Numerical Simulation on Flow Control for Drag Reduction of Revolution Body Using Dimpled Surface

Numerical simulation on the flow fields near the dimpled and the smooth revolution bodies are performed and compared by using SST k-ω turbulence model, to explain the reasons of friction and base drag reductions on the bionic dimpled surface and the control behaviors of dimpled surface to boundary layer near wall of the revolution body. The simulation results show that the dimpled surface reduces the skin friction drag through reducing the velocity gradient and turbulent intensity, and reduces the base drag through weakening the pumping action on the flow behind the revolution body caused by the external flow; the low speed rotating vortexes in the dimples segregate the external flow and the revolution body; and the low speed rotating vortexes forming in the bottom of dimples can produce negative skin friction.

Efficient loading of cesium atoms in a magnetic levitated dimple trap

We report a detailed study of magnetically levitated loading of ultracold ^(133)Cs atoms in a dimple trap.The atomic sample was produced in a combined red-detuned optical dipole trap and dimple trap formed by two small waist beams crossing a horizontal plane.The magnetic levitation for the ^(133)Cs atoms forms an effective potential for a large number of atoms in a high spatial density.Dependence of the number of atoms loaded and trapped in the dimple trap on the magnetic field gradient and bias field is in good agreement with the theoretical analysis.This method has been widely used to obtain the Bose–Einstein condensation atoms for many atomic species.

Prediction of Leakage from an Axial Piston Pump Slipper with Circular Dimples Using Deep Neural Networks

Oil leakage between the slipper and swash plate of an axial piston pump has a significant effect on the efficiency of the pump.Therefore,it is extremely important that any leakage can be predicted.This study investigates the leakage,oil film thickness,and pocket pressure values of a slipper with circular dimples under different working conditions.The results reveal that flat slippers suffer less leakage than those with textured surfaces.Also,a deep learning-based framework is proposed for modeling the slipper behavior.This framework is a long short-term memory-based deep neural network,which has been extremely successful in predicting time series.The model is compared with four conventional machine learning methods.In addition,statistical analyses and comparisons confirm the superiority of the proposed model.

Natural convection heat transfer enhancement of different nanofluids by adding dimple fins on a vertical channel wall

In this numerical study,natural flow and heat transfer of nanofluids with Al2O3,TiO2,Cu and CNT nanoparticles in a vertical channel with dimpled fins at Rayleigh number(Ra)of Ra=3.25×107 to Ra=1×108 are investigated by using the finite volume method.The obtained results revealed that,using CNT in volume fractions of 2%and 4%leads to significant heat transfer and atφ=6%,using TiO2 nanoparticles has a great effect on Nu number enhancement.Also,using solid nanoparticles in base fluid causes more uniform heat transfer distribution,especially in areas close to heated surface and by adding more volume fraction in base fluid,temperature level reduces.In general,according to temperature contours,reduction of wall temperature depends on the increase of Ra and volume fraction and the type of solid nanoparticles.

基于磁悬浮大体积交叉光学偶极阱的Dimple光阱装载研究

三维拉曼边带冷却后的铯原子样品装载于一个磁悬浮的大体积交叉光学偶极阱中,继续加载一个小体积的光学偶极阱后,实现了Dimple光学偶极阱对铯原子的高效装载.对不同磁场下磁悬浮大体积光阱的有效装载势能进行理论分析与实验测量,得出最优化的梯度磁场和均匀偏置磁场,获得了基于磁悬浮大体积光阱的Dimple光学偶极阱的装载势能曲线,实现了Dimple光学偶极阱对经拉曼边带冷却后俘获在磁悬浮的大体积光阱中的铯原子样品的有效装载.比较了Dimple光学偶极阱分别从拉曼边带冷却、大体积的交叉光阱和消除反俘获势后的磁悬浮大体积光阱装载的结果,将俘获在磁悬浮大体积光阱中的铯原子样品装载到Dimple光学偶极阱,铯原子样品的密度提高了约15倍.

