Improved Computational Model of Grid Cells Based on Column Structure

To simulate the firing pattern of biological grid cells,this paper presents an improved computational model of grid cells based on column structure.In this model,the displacement along different directions is processed by modulus operation,and the obtained remainder is associated with firing rate of grid cell.Compared with the original model,the improved parts include that:the base of modulus operation is changed,and the firing rate in firing field is encoded by Gaussian-like function.Simulation validates that the firing pattern generated by the improved computational model is more consistent with biological characteristic than original model.Besides,the firing pattern is badly influenced by the cumulative positioning error,but the computational model can also generate the regularly hexagonal firing pattern when the real-time positioning results are modified.

Biologically inspired model of path integration based on head direction cells and grid cells

Some neurons in the brain of freely moving rodents show special firing pattern. The firing of head direction cells(HDCs) and grid cells(GCs) is related to the moving direction and distance, respectively. Thus, it is considered that these cells play an important role in the rodents' path integration. To provide a bionic approach for the vehicle to achieve path integration, we present a biologically inspired model of path integration based on the firing characteristics of HDCs and GCs. The detailed implementation process of this model is discussed. Besides, the proposed model is realized by simulation, and the path integration performance is analyzed under different conditions. Simulations validate that the proposed model is effective and stable.

ADAPTIVE LAYERED CARTESIAN CUT CELL METHOD FOR THE UNSTRUCTURED HEXAHEDRAL GRIDS GENERATION

Adaptive layered Cartesian cut cell method is presented to solve the difficulty of the tmstructured hexahedral anisotropic Cartesian grids generation from the complex CAD model. ＂Vertex merging algorithm based on relaxed AVL tree is investigated to construct topological structure for stereo lithography （STL） files, and a topology-based self-adaptive layered slicing algorithm with special features control strategy is brought forward. With the help of convex hull, a new points-in-polygon method is employed to improve the Cartesian cut cell method. By integrating the self-adaptive layered slicing algorithm and the improved Cartesian cut cell method, the adaptive layered Cartesian cut cell method gains the volume data of the complex CAD model in STL file and generates the unstructured hexahedral anisotropic Cartesian grids.

Electrochemical Machining Analysis on Grid Cathode Composed of Square Cells

During the electrochemical machining (ECM), the cathodes designed by the existing methods are mainly unitary cathodes, which can be only used to produce the workpieces with the same shapes. However, there are few researches on designing cathodes for machining the different workpieces with the different surfaces. This paper presents the grid cathode composed of the square cells to produce the workpieces with different shapes. Three types of the square cells, 2.5 mm′2.5 mm, 3 mm′3 mm, and 4 mm′4 mm, are utilized to construct the plane, the slant, and the blade cathode. The material of the cathode and the anode is CrNi 18 Ti 9 , and the ingredient of electrolyte is 15% NaCl and 15% NaNO 3 . The machining equilibrium machining current and time are acquired and analyzed, the machining process and the workpiece quality are compared between using the grid cathode and the unitary cathode. Moreover, the machining errors on the workpiece surface are measured and analyzed, and the error reasons are traced and discussed to obtain the better surface quality of the workpiece. The experiment and analysis results show that the grid cathode can be used to manufacture the workpieces with complex shapes in certain range of the error. The workpiece quality improves with the size of the square cell being reduced, and if the square element is small enough, the workpiece quality is almost equal to the one machined by the unitary cathode. The proposed research realizes a single cathode machining the different workpieces with the different surfaces.

Cartesian Grid Method with Cut Cell in the Mold Filling Simulation

In this paper, a Cartesian grid method with cut cell has been developed to simulate mold filling of casting process. Cut cells at the cast-mold interface are generated on the Cartesian grid. With the boundary cut cells, a special treatment is necessary. That is Cartesian grid method with cut cell. A simple shape was tested and the cut cell method was compared with the traditional one on Cartesian grids. And, a developed method was applied to the real casting product simulation. Cartesian grid system causes momentum loss and unsound fluid flow patterns because of inaccurate generation of meshes. These problems have been improved by using cut cell method.

