Feature study of body-fitted Cartesian grids used in casting numerical simulation

A type of mesh called a body-fi tted Cartesian mesh,very different from the traditional structured body-fi tted mesh,is established.At f irst,the right parallelepiped mesh is generated,then,a feature analysis is done on the cross sections.These cross sections are the intersections of the casting shape with the right parallelepiped grids(under the Cartesian coordinate system).On the basis of the feature analysis,two sorts of body-f itted boundary grids,shape-keeping grids and shape-distortion grids,are def ined.Shape-distortion grids can be removed or weaken by increasing the number of grids or moving the coordinates of the mesh generation region,so actually the body-fitted Cartesian mesh generation is to get shape-keeping grids.A shape-keeping grid mainly consists of two sorts of surfaces(I type face and II type face),and each of them is joined by two types of points(I type point and II type point).If only these two types of points were given,the shape-keeping mesh would be constructed.In this paper,the cases of the above two boundary grids being generated were discussed.An algorithm was put forward to get the shape-keeping grids.Several body-fi tted Cartesian meshes generated on castings show the validity of the algorithm.The mesh generation examples show that the body-fi tted Cartesian mesh is more excellent than the right parallelepiped mesh in aspects of decreasing grids number and being closer to the shape of the casting solid.

Comparative Analysis of Equal and Unequal Grounding Grid Configurations by Compression Ratio and Least Square Curve Fitting Techniques

The primary aim of the power system grounding is to safeguard the person and satisfying the performance of the power systemtomaintain reliable operation.With equal conductor spacing grounding grid design,the distribution of the current in the grid is not uniform.Hence,unequal grid conductor span in which grid conductors are concentrated more at the periphery is safer to practice than equal spacing.This paper presents the comparative analysis of two novel techniques that create unequal spacing among the grid conductors:the least-square curve fitting technique and the compression ratio techniquewith equal grid configuration for both square and rectangular grids.Particle Swarm Optimization(PSO)is adopted for finding out one optimal feasible solution among many feasible solutions of equal grid configuration for both square and rectangular grids.Comparative analysis is also carried out between square and rectangular grids using the least square curve fitting technique as it results in only one unequal grid configuration.Simulation results are obtained by theMATLAB software developed.Percentage of improvement in ground potential rise,step voltage,touch voltage,and grid resistancewith variation in compression ratios are plotted.

Numerical Simulation of Flow Field in Tidal Estuary Using Body-Fitted Coordinate System

On the basis of the physical mechanism, a body-fitted coordinate system is developed. By using this system the boundaries in simulation and in real are fitted well, and simulation with great accuracy is achieved. A computation example indicates that compared to traditional two-dimensional computation methods, the body-fitted simulation has an advantange of better coincidence with the real and can be adopted in simulating flow fields in tidal estuaries.

Numerical Tidal Current Modeling Using Fine Boundary-Fitted Grids for Tidal Flats

Fine grids with small spacing in boundary-fitted coordinates are normally used to treat the computation of fluid dynamics for estuarine areas and tidal flats. However, the adoption of Cartesian components of velocity vectors in this kind of non-orthogonal coordinates will definitely result in a difficulty in solving implicitly the transformed momentum equations, and also complicate the wet-dry point judgement used for flood areas. To solve this problem, equations in terms of generalized contravariant velocity vectors in curvilinear coordinates are derived in the present study, by virtue of which, an Alternative-Direction-Implicit numerical scheme in non-orthogonal grids would then be easily obtained, and wet-dry point judgement would as well be largely simplified. A comparison is made between the explicit scheme and implicit scheme, showing that the present model is accurate and numerically stable for computations of fluid dynamics for estuarine areas and tidal flats.

