An improved large eddy simulation of two-phase flows in a pump impeller

An improved large eddy simulation using a dynamic second-order sub-grid-scale （SGS） stress model has been developed to model the governing equations of dense turbulent particle-liquid two-phase flows in a rotating coordinate system, and continuity is conserved by a mass-weighted method to solve the filtered governing equations. In the cur- rent second-order SGS model, the SGS stress is a function of both the resolved strain-rate and rotation-rate tensors, and the model parameters are obtained from the dimensional consistency and the invariants of the strain-rate and the rotation-rate tensors. In the numerical calculation, the finite volume method is used to discretize the governing equations with a staggered grid system. The SIMPLEC algorithm is applied for the solution of the discretized governing equations. Body- fitted coordinates are used to simulate the two-phase flows in complex geometries. Finally the second-order dynamic SGS model is successfully applied to simulate the dense turbu-lent particle-liquid two-phase flows in a centrifugal impeller. The predicted pressure and velocity distributions are in good agreement with experimental results.

Mobile bed thickness in skewed asymmetric oscillatory sheet flows

A new instantaneous mobile bed thickness model is presented for sediment transport in skewed asymmetric oscillatory sheet flows. The proposed model includes a basic bed load part and a suspended load part related to the Shields parameter, and takes into account the effects of mass conservation, phase-lag, and asymmetric boundary layer development, which are important in skewed asymmetric flows but usually absent in classical models. The proposed model is validated by erosion depth and sheet flow layer thickness data in both steady and unsteady flows, and applied to a new instantaneous sediment transport rate formula. With higher accuracy than classical empirical models in steady flows, the new formula can also be used for instantaneous sediment transport rate prediction in skewed asymmetric oscillatory sheet flows.

Clinical evaluation of testicular torsion presenting with acute abdominal pain in young males

Objective:To evaluate the features of testicular torsion presenting with acute abdominal pain and to raise awareness of testicular torsion with specific symptoms.Methods:From October 2005 to June 2016,nine patients with testicular torsion who presented with isolated acute abdominal pain rather than scrotal pain as their primary symptom were retrospectively reviewed.Data,including the age of patients,season at admission,initial medical history,external genital examination,emergency ultrasound findings,operative findings,duration of abdominal pain,complications,and follow-up results,were collected.Results:The average age of patients was 14 years(range 10-17 years).Seven patients whose genitals were not initially examined externally were misdiagnosed as having ordinary abdominal diseases.Surgical exploration revealed that all the involved testes necrotized,and orchidectomy was performed.In the other two patients,scrotal and testicular abnormalities were detected immediately on admission,and emergency surgical exploration determined that the involved testis remained vital,so orchiopexy was performed.The mean duration from symptom onset to diagnosis was 4 h(3-5 h)in the orchiopexy group and 37 h(18-72 h)in the orchidectomy group.Six patients were psychologically affected during postoperative follow-up.Neither recurrence of testicular torsion nor testicular atrophy was recorded.Conclusion:Acute abdominal pain can be the initial and sole symptom of testicular torsion in young males.Physicians should pay close attention to the specific clinical presentation of testicular torsion.

Unsteady Liquid Film Flow with a Prescribed Free-Surface Velocity

A liquid film flow over a flat plate is investigated by prescribing the unsteady interface velocity. With this prescribed surface velocity, the governing Navier–Stokes(NS) equations are transformed into a similarity ordinary differential equation, which is solved numerically. The flow characteristics is controlled by an unsteadiness parameter S and the flow direction parameter Λ. The results show that solutions only exist for a certain range of the unsteadiness parameter, i.e., S≤1 for Λ =-1 and S≤-2.815877 for Λ = 1. In the solution domain,the dimensionless liquid film thickness β decreases with S for both the cases. The wall shear stress increases with the decrease of S for Λ =-1. However, for Λ =-1 the shear stress magnitude first decreases and then increases with the decrease of S. There are no zero crossing points for the velocity profiles for both the cases. The profiles of velocity stay either positive or negative all the time, except for the wall zero velocity. Consequently,the vertical velocity becomes a monotonic function. To maintain the prescribed velocity, mass transpiration is generally needed, but for the shrinking film case it is possible to have an impermeable wall. The results are also an exact solution to the full NS equations.

