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.

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.

Numerical investigation of the influence of companion drops on drop-on-demand ink jetting

In this study we characterized and investigated the specific phenomenon of "companion drops" in the drop-ondemand(DOD) ink jetting process.A series of simulations based on a piezoelectric DOD printhead system is presented,adapting the volume-of-fluid(VOF) interface-capturing method to track the boundary evolution and model the interfacial physics.The results illustrate the causality between the generation of companion drops and droplet deviation behavior,as well as their close correlations with ink jetting straightness and printing accuracy.The characteristics of companion drops are summarized and compared with those of satellite drops.Also,a theoretical mechanism for the generation of companion drops is presented,and their effects and behaviors are analyzed and discussed.Finally,the effects of critical factors on the generation of companion drops are investigated and characterized based on variations in the printable pressure range.Recommendations are given for the suppression of companion drops and for the improvement of printing accuracy.

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.

Process development for green part printing using binder jetting additive manufacturing

Originally developed decades ago, the binder jetting additive manufacturing （B J-AM） process possesses various advantages compared to other additive manufacturing （AM） technologies such as broad material compat- ibility and technological expandability. However, the adoption of B J-AM has been limited by the lack of knowledge with the fundamental understanding of the process principles and characteristics, as well as the relatively few systematic design guideline that are available. In this work, the process design considerations for B J-AM in green part fabrication were discussed in detail in order to provide a comprehensive perspective of the design for additive manufacturing for the process. Various process factors, including binder saturation, in- process drying, powder spreading, powder feedstock characteristics, binder characteristics and post-process curing, could significantly affect the printing quality of the green parts such as geometrical accuracy and part integrity. For powder feedstock with low flowability, even though process parameters could be optimized to partially offset the printing feasibility issue, the qualities of the green parts will be intrinsically limited due to the existence of large internal voids that are inaccessible to the binder. In addition, during the process development, the balanced combination between the saturation level and in-process drying is of critical importance in the quality control of the green parts.

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.

Comparative analysis of CFD models for jetting fluidized beds:Effect of particle-phase viscosity

Under the Eulerian-Eulerian framework of simulating gas-solid two-phase flow, the accuracy of the hydrodynamic prediction is strongly affected by the selection of rheology of the particulate phase, for which a detailed assessment is still absent. Using a jetting fluidized bed as an example, this work investi- gates the influence of solid rheology on the hydrodynamic behavior by employing different particle-phase viscosity models. Both constant particle-phase viscosity model （CVM） with different viscosity values and a simple two-fluid model without particle-phase viscosity （NVM） are incorporated into the classical two- fluid model and compared with the experimental measurements. Qualitative and quantitative results show that the jet penetration depth, jet frequency and averaged bed pressure drop are not a strong func- tion of the particle-phase viscosity. Compared to CVM, the NVM exhibits better predictions on the jet behaviors, which is more suitable for investigating the hydrodynamics of gas-solid fluidized bed with a central jet.

Transient dynamic analysis for the ventilated supercavity under the action of tail jetting flow

Ventilated cavitation could be applied to underwater vehicles to achieve a high drag-reduction ratio.The ventilated supercavity may experience deformation,fluctuation,and instability under the influence of the high-speed jetting flow generated by the propulsion system.This study focuses on understanding the transient dynamics of a ventilated supercavity with jetting flow at the tail.Experiments are performed in an open water tunnel system with a high degassing rate.The evolution of the gas-liquid interface under different jetting flow rates is recorded in detail.A compressible multiphase model coupled with shear stress turbulence(SST)and surface capturing models is adopted herein to study the flow pattern in depth.As the jet velocity increases from subsonic to sonic speed,the flow field presents three different modes that could be identified as the transparent cavity(TC),transparent cavityjetting(TC-J),and deformed cavity-jetting(DC-J)modes.A new gas shedding scheme that couples twinvortex shedding with surface fluctuation shedding is observed in the TC mode.The variations in the internal flow structure and the local pressure vibration are discussed in detail.The transition of the flow pattern with dimensionless jetting momentum ratio and kinetic energy ratio is obtained.The obtained results could provide valuable insights into the control of the ventilated supercavity.

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。