Stress-state dependence of dynamic strain aging:Thermal hardening and blue brittleness

This study aims to discover the stress-state dependence of the dynamic strain aging(DSA)effect on the deformation and fracture behavior of high-strength dual-phase(DP)steel at different deformation temperatures(25-400°C)and reveal the damage mechanisms under these various configurations.To achieve different stress states,predesigned specimens with different geometric features were used.Scanning electron microscopy was applied to analyze the fracture modes(e.g.,dimple or shear mode)and underlying damage mechanism of the investigated material.DSA is present in this DP steel,showing the Portevin-Le Chatelier(PLC)effect with serrated flow behavior,thermal hardening,and blue brittleness phenomena.Results show that the stress state contributes distinctly to the DSA effect in terms of the magnitude of thermal hardening and the pattern of blue brittleness.Either low stress triaxiality or Lode angle parameter promotes DSA-induced blue brittleness.Accordingly,the damage mechanisms also show dependence on the stress states in conjunction with the DSA effect.

有为提高的超声可见性的特定的修正的脉管的刺针的评估: 在 vitro 学习

AIM:To determine which modification to a vascular puncture needle results in increased visualization during ultrasound(US)-guided vascular puncture.METHODS:We evaluated US images of a phantom made of degassed gelatin and each of the following four modified versions of a commercially available vascular puncture needle(18 G):re-cut needle,dimple needle,rough-surface needle(rough over the sections of needle located 3-6 mm from the tip),and a needle with four side holes(side holes covered by the sheath).An unmodified commercially available puncture needle was used as a control.Five interventional radiologists evaluated image quality according to the following classification grade:Ⅰ,invisible;Ⅱ,poor;Ⅲ,moderate;Ⅳ,good;Ⅴ,excellent.RESULTS:The highest score for needle visualization was obtained for the needle with four side holes.The re-cut needle scored the same as the control.Multiple comparisons were conducted using overall evaluation scores among the commercially available needle,dimple needle,rough-surface needle(3-6 mm),and the needle with four side holes.A significantly higher score was obtained for the needle with four side holes(P 【 0.05/6).CONCLUSION:The needle with four side holes was prominently visualized and gained a significantly higher score(compared with the other needles) in a phantom evaluation.

Dimpling Suppression by Chamfered Rotatable Cubic Punch in Reconfigurable Die Forming

The dimpling defects caused by conventional hemispherical punch in doubly curved sheet metal reconfigurable die forming process were considered.The rotatable cubic punch (RCP) was developed to suppress the dimpling defects more effectively and conveniently.The former punch contacts with the work-piece through a point-surface contact and the latter punch contacts with the work-piece through a surface-surface contact.A series of stamping experiments were carried out using three different punches (hemispherical punch,RCP,chamfered-RCP) with three different loads.Some finite element simulations about the stamping experiments were carried out.The dimple scales were evaluated through the dimple depths.The corresponding data were obtained by 3-D scanning and FE result analysis respectively.A 3-D plate forming machine was developed,in which chamfered-RCP was adopted.Plate forming experiments were carried out on this machine.The stamped samples show a clear basis for the performance of chamfered-RCP.The study provided a means to guide the design of punches for dimpling suppression used in reconfigurable die.

Effect of Surface Texturing on Lubricating Condition under Point Contact Using Numerical Analysis

The contact fatigue life of machine elements is affected by pitting, wear and so on, under heavier loading conditions. Increasing the fatigue life requires mainly the improvements of lubricating condition, operating condition and materials. In order to improve the lubricating condition, it is necessary to investigate the relation of the microscopic surface texturing and the contact modes of machine elements. In this paper, thus, the pressure and oil film thickness of the contact between sphere and the plate with 5 kinds surface texturing were calculated using a commercial software based on Reynolds equation. There was sufficient evidence to suggest that the dimple shape was the optimum texturing to increase the lubricating condition.

Improving effect on forming quality and accuracy using a polyurethane board positioning/resetting the discrete steel pad in multi-point forming

To improve the quality of multi-point die forming, a new approach using discrete steel pads was proposed. The formability of three different multi-point die forming processes was analyzed through numerical simulation and experiments. Numerical simulation and experimental results showed that the use of discrete steel pads in the multi-point forming process can substantially improve the stress–strain state on the plate and suppress dimple, straight-edge, and wrinkle defects. This analysis verified that the use of discrete steel pads in a multi-point forming process can effectively improve the quality and accuracy with which sheet metal is formed.

Some Aspects in Application of Microscopical and Microanalytical Techniques

This article considers collectively some of the most recent advances in the application of microscopicaland microanalytical techniques in materials science. including studies concerning rare metals. These comprise the highest resolution obtained with electron microscopy. observation of moire patterns in transmisionelectron microscopy (TEM), electro-dimpling before ion beam thinning as an effective step in the preparation of TEM samples, hydrogen problem in atom probe analysis, and a novel analysis technique-lasermicroprobe mass spectrometry (LAMMS).

