemented backfill based on the Weibull distribution characteristics of the microelement damage of the backfill and pore closure characteristics in the compression stage was constructed. Through numerical simulations, the nonlinear growth characteristics of stress in the specimen were revealed from the perspective of energy dissipation. The results showed that the nonlinear increase in stress originated mainly from pore closure and crack extension. The crack propagation in the backfill was divided into intermediate crack budding and symmetric crack propagation at the corners. The key signs of the peak stress and fracture of the specimen are the connection of the surface cracks and fracture surfaces on both sides. The proposed modified damage model was proven to be in relatively close agreement with the experimental results. The stress growth in the backfill exhibited a nonlinear-linear-nonlinear growth pattern before the peak stress. This study provides a theoretical basis for studying the strength characteristics and damage evolution of backfill, which is important for optimizing the material proportions and analyzing the stability of the quarry and other aspects.

A multiple risk coupled propagation model for emergency information considering government information and government mandatory measures

In the era of new media, it is crucial to investigate the transmission paths of emergency information due to the rising risk of such information. We take the risks caused by the dissemination of various heterogeneous negative information public opinion arising from the emergencies as the research object. Starting from the coupling of multiple risks and considering the behavioral impact of different government measures, we construct a three-layer coupling network S1I1S1-S2I2S2-UAU model between different types of negative information (Info1, Info2) and government information (Info3) diffusion, and analyze the coupling mechanisms of negative information and government information. Second, the MMCA is used to analyze the dissemination process and the diffusion threshold of government information. Finally, the rationality and effectiveness of the S1I1S1-S2I2S2-UAU model are verified by numerical simulation and real case. Our research results can help establish the cognitive of information risk coupling propagation law, providing support for government departments in controlling information risk.

Study on the superposition effect of stress waves and crack propagation law between blastholes at different angles

The drilling and blasting method is extensively employed in various industries such as mining and infrastructure construction. In the majority of blasting operations, strip-charges are predominantly utilized, while blastholes often exhibit an angled orientation in practical engineering scenarios. To investigate the stress wave superposition effect and the crack propagation law among blastholes at varying angles, this study employs a high-speed digital image correlation system to conduct blasting model experiments. The results indicate that: the fractal dimension of the crack propagation trajectory decreases progressively as the angle increases. the von Mises strain-time curve of the specimen initially increases and then decreases. As the angle between the blastholes widens, the fractal dimension of the crushing zone and blasting crack among the blast borehole decreases accordingly, suppressed the blasting effect of the blasted medium. On the central axis between the two holes, the stress superposition becomes more obvious in the direction away from the initiation point, and the peak value of strain is the highest at the bottom of the blastholes. When the angle between the blastholes is 30°, the strain in the specimen takes the longest to decline from peak to valley, and the blasting stress wave sustains its influence for an extended duration, thus maximizing the use of blasting energy. Conversely, when the angle between the blastholes is 0°, the specimen experiences the shortest duration of blasting action and the least efficient energy utilization.

Investigating the dispersion characteristics of symmetric and asymmetric modes in rails: A theoretical and experimental study

The propagation law of ultrasonic guided waves in waveguide structures is determined by their dispersion characteristics, and the number of guided waves in symmetric and antisymmetric modes in rails is significant, so the dispersion characteristics are very complex. In order to study the dispersion characteristics of symmetric and antisymmetric modes in rails, this paper derives the wave equation based on the SAFE method with higher order elements, and the correctness of the wavestructure calculation in the SAFE model is verified using the FE method. This paper focuses on the wavestructure state at 0 kHz and the wavestructure changes during mode crossing through and repulsive deflections, and for the first time experimentally verifies the phenomenon of wave structure exchange in rails. The main conclusions are that the dispersion curves between modes with the same symmetry show repulsive deflection, and the dispersion curves between modes with opposite symmetry show crossover; the wavestructure of the rail is mainly rigid body translation and rigid body rotation at frequencies close to 0 kHz; the guided wave at the intersection of symmetric and antisymmetric modes transforms into a fading wave that cannot be continuously propagated in rails; when the dispersion curves are close, the wavestructures between the two modes are linearly superimposed, and when the dispersion curves are deflected by repulsion, the wavestructures of the two modes are exchanged.

ERROR ANALYSIS OF VISUAL ODOMETRY FOR A SMALL SIZE UNMANNED AERIAL VEHICLE

Abstract. Usage of small size Unmanned Aerial Vehicle (UAV) with autonomous flight capability became widespread at both civil and military applications because of its low costs and ease of use. However, inertial or GPS based positioning and orientation sensors can be disabled at battlefields and the UAV losses its path in a short time. Visual odometry becomes a solution for the aforementioned hassle. Real-time detection of ground control points, matching the same control points at the stereo pair images and correcting the position and orientation data with least square adjustment are the challenges of visual odometry. In this study, error analysis of position and orientation of a UAV flying through mountainous region which cannot obtain any augmenting data for position and orientation is conducted by error propagation law. The flight of UAV is simulated with exact initial position and orientation data. Optic images of ground obtained by nadir directed camera are georeferenced using the digital elevation model of the region, interior and exterior camera parameters. The digital elevation model is used to correct the relief displacement. The stereo-pair image is obtained when the UAV flies 200 m and image coordinates of the common control points are detected by colinearity equations. Position and orientation of UAV is corrected by least square adjustment and the process is repeated for each obtained image acquired at 200 m interval. The analysis revealed that the precisions of horizontal and vertical positioning becomes 75 and 200 meter, respectively. The precision of roll angle becomes worse than 0.5 degree, while the precisions of pitch and yaw angle are estimate to be better that 0.1 degree.

