Mechanical and corrosion properties of full liquid phase sintered WE43 magnesium alloy specimens fabricated via binder jetting additive manufacturing

This study investigates full liquid phase sintering as a process of fabrication parts from WE43(Mg-4wt.%Y-3wt.%RE-0.7wt.%Zr)alloy using binder jetting additive manufacturing(BJAM).This fabrication process is being developed for use in producing structural or biomedical devices.Specifically,this study focused on achieving a near-dense microstructure with WE43 Mg alloy while substantially reducing the duration of sintering post-processing after BJAM part rendering.The optimal process resulted in microstructure with 2.5%porosity and significantly reduced sintering time.The improved sintering can be explained by the presence of Y_(2)O_(3)and Nd_(2)O_(3)oxide layers,which form spontaneously on the surface of WE43 powder used in BJAM.These layers appear to be crucial in preventing shape distortion of the resulting samples and in enabling the development of sintering necks,particularly under sintering conditions exceeding the liquidus temperature of WE43 alloy.Sintered WE43 specimens rendered by BJAM achieved significant improvement in both corrosion resistance and mechanical properties through reduced porosity levels related to the sintering time.

Fracture propagation law of temporary plugging and diversion fracturing in shale reservoirs under completion experiments of horizontal well with multi-cluster sand jetting perforation

This study conducted temporary plugging and diversion fracturing(TPDF)experiments using a true triaxial fracturing simulation system within a laboratory setting that replicated a lab-based horizontal well completion with multi-cluster sand jetting perforation.The effects of temporary plugging agent(TPA)particle size,TPA concentration,single-cluster perforation number and cluster number on plugging pressure,multi-fracture diversion pattern and distribution of TPAs were investigated.A combination of TPAs with small particle sizes within the fracture and large particle sizes within the segment is conducive to increasing the plugging pressure and promoting the diversion of multi-fractures.The addition of fibers can quickly achieve ultra-high pressure,but it may lead to longitudinal fractures extending along the wellbore.The temporary plugging peak pressure increases with an increase in the concentration of the TPA,reaching a peak at a certain concentration,and further increases do not significantly improve the temporary plugging peak pressure.The breaking pressure and temporary plugging peak pressure show a decreasing trend with an increase in single-cluster perforation number.A lower number of single-cluster perforations is beneficial for increasing the breaking pressure and temporary plugging peak pressure,and it has a more significant control on the propagation of multi-cluster fractures.A lower number of clusters is not conducive to increasing the total number and complexity of artificial fractures,while a higher number of clusters makes it difficult to achieve effective plugging.The TPAs within the fracture is mainly concentrated in the complex fracture areas,especially at the intersections of fractures.Meanwhile,the TPAs within the segment are primarily distributed near the perforation cluster apertures which initiated complex fractures.

Improving Suction Performance of Centrifugal Pumps by Using Jetting Device

Improving the suction performance of centrifugal pumps by using jetting device is presented. The theoretical analysis, experimental study and engineering implementation show that suction performance of centrifugal pump can be improved with jetting device and be used for delivering the liquid media requiring high suction performance, whereas the efficiency and head of the pump will decrease a little. The effect of feed-back jetting on suction performance is the most obvious at design point. The suitable rate of feed-back flow is 2%-5%.

Operation optimization of plugged screen cleanup by rotary water jetting

The rotary water jetting is one of the most important techniques for horizontal well cleanup.The jet flow is used to remove plugging particles from sand control screens to recover their permeability.Currently,the operation optimization of this technique depends mainly on experience due to absence of applicable evaluation and design models for removing plugging materials.This paper presents an experimental setup to simulate the cleanup process of plugged screens by rotary water jetting on the surface and to evaluate the performance of a jetting tool.Using real plugged screens pulled from damaged wells,a series of tests were performed,and the qualitative relationships between the cleanup efficiency and various operational parameters,such as the type of fluids used,flow rate,mode of tool movement,etc.,were obtained.The test results indicated that the cleanup performance was much better when the rotary jetting tool moved and stopped periodically for a certain time than that when it reciprocated at a constant speed.To be exact,it was desirable for the rotary jetting tool to move for 1.5-2 m and stop for 2-4 min,which was called the ＂move-stop-move＂ mode.Good cleanup performance could be obtained at high flow rates,and the flow rate was recommended to be no lower than 550-600 L/min.The test results also indicated that complex mud acid was better than clean water in terms of cleanup performance.Good cleanup efficiency and high screen permeability recovery could be achieved for severely plugged screens.Rotary jetting is preferred for the cleanup of horizontal wells with severely plugged screens,and the screen permeability recovery ratio may reach 20％ if optimized operation parameters were used.