A novel spherical-headed fascial dilator is feasible for second-stage ultrasound guided percutaneous nephrolithotomy:A pilot study

Objective:In second-stage percutaneous nephrolithotomy(PCNL),because the hydronephrosis has been decompressed,the dilated renal pelvis has resolved and the space is small.Consequently,introduction of the tip of the Amplatz dilator can cause injury to the opposite side of the renal-pelvic mucosa.In this study,we report the experimental and initial clinical performance of a spherical-headed fascial dilator developed specifically for second-stage PCNL.Methods:The novel spherical-headed dilator was compared with existing tapered-headed dilators in configuration and in puncture resistance utilizing a static puncture test.Subsequently,a pilot clinical study was conducted during which patients scheduled to undergo second-stage PCNL from June 2019 to October 2019 in our center were enrolled.A typical ultrasound guided PCNL procedure was performed with the exception that the new spherical-headed fascial dilator was substituted for a tapered-headed one.Results:Experimentally,stab resistance against polyethylene film was significantly increased using the novel spherical-headed dilator compared to the traditional tapered-headed dilators(p<0.005).In the clinical study,the novel dilators were successfully introduced into the renal pelvis and passed down the collecting system in all eight second-stage PCNL cases.There were no cases of renal pelvic perforation or brisk hemorrhage nor need for transfusion.

Viscous Slip MHD Flow over a Moving Sheet with an Arbitrary Surface Velocity

The magnetohydrodynamic（MHD） flow induced by a stretching or shrinking sheet under slip conditions is studied.Analytical solutions based on the boundary layer assumption are obtained in a closed form and can be applied to a flow configuration with any arbitrary velocity distributions. Seven typical sheet velocity profiles are employed as illustrating examples. The solutions to the slip MHD flow are derived from the general solution and discussed in detail. Different from self-similar boundary layer flows, the flows studied in this work have solutions in explicit analytical forms. However, the current flows require special mass transfer at the wall, which is determined by the moving velocity of the sheet. The effects of the slip parameter, the mass transfer at the wall, and the magnetic field on the flow are also demonstrated.

The Study of Tubing Vibration Mechanism in High Pressure Gas Well

Deep gas wells and gas fields have the characteristics of high pressure. The vibration of the tubing string during the production of gas wells causes the string to be subjected to severe stress and even dynamic fatigue failure. Therefore, this article is based on the dynamic finite element theory, aiming at the characteristics of large-size tubing strings in deep gas wells. The finite element mechanics model and mathematical model of the tubing string vibration of the packer of high-pressure gas wells were established, and the ANSYS software was re-developed. The finite element analysis program for the vibration dynamics of the unbuckled and buckled strings of gas wells was compiled with APDL, and the displacement of the longitudinal vibration of the tubing string of high-pressure gas wells was studied. According to different sizes of tubing strings currently used in deep gas wells and gas fields, simulation calculations are carried out, and the axial impact load and buckling damage laws of the tubing strings of the entire well section under different production rates are obtained. It provides a theoretical basis for the prediction of tubing string vibration law and measures to prevent tubing string vibration.

