Experimental Study on the Effects of A Breakwater on Wave Field Characteristics

Studies on the possible effects of a detached breakwater on the characteristics of the wavefield are carried out experimentally.A serpentine wave generator is used to generate both uni- andmulti-directional waves.Characteristics of the wave fields analyzed here include the wave fielddirectionality,and the probability distributions of surface elevations and of the wave heights.Owing to thepresence of the breakwater,waves outside the harbour are found to be reflected with,however,concen-trated energy within the harbour entrance.In general,wave heights can be approximated with a Rayleighdistribution,with occasional deviations from the theory.This occurs more frequently for waves with high-er peak frequency values than for those with lower values both for uni-and multi-directional waves.Sur-face elevations can be approximated with the Gaussian model.although the Edgeworth's form of the typeA Gram-Charlier series expansions would yield better fits.Wave directionality is found to have nodiscernible effects on     

Biological influences on morphology and bed composition of an intertidal flat

Biological activity is known to influence sediment strength at bed–water interfaces. However, its precise effect on geomorphology and on bed composition is not known. This paper proposes a parameterization of sediment destabilizing and stabilizing organisms on three parameters that describe the erosion and mixing processes of the sediment bed, namely the critical bed shear stress, the erosion coefficient and the bioturbation coefficient. This parameterization is included in a 3D sand–mud morphodynamic model to form the sand–mud–bio model. The performance of the sand–mud–bio model is demonstrated by testing it on the Paulinapolder intertidal flat in the Western Scheldt estuary of The Netherlands. Model results show that biological influences on sediment strength result in significant morphological change and bed composition variations. Destabilizing organisms always cause a significant decrease in mud content in the bed and an increase of erosion. On the other hand, stabilizing organisms can, but do not necessarily, cause an increase of mud content and additional sedimentation.     

Numerical studies on typhoon surges in the Northern Taiwan

A numerical model for the simulation of typhoon surge has been developed for the coastal areas of the northern Taiwan. Results from the model outputs are then used as a typhoon surge data bank for 7 main estuary areas in this region. The data bank consists of the historical typhoon events from 1980 to 2004. Both characteristic and frequency analyses of the typhoon surge in the coastal region have been studied. Using these data, a relation between the surge height and pressure distribution is obtained. It is shown that, either the numerical model, or the statistical equations presented in this paper, can be used to predict possible surge heights in the estuary areas with sufficient accuracy.     

Storm-generated,hummocky stratification on the outer-Scotian Shelf

Hummocky megaripples occur on Sable Island Bank, Scotian Shelf. Submersible observations show that the megaripples form during winter storms and are subsequently obliterated through bioturbation and fair-weather reworking. The megaripples of this study were underlain by a storm bed composed of: (A) a basal scoured and infilled gravel lag facies; (B) low-angle tangential crossbedding in gravel to coarse sand; (C) anisotropic hummocky stratification in medium sand; and (D) wave ripple cross-lamination in medium/fine sand. This sequence forms a tempestite bed created by a winter storm during our sampling program. Numerical simulation of bed conditions during the storm suggests that the hummocky megaripples and hummocky stratification formed together during late stages of storm decay from conditions of sheet flow. Near-bed wave motion during deposition exceeded steady currents by an order of magnitude.     

Estimation of extreme wave heights using GEOSAT measurements

Satellite technology has yielded a large database of global ocean wave heights which may be used for engineering applications. However, the sampling protocol used by the satellite leads to some difficulties in making use of these data for practical applications. These difficulties and techniques to estimate extreme wave heights using satellite measurements are discussed. Significant wave heights for a 50-year return period are estimated using GEOSAT measurements for several regions around North America. Techniques described here may be used for estimation of wave heights associated with any specified return interval in regions where buoy data are not readily available.     

