Computational uncertainty and optimal grid size and time step of the Lax-Friedrichs scheme for the 1D advection equation

本文对于应用Lax-Friedrichs格式数值求解一维平流方程,研究数值求解过程中产生的截断误差与舍入误差,以及两种误差逐层向高时间层传播的累积,得到新的数值解总误差上界的理论近似公式,以及最优格距和最优时间步长的理论公式.通过数值算例验证了所得公式的可靠性。然后,发现了两种不同机器精度下最优时间步长之比满足的一个仅与机器精度有关的普适关系.最后,理论验证了在网格比固定的情况下,此问题满足数值计算的不确定性原理,以及在机器有限精度下最优时间步长的必然存在。

Proof of the Monotonicity of Grid Size and Its Application in Grid-Size Selection for Mesoscale Models

Terrain characteristics can be accurately represented in spectrum space. Terrain spectra can quantitatively reflect the effect of topographic dynamic forcing on the atmosphere. In wavelength space, topographic spectral energy decreases with decreasing wavelength, in spite of several departures. This relationship is approximated by an exponential function. A power law relationship between the terrain height spectra and wavelength is fitted by the least-squares method, and the fitting slope is associated with grid-size selection for mesoscale models. The monotonicity of grid size is investigated, and it is strictly proved that grid size increases with increasing fitting exponent, indicating that the universal grid size is determined by the minimum fitting exponent. An example of landslide-prone areas in western Sichuan is given, and the universal grid spacing of 4.1 km is shown to be a requirement to resolve 90% of terrain height variance for mesoscale models, without resorting to the parameterization of subgrid-scale terrain variance. Comparison among results of different simulations shows that the simulations estimate the observed precipitation well when using a resolution of 4.1 km or finer. Although the main flow patterns are similar, finer grids produce more complex patterns that show divergence zones, convergence zones and vortices. Horizontal grid size significantly affects the vertical structure of the convective boundary layer. Stronger vertical wind components are simulated for finer grid resolutions. In particular, noticeable sinking airflows over mountains are captured for those model configurations.

OPTIMAL COARSE GRID SIZE IN DOMAIN DECOMPOSITION

In most domain decomposition (DD) methods, a coarse grid solve is employed to provide the global coupling required to produce an optimal method. The total cost of a method can depend sensitively on the choice of the coaxse grid size H. In this paper, we give a simple analysis of this phenomenon for a model elliptic problem and a variant of Smith's vertex space domain decomposition method [11, 3]. We derive the optimal value Hopt which asymptotically minimises the total cost of method (number of floating point operations in the sequential case and execution time in the parallel case), for subdomain solvers with different complekities. Using the value of Hopt, we derive the overall complexity of the DD method, which can be significantly lower than that of the subdomain solver

东湖杂交羊产羔性状的GWAS分析及候选基因GRID 2的验证

旨在研究影响东湖杂交羊产羔性状的关键基因并挑选关键基因的变异位点进行验证,以期为东湖杂交奶绵羊多羔性状的选育提供分子标记。本研究从西北农林科技大学金昌奶绵羊试验示范基地采集身体健康无疾病的东湖杂交二代奶绵羊168只进行全基因组重测序,GEMMA和SnpEff软件进行全基因组关联分析,KOBAS 3.0数据库对注释的基因进行富集分析,LDBlockShow软件对显著性最强SNPs周边的连锁区域进行连锁不平衡分析。使用竞争性等位基因特异性PCR(kompetitive allele-specific PCR,KASP)技术对GRID 2基因进行SNP的分型检测,统计该基因两个多态位点的遗传多样性参数,并将其与产羔性状进行关联分析。结果显示,全基因组关联分析确定了6号染色上1163个达到显著性水平的SNPs位点,通过对候选位点的注释,确定与产羔性状相关的候选基因BMPR 1B、PDLIM5、PDHA2、UNC 5C、GRID2、NFKB1、TSPAN5、STPG2、PPP 3CA。同时结合已有报道和最强关联区域的注释,选择GRID 2上的两个SNPs(g.35685218A>G和g.35685499C>T)作为候选位点。通过统计学分析发现,本研究中涉及的两个位点均处于P>0.05的哈代-温伯格平衡状态,表明这两个位点均没有受到过强选择,并且这两个位点与东湖杂交羊的产羔性状有显著关联,两个位点的野生型均处于优势状态,且两个位点在胎次增加时均值也增加。综上所述,GRID 2基因2个SNPs对东湖杂交奶绵羊产羔性状有显著影响,可以作为分子标记辅助选择的候选位点。本研究为提高东湖杂交奶绵羊产羔率,促进奶绵羊的遗传育种进展提供了坚实的理论依据。

