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利用高维Mbius变换群中的Clifford矩阵表示,在二元生成群中当f是双曲元素或严格抛物元素,且f和g有公共不动点时,对f和g的不动点,f和g的交换子的迹之间的关系进行了研究。得到它们等价的一个充要条件,还得出当f和g的交换子是严格抛物元素时,平面上的Jrgensen不等式在高维空间上仍成立。 相似文献
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为研究钻井船插桩对邻近平台群桩相互作用的影响,采用耦合欧拉拉格朗日(CEL)方法对桩靴贯入黏土层时邻近群桩中各桩荷载分担比、桩头附加位移及两桩相互作用系数进行了分析。首先通过对缩尺模型试验的数值分析,验证了CEL方法的可行性;然后进一步分析了桩靴贯入黏土层时对邻近群桩相互作用的影响;最后探讨了净间距、桩间距对群桩相互作用的影响。结果表明,在桩靴贯入中,前桩的荷载分担比大于后桩,且桩靴贯入至一定深度后,当净间距越小或桩间距越大时,前桩的荷载分担比越大、后桩的荷载分担比越小,但各桩的荷载分担比随桩靴贯入深度增加时的变化规律不变;净间距越大,桩头附加位移及相互作用系数越小;在桩靴贯入时,由于受群桩遮拦效应的影响,桩头附加位移及相互作用系数随桩间距的变化规律同插桩前有所不同,当桩间距大于3倍桩径时,随桩间距的增加而减小,当桩间距小于3倍桩径时,随桩间距的增加而增大。 相似文献
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熊凤兰 《中国海洋大学学报(自然科学版)》1990,(2)
本文定义了从X到Y的模糊变换σ_(g·f)和从Y到X的模糊变换σ_(g·f)~(-1)。当g(λ)=λ时这种变换便是查德提出的变换,即扩展原理。此外,还讨论了此变换的性质;指出其在代数系的同态,尤其是群同态方面的应用。并给出有关变换的唯一确定性定理。 相似文献
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初始缺陷对深海载人潜水器耐压球壳塑性稳定性影响 总被引：5，自引：0，他引：5
载人深潜器耐压球壳是中厚度壳结构,当结构发生失稳时,球壳结构的局部部位因为材料达到屈服极限而发生了塑性变形.将有限元分析与经典理论相结合,研究弹性屈曲模态缺陷、局部缺陷以及球壳整体圆度和厚度偏差对中厚度球壳结构的塑性稳定性的影响.计算结果表明中厚度球壳结构对初始缺陷并不很敏感,对球壳结构当局部缺陷范围刚好达到临界弧长时结构的承载力最弱.通过缺陷结构和完善结构的极限承载力比较,提供了初始缺陷影响曲线. 相似文献
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球柱组合壳是单壳体潜艇耐压船体结构的主要形式,其结构在极限载荷作用下的极限承载能力和变形是评估潜艇结构安全性的重要指标。 在试验模型基础上,根据三维实测初挠度数据建立含缺陷的球柱组合壳有限元模型,将极限强度计算结果与试验数据对比分析,结果表明:上述数值方法准确可靠,且缺陷的引入对于工程上潜艇结构的极限承载能力评估具有实际意义。 相似文献
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粉质土大量存在于黄河水下三角洲地区,粉土液化过程中具有类似流体的性质,可以把液化过程中的粉土视为黏性流体进行研究。基于流体力学中Stokes黏滞阻力原理,在波浪水槽试验基础上,设计了一套测量液化过程中粉土流变特性的拖球装置,并对其实用性进行验证。在铺设有粉土底床的波浪水槽中埋入可以水平滑动的小球,通过拖动小球在粉土中水平运动,测量小球所受阻力值的大小,用以计算液化粉土表观动力黏度。充分考虑试验中波浪要素、超孔压比等因素的影响。结果表明,该装置能够满足试验要求;波浪循环荷载作用下,观察到了孔压的累积至液化的过程;波浪参数对结果有较大影响,其中波高越大,表观黏度值越小;同一波高情况下,表观黏度随时间缓慢增加;随着超孔压比的升高,波浪作用下粉土表观黏度值逐渐减小。 相似文献
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利用Wolk提出的粒子追踪方程,通过等分频率法划分不规则波谱,利用MATLAB做粒子运动模拟计算,得到无因次化泰勒离散系数K/D随时间t变化的曲线;通过与Huang等得到的P-M谱的泰勒离散系数K/D计算结果比较证明了本计算方法的可靠性。采用该方法研究了不规则波条件下,波序列(同一谱型不同波面序列)和谱型(谱峰周期、有效波高、谱峰升高因子)对波浪离散系数的影响;计算结果表明:同一谱型不同波序列对泰勒纵向离散系数稳定值和稳定时间无影响;不规则波谱峰周期越大,纵向离散系数K/D越小,稳定时间越短;有效波高越大,纵向离散系数K/D越大,稳定时间越长;谱峰升高因子越大,泰勒离散系数K/D越大,稳定时间越长;与规则波相比,不规则波的泰勒离散系数K/D的值略小10%~30%。 相似文献
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深水海底管道S型铺设参数敏感性分析 总被引：5，自引：0，他引：5
以深水海底管道S型铺管法为研究对象,运用悬链线理论建立管道的静平衡微分方程,通过理论分析给出了迭代求解管道整体形态的数值计算方法,并开发相应的计算分析程序,分析了不同参数对张紧器张力和管道极限铺设水深的影响.结果表明,随着管道铺设水深、管径和壁厚、混凝土配重层厚度的增加,所需张紧器张力明显增大;当托管架底部倾角较大时,控制应变越大管道所需张力越小;当托管架底部倾角较小时,管道初始倾角越大、托管架半径越小管道所需张力越小.此外,管道的浮重度、托管架长度和半径、张紧器张拉能力、管道初始倾角对极限铺设水深有着重要的影响. 相似文献
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以液体石蜡为油相,以壳聚糖/α,β-甘油磷酸凝胶溶液为水相,用乳化法制备了壳聚糖/α,β-甘油磷酸凝胶微球,并对微球形态、粒径分布、溶胀性、蛋白吸附率、溶血率、体外降解率进行了分析。光学显微镜下显示,微球形态圆整,粒径主要分布在100～400μm;扫描电镜显示,微球内部为三维网络状结构,骨架清晰;pH=7.4的PBS缓冲液中干凝胶微球的溶胀率为218.08%,普通壳聚糖微球为70.98%;1和24h测得凝胶微球的蛋白吸附量分别为13.21和15.68μg/g,普通壳聚糖微球分别为3.71×103和4.83×103μg/g;微球的溶血率小于5%,血液相容性良好;体外降解实验显示,壳聚糖的脱乙酰度、黏度以及溶菌酶浓度对壳聚糖/α,β-甘油磷酸凝胶微球的降解性质产生影响。 相似文献
