共查询到20条相似文献,搜索用时 9 毫秒
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An algebraic variational multiscale–multigrid method is proposed for large-eddy simulation of turbulent variable-density flow at low Mach number. Scale-separating operators generated by level-transfer operators from plain aggregation algebraic multigrid methods enable the application of modeling terms to selected scale groups (here, the smaller of the resolved scales) in a purely algebraic way. Thus, for scale separation, no additional discretization besides the basic one is required, in contrast to earlier approaches based on geometric multigrid methods. The proposed method is thoroughly validated via three numerical test cases of increasing complexity: a Rayleigh–Taylor instability, turbulent channel flow with a heated and a cooled wall, and turbulent flow past a backward-facing step with heating. Results obtained with the algebraic variational multiscale–multigrid method are compared to results obtained with residual-based variational multiscale methods as well as reference results from direct numerical simulation, experiments and LES published elsewhere. Particularly, mean and various second-order velocity and temperature results obtained for turbulent channel flow with a heated and a cooled wall indicate the higher prediction quality achievable when adding a small-scale subgrid-viscosity term within the algebraic multigrid framework instead of residual-based terms accounting for the subgrid-scale part of the non-linear convective term. 相似文献
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遗传算法与最小二乘法在实验数据处理中的对比研究 总被引:1,自引:0,他引:1
采用遗传算法拟合甘油的黏度随温度的变化公式,并将得到的经验公式与采用传统的最小二乘法得到的公式比较.发现在处理某些非线性拟合问题时,采用最小二乘法并非最好,遗传算法得到的结论更优,方法也更简单. 相似文献
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建立了ICP-AES测定高浓度基体中微量杂质元素的偏最小二乘方法(PLS)。研究表明,PLS能有效校正高浓度基体干扰引起的测量误差,比多元光谱拟合法(MSF)能承受的基体浓度更高。当基体与杂质的含量比为1 000∶1~20 000∶1时,该方法的加标回收率在95%~105%之间。对于干扰效应与基体浓度呈非线性相关的体系,普通PLS的预测准确度不高,但使用基于样品浓度矩阵变换的偏最小二乘法(LIN-PPLS),则明显改善了预测的准确度。分别用MSF、普通PLS和LIN-PPLS对水系沉积物国家标准物质GBW07312中的Co,Pb和Ga进行测定,结果表明,LIN-PPLS的预测准确度优于普通PLS,而普通PLS的预测准确度优于MSF。 相似文献
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This article explores a method of optical transmission inspection of the basis weight on-line, by combining the modified least squares and optical processing technique. This process is developed to significantly target toward improving the mass quality analysis of the nonwoven material. The real-time scanning width piecewise least squares method and area-based strategy for determining based on the process quality of nonwoven manufacturing. To avoid the influence of ambient factors, the compensation controls device are adopted and successfully showed. Subsequently, the modified least squares method is used to obtain the suitable parameter transformation between the measured voltage and the nonwoven fabrics basis weight. The piecewise least squares method was obtained as the parameter transfer equation. We consider estimating and testing Cpk with the presence of on-line basis weight measurement errors. To obtain the true process precision Cp and integrated process capability index Cpk are presented to practitioners for their factory applications. 相似文献
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A novel signal processing method is proposed for sound field recording and reproduction using multiple parallel linear microphone and loudspeaker arrays. In sound field recording and reproduction, the problem is how to calculate the transfer filters that transform the signals recorded by microphones into the driving signals of the loudspeakers. The proposed method is based on the spatial Fourier transform in the horizontal angle combined with the least squares (LS) approach in the elevation angle. In the proposed method, the signals recorded by each linear microphone array and those that drive each loudspeaker array are decomposed into the wavenumber domain by the spatial Fourier transform in the horizontal direction. The transfer filters are then calculated by the LS approach in the wavenumber domain. As a result, the size of the matrix of each transfer function in the wavenumber domain is much smaller than that of the conventional LS approach in the temporal frequency domain (LSTF), and well-conditioned stable transfer filters can be obtained with low computational cost without regularization. Computer simulation results show that the proposed method reconstructed a sound field around the control points as accurately as the conventional LSTF. 相似文献
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Zhou Z Liu W Cui J Wang X Arias D Wen Y Bansal R Hao X Wang Z Peterson BS Xu D 《Magnetic resonance imaging》2011,29(2):230-242
Signal variation in diffusion-weighted images (DWIs) is influenced both by thermal noise and by spatially and temporally varying artifacts, such as rigid-body motion and cardiac pulsation. Motion artifacts are particularly prevalent when scanning difficult patient populations, such as human infants. Although some motion during data acquisition can be corrected using image coregistration procedures, frequently individual DWIs are corrupted beyond repair by sudden, large amplitude motion either within or outside of the imaging plane. We propose a novel approach to identify and reject outlier images automatically using local binary patterns (LBP) and 2D partial least square (2D-PLS) to estimate diffusion tensors robustly. This method uses an enhanced LBP algorithm to extract texture features from a local texture feature of the image matrix from the DWI data. Because the images have