FORCE ANALYSIS AND DYNAMIC SIMULATION OF THE PLAIN FLOWDISTRIBUTION PAIR IN A RADIALPISTON HYDRAULIC

New design of plain flow distributor of the radial piston low speed hydraulic motor is presented. On the basis of analyzing its static mathematic model and structural optimization, the kinetic characteristics of the distribution plates and the oil film between them are discussed in detail.

Effects of the computational domain on the secondary flow in turbulent plane Couette flow

A series of direct numerical simulations of the fully developed plane Couette flow at a Reynolds number of 6000（based on the relative wall speed and half the channel height h） with different streamwise and spanwise lengths are conducted to investigate the effects of the computational box sizes on the secondary flow（SF）. Our focuses are the number of counter-rotating vortex pairs and its relationship to the statistics of the mean flow and the SF in the small and moderate computational box sizes. Our results show that the number of vortex pairs is sensitive to the computational box size, and so are the slope parameter, the rate of the turbulent kinetic energy contributed by the SF, and the ratio of the kinetic energy of the SF to the total kinetic energy. However, the averaged spanwise width of each counter-rotating vortex pair in the plane Couette flow is found, for the first time, within 4（1 ± 0.25）h despite the domain sizes.

Distribution Performance Analysis and Experimental Research on the Port Plate Pairs of Low Speed High Torque Seawater Hydraulic Motor

The current research of seawater hydraulic motor mainly focused on piston motor and vane motor, but seldom regarded low speed high torque seawater hydraulic motor. Low speed high torque seawater hydraulic motor as a kind of energy conversion device and actuator plays an important role in seawater hydraulic transmission system. However, the physical and chemical properties of seawater, such as low viscosity, high causticity and poor lubrication, result in numerous problems. In this paper, the flow distribution characteristics of port plate pairs for the seawater hydraulic motor are investigated, and the leakage flow and power loss models of port plate pairs are established. Numerical simulations are carried out to examine the effects of water film, inlet pressure and rotating speed on the pressure distribution and leakage flow. And the friction and wear tests of port plate pairs are also carried out. Moreover, the test system of the seawater hydraulic motor is constructed and the performance of prototype with no-load or loading is conducted. The results indicate that the clearance of port plate pairs and inlet pressure have a significant effect on distribution characteristics, but the effect of rotating speed is not very obvious. The experimental results show that the minimum error rate can be maintained within 0.3% by the proposed flow model and the counter materials of 316 L against carbon-fiber-reinforced polyetheretherketone(CFRPEEK) are suitable for the port plate pairs of seawater hydraulic motor. Finally, based on the seawater hydraulic experiment platform, the volumetric efficiency of no-load and loading are obtained that the maximum can achieve 94.71% and 90.14%, respectively. This research work may improve the flow distribution performance, lubrication and the friction and wear properties, enhance energy converting efficiency of port plate pair and provide theoretical and technical support for the design of highperformance water hydraulic components.

Bifurcation and Chaos of Gear Pair System Supported by Long Journal Bearings Based on Turbulent Flow Effect and Nonlinear Suspension Effect

A systematic analysis of the dynamic behavior of a gear-bearing system with nonlinear suspension, turbulent flow effect, long journal bearing approximation, nonlinear oil-film force and nonlinear gear mesh force is performed in the present study. The dynamic orbits of the system are observed by bifurcation diagrams plotted using the dimensionless unbalance coefficient and the dimensionless rotational speed ratio as control parameters. The onset of chaotic motion is identified from the phase diagrams, power spectra, Poincaré maps, Lyapunov exponents and fractal dimension of the gearbearing system. The numerical results reveal that the system exhibits a diverse range of periodic, sub-harmonic, quasiperiodic and chaotic behaviors. The results presented in this study provide some useful insights into the design and development of a gear-bearing system for rotating machinery that operates in highly rotational speed and highly nonlinear regimes.

Debris Flow Hazard Assessment Using Set Pair Analysis Models:Take Beichuan County as an Example

Assessment of debris flow hazards is important for developing measures to mitigate the loss of life and property and to minimize environmental damage. Two modified uncertainty models, Set Pair Analysis （SPA） and modified Set Pair Analysis （mSPA）, were suggested to assess the regional debris flow hazard. A ease study was conducted in seven towns of the Beichuan county, Sichuan Province, China, to test and compare the application of these two models in debris flow hazard assessment. The results showed that mSPA only can fit for value-variables, but not for non value-variable assessment indexes, Furthermore, as for a given assessment index xi, mSPA only considers two cases, namely, when grade value increases with xi and when grade value decreases with xi. Thus, mSPA can not be used for debris flow hazard assessment but SPA is credible for the assessment because there are no limitations when using SPA model to assess the debris flow hazard. Therefore, in this study SPA is proposed for assessing debris flow hazard.