Hydrogen Smart-Grids: Smart Metering of Electricity from Hydrogen Fuel Cells

In the last decade, increasing applications of information technology (IT) within power industry has become a significant reality. As distributed power networks are gaining importance and renewables are getting a bigger ratio within energy production, Smart Grid applications have become essential, especially due to the intermittent nature of renewable energy resources. Smart Grid is a sustainable energy system that measures, checks, and controls the generation, transmission, and consumption of electrical energy in grids on all voltage levels. Smart Grid experts are driving forward the development of effective communication and information technologies for the build-up of intelligent power supply networks. Examples of these are control systems for the realization of virtual power plants, intelligent consumer data acquisition systems, and smart distribution management systems. Fuel cell-based hydrogen electricity, in comparison to other renewable energy sources, is more stable and predictable. Yet hydrogen power and smart-grids have many application points, mainly as means of energy storage. This study claims that hydrogen energy and smart-grids could also engage through an appliance of IT managed metering of hydrogen power production. Smart metering and management of hydrogen fuel cells would enable advanced planning of short-to-mid-term power productions and thus foster use of hydrogen power within distributed networks, as local community or industrial applications.

处理地下水模型单元疏干-湿润的两种算法对比研究

在使用网格单元中心差分格式的地下水模型中,对地下水网格单元“疏干(干)-湿润(湿)转化”的模拟极易引发模型迭代不收敛等异常情况,很大程度上影响模型的应用。本研究使用理想案例和丹麦应用实例,综合比较了MODFLOW模型的试算法与COMUS模型的全有效单元法对网格单元“干-湿转化”问题的模拟能力及算法特性。结果表明:(1)试算法的参数组合选取对模拟的收敛性和模拟结果都有明显影响,使用试算法时需要不断优化参数组合以避免模型迭代不收敛或模拟失真等异常情况,很大程度上增加了用户使用模型的难度和时间成本;(2)全有效单元法的模拟结果比试算法的模拟结果更具可靠性,全有效单元法的作用等同于理论上最优的试算法参数组合,使用全有效单元法时用户无需进行复杂的参数组合工作,因此该方法能有效降低模型的使用难度与模拟结果的不确定性;(3)全有效单元法中单元间水平向水力传导度算法实现了可以与经典调和平均法相比较的数值计算精度,说明全有效单元法在不涉及网格单元“干-湿转化”问题的地下水模拟中同样具有应用潜力。综上所述,全有效单元法更适用于处理地下水模型单元的疏干-湿润转化问题,并且有望在地下水数值模拟领域中得到更为广泛的应用。

基于Voronoicells的二维不规则自适应网格的生成及其应用

基于 Voronoi cells的数据结构和算法 ,给出了一种二维不规则自适应网格的生成方法 ,用 VisualC+ +语言在微机上开发了 Windows环境下网格自动生成的可视化软件。既可以得到 Voronoi cells网格 ,也可得到相应的 Delaunay triangles网格 ,网格生成的实例表明 ,本文方法所得到的网格非常适合于多尺度系统的流动问题的计算 。

用于高功率微波器件粒子模拟的三维柱坐标系共形网格生成技术

基于面向对象的C++语言研制三维柱坐标共形网格生成程序,对束-场互作用器件作共形网格剖分,为粒子模拟算法提供积分线元、面元。通过定义三维柱坐标网格体系如网格步长、网格索引、守护网格层、包围盒等数据,使模型的空间信息能转换成柱坐标网格信息。将轴上网格单元作特殊处理,使粒子模拟算法形式在轴上网格和在非轴上网格上保持一致。利用射线跟踪法得到属于模型子面、模型棱边的离散边界点,接着通过拓扑关系获得模型的顶点,保存上述三类离散边界点的拓扑信息和网格信息。将构建的基础网格元与边界点信息耦合,在离散网格体系中重构模型。用该共形网格剖分技术对相对论磁控管进行剖分,能够识别该磁控管的透明阴极、阳极和谐振腔等结构。

