SUSTech KCCommunity: 深圳国家应用数学中心
http://kc.sustech.edu.cn:80/handle/2SGJ60CL/229216
Sat, 09 Dec 2023 05:23:08 GMT2023-12-09T05:23:08ZUtility-Aware Time Series Data Release with Anomalies under TLDP
http://kc.sustech.edu.cn:80/handle/2SGJ60CL/609975
Title: Utility-Aware Time Series Data Release with Anomalies under TLDP
Authors: Yulian Mao; Qingqing Ye; Qi Wang; Haibo HuTue, 21 Nov 2023 09:42:48 GMThttp://kc.sustech.edu.cn:80/handle/2SGJ60CL/6099752023-11-21T09:42:48ZNumerical Modeling and Simulation of Fractured-Vuggy Reservoirs Based on Field Outcrops
http://kc.sustech.edu.cn:80/handle/2SGJ60CL/602365
Title: Numerical Modeling and Simulation of Fractured-Vuggy Reservoirs Based on Field Outcrops
Authors: Li，Sanbai; Kang，Zhijiang; Zhang，Yun
Description: We propose a novel workflow to investigate the complex flow behaviors and remaining oil distribution related to the oil–gas–water three-phase system based on information from typical outcrops of fractured-vuggy reservoirs. A refined geological model is built to represent the size, geometry, and spatial distribution of the karst caves and fractures extracted from the field outcrop photographs. The combination of the perpendicular bisector (PEBI) grid technique and the control-volume finite difference method is adopted for space discretization. We have validated the numerical model against experimental data. Numerical simulations were performed to explore the impacts of the permeability of karst cave and natural fractures and the position of natural water bodies upon oil production performance. Numerical results indicate that (1) the cave permeability has few impacts on the oil production, yet the fracture permeability plays a significant role in determining the oil recovery; (2) a higher permeability of the fractures will lead to a longer period of time for no-water oil production and, thus, a higher oil recovery; (3) the position of natural water body shows significant impacts on oil recovery, e.g., a short distance between the natural water body and the production well tends to form preferential passages, causing severe reduction of water flooding range; and (4) the distribution of remaining oil is controlled by spatial patterns of the fractured-vuggy system and reservoir development schemes. We found that the remaining oil is mainly distributed along the model boundaries and at the corner of the caves with single or multiple connection/s to fractures.Tue, 21 Nov 2023 06:11:41 GMThttp://kc.sustech.edu.cn:80/handle/2SGJ60CL/6023652023-11-21T06:11:41Z一种仿生机械腿及仿生机器人
http://kc.sustech.edu.cn:80/handle/2SGJ60CL/562073
Title: 一种仿生机械腿及仿生机器人
Authors: 潘阳; 余杰先
Abstract: 一种仿生机械腿及仿生机器人，其中，仿生机械腿包括腿骨件、驱使腿骨件作摆转运动的腿部舵机、驱使腿部舵机作摆转运动的髋部舵机、通过膝关节转动副连接腿骨件的足跟件以及连接在足跟件与髋部舵机的本体之间以用于吸收和/或传递足跟件承受的冲击力的腿部缓冲件。利用髋部舵机、腿部舵机、腿骨件、足跟件和腿部缓冲件共同组成一个封闭式的连杆机构，既可以通过腿部缓冲件来吸收部分冲击力，以实现减震缓冲的效果，又可以达到将冲击力转换为由机械腿整体及机械腿应用载体进行承担的效果，从而既可以大幅度提高机械腿本身的抗冲击能力，又能够为提高机械腿的运动能力（如行走速度、跳跃高度等）以及扩展机械腿的应用场景创造有利条件。
Description: 一种仿生机械腿及仿生机器人，其中，仿生机械腿包括腿骨件、驱使腿骨件作摆转运动的腿部舵机、驱使腿部舵机作摆转运动的髋部舵机、通过膝关节转动副连接腿骨件的足跟件以及连接在足跟件与髋部舵机的本体之间以用于吸收和/或传递足跟件承受的冲击力的腿部缓冲件。利用髋部舵机、腿部舵机、腿骨件、足跟件和腿部缓冲件共同组成一个封闭式的连杆机构，既可以通过腿部缓冲件来吸收部分冲击力，以实现减震缓冲的效果，又可以达到将冲击力转换为由机械腿整体及机械腿应用载体进行承担的效果，从而既可以大幅度提高机械腿本身的抗冲击能力，又能够为提高机械腿的运动能力（如行走速度、跳跃高度等）以及扩展机械腿的应用场景创造有利条件。Mon, 25 Sep 2023 09:27:48 GMThttp://kc.sustech.edu.cn:80/handle/2SGJ60CL/5620732023-09-25T09:27:48ZConstruction of storage codes of rate approaching one on triangle-free graphs
http://kc.sustech.edu.cn:80/handle/2SGJ60CL/560313
Title: Construction of storage codes of rate approaching one on triangle-free graphs
Authors: Huang，Hexiang; Xiang，Qing
Description: Consider an assignment of bits to the vertices of a connected graph Γ (V, E) with the property that the value of each vertex is a function of the values of its neighbors. A collection of such assignments is called a storage code of length |V| on Γ . In this paper we construct an infinite family of linear storage codes on triangle-free graphs with rates arbitrarily close to one.Thu, 21 Sep 2023 04:21:52 GMThttp://kc.sustech.edu.cn:80/handle/2SGJ60CL/5603132023-09-21T04:21:52ZDiscovery of Partial Differential Equations from Highly Noisy and Sparse Data with Physics-Informed Information Criterion
http://kc.sustech.edu.cn:80/handle/2SGJ60CL/560262
Title: Discovery of Partial Differential Equations from Highly Noisy and Sparse Data with Physics-Informed Information Criterion
Authors: Xu，Hao; Zeng，Junsheng; Zhang，Dongxiao
