Investigation of hydroxyl-terminated polybutadiene propellant breaking characteristics and mechanism impacted by submerged cavitation water jet

A submerged cavitation water jet(SCWJ)is an effective method to recycle solid propellant from obsolete solid engines by the breaking method.Solid propellant's breaking modes and mechanical process under SCWJ impact are unclear.This study aims to understand those impact breaking mechanisms.The hydroxyl-terminated polybutadiene(HTPB)propellant was chosen as the research material,and a self-designed test system was used to conduct impact tests at four different working pressures.The high-speed camera characterized crack propagation,and the DIC method calculated strain change during the impact process.Besides,micro and macro fracture morphologies were characterized by scanning electron microscope(SEM)and computed tomography(CT)scanning.The results reveal that the compressive strain concentration region locates right below the nozzle,and the shear strain region distributes symmetrically with the jet axis,which increases to 4% at first 16th ms,the compressive strain rises to 2% and 6% in the axial and transverse direction,respectively.The two tensile cracks formed first at the compression strain concentrate region,and there generate many shear cracks around the tensile cracks,and those shear cracks that develop and aggregate cause the cracks to become wider and cut through the tensile cracks,forming the tensile-shear cracks and the impact parts eventually fail.The HTPB propellant forms a breaking hole shaped conical after impact 10 s.The mass loss increases by 17 times at maximum,with the working pressure increasing by three times.Meanwhile,the damage value of the breaking hole remaining on the surface increases by 7.8 times while 2.9 times in the depth of the breaking hole.The breaking efficiency is closely affected by working pressures.The failure modes of HTPB impacted by SCWJ are classified as tensile crack-dominated and tensile-shear crack-dominated damage mechanisms.

Experimental research and energy analysis of a new type of dry ice powder pneumatic rock breaking technology

When the traditional drill and blast method is applied to rock crushing projects,it has strong vibration,loud noise and dust pollution,so it cannot be used in densely populated areas such as urban public works.We developed a supercritical CO_(2)true triaxial pneumatic rock-breaking experimental system,and conducted laboratory and field tests of dry ice powder pneumatic rock-breaking.The characteristics of the blast-induced vibration velocity waveform and the evolution of the vibration velocity and frequency with the focal distance were analyzed and discussed.The fracturing mechanism of dry ice powder pneumatic rock breaking is studied.The research results show that:(1)The vibration velocity induced by dry ice powder pneumatic rock breaking decays as a power function with the increase of the focal distance;(2)The vibration frequency caused by dry ice powder pneumatic rock breaking is mainly distributed in 1–120 Hz.Due to the dispersion effect,the dominant frequency of 10–30 Hz appears abnormally attenuated;(3)The traditional CO_(2)phase change fracturing energy calculation formula is also applicable to dry ice pneumatic rock breaking technology,and the trinitrotoluene(TNT)equivalent of fracturing energy is applicable to the Sadovsky formula;(4)Dry ice powder pneumatic rock breaking is shock wave and highenergy gas acting together to fracture rock,which can be divided into three stages,among which the gas wedge action of high-energy gas plays a dominant role in rock mass damage.

Rock breaking performance of the newly proposed unsubmerged cavitating abrasive waterjet

To improve the rock breaking ability, cavitating waterjet and abrasive waterjet are combined by using a coaxial low-speed waterjet generated around the periphery of a high-speed abrasive waterjet, and a new type of waterjet called unsubmerged cavitating abrasive waterjet(UCAWJ) is thus produced. The rock breaking performance of UCAWJ was compared with submerged cavitating abrasive waterjet(SCAWJ)and unsubmerged abrasive waterjet(UAWJ) by impinging sandstone specimens. Moreover, the effects of jet pressure, standoff distance, abrasive flow rate and concentration were studied by evaluating the specific energy consumption, and the area, depth, and mass loss of the eroded specimen. The results show that the artificially generated submerged environment in UCAWJ is able to enhance the rock breaking performance under the same operating parameters. Furthermore, the rock breaking performance of UCAWJ is much better at higher jet pressures and smaller standoff distances when compared with UAWJ. The greatest rock breaking ability of UCAWJ appears at jet pressure of 50 MPa and standoff distance of 32 mm, with the mass loss of sandstone increased by 370.6% and the energy dissipation decreased by 75.8%. In addition, under the experimental conditions the optimal abrasive flow rate and concentration are 76.5 m L/min and 3%, respectively.

