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1.
在标准实验室环境里，对超高分子量聚乙烯(UHMWPE)和高密度聚乙烯(HDPE)网线的拉伸力学性能进行了比较研究。结果表明：UHMWPE网线较HDPE网线具有较高的强度、拉伸模量和结强损失率；而HDPE网线较UHMWPE网线具有较高的断裂伸长率。结论可供渔具设计及网线材料选配时参考。  相似文献   

2.
The main purpose of this study is to establish a better understanding of the relationship between drag reduction and surface roughness. Experiments were conducted to measure the force and flow characteristics of a circular cylinder with different types of artificial surface roughness over the range 6 × 103 < Re < 8 × 104 (Re is based on the cylinder diameter D). The roughness cylinder was formed by covering the exterior surface of the cylinder with uniformly distributed (1) sandpaper, (2) netting, and (3) dimples. The roughness coefficient ranged from k/D = 0.0028 to 0.025 (k is the roughness height). A detailed quantitative measurement of the flow field around the cylinder using Particle Imaging Velocimetry (PIV) was carried out. The hydrodynamic force coefficients (drag and lift) of the rough cylinders are compared against those of a smooth cylinder measured under the same flow conditions. It is found that certain configuration of surface roughness significantly reduces the mean drag coefficient of the cylinder, particularly at large Reynolds numbers. In addition, the root-mean-square (r.m.s.) lift coefficient of the rough cylinders is considerably lower than that of a smooth cylinder.  相似文献   

3.
高强度聚乙烯菱形网目经编网片的力学性能初步研究   总被引：7，自引：0，他引：7  
给网箱设计与渔用材料的合理选配提供参考,初步研究了渔用高强度聚乙烯菱形网目经编网片(简称HSPE经编网片)的力学性能。研究结果表明,(1)在同等条件下,36股HSPE经编网片网目强力、网片纵向断裂强力分别比36股普通聚乙烯菱形网目经编网片(简称PE经编网片)增加了48.9%,11.6%,而前者的网片纵向断裂伸长率比后者减少了29.4%;(2)在相同网目长度条件下,36股HSPE经编网片网目强力、网片纵向断裂强力分别比42股锦纶菱形网目经编网片(简称PA经编网片)增加了27.2%,37.9%,而前者的网片纵向断裂伸长率比后者减少了33.6%;(3)36股HSPE经编网片较36股PE经编网片和42股PA经编网片具有性能价格比优势;HSPE经编网片在网箱养殖等渔业生产中推广应用上具有可行性。  相似文献   

4.
为给深水网箱设计与渔用材料的合理选配提供依据,应用ISO1806等对渔用高强度聚乙烯绞捻网片(以下简称HSPE绞捻网片)和普通聚乙烯绞捻网片(以下简称PE绞捻网片)的拉伸力学性能进行了比较研究。结果表明,(1)在同等条件下,36股HSPE绞捻网片的网目连接点断裂强力和网片单线断裂强力分别比52股PE绞捻网片增加了3.1%,3.7%;而前者的目脚直径和网片阻力可较后者减少19.6%。(2)对网片强力进行了再现性研究,36股HSPE和52股PE绞捻网片网目连接点断裂强力的标准偏差分别为35.93N,25.61N,再现性标准偏差分别为31.07N,36.93N;网片单线断裂强力的标准偏差分别为19.91N,13.49N,再现性标准偏差分别为20.48N,15.49N;网片强力测试数据的变异系数均小于4%;表示测试结果的分散性较小。(3)36股HSPE绞捻网片成本可较52股PE绞捻网片减少38.9%,其在渔业生产中进行推广应用具有可行性。(4)GB/T4925作为一个标准,对绞捻网片来说,存在不足,建议对GB/T4925进行修订。  相似文献   

