Propagation Law Of Waves Research Articles

Experimental Research on Directional Blasting in Pre-cutting Hard Coal Seam Roof

Aiming at the problem of impact ground pressure caused by the hard roof of goaf in coal mining face, the research on pre-cutting of hard coal seam roof by directional blasting was carried out. According to the principle of energy accumulation in directional blasting, a similar simulated experiment was designed on the basis of theoretical analysis of stress wave propagation law, crack development law and forced roof caving distance. The experimental results show that the roof is pre-cut by directional blasting, the integrity of the roof in front of the working face is reduced, effective pressure relief effect is obtained, the large area of overhanging roof in goaf is prevented, and the impact ground pressure disaster of the working face is relieved.

Experimental study of overpressure evolution laws and flame propagation characteristics after methane explosion in transversal pipe networks

To explore overpressure evolution laws and flame propagation characteristics after methane explosion in a complex pipe network, we established in the lab a transversal pipe network methane explosion experimental system and experimentally studied the explosive pressure wave propagation laws of premixed gases of three different methane concentrations (8%, 9.5%, and 11%). Experimental results indicate that an overpressure rising region will be formed in the transversal branch, which is due to the superposition of pressure waves after methane–air premixed gas explosion. However, the flame intensity generated by pressure wave is extremely small and the flame sustaining time is very short. In the parallel branch, maximum explosion overpressure presents a gradually descending trend, and flame propagation velocity presents a rising and then descending trend, but the flame sustaining time decreases first, then increases, and finally decreases again as the distance from the explosion source increases. The maximum explosion overpressure and flame propagation velocity of the gas with a 9.5% methane concentration are higher than 8% and 11%. The experimental study obtains a preliminary mastery of overpressure evolution laws and flame propagation characteristics after methane explosion in pipe networks. The results could provide important theoretical guidelines for the prevention and control of fuel gas explosion in urban pipe networks.

Dynamic Damage Mechanism of Coal Wall in Deep Longwall Face

The stability of coal wall in deep longwall face has always been a research hotspot. In this study, pure vibration signals in the coal wall during the operation of mining machinery were obtained for the first time, and their energy is mainly concentrated in 7–12 Hz. Besides, based on the law of stress wave propagation, with the coal wall of deep longwall taken as the research object, the theory of dynamic damage in coal wall was put forward from the perspective of dynamics. The results show that the loading and unloading waves generated by the mining machinery disturbance will be reflected and transmitted at the interface with different impedances, resulting in the formation of multiple unloading and loading waves and multiple tensile stress zones and stress concentration zones. These stress concentration zones tend to induce tensile stress generation and coal failure. As a result, the coal undergoes zonal failure and spalling. Through the vibration test of coal, it is found that the crack development of the coal sample can be divided into five stages, and the phenomena of zonal failure and spalling occur, which is consistent with the theory. At the same time, the sample that has gone through a large disturbance cannot be further damaged by a small disturbance, which is verified by the damage statistical constitutive model based on the isotropy hypothesis.

Microwave transmission performance of fused silica ceramics in microwave high-temperature heating

Compared with traditional heating methods, microwave heating is widely used in many industrial heating fields because of its advantages, such as material-selective heating, volumetric heating and high-efficiency heating. However, previous studies have shown that the heating mode depends on the transmission performance of refractory insulation materials. In this study, a commonly used refractory material (fused silica ceramics) for microwave heating was studied, according to the law of electromagnetic wave propagation in a single-layer plate, the power transmission coefficient (PTC) of the material at different thickness, temperature and frequency (915 MHz and 2360 MHz) was calculated and analysed, in order to design the refractory structure which has good microwave transmission performance in the whole microwave heating process. The results show that the transmission performance of fused silica ceramics fluctuates regularly with increasing thickness, and there are several microwave transmission peaks in the PTC patterns, the thicknesses corresponding to the transmission peaks at frequency 2360 MHz are in order 0.033 m, 0.065 m and 0.098 m; as the temperature increases, the position of the transmission peaks will shift to a smaller thickness, the transmission performance of fused silica ceramics decreases slightly with increasing temperature. Comparing the transmission performance of mullite, alumina (Al2O3) and fused silica ceramics, it was found that the fused silica ceramics have excellent transmission properties; especially it is at high temperature. The results of this study can provide guidance for the selection of refractory structure materials and sizes as well as the optimization of heating process parameters in high-temperature microwave heating.

