计算结构力学课堂教学中的弊病及解决措施

针对计算结构力学的课程特点及船舶与海洋工程专业硕士研究生的培养要求,分析该课程课堂教学中的问题。在此基础上针对教学过程中存在的问题,提出改革的思路,在教学过程中强化实验教学,注重学生解决实际问题能力以及编程技能的培养。分组讨论,提高学生自主学习的能力,提高课程的教学质量。

赤道焊缝残余应力影响的耐压球壳极限强度分析

耐压球壳的设计与建造是保证潜器安全的关键步骤,在建造过程中不可避免会产生赤道焊缝残余应力,可能会影响到结构的力学性能.因此,有必要研究赤道焊缝残余应力对耐压球壳极限强度的影响.文中采用ANSYS的APDL语言编制数值模拟程序,首先对高强度钢对接焊厚板残余应力进行了数值计算,在与文献试验结果相一致的基础上,获得了一套高强度钢对接焊厚板残余应力的高效数值模拟分析方法;然后应用该方法对Q345耐压球壳赤道焊缝残余应力进行数值模拟研究,分析赤道焊缝残余应力对球壳极限强度的影响,并与文献试验结果进行对比研究.总体上来说,赤道焊缝残余应力对Q345耐压球壳的极限强度的影响并不显著.最后文中建立了一套考虑赤道焊缝残余应力的高强度材料耐压球壳极限强度高效数值分析方法.研究成果可为后续进行的实尺度大型耐压球壳极限强度的分析提供相关研究参考.

连接刚度对船舶减振支架振动疲劳寿命的影响

当船舶动力设备受到各种交变载荷的作用时,易导致其支撑结构发生振动,从而失效甚至破坏.但目前对船舶减振支架结构的振动疲劳和弹性体刚度对其影响的研究较少.文中建立了船舶减振支架的有限元分析模型,对其进行模态分析和频率响应分析,然后基于功率谱密度法对该支架结构进行了振动疲劳分析.通过改变连接齿轮箱与支架的弹性体刚度,来分析其对减振支架结构振动疲劳寿命的影响.由分析可知,连接齿轮箱与支架的弹性体刚度对船舶减振支架结构的振动疲劳寿命有较大影响,并得出了支架刚度与寿命之间的关系,为更加合理可靠地进行结构振动疲劳寿命分析提供了相关理论依据.

拖航工况下半潜平台撑杆对波浪砰击的敏感性

半潜式平台拖行过程中,其撑杆等细长结构承受的波浪砰击对结构的安全性影响较大,相关船级社规范明确要求在进行结构分析时需考虑波浪砰击载荷。非定常的计算流体力学(CFD)方法能较为准确地解决复杂的黏性干涉效应、波浪爬升、波浪破碎和波浪砰击等实际工程问题。因此,以982半潜式海洋平台为研究对象,结合水池物理模型试验结果,对平台撑杆在拖行工况下遭受的波浪砰击进行研究。主要对半潜平台撑杆在3种流速、风速和斜浪的拖航工况下受到的砰击压力的敏感性进行分析,阐述撑杆在波浪砰击作用下的瞬态砰击压强分布情况,得到波浪砰击压力危险区域;同时,给出拖航工况下撑杆砰击压力系数的变化规律,为分析预报半潜式平台撑杆在复杂的拖航海况下受到的砰击压力提供参考。

Positional distribution of fatty acids on the glycerol backbone during the biosyn-thesis of glycerolipids in Ectocarpus fasciculatus

The biosynthesis of glycolipids in E.fascicula-tus was studied by 14C label and chase. The fatty acids in sulphoquinovosyl diacylglycerol (SQDG) were almost 16-car-bon and 18-carbon ones. In addition to the two fatty acids, monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG) contained 8.5 mol% and 31.0 mol% of eicosapentaenoic acid (20 : 5), respectively, and this fatty acid was usually distributed in the sn-1 position of the glyc-erol backbone. When plants were incubated with [2-14C] acetate, differences existed in the positional distribution of the labeled fatty acids in sn-1 and sn-2 among the three glycerolipids. In SQDG, 14C-labeled fatty acids were distributed uniformly in the sn-1 and sn-2 positions. In DGDG, 14C-labeled fatty acids were mainly distributed in the sn-2 position. In MGDG, the radioactivity of fatty acids in sn-1 position was far greater than that in sn-2 position after a 30 min pulse label, and the difference in radioactivity between the two positions

The photodamage process of pigments and proteins of PSI complexes from Spinacia Oleracea L.