Analysis of force and leakage in water hydraulic motor's piston pairs

The positive pressure between pistonwall and piston hole of inner curve water hydraulic motor’s piston pairs is analyzed.The flow field of the piston pairs is numerically calculated and analyzed by the use of computational fluid dynamics method.The pressure and velocity distribution of flow field at different clearance is analyzed in the paper.The results show that when the clearance is 4-8 μm,with the increase of clearance,the negative pressure and the velocity of piston chamber decrease significantly,the velocity and leakage flow of the clearance increase.However,when the clearance is 10 μm,the negative pressure and the velocity of plunger chamber increase suddenly.By comprehensive analysis,the cylinder annular clearance should be controlled to be near 8 μm.

Probabilistic Optimal Power Flow Considering the Dependence of Multiple Wind Farms Using Pair Diffusive Kernel Copula

As wind farms are commonly installed in areas with abundant wind resources,spatial dependence of wind speed among nearby wind farms should be considered when modeling a power system with large-scale wind power.In this paper,a novel bivariate non-parametric copula,and a bivariate diffusive kernel(BDK)copula are proposed to formulate the dependence between random variables.BDK copula is then applied to higher dimension using the pair-copula method and is named as pair diffusive kernel(PDK)copula,offering flexibility to formulate the complicated dependent structure of multiple random variables.Also,a quasi-Monte Carlo method is elaborated in the sampling procedure based on the combination of the Sobol sequence and the Rosen-blatt transformation of the PDK copula,to generate correlated wind speed samples.The proposed method is applied to solve probabilistic optimal power flow(POPF)problems.The effectiveness of the BDK copula is validated in copula definitions.Then,three different data sets are used in various goodness-of-fit tests to verify the superior performance of the PDK copula,which facilitates in formulating the dependence structure of wind speeds at different wind farms.Furthermore,samples obtained from the PDK copula are used to solve POPF problems,which are modeled on three modified IEEE 57-bus power systems.Compared to the Gaussian,T,and parametric-pair copulas,the results obtained from the PDK copula are superior in formulating the complicated dependence,thus solving POPF problems.

基于Pair Copula的随机潮流三点估计法

现有Copula等方法难以对多维风电功率准确建模,且传统的点估计法无法直接应用于风电功率具有相关性的场合。针对这一问题,提出基于Pair Copula和概率积分变换的随机潮流点估计法。首先采用Pair Copula对多维风电功率进行建模,然后使用点估计法在独立正态概率空间中采样,最后,依据概率积分变换,把采样点变换到实际风电功率的概率空间中进行潮流计算,从而使点估计法能够处理具有任意概率分布的多维风电功率。对澳大利亚多个风电场出力样本的建模和分析验证了Pair Copula模型的优越性,基于IEEE 118节点系统的算例验证了所提方法的有效性。

外负载对径向柱塞泵滑靴副流场特征和强度的影响

针对高压大排量径向柱塞泵在重载领域出现的滑靴副失效问题,在考虑油液黏温黏压特性的基础上,对滑靴副流体域展开数值计算和流固耦合仿真分析,探讨外负载对滑靴副流体域压力、流速、泄漏以及滑靴结构强度的影响。结果表明:当外负载从1.1×10^(8)N增加到1.2×10^(8)N时,吸油区滑靴副流体域的压力分布和数值基本不变,排油区滑靴副中心油腔压力增大1.5 MPa,流体域油膜的高压区面积增大,油液压力增大了0.05 MPa,油液流速稍有增加;滑靴副油液泄漏主要位于滑靴副边界处,高、低阻尼孔泄漏较小,随着外负载的增大,3处泄漏量都增大,单个滑靴副总泄漏量增大0.05 mL/s;外负载对滑靴强度影响较小,在排油区滑靴最大应力与变形发生在中心油腔处,此处是滑靴结构强度较为薄弱的地方。

轴向柱塞泵配流副油膜润滑及结构优化研究综述

在轴向柱塞泵中,配流副是最容易出现流量脉动和磨损失效的关键部件之一。分别研究油膜润滑、结构参数和液体性质等因素对轴向柱塞泵配流副性能的影响,重点总结归纳轴向柱塞泵配流副油膜润滑和结构优化的研究进展,提出改善配流副性能的规律和方法。最后对轴向柱塞泵配流副领域未来研究方向进行了总结与展望。

