Multiphysics modelling of fluid structure interaction using peridynamics

随着飞行速度与飞行高度的增加，流动结构愈发复杂。不规则的气动载荷和 热载荷可能会导致飞行器材料的变形、断裂和失效，进而反过来影响流场的演 化。精确模拟流固相互作用是航空航天工程中面临的巨大挑战。 本文从流体求解器、固体求解器和耦合算法三个角度入手，提出了一套新的 流固耦合算法，用于模拟可压缩流动与可变形结构之间的相互作用。该算法使用 键基近场动力学（Bond-BasedPeridynamics，BBPD）计算线弹性固体的变形、传 热和断裂，使用气体动理学格式（GasKineticScheme，GKS）模拟可压缩流体的 运动。流体域和固体域通过虚拟网格浸没边界法（ghost-cell immersedboundary method，GCIBM）耦合起来，实现流体和固体在同一框架下的共同演化。本文 的主要工作如下： (1) 介绍了近场动力学的基本理论，基于开源近场动力学计算程序开发了 热扩散模块，并对计算程序进行了数值验证。推导了键基近场动力学运动方程 和热扩散方程的控制方程和数值求解格式。利用预置裂纹的平板中裂纹的拓展， 带有裂纹的厚板中的热扩散和热载荷下膨胀的方柱三个算例验证了模型与新开 发的计算程序的正确性，展现了近场动力学在处理裂纹拓展问题时的独特优势。 这一程序为使用键基近场动力学模型进行流固力耦合和热耦合运算打下了基础。 (2) 开发了浸没边界法的程序，将GKS格式与虚拟网格浸没边界法结合起 来，用于流固耦合运算。介绍了气体动理学格式的理论，以及将气体动理学格式用 于可压缩Navier-Stokes方程的数值格式。通过零攻角与10∘攻角下NACA0012翼 型表面的亚声速绕流和超声速圆柱绕流的三个基准案例，展现了本文的GCIBM GKS算法的准确性。 (3) 提出了基于GKS，BBPD和GCIBM的新流固耦合算法，进行了数值实 验。使用气流冲击弹性平板的基准算例验证了计算框架的正确性。将计算框架应 用于气动力导致的材料内部裂纹拓展问题，展现了当前计算框架在气动力载荷 问题下的材料失效问题上独有的优势。还研究了气动热载荷下的材料内部热扩 散问题，展现了流-固-热耦合作用对于流场演化的影响。这些都为进一步开展热 载荷下的裂纹拓展问题以及流-固-力-热全耦合问题的研究打下了坚实的基础。</p

基于近场动力学的流固热耦合研究

随着飞行速度与飞行高度的增加，流动结构愈发复杂。不规则的气动载荷和热载荷可能会导致 飞行器材料的变形、断裂和失效，进而反过来影响流场的演化。精确模拟流固耦合现象是航空航天 工程中面临的巨大挑战。本文从流体求解器、固体求解器和耦合算法三个角度入手，提出了一套新 的流固耦合算法，用于模拟可压缩流动与结构之间的热相互作用。该算法使用键基近场动力学计算 固体的变形、断裂和传热，使用气体动理学格式模拟可压缩流体的运动。流体域和固体域通过虚拟 网格浸没边界法耦合起来，实现流体和固体在同一框架下的共同演化。本文研究了气动热载荷下的 材料内部热扩散问题，展现了流-固-热耦合作用对于流场演化的影响。这些都为进一步开展热载荷 下的裂纹拓展问题以及流-固-力-热全耦合问题的研究打下了坚实的基础。</p

An efficient explicit-implicit adaptive method for peridynamic modeling of quasi-static fracture formation and evolution

Understanding the quasi-static fracture formation and evolution is essential for assessing the mechanical properties and structural load-bearing capacity of materials. Peridynamics (PD) provides an effective computational method to depict fracture mechanics. The explicit adaptive dynamic relaxation (ADR) method and the implicit methods are two mainstream PD approaches to simulate evolution of quasi-static fractures. However, no comprehensive and quantitative studies have been reported to compare their accuracy and efficiency. In this work, we first develop an implicit method for bond-based peridynamics (BBPD) based on the full nonlinear equilibrium equation and the degenerate form of the bond failure function, where the Jacobian matrices are derived using the Newton-Raphson (NR) scheme. Subsequently, we analyze the solvability of the implicit BBPD scheme. Second, a consistent and comprehensive comparison of accuracy and efficiency of the explicit ADR and implicit methods is conducted, which reveals computational efficiency of the implicit methods and their limitations in accurately describing crack formation. Finally, by utilizing the unique advantage of both methods, we develop an adaptive explicit-implicit method and propose a switching criterion to deploy appropriate scheme accordingly. Four typical quasi-static problems are employed as the numerical experiments, which show the acceleration ratios of the current method range from 6.4 to 141.7 when compared to the explicit ADR. Therefore, the explicit-implicit adaptive method provides a powerful method to simulate quasi-static fracture formation and evolution

Measurement of integrated luminosity of data collected at 3.773 GeV by BESIII from 2021 to 2024

We present a measurement of the integrated luminosity e+e- of collision data collected by the BESIII detector at the BEPCII collider at a center-of-mass energy of Ecm = 3.773 GeV. The integrated luminosities of the datasets taken from December 2021 to June 2022, from November 2022 to June 2023, and from October 2023 to February 2024 were determined to be 4.995±0.019 fb-1, 8.157±0.031 fb-1, and 4.191±0.016 fb-1, respectively, by analyzing large angle Bhabha scattering events. The uncertainties are dominated by systematic effects, and the statistical uncertainties are negligible. Our results provide essential input for future analyses and precision measurements

Determination of the number of ψ(3686) events taken at BESIII

The number of ψ(3686) events collected by the BESIII detector during the 2021 run period is determined to be (2259.3±11.1)×106 by counting inclusive ψ(3686) hadronic events. The uncertainty is systematic and the statistical uncertainty is negligible. Meanwhile, the numbers of ψ(3686) events collected during the 2009 and 2012 run periods are updated to be (107.7±0.6)×106 and (345.4±2.6)×106, respectively. Both numbers are consistent with the previous measurements within one standard deviation. The total number of ψ(3686) events in the three data samples is (2712.4±14.3)×10^

Prediction of Energy Resolution in the JUNO Experiment

International audienceThis paper presents the energy resolution study in the JUNO experiment, incorporating the latest knowledge acquired during the detector construction phase. The determination of neutrino mass ordering in JUNO requires an exceptional energy resolution better than 3% at 1 MeV. To achieve this ambitious goal, significant efforts have been undertaken in the design and production of the key components of the JUNO detector. Various factors affecting the detection of inverse beta decay signals have an impact on the energy resolution, extending beyond the statistical fluctuations of the detected number of photons, such as the properties of liquid scintillator, performance of photomultiplier tubes, and the energy reconstruction algorithm. To account for these effects, a full JUNO simulation and reconstruction approach is employed. This enables the modeling of all relevant effects and the evaluation of associated inputs to accurately estimate the energy resolution. The study reveals an energy resolution of 2.95% at 1 MeV. Furthermore, the study assesses the contribution of major effects to the overall energy resolution budget. This analysis serves as a reference for interpreting future measurements of energy resolution during JUNO data taking. Moreover, it provides a guideline in comprehending the energy resolution characteristics of liquid scintillator-based detectors