海面对风应力的非定常响应

针对常垂直湍流系数和变垂直湍流系数两种情况，给出了开阔静止海面对风应力的非定常响应的解析表达式，并讨论了水深，风应力强弱对响应过程的影响，尽管没有考虑风场的非定常性，但本文的结果对理解海洋对风应力的非定常响应过程具有一定的帮助，对分析海面停风后的消衰过程也具有实际意义。通过与实测资料比较，认为垂直湍流系数模式要比常垂直湍流系数模式更为合理。     

单锚腿系泊系统动力计算的新方法

在Hamilton型拟变分原理体系下,建立了一种时间子域以三次和五次B样条函数插值的时间子域法,并将这种新方法用于单锚腿系泊系统的动力响应分析中。算例表明,新方法比传统的动力计算方法Wilson-θ法,在计算精度上有明显的优势,表明本方法能够用于计算单锚腿系泊系统的动力响应。     

Dynamic Response Behaviors of Upright Breakwaters Under Breaking Wave Impact

- The dynamic response behaviors of upright breakwaters under broken wave impact are analysed based on the mass-damper-spring dynamic system model. The effects of the mass, damping, stiffness, natural period, and impulse duration (or oscillation period) on the translation, rotation, sliding force, overturning moment, and corresponding dynamic amplifying factors are studied. It is concluded that the ampli-ying factors only depend on the ratio of the system natural period to impulse duration (or oscillation period) under a certain damping ratio. Moreover, the equivalent static approach to breakwater design is also discussed.     

Effect of Sea Level Variation on Tidal Characteristic Values for the East China Sea

1 .IntroductionTheglobalairtemperatureroseabout 0 .5～ 0 .6°Coverthepast 2 0thcentury ,andtheglobalmeansealevelincreasedbyabout2 0cmduringtheperiod .Theregionalmeansealevelriseswiththerisingglobalmeansealevel.Zuoetal.( 1 997)indicatedthatthemeanrisingrateofabsolutemeansealevelalongtheChinacoastontheassumptionofunifiedisostaticdatumis 2mm a .Woodworth( 1 999)analyzedsealevelspanning 1 76 8tothepresentinLiverpool,andobtainedaseculartrendforheperiodupto 1 880of0 .39± 0 .1 7mm a ,andatrendfort…     

Study on Key Technology of Using Shell Sand as Backfill for Sea Reclamation

1 .IntroductionEpicontinental sea or land could formfromcontinental shelf because of the decreasing sea levelduring Quaternary.There is a large-area shell sand deposit more than ten meters thick in the neriticzone of China .To use the abundant marine shell sandresource as engineering material for ocean engi-neering and port engineeringis veryimportant .Sand (Gred and Bjorn,1999) ,fine sand (Zhangetal .,2002) , mediumand coarse sand (Qiuet al .,1995) ,highly weathered stone ballast (Zhanetal…     

自升式平台冰激动力响应分析

应用ANSYS软件建立了平台和冰相互作用的有限元模型,构建了自升式平台的冰激振动模型,并计算基于2种冰力模型的自升式平台的动力响应。此动力分析方法具有建模方便和计算精度高的特点。以某自升式平台为例,计算了冰和平台结构相互作用的耦合效应,为自升式平台冰激振动安全评估提供了参考依据。     

Steady Response of a Ventilated Thermocline to Enhanced Ekman Pumping

The steady response of the ventilated thermocline to an increase in Ekman pumping is investigated, focusing on the effect of the mixed layer depth distribution on the subsurface density anomaly. We consider only the subtropical gyre, and the mixed layer is assumed to be deep in the northwest and shallow elsewhere with a narrow transition zone separating the deep and shallow mixed layer regions. At the intersection of this narrow transition zone and the outcrop line, low potential vorticity fluid is subducted into and ventilates the thermocline. In such a situation, an enhancement of the Ekman pumping confined to the northern subtropical gyre leads to pronounced subsurface cold anomalies in the southern subtropics, which is free of anomalous forcing. These density anomalies are much greater than those that occur when either the mixed layer depth is zonally uniform or the Ekman pumping is enhanced in the whole subtropical gyre. They are caused by anomalous changes in the trajectory of the low potential vorticity fluid in response to anomalous Sverdrup flow. This revised version was published online in July 2006 with corrections to the Cover Date.     

Wave-induced porewater pressure in a seabed with inhomogeneous permeability

We have developed an analytical treatment for the wave-induced response of a seabed with inhomogeneous permeability, by employing the boundary layer approximation. By assuming an exponential function for vertically distributed permeability, the inhomogeneous consolidation equation was formulated as Bessel's differential equation. Subsequently, we proposed some representative quantities for examining the effects of inhomogeneity of permeability. The main effects of inhomogeneity are that the boundary layer becomes thinner and the phase delay in the direction of depth becomes larger as the inhomogeneity becomes significant. In addition, it was shown that the boundary layer is properly evaluated by using the averaged permeability.     

Structural monitoring of offshore platforms using impulse and relaxation response

Monitoring offshore platforms, long span bridges, high rise buildings, TV towers and other similar structures is essential for ensuring their safety in service. Continuous monitoring assumes even greater significance in the case of offshore platforms, which are highly susceptible to damage due to the corrosive environment and the continuous action of waves. Also, since a major part of the structure is under water and covered by marine growth, even a trained diver cannot easily detect damage in the structure. In the present work, vibration criterion is adopted for structural monitoring of jacket platforms. Artificial excitation of these structures is not always practicable and ambient excitation due to wind and waves may not be sufficient for collecting the required vibration data. Alternate methods can be adopted for the same purpose, for example, the application of an impact or a sudden relaxation of an applied force for exciting the structure. For jacket platforms, impact can be applied by gently pushing the structure at the fender while relaxation can be accomplished by pulling the structure and then suddenly releasing it using a tug or a supply vessel in both cases. The present study is an experimental investigation on a laboratory model of a jacket platform, for exploring the feasibility of adapting vibration responses due to impulse and relaxation, for structural monitoring. Effects of damage in six members of the platform as well as changes in deck masses were studied. A finite element model of the structure was used to analyze all the cases for comparison of the results as well as system identification. A data acquisition and analysis procedure for obtaining the response signatures of the platform due to the impulse and relaxation procedure was also developed for possible adoption in on-line monitoring of offshore platforms. From the study, it has been concluded that both impulse and relaxation responses are useful tools for monitoring offshore jacket platforms. The present work forms the basis for the development of an automated, on-line monitoring system for offshore platforms, using neural networks.     

渭河下游河道调整过程中的复杂响应现象

应用系统复杂响应的原理研究三门峡水库上游渭河河道调整过程,表明上游河道河床形态对基面上升所作出的响应是复杂的,弯曲系数的变化为先减小而后增大,宽深比的变化是先增大后减小,比降由先减小而后增大,最后均趋于稳定.