DEM Numerical Simulation of Abrasive Wear Characteristics of a Bioinspired Ridged Surface

This paper presents numerical investigations into a ridged surface whose design is inspired by the geometry of a Farrer’sscallop.The objective of the performed research is to assess if the proposed Bioinspired Ridged Surface (BRS) can potentiallyimprove wear resistance of soil-engaging components used in agricultural machinery and to validate numerical simulationsperformed using software based on the Discrete Element Method (DEM).The wear performance of the BRS is experimentallydetermined and also compared with a conventional flat surface.Different size of soil particles and relative velocities between theabrasive sand and the testing surfaces are used.Comparative results show that the numerical simulations are in agreement withthe experimental results and support the hypothesis that abrasive wear is greatly reduced by substituting a conventional flatsurface with the BRS.

Numerical Modeling and Analysis of Grooved Surface Applied to Film Cooling

In order to improve the efficiency of film cooling, numerical investigation was carried out to study the effects of different film-cooled plates on surface heat transfer. Both grooved and non-grooved surfaces were concerned. The modeling was per- formed using Fluent software with the adoption of Shear-Stress Transport （SST） k-ωmodel as the turbulence closure. The coolant was supplied by a single film cooling hole with an inclination angle of 30°. The Mach numbers for the coolant flow and the mainstream flow were fixed at 0 and 0.6, respectively. At three blowing ratios of 0.5, 1.0 and 1.5, the aerodynamic behaviour of the mixing process as well as the heat transfer performance of the film cooling were presented. The numerical results were validated using experimental data extracted from a benchmark test. Good agreements between numerical results and the ex- perimental data were observed. For the film cooling efficiency, it shows that both local and laterally averaged cooling effectiveness can be improved by the non-smooth surface at different blowing ratios. Using the grooved surface, the turbulence intensity upon the plate can be reduced notably, and the mixing between the two flows is weakened due to the reduced turbu lence level. The results indicate that the cooling effectiveness of film cooling can be enhanced by applying the grooved surface.

Ejecta from periodic grooved Sn surface under unsupported shocks

Dynamic failure and ejection characteristics of a periodic grooved Sn surface under unsupported shock loading are studied using a smoothed particle hydrodynamics method. An ＂Eiffel Tower＂ spatial structure is observed, which is com- posed of high-speed jet tip, high-density jet slug, longitudinal tensile sparse zone, and complex broken zone between grooves. It is very different from the spike-bubble structure under supported shocks, and has been validated by detonation loading experiments. In comparison with that under supported shocks at the same peak pressure, the high-speed ejecta decreases obviously, whereas the truncated location of ejecta moves towards the interior of the sample and the total mass of ejecta increases due to the vast existence of low-speed broken materials. The shock wave profile determines mainly the total ejection amount, while the variation of V-groove angle will significantly alter the distribution of middle- and high-speed ejecta, and the maximum ejecta velocity has a linear corretation with the groove angle.

Lipid biomarker composition in surface sediments from the Carlsberg Ridge near the Tianxiu Hydrothermal Field

Hydrothermal venting has a profound effect on the chemical and biological properties of local and distal seawater and sediments. In this study, lipid biomarkers were analyzed to examine the potential influence of hydrothermal activity on the fate of organic matter(OM) in surface sediments around Tianxiu Hydrothermal Field in the Carlsberg Ridge(CR), Northwest Indian Ocean. By comparing the biomarker distributions of the samples with that of other typical hydrothermal sediments in the mid ocean ridge, it is shown that the location of the samples is not affected by the hydrothermal activity. The relatively low abundances of terrestrial n-alkyl lipids and riverine1,15-C_(32) diol suggested a minor contribution of terrigenous OM to the study area. The bacteria contributed predominantly to sedimentary marine OM;however, other marine source organisms, e.g., eukaryotes(i.e.,phytoplankton and fungi) could not be completely neglected. The marine-originated biomarkers showed significantly variable distributions between the two sediments, suggesting different dynamic physical and biogeochemical processes controlling the fate of marine OM. This study identified various diagnostic biomarkers(5,5-diethyl alkanes, diols and β-OH FAs), which may have significant environmental implications for future works in this region.