Investigation of wavelength effects on polycrystalline silicon damages using nanosecond pulse laser irradiation

Based on polyvinylidene fluoride(PVDF) piezoelectric sensing technology, this paper investigated the damage mechanism of polysilicon irradiated by three wavelengths (1064 nm, 532 nm, and 355 nm) of nanosecond pulsed laser. According to the damage characteristics of the polysilicon, the thermal shock damage mechanism of laser irradiation on polycrystalline silicon has been studied, and the propagation law of laser shock waves in the brittle materials has been explored. The results show that the melt spatter phenomenon of the polysilicon surface is caused by melting from the heat generated when the material absorbs high-energy laser photons, combined with the vapour pressure and plasma pressure. The main cause of the polysilicon material’s cleavage and destruction is the laser thermal stress. The corrugated field around the material’s radiation area is mainly the result of the coherent coupling of optics and thermodynamics. The peak value of the laser shock wave in polysilicon shows a linearly distributed attenuation.

Crack Propagation Law Affected by Natural Fracture and Water Jet Slot under Blast Loading

The natural fracture of rock has a strong effect on the law of explosion stress wave transmission and crack propagation during blasting. Based on the stress wave theory, the influential mechanism for both the law of transmission of the stress wave and of crack propagation due to natural fracture and water jet slot are analysed. Next, an experiment is conducted to understand the crack propagation law because of the effect of an explosion shock wave, and the evolution law of the blast stress wave and blast-induced crack propagation is simulated by ANSYS/LS-DYNA. The results indicate that the existence of the water jet slot not only promotes the generation of the main crack along its direction, but also promotes the generation of the secondary crack near the water jet slot because of the explosion shock wave. The direction of propagation of the secondary crack and the main crack are seriously affected by the natural fracture. In addition, if the distance between the blast hole and the natural fracture is too small, a smash area is formed; and with an increase in the distance between the blast hole and the natural fracture, the smash area becomes smaller, and the effect on the blast-induced crack becomes weaker.

Magnetic Reconnection Detonation in Supernova Remnants

Abstract As a key process that refreshes the interstellar medium (ISM), the dynamics and radiative properties of the supernova remnant (SNR) expansion front not only reflect the physical environment of the old ISM surrounding the supernova, but they also provide information about the refreshed ISM. However the expansion dynamics of SNRs cannot be simply explained by the conventional law of spherical shock wave propagation; on the other hand, the high-energy radiation requires an additional electron acceleration mechanism in the shock front beyond thermal collision. We consider herein the detonation wave description of the SNR expansion, in which magnetic reconnection follows the shock front and transfers the SNR magnetic field energy to both fluid thermal energy and particle kinetic energy. The structure of the magnetic reconnection detonation (MRD) is identified based on the scaling analysis in this paper. By applying the MRD description of the SNR expansion shock to the example of the Crab Nebula, this paper shows that the MRD description can explain both the accelerative expansion of the nebula as well as the origin of the luminous expanding shell.

Experimental Research on the Impactive Dynamic Effect of Gas-Pulverized Coal of Coal and Gas Outburst