Comparative Study of the Rock-breaking Mechanism of a Disc Cutter and Wedge Tooth Cutter by Discrete Element Modelling

The operation of a shield tunnel boring machine(TBM)in a high-strength hard rock stratum results in significant cutter damage,adversely affecting the thrust and torque of the cutter head.Therefore,it is very important to carry out the research on the stress characteristics and optimize the cutter parameters of cutters break high-strength hard rock.In this paper,the rock-breaking performance of cutters in an andesite stratum in the tunnel of Qingdao Metro Line No.8 was investigated using the discrete element method and theoretical analysis.The rock-breaking processes of a disc cutter and wedge tooth cutter were simulated by software particle flow code PFC^(3D),and the rock-breaking degree,stress of the cutter,and rock-breaking specific energy were analyzed.The rock damage caused by the cutter in a specific section was divided into three stages:the advanced influence,crushing,and stabilizing stages.The rock-breaking degree and the tangential and normal forces of the wedge tooth cutter are larger than that of the disc cutter under the same conditions.The disc cutter(wedge tooth cutter)has the highest rock-breaking efficiency at a cutter spacing of 100 mm(110 mm)and a penetration depth of 8 mm(10 mm),and the rock-breaking specific energy is 11.48 MJ/m^(3)(12.05 MJ/m^(3)).Therefore,two types of cutters with different penetration depths or cutter spacing should be considered.The number of teeth of wedge tooth cutters can be increased in hard strata to improve the rock-breaking efficiency of the shield.The research results provide a reference for shield cutterhead selection and cutter layout in similar projects.

A record-breaking high efficiency facilitated by hierarchical morphology in all polymer solar cells

Organic solar cells(OSCs) especially non-fullerene OSCs(NF-OSCs) are promising to become the next-generation of commercial applications and have received great attention from many researchers due to their typical advantages of low cost,light weight,and flexibility [1,2].

China’s import expo yields record-breaking deals, boosts global economy

The sixth China International Import Expo(CIIE),the world’s first national-level import-themed expo,saw a total of 78.41 billion U.S.dollars’worth of tentative deals reached for one-year purchases of goods and services,setting a record high.

增强上肢力量对提高街舞的重要性研究——breaking舞种

根据调查没有接受过或者自发进行上肢力量锻炼的人群中有95%以上认为breaking中的难度动作很难完成,其难度动作中较为基础简单的动作都完成的很吃力,但是经过上肢力量锻炼的人群中有87%以上认为breaking中的难度动作相对比较容易,自己练习起来比较容易,控制能力明显比没有经过锻炼的人群要强很多,能正确地发力。

Dynamic Response Behaviors of Upright Breakwaters Under Breaking Wave Impact

- The dynamic response behaviors of upright breakwaters under broken wave impact are analysed based on the mass-damper-spring dynamic system model. The effects of the mass, damping, stiffness, natural period, and impulse duration (or oscillation period) on the translation, rotation, sliding force, overturning moment, and corresponding dynamic amplifying factors are studied. It is concluded that the ampli-ying factors only depend on the ratio of the system natural period to impulse duration (or oscillation period) under a certain damping ratio. Moreover, the equivalent static approach to breakwater design is also discussed.

Wave Breaking Phenomena of Irregular Waves Combined with Opposing Current

- Experimental study and theoretical analysis show that the critical value of relative wave height (H/ d)b given by Goda and the critical wave steepness (H/ L)b given by Michell and Miche can be adopted as the spilling breaking indices of regular waves. According to the same principle, a systematic theoretical analysis and experiment of irregular waves have been done by the authors in order to solve the breaking problem of irregular waves. It is indicated that the authors’ method for determining wave breaking of regular waves can also be used for irregular waves.