CFD Model of Dense Gas-solid Systems in Jetting Fluidized Beds

A CFD code has been developed based on the conservation principles describing gas and solid flow in fluidized beds. This code is employed to simulate not only the spatiotemporal gas and solid phase velocities and voidage profiles in a two dimensional bed but also fluid dynamics in the jet region. The computational results show that gas flow direction is upward in the entire bed accompanied with random local circulations, whilst solid flow direction is upward at the center and downward near the wall. The radical reason of strong back mixing of solid particles and good transfer behavior between two phases is that the jet entrains solid particles. Numerical calculation indicates that gas velocity, solid velocity and pressure profile have a significant change when the voidage is 0 8. The simulated time averaged voidage profiles agree with the experimental results and simulated data reported by Gidaspow and Ettehadieh(1983). Therefore, CFD model can be regarded as a useful tool to study the jet characteristics in dense gas solid fluidized beds.

Chaotic Study in a Large Jetting Fluidized Bed with a Vertical Nozzle

The pressure fluctuation in a large jetting fluidized bed with a vertical nozzle was examined based on deterministic chaos theory. The effects of the jetting gas velocity and the static bed height on the correlation dimension were investigated. The correlation dimension increased with increasing jet gas velocity. At the same jet gas velocity, the higher the static bed height, the greater the correlation dimension is. The variations of correlation dimension and standard deviation of pressure fluctuation with gas jet velocity exhibited a similar shape and trend.

Binder jetting 3D printing process optimization for rapid casting of green parts with high tensile strength

Binder jetting 3D printing is a rapid,cost effective,and efficient moulding/core making process,which can be applied to a large variety of materials.However,it exhibits a relatively low green-part strength.This may cause the collapse of the printed parts during de-caking and the pick-up procedure,especially in the case of small-scale structures,such as thin walls,tips,and channels.In this work,polyvinyl alcohol(PVA)was used as the additive in coated sand powder.By exploiting the binding effect between the two composites(thermoplastic phenolic resin and PVA)triggered by the binder,bonding necks firmly form among the sand particles,improving the green-part strength of the coated sand printed parts.Experiments based on the Taguchi method were used to investigate the relationship between the process parameters and the green-part tensile strength.The following set of optimal process parameters was identified:50wt.%alcoholicity of the binder,75%binder saturation,0.36 mm layer thickness and 4.5wt.%PVA content.Further,the effect of such parameters on the green-part tensile strength was determined via statistical analysis.The green part of an engine cylinder head sand pattern with complex cavity structures was printed,and the green-part tensile strength reached 2.31 MPa.Moreover,the ZL301 aluminum alloy impeller shape casting was prepared using sand molds printed with the optimal process parameters.The results confirm that the proposed binder jetting 3D printing process can guarantee the integrity of the printed green parts and of small-size structures during de-caking and the pick-up procedure.Furthermore,the casting made from the printed sand molds exhibits a relatively high quality.

Bubbling to Jetting Transition during Argon Injection in Molten Steel

Bubbling to Jetting Transition is of the outmost importance in metallurgical processes given that the flow regime influences the refining rates, the refractory erosion, and the blockage of injection nozzles. Bubbling to jetting transition during subsonic bottom injection of argon in molten steel is studied here. The effect of the molten steel height, the injection velocity, the nozzle diameter, and the molten steel viscosity on the jet height and the bubbling to jetting transition is numerically analyzed using Computational Fluid Dynamics. Five subsonic argon injection velocities are considered: 5, 25, 50, 100 and 150 m/s. Three values of the metal height are taken into account, namely 1.5 m, 2 m and 2.5 m. Besides, three values of the nozzle diameters are considered: 0.001 m, 0.005 m and 0.01 m. Finally, three values of the molten steel viscosity are supposed: 0.0067, 0.1 and 1 kg/(m·s). It is observed that for the argon-molten steel system, the bubbling to jetting transition occurs for an injection velocity less than 25 m/s and that for the range of viscosities considered, the molten steel viscosity does not exert significant influence on the jet height and the bubbling to jetting transition. Due to the jet instability at subsonic velocities, a second transition, namely jetting to bubbling, is appreciated.