笛卡尔网格下不同湍流模型的壁面函数方法研究

自适应笛卡尔网格湍流模拟时,网格数目呈雷诺数的指数方量级增长,带来网格规模“灾难”问题。壁面函数方法可以将壁面第一层网格尺度放宽1~2个量级,是有效的解决办法之一,然而,由于笛卡尔网格的非贴体特性,壁面函数的实现及其与不同湍流模型的匹配是关键。针对这一问题,从经典的Spalding壁面函数出发,采用显式赋初值的方式,解决了壁面摩擦速度迭代求解初值敏感及分层壁面函数速度不光滑问题;基于切应力恒定的壁面条件,构造了多层虚拟网格的切向速度和湍流粘性系数,实现了笛卡尔网格下的壁面函数方法;采用结构系综理论,通过DNS数据标定,构造了湍动能随湍流粘性比率变化的关系式,实现了壁面函数与KDO湍流模型的匹配,并以平板T3b、湍流凸包和跨音速NACA0012翼型绕流为算例,与常用的SST、SA湍流模型壁面函数方法进行了对比分析。结果表明:该文提出的KDO湍流模型壁面函数法准确、可靠,且因其形式简单、计算量相对较小,有较大的推广应用价值。

自适应笛卡尔网格Ghost Cell方法研究

在笛卡尔网格中,利用Ghost Cell方法处理浸入边界,模拟二维无粘可压缩流。针对静止物体,比较了各种不同的Ghost Cell边界条件下的熵误差,总压误差,以及阻力系数。此外为提高激波分辨率,将Ghost Cell方法与基于叉树结构的自适应笛卡尔网格算法相结合,数值结果显示本文的方法是切实可行的。

基于大脑海马认知机理的主从式AUV协同定位方法

针对AUV协同定位系统中水声测距信息存在大量野值的问题,提出一种基于哺乳动物大脑海马体空间细胞认知机理启发的主从式AUV协同定位方法。首先,利用二维连续吸引子网络模型对网格细胞进行建模,并基于从艇速度与航向信息实现路径积分;其次,引入竞争性Hebb网络对多个网格细胞板自组织编码,从而基于多尺度网格细胞板加权生成具有单个放电活动包的位置细胞板;最后,将主从艇之间的水声测距量测信息转化为位置细胞放电活动,并利用其对位置细胞放电进行更新,从而校正从艇路径积分累积误差。由于位置细胞能够通过多次放电更新逐渐逼近真实位置,从而可以有效降低单一量测野值对于系统定位精度的影响。仿真实验结果表明,在水声测距量测噪声含有大量野值点而不满足高斯分布的情况下,所提出的类脑协同定位算法对量测噪声野值具有更高的鲁棒性,与有阈值判断的扩展卡尔曼滤波(EKF)协同定位算法相比定位精度提高28%。

自适应权重优化的树突状细胞算法

树突状细胞算法是人工免疫系统中先天免疫层的经典算法,该算法通过融合危险和安全信号发现异常。但树突状细胞算法在信号权重的取值上常需要根据数据特征手动设置,削弱了算法的自适应性。针对这一问题,引入了网格搜索法,在给定的权重范围内根据识别效果自动调整权重取值,得到适应不同类型和规模数据集的信号权重组合。在多个公开数据集上的实验结果表明自适应权重优化的树突状细胞算法能根据数据集特征自适应训练得到较合理的权重矩阵,减少了人工经验对算法准确率的影响,改进后的算法识别准确率、真阳性率等均高于原树突状细胞算法,并优于同类算法。

