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1.
Algorithm for HF radar vector current measurements 总被引：1，自引：0，他引：1
A new algorithm is proposed, called the stream function method (SFM) for producing vector current maps from radial data measured
by dual-site high frequency surface wave radar (HFSWR). In SFM, a scalar stream function is constructed under some oceanographic
assumptions. The function describes the two-dimensional (2-D) ocean surface water motion and is used to obtain the distribution
of vector currents. The performance of SFM is evaluated using simulated radial data, which demonstrates that SFM has advantages
over typical vectorial combination methods (VCM) both in error acceptance and robustness, and excels another method based
on least-squares fitting (LSF) in recovering the complicated current models. Furthermore, SFM is capable of providing the
total currents based on radials from single-site radar. We also test the assumptions of horizontal non-divergence in the simulation.
The new algorithm is applied to the field experiment data of Wuhan University’s ocean state measuring and analyzing radar
(OSMAR), collected in the coastal East China Sea during April 11–17, 2004. Quantitative comparisons are given between radar
results by three current algorithms and in-situ current meter measurements. Preliminary analysis of the vertical current shear is given based on the current meter measurements. 相似文献
2.
Several burial assessment surveys using a seabed plough have been carried out along routes on the United Kingdom continental shelf to assess their potential for cable burial. Detailed information on sediment thicknesses and characteristics within the top meter of the seabed was collected using a survey tool called the Plough Surveyor. Geophysical surveys along these routes have enabled correlation with the plough data. Results include the range of tensions, tension trace characteristics, and typical penetration, and these have been correlated with seabed types and thickness of sediment. 相似文献
3.
Rebecca A Woodgate Eberhard Fahrbach 《Deep Sea Research Part I: Oceanographic Research Papers》1999,46(12):75
We present observations of strong, episodic, bottom-intensified currents from two current meter moorings, each of a year's duration, placed in the central Greenland Sea at 75°N, 8°W, in a water depth of circa 3340 m. The events, recorded by the current meters placed some 50 m above the sea floor, occur about 4 times a year and last about a week. They show currents of up to 43 cm/s, turning in direction, occasionally modulated by a signal of the frequency of the Coriolis parameter or the semi-diurnal tide. The temperature record at the current meter however remains constant to 0.01°C. The current direction measured at overlying meters correlates well with that of the deepest meter – the current speed does not. Independent, geological data also show evidence of strong bottom flows in the area.We discuss possible mechanisms for these `benthic storms', including the hypothesis of a sediment driven plume descending from the East Greenland continental slope. These high energy events have implications for sedimentation, shelf-basin exchange and boundary mixing processes. Normal mode theory is used to justify the dynamical response of the system to such a bottom-trapped impulse. 相似文献
4.
《Oceanic Engineering, IEEE Journal of》2009,34(4):539-547
5.
Hae-Hoon Park 《Ocean Engineering》1993,20(2)
An indirect tension measurement method of a towing cable in midwater or a buoy cable is proposed using underwater acoustic positioning systems, etc., to give the in-water cable tension. The most simple and traditional cable tension measurement method is to apply a mechanical tension meter at the one end of the cable, but the method has limits in the aspects of continuous monitoring and manual operation. However, the technique in this study is to apply the Pode's analysis of the equilibrium configuration and tension of a flexible twine, in which the cable tension is given as a function of the geometric positions of both ends of the cable. A set of nonlinear integral equations is formulated and solved numerically by the Newton-Raphson method. Then the inclination angles and the tensions at the lower and the upper ends of the cable could be obtained. The derived method enables us to track a towed object, to measure the tension of a towing cable or a buoy cable and is also applicable to the remotely operated vehicle (ROV) tethered to a mother ship. 相似文献
6.
The performance of various directional instruments for practical oceanographic and coastal engineering applications is examined. The emphasis is put on the application of conventional current meters equipped with high resolution pressure sensors and three element arrays. Two simulation techniques have been used to produce input data with known frequency spectrum and known directional spreading. The directional spreading is determined by the maximum likelihood method and the resulting spreading is compared with the input spreading. The performance of a conventional current meter equipped with a high resolution pressure sensor depends on the width of the directional spreading of surface waves and on the frequencies under consideration. Even for very narrow directional spreading, the current meter response is acceptable for practical applications and for shallow water deployment. In general, the current meter directional response does not depend on the direction of the incident waves. The spatial array of three wave staffs deployed in shallow water shows a similar performance to that of the current meters when the dimension of the spatial array is of the order of 1 m. This performance also does not depend on the direction of the incident waves. 相似文献
7.
