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Search Results: 1 - 10 of 104136 matches for " Zhanhua Zhang "
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Description and Regulation of Drilling Completion Fluid Cake Structure  [PDF]
Xue Liu, Dong Ma, Pengfei Mu, Zhanhua Zhang, Junbo Yao
Open Journal of Yangtze Oil and Gas (OJOGas) , 2018, DOI: 10.4236/ojogas.2018.34025
Abstract: In the process of oil and gas well drilling and completion, under the action of positive pressure gradient or self-absorption, drilling and completion fluid solid phase particles block the reservoir pore and form the filter cake. The filter cake plays a vital role in reservoir protection, and is closely related to the oil and gas well productivity from cake formation to remove. The filter cake is always expected to be thin, tough, with low permeability and easy to remove. Many scholars made a lot of research from the filter cake layer structure, space truss structure, pore structure and the structure of fractal structure of filter cake. However, the researches on the structure of the filter cake are mainly conducted qualitatively at home and abroad, while the quantitative research progress is slow. At the same time, the research on the relationship between the filter cake structure and its performance is also relatively weak. In recent years, with the wide application of horizontal wells, it has called widespread attention on how to effectively remove filter cake in order to improve the oil and gas well production capacity at home and abroad. The widely-used filter cake removal technology mainly includes natural clear, mechanical removal, chemical removal and biological removal technology currently. Among them, the biological removal technology is developed in recent years as a new type of filter cake removal technology. With the further development of mud cake removal technology and downhole filter cake removing circumstance with increasing complexity, a single filter cake removal technology cannot completely meet the requirements. The filter cake removal technology is developing in the direction of the composite to clear, in order to obtain ideal filter cake removal effect.
Almost Surely Asymptotic Stability of Exact and Numerical Solutions for Neutral Stochastic Pantograph Equations
Zhanhua Yu
Abstract and Applied Analysis , 2011, DOI: 10.1155/2011/143079
Abstract: We study the almost surely asymptotic stability of exact solutions to neutral stochastic pantograph equations (NSPEs), and sufficient conditions are obtained. Based on these sufficient conditions, we show that the backward Euler method (BEM) with variable stepsize can preserve the almost surely asymptotic stability. Numerical examples are demonstrated for illustration.
Almost Surely Asymptotic Stability of Numerical Solutions for Neutral Stochastic Delay Differential Equations
Zhanhua Yu,Mingzhu Liu
Discrete Dynamics in Nature and Society , 2011, DOI: 10.1155/2011/217672
Abstract: We investigate the almost surely asymptotic stability of Euler-type methods for neutral stochastic delay differential equations (NSDDEs) using the discrete semimartingale convergence theorem. It is shown that the Euler method and the backward Euler method can reproduce the almost surely asymptotic stability of exact solutions to NSDDEs under additional conditions. Numerical examples are demonstrated to illustrate the effectiveness of our theoretical results. 1. Introduction The neutral stochastic delay differential equation (NSDDE) has attracted much more attention, and much work (see [1–4]) has been done. For example, Mao [2] studied the existence and uniqueness, moment and pathwise estimates, and the exponential stability of the solution to the NSDDE. Moreover, Mao et al. [4] studied the almost surely asymptotic stability of the NEDDE with Markovian switching: Since most NSDDEs cannot be solved explicitly, numerical solutions have become an important issue in the study of NSDDEs. Convergence analysis of numerical methods for NSDDEs can be found in [5–7]. On the other hand, stability theory of numerical solutions is one of the fundamental research topics in the numerical analysis. For stochastic differential equations (SDEs) as well as stochastic delay differential equations (SDDEs), moment stability and asymptotic stability of numerical solutions have received much more attention (e.g., [8–13] for moment stability and [12–14] for asymptotic stability). Recently, Wang and Chen [15] studied the mean-square stability of the semi-implicit Euler method for NSDDEs. We aim in this paper to study the almost surely asymptotic stability