配合间隙对柱塞-滑靴组件动力学及油膜润滑特性的影响

球铰副油膜对轴向柱塞泵工作性能和稳定性具有重要影响,其润滑行为受滑靴和柱塞多自由度动力学行为影响。该研究分析配合间隙对振动响应和油膜润滑特性的影响,建立了滑靴和柱塞多自由度运动与球铰副油膜润滑行为耦合的动力学模型。首先,使用拉格朗日法对滑靴和柱塞的动力学方程进行推导,通过NewMark-β法求解滑靴和柱塞的振动响应;然后,根据滑靴和柱塞的姿态变化结合雷诺方程建立球铰副油膜厚度场-压力场耦合模型;最后,分析在不同配合间隙下滑靴和柱塞的振动响应及油膜润滑特性的变化规律。研究结果表明,配合间隙对滑靴和柱塞的振动响应及球铰副油膜润滑特性的影响显著,适当减小配合间隙可减少泵的泄漏,从而提高整体效率。

表面织构对微型轴向柱塞泵滑靴副摩擦学性能的影响研究

为减小微型轴向柱塞泵滑靴副的摩擦因数并提高油膜润滑性能,在滑靴底部设计椭圆微织构,建立滑靴副几何模型,并采取流场仿真对滑靴底部的油膜压力场以及剪切场进行求解分析,发现采取微织构能够减小滑靴底部的摩擦因数。为了进一步增强动压效应的作用,提升支承力并减小摩擦因数,通过Design-Expert响应面分析设计实验水平表进行计算分析,以泄漏量最小、支承力最大及摩擦因数最小为目标函数建立数学模型,最终得到微织构的优化尺寸。优化后滑靴副的油膜润滑性能得到提高,优化后的参数可作为柱塞泵结构优化的依据。

WAKE PATTERNS OF FLOW PAST A PAIR OF CIRCULAR CYLINDERS IN SIDE-BY-SIDE ARRANGEMENTS AT LOW REYNOLDS NUMBERS

A flow past two side-by-side identical circular cylinders was numerically investigated with the unstructured spectral element method. From the computational results at various non-dimensional distances between cylinder centers T/D and the Reynolds number Re, a total of nine kinds of wake patterns were observed： four steady wake patterns, including single bluff-body steady pattern, separated double-body steady pattern and transition steady pattern for sub-critical Reynolds numbers and biased steady pattern for super-critical Reynolds numbers, and five unsteady wake patterns, including single bluff-body periodic pattern, biased quasi-steady pattern, quasi-periodic （flip-flopping） pattern, in-phase-synchronized pattern and anti-phase-synchronized pattern. Time evolution of lift and drag coefficients corresponding to each unsteady wake pattern was given.

基于多目标粒子群算法的配流副结构优化设计

由于柱塞泵配流副的结构相对复杂,传统的试凑法不仅会加长设计周期,且难以获得最佳结构参数。为兼顾配流副多项性能指标,以某轴向柱塞泵端面配流副作为研究对象,建立端面配流副结构的数学模型,利用自适应网格与拥挤距离的多目标粒子群算法对模型求解。结果表明:算法的目标函数均保持良好的收敛性和全局适应性,定义的配流副参数变量能找到Pareto最优解,同时维持了解集良好的分布性,提高了结构优化设计的效率;优化后的配流副油膜刚度增大,且在不同油膜厚度与供油压力下,优化后的配流副泄漏流量比优化前降低8.6%左右,验证了模型和算法的适用性与优越性。

区域粮食虚拟水流动经济社会影响效应分析

虚拟水流动是水资源在空间上再分配的一种重要表现形式,作为虚拟水的载体,粮食贸易运输过程中伴随着虚拟水的流动。中国人口和资源与粮食生产呈现明显的空间错位,虚拟水流动格局、水土资源分布、经济社会发展情况的空间匹配度较差。在现阶段虚拟水-实体水耦合分析探究粮食虚拟水流动资源环境效应的基础上,增添其对经济社会的影响效应分析,可以进一步优化资源调配,促进区域可持续发展。本研究以中国内地31省份为研究区,以省级行政区划为研究单元,分析了1997—2021年间粮食虚拟水流动的时空演变格局;通过空间聚类分析以及虚拟水-经济社会化数据耦合分析明确了粮食虚拟水调运的空间聚类情况,解析了主要输入和输出省份粮食虚拟水的调运量与经济社会发展的相关关系;选取9个主要经济社会影响因子,将灰色关联度和集对分析方法结合探讨了经济社会影响因子对粮食虚拟水流动影响效应的空间差异。结果表明:粮食虚拟水流动总体呈现从“缺水”的北方流向“富水”的东南区域,从经济欠发达地区流向经济发达地区的趋势,且经济社会系统在一定程度上影响了粮食虚拟水的流动。根据经济社会因子对不同省份粮食虚拟水流动的影响效应,将各省份粮食虚拟水流动的经济社会关联类型划分为产业关联型、社会关联型和资源关联型。综上,促进区域间协调发展与产业结构优化将是解决我国粮食虚拟水流动伴生的自然环境与经济社会负反馈效应的重要解决途径。