been transformed to local texture matrices, we are able to extract discriminating information that identifies outliers in the data set by extending a traditional one-dimensional PLS algorithm to a two-dimension operator. The class-membership matrix in this 2D-PLS algorithm is adapted to process samples that are image matrix, and the membership matrix thus represents varying degrees of importance of local information within the images. We also derive the analytic form of the generalized inverse of the class-membership matrix. We show that this method can effectively extract local features from brain images obtained from a large sample of human infants to identify images that are outliers in their textural features, permitting their exclusion from further processing when estimating tensors using the DWIs. This technique is shown to be superior in performance when compared with visual inspection and other common methods to address motion-related artifacts in DWI data. This technique is applicable to correct motion artifact in other magnetic resonance imaging (MRI) techniques (e.g., the bootstrapping estimation) that use univariate or multivariate regression methods to fit MRI data to a pre-specified model. 相似文献
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I.IntroductinnWithmoreandmoremulthetoreyworkshopsandmultifunctinnaltallbuildingsarebeingconstructednowadays,thereshowsanincreasingtrendformachinesandequlpmentstobemoulltedonupperlloors.Inthesituationofmachinesrunningonupperfloors,thetraditionaltheoryisnotValidbecausetheflooritselfisaflewhlestructure.Therefore,itisinagreatdemandtostudyonthedynaInicillteractionofmachinescoupledwithflekiblefoundationsalldtoproposearesonableandeffectiveapproachtocontrolvibrationandtosuppressnoise.Formachineryonu… 相似文献
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By using the extended Harrison and Estabrook's differential forms approach, in this paper, we investigate the Lie symmetries of the continuous and discrete dispersive long waves system, respectively. Based on this method, two closed ideals written in terms of a set of differential forms are constructed for the dispersive long waves systems. Furthermore, some invariant solutions are presented for such systems. By a direct computation, it is shown that the discrete dispersive long waves system admits a Kac-Moody-Virasoro type and a Virasoro-like type Lie algebra, respectively. Finally, we present an interesting relationship between the continuous case and a modified dispersive long waves system, which can be used to find nonlocal properties for such systems with each other. 相似文献
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在(1 1)维非线性动力学系统,人们发现不同的局域激发模式分别存在于不同的非线性系统.可是最近的若干研究表明,在高维非线性动力学系统中,如果选取适当的边值条件或初始条件时,人们可以同时找到若干不同的局域激发模式,如:紧致子、峰孤子、呼吸子和折叠子等.本文的主要目的是寻找(1 1)维非线性耦合Ito系统中的不同的局域激发模式.首先,基于一个特殊的Painlev-éBacklund变换和线性变量分离方法,求得了该系统具有若干任意函数的变量分离严格解.然后,根据得到的变量分离严格解,通过选择严格解中的任意函数,引入恰当的单值分段连续函数和多值局域函数,成功找到了耦合Ito系统若干有实际物理意义的单值和多值局域激发模式,如:峰孤子,紧致子和多圈孤子等. 相似文献
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Complex solutions and novel complex wave localized excitations for the(2+1)-dimensional Boiti–Leon–Pempinelli system 下载免费PDF全文
With the help of the symbolic computation system Maple, the Riccati equation mapping approach and a linear variable separation approach, a new family of complex solutions for the (2+ 1)-dimensional Boiti-Leon-Pempinelli system (BLP) is derived. Based on the derived solitary wave solution, some novel complex wave localized excitations are obtained. 相似文献
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New exact excitations and soliton fission and fusion for the (2+1)-dimensional Broer-Kaup-Kupershmidt system 总被引:3,自引:0,他引:3 下载免费PDF全文
With the help of an extended mapping approach, a series of new types of exact excitations with two arbitrary functions of the (2 1)-dimensional Broer-Kaup-Kupershmidt (BKK) system is derived. Based on the derived solitary wave excitation, some specific soliton fission and fusion solutions of the higher-dimensional BKK system are also obtained. 相似文献
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We studied the effect of ultrasonication extraction technology combined with ammonium sulfate/ethanol aqueous two-phase system (ATPS) for the separation of lithospermic acid B (LAB) from Salvia miltiorrhiza Bunge. According to the literature and preliminary studies, ammonium sulfate concentration, ethanol concentration, pH, ultrasonication power, ultrasonication time and the ratio of solvent-to-solid were investigated using a single factor design to identify the factors affecting separation. Taking into consideration a simultaneous increase in LAB recovery (R (%)) and partition coefficient (K), the best performance of the ATPS was obtained at 25 °C and pH 2 using ammonium sulfate 22% (w/w) and ethanol 30% (w/w). To keep the solvent-to-solid ratio at 10, response surface methodology was used to find the optimal ultrasonication power and ultrasonication time. Quadratic models were predicted for LAB yield in the upper phase. Optimal conditions of 572.1 W ultrasonication power and 42.2 min produced a maximum yield of LAB of 42.16 mg g−1 sample. There was no obvious degradation of LAB with ultrasound under the applied conditions, and the experimental yield of LAB was 42.49 mg g−1 sample and the purity was 55.28% (w/w), which was much higher than that obtained using conventional extraction. The present study demonstrated that ultrasound coupled with aqueous two-phase systems is very efficient tool for the extraction and purification of LAB from Salvia miltiorrhiza Bunge. 相似文献