DIMPLE FORMATION ON FRACTURE SURFACE OF STEEL 55SiMnMo

The fracture surface of the normalized steel 55SiMnMo was observed,under tensile device at- tached on the SEM,to be of ductile dimple feature on the bainite which is composed of lath ferrite and austenite platelet.The dimple is essentially nucleated in the ferrite.Because the austenitic plastic deformation is remarkable during fracturing,the tear ridge of dimple is very sharp.

Investigation on the Tensile Properties and Fracture Characteristics of Amorphous Ribbons Fe81.50B1.40Si7.95Nb7.37Cu1.73P0.05

A number of Fe-Si-B amorphous ribbons are made by using melt spinning method. The microstructure, mechanical and other relevant properties of thin amorphous ribbons of Fe81.50B1.40Si7.95Nb7.37Cu1.73P0.05 alloy at room temperature were studied with several equipment including Differential scanning calorimetry (DSC), X-ray diffraction (XRD),Scanning electron microscope (SEM), and tensile machine. Significantly different microstructures exist between the free and wheel face of the thin amorphous ribbons. The free face is smooth while the wheel face is coarse with a great number of micro voids on the surface. Experimental results show that the tensile strength and elastic modulus of thethin amorphous ribbons at room temperature are 1951 MPa and 70 GPa. In addition, the amorphous ribbons possess reasonable tensile elongation (2.46%). The fracture appearance of amorphous ribbons of Fe81.50B1.40Si7.95Nb7.37Cu1.73P0.05 alloyis a mixed mode of ductile and brittle fracture which includes dimples and partial cleavage fracture similar to the crystalline materials. The dimple feature proves that it still has plastic characteristics on the micro scale.

TENSILE FRACURE IN AN Al-Li ALLOY 8090

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Influence of Surface Properties Modified with Fine Shot Peening on Scuffing

Recently, gears of high strength, reliability, and surface-damage-resistant under severe service conditions are required to achieve the weight saving and downsizing of a product. For the high-speed condition in particular, it is important to understand the influence of the surface properties on the scuffing resistance. If the effective surface profile to improve the lubrication property was found, the metal surfaces could be obtained with both surface strength and surface lubricity. Herein, the influence of surface properties modified with fine shot peening, which can form the arbitrary surface profile, on the scuffing resistance in the rolling-sliding contact machine element, was investigated. The scuffing test was performed using a two-cylinder rolling contact test machine. In a specific sliding, a faster roller of 60% and a sliding velocity of 1.75 m/s were utilized. The scuffing test results with shot-peened test rollers and those with non-shot-peened test roller were compared. The influence of the surface roughness of the shot-peened test roller was also discussed. We found that the shot-peened roller had a better scuffing resistance compared with the roller without the shot-peening process.

ASYMMETRIC DYNAMIC INSTABILITY OF AXISYMMETRIC POLAR DIMPLING OF THIN SHALLOW SPHERICAL SHELLS

If the parameter , which measures the thickness-to-rise of the sliell, is small, the axismnnetrie polar dimpling oj .shallow .spherical .shell due to quadratic pressure distribution i.s dynamic instability, i.e., a small perturbation can change il to an asymmetric polar dimple mode. In two cases, the problem can be reduced to an eigenvalue problem where T can approximately be reduced to a Sturm-Liouvi/le operator if The existence of at least one real eigenvalue of T, which means that the axisyntmetric polar dimpling is dynamically unstable, i.s proved by spectral theorem or Hilbert theorem. Furthermore, an eigenfunction, which represents one of the asymmetric modes of the unstable dimple shell, belonging to an eigenvalue of T, is found.

