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NUMERICAL STUDIES OF A CLASS OF COMPOSITE PRECONDITIONERS

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Journal of Computational Mathematics 2014年第2期32卷 136-151页

作者： qiang niu Michael Ng Mathematics and Physics Centre Xi'an Jiaotong-Liverpool University Suzhou 215123 China Department of Mathematics Hong Kong Baptist University Kowloon Tong Hong Kong

In this paper, we study a composite preconditioner that combines the modified tangential frequency filtering decomposition with the ILU（O） factorization. Spectral property of the composite preconditioner is examined by the approach of Fourier analysis. We illustrate that condition number of the preconditioned matrix by the composite preconditioner is asymptotically bounded by O（hp -2/3） on a standard model problem. Performance of the composite preconditioner is compared with other preconditioners on several problems arising from the discretization of PDEs with discontinuous coefficients. Numerical results show that performance of the proposed composite preconditioner is superior to other relative preconditioners.

关键词： Preconditioner ILU Tangential frequency filtering decomposition GMRES.

Study of heat transfer by using DEM–CFD method in a randomly packed pebble-bed reactor

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Nuclear Science and Techniques 2019年第2期30卷 123-134页

作者： qiang niu Na-Xiu Wang Shanghai Institute of Applied Physics Chinese Academy of Sciences CAS Innovative Academies in TMSR Energy System Chinese Academy of Sciences University of Chinese Academy of Sciences

The pebble-bed reactor is one of the most promising designs for the nuclear energy industry. In this paper,a discrete element method-computational fluid dynamics(DEM-CFD) approach that includes thermal conduction, radiation, and natural convection mechanisms was proposed to simulate the thermal-fluid phenomena after the failure of forced circulation cooling system in a pebble-bed core. The whole large-scale packed bed was created using the DEM technique, and the calculated radial porosity of the bed was validated with empirical correlations reported by researchers. To reduce computational costs, a segment of the bed was extracted, which served as a good representative of the large-scale packed bed for CFD calculation. The temperature distributions simulated with two different fluids in this DEM-CFD approach were in good agreement with SANA experimental data. The influence of the natural convection mechanism on heat transfer must be taken into account for coolants with strong convective capacity. The proposed DEM-CFD methodology offers a computationally efficient and widely applied method for understanding the heat transfer process in a pebble-bed core. The method can also be easily extended to assess the passive safety features of newly designed fluoride-salt-cooled pebble-bed reactors.

关键词： Discrete element method Computational fluid dynamics Pebble bed Heat transfer Natural convection

An Investigation of Restarted GMRES Method by Using Flexible Starting Vectors

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Numerical Mathematics(Theory,Methods and Applications) 2010年第3期3卷 338-351页

作者： qiang niu Lin-Zhang LU BNU-HKBU United International College Zhuhai 519085 China. School of Mathematics and Computer Science Guizhou Normal University Guiyang 550001 China. School of Mathematical Sciences Xiamen University Xiamen 361005 China.

We discuss a variant of restarted GMRES method that allows changes of the restarting vector at each cycle of *** merit of the variant is that previously generated information can be utilized to select a new starting vector,such that the occurrence of stagnation be mitigated or the convergence be *** more appealing utilization of the new method is in conjunction with a harmonic Ritz vector as the starting vector,which is discussed in *** experiments are carried out to demonstrate that the proposed procedure can effectively mitigate the occurrence of stagnation due to the presence of small eigenvalues in modulus.

关键词： Linear systems of equations Arnoldi process GMRES harmonic Ritz vector.

A RELAXED HSS PRECONDITIONER FOR SADDLE POINT PROBLEMS FROM MESHFREE DISCRETIZATION＊

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Journal of Computational Mathematics 2013年第4期31卷 398-421页

作者： Yang Cao Linquan Yao Meiqun Jiang qiang niu School of Transportation Nantong University Nantong 226019 China School of Urban Rail Transportation Soochow University Suzhou 215006 China School of Mathematical Sciences Soochow University Suzhou 215006 China Mathematics and Physics Center Xi 'an Jiaotong-L iverpool University Suzhou 215123 China