The rock breaking and ROP increase mechanisms for single-tooth torsional impact cutting using DEM

Torsional impact drilling is a new technology which has the advantages of high rock-breaking efficiency and a high rate of penetration(ROP).So far,there is no in-depth understanding of the rock-breaking mechanism for the ROP increase from torsional impact tools.Therefore,it has practical engineering significance to study the rock-breaking mechanism of torsional impact.In this paper,discrete element method(DEM)software(PFC2 D)is used to compare granite breaking under the steady and torsional impacting conditions.Meanwhile,the energy consumption to break rock,microscopic crushing process and chip characteristics as well as the relationship among these three factors for granite under different impacting frequencies and amplitudes are discussed.It is found that the average cutting force is smaller in the case of torsional impact cutting(TIC)than that in the case of steady loading.The mechanical specific energy(MSE)and the ratio of brittle energy consumption to total energy are negatively correlated;rock-breaking efficiency is related to the mode of action between the cutting tooth and rock.Furthermore,the ROP increase mechanism of torsional impact drilling technology is that the ratio of brittle energy consumption under the TIC condition is larger than that under a steady load;the degree of repeated fragmentation of rock chips under the TIC condition is lower than that under the steady load,and the TIC load promotes the formation of a transverse cracking network near the free surface and inhibits the formation of a deep longitudinal cracking network.

Differentiation and analysis on rock breaking characteristics of TBM disc cutter at different rock temperatures

In order to study rock breaking characteristics of tunnel boring machine(TBM) disc cutter at different rock temperatures,thermodynamic rock breaking mathematical model of TBM disc cutter was established on the basis of rock temperature change by using particle flow code theory and the influence law of interaction mechanism between disc cutter and rock was also numerically simulated.Furthermore,by using the linear cutting experiment platform,rock breaking process of TBM disc cutter at different rock temperatures was well verified by the experiments.Finally,rock breaking characteristics of TBM disc cutter were differentiated and analyzed from microscale perspective.The results indicate the follows.1) When rock temperature increases,the mechanical properties of rock such as hardness,and strength,were greatly reduced,simultaneously the microcracks rapidly grow with the cracks number increasing,which leads to rock breaking load decreasing and improves rock breaking efficiency for TBM disc cutter.2) The higher the rock temperature,the lower the rock internal stress.The stress distribution rules coincide with the Buzin Neske stress circle rules: the maximum stress value is below the cutting edge region and then gradually decreases radiant around; stress distribution is symmetrical and the total stress of rock becomes smaller.3) The higher the rock temperature is,the more the numbers of micro,tensile and shear cracks produced are by rock as well as the easier the rock intrusion,along with shear failure mode mainly showing.4) With rock temperature increasing,the resistance intrusive coefficients of rock and intrusion power decrease obviously,so the specific energy consumption that TBM disc cutter achieves leaping broken also decreases subsequently.5) The acoustic emission frequency remarkably increases along with the temperature increasing,which improves the rock breaking efficiency.

Circulation Features Associated with the Record-breaking Typhoon Silence in August 2014

Climatologically, August is the month with the most tropical cyclone(TC) formation over the western North Pacific(WNP) during the typhoon season. In this study, the reason for abnormal TC activity during August is discussed—especially August 2014, when no TCs formed. The large-scale background of August 2014 is presented, with low-level large-scale easterly anomalies and anticyclonic anomalies dominating over the main TC genesis region, a weak monsoon trough system,and a strong WNP subtropical high(WPSH), leading to significantly reduced low-level convergence, upper-level divergence,and mid-level upward motion. These unfavorable large-scale conditions suppressed convection and cyclogenesis. In August2014, equatorial waves were inactive within the negative phase of the Madden–Julian Oscillation(MJO), with fewer tropical disturbances. Although the low-level vorticity and convection of those disturbances were partly promoted by the convective envelopes of equatorial waves, the integral evolution of disturbances, as well as the equatorial waves, were suppressed when propagating into the negative MJO phase. Moreover, the upper-level potential vorticity(PV) streamers associated with anticyclonic Rossby wave breaking events imported extratropical cold and dry air into the tropics. The peripheral tropospheric dryness and enhanced vertical wind shear by PV streamer intrusion combined with the negative MJO phase were responsible for the absence of TC formation over the WNP in August 2014.