Finite-difference modeling with variable grid-size and adaptive time-step in porous media

Forward modeling of elastic wave propagation in porous media has great importance for understanding and interpreting the influences of rock properties on characteristics of seismic wavefield. However,the finite-difference forward-modeling method is usually implemented with global spatial grid-size and time-step; it consumes large amounts of computational cost when small-scaled oil/gas-bearing structures or large velocity-contrast exist underground. To overcome this handicap,combined with variable grid-size and time-step,this paper developed a staggered-grid finite-difference scheme for elastic wave modeling in porous media. Variable finite-difference coefficients and wavefield interpolation were used to realize the transition of wave propagation between regions of different grid-size. The accuracy and efficiency of the algorithm were shown by numerical examples. The proposed method is advanced with low computational cost in elastic wave simulation for heterogeneous oil/gas reservoirs.

Accuracy Comparison of Gridded Historical Cultivated Land Data in Jiangsu and Anhui Provinces

The spatial resolution of source data, the impact factor selection on the grid model and the size of the grid might be the main limitations of global land datasets applied on a regional scale. Quantitative studies of the impacts of rasterization on data accuracy can help improve data resolution and regional data accuracy. Through a case study of cropland data for Jiangsu and Anhui provinces in China, this research compared data accuracy with different data sources, rasterization methods, and grid sizes. First, we investigated the influence of different data sources on gridded data accuracy. The temporal trends of the History Database of the Global Environment （HYDE）, Chinese Historical Cropland Data （CHCD）, and Suwan Cropland Data （SWCD） datasets were more similar. However, differ- ent spatial resolutions of cropland source data in the CHCD and SWCD datasets revealed an average difference of 16.61% when provin- cial and county data were downscaled to a 10 x 10 km2 grid for comparison. Second, the influence of selection of the potential arable land reclamation rate and temperature factors, as well as the different processing methods for water factors, on accuracy of gridded datasets was investigated. Applying the reclamation rate of potential cropland to grid-processing increased the diversity of spatial distri- bution but resulted in only a slightly greater standard deviation, which increased by 4.05. Temperature factors only produced relative disparities within 10% and absolute disparities within 2 km2 over more than 90% of grid cells. For the different processing methods for water factors, the HYDE dataset distributed 70% more cropland in grid cells along riverbanks, at the abandoned Yellow River Estuary （located in Binhai County, Yancheng City, Jiangsu Province）, and around Hongze Lake, than did the SWCD dataset. Finally, we ex- plored the influence of different grid sizes. Absolute accuracy disparities by unit area for the year 2000 were within 0.1 km2 at a 1 km2 grid size, a 25% improvement over the 10 km2 grid size. Compared to the outcomes of other similar studies, this demonstrates that some model hypotheses and grid-processing methods in international land datasets are truly incongruent with actual land reclamation proc- esses, at least in China. Combining the model-based methods with historical empirical data may be a better way to improve the accuracy of regional scale datasets. Exploring methods for the above aspects improved the accuracy of historical crop/and gridded datasets for finer regional scales.