In this paper, a relaxed Hermitian and skew-Hermitian splitting （RHSS） preconditioner is proposed for saddle point problems from the element-free Galerkin （EFG） discretization method. The EFG method is one of the most widely used meshfree methods for solving partial differential equations. The RHSS preconditioner is constructed much closer to the coefficient matrix than the well-known HSS preconditioner, resulting in a RHSS fixed-point iteration. Convergence of the RHSS iteration is analyzed and an optimal parameter, which minimizes the spectral radius of the iteration matrix is described. Using the RHSS pre- conditioner to accelerate the convergence of some Krylov subspace methods （like GMRES） is also studied. Theoretical analyses show that the eigenvalues of the RHSS precondi- tioned matrix are real and located in a positive interval. Eigenvector distribution and an upper bound of the degree of the minimal polynomial of the preconditioned matrix are obtained. A practical parameter is suggested in implementing the RHSS preconditioner. Finally, some numerical experiments are illustrated to show the effectiveness of the new preconditioner.

关键词： Meshfree method Element-free Galerkin method Saddle point problems Pre-conditioning HSS preconditioner Krylov subspace method.

Multi-Sensor Estimation for Unreliable Wireless Networks with Contention-Based Protocols

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Journal of Computer Science & Technology 2018年第5期33卷 1072-1085页

作者： Shou-Wan Gao Peng-Peng Chen Xu Yang qiang niu Key Laboratory of Gas and Fire Control for Coal Mines China University of Mining and Technology Xuzhou 221116 China School of Computer Science and Technology China University of Mining and Technology Xuzhou 221116 China

The state estimation plays an irreplaceable role in many real applications since it lays the foundation for decision-making and control. This paper studies the multi-sensor estimation problem for a contention-based unreliable wireless network. At each time step, no more than one sensor can communicate with the base station due to the potential contention and collision. In addition, data packets may be lost during transmission since wireless channels are unreliable. A novel packet arrival model is proposed which simultaneously takes into account the above two issues. Two scenarios of wireless sensor networks （WSNs） are considered： the sensors transmit the raw measurements directly and the sensors send the local estimation instead. Based on the obtained packet arrival model, necessary and sufficient stability conditions of the estimation at the base station side are provided for both network scenarios. In particular, all offered stability conditions are expressed by simple inequalities in terms of the packet arrival rates and the spectral radius of the system matrix. Their relationships with existing related results are also discussed. Finally, the proposed results are demonstrated by simulation examples and an environment monitoring prototype system.

关键词： wireless sensor network packet loss state estimation contention-based protocol

Investigation of the sliding friction behaviors of locust on slippery plates

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Chinese Science Bulletin 2009年第24期54卷 4549-4554页

作者： WANG LiXin ZHOU qiang Xu ShuYan niu HuLi Department of Mechatronic Engineering China Agricultural University Beijing 100083 China

The slippery trapping plate in swarm locust control is a method of realizing resource utilization of locust and avoiding pesticide residues in the entironment. Some slippery plates with different material composition or surface characteristic were investigated through the sliding tests of locust on slippery plates, and sliding rubbing behaviors of locusts on the plate were observed by means of CCD video monitoring system. Poor sliding character of silicate glass to locust was verified, which is in accordance with the adhesive effect generated by secretion of locust feet pads on the smooth surface. And also, PVC plastic plate presents a poor sliding character to locusts, because the soft surface of PVC can permit claws of locust feet to engender mechanical interlock on the surface. The zinc plate shows a considerable slippery ratio for locusts because of the appropriate surface characteristic and material property. Photoelectric stimulation for resting locust can promote the movement of locust. Accordingly, the contact form of locust feet and abdomen on slippery plates is changed and contact area is reduced severely, so the sliding effect of locust on slippery plates is strengthened effectively. These results supply a suitable theoretical foundation for manufacturing locust slippery trapping plates and trapping units, and indicate the important role of photoelectric stimulating factors in biotribology.