Body-Fitted Momentum Source Method for Predicting Rotor Aerodynamics Characteristics in Hover

To gain high efficiency for the simulation of the aerodynamic characteristics of the rotor in hover,body?fitted momentum source(BFMS)method is proposed.In this method,the actual blade geometry is represented by the single layer of volume grid surrounding the blade.Aiming at correctly simulating the aerodynamic characteristics of the discrete cells along the chordwise of blade airfoil section,a new distributed force model is proposed.For comparison,the RANS method with S?A turbulence model and the steady rotor momentum source(SRMS)method based on embedded grid systems are established,respectively.And the grid connecting methodology is improved to embed the blade into the background grids for the three methods.Then,simulations are performed for the hovering Caradonna?Tung rotor by these methods,and the calculated results are compared with the available experimental data.Moreover,the pressure distributions along the blade are compared with the conventional momentum source methods.It is demonstrated that the BFMS method can be employed as an effective approach to predict rotor aerodynamic characteristics with a low computational resource and reasonable accuracy.

Modelling Three-Dimensional Winds on a NW Pacific Region of Mexico Using Boundary-Fitted Grids

In this study, the momentum equations describing an atmospheric flow over a NW Pacific region of Mexico are solved numerically. In order to capture the complex flow-topography interactions with detail, a combination of a numerical wind model in full 3D curvilinear coordinates, along with a high resolution boundary-fitted grid is used. Boundary conditions were obtained from ten years (2002-2012) of measured offshore wind data. Prevailing winds from April to September during that period of observations were selected for the simulations. For the cases analyzed, it was found that at the points of the study region (PSS, PSM, PM), wind speed increased about 10% to 20% of its offshore values, while inland they decreased about 86% to 96%. This spatial behavior agreed very well with the observed local winds. A coastal jet (CJ), 35 km long with speeds about 1.5 - 2 m/s, emanating from PSS was found for NNW winds. Modeled winds were also used to compute wind stresses, wind stress curl, and CUI fields. Wind stress values agreed very well to those reported in the literature. High values of wind stress curl, and CUI were found at the lee of the points (PSS, PSM, PM). Indirect estimations of sea surface currents were about 15 - 20 cm/s offshore and 5 - 10 cm/s at the coast.

2-D boundary-fitted coordinate grid generation for casting with complex shape

In order to overcome the zigzag grids generated by conventional finite difference method on complicated casting boundaries in the simulation of casting process, the generation program for 2-D boundary-fitted coordinate grid has been developed by solving a set of partial differential equations (PDE) numerically. The STL format files were treated as input data for 2-D physical regions. The equipartition method for boundary points was used to improve the self-adaptability of grid according to the characteristic of the STL format files. The program was demonstrated through some examples. The comparison between the conventional finite difference method and the proposed method shows that this program is effective and flexible for generation of boundary-fitted grid in any arbitrary 2-D complex domain, and the grid is in accordance with the variety of boundary curvature finely. The program also provides two types of boundary-fitted grids for double-connected region, O-type and C-type. The limitation of the step-like boundary with the rectangle grid could be avoided effectively. Therefore, the computational accuracy and efficiency would be improved and the computational time would be saved significantly by the application of boundary-fitted grids.

Physical activity, physical fitness, and body mass index in the Chinese child and adolescent populations： An update from the 2016 Physical Activity and Fitness in China The Youth Study

In this special issue of the Journal of Sport and Health Science,analyses of the most recent national prevalence estimates from the 2016 Physical Activity and Fitness in China—The Youth Study(PAFCTYS)are presented.These include the prevalence of moderate-to-vigorous physical activity(MVPA)。

Body Mass Index and Health Related Physical Fitness in Saudi Girls and Adolescents Aged 8 - 15 Years

Health related physical fitness (HRPF) is considered to be an indirect marker of a person’s health and wellbeing, reflecting the interplay and integration of many persons’ systems and body functions. Purpose: To investigate the relationship between body mass index (BMI) and HRPF in a national cross-sectional sample of Saudi girls and adolescents. Methods: Weight, height and four components of HRPF (body fat composition, strength and endurance, flexibility and cardio-respiratory fitness) were measured in three age groups [(8 - 10), (11 - 12) and (13 - 15) years]. Pearson correlation coefficient and regressions analysis using a non-linear quadratic model were used to evaluate the relationship between BMI and HRPF in three age groups. Results: The results revealed variable relationships among tests. Lower scores in body fat composition and cardio-respiratory fitness were associated with higher body mass indexes in each age group. Also lower scores in muscle strength and endurance were recorded in girls aged from 11 to 15 years. Relationships between BMI and flexibility differed among age groups. Conclusion: BMI significantly and differentially influenced individual HRPF, but effects varied with age. Higher body mass indexes were generally associated with lower HRPF. The level of HRPF determined by this study may serve as an indicator of potential health risks that overweight and obese children girls and adolescents faced.