Conductive fibers for biomedical applications

Bioelectricity has been stated as a key factor in regulating cell activity and tissue function in electroactive tissues.Thus,various biomedical electronic constructs have been developed to interfere with cell behaviors to promote tissue regeneration,or to interface with cells or tissue/organ surfaces to acquire physiological status via electrical signals.Benefiting from the outstanding advantages of flexibility,structural diversity,customizable mechanical properties,and tunable distribution of conductive components,conductive fibers are able to avoid the damage-inducing mechanical mismatch between the construct and the biological environment,in return to ensure stable functioning of such constructs during physiological deformation.Herein,this review starts by presenting current fabrication technologies of conductive fibers including wet spinning,microfluidic spinning,electrospinning and 3D printing as well as surface modification on fibers and fiber assemblies.To provide an update on the biomedical applications of conductive fibers and fiber assemblies,we further elaborate conductive fibrous constructs utilized in tissue engineering and regeneration,implantable healthcare bioelectronics,and wearable healthcare bioelectronics.To conclude,current challenges and future perspectives of biomedical electronic constructs built by conductive fibers are discussed.

Laser Ablation and Chemical Oxidation Synergistically Induced Micro/Nano Re-entrant Structures for Super-Oleophobic Surface with Cassie State

Generally,re-entrant structures are a key part of fabricating superoleophobic surfaces,and this structure appears in almost all kinds of published research articles regarding superoleophobicity.However,the application of related fabrication methods is usually too complex and costly in real practice.In this paper,we present a simple method to generate micro-cauliflower structures,which work as re-entrant structures in microcone arrays,to promote the formation of superoleophobic surfaces.The heating process after alkali-assisted surface oxidation is the main reason for the appearance of a micro-ball structure,and the oxidation time can influence the size of the micro-ball.To the best of our knowledge,the influence of the heating process after alkali-assisted surface oxidation on the birth of the micro-ball structure is seldom researched.A low-surface-energy treatment was also analyzed in influencing the size of the re-entrant structure and its relative wettability.Droplets of 5μl of n-decane show contact angles of 155±1°on the as-prepared superoleophobic surface,and air pockets can be clearly seen underneath,indicating a stable Cassie contacting state and a promising application value in the near future.

基于双流体模型的尊村泵站双吸离心泵泥沙磨损

黄河尊村二级泵站的高效稳定运行一直都受水泵的泥沙磨损问题制约,其影响因素包括过泵水流的泥沙体积分数和泥沙粒径.采用双流体模型对尊村二级泵站的双吸离心泵内水沙两相流进行数值模拟,在模型中考虑了颗粒动态尺度对颗粒湍动扩散系数的影响,以及颗粒的惯性和湍动对相间阻力的影响;采用Oka磨损模型计算了泵内泥沙磨损.模拟了由4种典型泥沙体积分数和4种典型泥沙粒径组合成的16种入口泥沙工况,在此基础上研究了入口泥沙体积分数和泥沙粒径对泵内磨损的影响规律.结果表明,不同泥沙条件下该泵发生严重磨损的区域主要位于叶片和蜗壳,其中叶片中后部和蜗壳隔舌的磨损最为严重.随着入口泥沙体积分数增加,叶片和蜗壳的磨损速率呈线性趋势上升;随着泥沙粒径的增加,叶片和蜗壳的磨损速率呈现小幅度增加,且磨损速率增长斜率随粒径增加逐渐放缓.根据该结果,可采取措施降低过泵水流中的泥沙体积分数和泥沙粒径以缓解双吸离心泵内的泥沙磨损.

Development of a polycaprolactone/poly(p-dioxanone)bioresorbable stent with mechanically self-reinforced structure for congenital heart disease treatment

