Laboratory investigation on wave transmission through two rows of perforated hollow piles     

Subba Rao  N. B. S. Rao  V. S. Sathyanarayana 《Ocean Engineering》1999,26(7):444

Experimental investigations on perforated hollow piles in two rows were conducted in a two dimensional wave flume. The influence of water depth, incident wave steepness, clear spacing between the piles and the spacing of pile rows on transmission coefficient have been studied. The effect of staggering of piles in rows is investigated. The results are also compared with the results of experiments on piles without perforations. The investigations have revealed that perforated piles attenuate more wave energy than non-perforated piles. The transmission coefficient K_t decreases as the wave steepness increases for both non-perforated and perforated piles. For non-perforated piles as relative clear spacing between the piles (b/D) decreases, for waves of higher steepness, K_t decreases while for perforated piles as b/D decreases, K_t is decreasing for all the steepness considered. As the relative clear spacing between the pile rows (B/D) increases K_t initially decreases till B/D is around one and later it starts increasing for both non-perforated and perforated piles. Staggering of piles has little effect on K_t. It is also found that water depth has insignificant influence on transmission coefficient at higher steepness for both perforated and non-perforated piles. Wave period alone does not directly influence transmission coefficient K_t.  相似文献   

The beam attenuation to chlorophyll ratio: an optical index of phytoplankton physiology in the surface ocean?   总被引：1，自引：0，他引：1  

Michael J. Behrenfeld  Emmanuel Boss 《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(12):1537-1549

The particulate beam attenuation coefficient (c_p) is proportional to the concentration of suspended particles in a size domain overlapping that of the phytoplankton assemblage. c_p is largely insensitive to changes in intracellular chlorophyll concentration, which varies with growth irradiance (a process termed ‘photoacclimation’). Earlier studies have shown that the ratio of c_p:chlorophyll (i.e., c_p^*) exhibits depth-dependent changes that are consistent with photoacclimation. Similar relationships may likewise be expected in the horizontal and temporal dimensions, reflecting changes in mixing depth, incident irradiance, and light attenuation. A link between c_p^* and more robust photoadaptive variables has never been explicitly tested in the field. Here we use five historical field data sets to directly compare spatial and temporal variability in c_p^* with two independent indices of photoacclimation: the light-saturated, chlorophyll-normalized photosynthetic rate, P^b_opt, and the light-saturation index, E_k. For the variety of oceanographic conditions considered, a first-order correlation emerged between c_p^* and P^b_opt or E_k. These simple empirical results suggest that a relationship exists between a bio-optical variable that can potentially be retrieved remotely (c_p^*) and physiological variables crucial for estimating primary productivity in the sea.  相似文献   

Coupled climate-society modeling of a realistic scenario to achieve a sustainable Earth     

Motoyoshi Ikeda 《Journal of Oceanography》2011,67(1):113-126

A conceptual model was developed to project the global warming for this century. This model incorporated several important factors associated with the climate and society. Under the forcing of anthropogenic carbon dioxide, the climate system is represented by a global mean surface air temperature (SAT) and carbon storage, which is separated into the atmosphere, land and oceans. The SAT rises due to the atmospheric carbon, which is partially absorbed by the terrestrial ecosystem and the ocean. These absorption rates are reduced by the rising SAT. The anthropogenic carbon dioxide is emitted by society, which is described by global energy production (P) and energy efficiency/carbon intensity (E), yielding a rate of P/E. P consists of the energy production per capita (H) and the population (M) in developed countries and regions, P = H × M. These society components were set to grow, based on the historical record from the last 50 years, while societal incentives to reduce the growth rate H and to increase E in proportion to the increase in SAT were introduced. It is shown that, among the basic scenarios in the Special Report on Emissions Scenarios (SRES) for this century, medium-level carbon emission—where the growth rate of H is reduced by 30% and E is doubled, with 1°C of warming—could be achieved. Until the end of this century, both the terrestrial ecosystem and the oceans act as sinks. If societal incentives are eliminated, carbon emission approaches the upper limit considered in the SRES scenarios, and the terrestrial ecosystem changes into a source of carbon dioxide. Since H and E are closely related to lifestyle and technology, respectively, individuals in the developed countries are urged to change their lifestyles, and institutions need to develop low-carbon technologies and spread them to developing countries. When society achieves medium-level carbon emission for a couple of centuries, oceanic absorption was found to become more crucial than terrestrial absorption, so oceanic behavior has to be estimated more accurately.  相似文献   