Coal and gas outburst is one of the major serious natural disasters during underground coal, and the shock air flow produced by outburst has a huge threat on the mine safety. In order to study the two-phase flow of a mixture of pulverized coal and gas of a mixture of pulverized coal and gas migration properties and its shock effect during the process of coal and gas outburst, the coal samples of the outburst coal seam in Yuyang Coal Mine, Chongqing, China were selected as the experimental subjects. By using the self-developed coal and gas outburst simulation test device, we simulated the law of two-phase flow of a mixture of pulverized coal and gas in the roadway network where outburst happened. The results showed that the air in the roadway around the outburst port is disturbed by the shock wave, where the pressure and temperature are abruptly changed. For the initial gas pressure of 0.35 MPa, the air pressure in different locations of the roadway fluctuated and eventually remain stable, and the overpressure of the outburst shock wave was about 20~35 kPa. The overpressure in the main roadway and the distance from the outburst port showed a decreasing trend. The highest value of temperature in the roadway increased by 0.25 °C and the highest value of gas concentration reached 38.12% during the experiment. With the action of shock air flow, the pulverized coal transportation in the roadway could be roughly divided into three stages, which are the accelerated movement stage, decelerated movement stage and the particle settling stage respectively. Total of 180.7 kg pulverized coal of outburst in this experiment were erupted, and most of them were accumulated in the main roadway. Through the analysis of the law of outburst shock wave propagation, a shock wave propagation model considering gas desorption efficiency was established. The relationships of shock wave overpressure and outburst intensity, gas desorption rate, initial gas pressure, cross section and distance of the roadway were obtained, which can provide a reference for the protection of coal and gas outburst and control of catastrophic ventilation.

Dynamic response of single-layer reticulated shell with explosion-protection wall under blast loading

To investigate the structural dynamic response of long span reticulated shell under external blast loading considering explosion-protection wall, explicit finite element (FE) programme LS-DYNA is used to set up the analytical model of explosion-protection wall corresponding to an experiment to grasp the propagation law of blast shock waves around the wall. The results of simulation and experiment are compared and the results verify the creditability and applicability of numerical simulation by using ALE (Arbitrary-Lagrange-Euler) algorithm. A Kiewitt8 single-layer reticulated shell of refinement with span of 40 m is established to simulate the responses of structure considering explosion-protection wall, which contains reticulated shell member, purlin hanger, purlin, rivet and roof boarding. According to simulation results from the maximum nodal displacement, average plastic strain and yielding degree of cross section of reticulated shell member, the dynamic response laws are proposed based on varying parameters, including height, position, length, material of the explosion-protection wall, rise-span ratio of reticulated shell and TNT explosive weights. Meanwhile, the influence rules of explosion-protection wall and structure on diffraction and reflection action of blast shock wave are obtained. In addition, the adverse height of the explosion-protection wall for reticulated shell with span of 40 m under external blast loading is proposed. Four damage types of reticulated shell with the explosion-protection wall subject to external blast loading are defined by summarizing all the structural response of FE numerical models, which could provide reference for reasonable explosion-proof design for reticulated shell structure.

Study of blasting seismic effects of underground powerhouse of pumped storage project in granite condition

Though the test of blasting vibration, the blasting seismic wave propagation laws in southern granite pumped storage power project are studied. Attenuation coefficient of seismic wave and factors coefficient are acquired by the method of least squares regression analysis according to Sadaovsky empirical formula, and the empirical formula of seismic wave is obtained. This paper mainly discusses on the test of blasting vibration and the procedure of calculation. Our practice might as well serve as a reference for similar projects to come.

A New Mathematical Model for Predicting the Surface Vibration Velocity on the Step Topography

In order to control production blasting and optimize mining operation, it is important to study the step topography vibration amplification and attenuation effect in the open‐pit mine. Surface particle vibration velocity attenuation characteristics, the formation, and change rules of the terrain effect were studied by analyzing the field measured data. Results show that local amplification effect and local attenuation amplification effect of particle vibration velocity are obvious. Amplification effect associates with bench height, and the attenuation effect is closely related with the distance from the vibration source and distance from the top. With the increase of elevation, vibration magnification of the particle on the top was 1.1∼1.4. Because of the influence of the terrain effect, particle vibration velocity on the slope toe was obviously inhibitory. Based on the measured data, elevation amplification factor and clamping effect factor which influence blasting vibration velocity are put forward, and a new mathematical model considering the attenuation coefficient, the elevation amplification coefficient, and the clamping effect coefficient for predicting the blasting vibration velocity of the step topography is further improved. The regression analysis results show that the fitting coefficient of determination of the new prediction model is 0.8152 in horizontal and 0.8902 in vertical, respectively, and the prediction error is less than 20%, which is much better than other formulas. This new model provides effective reference for blasting seismic wave propagation law research of slope engineering.