of Euler-type methods for NSDDEs using the discrete semimartingale convergence theorem. The discrete semimartingale convergence theorem (cf. [16, 17]) plays an important role in the almost surely asymptotic stability analysis of numerical solutions to SDEs and SDDEs [17–19]. Using the discrete semimartingale convergence theorem, we show that Euler-type methods for NSDDEs can preserve the almost surely asymptotic stability of exact solutions under additional conditions. In Section 2, we introduce some necessary notations and state the discrete semimartingale convergence theorem as a lemma. In Section 3, we study the almost surely asymptotic stability of exact solutions to NSDDEs. Section 4 gives the almost surely asymptotic stability of the Euler method. In Section 5, we discuss the almost surely asymptotic stability of the backward Euler method. Numerical experiments are presented in Section 6. 2. Preliminaries Throughout this
The Meshless Local Petrov-Galerkin Method for Large Deformation Analysis of Hyperelastic Materials
De'an Hu,Zhanhua Sun
ISRN Mechanical Engineering , 2011, DOI: 10.5402/2011/967512
Abstract: Nonlinear formulations of the meshless local Petrov-Galerkin method (MLPG) are presented for the large deformation analysis of hyperelastic materials which are considered to be incompressible or nearly incompressible. The MLPG method requires no explicit mesh in computation and therefore avoids mesh distortion difficulties. In this paper, a simple Heaviside test function is chosen for reducing the computational effort by simplifying domain integrals for hyperelasticity problems. Trial functions are constructed using the radial basis function (RBF) coupled with a polynomial basis function. The plane stress hypothesis and a pressure projection method are employed to overcome the incompressibility or nearly incompressibility in the plane stress and plane strain problems, respectively. Effects of the sizes of local subdomain and interpolation domain on the performance of the present MLPG method are investigated. The behaviour of shape parameters of multiquadrics (MQ) function has been studied. Numerical results for several examples show that the present method is effective in dealing with large deformation hyperelastic materials problems. 1. Introduction An important class of materials is the hyperelastic materials in engineering. These materials are commonly subjected to large elastic deformations. Due to the highly nonlinear nature of the governing differential equations, analytical solutions exist for only a few problems involving simple geometries and constitutive laws [1]. Then a number of numerical schemes have been used to solve this problem. Despite the finite element method (FEM) is now a standard analysis tool for the finite deformation problem. The application of FEM to large strain problems still has some important drawbacks that cannot be overcome, due to extremely large deformations and the incompressible or nearly incompressible nature of hyperelastic materials. Many FEMs have been developed to handle the volumetric locking and pressure oscillation difficulty resulting from the incompressibility or nearly incompressibility constraint, but the excessive mesh distortion is still reducing the convergence ratio and the overall accuracy of solution [2]. Normally this requires remeshing steps and the corresponding projection of the current results in FEM, thus in this case the standard FEM formulations become ineffective or inaccurate without additional improvements [3]. Recently, the analysis of hyperelastic materials also has been presented in the boundary element method (BEM) [4, 5]. However, there exist additional problem of singular integrals
On Solutions of Quasilinear Degenerate Parabolic Equations


数学物理学报(A辑) , 2005,
Abstract: In this paper, the author gives the definition of a new general solution for qu asilinear degenerate parabolic equation pa_t{u}+pa_x{f(u)}=pa_xx{A(u(x,t))}∈R^2_+×(0,+∞) , u(x,0)=u_0(x),x∈R and get its existence by DivCurl Lemma.
Tetraimidazolium hexa-μ4-oxido-dodeca-μ2-oxido-dodecaoxidohexaarsenate(III)hexamolybdenum(VI)cuprate(II)
Meiduo Liu,Zhanhua Su,Yongchen Shang
Acta Crystallographica Section E , 2010, DOI: 10.1107/s1600536810037414
Abstract: The title compound, (C3H5N2)4[As6CuMo6O30], is made up of a centrosymmetric anionic cluster and four imidazolium cations. In the cluster, the central CuII atom is six-coordinated and lies on an inversion center. Adjacent clusters are linked via N—H...O hydrogen bonds between the imidazole cations and polyoxidoanions into a three-dimensional supramolecular architecture.
