肋骨不等间距布置对圆柱壳振动特性的影响

  目的  对多自由度系统直接采取理论解析的方法进行局域化研究具有一定的困难,为此,将运用单通带近似的等效方法对多自由度系统进行局域化研究。  方法  以梁模型为研究对象进行局域化研究,通过单通带近似的等效方法预报不等间距梁的局域化因子,将等效方法的局域化因子预报结果与统计扰动方法的结果进行对比,验证等效方法的正确性,以及通过不等间距梁的有限元模型验证等效方法的有效性。  结果  结果表明：采用单通带近似的等效方法对多自由度系统进行局域化分析具有可行性。  结论  该方法有效规避了对多自由度系统进行复杂解析的困难,实现了对多自由度系统开展局域化定量分析的工程化使用。     

水下圆柱壳自由场声辐射特性的获取

  目的  为了进一步提高鱼雷通过声自导识别复杂水面目标的精度,对随机起伏海面及水面船舶运动姿态下的声散射特性进行模拟研究。  方法  基于Kirchhoff近似和六自由度运动分解合成的方法,建立水面船舶目标多路径声散射简化预报模型。在该模型中,海面波浪对船舶六自由度运动幅度和周期的影响由经验统计值描述,通过旋转矩阵和平移矩阵,实现目标各顶点在连续运动状态下的坐标变换。基于此,利用所建预报模型,分析不同水平探测角下船舶六自由度运动分别对声散射特性的贡献度和影响。  结果  研究表明：横摇和艏摇对正横探测方位角的声散射影响较大,纵摇对艏、艉向声散射影响较大。此外,建立了船舶运动姿态与目标声散射回波特性的关系。  结论  研究结果可为声呐设备对水面目标主动声探测提供技术支撑。     

多学科设计优化研究应用现状综述

多学科设计优化是一种通过充分探索和利用系统中的相互作用的协同机制来设计复杂系统工程和子系统的方法论。综述了多学科设计优化研究和应用领域的当前进展,并针对多学科设计优化发展的两大难题——计算代价和组织复杂性,介绍了多学科设计优化的主要内容。然后分别介绍了当前处理多学科设计优化的两种方法——试验设计和多学科优化算法。船舶和海洋工程结构物设计也是一个涉及到多个学科的系统工程,然而多学科设计优化的应用却很少,因此实现船舶与海洋工程结构设计的多学科设计优化也必将具有十分广阔的前景。     

Extreme Stability of Functional Differential Equations with Finite Delay

This paper obtained some theorems that can ascertain the zero solution of Junctional differential equations are extremely unitormly stable, extremely asymptotically stable or extremely umlormly asymptotically stable. In the obtained theorems, the derivative of Liapunov function on t along the solutions of Junctional differential equations is not required to be always negative, especially, it may be even positive.     

粉质粘土及粉土地基承载力分布概型的最佳平方逼近

利用搜集到的石家庄市区粉质粘土及粉土互层土层上91个点载荷试验数据,运用最佳平方逼近法建立了地基承载力概率分布模型,给出石家庄市区粉质粘土及粉土互层地基极限承载力的多项式分布公式,并与经典正态和对数正态分布模型进行比较,说明其更接近实际分布,精度较高。对以后具体工程设计参数的优选具有重要意义。     

Using kinematic driving data to detect sleep apnea treatment adherence

People spend a significant amount of time behind the wheel of a car. Recent advances in data collection facilitate continuously monitoring this behavior. Previous work demonstrates the importance of this data in driving safety but does not extended beyond the driving domain. One potential extension of this data is to identify driver states related to health conditions such as obstructive sleep apnea (OSA). We collected driving data and medication adherence from a sample of 75 OSA patients over 3.5 months. We converted speed and acceleration behaviors to symbols using symbolic aggregate approximation and converted these symbols to pattern frequencies using a sliding window. The resulting frequency data was matched with treatment adherence information. A random forest model was trained on the data and evaluated using a held-aside test dataset. The random forest model detects lapses in treatment adherence. An assessment of variable importance suggests that the important patterns of driving in classification correspond to route decisions and patterns that may be associated with drowsy driving. The success of this approach suggests driving data may be valuable for evaluating new treatments, analyzing side effects of medications, and that the approach may benefit other drowsiness detection algorithms.     