关键词：摩擦行为蝗虫滑片滑动 PVC塑料板表面特性视频监控系统硅酸盐玻璃

Correlation Between Microstructure and Mechanical Properties of 2219-T8 Aluminum Alloy Joints by VPTIG Welding

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Acta Metallurgica Sinica(English Letters) 2017年第5期30卷 438-446页

作者： Lan-qiang niu Xiao-Yan Li Liang Zhang Xiao-Bo Liang Mian Li College of Materials Science and Engineering Beijing University of TechnologyBeijing 100124China

In this study, 2219-T87 aluminum alloys were butt welded by the double-pass tungsten inert gas arc welding process. And the softening behavior of fusion zone（FZ） and heat-affected zone（HAZ） was evaluated with the analysis of welding temperature field, grain size, alloying element distribution and precipitates evolution. Results show that the two FZs are almost the weakest regions in the joint, where the microhardness value is 76 and 78 HV, respectively. Microhardness of the HAZ generally grows along with increasing distance from fusion line except a valley value at the distance of about 4.5 mm. The mean grain size of two FZs is about 74.4 and 79.2 lm, whereas 41.5, 44.9 and 43.4 lm for the two measured HAZs and base metal（BM）, respectively. There is about 60.4% and 54.2% Cu consumed in the coarse whitish particles of FZs that have little strengthening effect, while the percentage is about 24.6% of BM that is almost the same as HAZ. A large number of strengthening phases h0 distribute dispersively in BM, whereas hardly any precipitates exist in FZ and HAZ adjacent to FZ. So the coarsening of grain size, reduction and segregation of alloying element content, and the precipitate evolution are regarded as the main causes of softening in FZ, while the precipitate evolution is the main factor of softening in HAZ.

关键词： 2219-T87 Aluminum alloy TIG welding Fusion zone Heat-affected zone Softening behavior

A New Well-Balanced Finite Volume CWENO Scheme for Shallow Water Equations over Bottom Topography

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Advances in Applied Mathematics and Mechanics 2023年第6期15卷 1515-1539页

作者： Wei Guo Ziming Chen Shouguo Qian Gang Li qiang niu School of Mathematics and Statistics Qingdao UniversityQingdaoShandong 266071China Department of Applied Mathematics Xi’an Jiaotong–Liverpool UniversitySuzhouJiangsu 215123China

In this article,we develop a new well-balanced finite volume central weighted essentially non-oscillatory(CWENO)scheme for one-and two-dimensional shallow water equations over uneven *** well-balanced property is of paramount importance in practical applications,where many studied phenomena can be regarded as small perturbations to the steady *** achieve the well-balanced property,we construct numerical fluxes by means of a decomposition algorithm based on a novel equilibrium preserving reconstruction procedure and we avoid applying the traditional hydrostatic reconstruction technique *** decomposition algorithm also helps us realize a simple source term *** rigorous theoretical analysis and extensive numerical examples all verify that the proposed scheme maintains the well-balanced property ***,extensive numerical results strongly suggest that the resulting scheme can accurately capture small perturbations to the steady state and keep the genuine high-order accuracy for smooth solutions at the same time.

关键词： Shallow water equations source term CWENO scheme decomposition algorithm well-balanced property

AHigh-OrderWell-Balanced Discontinuous Galerkin Method Based on the Hydrostatic Reconstruction for the Ripa Model

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Advances in Applied Mathematics and Mechanics 2020年第6期12卷 1416-1437页

作者： Jiaojiao Li Gang Li Shouguo Qian Jinmei Gao qiang niu School of Mathematics and Statistics Qingdao UniversityQingdaoShandong 266071China Department of Mathematical Sciences Xi’an Jiaotong-Liverpool UniversitySuzhouJiangsu 215123China

In this work,we present a high-order discontinuous Galerkin method for the shallow water equations incorporating horizontal temperature gradients(also known as the Ripa model),which exactly maintains the lake at rest steady ***,we propose original numerical fluxes defined on the basis of the hydrostatic reconstruction idea and a simple source term *** novel approach allows us to achieve the well-balancing of the discontinuous Galerkin method without ***,the proposed method retains genuinely high-order accuracy for smooth solutions and it shows good resolution for discontinuous solutions at the same *** numerical analysis as well as extensive numerical results all verify the good performances of the proposed method.

关键词： Ripa model lake at rest steady state source term discontinuous Galerkin method,well-balancing property hydrostatic reconstruction.