Snapshot-based Balanced Truncation for Linear Time-periodic Systems
Zhanhua Ma,Clarence W. Rowley,Gilead Tadmor
Mathematics , 2007,
Abstract: We introduce an algorithm based on a method of snapshots for computing approximate balanced truncations for discrete-time, stable, linear time-periodic systems. By construction, this algorithm is applicable to very high-dimensional systems, even with very high-dimensional outputs (or, alternatively, very high-dimensional inputs). An example is shown to validate the method.
Reduced order models for control of fluids using the Eigensystem Realization Algorithm
Zhanhua Ma,Sunil Ahuja,Clarence W. Rowley
Mathematics , 2009, DOI: 10.1007/s00162-010-0184-8
Abstract: In feedback flow control, one of the challenges is to develop mathematical models that describe the fluid physics relevant to the task at hand, while neglecting irrelevant details of the flow in order to remain computationally tractable. A number of techniques are presently used to develop such reduced-order models, such as proper orthogonal decomposition (POD), and approximate snapshot-based balanced truncation, also known as balanced POD. Each method has its strengths and weaknesses: for instance, POD models can behave unpredictably and perform poorly, but they can be computed directly from experimental data; approximate balanced truncation often produces vastly superior models to POD, but requires data from adjoint simulations, and thus cannot be applied to experimental data. In this paper, we show that using the Eigensystem Realization Algorithm (ERA) \citep{JuPa-85}, one can theoretically obtain exactly the same reduced order models as by balanced POD. Moreover, the models can be obtained directly from experimental data, without the use of adjoint information. The algorithm can also substantially improve computational efficiency when forming reduced-order models from simulation data. If adjoint information is available, then balanced POD has some advantages over ERA: for instance, it produces modes that are useful for multiple purposes, and the method has been generalized to unstable systems. We also present a modified ERA procedure that produces modes without adjoint information, but for this procedure, the resulting models are not balanced, and do not perform as well in examples. We present a detailed comparison of the methods, and illustrate them on an example of the flow past an inclined flat plate at a low Reynolds number.
Genomic survey, expression profile and co-expression network analysis of OsWD40 family in rice
Yidan Ouyang, Xiaolong Huang, Zhanhua Lu, Jialing Yao
BMC Genomics , 2012, DOI: 10.1186/1471-2164-13-100
Abstract: In this study, we identify and analyze 200 potential OsWD40 genes in rice, describing their gene structures, genome localizations, and evolutionary relationship of each member. Expression profiles covering the whole life cycle in rice has revealed that transcripts of OsWD40 were accumulated differentially during vegetative and reproductive development and preferentially up or down-regulated in different tissues. Under phytohormone treatments, 25 OsWD40 genes were differentially expressed with treatments of one or more of the phytohormone NAA, KT, or GA3 in rice seedlings. We also used a combined analysis of expression correlation and Gene Ontology annotation to infer the biological role of the OsWD40 genes in rice. The results suggested that OsWD40 genes may perform their diverse functions by complex network, thus were predictive for understanding their biological pathways. The analysis also revealed that OsWD40 genes might interact with each other to take part in metabolic pathways, suggesting a more complex feedback network.All of these analyses suggest that the functions of OsWD40 genes are diversified, which provide useful references for selecting candidate genes for further functional studies.Proteins characterized by conserved motifs may belong to a gene family, which were represented by structural or functional similarity and evolutionary relationships. WD40 proteins are a group of proteins that are highly conserved in evolution and are extremely abundant across a wide range of eukaryotic organisms [1]. Structurally, these proteins are characterized by the presence of approximately 40 amino acids core region, which contains a glycine-histidine (GH) dipeptide at the N terminus and a tryptophan-aspartate (WD) dipeptide at the C terminus separated by a region of variable lengths [2]. Usually, the WD40 protein contains several tandemly repeated units of such motif, which are required to form the secondary structure [3]. The structure of several WD40 proteins has
Measurement of Forces Acting on Cylinder in Oscillating Water Flow

Yuan Maozhu Li zhanhua,

实验力学 , 1988,
Abstract: The experimental method of measuring forces acting on a cylinder in oscillating water flow is described. Results are given for inline and transvarse forces. Especially, the frequency spectrums of these kinds of forces are also given.
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