Recent progress in bioresorbable stents(BRSs)has provided a promising alternative for treating coronary artery disease.However,there is still lack of BRSs with satisfied compression and degradation performance for pediatric patients with congenital heart disease,leading to suboptimal therapy effects.Here,we developed a mechanically self-reinforced composite bioresorbable stent(cBRS)for congenital heart disease application.The cBRS consisted of poly(p-dioxanone)monofilaments and polycaprolactone/poly(p-dioxanone)core-shell composite yarns.Interlacing points in cBRS structure were partially bonded,offering the cBRS with significantly higher compression force compared to typical braids and remained good compliance.The suitable degradation profile of the cBRS can possibly preserve vascular remodeling and healing process.In addition,the controllable structural organization provides a method to customize the performance of the cBRS by altering the proportion of different components in the braids.The in vivo results suggested the cBRS supported the vessel wall similar to that of metallic stent.In both abdominal aorta and iliac artery of porcine,cBRS was entirely endothelialized within 1 month and maintained target vessels with good patency in the 12-month follow-up.The in vivo degradation profile of the cBRS is consistent with static degradation results in vitro.It is also demonstrated that there is minimal impact of pulsatile pressure of blood flow and variation of radial force on the degradation rate of the cBRS.Moreover,the lumen of cBRS implanted vessels were enlarged after 6 months,and significantly larger than the vessels implanted with metallic stent in 12 months.

Ultrastretchable and wearable conductive multifilament enabled by buckled polypyrrole structure in parallel

Stretchable conductive fibers have attracted much attention due to their potential use in wearable electronics.However,the ultrahigh strain insensitive conductivity is hindered by mechanical mismatch in Young’s modulus and failure of stretchable structures under large deformation.This challenge is addressed with a conductive and elastic multifilament made of the polyurethane monofilaments that are surface-coated with buckled polypyrrole(PPy)of which flexibility is improved by sodium sulfosalicylate.Such parallel conductive monofilaments with PPy buckling on surface reduce the influence of cracks in the conductive coating on the overall conductivity,displaying an ultra-high strain insensitive behavior(quality factor Q=10.9).Remarkably,various complex forms of wearable electronic textiles made by this conductive multifilament maintain the strain-insensitive behavior of the original multifilament,even upon the large deformation of human joint.This multifilament with wrinkled PPy has attractive advantages in the application of super-stretched wearable electronic devices.

Ultrathin,elastic,and self-adhesive nanofiber bio-tape:An intraoperative drug-loading module for ureteral stents with localized and controlled drug delivery properties for customized therapy

During the postoperative management of urinary diseases,oral or intravenous administration of drugs and implanting ureteral stents are usually required,making localized drug delivery by ureteral stent a precise and effective medication strategy.In the traditional drug loading method,the drug was premixed in the implants in production lines and the versatility of drugs was restricted.However,the complex situation in the urinary system fails the possibility of finding a“one fits all”medication plan,and the intraoperative drug-loading of implants is highly desired to support customized therapy.Here,we designed an ultrathin(8μm),elastic,and self-adhesive nanofiber bio-tape(NFBT)that can easily encapsulate drugs on the stent surface for controllable localized drug delivery.The NFBT exhibited high binding strength to a ureteral stent,a sustained release over 7 d in PBS for hydrophilic drug,and a zero-order release curve over 28 days for the hydrophobic drug nitrofurantoin(NFT).Further in vivo experiments using a porcine ureteral tract infection model demonstrated that NFBT loaded with NFT could significantly reduce the bacterial concentration in urine.The total amount of NFT delivered by the NFBT was about 2.68 wt%of the recommended dose for the systemic administration.

A regeneration process-matching scaffold with appropriate dynamic mechanical properties and spatial adaptability for ligament reconstruction

Ligament regeneration is a complicated process that requires dynamic mechanical properties and allowable space to regulate collagen remodeling.Poor strength and limited space of currently available grafts hinder tissue regeneration,yielding a disappointing success rate in ligament reconstruction.Matching the scaffold retreat rate with the mechanical and spatial properties of the regeneration process remains challenging.Herein,a scaffold matching the regeneration process was designed via regulating the trajectories of fibers with different degradation rates to provide dynamic mechanical properties and spatial adaptability for collagen infiltration.This core-shell structured scaffold exhibited biomimetic fiber orientation,having tri-phasic mechanical behavior and excellent strength.Besides,by the sequential material degradation,the available space of the scaffold increased from day 6 and remained stable on day 24,consistent with the proliferation and deposition phase of the native ligament regeneration process.Furthermore,mature collagen infiltration and increased bone integration in vivo confirmed the promotion of tissue regeneration by the adaptive space,maintaining an excellent failure load of 67.65%of the native ligament at 16 weeks.This study proved the synergistic effects of dynamic strength and adaptive space.The scaffold matching the regeneration process is expected to open new approaches in ligament reconstruction.