A Study on the Performances of Solar Air Collectors Having a Hemispherical Dimple on the Absorber Plate

In order to increase the efficiency of solar air collectors,a new variant with a protrusion is proposed in this study,and its performances are analyzed from two points of view,namely,in terms of optics and thermodynamics aspects.By comparing and analyzing the light paths of the protrusion and the dimple,it can be concluded that when sunlight shines on the dimple,it is reflected and absorbed multiple times,whereas for the sunlight shining on the protrusion,there is no secondary reflection or absorption of light.When the lighting area and the properties of the surfaces are the same,the absorption rate of the dimple is 10.3 percentage points higher than that of the protrusion.In the range of Reynolds number from 3000 to 11000,numerical simulations about the effects of the relative height(e/Dh=0.033–0.1)and relative spacing(p/e=4.5–8.5)of protrusions on air heat transfer and flow resistance show that,in terms of comprehensive evaluation coefficient(PF),the best relative height is 0.085,when the relative spacing is 5.A correlation of Nu and f with Re,e/Dh and p/e is obtained by linear regression of the results,in order to provide a useful reference for the design and optimization of this kind of solar air collector.

Numerical Investigation of Flow and Heat Transfer in Vane Impingement/Effusion Cooling with Various Rib/Dimple Structure

By investigating heat transfer and flow structures of dimples,orthogonal ribs,and V-shaped ribs in the impingement/effusion cooling,the article is dedicated to selecting a best-performing internal cooling structure for a turbine vane.The overall cooling effectiveness and coolant consumption are adopted to evaluate the cooling performance.To analyze the influence of structural modification,the flow field is investigated on chordwise/spanwise sections and the target surface.The blockage effect on crossflow can protect jet flow,resulting in higher heat transfer performance of the target surface.Ribs own a stronger blockage effect than dimples.Compared with the blockage effect,the influence of the rib shape is negligible.By installing dimples between ribs,heat transfer is augmented further.The introduction of ribs/dimples leads to higher discharge coefficients of jet nozzles but lower discharge coefficients of film holes.Thus,the film cooling deteriorates.Meanwhile,the installation of the ribs and dimples decreases total coolant consumption.The effect of ribs/dimples on heat transfer and effusion condition of internal and external cooling is analyzed.The best-performing cooling structure is the target surface with dimples and orthogonal ribs,which decreases the wall temperature and coolant consumption by 14.57-28.03 K and 1.19%-1.81%respectively.This article concludes the flow mechanism for dimples and influence factors on the cooling performance,which may serve as guidance for the turbine vane design.

Drag reduction of wall bounded incompressible turbulent flow based on active dimples/pimples

The control of turbulence by dimples/pimples has drawn more and more attention. The objective of this paper is to investigate the effectiveness of the active dimples/pimples for the drag reduction in the incompressible turbulent flow. Firstly, the drag reduction by the opposition control based on active dimples/pimples at the lower wall is studied via the direct numerical simulation of the turbulent channel flow. It is found that large active dimples/pimples can not suppress the streamwise vortices significantly and thus almost no drag reduction is achieved. Small active dimples and pimples with the diameter of one fourth of the streak width can both reduce the friction drag, but pimples will induce a larger pressure drag than dimples. Then the suboptimal control scheme is examined based on small active dimples using the spanwise wall shear information only, It is shown that the friction drag decreases by about 4.5% but the total drag is only reduced by about 2.7% abated by the pressure drag. Compared with the actuation of the all-point blowing/suction or the all-point wall movement, the effectiveness of the turbulent drag reduction based on active shallow dimples is much smaller.

Running-in friction of hip joint replacements can be significantly reduced:The effect of surface-textured acetabular cup

Hip joint replacements represent the most effective way of treatment for patients suffering from joint diseases.Despite the rapid improvement of implant materials over the last few decades,limited longevity associated with wear-related complications persists as the main drawback.Therefore,improved tribological perfor-mance is required in order to extend the service life of replacements.The effect of surface texturing of ultra-high molecular weight polyethylene(UHMWPE)acetabular cup was investigated in the present study.Unique tilling method was utilized for manufacturing the dimples with controlled diameter and depths on the contact surface of the cup.The experiments with four commercial femoral components and two model lubricants were realized.The main attention was paid to a coefficient of friction considering the differences between the original and the dimpled cups.Results showed remarkable lowering of friction,in general.Focusing on the simulated human synovial fluid,friction was reduced by 40%(alumina ceramic),38.8%(zirconia toughened ceramic),25.5%(metal),and 9.9%(oxinium).In addition,the dimples helped to keep the friction stable without fluctuations.To conclude,the paper brings a new insight into frictional behaviour of the hip replacements during running-in phase which is essential for overall implant lifespan.It is believed that proper surface texturing may rapidly improve the life quality of millions of patients and may lead to considerable financial savings.