Spectra, energy, and fractal characteristics of blast waves

Using a portable microseismic monitoring instrument, we monitored blast waves at different distances from the blast center and analyzed their spectra, wavelet packet energies, and fractal characteristics. The results show that with increasing blast–center distance, the main frequency bands become narrow and the main frequency decay is governed by a power law (f = 424.98 l −0.72). The energy of the wavelet packet is concentrated within the main frequency; energies associated with high frequency bands decay quickly, whereas for the low frequency bands (low to 78 Hz), the percentage of the total energy in these bands presents a rising trend of around 42% and 71% at blast–center distance 30 m and 110 m, respectively. In addition, the correlation dimension D of the blast wave tends to decrease with increasing blast–center distance; the correlation dimension D is 3.55 at distance 30 m and decreases to 1.26 at distance 110 m. The blast waves frequency spectra, wavelet packet energies, and fractal characteristics are inherent unity. These results provide an important basis for further study on the propagation law of blast waves in coal mines.

Amplification and attenuation effect of blasting vibration on step topography

The present study investigates the growth and variation of the amplification effect in the propagation of the blasting vibration velocity in step topography. The results indicate that the blast vibration elevation amplification effect on a single step occurs at a certain distance and elevation; the peak particle velocity magnification of the top of the slope doesn't increase monotonously with the increase of the elevation; and the magnification decreases when the elevation exceeds a certain critical value. The elevation exerts an effect of both amplification and attenuation on the blasting vibration velocity. According to the data analysis of the numerical simulation and the field experiment, a model of the blasting vibration velocity prediction on step topography was presented, providing reference for the research of blasting seismic wave propagation law in similar slope projects.

Propagation Characteristics of Blasting Stress Waves in Layered and Jointed Rock Caverns

The existence of joint fissures makes explosive actions between rock masses more complex. Therefore, it is of great significance to carry out experiments studying blasting stress waves propagating in jointed rock masses. Based on the Froude Similarity principle, the geological mechanical models of intact rock masses and jointed rocks have been proposed. A blasting vibration experiment was carried out and demonstrated that the propagation of the blasting stress waves and changing structures have an important relationship. A numerical simulation of the blasting stress wave propagation law in a layered jointed rock mass was carried out. This study found that with an increase in the joint angle, the peak velocity of blasting stress wave, transmission coefficient and reflection coefficient all gradually increased, while the attenuation coefficient gradually decreased. With an increase in joint spacing, the attenuation rate of the blasting stress waves increased.

Influence of the connecting condition on the dynamic buckling of longitudinal impact for an elastic rod

The stress wave propagation law and dynamic buckling critical velocity are formulated and solved by considering a general axial connecting boundary for a slender elastic straight rod impacted by a rigid body. The influence of connecting stiffness on the critical velocity is investigated with varied impactor mass and buckling time. The influences of rod length and rod mass on the critical velocity are also discussed. It is found that greater connecting stiffness leads to larger stress amplitude, and further results in lower critical velocity. It is particularly noteworthy that when the connecting stiffness is less than a certain value, dynamic buckling only occurs before stress wave reflects off the connecting end. It is also shown that longer rod with larger slenderness ratio is easier to buckle, and the critical velocity for a larger-mass rod is higher than that for a lighter rod with the same geometry.

On the dynamic compression of cellular materials with local structural softening

Analytical and numerical analyses are carried out in order to reveal the importance of the cellular materials topology for their dynamic compaction. The aim is to distinguish between the deformation and energy absorption mechanisms of materials which exhibit local structural softening, such as out-of-plane loaded honeycomb, and materials with local structural hardening (foam). It is shown that the dynamic out-of-plane compaction of honeycombs does not obey the law of shock wave propagation and a new phenomenological model of the velocity attenuation is proposed. It is revealed that the absorbed energy by the honeycomb is proportional to the area under the dynamic stress-strain curve, which is defined by the foil material properties, in contrast to the shock-wave propagation model where the absorbed energy is proportional to the area under the shock chord. Comparisons with the predictions of the Rigid Perfectly-Plastic Locking (RPPL) model, which approximates well the average quasi-static stress-strain characteristic of a honeycomb, are discussed. Special attention is given to the effects of neglecting the honeycomb topology on their response to impact loading.Finite element simulations are carried out to verify the proposed theoretical model revealing the major factors which influence the dynamic response of out-of-plane loaded honeycombs to high velocity impact.