基于Best-Fit技术的白车身自动尺寸调整功能研究与应用

随着Best fit技术在北京奔驰的使用,传统的人工装配白车身四门两盖工作已经逐步被更加机械化、自动化、智能化的机器人装配所取代,本文通过Best fit技术在北京奔驰汽车装配制造过程的应用实践,结合Best fit技术的基本原理,在此基础上,介绍了车门尺寸在装配过程中的自动调整功能,该功能使车门装配尺寸结果更接近设置的理论目标值,同时使Best fit装配的稳定性进一步提升,提高生产效率。

贵州地方鸡种体重生长曲线的拟合分析

为探究贵州省赤水乌骨鸡、黔东南小香鸡、乌蒙乌骨鸡、威宁鸡和贵州黄鸡这5个地方鸡种生长发育规律,采用Logistic、Gompertz和von Bertalanffy 3种非线性模型对5个地方鸡种的生长曲线进行拟合,选取5个品种鸡各60只,公母各30只,测定0、2、4、6、8、10、12、14、16、18周龄时的体重。结果:5个品种鸡的生长趋势一致,3个模型均能较好地拟合5个品种鸡的生长变化情况,拟合度均在0.98以上,其中von Bertalanffy模型对5个品种鸡的生长曲线拟合效果最好;同时期的鸡体重以贵州黄鸡最重,黔东南小香鸡最轻,赤水乌骨鸡、乌蒙乌骨鸡和威宁鸡相近;5个品种鸡的拐点周龄分别为9.2、7.9、7.3、8.9和8.4,拐点体重分别为870.71、509.18、708.29、834.35和945.52 g。通过拟合的生长曲线模型对鸡体重进行评估,可为贵州省地方鸡的科学饲养、品种资源利用及选育提供依据。

基于2D人体图像特征学习的女西装合体性判别

为解决服装远程定制和网络购衣过程中服装合体性无法预先判断的问题,文章提出利用2D人体图像判断女西装合体性。首先采集了462名18~25周岁青年女性的2D图像及3D尺寸,建立人体数据集。并制作10件虚拟女西装,建立服装数据集。其次提取用于女西装合体性判别的服装特征、2D人体图像关键点距离特征和整体特征。基于感性工学原理,采用专家评价法获取女西装合体性评价标签。最后利用贝叶斯分类器建立女西装合体性判别模型。研究结果显示,将文章提出的特征应用于基于贝叶斯算法的女西装合体性判别模型判别准确率可达到84.8%,说明提出的服装合体性评价指标有效,可以用于基于2D图像的服装合体性预测。

基于风雨综合指数的安徽省台风灾害房屋风险评估方法

台风致灾因子具有多重性,相对于其他灾种其风险评估更加复杂。采用安徽省81个国家气象站及1035个区域气象站台风过程逐日降水量、最大风速资料,构建台风风雨综合指数;利用台风风雨综合指数及孕灾环境影响系数,开展台风致灾危险性评估;基于自然灾害风险系统理论,综合致灾危险性、承灾体暴露度和脆弱性信息,评估安徽省台风灾害房屋风险。结果表明:影响安徽省台风年均个数为1.9个,持续天数以2~4 d居多;台风降水南部多于北部、山区多于平原。台风致灾高危险区位于皖南山区和大别山区,较高危险区位于江淮之间东部,低危险区位于沿淮淮北大部及江淮之间西北部。台风灾害房屋高及较高风险区主要分布在大别山区、江淮之间东部及皖南山区,这些区域海拔总体较高,台风过境易引发山洪地质灾害,加之房屋脆弱性较高,房屋倒塌及损毁风险高;中等风险区位于沿淮至江淮之间、江南部分地区,呈零星分布;较低和低风险区位于淮河以北中西部、沿江部分地区及城市主城区。利用全省各县区台风造成的房屋倒损数据,从空间一致性及散点相关对区划结果进行验证得到,区划结果与灾损具有高度的空间一致性,二者散点相关通过0.01的显著性水平检验,安徽省台风灾害房屋风险区划结果与实际情况基本吻合。