水下爆炸冲击波数值仿真精度研究

在水下爆炸数值仿真研究中,网格尺寸和一次项人工粘性系数对冲击波峰值压力计算结果有较大影响。在预定计算精度条件下,快速确定网格尺寸及人工粘性对数值计算意义重大。为此,文中基于LSDYNA有限元软件,建立78 g三硝基甲苯(TNT)二维水下爆炸数值计算模型,重点分析网格尺寸和一次项粘性系数对水下爆炸冲击波峰值压力和整体计算误差的影响规律。结果表明,随着网格密度因子的增大,计算峰值压力对网格的敏感性降低,且网格密度较大时,过小的一次项系数会导致计算峰值压力与经验公式值的相对误差增大。在此基础上获得20%范围内误差与网格尺寸、粘性系数之间的关系,并构建出可用于快速确定网格尺寸和一次项人工粘性系数的误差预估模型,通过0.2~5000 kg范围内的TNT柱形装药(长径比为1)和球形装药的水下爆炸计算,验证了预估模型的普适性,可为二维中近场范围内的水下爆炸冲击波数值仿真计算研究提供参考。

网格尺寸效应对蜂窝空腹楼盖静力性能的影响

使用ANSYS有限元结构分析软件,针对正六边形蜂窝型空腹夹层板楼盖进行分析。分析影响正六边形蜂窝型空腹夹层板楼盖中划分网格的尺寸效应,对比分析了此种结构与正交正放网格空腹夹层楼盖的网格尺寸与楼盖承载能力之间的效应关系。结果表明,正六边形蜂窝型空腹夹层板的网格尺寸效应比较明显,在合适的网格尺寸下,其钢-混凝土共同作用更加充分,经济效益更加优秀。此外,分析了混凝土表层板厚度对此种结构网格尺寸效应的影响,结果表明,增加混凝土表层板厚度,对于楼盖的承载力有正向增益,同时对结构的网格尺寸效应影响较大。

基于分群结构的有源配电网储能优化配置

随着新型电力系统中源、网、荷、储资源交互程度的提高,考虑储能与源网荷的时序耦合特性在储能规划中显得尤为重要。为减少有源配电网的网损,提升配网的节点电压水平,并实现削峰填谷的功能,该文提出一种基于集群划分的有源配电网分布式储能选址定容方法。首先,根据配电网电气距离模块度、源荷有功匹配度以及集群功率波动度对有源配电网进行集群划分;其次,以集群为单位对储能进行规划,以电网脆弱性指标、有功网损、综合费用最小为目标,通过嵌入潮流的混合智能求解算法求解储能系统的位置和容量;最后,在改进的IEEE-33节点系统中进行仿真测试。结果表明:有源配电网的网损减少19.0%,同时电压波动指标和电网脆弱性指标分别降低15.9%和9.1%,从而提高了系统的节点电压水平。此外,峰谷差减少22%,实现削峰填谷。这证明所提出方法的有效性。

计算网格对乳腺癌改良根治术后调强放射治疗计划质量的影响

目的探讨计算网格(GS)对乳腺癌改良根治术后调强放射治疗(IMRT)计划质量的影响。方法选取2022年1月至2023年12月于医院接受乳腺癌改良根治术后IMRT的15例患者作为研究对象,首先采用3 mm GS设计IMRT计划(3 mm计划),然后改变GS为2 mm(其余参数不变),重新设计计划(2 mm计划)。比较两种计划的计划靶区(PTV)剂量学指标[包括D2%、D98%、D_(mean)、均匀性指数(HI)及适形性指数(CI)]、危及器官(OARs)剂量学指标(患侧肺V_(5)、V_(20)、V_(30)、D_(mean)及健侧肺V_(5)、心脏D_(mean)、脊髓D_(max)),以及机器跳数(MU)和优化时间(OT)。结果PTV剂量学指标中,2 mm计划的D_(mean)低于3 mm计划,CI高于3 mm计划,差异均有统计学意义(P<0.05);OARs剂量学指标中,2 mm计划的脊髓D_(max)低于3 mm计划,差异有统计学意义(P<0.05);2 mm计划的OT为3 mm计划的2.96倍,差异有统计学意义(P<0.05)。结论2 mm GS IMRT计划的剂量学指标优于3 mm计划,对脊髓的保护效果更优,但计算效率更低。因此,设计乳腺癌改良根治术后IMRT计划时,应合理选择GS,以达到剂量计算准确性和计算效率的最佳平衡。