新型无困油齿轮泵齿轮副型线优化与工作过程模拟

齿轮泵齿轮副的型线对齿轮泵性能影响极大。传统的渐开线型齿轮泵齿轮存在困油现象,产生局部高压,对其运行产生极大的危害。通过型线设计,来解决齿轮泵困油现象。基于曲线啮合理论,采用圆弧和高次曲线,构建一种新型双圆弧-高次曲线齿轮副,消除了齿轮泵的困油现象。进而,建立其几何模型并推导出型线方程,通过数值模拟,分析新型无困油齿轮泵的流场变化规律,并与现有齿轮泵进行对比。结果表明:新型齿轮泵消除了困油现象,型线组成简单,便于优化设计;此外,新型齿轮泵的工作性能更佳,流场更均匀。

Planar laser scattering visualization of streamwise vortex pairs in a Mach 6 flow

A series of cross-sectional flow fields of Counterrotating Vortex Pairs(CVPs) generated by a large-scale ramp vortex generator is observed using an ice-cluster-based Planar Laser Scattering(PLS) method in a shock tunnel with a nominal flow Mach number of 6. Combined with a numerical simulation, two streamwise CVPs with opposite rotating directions are identified in the wake flow of the vortex generator with an absence of a boundary layer, namely, a Primary CVP(PCVP) and a Secondary CVP(SCVP). The wake flow is divided into two stages with different features of the PCVP and SCVP. In Stage Ⅰ, the PCVP and SCVP gradually mature, and the flow is relatively stable. In Stage Ⅱ, the PCVP and SCVP depart from each other, and the flow becomes unstable. The profiles of the transverse velocity in the spanwise symmetry plane induced by the PCVP and SCVP do not obey the scaling law of CVPs immersed in the boundary layer. A new scaling law is proposed, in which the transverse distances between adjacent saddle points in the cross-sectional flow field are used as the characteristic lengths for the PCVP and SCVP. After this new scaling procedure, the profiles of transverse velocity induced by the PCVP and SCVP at different streamwise locations collapse well. Moreover, the PLS images show that the mixing between the CVPs and the outside high-momentum flow becomes evident at approximately 5.5 times the height of the vortex generator, which is earlier than that immersed in the boundary layer. These findings enrich the knowledge of CVPs in the hypersonic regime, especially in the absence of the boundary layer.

复杂光照条件下基于光流的水运航道流速检测算法

实时准确的河流表面流速数据是现代化水运调度和防洪的重要依据,但传统的仪器测速法大多需要人工实地参与,危险系数高且无法满足大规模系统部署的要求。相比之下,图像测速法不需要直接接触河流,可以依据摄相机获取的连续帧得到近乎实时的速度信息。然而,光流估计作为当前主流的图像测速法,是针对刚体运动提出的,没有考虑流体本身的性质,在河流表面等相似度高的场景中泛化能力较弱。为提高基于光流估计循环全对场变换(RAFT)模型的水流流速算法估算精度,提出一种改进的光流估计测速方法。在特征提取部分增加卷积块注意力模块(CBAM),增强其对河流表面波纹和示踪粒子运动的识别能力。通过优化光流迭代更新部分的损失函数,引入能体现流体运动特征的角误差损失和旋度散度平滑损失,并且为损失函数匹配随迭代次数呈指数增长的权重因子,突出高次迭代结果对于整体结果的显著影响。为验证改进方法的有效性,使用不同场景河流数据集对其进行性能评估,结果表明,该方法在复杂光学噪声场景下的平均相对误差为11.37%,具有较好的鲁棒性,能够生成更精准的表面速度空间分布图。

双扭线流量管测量方法数值研究

围绕双扭线流量管测量方法中,测量截面静压不均匀和附面层修正方法两个影响因素,采用数值仿真的方法模拟了双扭线流量管试验测量,分析了测量截面静压不均匀和附面层修正方法对流量测量的影响。结果表明:静压测量截面距离双扭线切点越近,测量截面静压不均匀性对主流区流量计算偏差的影响越大,可通过建立静压关联关系式进行修正;试验中采用积分法计算附面层流量时,近壁区速度分布与线性分布存在差异,导致第1个测点与壁面间区域积分流量存在偏差,可按指数分布规律重构近壁区速度进行修正。

基于SNA的西安入境旅游市场“倒二八”结构研究

通过构建西安与国内主要旅游城市之间的入境旅游流关系网络,应用社会网络分析法,从整体和宏观联系的视角,研究西安与国内主要旅游城市之间的入境旅游流关系,从中揭示西安入境旅游市场"倒二八"结构的成因,提出尽快提高西安的航空可达性,借机世园会撬动港澳台市场,与桂林、成都、昆明等西部城市联合开拓入境旅游市场等扭转西安"倒二八"入境旅游市场结构的建议,为破解西安入境旅游市场"倒二八"结构难题、拓展西安入境旅游市场提供理论指导。