利用TOPEX/Poseidon高度计资料提取的太平洋M₂内潮能通量分布     

张效谦  梁鑫峰  周磊 《海洋学报》2005,27(5):9-14

基于内波动力学方程,提出利用TOPEX/Poseidon高度计资料提取内潮的方法.利用该方法,结合1992年10月到2002年6月共10a的TOPEX/Poseidon高度计资料和Levitus(1998)资料,给出了整个太平洋M₂内潮能通量的分布,并与观测资料进行比测,两者符合较好.同时也发现沿整个太平洋边界M₂内潮能通量向大洋内部输入的总功率为58.4GW,其中北太平洋对此贡献为30.2GW,南太平洋为28.2GW,可见南、北太平洋的贡献是基本相等的.东太平洋的总量为17.8GW,而西太平洋为40.6GW,两者差异较大(以160°W作为东、西太平洋分界线).  相似文献   

Using the acoustic-pulse conservation law in estimating the energy of surface acoustic sources by remote sounding     

S.?N.?KulichkovEmail author  O.?Ye.?Popov  A.?A.?Mishenin  I.?P.?Chunchuzov  O.?G.?Chkhetiani  N.?D.?Tsybulskaya 《Izvestiya Atmospheric and Oceanic Physics》2017,53(6):603-612

The atmospheric effect on the characteristics of infrasonic signals from explosions has been studied. New methods have been proposed to remotely estimate the energy of explosions using the data of infrasonic wave registration. One method is based on the law of conservation of acoustic pulse I, which is equal to the product of the wave profile area S/2 of the studied infrasonic signal and the distance to the source E_I [kt] = 1.38 × 10^–10 (I [kg/s])^1.482. The second method is based on the relationship between the explosion energy and the dominant period T of the recorded signal, EТ [kt] =1.02 × (Т [s]²/σ)^3/2, where σ is a dimensionless distance used for determining the degree of manifestation of nonlinear effects in the propagation of sound along ray trajectories. When compared to the conventional E_W (Whitaker’s) relation, the advantage of the EI relation is that it can be used for pulsed sources located at an arbitrary height over the land surface and having an arbitrary form of the initial-pulse profile and for any type of infrasonic arrivals. A distinctive feature of the expression for E_Т is that the atmospheric effect on the characteristics of recorded infrasonic signals is explicitly taken into account. These methods have been tested using infrasonic data recorded at a distance of 322 km from the sources (30 explosions caused by a fire that occurred at the Pugachevo armory in Udmurtia on June 2, 2011). For the same explosion, empirical relations have been found between energy values obtained by different methods: E_I = 1.107 × E _W , E _Т = 2.201 × E _I .  相似文献   

Transverse mixing and surface heat exchange in the Waikato River: A comparison of two models     

J. Christopher Rutherford  Bryan L. Williams  Ray A. Hoare 《新西兰海洋与淡水研究杂志》2013,47(3-4):435-452

Abstract

Two mathematical models of different complexity were used to study transverse dispersion and surface heat transfer in the lower Waikato River. A simple analytical streamtube model (HPLUME) gave adequate temperature predictions in a reach where the channel was fairly regular but performed poorly where there were extensive shallows. In the latter reach, a two‐dimensional numerical model (SYSTEM21) gave good temperature and flow predictions once properly calibrated. Model calibration proved to be difficult in the Waikato River because the natural river temperature varied significantly along the channel. A search method was developed to estimate both the transverse dispersion and surface heat exchange coefficients from measured plume temperature profiles based on the observation that transverse variations in natural temperature were small. This method was used to calibrate SYSTEM21 in two separate reaches. Coefficient estimates were sensitive to measurement errors and slight departures in homogeneity of natural temperature and it would be desirable to corroborate the estimates of E_z using dye tests. In the upper reach, the average transverse dispersion coefficient was E_z/hu? = 1 which is high but within the range of published values. A sharp bend and buoyant spreading contributed to the high E_z value. E_z increased with river flow because both h and u? increase with flow. In the lower reach, E_z/hu? = 0.1 which is lower than expected but islands may have affected the model calibration. The surface heat exchange coefficient averaged K = 84–167 W m^?2 s^?1 °C^?1 which falls within the range of published values. No significant relationship could be found between surface heat exchange coefficient and meteorological variables.  相似文献