Adrian N. Bowen 《Marine Geophysical Researches》1984,6(3):275-293
A seismic reflection profiling system utilising a surface air gun source and a deep-towed horizontal hydrophone streamer has been developed for high resolution studies in the deep ocean. The instrument is deployed on a conventional armoured single conductor cable at depths of up to 6 km. Seismic data from the 30 m long streamer is wide-band frequency modulated up the towing cable to the ship together with a high frequency monitor from a 3.5 kHz echo-sounder mounted on the instrument package. The geometry of the system allows an order of magnitude improvement in spatial resolution compared with that obtained from standard surface source/receiver configurations. The summed hydrophones of the streamer attenuate cable-generated mechanical noise, and the 3.5 kHz sea-surface and bottom reflected returns provide receiver positioning information. The system has been successfully deployed at depths of 5 km in the Vema Fracture Zone in the North Atlantic, and although initially difficulties were experienced in balancing the streamer, subsequent profiles across the transform fault show details of sub-bottom structure which on conventional surface records are generally masked by diffraction hyperbolae. 相似文献
8.
Mooring tension and motion characteristics of a submerged fish reef with net in waves and currents using numerical analysis 总被引：2，自引：0，他引：2
A numerical model was used to analyze the motion response and mooring tension of a submerged fish reef system. The system included a net attached to a rigid structure suspended up from the bottom with a single, high tension mooring by fixed flotation. The analysis was performed by using a Morison equation type finite element model configured with truss elements. Input forcing parameters into the model consisted of both regular and irregular waves, with and without a steady current. Heave, surge and pitch dynamic calculations of the reef structure were made. Tension response results of the attached mooring line were also computed. Results were analyzed in both the time and frequency domain in which appropriate, linear transfer functions were calculated. The influence of the current was more evident in the tension and heave motion response data. This is most likely the result of the large buoyancy characteristics of the reef structure and the length of the mooring cable. Maximum mooring component tension was found to be 13.9 kN and occurred when the reef was subjected to irregular waves with a co-linear current of 1.0 m/s velocity. The results also showed that the system had little damping (in heave) with damped natural periods of 2.8 s. This combination of system characteristics promotes a possible resonating situation in typical open sea conditions with similar wave periods. 相似文献
9.
Accurate estimates of net residual discharge in tidally affected rivers and estuaries are possible because of recently developed ultrasonic discharge measurement techniques. Ultrasonic measurement methods consist of: 1) the use of ultrasonic instruments for the measurement of a representative “index” velocity used for in situ estimation of mean water velocity and 2) the use of the acoustic Doppler current discharge measurement system to calibrate the index velocity measurement data. Methods used to calibrate (rate) the index velocity to the channel velocity measured using the Acoustic Doppler Current Profiler are the most critical factors affecting the accuracy of net discharge estimation. The index velocity first must be related to mean channel velocity and then used to calculate instantaneous channel discharge. Finally, discharge is low-pass filtered to remove the effects of the tides. An ultrasonic velocity meter discharge-measurement site in a tidally affected region of the Sacramento-San Joaquin Rivers was used to study the accuracy of the index velocity calibration procedure. Calibration data consisting of ultrasonic velocity meter index velocity and concurrent acoustic Doppler discharge measurement data were collected during three time periods. Two sets of data were collected during a spring tide (monthly maximum tidal current) and one of data collected during a neap tide (monthly minimum tidal current). The relative magnitude of instrumental errors, acoustic Doppler discharge measurement errors, and calibration errors were evaluated 相似文献
10.
Kuh Kim Yun Bae Kim Jong Jin Park SungHyun Nam Kyung-Ae Park Kyung-Il Chang 《Ocean Science Journal》2005,40(1):25-44
Long-term, continuous, and real-time ocean monitoring has been undertaken in order to evaluate various oceanographic phenomena
and processes in the East/Japan Sea. Recent technical advances combined with our concerted efforts have allowed us to establish
a real-time monitoring system and to accumulate considerable knowledge on what has been taking place in water properties,
current systems, and circulation in the East Sea. We have obtained information on volume transport across the Korea Strait
through cable voltage measurements and continuous temperature and salinity profile data from ARGO floats placed throughout
entire East Sea since 1997. These ARGO float data have been utilized to estimate deep current, inertial kinetic energy, and
changes in water mass, especially in the northern East Sea. We have also developed the East Sea Real-time Ocean Buoy (ESROB)
in coastal regions and made continual improvements till it has evolved into the most up-to-date and effective monitoring system
as a result of remarkable technical progress in data communication systems. Atmospheric and oceanic measurements by ESROB
have contributed to the recognition of coastal wind variability, current fluctuations, and internal waves near and off the
eastern coast of Korea. Long-term current meter moorings have been in operation since 1996 between Ulleungdo and Dokdo to
monitor the interbasin deep water exchanges between the Japanese and Ulleung Basins. In addition, remotely sensed satellite
data could facilitate the investigation of atmospheric and oceanic surface conditions such as sea surface temperature (SST),
sea surface height, near-surface winds, oceanic color, surface roughness, and so on. These satellite data revealed surface
frontal structures with a fairly good spatial resolution, seasonal cycle of SST, atmospheric wind forcing, geostrophic current
anomalies, and biogeochemical processes associated with physical forcing and processes. Since the East Sea has been recognized
as a natural laboratory for global oceanic changes and a clue to abrupt climate change, we aim at constructing a 4-D continuous
real-time monitoring system, over a decade at least, using the most advanced techniques to understand a variety of oceanic
processes in the East Sea. 相似文献
11.