时域有限水深格林函数及其导数的数值计算

精确快速地求取有限水深格林函数及它的导数是应用时域法求解有限水深水动力学问题的关键.通过对有限水深格林函数在不同区域渐近特性的分析,给出了使用多维Chebyshev多项式和渐近展开式快速近似计算有限水深格林函数及它的导数的方法.近似方法与直接积分方法的比较表明近似方法的计算工作量大幅减少,可以给出足够精度的计算结果.     

刚性-压力敏感性材料界面I型准静态扩展裂纹尖端场

为了研究船用工程复合材料的界面裂纹特性,建立了刚性-压力敏感粘弹塑性材料Ⅰ型准静态扩展裂纹的力学模型.在稳态扩展阶段,应力和应变具有相同的奇异量级,即(σ,ε)∝γ<'-1/(n-1)>.引入Airy应力函数,通过渐近分析得出了裂纹尖端应力和应变的分离变量形式的渐近解,并采用打靶法求得了裂纹尖端应力和应变的数值结果.数值计算结果表明,界而裂尖场主要受材料的泊松比和幂硬化指数的控制.通过对裂纹尖端场的渐近分析,从应变角度出发,提出了刚性一压力敏感性材料界面Ⅰ型准静态扩展裂纹的断裂判据.     

多学科设计优化算法比较及其在船舶和海洋平台设计上的应用

多学科设计优化(Multidiseiplinary Design Optimization,简称MDO)是一种通过充分探索和利用系统中的相互作用的协同机制来设计复杂系统工程和子系统的方法论.多学科设计优化算法是其核心部分,也是研究最活跃的领域.文中首先介绍了MDO算法的定义、分类和发展,然后从算法的来源和目的、优化过程、优缺点、改进方法和应用情况等五个方面对四种基于分解技术的MDO算法进行了综述,进而对比了这四种算法的异同点.最后,针对船舶和海洋平台设计的具体特点,归纳了适合于船舶或海洋平台多学科设计优化的MDO算法所需要具备的特征,并建议使用基于近似模型的协同优化算法或BUSS 2000算法进行船舶和海洋平台的多学科设计优化.     

Asymmetric regular sampling SPWM method based on tangent-secant midpoint approximation applied to intermediate frequency inverter power supply北大核心CSCD

［Objective］In order to reduce the switching frequency of an intermediate frequency inverter power supply, ensure the quality of the output waveform and realize digitalization easily, a SPWM sampling method based on a tangent-secant midpoint approximation is proposed. ［Methods］It is proven by deduction that the quantitative relationship of the natural sampling method can be approximated, and a Matlab/Simulink simulation model is built. The algorithm is designed and applied to an intermediate frequency inverter device, and the correctness of the proposed method is verified in the two aspects of simulation and experiment. ［Results］The simulation results show that the total harmonic distortion (THD) of the output waveform based on the tangent-secant midpoint approximation method is 2.64%, lower than the 3.99% of the symmetrical regular sampling method. The waveform quality of the tangent-secant midpoint approximation method is obviously better than that of the symmetrical regular sampling method, as it not only reduces the switching frequency but also takes into account the requirements of THD. ［Conclusions］SPWM sampling based on tangent-secant midpoint approximation is applied to the intermediate frequency power supply and is able to effectively overcome the shortcomings of the low-quality output waveform and high switching frequency of the symmetrical regular sampling method. Both theoretical analysis and engineering practice verify the rationality and correctness of the proposed method, and it can be widely extended to the field of intermediate frequency power supply installation. © 2022 Journal of Clinical Hepatology. All rights reserved.