Description: Data-driven discovery of partial differential equations (PDEs) has recently made tremendous progress, and many canonical PDEs have been discovered successfully for proof of concept. However, determining the most proper PDE without prior references remains challenging in terms of practical applications. In this work, a physics-informed information criterion (PIC) is proposed to measure the parsimony and precision of the discovered PDE synthetically. The proposed PIC achieves satisfactory robustness to highly noisy and sparse data on 7 canonical PDEs from different physical scenes, which confirms its ability to handle difficult situations. The PIC is also employed to discover unrevealed macroscale governing equations from microscopic simulation data in an actual physical scene. The results show that the discovered macroscale PDE is precise and parsimonious and satisfies underlying symmetries, which facilitates understanding and simulation of the physical process. The proposition of the PIC enables practical applications of PDE discovery in discovering unrevealed governing equations in broader physical scenes.Thu, 21 Sep 2023 04:05:38 GMThttp://kc.sustech.edu.cn:80/handle/2SGJ60CL/5602622023-09-21T04:05:38ZA priori error estimates of two monolithic schemes for Biot's consolidation model
http://kc.sustech.edu.cn:80/handle/2SGJ60CL/560247
Title: A priori error estimates of two monolithic schemes for Biot's consolidation model
Authors: Gu，Huipeng; Cai，Mingchao; Li，Jingzhi; Ju，Guoliang
Description: This paper concentrates on a priori error estimates of two monolithic schemes for Biot's consolidation model based on the three-field formulation introduced by Oyarzúa et al. (SIAM J Numer Anal, 2016). The spatial discretizations are based on the Taylor–Hood finite elements combined with Lagrange elements for the three primary variables. We employ two different schemes to discretize the time domain. One uses the backward Euler method, and the other applies the combination of the backward Euler and Crank-Nicolson methods. A priori error estimates show that both schemes are unconditionally convergent with optimal error orders. Detailed numerical experiments are presented to validate the theoretical analysis.Thu, 21 Sep 2023 04:03:24 GMThttp://kc.sustech.edu.cn:80/handle/2SGJ60CL/5602472023-09-21T04:03:24ZHölder stability and uniqueness for the mean field games system via Carleman estimates
http://kc.sustech.edu.cn:80/handle/2SGJ60CL/560154
Title: Hölder stability and uniqueness for the mean field games system via Carleman estimates
Authors: Klibanov，Michael V.; Li，Jingzhi; Liu，Hongyu
Description: We are concerned with the mathematical study of the mean field games system (MFGS). In the conventional setup, the MFGS is a system of two coupled nonlinear parabolic partial differential equation (PDE)s of the second order in a backward–forward manner, namely, one terminal and one initial condition are prescribed, respectively, for the value function and the population density. In this paper, we show that uniqueness of solutions to the MFGS can be guaranteed if, among all four possible terminal and initial conditions, either only two terminals or only two initial conditions are given. In both cases, Hölder stability estimates are proven. This means that the accuracies of the solutions are estimated in terms of the given data. Moreover, these estimates readily imply uniqueness of corresponding problems for the MFGS. The main mathematical apparatus to establish those results is two new Carleman estimates, which may find application in other contexts associated with coupled parabolic PDEs.Thu, 21 Sep 2023 03:49:56 GMThttp://kc.sustech.edu.cn:80/handle/2SGJ60CL/5601542023-09-21T03:49:56ZBackflow structures in turbulent pipe flows at low to moderate Reynolds numbers
http://kc.sustech.edu.cn:80/handle/2SGJ60CL/559855
Title: Backflow structures in turbulent pipe flows at low to moderate Reynolds numbers
Authors: Chen，Xue; Chung，Yongmann M.; Wan，Minping