A Qualitative Study of the Influence of Grooved Mold Surface Topography on the Formation of Surface Marks on As-Cast Ingots of Aluminum Alloy 3003

The effects of the wavelength and orientation of machined grooves on a mold surface, casting speed, and melt superheat on the formation of surface marks on as-cast ingots were studied with an immersion casting tester and copper mold chill blocks. The mold surface topographies included a polished smooth surface, and those with machined unidirectional parallel contoured grooves oriented either parallel (vertical) or perpendicular (horizontal) to the casting direction. The unidirectional grooves were 0.232 mm deep with wavelength or spacing between 1 and 15 mm. The casting speed and melt superheat were between 1 and 200 mm/s, and 10 and 50 K, respectively. Two primary types of surface marks were observed on ingots cast with the copper mold with smooth surface topography, namely the finer and closely spaced ripples (Type I), and the widely spaced but coarser laps (Type II). The latter were more prevalent at the higher casting speeds and melt superheats. Qualitatively, formation of both types of surface marks on the as-cast ingots of the aluminum alloy 3003 appeared to be alleviated by increase in casting speed and melt superheat, and by the use of molds with grooved surface topography. In fact, casting with a mold surface with 1 mm spaced grooves that are perpendicular to the casting direction eliminated the formation of surface marks at casting speeds greater than 1 mm/s. It also improved the uniformity of the ingot subsurface microstructure and eliminated the associated subsurface segregation.

Analytical analysis of surface potential for grooved-gate MOSFET

The improvement of the characteristics of grooved-gate MOSFETs compared to the planar devices is attributed to the corner effect of the surface potential along the channel. In this paper we propose an analytical model of the surface potential distribution based on the solution of two-dimensional Poisson equation in cylindrical coordinates utilizing the cylinder approximation and the structure parameters such as the concave corner θ0. The relationship between the minimum surface potential and the structure parameters is theoretically analysed. Results confirm that the bigger the concave corner, the more obvious the corner effect. The corner effect increases the threshold voltage of the grooved-gate MOSFETs, so the better is the short channel effect （SCE） immunity.

Azimuthal anchoring of a nematic liquid crystal on a grooved interface with anisotropic polar anchoring

Zhang Y J et al.[Zhang Y J,Zhang Z D,Zhu L Z and Xuan L 2011 Liquid Cryst.38 355] investigated the effects of finite polar anchoring on the azimuthal anchoring energy at a grooved interface,in which polar anchoring was isotropic in the local tangent plane of the surface.In this paper,we investigate the effects of both isotropic and anisotropic polar anchoring on the surface anchoring energy in the frame of Fukuda et al.’s theory.The results show that anisotropic polar anchoring strengthens the azimuthal anchoring of grooved surfaces.In the one-elastic-constant approximation（K11 = K22 = K33 = K）,the surface-groove-induced azimuthal anchoring energy is entirely consistent with the result of Faetti,and it reduces to the original result of Berreman with an increase in polar anchoring.Moreover,the contribution of the surface-like elastic term to the Rapini-Papoular anchoring energy is zero.

A novel spoof surface plasmon polariton structure to reach ultra-strong field confinements

Ultrathin corrugated metallic structures have been proved to support spoof surface plasmon polariton (SPP) modes on two-dimension (2D) planar microwave circuits.However,to provide stronger field confinement,larger width of strip is required to load deeper grooves,which is cumbersome in modern large-scale integrated circuits and chips.In this work,a new spoof SPP transmission line (TL) with zigzag grooves is proposed.This new structure can achieve stronger field confinement compared to conventional one with the same strip width.In other words,the proposed spoof SPP TL behaves equivalently to a conventional one with much larger size.Dispersion analysis theoretically indicates the negative correlation between the ability of field confinement and cutoff frequencies of spoof SPP TLs.Numerical simulations indicate that the cutoff frequency of the proposed TL is lower than the conventional one and can be easily modified with the fixed size.Furthermore,two samples of the new and conventional spoof SPP TLs are fabricated for experimental demonstration.Measured S-parameters and field distributions verify the ultra-strong ability of field confinement of the proposed spoof SPP TL.Hence,this novel spoof SPP structure with ultra-strong field confinement may find wide applications in microwave and terahertz engineering.