高速铁路建设网格化管理体系研究与应用

针对我国铁路工程建设项目规模不断扩大、工程复杂程度和安全风险越来越高等问题,基于网格化管理概念与方法,提出一套较为完整的高速铁路建设网格化管理体系。根据陕西省高铁建设工程的特点,借鉴较为成熟的社区网格化管理模式,将高铁建设工程以标段为独立体划分为若干个网格单元,通过硬件设施配备和软件制度机制建立,实时实地掌握和控制工程施工现场安全情况,有效进行施工安全管理。实践结果表明,通过建立健全现场网格化管理体系,以网格为单位,设置专人或充分利用作业队伍骨干力量,分片包干、专人管理,同时将劳务工驻地纳入网格化管理范畴,实行社区化管理,在陕西省高铁建设工程中取得了较好应用效果。最终得出将网格化管理应用于高铁建设工程中是可行的,陕西省高铁建设网格化管理实践可为其他铁路、公路和类似土建工程项目提供借鉴和参考。

构网型风氢耦合系统电解槽轮值优化控制

针对制氢电解槽阵列能量分配效率偏低的问题,文中结合电解槽自身物理特性和整体系统要求,分析电解槽阵列输入功率与效率的耦合关系。构建多电解槽阵列的效率函数和约束条件,通过拉格朗日函数将其转化为无约束问题,以实现电解槽阵列功率自适应分配的控制,保证系统处于最优工作状态。在最优工作状态进行电解槽阵列轮值优化控制策略,提高电解槽的使用寿命。考虑风电功率波动情况,提出构网型直驱风电机组,提高并网点的电压和频率稳定性。最后通过MATLAB/Simulink搭建的风氢耦合模型进行验证,与传统能量分配方式相比,该方法可以明显提升电解槽阵列协调工作效率,同时也增加了电解槽的使用寿命,为风电的大规模制氢提供了有效途径。

面向皮肤组织工程支架的三维多孔点阵结构制备及拉伸特性研究

数字光处理(Digital Light Process,DLP)成型方法具有成型速度快、成型精度高的特点,能够较好用于微小尺寸结构的制备。因此,设计了一种以人工拓扑优化的正方体网格为单胞,并将该单胞沿空间进行周期性扩展,获得新型三维多孔点阵结构。配制了一种具有柔弹性的光敏树脂,选择DLP成型法进行实验制备。探究了DLP打印对该点阵结构成型的影响因素和成型效果,制备出了结构完整、无淤塞的样品,并通过该结构样品的单轴拉伸实验,研究其拉伸力学性能。结果表明,DLP打印所制备的该新型多孔结构,其内部孔隙清晰、连通性好,且孔隙率均达到了80%以上,拉伸断裂伸长率也均在85.6%以上,其中点阵结构3的拉伸韧性最大,其综合拉伸特性最优。该结构可广泛应用于皮肤组织工程支架、柔性电极、易碎品装夹夹具等。

基于细菌避障策略的无人艇集群自主巡航方法

针对无人艇集群执行巡航任务中的避障问题,提出了一种动态避障算法。首先,获取无人艇周边水域的方形网格轨迹单元态势矩阵;然后,借鉴细菌游走觅食原理,在方形网格轨迹单元集合中,动态匹配最佳避障路径;最后,在动态避障基础上,将无人艇自主巡航过程划分为向目标行进、动态避障、返航补给等阶段,实现无人艇集群对划定水域的常态化巡航。仿真实验结果表明,所提方法对静态点、面障碍以及移动障碍均具有高效的规避能力,在算法基础上,能够实现无人艇集群的常态化无人值守巡航。该算法不仅适合无人艇的避障问题,在其他异构无人装备中也具有广阔的应用前景。

不同工况下光储氢微网系统协调控制策略

针对光储氢微网系统运行时系统内部功率协调分配、切换平滑度以及电压稳定性等问题,提出一种考虑系统不同需求指令的功率分层协调运行策略。以提升系统稳定性、光氢系统结合度以及平滑运行为目的,搭建光储氢微网系统仿真模型,一方面,通过分层控制实现系统指令层与被控层之间的协调运行,并以上网电价为判断指标,保障系统经济性运行;另一方面,基于系统运行模式将系统运行工况分为8种,并通过多功率协调控制策略使得光储氢微网系统能够稳定运行、工况切换平滑以及母线电压稳定。最后通过仿真验证所建模型与控制策略的正确性与有效性。

