空气中非光滑凹坑面减阻性能仿真研究(英文)

仿生非光滑表面减阻技术有重要研究价值,但目前相关理论不完善。为进一步分析凹坑面在空气中的减阻效果与减阻性能,对一系列半圆与间隔组成的变尺寸凹坑面进行数值计算。结果表明,6个模型中最佳减阻模型在来流速度为6m/s时,减阻率达25.927%,减阻效果明显;最后分析了凹坑尺寸对于凹坑面减阻的影响及减阻规律。

空气中非光滑凸包面减阻性能的数值仿真研究

在表面减阻性能的研究中,凸包面减阻技术源于仿生动物表面的微观结构,可以运用到大型飞机表面减阻问题具有重要研究价值。问题在于微观结构形状尺寸、不同介质、不同来流速度等多种因素与减阻效果有关。为研究凸包面在空气介质中速度对减阻能力的影响,采用数值仿真和理论分析的研究方法,对凸包面在空气中速度1m/s^10m/s范围内的流场用Fluent6.3软件进行数值仿真计算。选用了N-S方程,RNGK-ε湍流模型,仿真结果表明,研究的模型在来流速度6m/s时减阻效果明显,总减阻率为24.512%。数值模拟数据与理论计算数据进行比较,保证结果值的可靠性,分析发现凸包单元使凸包附近流场发生改变,凸包面具有较好减阻能力,并优化得到较好减阻方案。

空气中不同间隔凹坑面的减阻性能仿真

仿生非光滑凹坑面减阻技术具有重要的经济价值和军事价值,但目前相关理论不完善。凹坑面减阻效果与其结构形态、来流速度、流体介质等有关,为了进一步分析凹坑面的减阻效果及减阻机理,对具有凹坑变间隔排列非光滑面在空气介质不同速度下的流场进行数值仿真计算。结果表明,模型9(r=0.5s=h=0.25mm,a=5mm)达到局部最优减阻效果,在来流速度为6m/s时,总减阻量为25.927%。最后分析了间隔对凹坑面减阻影响。间隔长度相对于凹坑面尺寸有个合适数值。

基于漏斗函数双电机伺服系统跟踪与同步控制

针对双电机驱动伺服系统具有未知非线性的问题,提出一种基于漏斗函数的跟踪与同步控制方案。首先,利用神经网络逼近和补偿复杂的非线性,在此基础上,引入滤波技术解决传统反步控制的“计算爆炸”问题,同时引入非光滑漏斗误差面确保系统的状态量被约束在预定义的漏斗边界内,结合改进的漏斗函数和反步设计技术设计了一种自适应量化漏斗跟踪控制方案。为了同时保证双电机的同步运行,同步控制器采用了平均偏差耦合策略,实现了双电机伺服系统的跟踪与同步控制。仿真结果表明,该方法可以实现对负载的跟踪以及双电机的同步。

同时考虑张拉-剪切破坏的边坡稳定性分析

针对目前边坡稳定性分析的强度折减法中广泛采用的Mohr-Coulomb准则仅考虑剪切破坏会过高估计边坡土体的抗拉强度,与实际工程中常见的位于坡体后缘的拉裂缝不符的问题,引入土体的张拉-剪切复合屈服准则,分别采用Mohr-Coulomb准则、Rankine准则考虑剪切、张拉作用的影响;根据张拉-剪切复合屈服准则的非光滑性,通过将非光滑屈服面的塑性本构积分简化为混合互补问题,提出用于弹塑性本构积分的投影收缩算法。结果表明:在分析边坡的稳定性时,不考虑张拉破坏会过高估计边坡的安全性并且安全系数的差值随着坡角的增大而逐渐增大,最大差值达到20%;对于含软弱夹层的分层边坡,即使边坡的坡角较小,是否考虑张拉破坏的边坡后缘的破坏特征仍存在显著区别。

Numerical simulation of effect of bionic V-riblet non-smooth surface on tire anti-hydroplaning

Inspired by the idea that bionic non-smooth surfaces(BNSS) can reduce fluid adhesion and resistance, and the effect of bionic V-riblet non-smooth structure arranged in tire tread pattern grooves surface on anti-hydroplaning performance was investigated by using computational fluid dynamics(CFD). The physical model of the object(model of V-riblet surface distribution, hydroplaning model) and SST k-ω turbulence model were established for numerical analysis of tire hydroplaning. With the help of a orthogonal table L16(45), the parameters of V-riblet structure design compared to the smooth structure were analyzed, and obtained the priority level of the experimental factors as well as the best combination within the scope of the experiment. The simulation results show that V-riblet structure can reduce water flow resistance by disturbing the eddy movement in boundary layers. Then, the preferred type of V-riblet non-smooth structure was arranged on the bottom of tire grooves for hydroplaning performance analysis. The results show that bionic V-riblet non-smooth structure can effectively increase hydroplaning velocity and improve tire anti-hydroplaning performance. Bionic design of tire tread pattern grooves is a good way to promote anti-hydroplaning performance without increasing additional groove space, so that tire grip performance and roll noise are avoided due to grooves space enlargement.

Design of a new bionic diamond bit and its experimental study

Bionics was applied in the design of the impregnated diamond bit. Based on previous resehrch and the 63# bit matrix formula, a new non-smooth bionic impregnated diamond bit with a single circular ring was designed and manufactured, and also tested indoor. The results were satisfactory. During its shape contacted surface system, non-smooth shape display some structure merits such as decreasing resistance. It was obvious that the drilling efficiency of the bionics bit is much higher than that of ordinary＇s one, and so does the working life of bionic bit.

Skin friction reduction characteristics of variable ovoid non-smooth surfaces

The use of bionic non-smooth surfaces is a popular approach for saving energy because of their drag reduction property. Conventional non-smooth structures include riblets and dimples. Inspired by sand dunes, a novel variable ovoid non-smooth structure is proposed in this study. The body of the variable ovoid dimple was designed based on three size parameters, the radius, semimajor, and depth, and a 3D model was created based on UG software. The constructed variable dimples were placed in a rectangular array on the bottom of a square tube model. Following ANSYS meshing, the grid model was imported into FLUENT, where the flow characteristics were calculated. Results of skin friction reduction were achieved and the effect of the design parameters on different variable ovoid dimples was obtained by orthogonal testing. Various aspects of the skin friction reduction mechanism were discussed including the distribution of velocity vectors, variation in boundary layer thickness, and pressure distribution.

Bionic surface design of cemented carbide drill bit

The development of a high-performance cemented carbide drill bit is of great significance to the reduction of rock drilling-cost. The non-smooth features of a biological surface provide an insight into how they can obtain low friction and good wear resistance with evolving surface morphology. By analyzing the mechanism of the surface of a dung beetle for reducing soil wear and adherence, we design a cemented carbide drill bit with a bionic surface, which is expected to have superior anti-wearing and anti-sticking properties for drilling the soft coal seam. Inspired from the characteristics of the head and pronotum surface of the dung beetle, optimized non-smooth surface of the drill bit was constructed. The working performance of this innovative drill was experimentally tested. With comparative experiments under the identical drilling conditions, the wear rates, drilling times of conventional drills and bionic drills were measured. Compared with the conventional counterpart, the drill designed exhibits better performance in reducing wear and sticking drilling-breaks, therefore achieving higher levels of efficiency. The diameter of the dome and pit on the bit surface is in the range of 0.8–1.2 mm, and the bionic drill bits could get better performance with preferable drilling speeds and wear rates.