Dynamic response of jetting and cementing bucket platform to wave and current loading

The jetting and cementing bucket platform （JCBP） is a new type offshore oil-drilling platform. This paper aims to establish an analysis method for calculating the dynamic response of this platform. Based on the theory of elastic half space, the dynamic stiffness and damping of the platform＇ s foundation were obtained and attached to the end of the platform＇ s main jackets as a boundary condition. Then using finite element method （FEM）, the dynamic response of the platform due to wave and current loading was calculated. Furthermore, the whole platform＇ s finite element model was established and the dynamic response of the platform was calculated. The numerical results demonstrate that the present method by the usage of elastic half space theory and FEM is simple and it is reliable and efficient to calculate dynamic behavior of the platform in response to wave and current loading.

Simulation and Experimental Investigation of Jetting Penetrator Charge at Large Stand-off Distance

In order to study and apply the penetration performance of jetting penetrator charge at long stand-off distance, three jetting penetrator charges(JPC), including spherical cone liner, truncated wide-angle liner and spherical segment liner, are designed. The numerical simulation analysis of the formation, elongation and penetration processes of rod-like jet is conducted by using LS-DYNA software. And the penetrating test is carried out at long stand-off distance. The test results show that the rod-like jet formed by the optimized spherical segment liner can pierce through a 90mm thick 45# steel target at 20 charge diameters(CD) stand-off distance when the charge detonation mode is a central point initiation, and the penetration depth can be up to 1.6CD. It is concluded that, at 20 CD stand-off distance, the penetration performance of JPC with spherical segment liner is the best, that of truncated wide-angle liner takes second place, and that of spherical cone liner is the worst.

Mechanism and numerical simulation of pressure stagnation during water jetting perforation

When perforating with an abrasive water jet, it is possible that the pressure in the hole （perforation） will be higher than that in the annulus because of water jet blasting against the hole wall, which also is the theoretical basis for the technology of hydro-jet fracturing. This paper analyzes the mechanism of generating pressure stagnation in water jet hole, and puts forward a new concept of hydroseal. Then, the distribution of pressure in the hole was simulated with the finite element method. The simulation results showed that the pressure in the hole was higher than that in the annulus. Also, the lower the annular pressure （confining pressure） and the higher the blasting pressure, the greater the pressure difference. An experiment indicated that the cement sample was lifted up under the pressure stagnation in the hole, which proved the finite element simulation results obviously.

Jetting of a near-wall cavitation bubble induced by another tandem bubble

Double bubbles near a rigid wall surface collapse to produce a significant jet impact,with potential applications in surface cleaning and ultrasonic lithotripsy.However,the dynamic behaviors of near-wall bubbles remain unexplored.In this study,we investigate the jetting of a near-wall bubble induced by another tandem bubble.We define two dimensionless standoff distances,γ_(1),γ_(2),to represent the distances from the center of the near-wall bubble to the rigid wall and the center of controlling bubble to the center of the near-wall bubble,respectively.Our observations reveal three distinct jetting regimes for the near-wall bubble:transferred jetting,double jetting,and directed jetting.To further investigate the jetting mechanism,numerical simulations are conducted using the compressibleInterFoam solver in the open-source framework of OpenFOAM.A detailed analysis shows that the transferred jet flow is caused by the pinch-off resulting from the axial contraction velocity at the lower end of the near-wall bubble being greater than the vertical contraction velocity,leading to a maximum jet velocity of 682.58 m/s.In the case of double jetting,intense stretching between the controlling bubble and the wall leads to a pinch-off and a double jetting with a maximum velocity of 1096.29 m/s.The directed jet flow is caused by the downward movement of the high-pressure region generated by the premature collapse of the controlling bubble,with the maximum jet velocity reaching 444.62 m/s.