广场舞和健步走锻炼对绝经后女性体成分影响的研究

为探讨长期广场舞与健步走锻炼在改善绝经后女性体成分方面的优劣以及锻炼年限与体成分之间的相关关系,本研究招募长期分别以广场舞与健步走锻炼为主的绝经后女性各40人(广场舞组和健步走组),长期为非体育人口的绝经后女性40人(对照组),测量其体成分。结果显示:除了骨骼肌外,广场舞组各指标值与对照组之间均具有统计学差异(P<0.05);健步走组体脂肪、体脂率和健康评估指标值与对照组之间均具有统计学差异(P<0.05);广场舞组体脂率指标值显著低于健步走组(P<0.05)。在相关性方面,广场舞组绝经后女性锻炼年限均分别与体脂肪、体脂率、骨肌比和健康评估指标值间存在高度负相关关系(P<0.01);健步走组绝经后女性的锻炼年限与体脂率指标值之间呈高度负相关关系,而与体脂肪、骨肌比和健康评估指标值之间呈中度正相关关系(P<0.01)。结果表明:长期广场舞与健步走锻炼均能改善绝经后女性的体成分,主要表现为降低体脂,提高健康水平,且广场舞的改善效果优于健步走。广场舞与健步走的锻炼年限与绝经后女性的体脂肪、体脂率、骨肌比和健康评估均呈高度相关关系,但广场舞锻炼的相关程度大于健步走锻炼,这可能与广场舞锻炼的运动强度高于健步走有关。

公共体育服务融入基层网格化管理的意义解析与路径探索

网格化管理是基层政府在科层制体系内利用信息技术实现政府管理流程再造的创新性举措,其普及程度与应用范围日益扩大,呈现出向公共服务领域倾斜的趋势。公共体育服务融入基层网格化管理有助于推动公共体育服务管理重心下移,有助于强化公共体育服务供给的多部门协同,有助于改善公共体育服务供需错位问题,有助于促进公共体育服务的“管监评分离”;然而,其实践层面也可能引发公共体育服务管理的形式化问题,呈现公共体育服务管理的新碎片化状态,挤压体育社会组织和市场组织参与公共体育服务供给的空间,弱化社区自治组织在公共体育服务供给上的作用。公共体育服务融入基层网格化管理的路径主要包括将社会体育指导员、体育场地纳入网格化管理的资源库,将全民健身工作领导协调机制嵌入网格化管理的联动中心,将体育社会组织、市场组织吸纳进网格化管理的合作框架,将社区自治与网格化管理有机衔接4个方面。

大学生体质健康促进模型的构建研究

本研究通过收集838名大学生的体成分和学生国民体质监测多维数据,运用结构方程模型算法,构建了一个综合而精细的体质健康结构数字化模型。研究表明,肌肉健壮因子、脂肪肥胖因子和心血管功能因子是大学生体质健康的关键指标,它们共同促进细胞健康因子水平。基于此,建议大学体育应更加关注力量和有氧能力的课程内容设置和课外锻炼指导,加强健康生活方式教育等,更高效地促进大学生体质健康水平。建议通过数字化技术开展多样性健康教育,搭建网络平台形成提升学生健康的社会合作关系,拓宽数字化背景下大学体育课程教学方法,更好地服务于学生体质健康促进多元需求。