Integrated transcriptome and proteome analysis provides insight into chilling-induced dormancy breaking in Chimonanthus praecox

Chilling has a critical role in the growth and development of perennial plants.The chilling requirement(CR)for dormancy breaking largely depends on the species.However,global warming is expected to negatively affect chilling accumulation and dormancy release in a wide range of perennial plants.Here,we used Chimonanthus praecox as a model to investigate the CR for dormancy breaking under natural and artificial conditions.We determined the minimum CR(570 chill units,CU)needed for chilling-induced dormancy breaking and analyzed the transcriptomes and proteomes of flowering and non-flowering flower buds(FBs,anther and ovary differentiation completed)with different CRs.The concentrations of ABA and GA3 in the FBs were also determined using HPLC.The results indicate that chilling induced an upregulation of ABA levels and significant downregulation of SHORT VEGETATIVE PHASE(SVP)and FLOWERING LOCUS T(FT)homologs at the transcript level in FBs when the accumulated CR reached 570 CU(IB570)compared to FBs in November(FB.Nov,CK)and nF16(non-flowering FBs after treatment at 16℃for−300 CU),which suggested that dormancy breaking of FBs could be regulated by the ABA-mediated SVP-FT module.Overexpression in Arabidopsis was used to confirm the function of candidate genes,and early flowering was induced in 35S::CpFT1 transgenic lines.Our data provide insight into the minimum CR(570 CU)needed for chilling-induced dormancy breaking and its underlying regulatory mechanism in C.praecox,which provides a new tool for the artificial regulation of flowering time and a rich gene resource for controlling chilling-induced blooming.

Numerical Simulation of Breaking Wave Generated Sediment Suspension and Transport Process Based on CLSVOF Algorithm

The sediment suspension and transport process under complex breaking wave situation is investigated using large eddy simulation(abbreviated as LES hereafter) method. The coupled level set(LS) and volume of fluid(VOF) method is used to accurately capture the evolution of air-water interface. The wall effect at the bottom is modeled based on the wave friction term while the complicate bottom boundary condition for sediment is tackled using Chou and Fringer's sediment erosion and deposition flux method. A simulation is carried out to study the sediment suspension and transport process under periodic plunging breaking waves. The comparison between the results by CLSVOF method and those obtained by the LS method is given. It shows that the latter performs as well as the CLSVOF method in the pre-breaking weak-surface deformation situation. However, a serious mass conservation problem in the later stages of wave breaking makes it inappropriate for this study by use of the LS method and thus the CLSVOF method is suggested. The flow field and the distribution of suspended sediment concentration are then analyzed in detail. At the early stage of breaking, the sediment is mainly concentrated near the bottom area. During the wave breaking process, when the entrapped large-scale air bubble travels downward to approach the bottom, strong shear is induced and the sediment is highly entrained.

Comparisons of Computational and Experimental Results of Solitary Wave Breaking

- In this paper, the solitary wave deformation along a gentle slope and the impact pressure, on the wall are investigated experimentally and the results are compared with numerical results obtained based on the volume of fluid (VOF) method. The topography used in the experiment consists of three segments. The left segment is a 1:4 slope, the middle segment 1 :SO slope and the right segment a horizontal bed. Both the wave heights and breaking points obtained from numerical simulation and experiments are in good agreement. Numerical results give reasonable pressure distributions of breaking waves on the wall.

Vibrating-Rocking Motion of Caisson Breakwater Under Breaking Wave Impact

The possible motions of a caisson breakwater under dynamic load excitation include vibrating, vibrating-sliding andvibrating-rocking motions. The models of vibrating motion and vibrating-sliding motion have been proposed in an earlypaper. In this paper, a model of vibrating-rocking motion of caisson breakwaters under breaking wave impact is presented, which can be used to simulate the histories of vibrating-rocking motion of caisson breakwaters. The effect of rocking motion on the displacement, rotation, sliding force and overturning moment of breakwaters is investigated. In casethe overturning moment exceeds the stability moment ofa caisson, the caisson may only rock. The caisson overturns only in case the rocking angle exceeds the critical angle. It is shown that the sliding force and overturning moment of break-waters can be reduced effectively due to the rocking motion. It is proposed that some rocking motion should be allowedin breakwater design.

