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We are now developing a prototype of a 3000-m class underwater glider for virtual mooring. The vehicle glides back and forth between the sea surface and the seabed collecting ocean data at a specific point. Hydrodynamic forces act...
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We are now developing a prototype of a 3000-m class underwater glider for virtual mooring. The vehicle glides back and forth between the sea surface and the seabed collecting ocean data at a specific point. Hydrodynamic forces acting on the half-size model were measured to determine the optimal wing shape. Next, to obtain the dynamical–hydrodynamic coefficients, forced oscillation tests were carried out using the optimally shaped model. Finally, the motions of the glider were simulated using the hydrodynamic coefficients obtained from these model experiments. The experimental and calculated results are shown in this paper.
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An obstacle mode station-keeping strategy that considers obstacles in the station-keeping center area is proposed for wave gliders (WGs) to cope with special applications such as oil spill monitoring on drilling platforms and obse...
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An obstacle mode station-keeping strategy that considers obstacles in the station-keeping center area is proposed for wave gliders (WGs) to cope with special applications such as oil spill monitoring on drilling platforms and observation around the island. Different from the traditional station-keeping strategy which requires closing in the preset position as much as possible, this strategy uses the adaptive integral line of sight (AILOS) algorithm to make the WG sail around the preset obstacle area. A partitioning control strategy based on distance error is introduced to divide three areas according to the risk level: warning area, escape area and obstacle area. A tan-type barrier Lyapunov function (BLF) is introduced into the warning area control method to determine the boundary. To avoid the potential risk of collision, the escape area control strategy is to make the WG move away from the obstacle area as quickly as possible. Simulation and sea trial results verified the capability of the proposed station-keeping strategy in a stable ocean environment and the station-keeping safety of the WG using this strategy under extreme situations.
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As Webmaster for the Claude Moore Health Sciences Library at the University of Virginia, I've been thinking a lot about the future of our special collections. While collection development and serial librarians grapple with serious...
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As Webmaster for the Claude Moore Health Sciences Library at the University of Virginia, I've been thinking a lot about the future of our special collections. While collection development and serial librarians grapple with serious questions about maintaining and archiving digital content, I am beginning to think about our library's next two digitization projects. While the debate over ownership of and access to digital resources heats up, I am thinking of ways to better market our digitized collections to the world. And while electronic resource librarians begin to demand better interfaces to online collections, I'm wondering if any of my content would be usable on a PDA or Tablet PC. How can I afford to focus so much on the materials' future while we're still working hard to make them accessible today? Because we at the Claude Moore Health Sciences Library own our collections, and XML (Extensible Markup Language) is going to provide the framework for sustaining them in digital form.
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The vertical structural variability of the diurnal internal tide (DIT) with a mode-1 wavelength of ~420 km inside a mesoscale baroclinic anticyclonic eddy was examined based on observations by a single virtual-moored (VM) Slocum g...
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The vertical structural variability of the diurnal internal tide (DIT) with a mode-1 wavelength of ~420 km inside a mesoscale baroclinic anticyclonic eddy was examined based on observations by a single virtual-moored (VM) Slocum glider. During the glider observational period from 10 to 19 September 2018, the eddy traveled northward at approximately 50?km, allowing the glider to scan a cross section of 50?km wide and 800?m deep inside the eddy. VM observations showed that DIT experienced a noticeable vertical structural variability near the eddy center. In a range of 30?km horizontally from the eddy center (inner center), DIT’s vertical displacements were significantly intensified in the 400–800-m depth below the eddy. In the range of 30–50 km from the eddy center (outer center), DIT was almost uniformly distributed from the surface to 800-m depth. Owing to the spatiotemporally restricted dataset by the glider, the significance of DIT’s modulation observed inside the eddy can be questionable. As a result of comparing DIT’s vertical structural variability in two domains in terms of available potential energy (APE) and horizontal kinetic energy (HKE) using CTDs inside the eddy and ADCPs outside the eddy, DIT’s vertical structure inside the eddy was significantly distinguished from that outside the eddy. The relative vorticity inside the eddy was estimated based on the satellite dataset; it was negatively great in the inner center (approximately 0.35 – 0.25f) and small in the outer center (approximately 0.2 – 0.1f). These observational behaviors indicate a close relationship between them; the vorticity-dependent modulation of the DIT seems to be observationally confirmed inside the eddy. Further, in order to examine the energy transferring behavior in low vertical modes, a wavenumber spectral analysis was performed on the DIT displacements and the lowest four wavenumbers, K z (1) through K z (4), showed a similar behavior to those observed in DIT’s vertical structural variability inside of the eddy; the relative power of the sum of K z (2) ~ K z (4) with respect to K z (1) was strong in the inner center and weakened in the outer center. These results seem to support that the wave–eddy interaction is non-uniform inside the eddy and partially depends on the relative vorticity.