不同晶粒度测量方法的结果比对

分别采用截点法和面积法对GB/T 6394-2017标准图谱中5张第I系列评级图进行晶粒度测量,并对结果进行比对分析。结果表明:采用不同测量方法得出的晶粒度级别存在偏差;以矩形面积法结果为基准进行比对时,使用截点法的横纵测量网格线进行截点计数得到的结果最合理,精确度在0.15级范围内。在进行等轴晶粒度测量时,使用截点法更简便、快捷,建议采用截点法的横纵测量网格来测量晶粒度。

利用PixelGrid软件实现航空影像高保真高效率DSM的生产

针对目前市面上制作的DSM信息表达不丰富、效率不高的问题,该文提出了采用PixelGrid生产高保真高效率DSM的工艺流程,主要从不同重叠度、不同量化级别影像、不同格网尺寸等3方面进行DSM成果的影响因素分析。该文详细阐述了利用PixelGrid软件进行生产试验,得出重叠度大小的方法、不同量化级别影像和匹配格网大小的方法,对生产高保真高效率的DSM成果具有一定借鉴意义。

光伏并网对配电网继电保护影响特性分析

光伏发电因其供电可靠性高且投资成本低的特征被广泛应用于发电产业,随着光伏并网规模不断增大,传统的继电保护特性发生改变,原有继电保护方案不再能够满足电网安全运行的要求。对光伏发电的基本特点进行分析。首先,分析了光伏并网前后各位置保护电流的变化特性。然后,基于故障工况分析了光伏并网后保护电流的变化对继电保护正确动作造成的影响,并分析了不同容量光伏电源并入工况下的保护电流变化特性。最后,基于MATLAB仿真软件对前述分析进行仿真验证,结果充分证明理论分析的正确性,研究成果对优化继电保护动作具有指导意义。

Clinical study using novel endoscopic system for measuring size of gastrointestinal lesion

AIM: To verify the performance of a lesion size measurement system through a clinical study.

水下爆炸三维数值模拟特征参量敏感性分析

为探究水下爆炸三维数值模拟时网格尺寸和计算水域大小对计算精度的影响,并给出可平衡三维水下爆炸数值模拟精度与效率的参数设置,基于LS-DYNA水下爆炸三维自由场计算模型,以水下爆炸冲击波峰值、气泡脉动特性以及水域运动特性为衡量指标,在50~300 kg炸药爆炸质量下,分别分析了网格尺寸、水域大小对数值模拟精度的影响。研究结果表明:网格尺寸不大于1倍装药半径、炸药中心点到水域边界距离不小于4倍气泡最大膨胀半径时,软件可较为准确地模拟水下爆炸冲击波及第1次气泡脉动全过程。综合考虑计算精度与计算效率,建议进行水下爆炸数值模拟时,网格尺寸不大于1倍装药半径、炸药中心到水域边界距离不小于4倍气泡最大膨胀半径。

Optimizing QoS performance of service requests in grid

Workload of each service class varies dynamically in the grid environment, making the static service pool size allocation scheme unable to guarantee the QoS requirement of each service class. In this paper, we link the issue of dynamical service pool size allocation scheme with QoS requirement under the varying workload, and formulate the QoS performance of service requests in the grid environment by queue theory. Combined Lagrangian optimization with a bisearch approach, the problem of optimally allocating service pool size scheme is resolved. Simulation results show efficiency of the optimal service pool size allocation scheme.