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拖网选择性引起的鱼类表型性状选择差的初步研究 总被引：5，自引：0，他引：5
本文应用数值模拟的方法,研究了拖网选择性引起的鱼类表型性状(生长速率K、极限体长L∞、初次性成熟年龄Am)的选择差,通过假设不同的白噪音CV、自然死亡系数M、极限体长L∞、种群的样本大小Ss及网目尺寸Ms来估算鱼类表型性状的选择差在最大捕捞死亡系数逐渐加强时的变化情况。模拟结果表明捕捞死亡系数越大,造成的K、L∞、Am选择差也越大,并且Am的选择差增大的速率比K、L∞的小。白噪音越大,自然死亡系数越大,种群受捕捞影响产生的K、L∞、Am的选择差越大;极限体长的大小和种群的样本大小对K、L∞、Am的选择差的影响不大;网目尺寸越大,K、L∞、Am的选择差越小。随着最大捕捞死亡系数的增大,种群的生长速率变大,极限体长变小,初次性成熟年龄提前。表明了捕捞压力造成鱼类生存环境的变化,鱼类种群发生自适应进化响应,表现在表型性状的变化,且捕捞强度越大,环境差异越大,导致的表型性状选择差越大。 相似文献
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S. J. Wheeler 《Marine Georesources & Geotechnology》2013,31(2):113-129
Abstract Where undissolved gas occurs within fine‐grained marine sediments it usually takes the form of discrete bubbles that are much larger than the normal void spaces. The possibility of buoyancy‐induced movement of these relatively large bubbles must be included when considering the transport of gas through marine sediments. A theoretical analysis shows that, under static loading conditions, bubbles larger than a critical size should have sufficient buoyancy to move upward through a fine‐grained sediment stratum, whereas bubbles smaller than the critical size should remain fixed in position. The critical radius is directly proportional to sediment shear strength, and bubbles of a realistic size should move upward only in extremely weak sediments. Further theoretical analysis shows that the critical bubble size is reduced under cyclic loading conditions, but movement of typical‐sized bubbles should still be restricted to sediments of low shear strength. A simple laboratory experiment provides support for the conclusions of the theoretical analysis. The results indicate that buoyancy‐induced movement of relatively large gas bubbles in fine‐grained sediments is most likely to occur under storm loading conditions and is unlikely to occur at depths greater than a few meters below the seabed. 相似文献
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The Eulerian?Lagrangian method (ELM) has been used by many ocean models as the solution of the advection equation, but the numerical error caused by interpolation imposes restriction on its accuracy. In the present study, hybrid N-order Lagrangian interpolation ELM (LiELM) is put forward in which the N-order Lagrangian interpolation is used at first, then the lower order Lagrangian interpolation is applied in the points where the interpolation results are abnormally higher or lower. The calculation results of a step-shaped salinity advection model are analyzed, which show that higher order (N=3?8) LiELM can reduce the mean numerical error of salinity calculation, but the numerical oscillation error is still significant. Even number order LiELM makes larger numerical oscillation error than its adjacent odd number order LiELM. Hybrid N-order LiELM can remove numerical oscillation, and