Constructing Nanoscale Topology on the Surface of Microfibers Inhibits Fibroblast Fibrosis

Fibrosis is a common problem in soft tissue regeneration,often caused by the differentiation of fibroblasts into myofibro-blasts.Because of the nanoscale topology that regulates the mechanical transduction of cells,nanofibers or nanoparticles are commonly used to modulate fibroblast differentiation.However,the strength of nanofibers is insufficient,and the physi-ological toxicity of nanoparticles still remains to be verified.In this study,self-induced crystallization was used to construct nano-protrusions on the random and aligned polycaprolactone microfibers to regulate the behavior of fibroblasts.The results revealed that the mechanical properties of microfibers with a nanoscale topology were improved.Immunofluorescence staining manifested that nano-protrusions impeded the activation of integrins and vinculins,thereby inhibiting the nuclear transfer of Yes-associated protein,resulting in a decrease in the expression ofα-smooth muscle actin.Nanoscale topology of microfibers hampered the activation of the Rho/ROCK signalling pathway.In general,we used a simple process to con-struct a fibrous scaffold with a micro-nano multilevel structure.This structure can hinder the transformation of fibroblasts into myofibroblasts on both random and aligned fibers,which is expected to prevent fibrosis.

Applications of Three-Dimensional LBM-LES Combined Model for Pump Intakes

Lattice Boltzmannmodel(LBM)in conjunction with an accurate Large Eddy Simulation(LES)technology was proposed to simulate various vortical structures and their evolutions in open pump intakes.The strain rate tensor in the LES model is locally calculated by means of non-equilibrium moments based on Chapman-Enskog expansion,and bounce-back scheme was used for non-slip condition on solid walls and reflection scheme for free surface.The presentedmodel was applied to investigate free-surface and wall-attached vortices for different water levels and flow rate.The vortex position,shapes and vorticities were predicted successfully under three flowing cases(i.e.critical water level(CWL),lower water level,lower flow rate),and the numerical velocity and streamline distribution were analyzed systematically.For CWL based on Froude number considering open channel flows,the shape and the location of various dynamic vortices were captured.Compare to the experimental results of CWL,more vortices were predicted for lower water level,and less vortices were observed for lower flow rate.The predicted velocities and vortex locations are in good agreement with the experimental of a small physical model.The comparisons demonstrated the feasibility and stability of above-mentioned model and numerical method in predicting vortex flows inside open pump intakes.

Customized and in situ fenestrated stent-grafts:A reinforced poly-ε-caprolactone branch cuff designed to prevent type III endoleaks and enhance hemodynamics

Superior long-term anchorage of the bridging stent-grafts from the fenestrated main body endograft could be achieved with the addition of a flared cuff,capable of preventing the previously observed fabric fraying around the fenestration as a result of the balloon angioplasty of the seal zone.This novel stent cuff design will also facilitate more complete biointegration of the devices,eliminate the hemodynamic variation as well as significantly reduce the possibility of a Type III endoleak.The feasibility of this concept is demonstrated by observations made from in-situ tests performed in a Beta endograft design.Flared cuffs made of poly(ε-caprolactone)supported with a weft-knitted polyester structure can be manufactured with various configurations to optimize the transition from the main body of the endograft,thus preventing the currently marketed designs’hemodynamic perturbation while also promoting endograft biointegration.This concept represents an evolution in branch graft design,which may enhance the long-term durability of customized fenestrations and open new applications for in-vivo graft fenestration in the near future.Further ongoing investigation to optimize its structure,X-ray opacity,fixation to the flared stent,and material biocompatibility are still required to build upon this concept’s proof.