In order to investigate the effect of internal friction of umbilical cable on its vortex-induced vibration(VIV)responses, the experimental study on VIV of bond umbilical cable(BUC) and un-bond umbilical cable(UBUC) was carried out in an experimental tank. A current generator in the laboratory simulated the uniform current, and the current velocities were observed in real time by using a Doppler Velocimeter. In addition, different sizes of top tension were applied to the umbilical cable model. The VIV responses of the umbilical cable model were measured by using Fiber Bragg grating(FBG) strain sensors. The displacement responses of umbilical cable model were reconstructed based on the experimental strain data processed by modal superposition method. In this paper, the traveling wave characteristics, the spatial-temporal distribution characteristics of frequency and fatigue damage of the BUC and UBUC under VIV are studied. The experimental results show that there are obvious differences between BUC and UBUC in the response characteristics of VIV. The UBUC appears the traveling wave sooner than BUC, but its standing wave characteristics are more obvious than those of BUC at high velocities. Compared with BUC, the spatial-temporal distribution of UBUC frequencies appears wide-band distribution sooner, but has narrower bandwidth in the "lock-in" state. The level of fatigue damage of BUC was approximately the same as that of UBUC. 相似文献
12.
A two-degree freedom model for an ALT-tanker system is established corresponding to the pitch of the ALT and the surge of the tanker.Tension in the mooring cable between the ALT and the tanker is represented by an unsymmetrical,piecewise-nonlinear function.Wave load on the tower is evaluated by use of the Morison equation.The first order wave load acting on the tanker is calculated by the linear diffraction theory based on the 2-D Helmholtz equation,and the near field approach of Pinkster is used to evaluate the second order drift force.The dynamic equation of motion is established based on the principle of D'lembert.Dynamic response and cable tension of a mooring system composed of an 88.4 m ALT and a 100000 t grade tanker are calculated.The influence of wave frequency,wave excitation amplitude,wind and current force on ALT-tanker motion and cable tension is discussed. 相似文献
13.
Comprehensive wind tunnel measurements have been made of the drag coefficients of both the body and the faired cable of a towed system. The drag data has been embodied in theoretical calculations of the depth attained in tow, at speed up to 3 m s−1 (6 knots) with scopes up to 135 m (440 ft). The agreement with sea trial observations is excellent.The work has highlighted the importance of accounting for the variation of faired cable drag with cable angle and has shown that the drag increments due to gaps and misalignments between individual fairing elements cannot be ignored.Methods are derived for estimating these effects for application to other faired cable towed systems. 相似文献
14.
Directional wave information from the SeaSonde 总被引：1，自引：0，他引：1
This paper describes methods used for the derivation of wave information from SeaSonde data, and gives examples of their application to measured data. The SeaSonde is a compact high-frequency (HF) radar system operated from the coast or offshore platform to produce current velocity maps and local estimates of the directional wave spectrum. Two methods are described to obtain wave information from the second-order radar spectrum: integral inversion and fitting with a model of the ocean wave spectrum. We describe results from both standard- and long-range systems and include comparisons with simultaneous measurements from an S4 current meter. Due to general properties of the radar spectrum common to all HF radar systems, existing interpretation methods fail when the waveheight exceeds a limiting value defined by the radar frequency. As a result, standard- and long-range SeaSondes provide wave information for different wave height conditions because of their differing radar frequencies. Standard-range SeaSondes are useful for low and moderate waveheights, whereas long-range systems with lower transmit frequencies provide information when the waves are high. We propose a low-cost low-power system, to be used exclusively for local wave measurements, which would be capable of switching transmit frequency when the waveheight exceeds the critical limit, thereby allowing observation of waves throughout the waveheight range. 相似文献
15.