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Smoothed particle hydrodynamics (SPH) method is widely recognized as the accurate approach to predict the fluid-structure interaction. However, the lack of mooring force in the program severely limits its research on the motion re...
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Smoothed particle hydrodynamics (SPH) method is widely recognized as the accurate approach to predict the fluid-structure interaction. However, the lack of mooring force in the program severely limits its research on the motion response of floating structures. In this paper, based on the dynamic analysis theory of the lumped-mass method, combined simultaneously with the characteristics of SPH method, a dynamic mooring force calculation method suitable for SPH is proposed as follows: The mooring line is divided into a series of virtual particles, which contains the inherent attribute parameters of the mooring line, and embeds it in the SPH program. The force of each virtual particle is calculated and then coupled with the motion equation for the hull at each time step. The numerical method has been validated with the results of the flume test. Numerical simulations are examined so as to determine the hydrodynamic performance and interaction of breakwater with surfaces waves. Finally, the effects of the structural width and wave characteristics on wave attenuating effect are studied.
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The Argo Global Ocean Observing Network has remained the preeminent ocean observation network worldwide. Since the Argo buoys lack freedom of lateral movement, their wave-following working characteristics prevent them from complet...
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The Argo Global Ocean Observing Network has remained the preeminent ocean observation network worldwide. Since the Argo buoys lack freedom of lateral movement, their wave-following working characteristics prevent them from completing the long-term observations in the designated sea area. Long-term monitoring of designated waters is often required, for example, to study the impacts of seabed mining on the marine environment in the surrounding sea area. To solve this problem, a portable underwater profiler (PUP) that combines the functionalities of profiling buoys and underwater gliders was devised. The PUP employs a center of gravity adjustment mechanism utilizing the double-weight block approach, enabling the pitch angle adjustment within -90° to 0°. Remarkably, the PUP weighs only 11.25 kg, meeting the requirements for rapid deployment. Furthermore, the prediction method of the ocean current velocity was optimized by employing the full-depth-averaged ocean current velocity instead of the depth-averaged ocean current velocity. To ensure continuous observation operations of the PUP within designated sea areas, a horizontal displacement correction strategy (HDCS) based on the virtual mooring concept is proposed. The effectiveness of the HDCS has been preliminarily validated through simulations and further confirmed through lake trials conducted in Qiandao Lake.
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Bottom-resting capability will enable an autonomous underwater glider (AUG) to perform long-duration virtual mooring. However, the tracking control of AUG soft landing on the seabed faces a number of challenges. It is crucial that...
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Bottom-resting capability will enable an autonomous underwater glider (AUG) to perform long-duration virtual mooring. However, the tracking control of AUG soft landing on the seabed faces a number of challenges. It is crucial that the controller is able to incorporate many important factors, e.g., model uncertainty, environmental disturbances and limited dynamic range of actuators. This study first formulates the soft landing tracking control problem of AUG for persistent virtual mooring. An adaptive robust control scheme based on sliding mode control with a nonlinear disturbance observer is proposed that can effectively solve the challenges aroused by parametric uncertainty and unknown time-varying external disturbances. Moreover, the effect of input constraints of the AUG system is analyzed for the first time and is damped through a dynamic auxiliary compensator. Finally, simulation results demonstrate the superiority and inherent robustness of the proposed control scheme, in comparison with other techniques.
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This study proposes a framework for comparative study on three different positioning solutions for mobile offshore drilling units (MODUs) using high modulus polyethylene (HMPE) ropes, including active mooring with an HMPE rope, co...
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This study proposes a framework for comparative study on three different positioning solutions for mobile offshore drilling units (MODUs) using high modulus polyethylene (HMPE) ropes, including active mooring with an HMPE rope, conventional dynamic positioning (DP) and active hybrid position-keeping (AHP-K). The goal of the positioning systems is to keep the MODU above the wellhead with acceptable riser-angle loading, minimal energy consumption, reduced underwater noise generation, and harmful emissions. This is the first time a holistic study has been performed on positioning that factors in the financial and environmental costs. The time domain simulation, which includes sea-state, wind, and current profiles, is performed with a well-developed software architecture and control algorithms for MODU position-keeping. The case study addresses a MODU drilling in the Barents Sea. Simulation results show that AHP-K is more efficient compared to the other two positioning solutions for drilling operations in the studied environment.
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