With the collapse of cavitation bubbles near the wall,micro-jets and shock waves will be formed,to generate a high-pressure load and to cause the cavitation damage on the surface of the hydraulic machinery.Due to the ...With the collapse of cavitation bubbles near the wall,micro-jets and shock waves will be formed,to generate a high-pressure load and to cause the cavitation damage on the surface of the hydraulic machinery.Due to the rapid development of the cavitation bubble collapse process(in the time scale of hundred nanoseconds),the time resolution of the conventional high-speed cameras should reach more than one million frames per second,which will limit the spatial resolution,and obscure the details of the cavitation bubble shape near the cavitation bubble collapse moment.In this paper,with the help of the laser cavitation bubble photogrammetry system with nanosecond-micron space-time resolution,the experiment is carried out for the cavitation bubble collapse morphology evolution near the wall.The morphological characteristics of the cavitation bubble collapse at specific times are analyzed.With the help of the OpenFOAM code,the collapse process of the cavitation bubble near the solid wall is calculated.It is shown that the cavitation bubble near the wall collapses in an axial symmetric heart shape and the micro-jet directed to the wall will pull the cavitation bubble towards the wall.The counter-jet generated in the rebound stage will drive the cavitation bubble to move away from the wall.The numerical simulation of the cavitation bubble shape in the collapse period is well consistent with the experimental results,but the ability to capture the shock wavefront needs to be improved.Under the conditions studied in this paper,the cavitation bubble collapse micro-jet velocity can reach up to a hundred meters per second both in the experiment and the numerical simulation.展开更多
The so-called fourth-generation biodegradable vascular stent has become a research hotspot in thefield of bioengineering because of its good degradation ability and drug-loading characteristics.However,the preparation...The so-called fourth-generation biodegradable vascular stent has become a research hotspot in thefield of bioengineering because of its good degradation ability and drug-loading characteristics.However,the preparationof polymer-degraded vascular stents is affected by known problem such as poor processflexibility,low formingaccuracy,large diameter wall thickness,limited complex pore structure,weak mechanical properties of radial support and high process cost.In this study,a deposition technique based on a high-voltage electric-field-driven continuous rotating jet is proposed to fabricate fully degraded polymer vascular stents.The experimental results showthat,due to the rotation of the deposition axis,the deposition direction of PCL(polycaprolactone)micro-jet isalways tangent to the surface of the deposition axis.The direction of the viscous drag force is also consistent withthe deposition direction of the jet.It is shown that by setting different rotation speeds of deposition axisωandlinear motion speeds of the nozzle V,the direction of rotation,pitch and angle of the individual printed spiralcurve can be precisely tuned.In the process of multiple spiral curves matching the deposition forming thin walltube mesh,the mesh shape and size of the thin wall tube can be accurately controlled by changing the number ofmatching spiral curves and the size of the matching position bias distance.Finally,the characteristics of a PCLtubular stent sample(with uniform-size microfibers and mesh shape),fabricated under the appropriate processparameters are described in detail.展开更多
A medical device of micro-jet injection for drug delivery is described in this paper. The device is powered by a Lorentz force driver (or voice coil motor, VCM) and is able to perform pulsed injection through controll...A medical device of micro-jet injection for drug delivery is described in this paper. The device is powered by a Lorentz force driver (or voice coil motor, VCM) and is able to perform pulsed injection through controlling the direction of the current passing through the device. The driving force and the resulting injection pressure are also controllable through control of the current intensity of the VCM. A physical model was established by combining the existing jet injection model with the relationship of the driving force obtained from a finite-element-method (FEM) analysis, and was verified by experimental measurements. The numerical calculation of the physical model reveals the relationship between the injection pressure and the current intensity of VCM under system conditions. In normal cases, the injection dose can be varied. Thus the relationship between the current intensity of VCM and the dose value was numerically obtained under the condition for the maximum injection pressure to be above a threshold value. These results can be used for optimization of the device.展开更多
Cavitation as a hydrodynamic phenomenon exists widely in water conservancy, shipbuilding, chemical and many other industries.Previous cavitation bubble dynamic studies mainly focused on single cavitation bubbles and t...Cavitation as a hydrodynamic phenomenon exists widely in water conservancy, shipbuilding, chemical and many other industries.Previous cavitation bubble dynamic studies mainly focused on single cavitation bubbles and their interaction with the wall. This paper studies the interaction between two cavitation bubbles under conditions with or without a wall. The results show that if the inception of two cavitation bubbles is not synchronized, the cavitation bubble of early inception collapse backwards the cavitation bubble of later inception; if the inception of two cavitation bubbles is synchronized, the two bubbles collapse towards each other; if a wall exists nearby, no matter whether the line connecting the centers of the two cavitation bubbles is vertical or parallel to the wall, the two cavitation bubbles collapse towards each other and then gradually merge, and the merged collapse body quickly moves to the wall. It is suggested that, as the number of cavitation bubbles increases, the cavitation erosion effect is not simply increased proportionally. Instead, mutual inhibitory effect may be demonstrated.展开更多
In the paper, the enhanced measurements of the laser micro-jet processing are discussed. In fact, within pure water breakdown threshold of laser, the less focal which focused with the appropriate focusing lens and the...In the paper, the enhanced measurements of the laser micro-jet processing are discussed. In fact, within pure water breakdown threshold of laser, the less focal which focused with the appropriate focusing lens and the small nozzle of water chamber enhance the laser power density ,at the same time, the laser beam transport in the wave guided water with the proper total reflection angle. The laser power which depended on the properties of the diameter, the coupling water chamber and the coupling efficiency of the micro-jet and laser beam expect of the properties of laser.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.5217090233).