海带综合利用的进一步研究

海带类的工业利用在国外从17世纪末就开始,19世纪中叶起陆续出现了一些综合利用的方法。近20年来在这方面进行研究工作较多的国家有日本、英国、苏联等。 近几年来,我国由于大力开展了海带的人工养殖,产量猛增,为工业利用提供了必要的基础。我们在研究了海带综合利用中的两个关键性问题一一原料处理和主产品褐藻酸的提取条件——之后,接着开始了综合利用方法的研究。 国外所研究的海带综合利用要点和缺点大致是： 1. 从同一份海带中综合考虑的产品大多是褐藻酸、碘和甘露醇,而很少同时考虑氯化鉀、褐藻淀粉等其他产品; 2. 水溶性成分是用稀酸提取,这不仅消耗酸和中和用碱,而且对褐藻酸会带来很不利的影响; 3. 甘露醇和碘的分离也各有不同：高桥等推荐用铜沉淀法;英国则直接用酒精从海藻中提取甘露醇,或从稀酸提取液中加有机药品制成水不溶性甘露醇衍生物。前者所需铜盐量相当大,且对于氯化鉀、褐藻淀粉的分离研究不利;后者直接以酒精煮沸海藻,必将显著减低褐藻酸粘度,而水不溶性甘露醇沉淀的制备则成本太高,无多大实用价值。 我们认为,要寻求一个较全面、合理、轻济、简易的综合利用流程,首先应考虑： 1. 各种成分如褐藻酸、甘露醇、碘、氯化鉀、褐藻淀粉等的全面利用的流程; 2. 以水代替稀酸作提取剂;同时确定各种产品的适宜分离条件等。 综合利用流程的初步轮廓和结果已于1959年初提出。其后至1960年初这段时间内,我们对于各产品的分离条件和在各步骤中的产率等方面作了比较系统的进一步实验,并且对于先前提出的流程作了部分修正、补充。     

Advanced performance in geotechnical engineering using tomography analysis

This paper presents the technique to demonstrate reliable two-dimensional (2-D) tomography of near-surface soil through multichannel analysis of surface wave (MASW) method. The MASW method is used as seismic method for determining the shear wave velocity profile of near-surface soil with better performance. Normally, this method represents one-dimensional (1-D) soil layer profile to delineate anomalous subsurface materials and detect soil characteristics in geotechnical investigations. Conventionally, the MASW method is able to represent depth corresponding shear wave velocity through 1-D representation. In this paper, this method is improved through representation of depth and distance versus shear wave velocity profile using 2-D tomography analysis in geotechnical investigations. The outcomes of the newly developed method are more reliable and informative in comparison to the outcome of the conventional MASW method. The significance of this research is incorporating advanced tomography technique with MASW method to obtain 2-D tomography of geotechnical characteristics with consistency.     

A Hall MHD model to study energetic charged particle events produced during fluctuations in the interplanetary magnetic field intensity

Energetic charged particles, which are often observed in solar active regions, may be also produced in interplanetary space due to the decoupling of ions and electrons in plasma. The Hall term in general Ohm's law is generally thought to be responsible for the decoupling of electrons and ions in plasma during magnetic reconnection. In this paper, a Hall MHD model is developed to study energetic charged particle events produced during fluctuations in the interplanetary magnetic field intensity. Two energetic charged particle events are used to test this model. It is concluded that the Hall effect does not only play the important role in the process of magnetic reconnection, but also in energetic charged particle events produced during fluctuations in the interplanetary magnetic field intensity.     

Temperature et microturbulence dans les regions externes des protuberances

A spectroscopic investigation of a quiescent prominence has been performed: the line profiles of the H and K lines have been carefully determined in all regions of the prominence where these emissions are likely to originate in optically thin layers. Therefore we have been able to study the electron temperature T _e and the microturbulent velocity in the outer parts of the prominence. We find that on the average, T _e = 5700 K (Figure 1) and = 6.7 km s^-1 (Figure 2) which are in very good agreement with classical data. Figure 3 represents the radial velocity measurements and Figure 4 the ratio of the total intensity of H to K lines. Thus the prominence we have observed does not show for T _e and the regular increase outward which has been described by Hirayama (1971). On the other hand increases towards the Equator, in the dynamically active part of the prominence, which could indicate that represents the effect of macroturbulence rather than microturbulence (Kawaguchi, 1966). In this part of the prominence only the K line is in emission and the average value of the microturbulence is 9.4 km s^-1, the radial velocity is also generally increasing. At last, according to the absolute intensities of the H and K lines, the electron density in the outer layers of the prominence is no more than 1 × 10¹⁰ cm^-3.