16.
Fine sediment resuspension dynamics in a large semi-enclosed bay 总被引：3，自引：0，他引：3
A field study was conducted to investigate fine sediment resuspension dynamics in Moreton Bay, a large semi-enclosed bay situated in South East Queensland, Australia. One S4ADW current meter and three OBS sensors were used to collect the field data on tides, mean currents, waves and suspended sediment concentrations in a mean water depth of 6.1 m for about 3 weeks. Two small cleaning units were specially designed to automatically clean the OBS sensors several times every hour to avoid biological growth on the OBS sensors. Based on the collected field data, the main driving force for fine sediment resuspension is found to be the storm wind-waves generated locally in the Bay, not the tidal current or penetrated ocean swell. The critical wind-wave orbital velocity for sediment resuspension was determined to be Urms=7 cm/s and the critical bed shear stress τcr=0.083–0.095 Pa at this study site. 相似文献
17.
Grosskopf W. Aubrey D. Mattie M. Mathiesen M. 《Oceanic Engineering, IEEE Journal of》1983,8(4):254-271
Five measurement strategies (four in situ, one remote) for estimating directional wave spectra were intercompared in a 1980 experiment at the Coastal Engineering Research Center's Field Research Facility in Duck, NC. The systems included two pressure sensor/biaxial current meter combinations (different manufacturers), a triaxial acoustic current meter, an SXY gauge (square array of four pressure sensors), and a shore-based imaging radar. A detailed error analysis suggests sources for differences in estimated wave spectra from the different instruments; in general, they intercompare favorably. The major deviation among in situ gauges was associated with the triaxial acoustic current meter. Reliance on a vertical velocity measurement (instead of a direct pressure or sea-surface elevation measurement) can contribute additional uncertainty in directional spectral estimates. The imaging radar was successful in distinguishing multiple wave trains at the same frequency, which was not possible with the simple spectral estimation analysis applied to in situ data. However, the radar is not useful in providing accurate estimates of spectral density, nor in distinguishing multiple wave trains of different frequencies coming from the same direction. Selection of a measurement strategy for a particular need depends on the precise data requirements for that application. Although the five tested intercompared well, in practice not all are equally suitable for every application. 相似文献
18.
Irish J.D. Morey K.E. Needell G.J. Wood J.D. 《Oceanic Engineering, IEEE Journal of》1991,16(4):319-328
To measure oceanographic parameters such as currents, temperature, conductivity, pressure, and suspended sediment concentrations, two film-recording current meters were upgraded with microprocessor-controlled data recorders and additional sensors. Two telemetry links relay data and allow the in situ operation of the remote instrument to be checked. In one configuration, the bottom-mounted current meter communicated by a 35-m-long wire to a small surface spar buoy, and then by a packet radio link to a nearby ship. In another development, the current meter relays data to a controller and buoyant data capsule on the bottom instrument package. The controller collects and processes the data from the current meter and periodically transfers these processed data to a data capsule and releases it. When released, the capsule rises to the surface and transmits its data to shore via the ARGOS satellite, while acting as a satellite tracked drifter 相似文献
19.
D.T. Pugh 《Ocean Engineering》1982,9(4):361-372
The need to obtain realistic estimates of extreme currents for the design of off-shore structures requires optimum use to be made of the data available. Methods of applying joint tide-surge probability techniques to the data are considered, and illustrated by analysis of one year of current meter observations in the North Sea. Tidal and meteorologically-induced vector components of the total observed current vector are isolated and their separate two-dimensional frequency distributions are computed. These distributions are then recombined to give probabilities of extreme total currents from several directions. 相似文献
20.
This paper analyses nonlinear dynamics of cable towed body system. The cable has been modeled and analyzed using a new nodal position finite element method, which calculates the position of the cable directly instead of the displacement by the existing finite element method. The newly derived nodal position finite element method eliminates the need of decoupling the rigid body motion from the total motion, where numerical errors arise in the existing nonlinear finite element method, and the limitation of small rotation in each time step in the existing nonlinear finite element method. The towed body is modeled as a rigid body with six degrees of freedom while the tow ship motion is treated as a moving boundary to the system. A special procedure has been developed to couple the cable element with the towed body. The current approach can be used as design tool for achieving improved directional stability, maneuverability, safety and control characteristics with the cable towed body. The analysis results show the elegance and robustness of the proposed approach by comparing with the sea trial data. 相似文献