Geometrical condition for observing Talbot effect in plasmonics infinite metallic groove arrays

The plasmonics Talbot effect in metallic layer with infinite periodic grooves is presented in this study. Numerical approach based on the finite element method is employed to verify the derived Talbot carpet on the non-illumination side. The groove depth is less than the metallic layer thickness; however, for specific conditions, surface plasmons polaritons(SPPs)can penetrate through grooves, propagate under the metallic layer, and form Talbot revivals. The geometrical parameters are specified via groove width, gap size, period, and wavelength, and their proper values are determined by introducing two opening ratio parameters. To quantitatively compare different Talbot carpets, we introduce new parameters such as R-square that characterizes the periodicity of Talbot images. The higher the R-square of a carpet, the more coincident with non-paraxial approximation the Talbot distance becomes. We believe that our results can help to understand the nature of SPPs and also contribute to exploring this phenomenon in Talbot-image-based applications, including imaging, optical systems, and measurements.

Addendum to: An Approach to Hierarchical Clustering via Level Surfaces and Convexity

This article is an addendum to the 2001 paper [1] which investigated an approach to hierarchical clustering based on the level sets of a density function induced on data points in a d-dimensional feature space. We refer to this as the “level-sets approach” to hierarchical clustering. The density functions considered in [1] were those formed as the sum of identical radial basis functions centered at the data points, each radial basis function assumed to be continuous, monotone decreasing, convex on every ray, and rising to positive infinity at its center point. Such a framework can be investigated with respect to both the Euclidean (L2) and Manhattan (L1) metrics. The addendum here puts forth some observations and questions about the level-sets approach that go beyond those in [1]. In particular, we detail and ask the following questions. How does the level-sets approach compare with other related approaches? How is the resulting hierarchical clustering affected by the choice of radial basis function? What are the structural properties of a function formed as the sum of radial basis functions? Can the levels-sets approach be theoretically validated? Is there an efficient algorithm to implement the level-sets approach?

Very High Cycle Fatigue Behaviors and Surface Crack Growth Mechanism of Hydrogen-Embrittled AISI 304 Stainless Steels

The influence of hydrogen embrittlement on the fatigue behaviors of AISI 304 stainless steel is investigated. The fatigue endurance limits of the untreated and hydrogen-embrittled materials were almost the same at 400 MPa, and hydrogen embrittlement had little influence even though the sample contained about 8.1 times more hydrogen. Thus, the sensitivity of hydrogen gas in this material is very low. A surface crack initiation, growth, coalescence, and micro ridge model is proposed in this study. Slip line formation?⇒microcrack formation?⇒increases in the crack width, and blunting of the crack tip as it grows?⇒formation of many slip lines because of deformation in the shear direction?⇒growth of the crack in the shear direction, forming micro ridges, coalescence with adjacent cracks ⇒?continuous initiation, growth, coalescence, and ridge formation of surface cracks and specimen breakage.

Numerical Analysis of the Hydrodynamic Lubrication of Micro-grooved Friction Pair

A growing interest is given to the hydrodynamic lubricated friction pair with surface textured. Because of its relatively simple processing methods and low manufacturing costs,micro-groove has become the most valuable form of surface texture,and definitely has broad application prospects in mechanical engineering. Based on numerical simulation,the present study aims to examine the effects of surface forms and cross-section types of micro-groove on the hydrodynamic lubrication performance,and to find out the optimal structural parameter for designing logical micro-grooves. Different surface form and cross-section types are designed to maximize the texture hydrodynamic effect. The average pressure of such microgrooved surface is evaluated in detail,and the variation trends with changes of the length of micro-groove,lp,or the depth,hp,are discussed. The theoretical results show that micro-grooves with rational design contribute to the improvement of hydrodynamic lubrication performance of friction pair largely. For a specific micro-grooved friction pair,the optimal surface form and crosssection type make the lubrication performance best.