Recent progress on the jetting of single deformed cavitation bubbles near boundaries

Cavitation occurs widely in nature and engineering and is a complex problem with multiscale features in both time and space due to its associating violent oscillations. To understand the important but complicated phenomena and fluid mechanics behind cavitation, a great deal of effort has been invested in investigating the collapse of a single bubble near different boundaries. This review aims to cover recent developments in the collapse of single bubbles in the vicinity of complex boundaries, including single boundaries and two parallel boundaries, and open questions for future research are discussed. Microjets are the most prominent features of the non-spherical collapse of cavitation bubbles near boundaries and are directed toward rigid walls and away from free surfaces. Such a bubble generally splits, resulting in the formation of two axial jets directed opposite to each other under the constraints of an elastic boundary or two parallel boundaries. The liquid jet penetrates the bubble, impacts the boundary, and exerts a great deal of stress on any nearby boundary. This phenomenon can cause damage, such as the erosion of blades in hydraulic machinery, the rupture of human blood vessels, and underwater explosions, but can also be exploited for applications, such as needle-free injection, drug and gene delivery, surface cleaning, and printing. Many fascinating developments related to these topics are presented and summarized in this review. Finally, three directions are proposed that seem particularly fruitful for future research on the interaction of cavitation bubbles and boundaries.

Eulerian simulations of bubbling and jetting regimes in a fluidized bed

The mode of gas-injection is known to influence the local bubbling and jetting behavior in gas-solid fluidized beds.The resultant bubbling behavior influences the mixing and distribution of the gas and solid phases,which in turn can influence heat and mass transfer,and reaction performance in large-scale gas-solid fluidized beds.In the present work,we simulated unary gas-solid flow of particles differing in density,fluidized using uniform and two-jet distributors at different UG.The predictions are validated using the measured local gas-phase area fraction fluctuations,bubble size distribution,and bubble rise velocity.The effect of the models used for calculation of gas-solid drag(βgs),solids frictional pressure(Psf),and specularity coefficient(φ)on the bubbling characteristics under dense and dilute flow con-ditions are analysed.Under dense bed condition(UG=1.1 Umf),an increase in the Psf and φ led to an increase in solids viscosity,which in turn led to a decrease in the bubble rise velocity and size.In the case of the two-jet distributor,an increase in βgs predicted merging of the larger jets and formation of larger bubbles.Further,to predict the different jetting regimes(isolated jets,breakage/merging of jets,and generation of larger bubbles)at different UG correctly,we show that different βgs models are required.Whereas,in the case of gas-solid flows comprised of particles of different density fluidized with the uniform distributor,a single βgs model predicted the bubbling characteristics reasonably well with measurements.

Jetting Method in Patternless Casting Manufacturing Technique

In this paper, by studying the different kinds of jetting system in patternless casting manufacturing (PCM) technique, the different types of jetting mode are tested which affect whether PCM process can be done successful. The two different kinds of jetting device and their control circuits are designed based on which the relationship between the jetting system and amount of the catalyst flow is analyzed. The experiments show that the amount of the catalyst by using discrete jetting mode in the discrete jetting device is much lower than that by using continuous jetting mode in the discrete jetting device and in the continuous device when the pressured is fixed. At the same time, in the discrete jetting mode the amount of the catalyst flow can also be changed by adjusting the pulse frequency and its duty cycle, this can ensure the strength of the sand mould. The flow of catalyst in this discrete jetting device can match the scanning speed of the jetting device in real time which will improve the resolution and building precision of casting mould. When the amount of the catalyst jetting is too large, PCM process will fail.

