The Fig。 15 adds the response for free-free ends bound- ary conditions。 The comparison confirms that the first two peaks are entirely identical。 Differences begin af- terwards, from the third peak which corresponds to the reflection of the Gc group at what is then a free end。
Let’s note that the time range of this figure is not wide enough to show that differences also concerns the low frequency response of course。
Fig。 15 : Time histories of the bending moment in free-free and clamped-free ends configurations, in thesame element
Effect of a discontinuity of inertia moment of cross- section
In order to study the effect of a discontinuity of geomet- rical characteristics, a semi-infinite beam was consid- ered again。 It was pided into two homogeneous sec- tions differing by their inertia moment of cross-section (500 and 1000 m4)。 A wave train was generated in the second respective section with a transverse pressure load of 10 ms duration。
As pointed by theory, at their arrival at the discontinu- ity, each harmonic wave separates in a transmitted wave in the following section and a reflected one in the sec- tion of origin。 Thus, in comparison with the response without discontinuity (see Fig。 16), the signals change in both sections。 This phenomenon concerns the ampli- tude, but also frequency and celerity of each harmonic wave as both depend on the inertia moment。
With discontinuity Without discontinuity Without discontinuity
With discontinuity
With discontinuity Without discontinuity
Time (s)Fig。 16 : Time histories of the bending moment in a semi- infinite beam with and without discontinuity of inertia moment of cross-section, at three locations
Application to a beam of homogeneous characteristics by section
The previous 280 m length beam was uniformly discre- tized in 100 elements spread over 20 sections of same length each, but with different characteristics (cross- section area, shear factor, inertia moment of cross- section) representative of a passenger ship, and so pre- senting a discontinuity between the sections。 Load char- acteristics were unchanged and impulse was took the same for any duration。
As previously described, each discontinuity point is responsible of a transmission/reflection phenomenon, what considerably complicates the propagation mecha- nism so that it becomes rapidly difficult to follow the history of the dispersing wave trains。 But finally, the response is characterized by shock peaks for the shortest durations 1 and 10 ms (see Fig。 17), like the entirely homogeneous case。 For them, the maximum amplitude of the first peak occurs at the middle of the beam。 Fur- thermore, the comparison with the entirely homogene- ous case (with =0。063) reveals that the amplitude of the first peak is slightly lower for the sectioned beam (see Fig。 18)。 Finally, it has to be noticed that low fre- quencies are different obviously。
摘要在砰击响应方面，一种快速的动态方法被用来研究船体桁梁对横向冲击负载的响应，同时考虑 到弯曲波船舶和横向振动现象。虽然负荷给予了理想化，但是对与响应有关的主要特征参数及其变 化进行了研究。同时，随着越来越多代表性数据的出现，梁特征的复杂性也逐渐提升。最后与完整 3D 模型进行了实验对比。
毕业论文关键词砰击；冲力；铁摩辛柯；梁；传播；弯曲波；振动
0。 命名
A:横截面面积 c:波速（相速度） E：杨氏模量 G:剪切模量
k:波数
：剪切系数（调整系数）
:单位质量密度
：角频率
1。 引言 横向载荷冲击下船体梁的瞬态响应英文文献和中文翻译(6):http://www.youerw.com/fanyi/lunwen_94988.html