Large Eddy Simulation for Wave Breaking in the Surf Zone

In this paper, the large eddy simulation method is used combined with the marker and cell method to study the wave propagation or shoaling and breaking process. As wave propagates into shallow water, the shoaling leads to the increase of wave height, and then at a certain position, the wave will be breaking. The breaking wave is a powerful agent for generating turbulence, which plays an important role in most of the fluid dynamic processes throughout the sarf zone, such as transformation of wave energy, generation of near-shore current and diffusion of materials. So a proper numerical model for describing the turbulence effect is needed. In this paper, a revised Smagorinsky subgrid-scale model is used to describe the turbulence effect. The present study reveals that the coefficient of the Smagorinsky model for wave propagation or breaking simulation may be taken as a varying function of the water depth and distance away from the wave breaking point. The large eddy simulation model presented in this paper has been used to study the propagation of the solitary wave in constant water depth and the shoaling of the non-breaking solitary wave on a beach. The model is based on large eddy simulation, and to track free-surface movements, the Tokyo University Modified Marker and Cell (TUMMAC) method is employed. In order to ensure the accuracy of each component of this wave mathematical model,several steps have been taken to verify calculated solutions with either analytical solutions or experimental data. For non-breaking waves, very accurate results are obtained for a solitary wave propagating over a constant depth and on a beach. Application of the model to cnoidal wave breaking in the surf zone shows that the model results are in good agreement with analytical solution and experimental data. From the present model results, it can be seen that the turbulent eddy viscosity increases from the bottom to the water surface in surf zone. In the eddy viscosity curve, there is a turn-point obviously, dividing water depth into two parts; in the upper part, the eddy viscosity becomes very large near the wave br eaking position.

Numerical Simulation of Breaking Wave Based on Higher-Order Mild Slope Equation

The 'surface roller' to simulate wave energy dissipation of wave breaking is introduced into the random wave model based on approximate parabolic mild slope equation in this paper to simulate the random wave transportation including diffraction, refraction and breaking in nearshore areas. The roller breaking random wave higher-order approximate parabolic equation model has been verified by the existing experimental data for a plane slope beach and a circularshoal, and the numerical results of random wave breaking model agree with the experimental data very well. This modelcan be applied to calculate random wave propagation from deep to shallow water in large areas near the shore over natural topography.

Effect of the number of irradiation holes on rock breaking under constant laser energy

The use of mechanical drilling in accessing energy resources stored in deep and hard rock formations is becoming increasingly challenging.Thus,laser irradiation has emerged as a novel drilling method with considerable in this context.This study examines the variation of rock fracture length,fracture tortuosity,hole size,and rock breaking efficiency for a different number of holes and laser power,based on the constant total energy of laser irradiation.As indicated by the results,increasing the laser power increases the laser intensity,which helps increase the hole diameter and depth.Moreover,for the same laser power,increasing the number of irradiated holes reduces the laser energy absorbed by each hole,which is not conducive to increasing the hole depth.As the number of holes increases,the mass loss of the rock also increases,while both specific energy(SE)and modified specific energy(MSE)decrease.When the number of holes remains the same,the mass of the shale removed by low power is less than that removed by high power,while SE and MSE have an inverse relation with power.Therefore,high laser power and multiple-hole irradiation are more conducive to rock breaking.Besides,the fracture length and fracture tortuosity of the rock irradiated by the low laser power will increase first and then decrease with the increase in the number of holes,and reach the peak value when the irradiation takes place through three holes.When a high-power laser irradiates the rock,the fracture length and tortuosity will increase with the increase in the number of irradiation holes.This is because a rock irradiated by low power dissipates more energy,with the result that the energy absorbed by the sample with four irradiation holes is not enough to break the rock quickly.This study is expected to provide some guidance to break rock for drilling deep reservoirs and hard rock formations using laser irradiation.

Vibrating-Sliding Motion of Caisson Breakwaters Under Various Breaking Wave Impact Forces

Sliding is one of the principal failure types of caisson breakwaters and is an essential content of stability examination in caisson breakwater design. Herein, the mass-spring-dashpot model of caisson-base system is used to simulate the vibrating-sliding motion of the caisson under various types of breaking wave impact forces, i.e., single peak impact force, double peak impact force, and shock-damping oscillation impact force. The effects of various breaking wave impacts and the sliding motion on the dynamic response behaviors of caisson breakwaters are investigated and the calculation of relevant system parameters is discussed. It is shown that the dynamic responses of the caisson are significantly different under different types of breaking wave impact forces even when the amplitudes of impact forces are equal. The amplitude of dynamic response of the caisson is lower under single peak impact excitation than that under double peak impact or shock-damping oscillation impact excitation. Though the displacement of the caisson is large due to sliding, the rotation, the sliding force and the overturning moment of the caisson are significantly reduced.