Small and Mid-Size Pump-Turbines with Variable Speed

The stability of the grid is jeopardized with the large percentage of non-dispatchable renewables like wind power and also with increasing solar power. This creates various problems because these forms of energy are very volatile and difficult to predict. In most countries the in-feed of these sources must not be curtailed. In addition most of the renewables do not provide short circuit capacity and inertia in the same way as classical units and so further worsen the stability of the grid. The growing exploitation of wind and solar might be limited due to grid stability problems. In order to compensate those problems a large amount of reserve capacity is needed and therefore new technologies for electricity storage are required. Hydraulic pumped storage—the classical storage technology—has some disadvantages. These plants are in mountain regions often far away from wind farms. The distance to the wind farms mean additional loading for the already stressed grid and additional transmission losses. To compensate the very volatile wind energy, the pump input power should be varied continuously. This is so far only possible with variable speed units. Up to now double-fed asynchronous motor-generators are used which are rather expensive. In order to provide a solution for the described situation, ANDRITZ HYDRO has developed a new innovative concept of decentralized pump storage plants. Small standardized pump turbines are combined with a synchronous motor-generator and a full size converter which allows speed variation in pump and turbine mode over a wide range. These plants can be built locally close to wind farms and other sources to be balanced, allowing the increase of renewable energy without increasing the transmission line capacity. For the future smart grids this will be a key storage technology. This concept is reliable, innovative and more economic than other storage technologies.

大面积曲面铝板幕墙平整度控制技术

对建筑幕墙在大面积铝复合板施工前、中、后期对平整度方面如何做好控制进行了阐述。在铝板的材质选用、铝板板厚、分格的尺寸、加强肋的设置、板面涂层等方面做好前期的准备工作。在施工过程中测量定位、现场加工及强行装配等各方面做好精度和质量的把控等工序出现问题时进行调整。做出对此类工程平整度的优化建议,对此类工程,具有参考意义。

断裂仿真中的网格尺寸效应与断裂曲线修正

有限元仿真模拟方法可实现对结构材料从变形到破坏全过程的有效预测,而仿真模型建立的精度对于预测的准确性至关重要。应用有限元对标优化方法建立DP780材料的光滑拉伸、缺口拉伸及剪切拉伸试样的准静态仿真模型。划分不同网格尺寸,逆推得到材料的大变形本构曲线,以及各试样的应力三轴度、罗德角参数,系统研究了网格尺寸对材料拉伸本构曲线及韧性断裂参数逆推结果的影响。基于Lou-Huh(2012)断裂准则模型建立了不同网格尺寸下的断裂曲线。采用GISSMO理论建立断裂应变的网格尺寸效应修正函数,并对平面应力条件下的断裂曲线进行修正。研究结果表明:随着网格的细化,塑性应变-真应力曲线的对标结果向大应变方向延伸并趋于收敛,相同试样所标定的应力三轴度值与临界断裂应变值增大。随着网格尺寸的增大,临界断裂应变呈现指数形式递减,网格尺寸大于2 mm后趋于平稳。基于网格尺寸效应修正的韧性断裂模型可有效降低材料断裂仿真分析对网格尺寸的敏感性。

提升新能源电力系统稳定性的构网型变流器选址定容方法

新能源发电设备的大量接入显著改变了现代电网的动态特性,给电网的安全稳定带来了挑战,其中由锁相环带宽与电网强度不匹配导致的次/超同步振荡问题尤为严重。已有研究表明,外特性表现近似为电压源的构网型变流器能够减少由锁相环主导的新能源电力系统小干扰稳定问题,并且为系统提供较强的电压支撑能力,但基于构网型变流器的储能系统对多新能源馈入系统稳定性的作用机理及其选址定容优化方法仍不清晰。为此,文中揭示了基于构网型变流器的储能系统对多新能源馈入系统小干扰稳定性的提升作用机理,从提升系统稳定裕度的角度研究了基于构网型变流器的储能系统选址定容优化方法。最后,基于算例验证了所提方法的有效性。