纳米凹槽表面结冰的分子动力学模拟研究

采用分子动力学模拟方法建立了水在金表面结冰的模型,在疏水表面上引入亲水纳米凹槽结构,模拟研究了纳米凹槽表面上的冰成核过程,揭示了凹槽深宽比对冰成核的影响规律和机制.结果表明,在疏水表面引入亲水纳米凹槽结构并改变表面的凹槽宽度,可以调节疏水表面的结冰过程.当纳米凹槽与六边形冰结构相匹配时,凹槽内部更容易形成冰核,可以提高疏水表面的冰成核率的效果,其表面成核率接近与亲水表面成核率.当纳米凹槽结构与六边形冰结构不匹配时,凹槽内不易形成冰核,结冰过程受到抑制.为提高疏水表面成核率提供了新方法,为控制疏水表面冰成核位置和冰生长方向提供了新思路.

江苏沿海沙脊群表层沉积物Pb同位素特征及对物源的指示

为进一步查明江苏沿海沙脊群沉积物的来源,分析了该区域沉积物酸不溶组分Pb同位素特征。结果表明,远岸沙脊群陆向区域沉积物Pb同位素比值与近岸沙脊群相似,暗示其在潮波作用下有向岸运移的趋势。铅钕同位素分析揭示长江及周边河流沉积物在长江冲淡水和东海沿岸流作用下输移至远岸沙脊群海向区域。在苏北沿岸流作用下,老黄河三角洲沉积物输入对近岸沙脊群及远岸沙脊群陆向区域有影响;相反,诸如现代黄河口、济州岛和韩国河流等地沉积物输入对江苏沿海沙脊群的影响较弱。

飞秒激光加工参数对RB-SiC表面形貌的影响

目的揭示飞秒激光加工参数对反应烧结碳化硅(Reaction-Bounded Silicon Carbide,RB-SiC)表面形貌的影响规律。方法通过改变激光能量密度和有效脉冲数,研究RB-SiC表面烧蚀槽的形貌变化规律,确定飞秒激光加工RB-SiC的去除机理。采用扫描电镜、共聚焦显微镜、X射线能谱仪和拉曼光谱仪分析RB-SiC烧蚀前后的表面形貌演变行为。结果激光能量密度在0.62~10.48 J/cm^(2)时,Si富集区域形成凹陷结构,SiC颗粒区域形成周期性结构(Laser-Induced Periodic Surface Structures,LIPSS),周期约为970 nm。随着激光能量密度的增加,凹陷结构扩大加深,表面球形纳米颗粒增多,烧蚀槽宽度呈对数增长。有效脉冲数在69~1379,Si富集区域的去除量高于SiC颗粒区域的去除量。随着有效脉冲数增加,烧蚀槽深度显著加深,凹陷结构扩展成深坑结构,飞溅至烧蚀槽外侧的纳米颗粒聚集成团簇物,由Si、SiC和非晶态SiO_(2)构成的沉积物在烧蚀槽边缘形成堆积层。结论降低激光能量密度能够减少RB-SiC表面凹陷和纳米颗粒,有助于提升烧蚀形貌的一致性。增加有效脉冲数会促进烧蚀槽底部深坑结构的产生,进而扩大Si与SiC去除量之间的差异。

基于综合熵权-信噪比的球轴承外圈沟道ELID磨削加工参数优化

为提高球轴承外圈沟道表面的加工质量,实现对电解在线砂轮修整ELID磨削加工试验中摆动参数、磨削参数的精确控制,设计正交试验并基于试验数据建立表面质量与加工参数之间的二阶响应模型和指数回归模型;通过熵权理论确定表面粗糙度与轮廓度的综合权重,最终获得最优加工参数,并结合信噪比的基本特性分析加工参数对表面质量的影响程度。结果表明:指数回归模型对表面粗糙度预测较为精确,二阶响应模型对轮廓度预测较为精确,误差均在5%以下;表面粗糙度、轮廓度综合权重分别为0.4568,0.5432,最优加工参数为摆动幅度11°、摆动速度6°/s、砂轮转速19500 r/min、工件转速50 r/min;加工参数的影响程度由大到小依次为摆动幅度、摆动速度、工件转速、砂轮转速。