Description: The statistical characteristics and the evolution of the backflow structures are investigated in wall-bounded flows at Reynolds numbers up to. The backflow is caused by the joining of large-scale high- and low-speed structures in the vicinity of the wall and is formed at the tail tip of the low-speed structure. The distribution density of the backflow structures and the percentage area of the backflow region on the wall both increase with the Reynolds number. The backflow structures have an average lifespan of 8 wall units which is found to be slightly longer in the pipe than the channel, and they are convected downstream at the average velocities of the buffer region of approximately 10 wall units, similar to Cardesa et al. (J. Fluid Mech., vol. 880, 2019, R3). The backflow structures occasionally split and merge, and can form detached from the wall. Evidence shows that the split, merged and wall-detached backflow structures are caused by the near-wall structures. The split backflow structures are on average, larger and more spanwise-elongated which are split due to the spanwise shearing of the near-wall streaks. A backflow structure is formed detached from the wall when the trailing end of its carrier low-speed structure 'sits' on the near-wall high-speed streaks. The wall-detached backflow structures tend to become wall-attached by approaching the wall when undergoing a similar life cycle to the normal backflow of growth and decay with spanwise elongation because the backflow region at the tail of the low-speed structure is continuously pressed down to the wall by the high-speed structure driven by persistent vortical structures in the buffer region.Thu, 21 Sep 2023 02:42:48 GMThttp://kc.sustech.edu.cn:80/handle/2SGJ60CL/5598552023-09-21T02:42:48ZEnsemble data assimilation-based mixed subgrid-scale model for large-eddy simulations
http://kc.sustech.edu.cn:80/handle/2SGJ60CL/559773
Title: Ensemble data assimilation-based mixed subgrid-scale model for large-eddy simulations
Authors: Wang，Yunpeng; Yuan，Zelong; Wang，Jianchun
Description: An ensemble Kalman filter (EnKF)-based mixed model (EnKF-MM) is proposed for the subgrid-scale (SGS) closure in the large-eddy simulation (LES) of turbulence. The model coefficients are determined through the EnKF-based data assimilation technique. The direct numerical simulation (DNS) results are filtered to obtain the benchmark data for the LES. Reconstructing the correct kinetic energy spectrum of the filtered DNS (fDNS) data has been adopted as the target for the EnKF to optimize the coefficient of the functional part in the mixed model. The proposed EnKF-MM framework is subsequently tested in the LES of both the incompressible homogeneous isotropic turbulence and turbulent mixing layer. The performance of the LES is comprehensively examined through the predictions of the flow statistics including the velocity spectrum, the probability density functions (PDFs) of the SGS stress, the PDF of the strain rate, and the PDF of the SGS energy flux. The structure functions, the evolution of turbulent kinetic energy, the mean flow, the Reynolds stress profile, and the iso-surface of the Q-criterion are also examined to evaluate the spatial-temporal predictions by different SGS models. The results of the EnKF-MM framework are consistently more satisfying compared to the traditional SGS models, including the dynamic Smagorinsky model, the dynamic mixed model, and the velocity gradient model, demonstrating its great potential in the optimization of SGS models for the LES of turbulence.Thu, 21 Sep 2023 02:29:49 GMThttp://kc.sustech.edu.cn:80/handle/2SGJ60CL/5597732023-09-21T02:29:49ZAn efficient quasi-Monte Carlo method with forced fixed detection for photon scatter simulation in CT
http://kc.sustech.edu.cn:80/handle/2SGJ60CL/559761
Title: An efficient quasi-Monte Carlo method with forced fixed detection for photon scatter simulation in CT
Authors: Lin，Guiyuan; Deng，Shiwo; Wang，Xiaoqun
Description: Detected scattered photons can cause cupping and streak artifacts, significantly degrading the quality of CT images. For fast and accurate estimation of scatter intensities resulting from photon interactions with a phantom, we first transform the path probability of photons interacting with the phantom into a high-dimensional integral. Secondly, we develope a new efficient algorithm called gQMCFFD, which combines graphics processing unit(GPU)based quasi-Monte Carlo (QMC) with forced fixed detection to approximate this integral. QMC uses low discrepancy sequences for simulation and is deterministic versions of Monte Carlo. Numerical experiments show that the results are in excellent agreement and the efficiency improvement factors are 4 * 46 times in all simulations by gQMCFFD with comparison to GPU-based Monte Carlo methods. And by combining gQMCFFD with sparse matrix method, the simulation time is reduced to 2 seconds in a single projection angle and the relative difference is 3.53%.Thu, 21 Sep 2023 02:28:13 GMThttp://kc.sustech.edu.cn:80/handle/2SGJ60CL/5597612023-09-21T02:28:13Z