Research on explosion venting characteristics of CH4/H2/Air mixture in square explosion vessels

Hydrogenation of methane (CH4) is an important means of achieving energy savings and large-scale hydrogen (H2) transportation. Explosion venting is considered to be an effective method to reduce the risk of gas explosions. To investigate the parameters of the explosion characteristics of CH4/H2/Air premixed fuel under venting conditions, the explosion characteristics and the dynamic propagation law of venting flame in CH4/Air mixtures with 5% concentration were studied in 20 L and 40 L square explosion venting vessels. The development process of flames inside vessels, the evolution characteristics of explosive venting flames, and the changes in explosion pressure were tested using a high-speed camera and pressure sensors. The maximum explosion pressure, the maximum explosion pressure rise rate, and the maximum flame velocity increased first and then decreased with the addition of H2. However, the maximum flame length increased continuously with the increase of H2. With the increase of hydrogenation, the maximum flame area showed an exponential increase. At equivalence ratio less than 1, the effect of hydrogenation on the flame area was much attenuated than that at equivalence ratio was greater than 1.

Assessing the thermal conductivity of amorphous SiN by approach-to-equilibrium molecular dynamics.

First-principles molecular dynamics combined with the approach-to-equilibrium molecular dynamics methodology is employed to calculate the thermal conductivity of non-stoichiometric amorphous SiN. This is achieved by implementing thermal transients in five distinct models of different sizes along the direction of the heat transport. Such models have identical structural features and are representative of the same material, thereby allowing for a reliable analysis of thermal conductivity trends as a function of the relevant cell dimension. In line with the known physical law of heat propagation at short scale, the thermal conductivity increases in size with the direction of heat transport. The observed behavior is rationalized accounting for previous results on crystalline and amorphous materials, thus providing a unified description holding for a large class of materials and spanning a wide range of heat propagation lengths.

Modeling and simulation analysis of hydroacoustic field under ice

In order to study the effect of polar ice on sound propagation in seawater, the finite element method was used to establish a seawater sound propagation model with and without ice, and the influence of the presence of ice on the seawater sound propagation law was analyzed. The simulation results show that the energy of sound propagation in seawater has a certain loss when there is an ice layer compared with the case of no ice layer. Through frequency domain analysis, the propagation process of sound energy in seawater can be clearly seen. Normally, the sound energy generated by a point source at a suitable location will return to the seawater after passing through the sea surface, while after the addition of the ice layer, part of the sound energy generated by the point source will be lost to the air through the ice layer, resulting in a reduction of the acoustic energy returned to the seawater. As a result, there is less acoustic energy in the seawater than in the ice-free case.

Research Progress and Preventive Measures of Combustible Dust Explosion

The research on explosion characteristics of metal dust is reviewed. Summarize and condense the main research results in the field of dust explosion. Its contents include: explosion propagation law, lower explosion limit concentration, maximum explosion pressure, maximum pressure rise rate and ignition source causing dust explosion. Finally, some prevention and mitigation measures for dust explosion are put forward.

Dynamic response of aluminum-graphene layered nanocomposites under shock compression and release based on atomistic simulations

To understand the role of aluminum-graphene (Al-Gr) interface, molecular dynamics simulations have been conducted to investigate the dynamic response of Al-Gr layered nanocomposites. The propagation law of shock waves is revealed and the dislocation nucleation at Al-Gr interface may dominate the plastic deformation mechanism at low impact velocities, which results in the propagation of stepped waveforms. In other words, Gr facilitates dislocation nucleation and its full development in each Al layer. At high impact velocities, Gr can hinder the forward propagation of BCC Al, although Gr can promote BCC nucleation. During shock release, Gr reduces the spall strength of the Al-Gr layered nanocomposites, and then the fracture is dominated by interface fracture, exhibiting single-layer or multi-layer delamination. Gr is found to undergo bending and folding, but Gr remains intact owing to its exceptionally high tensile strength and resistance to high temperatures. With the development of voids and cracks near the Al-Gr interface, the Al layer undergoes significant geometric deformation without internal fragmentation..

Exploring the mechanism of improving the pressure fluctuation of double suction centrifugal pump by impeller stagger.

