异常波及其对海上结构铃振现象的影响

海上结构物的铃振(Ringing)现象是新近发现的一种高频共振响应现象,对结构物有显著的破坏作用。从实测资料中发现,在恶劣海况下发生的具有强非线性和非对称性的异常波(Freakwave)有可能引起海上结构物的铃振响应。文中综述了可能引起铃振响应的异常波的研究现状及成果,分析了其能量分布,并指出异常波是海上结构物产生铃振现象的机理之一。     

稳定控制回路振铃现象的消除及其关键参数的选择

该文针对导弹稳定控制回路对象讨论Dahlin控制器设计问题。在复频域分析的基础上探讨了二阶对象期望闭环传递函数的合理形式。通过对期望闭环传递函数和控制对象的分析找到了导致二阶对象Dahlin控制器产生振铃的原因,给出了判定振铃产生的条件,并且提出了修正设计方法以及解决振铃现象中关键参数选择的问题。     

High speed tensile test of steel sheets for the stress-strain curve at the intermediate strain rate

This paper presents stress-strain curves of steel sheets for an auto-body obtained at intermediate strain rates with a servo-hydraulic type high speed tensile testing machine. The apparatus has the maximum stroke velocity of 7.8 m/sec to obtain the tensile material properties at a strain rate of up to 500/sec. A special jig fixture is specially designed for accurate acquisition of tensile loads with reduction of the load-ringing phenomenon induced by unstable stress wave propagation at high strain rates. Tensile testing of steel sheets for an auto-body was carried out to obtain stress-strain curves of mild steel and advanced high strength steels at strain rates ranged from 1/sec to 200/sec. The test results provide interesting information regarding the stress-strain curves at intermediate strain rates ranged from 1/sec to 200/sec and demonstrate that strain rate hardening is strongly coupled with strain hardening.