文摘With the collapse of cavitation bubbles near the wall,micro-jets and shock waves will be formed,to generate a high-pressure load and to cause the cavitation damage on the surface of the hydraulic machinery.Due to the rapid development of the cavitation bubble collapse process(in the time scale of hundred nanoseconds),the time resolution of the conventional high-speed cameras should reach more than one million frames per second,which will limit the spatial resolution,and obscure the details of the cavitation bubble shape near the cavitation bubble collapse moment.In this paper,with the help of the laser cavitation bubble photogrammetry system with nanosecond-micron space-time resolution,the experiment is carried out for the cavitation bubble collapse morphology evolution near the wall.The morphological characteristics of the cavitation bubble collapse at specific times are analyzed.With the help of the OpenFOAM code,the collapse process of the cavitation bubble near the solid wall is calculated.It is shown that the cavitation bubble near the wall collapses in an axial symmetric heart shape and the micro-jet directed to the wall will pull the cavitation bubble towards the wall.The counter-jet generated in the rebound stage will drive the cavitation bubble to move away from the wall.The numerical simulation of the cavitation bubble shape in the collapse period is well consistent with the experimental results,but the ability to capture the shock wavefront needs to be improved.Under the conditions studied in this paper,the cavitation bubble collapse micro-jet velocity can reach up to a hundred meters per second both in the experiment and the numerical simulation.
基金supported by the National Natural Science Foundation of China(Grant Nos.51305128 and 52005059)The Key Scientific and Technological Project of Henan Province(Grant Nos.242102231054 and 242102220073)The Provincial Graduate Quality Engineering Project(Grant No.YJS2024JD38)。
文摘The so-called fourth-generation biodegradable vascular stent has become a research hotspot in thefield of bioengineering because of its good degradation ability and drug-loading characteristics.However,the preparationof polymer-degraded vascular stents is affected by known problem such as poor processflexibility,low formingaccuracy,large diameter wall thickness,limited complex pore structure,weak mechanical properties of radial support and high process cost.In this study,a deposition technique based on a high-voltage electric-field-driven continuous rotating jet is proposed to fabricate fully degraded polymer vascular stents.The experimental results showthat,due to the rotation of the deposition axis,the deposition direction of PCL(polycaprolactone)micro-jet isalways tangent to the surface of the deposition axis.The direction of the viscous drag force is also consistent withthe deposition direction of the jet.It is shown that by setting different rotation speeds of deposition axisωandlinear motion speeds of the nozzle V,the direction of rotation,pitch and angle of the individual printed spiralcurve can be precisely tuned.In the process of multiple spiral curves matching the deposition forming thin walltube mesh,the mesh shape and size of the thin wall tube can be accurately controlled by changing the number ofmatching spiral curves and the size of the matching position bias distance.Finally,the characteristics of a PCLtubular stent sample(with uniform-size microfibers and mesh shape),fabricated under the appropriate processparameters are described in detail.
文摘A medical device of micro-jet injection for drug delivery is described in this paper. The device is powered by a Lorentz force driver (or voice coil motor, VCM) and is able to perform pulsed injection through controlling the direction of the current passing through the device. The driving force and the resulting injection pressure are also controllable through control of the current intensity of the VCM. A physical model was established by combining the existing jet injection model with the relationship of the driving force obtained from a finite-element-method (FEM) analysis, and was verified by experimental measurements. The numerical calculation of the physical model reveals the relationship between the injection pressure and the current intensity of VCM under system conditions. In normal cases, the injection dose can be varied. Thus the relationship between the current intensity of VCM and the dose value was numerically obtained under the condition for the maximum injection pressure to be above a threshold value. These results can be used for optimization of the device.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51179114 & 51409180)the National Basic Research Program of China (Grant No. 2013CB035905)the China Postdoctoral Science Foundation (Grant No. 2014M562324)
文摘Cavitation as a hydrodynamic phenomenon exists widely in water conservancy, shipbuilding, chemical and many other industries.Previous cavitation bubble dynamic studies mainly focused on single cavitation bubbles and their interaction with the wall. This paper studies the interaction between two cavitation bubbles under conditions with or without a wall. The results show that if the inception of two cavitation bubbles is not synchronized, the cavitation bubble of early inception collapse backwards the cavitation bubble of later inception; if the inception of two cavitation bubbles is synchronized, the two bubbles collapse towards each other; if a wall exists nearby, no matter whether the line connecting the centers of the two cavitation bubbles is vertical or parallel to the wall, the two cavitation bubbles collapse towards each other and then gradually merge, and the merged collapse body quickly moves to the wall. It is suggested that, as the number of cavitation bubbles increases, the cavitation erosion effect is not simply increased proportionally. Instead, mutual inhibitory effect may be demonstrated.
文摘In the paper, the enhanced measurements of the laser micro-jet processing are discussed. In fact, within pure water breakdown threshold of laser, the less focal which focused with the appropriate focusing lens and the small nozzle of water chamber enhance the laser power density ,at the same time, the laser beam transport in the wave guided water with the proper total reflection angle. The laser power which depended on the properties of the diameter, the coupling water chamber and the coupling efficiency of the micro-jet and laser beam expect of the properties of laser.