5.
Fiber reinforced polymer composite deck panels are effectively used in the construction of offshore structures such as pontoons, floating docks, oil drilling platforms, ocean thermal energy conversion (OTEC) systems and harbor structures due to their excellent corrosion and fatigue resistance, high strength to weight ratio and stiffness to weight ratio and less maintenance cost. The main objective of this investigation is to study the load–deflection behavior of glass fiber reinforced polymer (GFRP) composite deck panels under static loading. Three prototype GFRP composite deck panels each with a size of 3000 mm×1000 mm×300 mm were fabricated using hand lay-up process and tested under a factored load of AASHTO HS20/IRC Class A wheeled vehicle. The deck panels were analyzed using the standard FE software, ANSYS. Maximum deflection and strain at factored load, and flexural and shear rigidities were calculated in the FE analysis and compared with the experimental data, and also with the specifications given by the Ohio Department of Transportation (ODOT), USA. From this study, it is concluded that the fabricated GFRP deck panels satisfied the performance criteria specified by ODOT and can be used in berthing structures, bridges in coastal regions, offshore oil platforms, OTEC systems and also in seismic prone areas.  相似文献   

6.
Large-amplitude internal solitary waves (or “solitons”) occurring in packets near the shelf break in the Bay of Biscay are well-documented and understood. The presence of similar features has now also been reported in the central Bay, ≈150 km from the nearest shelf break topography. The present paper analyses available remote-sensing synthetic aperture radar (SAR) data from the ERS satellites in this region. By doing so, we are able to provide convincing support for the hypothesis that these waves, instead of having travelled along the thermocline from the shelf break, are instead generated locally in the central Bay by the surfacing of a beam of internal tidal energy originating from the shelf break. This reinforces the results of a previous independent study, while at the same time providing a much more extensive investigation than was then possible. We have also exploited the large swath width (100 km) and high spatial resolution (100 m×100 m) of the SAR to examine for the first time the full surface structure of the internal waves in the central Bay, which are found to have a mean wavelength of 1.35 km, and a mean along-crest “coherence” length of 21.55 km.  相似文献   

7.
We describe experiments with multi-directional focused waves interacted with a vertical circular cylinder in a 3D wave basin. The focus of this study is on the run-up of multi-directional focused waves, wave forces, and wave pressures on the cylinder. Part I, the study on wave run-up, has already been presented by Li et al. (2012). In this paper, the analysis of the wave force on the vertical cylinder is presented.In this experiment, a cylinder with 0.25 m in diameter was adopted and different wave parameters, such as focused wave amplitude, peak frequency, frequency bandwidth and directional spreading index, are considered. The model scale kpa (kp is the wave number corresponding to peak frequency, a is the radium of the cylinder) varies from 0.32 to 0.65. The maximum forces of multi-directional focused wave on cylinder were measured and investigated. The results showed that the wave parameters have a significant influence on the wave force, and that the spatial profile of the surface of multi-directional focused wave can also affect its force on the cylinder, which is different from two-dimensional wave. In addition, the ‘secondary loading cycle’ phenomenon was also observed and discussed. In our experiments, the ‘secondary loading cycles’ occur when kA > 0.36 for all cases. While in some referred small scale experiments, the secondary load cycles are observed even for kA = 0.2, when the waves are longer enough. To larger model scale, the pronounced secondary load cycle occurs with larger wave steepness waves.  相似文献   

8.
Beyond the shelf break at ca. 150 m water depth, sulfate reduction is the only important process of organic matter oxidation in Black Sea sediments from the surface down to the sulfate–methane transition at 2–4 m depth. Sulfate reduction rates were measured experimentally with 35SO42−, and the rates were compared with results of two diffusion-reaction models. The results showed that, even in these non-bioirrigated sediments without sulfide reoxidation, modeling strongly underestimated the high reduction rates near the sediment surface. A hybrid modeling approach, in which experimentally measured rates in the upper sediment layers force a model that includes also the deeper layers, probably provides the most realistic estimate of sulfate reduction rates. Areal rates of sulfate reduction were 0.65–1.43 mmol SO42− m−2 d−1, highest in sediments just below the chemocline. Anaerobic methane oxidation accounted for 7–11% of the total sulfate reduction in slope and deep-sea sediments. Although this methane-driven sulfate reduction shaped the entire sulfate gradient, it was only equivalent to the sulfate reduction in the uppermost 1.5 cm of surface sediment. Methane oxidation was complete, yet the process was very sluggish with turnover times of methane within the sulfate–methane transition zone of 20 yr or more.  相似文献   