The pressure fluctuation in the volute can be effectively reduced when the impeller of the double-suction pump is staggered, but the mechanism of this reduction is still unclear. At the same time, the traditional analysis method cannot realize the visualization of pressure fluctuation. The purpose of this article is to explore the spatial distribution, propagation, and attenuation law of pressure fluctuation, and on this basis, to research the reason why staggered impeller reduce pressure fluctuation. A new method called Pulse tracking network (PTN) was used in this article. Compared with the traditional method, which only analyzes the pressure fluctuation at scattered points, this method greatly improves the spatial resolution of the pressure fluctuation. In particular, the phase analysis is a major highlight of the method. Staggered impeller significantly reduced the pressure fluctuation intensity dominated by blade passing frequency. At the same time, the propagation of the pressure fluctuation in the volute changed from radial to circumferential in the volute cross-section. Staggered impeller can effectively reduce pressure fluctuation, and the circumferential propagation caused by it is considered to be the main reason for it.

A coupled hydro-thermo-mechanical model based on TLF-SPH for simulating crack propagation in fractured rock mass

In this paper, a hydro-thermo-mechanical coupling model based on the smoothed particle hydrodynamics with total Lagrangian formula (HTM-TLF-SPH) is proposed to simulate the crack propagation and instability process of fractured rock mass. TLF-SPH uses the Lagrangian kernel approximation, that is, the kernel function and its gradient need only be calculated once in the initial configuration, which is much more efficient than the smoothed particle hydrodynamics (SPH) based on the Euler kernel approximation. In TLF-SPH, particles interact with each other through virtual link, and the crack propagation path of rock mass is tracked dynamically by capturing the fracture of virtual link. Firstly, the accuracy and robustness of the HTM-TLF-SPH coupling model are verified by a reference example of drilling cold shock, and the simulation results agree well with the analytical solutions. Then, the crack propagation law of surrounding rock and the evolution characteristics of physical fields (displacement, seepage and temperature fields) after excavation and unloading of deep roadway under the coupling condition of hydro-thermo-mechanical are investigated. In addition, the seepage and heat transfer processes of the surrounding rock of Daqiang coal mine under different coupling conditions are successfully simulated. Meanwhile, the effect of the boundary water pressure difference on the temperature and seepage fields under the hydro-thermal coupling condition is quantitatively analyzed.

Numerical study on crack propagation of CO2 fracturing in tight sandstone reservoir considering fluid-solid-temperature coupling

Tight sandstone has a tight structure and low natural production capacity, usually requiring the use of fracturing technology to achieve industrial production. Supercritical CO2 fracturing has attracted much attention due to its clean and efficient properties. In this paper, using the principles of damage mechanics, the crack propagation law during supercritical CO2 fracturing was studied by using numerical methods. The influence of different factors on the fracture propagation patterns is analyzed. Results indicate that supercritical CO2 fracturing can form complex fracture distribution patterns. This mode is divided into three different stages: slow fracture propagation, rapid fracture propagation, and rigid fracture propagation. In addition, highly heterogeneous formations generate more secondary fractures but limit their expansion.

Experimental Investigation of Fracture Propagation in Clayey Silt Hydrate-Bearing Sediments

More than 90% of the natural gas hydrate resources are reserved as marine clayey silt sediments. It is of great significance to efficiently develop a clayey silt hydrate. At present, there are problems of low single well production and small depressurization range in its production test, which is still a long way from commercial exploitation. The combination of hydraulic fracturing technology and other methods such as depressurization method is regarded as one of the potential technical means to achieve the commercial exploitation of the hydrate. However, compared with shale gas reservoirs and coalbed methane reservoirs, clayey silt hydrate reservoirs have special mechanical properties, resulting in unique hydraulic fracturing processes. Therefore, it is necessary to study the fracture initiation and propagation laws of clayey silt hydrate reservoirs. To this end, we carried out large-scale (30 × 30 × 30 cm) true triaxial hydraulic fracturing experiments using a simulated material with similar mechanics, porosity, and permeability to clayey silt hydrate-bearing sediments. The effects of completion method, fracturing method, and fracturing fluid displacement on hydraulic fracture propagation of clayey silt hydrate-bearing sediments were studied. The results showed that a perforated completion can significantly increase the fracture reconstruction area and decrease the fracture initiation pressure compared to an open hole completion. Due to the small horizontal stress difference, it is feasible to carry out temporary plugging fracturing in clayey silt hydrate reservoirs. Temporary plugging fracturing can form steering fractures and significantly improve fracture complexity and fracture area. Increasing the fracturing fluid displacement can significantly increase the fracture area as well. When conducting fracturing in clayey silt hydrate-bearing sediments, the fracturing fluid filtration area is obviously larger than the fracture propagation area. Therefore, it is recommended to use a high-viscosity fracturing fluid to reduce the filtration of the fracturing fluid and improve the fracturing fluid efficiency. This study preliminarily explores the feasibility of temporary plugging fracturing in clayey silt hydrate reservoirs and analyzes the effect of completion methods on the propagation of fracturing fractures, which can provide a reference for the research conducted on the fracturing stimulation of clayey silt hydrate reservoirs.