Purified PSI complexes from Spinacia Oleracea L. were exposed to the strong light (PFD=2300μmol m-2s-1) for various period. Along with the illumination the photo-damage process of pigments and proteins of PSI complexes was investigated using absorption, fluorescence, circular dichroism (CD) spectroscopy and SDS-PAGE. It was found from the optical absorption spectra that the maximal ab-sorbance of PSI complexes decreased and maximal peaks blue-shifted during the illumination, and the forth derivative spectra demonstrated that the absorbance decreasing at red region mainly resulted from the aborbance decreasing of the long wavelength Chla, implying that the long-wavelength Chla was readily to be bleached. The CD signals contributed by LHCI decreased more rapidly than other CD signals con-tributed by Chla and Carotenoid, indicating that the LHCI was more sensitive to light than core complexes. It was observed by SDS-PAGE that some small polypeptides of PSI complexes were damaged earlier than reaction

Simulation for the primary electronic donor of photosystem II in vitro

Histidine coordinated to Chl a is a distinct characteristic of Chl a in vivo. By usinghistidine analogue of 1-methylimidazole (C4H6N2) and measuring the UV/vis absorption, CD and MCD spectra of the interaction between C4H6N2and Chl a in CCI4, we have obtained that: (i) In pure CCI4 solvent, Chl a molecule is in five-coordinate state, and two Chl a molecules form an asymmetric compact-dimer with strong coupling interaction. We propose that the two Chl a molecules are connected by two unequally coordinated Mg-O bonds (the two oxygen atoms come from the C=O of C131 keto and C17 ester, respectively); (ii) when the molar ratio of C4H6N2/Chl a is 0.5 or 1 (corresponding to 2Chl a #1C4H6N2 and 2Chl a ·2C4H6N2, respectively), significant changes have been observed in the absorption, CD and MCD spectra, which indicate that the Chl a remains in dimer form, but the coupling interaction between them reduces greatly. We postulate that C4H6N2 replaces the ligation of C=O of C17 ester and C131 keto to Mg atoms

Effects of different aggregation forms of LHC Ⅱ from Bryopsis corticulans on the excited state properties of Chl a

Steady-state and time-resolved fluo- rescence spectroscopies have been used to study the excited state properties of Chl a in different ag- gregation forms of light-harvesting complex II (LHC II) from an intertidal green alga, Bryopsis corticulans, i.e. LHC II monomer, trimer and oligomer. When either Chl a or Chl b was selectively excited, the observed decrease in Chl a fluorescence in the oligomer is proved to be caused mainly by the fast fluorescence quenching among Chl a molecules, rather than by the decrease in Chl b-to-Chl a singlet excitation transfer efficiency. Analyses of the picosecond time-resolved fluorescence kinetics identified two exponential de- cay components in all of the three forms of LHC II: a longer-lived component (4.1―4.7 ns) originating from fluorescence emission of Chl a, and a shorter-lived one (135―540 ps) from the rapid equilibration of singlet excitation among Chl a molecules. The time constant of excitation equilibration is 135 ps in oli- gomer, 520 ps in trimer and 540 ps in monomer. These results imply that LHC II in oligomer form is inherently able to quench Chl a excitation, a mecha- nism which may be related to the photoprotection of PS II via changing the degree of LHC II aggregation in Bryopsis corticulans.

Mutagenesis of Ser^(24) of cytochrome b559 α subunit affects PSII activities in Chlamydomonas reinhardtii

In order to study the functions of cytochrome b559 (Cyt b559) in photosystem two (PSII) activity, mutant S24F of Chlamydomonas reinhardtii was constructed using site directed mutagenesis, in which Serine24 (Ser24) locating downstream of Histidine23 (His23) in α subunit of Cyt b559 was replaced by Phenylalanine (Phe). Physiological and biochemical analysis showed that mutant S24F could be grown photoautotrophically or photoheterotrophically. However, their growth rate was slower either on HSM or TAP medium than that of the control; Analysis of PSII activity revealed that its oxygen evolution was about 71% of wild type (WT); The Photochemical efficiency of PSII (Fv/Fm) of S24F was reduced 0.23 compared with WT; S24F was more sensitive to strong light irradiance than the wild type; Furthermore, SDS-PAGE and Western-blotting analysis indicated that the expression levels of α subunit of Cyt b559, LHCII and PsbO of S24F were a little less than those of the wild type. Overall, these data suggests that Ser24 plays a significant role in making Cyt b559 structure maintain PSII complex activity of oxygen evolution although it is not directly bound to heme group.