9.
In this study, a three-way factorial experimental design was used to investigate the diurnal changes of photosynthetic activity of the intertidal macroalga Sargassum thunbergii in response to temperature, tidal pattern and desiccation during a simulated diurnal light cycle. The maximum (Fv/Fm) and effective (ΦPSII) quantum yields of photosystem II (PSII) were estimated by chlorophyll fluorescence using a pulse amplitude modulated fluorometer. Results showed that this species exhibited sun-adapted characteristics, as evidenced by the daily variation of Fv/Fm and ΦPSII. Both yield values decreased with increasing irradiance towards noon and recovered rapidly in the afternoon suggesting a dynamic photoinhibition. The photosynthetic quantum yield of S. thunbergii thalli varied significantly with temperature, tidal pattern and desiccation. Thalli were more susceptible to light-induced damage at high temperature of 25 °C and showed complete recovery of photosynthetic activity only when exposed to 8 °C. In contrast with the mid-morning low tide period, although there was an initial increase in photosynthetic yield during emersion, thalli showed a greater degree of decline at the end of emersion and remained less able to recover when low tide occurred at mid-afternoon. Short-term air exposure of 2 h did not significantly influence the photosynthesis. However, when exposed to moderate conditions (4 h desiccation at 15 °C or 6 h desiccation at 8 °C), a significant inhibition of photosynthesis was followed by partial or complete recovery upon re-immersion in late afternoon. Only extreme conditions (4 h desiccation at 25 °C or 6 h desiccation at 15 °C or 25 °C) resulted in the complete inhibition, with little indication of recovery until the following morning, implying the occurrence of chronic PSII damage. Based on the magnitude of effect, desiccation was the predominant negative factor affecting the photosynthesis under the simulated daytime irradiance period. These results may explain the distribution pattern of this species in natural habitats, where it is generally restricted to tide pools in the intertidal zone of wave-swept rocky shores which could provide shelter from desiccation stress during low tide.  相似文献   

10.
《Coastal Engineering》2006,53(8):675-690
It is important to accurately locate the wave breaking region for the calculation of nearshore hydrodynamics. Energy from breaking waves drives hydrodynamic phenomena such as wave set-up, set-down, wave run-up, longshore currents, rip currents, and nearshore circulation. Numerous studies have been undertaken to describe when and where wave breakings occurs. Recent development of computer resources permits the use of phase-resolving numerical models for the study of wave propagation, transformation, and nearshore hydrodynamics. This requires new types of wave breaking criteria for the numerical model. The Relative Trough Froude Number (RTFN) is a new wave breaking criterion. This model is based on the moving hydraulic jump concept, therefore it satisfies properly posed boundary-value conditions. It has been experimentally proved that a critical RTFN at the initiation of wave breaking is consistent with and without the presence of an opposing current, but previous efforts did not investigate the theory for the critical value. This paper provides a theoretical analysis and a numerical analysis to demonstrate why the RTFN theory works as a wave breaking initiation (trigger) index. The theoretical analysis provides a universal constant for the initiation of wave breaking for all water depths assuming the Miche formula properly describes the wave breaking condition. A subroutine for wave breaking in a numerical model, FUNWAVE was modified to include the RTFN trigger. The numerical model was calibrated with data from wave tank experiments, and it was found that the critical condition is very close to the theoretical number, CTFN = 1.45. A second paper (in preparation) provides details of the theory and experiments for a second criterion for termination of wave breaking. The time scale for the establishment of the breaking region i.e., between the initiation position and termination position, depends upon the additional momentum present under turbulent condition within the breaking wave. This subject is not considered herein.  相似文献   

