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This paper discusses the design and initial testing of a novel hydrophone array system dubbed the Underwater Inflatable Co-prime Sonar Array (UICSA). The UICSA will be a crucial component of an underwater deployable sensing network that can be rapidly deployed using compact autonomous underwater vehicles (AUVs). The UICSA initially is packed in a compact container to fit the payload space of an AUV. After deployment, the UICSA expands to its predetermined full length to acquire sensing data for source localization. More specifically, the mechanical compression of the UICSA is achieved through a non-rigid array support structure, which consists of flexible inflatable segments between adjoining hydrophones that are folded in order to package the UICSA for deployment. The system exploits compression in hydrophone layouts by utilizing a sparse array configuration, namely the co-prime array since it requires fewer hydrophones than a uniform linear array of the same length to estimate a given number of sources. With two-way compression, the storage, handling, and transportation of the compactly designed UICSA is convenient, particularly for the AUVs with limited payload space. The deployment concept and process are discussed, as well as the various UICSA designs of different support structures are described. A comparison of the various mechanical designs is presented and a novel hybrid-based expansion prototype is documented in detail. Laboratory study results of the UICSA prototype are presented that include water-swollen material tests in a pressurized environment and water tank validation of the inflation process. The UICSA prototype also has been deployed in the Harbor Branch channel to validate the performance, the related field test details and source localization results.

Aquaculture, especially fish farming, plays a vital role in ensuring food security in the United States and worldwide. However, for fish farming to be sustainable and economically viable, drastic improvements to the current labor-intensive and resource-inefficient operations are required. The hybrid aerial/underwater robotic system (HAUCS) aims to bring fundamental innovations to how pond-based farms operate. HAUCS is an end-to-end framework that consists of three principal subsystems: 1) a team of collaborative aero-amphibious robotic sensing platforms integrated with water quality sensors; 2) a land-based home station that can provide automated charging and sensor cleaning; and 3) a backend processing center that includes a machine-learning-based water quality prediction model and farm control center. HAUCS will be capable of collaborative monitoring and decision-making on farms of varying scales. The HAUCS platform, payload, and prediction model are discussed. The initial deployment of the HAUCS framework at a land-based aquaculture fish farm is presented.

To solve problems of unsatisfactory velocity distribution, low oxygen filling efficiency, difficult control of dissolved oxygen content, and contradiction between oxygen filling capacity and power efficiency in aerator operation, an airfoil with a logarithmic spiral as a busbar and a NACA0012 airfoil as a cross section was proposed based on the characteristics of linear and operating parameters of blades. The CFD Software Fluent was used to simulate and to analyze the influence of the airfoil blade on the oxygen mass transfer, stirring, and pushing flow in an oxidation ditch. Three factors, including the impeller rotating speed, immersion depth and the blade incline angle, related to aeration efficiency of the surface aerator, were studied by experiments, and the maximum dynamic efficiency of two types of impellers with different blade inclination angles was found.

Performance of a NACA 634-021 hydrofoil in motion under and in close proximity of a free surface for a large range of angles of attack is studied. Lift and drag coefficients of the hydrofoil at different submergence depths are investigated both numerically and experimentally, for 0° ≤ AoA≤30° at a Reynolds number of 105. The results of the numerical study are in good agreement with the experimental results. The agreement confirms the new finding that for a submerged hydrofoil operating at high angles of attack close to a free surface, the interaction between the hydrofoil-motion induced waves on the free surface and the hydrofoil results in mitigation of the flow separation characteristics on the suction side of the foil and delay in stall, and improvement in hydrofoil performance. In comparing with a baseline case, results suggest a 55% increase in maximum lift coefficient and 90% average improvement in performance for, based on the lift-to-drag ratio, but it is also observed significant decrease of lift-to-drag ratio at lower angles of attack. Flow details obtained from combined finite volume and volume of fluid numerical methods provide insight into the underlying enhancement mechanism, involving interaction between the hydrofoil and the free surface.