基于前视声呐图像的AUV目标识别与跟踪

声呐图像由于水体不均匀、边界不规则以及声呐设备本身性能的限制,导致图像噪声明显、亮度不均、分辨率低,使得水下AUV装备在使用前视声呐进行水下目标检测时难度较大。针对该问题,基于m750d声呐探测获得的AUV声呐数据,进行了数据提取、高斯滤波处理、扇形映射处理,并采用Jet映射对声呐灰度图像进行了伪彩色映射提高数据标注速度和精度,制作获得了4组2 500张声呐图像的AUV目标检测数据集;采用YOLOv4-tiny目标检测算法开展AUV目标检测研究,研究结果表明该方法在该数据集上表现优秀,mAP@0.50达到94.17%,FPS在22帧左右,说明该轻量级网络在水下AUV目标识别与跟踪应用上具有较好的应用价值。

Assessment of Wet Season Precipitation in the Central United States by the Regional Climate Simulation of the WRFG Member in NARCCAP and Its Relationship with Large-Scale Circulation Biases

Assessment of past-climate simulations of regional climate models(RCMs)is important for understanding the reliability of RCMs when used to project future regional climate.Here,we assess the performance and discuss possible causes of biases in a WRF-based RCM with a grid spacing of 50 km,named WRFG,from the North American Regional Climate Change Assessment Program(NARCCAP)in simulating wet season precipitation over the Central United States for a period when observational data are available.The RCM reproduces key features of the precipitation distribution characteristics during late spring to early summer,although it tends to underestimate the magnitude of precipitation.This dry bias is partially due to the model’s lack of skill in simulating nocturnal precipitation related to the lack of eastward propagating convective systems in the simulation.Inaccuracy in reproducing large-scale circulation and environmental conditions is another contributing factor.The too weak simulated pressure gradient between the Rocky Mountains and the Gulf of Mexico results in weaker southerly winds in between,leading to a reduction of warm moist air transport from the Gulf to the Central Great Plains.The simulated low-level horizontal convergence fields are less favorable for upward motion than in the NARR and hence,for the development of moist convection as well.Therefore,a careful examination of an RCM’s deficiencies and the identification of the source of errors are important when using the RCM to project precipitation changes in future climate scenarios.

Assessment of compressive strength of jet grouting by machine learning

Jet grouting is one of the most popular soil improvement techniques,but its design usually involves great uncertainties that can lead to economic cost overruns in construction projects.The high dispersion in the properties of the improved material leads to designers assuming a conservative,arbitrary and unjustified strength,which is even sometimes subjected to the results of the test fields.The present paper presents an approach for prediction of the uniaxial compressive strength(UCS)of jet grouting columns based on the analysis of several machine learning algorithms on a database of 854 results mainly collected from different research papers.The selected machine learning model(extremely randomized trees)relates the soil type and various parameters of the technique to the value of the compressive strength.Despite the complex mechanism that surrounds the jet grouting process,evidenced by the high dispersion and low correlation of the variables studied,the trained model allows to optimally predict the values of compressive strength with a significant improvement with respect to the existing works.Consequently,this work proposes for the first time a reliable and easily applicable approach for estimation of the compressive strength of jet grouting columns.

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.

Interdecadal variability of summer precipitation in the Three River Source Region: Influences of SST and zonal shifts of the East Asian subtropical westerly jet

Summer precipitation in the Three Rivers Source Region(TRSR)of China is vital for the headwaters of the Yellow,Yangtze,and Lancang rivers and exhibits significant interdecadal variability.This study investigates the influence of the East Asian westerly jet(EAWJ)on TRSR rainfall.A strong correlation is found between TRSR summer precipitation and the Jet Zonal Position Index(JZPI)of the EAWJ from 1961 to 2019(R=0.619,p<0.01).During periods when a positive JZPI indicates a westward shift in the EAWJ,enhanced water vapor anomalies,warmer air,and low-level convergence anomalies contribute to increased TRSR summer precipitation.Using empirical orthogonal function and regression analyses,this research identifies the influence of large-scale circulation anomalies associated with the Atlantic–Eurasian teleconnection(AEA)from the North Atlantic(NA).The interdecadal variability between the NA and central tropical Pacific(CTP)significantly affects TRSR precipitation.This influence is mediated through the AEA via a Rossby wave train extending eastward along the EAWJ,and another south of 45°N.Moreover,the NA–CTP Opposite Phase Index(OPI),which quantifies the difference between the summer mean sea surface temperatures of the NA and the CTP,is identified as a critical factor in modulating the strength of this teleconnection and influencing the zonal position of the EAWJ.