11.
The water mass structure and circulation of the continental shelf waters west of the Antarctic Peninsula are described from hydrographic observations made in March–May 1993. The observations cover an area that extends 900 km alongshore and 200 km offshore and represent the most extensive hydrographic data set currently available for this region. Waters above 100–150 m are composed of Antarctic Surface Water and its end member Winter Water. Below the permanent pycnocline is a modified version of Circumpolar Deep Water, which is a cooled and freshened version of Upper Circumpolar Deep Water. The distinctive signature of cold and salty water from the Bransfield Strait is found at some inshore locations, but there is little indication of significant exchange between Bransfield Strait and the west Antarctic Peninsula shelf. Dynamic topography at 200 m relative to 400 m indicates that the baroclinic circulation on the shelf is composed of a large, weak, cyclonic gyre, with sub-gyres at the northeastern and southwestern ends of the shelf. The total transport of the shelf gyre is 0.15 Sv, with geostrophic currents of order 0.01 m s-1. A simple model that balances across-shelf diffusion of heat and salt from offshore Upper Circumpolar Deep Water with vertical diffusion of heat and salt across the permanent pycnocline into Winter Water is used to explain the formation of the modified Circumpolar Deep Water that is found on the shelf. Model results show that the observed thermohaline distributions across the shelf can be maintained with a coefficient of vertical diffusion of 10-4 m2 s-1 and horizontal diffusion coefficients for heat and salt of 200 and 1200 m2 s-1, respectively. When the effects of double diffusion are included in the model, the required horizontal diffusion coefficients for heat and salt are 200 and 400 m2 s-1, respectively.  相似文献   

12.
Measurements of dissolved inorganic carbon (DIC), pH, total alkalinity (TA), and partial pressure of CO2 (pCO2) were conducted at a total of 25 stations along four cross shelf transects in the East China Sea (ECS) in January 2008. Results showed that their distributions in the surface water corresponded well to the general circulation pattern in the ECS. Low DIC and pCO2 and high pH were found in the warm and saline Kuroshio Current water flowing northeastward along the shelf break, whereas high DIC and pCO2 and low pH were mainly observed in the cold and less saline China Coastal Current water flowing southward along the coast of Mainland China. Difference between surface water and atmospheric pCO2 (ΔpCO2), ranging from ~ 0 to ? 111 μatm, indicated that the entire ECS shelf acted as a CO2 sink during winter with an average flux of CO2 of ?13.7 ± 5.7 (mmol C m? 2 day? 1), and is consistent with previous studies. However, pCO2 was negatively correlated with temperature for surface waters lower than 20 °C, in contrast to the positive correlation found in the 1990s. Moreover, the wintertime ΔpCO2 in the inner shelf near the Changjiang River estuary has appreciably decreased since the early 1990s, suggesting a decline of CO2 sequestration capacity in this region. However, the actual causes for the observed relationship between these decadal changes and the increased eutrophication over recent decades are worth further study.  相似文献   

13.
A renewable energy harvester using the piezoelectric effect is developed for the ocean tidal and wind flow. The harvester is made of connected driving blades to an octo-generator, which has a rotator with n blades and a stator attached by eight mass-spring-piston-cylinder-piezoelectricity devices. The resonance and force magnification are utilized to increase the power output of the harvester. A corresponding mathematical model is developed to calculate the root mean square of the generated electric power. The simulation results indicate that the generated power is largely enhanced when the near-resonant condition is established. The power increases with increases in the magnetic flux density, the large-to-small diameter ratio of the cylinder, the size of magnetic bar face, and decreases in the gap between two magnetic faces and the size of the piezoelectric bar face. A generated power of 5 kW is realized by the harvester working under an ocean tidal speed, V = 1.75 m/s, and its geometric and material properties of driving length L = 7.5 m, spring constant kv = 65000 N/m, gap between the two magnets s = 0.0015 m, large to small diameter ratio of the cylinder z = 6, and magnetic flux density Br = 1.45 T.  相似文献   