西藏不同地区藏族大学生身体素质状况及影响因素研究

目的:比较西藏不同地区藏族大学生身体素质状况并分析影响因素。方法:按国家学生体质健康标准进行测试,采用卡方检验和二元Logistic模型对西藏民族大学3428名藏族大学生身体素质合格率及影响因素进行统计学分析。结果:共测试藏族大学生3428名,身体素质总合格率为83.34%,其中山南市大学生身体素质合格率为95.53%,林芝为92.05%,日喀则为84.70%,昌都为82.33%,拉萨为78.34%,那曲为75.57%。山南、林芝大学生身体素质合格率显著高于日喀则、昌都、拉萨和那曲,日喀则合格率显著高于拉萨和那曲。藏族大学生低体重、超重和肥胖者身体素质合格率显著低于体重正常者,肥胖者合格率显著低于低体重和超重者。单项指标合格率比较发现,立定跳远合格率最高为昌都(60.5%),最低为山南(46.8%);坐位体前屈合格率最高为山南(95.0%),最低为那曲(87.4%);800m/1000m合格率最高为山南(93.9%),最低为日喀则(76.7%)。BMI、地区均为身体素质测试是否合格的影响因素,低体重、超重、肥胖是藏族大学生身体素质合格的危险因素,而山南是藏族大学生身体素质合格的保护因素。结论:BMI和地区是藏族大学生身体素质的影响因素。

组合运动干预对肥胖女青少年身体成分、心血管风险因素及心肺适能影响的研究

背景目前,全球范围内肥胖儿童青少年数量急剧增加,其中,5~19岁人群肥胖患病率约增加了8倍,2~4岁儿童肥胖患病率约增加了1倍。运动干预对于改善肥胖和增强心肺适能具有重要影响。但缺乏组合运动干预对14~16岁肥胖女青少年影响的研究。目的探讨12周组合运动干预对肥胖女青少年身体成分、心血管风险因素及心肺适能的影响。方法于2022年5—7月在山东曲阜市选取14~16岁肥胖女青少年48名作为研究对象,将48名研究对象进行编号,然后利用随机数字分为试验组(24名)和对照组(24名)。试验组根据纳排标准最后纳入20名女生,整个干预过程持续12周,包括跳绳运动干预和跆拳道运动干预;而对照组在整个12周中不进行任何运动干预和其他饮食或者药物干预。分别在12周运动干预前和运动干预后检测受试者身高、体质量、体脂率、腰围、BMI、血压、空腹血糖(FPG)、胰岛素、胰岛素抵抗指数(HOMA-IR)及最大摄氧量(VO_(2max))等,并比较两组及干预前后各指标的差异。采用Pearson相关性分析探讨肥胖女青少年体脂率、腰围与VO_(2max)的相关性。结果干预前,两组女生年龄、身高、体质量、体脂率、腰围、BMI、收缩压(SBP)、舒张压(DBP)、脉压、FPG、胰岛素、HOMAIR、最大完成次数(Laps)、最大跑速(MAS)、VO_(2max)比较,差异均无统计学意义(P>0.05);12周运动干预后,试验组女生体脂率、腰围、SBP、DBP、FPG、胰岛素、HOMA-IR均低于对照组,而Laps、MAS、VO_(2max)高于对照组(P<0.05);与干预前比较,12周运动干预后试验组女生体脂率、腰围、SBP、DBP、FPG、胰岛素、HOMA-IR均降低,而Laps、MAS、VO_(2max)升高(P<0.05)。相关性分析结果显示,肥胖女青少年体脂率、腰围与VO_(2max)呈负相关(r=-0.55,P<0.001;r=-0.41,P<0.001)。结论12周组合运动干预能够改善肥胖女青少年身体成分和心血管风险因素,同时也能够通过增加VO_(2max)来增强心肺适能。

基于多正弦信号注入的大功率并网逆变器电网阻抗在线测量技术研究

文中研究基于多正弦扰动信号注入的大功率并网逆变器电网阻抗测量技术。选取多正弦信号作为电压扰动,参考空间光场理论中的Gerchberg-Saxton相位恢复算法对扰动信号进行优化设计;剪辑函数作为其中的关键要素,能够决定扰动信号时域波峰的剪辑速度和剪辑能力;为提升上述性能,提出采用反正切函数代替传统算法中的对数剪辑函数,仿真结果表明,相位恢复算法的剪辑性能得到大幅提升;随后,通过逆变器将扰动信号注入电网,采用Gauss-Newton非线性最小二乘法对采集到的扰动信号特征谐波频率点的信息进行曲线拟合,获取当前电网阻抗信息;最后,于搭建的1.5 MW并网逆变器RT-Lab平台进行多弱电网场景下的阻抗测量实验,实验结果验证了此方案的有效性和准确性。