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201.
It is important to assess the consequences of ship encounters with abnormal waves due to the perceived dangers of such encounters. A starting point for this is the assessment of global loads, with a focus on examining how the design rules fare with respect to loads induced by abnormal wave encounters. This paper presents the results of an experimental investigation into the global wave induced loads experienced in a range of abnormal sea states. Results are obtained for a segmented, flexible backbone model of a typical naval frigate. Abnormal wave encounters result in a significant increase in the global wave-induced loads compared to the equivalent random sea, with slamming becoming considerably more severe. Through comparisons with the experimental measurements it is concluded that the design rules which allow for an extreme wave encounter provide a reasonable safety margin for the global loads in abnormal waves, although discrepancies occur towards the aft of the vessel. Further investigation of the amount and conditions in which the design rules may be exceeded by an abnormal wave encounter is required. 相似文献
202.
203.
M. R. S. C. Bose G. Thomas R. Palaninathan S. P. Damodaran P. Chellapandi 《Experimental Mechanics》2001,41(2):144-150
This paper presents the results of an experimental study on the buckling of scaled-down models of the inner vessel used in
nuclear reactor structures. The inner vessel, a shell of composite geometry, consists of two cylindrical shells connected
by conical and torus shells. There are six stand-pipes on the conical portion of the vessel carrying heat exchangers and pumps.
Scaled-down models of the inner vessel are made by the conventional fabrication methods (rolling, welding) and are tested
in the present study. The test setup consists of a loading system for applying concentrated load on the stand-pipes, an air
compressor for applying internal pressure and the related instrumentation. Imperfection scans are carried out in a specially
fabricated experimental setup using linear variable differential transformers (LVDTs) before and during loading. Using the
scanned raw data, the initial geometric imperfections and eccentricity between the LVDTs and the specimen axes at different
axial locations are calculated. The results show that the maximum initial imperfections are on the order of 1.75 times the
wall thickness; generally, the growth of deformation patterns with loading resembles the shapes of initial imperfections,
and the growth is predominant on lower cylinder and torus regions. The general purpose, finite element-based software, ABAQUS,
is used to obtain the analytical values. The initial imperfections measured on the experimental models are incorporated into
the finite element models. The agreement between experimental and analytical buckling loads is within about 30 percent error. 相似文献
204.
对在快增殖反应堆堆本性的裙座上和在主容器上分别有初始缺陷时,进行了地震作用下静态屈曲模拟分析,采用Sup-SAP93程序,先分析了元初始缺陷的堆本体在室温(20℃)和高温(400℃)、无液压和有液压时在模拟水平地震激励下的屈曲荷载与屈曲模态。然后,假设两种初始缺陷分布,第一种是用室温和无液体时无初始缺陷的堆本体在模拟水平地震激励下计算得到的屈曲模态作为初始缺陷的形状。第二种是用公式确定初始缺陷纵向波数及最大值。计算结果表明,无论是室温还是高温,无论有无液压,无论初始缺陷在裙座还是在主容器上,屈曲都发生在裙座上。随着裙座初始缺陷的增大,屈曲荷载下降。而主容器上初始缺陷对屈曲荷载几乎没有影响。 相似文献
205.
锥形血管入口区域内管壁与血液的耦合运动 总被引:6,自引:0,他引:6
本文研究了锥形血管入口区域内血管壁与血液间的耦合问题。对具有锥度角的弹性血管入口区域内的管壁运动和血液流动建立的相互耦合作用的数学模型,在满足相应的边界条件下求得了一组血液流动的速度分布公式、压力分布公式以及管壁运动公式,得出了一些重要的结论。 相似文献
206.
207.
衍射时差法(Time of flight diffraction,TOFD)技术是一种能够探测和精确测量缺陷尺寸的新型超声无损检测方法,针对该检测方法具有缺陷检出率高、缺陷定位定量精度高等优点。本文采用商业有限元软件ABAQUS,对汽包筒体与球形封头不等厚对接和超高压水晶釜两种特殊几何构件进行了超声TOFD技术的二维数值模拟研究,分析了超声波在这两种构件中的传播特性和规律。经分析从构件表面不同位置接收到的波型,当构件中存在损伤时,通过接收损伤所引起的衍射波,可判断构件中是否存在缺陷。模拟结果表明能够将超声TOFD技术应用于这两种特殊结构的压力容器构件,可扩大超声TOFD技术的应用范围。 相似文献
208.
《Ultrasonics sonochemistry》2014,21(5):1866-1874
This study investigated the mechanical bioeffects exerted by acoustic droplet vaporization (ADV) under different experimental conditions using vessel phantoms with a 200-μm inner diameter but different stiffness for imitating the microvasculature in various tumors. High-speed microscopy, passive cavitation detection, and ultrasound attenuation measurement were conducted to determine the morphological characteristics of vascular damage and clarify the mechanisms by which the damage was initiated and developed. The results show that phantom erosion was initiated under successive ultrasound exposure (2 MHz, 3 cycles) at above 8-MPa peak negative pressures (PNPs) when ADV occurred with inertial cavitation (IC), producing lesions whose morphological characteristics were dependent on the amount of vaporized droplets. Slight injury occurred at droplet concentrations below (2.6 ± 0.2) × 106 droplets/mL, forming shallow and rugged surfaces on both sides of the vessel walls. Increasing the droplet concentration to up to (2.6 ± 0.2) × 107 droplets/mL gradually suppressed the damage on the distal wall, and turned the rugged surface on the proximal wall into tunnels rapidly elongating in the direction opposite to ultrasound propagation. Increasing the PNP did not increase the maximum tunnel depth after the ADV efficiency reached a plateau (about 71.6 ± 2.7% at 10 MPa). Increasing the pulse duration effectively increased the maximum tunnel depth to more than 10 times the diameter of the vessel even though there was no marked enhancement in IC dose. It can be inferred that substantial bubble generation in single ADV events may simultaneously distort the acoustic pressure distribution. The backward ultrasound reinforcement and forward ultrasound shielding relative to the direction of wave propagation augment the propensity of backward erosion. The results of the present work provide information that is valuable for the prevention or utilization of ADV-mediated mechanical bioeffects in clinical applications. 相似文献
209.
210.
李勇 《中国科学A辑(英文版)》2002,45(7)
By identifying the dates of the Zhouji materials (one kind of oracle bone) during the period of King Xin (also called Zhou the last monarch in Shang Dynasty), this paper establishes a new "Direct Solving Method" (DSM) to solve the chronology problems in the Shang and Zhou dynasties. The mathematical models are more suitable for those materials with the Ganzhi (the Heavenly Stems and Earthly Branches, the Chinese ancient date recorded method being of the 60-day cycle, that the repetitive cycle is independent of any astronomical parameter, each day within this cycle has its own name and can also be expressed by the numbers from l to 60) record of the date, lunar month, and their year intervals and all of them are in history documents, oracle bones and bronze vessels. For example, taking the 12 Zhouji materials in the period of King Xin,we derive the two best results of the first year when Xin assumed the reins of government in probably 1063 BC or 1052 BC. 相似文献