A Study of Polycrystalline Silicon Damage Features Based on Nanosecond Pulse Laser Irradiation with Different Wavelength Effects.

Based on PVDF (piezoelectric sensing techniques), this paper attempts to study the propagation law of shock waves in brittle materials during the process of three-wavelength laser irradiation of polysilicon, and discusses the formation mechanism of thermal shock failure. The experimental results show that the vapor pressure effect and the plasma pressure effect in the process of pulsed laser irradiation lead to the splashing of high temperature and high density melt. With the decrease of the laser wavelength, the laser breakdown threshold decreases and the shock wave is weakened. Because of the pressure effect of the laser shock, the brittle fracture zone is at the edge of the irradiated area. The surface tension gradient and surface shear wave caused by the surface wave are the result of coherent coupling between optical and thermodynamics. The average propagation velocity of laser shock wave in polysilicon is 8.47 × 103 m/s, and the experiment has reached the conclusion that the laser shock wave pressure peak exponentially distributes attenuation in the polysilicon.

Global historical archive of wind waves based on Voluntary Observing Ship data

A new global archive of wind wave characteristics has been developed based on Voluntary Observing Ship (VOS) data for the period of 1888–2015. In addition to the basic meteorological variables, we have derived the records of visually observed heights, periods, and wind sea and swell directions. The main parameters have been supplemented by significant wave height and dominant period estimates, as well as wave geometry characteristics: steepness, wave age, and wavelength. Multistage quality control has been applied to correct or eliminate spurious values. Data are presented as individual records for every month and as original monthly means fields for every parameter. Easy access and use, along with representative data, make the new archive particularly special and applicable in different ways without any additional preprocessing. Visual wave observations assimilated in the new archive can be used to develop global and regional climatologies, estimate extreme wave characteristics and long-term trends in wave climate, verify and compare them with satellite measurements and model analysis, and test the theoretical laws of ocean wave development and propagation.

Research on propagation laws of explosion shock wave inside metro station

Considering the actual needs of safety measures of explosion accidents or terrorist attacks in large complex buildings, numerical simulations of explosions in metro station are studied in this paper. A three-dimensional solid model of the metro station is created, and then the Eulerian three-dimensional multi-material parallel hydrocode PMMIC-3D which was proposed in 2014 (Ning et al., 2014) is used to simulate the explosion shock wave propagation laws in different conditions. In the simulation models, different reference positions were set to obtain the attenuation laws and the pressure-time curves of explosion shock waves. According to the numerical results, the range where shock waves can cause harm on human health was estimated based on the NATO (North Atlantic Treaty Organization) and the U.S. DOD (Department of defense) specifications. The influences of the stairs and pillars in the metro station, the explosive quality and the setting of the wall materials were also taken into consideration. Besides, the shock wave propagation and pressure variation of these different conditions were discussed. In addition, some prevention measures against this explosion scenario were provided to reduce the damage on human and structures.

Propagation law of shock waves in single layer spherical lattice shell under internal explosion

Using software of finite element analysis LS-DYNA, in this paper we performed numerical simulation on the propagation law of shock waves in single layer spherical lattice shell under the effect of internal explosion, obtained the laws of propagation, reflection, convergence and peak appeared of shock waves, concluded that the damage of enclosed structure is closely related to, initial overpressure peak, and partial secondary overpressure peak, analyzed the influences of explosive quantity, explosion center height, and explosive eccentric position on the propagation law of shock waves. Based on the results of numerical simulation, we concluded joint area between lattice shell top and wall shell is the key location for explosion venting and pointed out the calculation formula of overpressure peak on structure surface of higher fitting precision is feasible.