14.
We examined the bioaccumulation and trophic transfer of mercury in two marine finfish species, striped bass (Morone saxatilis) and tautog (Tautoga onitis), collected from the Narragansett Bay (Rhode Island, USA). For each of these target fish, white muscle tissue was analyzed for total mercury (Hg) and results were evaluated relative to fish age, body size, and Hg content of preferred prey. Dietary and stable isotope analysis was also used to elucidate the effect of trophic processes on Hg concentrations in fish. The Hg content of muscle tissue was positively correlated with fish age and length for both species, although striped bass accumulated Hg faster than tautog. Accelerated Hg bioaccumulation in striped bass is consistent with its high trophic level (trophic level = 4.07) and Hg-enriched prey (forage fish and macrocrustaceans; mean Hg content = 0.03 mg Hg kg wet wt?1). In contrast, tautog maintain a lower trophic status (trophic level = 3.51) and consume prey with lower Hg levels (mussels and crabs; mean Hg content = 0.02 mg Hg kg wet wt?1). Despite differences in Hg bioaccumulation between target fish, the mean Hg concentration of tautog exceeded levels in striped bass (0.24 and 0.16 mg Hg kg wet wt?1, respectively) due to a disparity in age-at-catch between sampled groups (mean age of tautog and bass = 11.3 and 4.3 yr, respectively). Taking into account legal minimum catch lengths further revealed that 75.0% of legal-size striped bass (>70.2 cm TL; n = 4) and 44.8% of tautog (>40.6 cm TL; n = 29) had Hg levels beyond the US EPA regulatory threshold of 0.3 mg Hg kg wet wt?1. Moreover, Hg-length relationships suggest that each target fish meets this threshold near their minimum legal catch length. Our findings reiterate the value of species ecology to improve predictions of fish Hg and permit better management of human contamination by this important dietary source.  相似文献   

15.
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16.
When fluid flow passes a cylinder, the drag crisis phenomenon occurs between the sub-critical and the super-critical Reynolds numbers. The focus of the present studies was on the numerical prediction of the drag crisis based on CFD methods. In this work, block structured meshes with refined grids near the cylinder surface and in the downstream were employed. Both 2D and 3D simulations were performed using various turbulence models, including the SST k − ω model, the k − ϵ model, the SST with LCTM, the DES model, and the LES model. In the convergence studies, the effects of the grid size, the time step, the first grid size and the aspect ratio (for 3D simulations) on the solutions were examined. The errors due to spatial and time discretizations were quantified according to a V&V procedure. Validation studies were carried out for various Reynolds numbers between Re = 6.31 × 104 and 7.57 × 105. The averaged drag force, the RMS of lift force and the Strouhal number were compared with experimental data. The studies indicated that standard 2D and 3D RANS methods were inadequate to capture the drag crisis phenomenon. The LES method however has the potential to address the problem.  相似文献   

17.
To investigate the biological impact of polycyclic aromatic hydrocarbons (PAHs) on reproductive system, scallops Chlamys farreri were continuously exposed to benzo[a]pyrene (BaP) (0.5, 3, 10 μg L?1) during 15 days. DNA damage and histological alterations were examined in female gonad. DNA strand break levels significantly increased after 12 h exposure, and remained high and significantly different from control values until the end of the exposure. In the ovaries of the scallops exposed to 10 μg L?1 BaP for ten days, histological analysis showed that the cytoplasts of the oocytes in the outer layer of the ovaries became sparse, and the nuclear membranes were obscure. Damaging effects on ovaries and oocytes were more severe after 15 days exposure. Degenerating oocytes increased and the connective tissue of the ovary envelops became loose. Electron microscopic examination revealed ultrastructural aspects of degenerating oocyte and degenerated oocyte after 15 days exposure.  相似文献   