栅元格架对5×5燃料组件轴向交混系数分布的影响

提高燃料组件轴向温度分布计算的精确性,有利于准确预测CHF点的发生位置,而交混系数对轴向温度分布准确计算具有重要影响。本研究采用数值模拟结合子通道分析程序的方法,对装配栅元格架的5×5燃料组件轴向不同位置处的流动交混进行研究。对栅元格架建立几何模型,选取SST湍流模型进行计算,完成网格敏感性分析,在额定工况下得到轴向不同位置的子通道温度分布。将子通道分析程序计算值与数值模拟实验值相结合,共同确定装配栅元格架的燃料组件轴向不同位置的交混系数。计算结果表明:在加热段前端,交混系数明显比光棒束段相同位置要高,后随着栅元格架的影响减弱,交混系数随轴向的变化同光棒束段相同。

电化学脱合金Ti6Al4V基台对人牙龈成纤维细胞的影响

目的探讨电化学脱合金Ti6Al4V基台对人牙龈成纤维细胞(human gingival fibroblasts,HGFs)的影响,为种植基台表面改性设计提供实验依据。方法根据试样不同表面进行分组:NC组(阴性对照,光滑表面无其他处理)、NM-1组(纳米网-1,1 mol/L NaOH电化学脱合金处理1 h,电压2 V)、NM-2组(纳米网-2,5 mol/L NaOH电化学脱合金处理1 h,电压2 V)。扫描电镜(scanning electron microscopy,SEM)观察不同试样表面形貌及HGFs在其表面的黏附状态,接触角测量仪测定试样表面亲水性。CCK-8评估HGFs在不同试样表面的增殖情况;qRT-PCR检测HGFs在不同试样表面Ⅰ型胶原(collagenⅠ,COL1A1)、Ⅲ型胶原(collagenⅢ,COL3A1)、纤连蛋白1(fibronectin 1,FN1)、黏着斑激酶(focal adhesion kinase,FAK)、黏着斑蛋白(vinculin,VCL)、整合素α2(integrinα2,ITGA2)、整合素β1(integrinβ1,ITGB1)等黏附相关基因表达水平;免疫荧光染色,激光共聚焦显微镜(confocal laser scanning microscope,CLSM)观察HGFs在不同试样表面vinculin蛋白表达情况;天狼猩红染色评价HGFs在不同试样表面胶原纤维分泌合成情况。结果SEM观察到NM-1组和NM-2组表面形成有序均一的三维网状结构,网格直径NM-1组约为30 nm,NM-2组约为150 nm;NM-1组和NM-2组对比NC组,水接触角显著下降(P<0.0001);NM-1组细胞增殖能力较NC组显著提高(P<0.01),NM-1组和NM-2组的水接触角及细胞增殖能力差异无统计学意义(P>0.05)。SEM镜下可见HGFs黏附24 h后在各组试样表面均黏附良好,NM-1组和NM-2组细胞与NC组对比伸展面积更大,形态纤长,细胞伪足更发达。qRTPCR结果显示NM-1组中COL1A1、COL3A1、FN1、FAK、VCL等黏附相关基因表达水平显著高于NC组和NM-2组(P<0.01)。vinculin蛋白免疫荧光结果表明,NM-1组vinculin蛋白表达水平最高,单个细胞黏着斑数量最多(P<0.01)。天狼猩红染色结果显示NM-1组胶原纤维分泌合成量最高(P<0.0001)。结论Ti6Al4V经电化学脱合金改性后所构建的三维纳米网状结构有促进HGFs黏附增殖和胶原分泌合成的作用,其中网格直径约为30 nm的NM-1组对HGFs的促进作用明显。