it significantly reduces the mean numerical error when N is even and the current is in fixed direction, while it makes less effect on mean numerical error when N is odd or the current direction changes periodically. Hybrid odd number order LiELM makes less mean numerical error than its adjacent even number order LiELM when the current is in the fixed direction, while the mean numerical error decreases as N increases when the current direction changes periodically, so odd number of N may be better for application. Among various types of Hybrid N-order LiELM, the scheme reducing N-order directly to 1st-order may be the optimal for synthetic selection of accuracy and computational efficiency. 相似文献
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This paper aims to present the critical top tension for static equilibrium configurations of a steel catenary riser（SCR） by using the finite element method. The critical top tension is the minimum top tension that can maintain the equilibrium of the SCR. If the top tension is smaller than the critical value, the equilibrium of the SCR does not exist. If the top tension is larger than the critical value, there are two possible equilibrium configurations. These two configurations exhibit the nonlinear large displacement. The configuration with the smaller displacement is stable, while the one with larger displacement is unstable. The numerical results show that the increases in the riser＇s vertical distances, horizontal offsets, riser＇s weights, internal flow velocities, and current velocities increase the critical top tensions of the SCR. In addition, the parametric studies are also performed in order to investigate the limit states for the analysis and design of the SCR. 相似文献
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1Introduction Satelliteimagerycanbecomeavaluablecompo nentinageographicinformationsystem(GIS)data baseonlyafterithasbeengeo referencedtoaground coordinatesystemwiththedesiredprojection(Mei,etal.,2001;Wang,etal.,2002).Allimagesre ceivedatagroundreceivingst… 相似文献
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L. Vandenbulcke J.-M. Beckers A. Barth M. Aidonidis F. Ardhuin C. Fratianni D. Pallela M. Tudor P. Martin M. Rixen 《Progress in Oceanography》2009,82(3):149-167
The prediction of surface drift of floating objects is an important task, with applications such as marine transport, pollutant dispersion, and search-and-rescue activities. But forecasting even the drift of surface waters is very challenging, because it depends on complex interactions of currents driven by the wind, the wave field and the general prevailing circulation. Furthermore, although each of those can be forecasted by deterministic models, the latter all suffer from limitations, resulting in imperfect predictions. In the present study, we try and predict the drift of two buoys launched during the DART06 (Dynamics of the Adriatic sea in Real-Time 2006) and MREA07 (Maritime Rapid Environmental Assessment 2007) sea trials, using the so-called hyper-ensemble technique: different models are combined in order to minimize departure from independent observations during a training period; the obtained combination is then used in forecasting mode. We review and try out different hyper-ensemble techniques, such as the simple ensemble mean, least-squares weighted linear combinations, and techniques based on data assimilation, which dynamically update the model’s weights in the combination when new observations become available. We show that the latter methods alleviate the need of fixing the training length a priori, as older information is automatically discarded.When the forecast period is relatively short (12 h), the discussed methods lead to much smaller forecasting errors compared with individual models (at least three times smaller), with the dynamic methods leading to the best results. When many models are available, errors can be further reduced by removing colinearities between them by performing a principal component analysis. At the same time, this reduces the amount of weights to be determined.In complex environments when meso- and smaller scale eddy activity is strong, such as the Ligurian Sea, the skill of individual models may vary over time periods smaller than the forecasting period (e.g. when the latter is 36 h). In these cases, a simpler method such as a fixed linear combination or a simple ensemble mean may lead to the smallest forecast errors. In environments where surface currents have strong mean-kinetic energies (e.g. the Western Adriatic Current), dynamic methods can be particularly successful in predicting the drift of surface waters. In any case, the dynamic hyper-ensemble methods allow to estimate a characteristic time during which the model weights are more or less stable, which allows predicting how long the obtained combination will be valid in forecasting mode, and hence to choose which hyper-ensemble method one should use. 相似文献
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自Goda于1970年提出谱峰度参量Qp以来,迄今表征波群强度的因子己有十多种.对文中提及的较常用的11种因子即以后被称为现有波群因子,各作者都强调自己的优点,但何者为较好,直至目前尚无客观的评价.依据从三个测点获得的111组数据对现有波群因子予以检验,若某一因子在较短的记录长度内有连续三个值且其中最大值和最小值满足:(最大值减最小值)不大干0.005,则被称为稳定的波群因子;若这种因子又满足三个条件,即它在任一序数中出现的次数最多、在整条记录中出现的总次数最多和在整条记录的最初1280s内出现率最大,则被称为较佳波群因子.就检验的个例而言,(波高的)平均连长(L1)和波高与周期的相关系数［RHT(0)]就是这种因子.将这两个因子连结起来,今后称之为联合波群因子.因此,建议以此联合波群因子表征波群强度将会较前人采用的单因子的为好. 相似文献
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根据1978—1980年渤海及北黄海70个测站的表、底层温、盐资料,用预先给定控制临界值的聚类方法,在该海域划分出5个水团。分析结果表明。1.渤黄海暧水团在冬季为高盐特征,夏季为中盐性质;其分布范围在冬—春季较小而夏—秋季较大。2.渤海水团为中温中盐性质:其温、盐度变化较小而冬—春季范围较大。3.黄海冷水团是一个高盐水团,它在5个水团中保守性最强,而从5月至8月范围较大。4.渤海沿岸水是一个不稳定的水团,其盐度较低,温度变化较小,春季和秋季范围较大而夏季和冬季较小。5.江河冲淡水是温度变化较大的低盐水,其范围夏季大而冬季小。水团的分布,在地理位置上是从该海区之东向西,一层套一层,而各水团在不同季节有自己的模式。此外,本文还探讨了水团消长变化和渔场的关系。 相似文献