METHOD–OF–LINES SOLUTION OF TIME–DEPENDENT TWO–DIMENSIONAL NAVIER–STOKES EQUATIONS

A novel approach to the development of a code for the solution of the time-dependent two-dimensional Navier–Stokes equations is described. The code involves coupling between the method of lines (MOL) for the solution of partial differential equations and a parabolic algorithm which removes the necessity of iterative solution on pressure and solution of a Poisson-type equation for the pressure. The code is applied to a test problem involving the solution of transient laminar flow in a short pipe for an incompressible Newtonian fluid. Comparisons show that the MOL solutions are in good agreement with the previously reported values. The proposed method described in this paper demonstrates the ease with which the Navier–Stokes equations can be solved in an accurate manner using sophisticated numerical algorithms for the solution of ordinary differential equations (ODEs).     

AN UNFACTORED IMPLICIT MOVING MESH METHOD FOR THE TWO-DIMENSIONAL UNSTEADY N–S EQUATIONS

An unfactored implicit time-marching method for the solution of the unsteady two-dimensional Reynolds-averaged thin layer Navier–Stokes equations is presented. The linear system arising from each implicit step is solved by the conjugate gradient squared (CGS) method with preconditioning based on an ADI factorization. The time-marching procedure has been used with a fast transfinite interpolation method to regenerate the mesh at each time step in response to the motion of the aerofoil. The main test cases examined are from the AGARD aeroelastic configurations and involve aerofoils oscillating rigidly in pitch. These test cases have been used to investigate the effect of various parameters, such as CGS tolerance and laminar/turbulent transition location, on the accuracy and efficiency of the method. Comparisons with available experimental data have been made for these cases. In order to illustrate the application of the mesh generator and flow solver to more general flows where the aerofoil deforms, results for an NACA 0012 aerofoil with an oscillating trailing edge flap are also shown.     

粉末微波滤波器的制备和特性

利用通电导线的电磁感应和铜粉的趋肤效应,试制了在超导量子计算实验系统中使用的粉末微波滤波器.滤波器的频率响应随频率升高而平缓下降,在1GHz左右衰减至-80dB.我们分析了滤波器的原理,并通过改变参数对滤波器性能的变化进行了详细的研究.     

轴流式水轮机三维非定常湍流计算及压力脉动预测

水轮机的稳定性研究是目前工程上大型水轮机组流动分析的重要课题,本文以某水电站的大型轴流转桨式水轮机原型为基础建立计算模型,完成了从蜗壳进口到尾水管出口整个流道的非定常湍流计算,预测了固定导叶进口、转轮后、尾水管进口等多个位置的压力脉动,并利用FFT变换进行分析得到了压力脉动的频率和幅值,探讨了水轮机全流道内压力脉动产生和传播的原理．     

压气机非定常叶顶间隙流的数值模拟研究

利用数值方法研究了某低速轴流孤立压气机转子中非定常叶顶间隙流的流动特征和频率特性。结果显示转子顶部区域的压力脉动主要来源于叶顶泄漏涡的非定常波动。波动的具体形式表现为泄漏涡瞬态空间位置、尺度和形态的周期性变化,波动频率为1266 Hz。     

离心泵在启动阶段的水力特性研究

针对工作的离心泵,分析了其内部流体的流动情况,建立了在非稳定工况下操作的理论扬程公式,非稳态理论扬程包括旋转加速附加扬程和水流加速消耗扬程以及由于流动速度变化引起泵壳中的附加压力而产生的扬程。在离心泵的启动阶段,对其在不同阀门开度下的水力性能进行了试验研究。测量了瞬时转速、流量、扬程随时间的变化关系,并把试验结果进行修正。由于启动时一部分扬程用来提供流体加速,压力传感器测量不到,因此必须把试验扬程加以修正。将理论计算与修正的试验结果进行了比较分析,两者基本吻合。     

A survey on HHL algorithm: From theory to application in quantum machine learning

The Harrow-Hassidim-Lloyd (HHL) algorithm is a method to solve the quantum linear system of equations that may be found at the core of various scientific applications and quantum machine learning models including the linear regression, support vector machines and recommender systems etc. After reviewing the necessary background on elementary quantum algorithms, we provide detailed account of how HHL is exploited in different quantum machine learning (QML) models, and how it provides the desired quantum speedup in all these models. At the end, we briefly discuss some of the remaining challenges ahead for HHL-based QML models and related methods.     

复合材料失效判据有效性验证方法研究

为系统地验证复合材料失效判据计算精度和有效性范围,给出了4种材料体系、6种铺层形式的层合板在单轴、双轴载荷下的失效试验数据,用以评估复合材料失效判据在单向层合板失效包线、多向层合板初始失效包线、多向层合板最终失效包线、层合板变形及层合板的破坏特性等五个方面的预测能力。并根据验证方法和有效性评估策略对失效判据计算精度进行量化考核,给出了失效判据在五个层面上的计算精度。     

压气机悬臂静叶流场非定常数值模拟

以现代高压压气机一排悬臂静叶与一排转叶组成的典型级为研究对象,采用非定常数值模拟方法,分析了非定常与定常数值模拟计算得出的级特性线以及峰值效率点气动参数在展向分布的差异,并对悬臂静叶内部流场结构进行了详细分析,结果表明:当悬臂静叶的轮毂设计间隙为2.5%叶高时,非定常计算的综合喘振裕度比定常大5.85%;在峰值效率点工况下,悬臂静叶总压损失和转子效率的非定常影响范围在10%以内,转叶进口相对气流角沿展向分布的影响在0.5°以内。悬臂静叶根部10%叶高以下区域出现了明显的泄漏流动,3.4%叶高压力系数变化最大,轮毂泄漏流起始于20%弦长附近,发展到70%弦长位置时泄漏损失最大,随后逐渐减弱.     

A Probabilistic Re-Intepretation of Confidence Scores in Multi-Exit Models

In this paper, we propose a new approach to train a deep neural network with multiple intermediate auxiliary classifiers, branching from it. These ‘multi-exits’ models can be used to reduce the inference time by performing early exit on the intermediate branches, if the confidence of the prediction is higher than a threshold. They rely on the assumption that not all the samples require the same amount of processing to yield a good prediction. In this paper, we propose a way to train jointly all the branches of a multi-exit model without hyper-parameters, by weighting the predictions from each branch with a trained confidence score. Each confidence score is an approximation of the real one produced by the branch, and it is calculated and regularized while training the rest of the model. We evaluate our proposal on a set of image classification benchmarks, using different neural models and early-exit stopping criteria.