18.
The distribution of dissolved organic carbon (DOC) and nitrogen (DON) and particulate organic carbon (POC) and nitrogen (PON) was studied on a transect perpendicular to the Catalan coast in the NW Mediterranean in June 1995. The transect covered a hydrographically diverse zone, including coastal waters and two frontal structures (the Catalan and the Balear fronts). The cruise was conducted during the stratified period, characterized by inorganic nutrient depletion in the photic zone and a well established deep chlorophyll a maximum. DOC concentrations were measured using a high-temperature catalytic oxidation method, and DON was determined directly, with an update of the Kjeldahl method, after removal of inorganic nitrogen.The ranges of DOC and DON concentrations were 44–95 μM-C and 2.8–6.2 μM-N. The particulate organic matter ranged between 0.9 and 14.9 μM-C and from 0.1 to 1.7 μM-N. The DOC : DON molar ratio averaged 15.5±0.4, and the mean POC : PON ratio was 8.6±0.6. The distribution of dissolved organic matter (DOM) was inverse to that of the salinity. The highest concentrations of DOM were found in coastal waters and in the stations affected by the Catalan front, located at the continental shelf break.It was estimated that recalcitrant DOM constituted 67% of the DOM pool in the upper 50 m. The data suggest that accumulation of DOC due to the decoupling of production and consumption may occur in the NW Mediterranean during stratification and that the organic matter exported from the photic layer is dominated by C-rich material.  相似文献   

19.
Elephant seals are wide-ranging, pelagic, deep-diving (average of 400–600 m) predators that typically travel to open waters and continental shelf edges thousands of kilometers from their land breeding colonies. We report a less common pattern of foraging in the shallow waters of a continental shelf. Southern elephant seals, Mirounga leonina, that breed at Península Valdés (Argentina), face an extended (∼1,000,000 km2; 400–700 km-wide, depending on track), shallow (<150 m) and seasonally productive plateau, the Patagonian shelf. Adults of both sexes usually cross it in rapid transit to other potential foraging grounds on the shelf edge or in the Argentine Basin, but 2–4 year-old juveniles spread over the plateau and spent months in shallow waters. This behavior was recorded for 9 seals (5 males and 4 females) of 23 satellite-tracked juveniles (springs of 2004 and 2005) and for 2 subadult males studied in previous seasons. Trips included travel trajectories and time spent in areas where swim speed decreased, suggesting foraging. Preferred locations of juvenile females were in the proximity of the shelf break, where stratified waters had relatively high phytoplankton concentrations, but young and subadult males used the relatively cold (7–8 °C), low-salinity (∼33.3) mid-shelf waters, with depths of 105–120 m and a poorly stratified water column. Three of the latter seals, instrumented with time–depth recorders, showed dives compatible with benthic feeding and no diel pattern of depths distribution. Regions of the mid-shelf were used in different seasons and were associated with low chlorophyll-a concentration at the time of the visit, suggesting that surface productivity does not overlap with putative quality habitat for benthic foragers. Benthic diving on the shallow mid-shelf would be a resource partitioning strategy advantageous for young males prior to greater energetic demands of a high growth rate and a large body size. Later in life, the more predictable, bathymetry-forced, shelf-break front may offer the food resources that explain the uninterrupted increase of this population over several decades.  相似文献   

20.
A fuzzy inference system (FIS) and a hybrid adaptive network-based fuzzy inference system (ANFIS), which combines a fuzzy inference system and a neural network, are used to predict and model longshore sediment transport (LST). The measurement data (field and experimental data) obtained from Kamphuis [1] and Smith et al. [2] were used to develop the model. The FIS and ANFIS models employ five inputs (breaking wave height, breaking wave angle, slope at the breaking point, peak wave period and median grain size) and one output (longshore sediment transport rate). The criteria used to measure the performances of the models include the bias, the root mean square error, the scatter index and the coefficients of determination and correlation. The results indicate that the ANFIS model is superior to the FIS model for predicting LST rates. To verify the ANFIS model, the model was applied to the Karaburun coastal region, which is located along the southwestern coast of the Black Sea. The LST rates obtained from the ANFIS model were compared with the field measurements, the CERC [3] formula, the Kamphuis [1] formula and the numerical model (LITPACK). The percentages of error between the measured rates and the calculated LST rates based on the ANFIS method, the CERC formula (Ksig = 0.39), the calibrated CERC formula (Ksig = 0.08), the Kamphuis [1] formula and the numerical model (LITPACK) are 6.5%, 413.9%, 6.9%, 15.3% and 18.1%, respectively. The comparison of the results suggests that the ANFIS model is superior to the FIS model for predicting LST rates and performs significantly better than the tested empirical formulas and the numerical model.  相似文献   

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