取向型微沟槽高速球铣加工制备方法及其减摩性能研究

探究直接利用高速球铣加工工艺制备取向型表面微沟槽织构的方法,并对该类型表面微织构的减摩性能进行研究.鉴于高速球铣加工工艺走刀路径灵活可变、表面材料残留几何尺寸与分布形态具备可控性的特点,利用Matlab仿真对高速球铣加工表面形貌进行预测,通过高速球铣加工试验验证仿真结果,并基于流体动压润滑理论,结合Fluent流体仿真分析与高速环-块摩擦磨损试验,对该类型表面微织构的减摩性能进行分析.当切削参数选用径向切深明显大于每齿进给量的组合时,高速球铣加工表面残留材料能够形成明显的微沟槽形貌,且微沟槽特征的取向可由球头铣刀的走刀路径进行控制;微沟槽承载能力与其取向密切相关,随着微沟槽取向角由90°减小至20°,负压区与正压区范围呈现扩大趋势,油膜内逆流效应逐渐减弱,动压效应逐渐增强,微沟槽承载能力提高了20.64%,表面摩擦系数由0.02845降低至0.02165;然而,当取向角过小时,负压区与正压区的范围过小,不能形成有效的收敛楔,微沟槽承载能力下降,表面摩擦系数上升.通过高速球铣加工工艺能够实现取向型表面微沟槽织构的可控制备,且该类表面的减摩性能与取向角α密切相关,在本文研究范围内,取向角为20°时表现出最小的摩擦系数与最高的油膜承载力.本文研究结果可为表面织构造型方法提供一种新思路,能够为满足零件表面的减摩需求提供很好的解决方法.

不同侧隙卸荷槽时齿轮泵理论流量的创新计算

为克服齿轮泵理论流量、排量及脉动系数计算方法的局限性与复杂性,从一个完整啮合齿面所产生的理论齿面流量入手,提出双卸荷槽间距内的理论齿面流量即为泵理论输出流量的新方法。以1.0和0.5代表侧隙的有和无,双卸荷槽对称线相对于齿轮副中心线的无量纲不对称宽度为变量,构建出理论输出流量特性的相关简洁式。结果表明:同等侧隙类型下无卸荷槽与单侧卸荷槽下的理论排量相同,有侧隙、单侧卸荷槽下的类型系数经典式确实有误;无侧隙、对称卸荷槽类型下的理论排量更大,流量脉动更小,但困油现象更严重;尤其单侧卸荷槽下的流量脉动很大和困油现象很严重,不建议采用等。本文提出的新方法原理更清晰,公式更简洁,结果更可靠,通用性更强。

聚合物真空绝缘子表面二级微结构

为研究绝缘子表面二级微结构的耐压提升机制,将表面二级微结构拆分为两种子结构,也即是表面微孔结构与表面微槽结构,并通过复合材料制备、激光处理、酸液选择性腐蚀等方式制备出表面二级微结构与相应的两种子结构。对三种结构分别进行沿面耐压性能测试,结果表明表面微孔与表面微槽均能有效地提升绝缘子的真空沿面耐压性能,而二者组合形成的表面二级微结构能够进一步提升绝缘子的真空沿面耐压性能。该结果表明通过将表面结构进行合理的组合能够实现对绝缘子表面闪络发展的多重、协同抑制,进一步提升绝缘子的真空沿面耐压水平。

电机轴承油膜击穿电压阈值的计算及测试

变频器的广泛应用使变频供电引起的电机轴承电蚀问题日益凸显,为提出合理的抑制方案,需要界定轴承油膜击穿电压阈值。通过理论分析获得轴承最小油膜厚度,在此基础上建立油膜击穿微区的仿真模型,计算不同载荷、转速、温度下击穿电压阈值的变化,结果表明:低速、高温、大载荷工况下的击穿电压阈值会降低,更容易产生放电击穿电流;研究了轴承表面粗糙度对轴承油膜击穿电压阈值的影响,发现轴承表面粗糙度较大时,轴承油膜更易被击穿;搭建轴电压测试平台测试击穿电压阈值随温度和转速的变化,规律与仿真分析一致。