The water exchange capacity of a shallow coastal lagoon is sensitive to its environment and hydrodynamics. In this study, the responses of hydrology and climate change on the water exchange characteristics of such a shallow environment are investigated in the Qilihai lagoon. Water circulation and transport are simulated by a numerical model and the water exchange capacity is evaluated by the water flushing and residence time. Our analysis reveals that water exchange with seasonal characteristics is the strongest in summer due to large runoff and is the weakest in winter due to ice roughness. The shallow terrain variation influences water exchange, which is more obvious for the transverse rather than longitudinal direction. Without an ice cover, runoff is the most significant influence on water exchange. This effect is nonlinear and in accordance with a two-terms exponential formula. Water transport time can be significantly reduced by the presence of wind. Westerly winds accelerate water exchange the most. The influence of mean water level on water exchange can be separated into two phases dominated by bathymetry. Ice dominates water exchange and mainly influences the shallow area during winter. Furthermore, the presence of chlorophyll-a positively correlates with water exchange dominated by hydrodynamics. The distribution of sedimentary heavy metal contamination has no direct link with water exchange, which mainly occurs in tidal inlets and the river mouth, and is controlled by source loading. Our results support the current understanding of what mechanisms influence water exchange capacity and establish a theoretical foundation for environmental protection in global shallow coastal lagoon regions.

National navies equip their submarines with Autonomous Underwater Vehicle (AUV) technology. It has become an important component of submarine development in technologically-advanced countries. Employing advanced and reliable recovery systems directly improves the safety and operational efficiency of submarines equipped with AUVs. In this paper, based on aerial refueling technology, a cone-shaped recovery system with two different guiding covers (closed structure and frame structure) is applied to the submarine. By taking the Suboff model as the research object, STAR-CCM was used to study the influence of the installation position of the recovery system, and the length of the rigid rod, on the Suboff model. It was found that when the recovery system is installed in the middle and rear of the Suboff model at the same velocity and the same length of the rigid rod, the Suboff model has the good stability and less drag. It experiences the largest drag when being installed in the front of the rigid rod. Moreover, when the recovery system is installed in the front and middle of the rigid rod, the drag increases as its length increases, and the lift decreases as its length increases. Compared with the closed structure guiding cover, the Suboff model will have less drag and better stability when the recovery system uses the frame structure guiding cover. Besides, the deflection and vibration of the rigid rod were also analyzed via mathematical theory.

In this paper, uniaxial compression tests on layered rock specimens are numerically modelled using the discrete element method to investigate the effect of a soft interlayer on the strength and deformation of rock specimens. For these simulations, the thickness and dip angle of the soft interlayer were varied. Thirty-five numerical models for different cases were established after calibrating the micro-mechanical parameters of the hard and soft rock materials. The computational results were analysed in terms of three aspects: the stress–strain curves, micro-crack propagation patterns, and particle velocity fields. The stress–strain curves indicate that increasing the thickness and dip angle of the soft interlayer causes the peak stress and ultimate strain to drop by up to 42% and 34%, respectively. The thickness of the soft interlayer has a greater influence than that of the soft interlayer dip angle on the uniaxial mechanical behaviour of the rock specimen. Additionally, crack propagation patterns and particle motion in the layered rock models indicate that the cracks develop preferentially along the soft interlayer and that the notable failure features of the layered rock models are stepped failure modes that occur at greater dip angles.

Utilizing deployable morphing structures in ocean engineering applications is a practice in its infancy. We propose an inflatable tubular beam using a hydrogel bead's ability to absorb water to achieve the desired structural shape and strength. It is therefore essential to know the strength of the morphed structure. The first step is to study the strength of the simple structural element. This paper focuses on the numerical modelling of bending tests on inflatable tubular structures filled with hydrogel beads to elucidate the various deformations of multiple compositions of bead/tube structures using the discrete element method. The properties of the tubes and beads were obtained, then calibrations of the micro numerical parameters were conducted. Twenty-four cases of bending tests were simulated. The results show that the degree to which the beads are filled, along with the bead's radius, have a direct effect on the composite structure's strength against deformation.

Efficient capture of wind energy requires optimal dynamic performance of turbine blades, desirably including delaying stall to higher angles of attack (AoAs). Stall is associated with flow separation close to the leading edge on the suction side of a blade so that delaying flow separation mitigates this condition. Merits of passive slots in wings for increasing their lift are well known. Typically, however, the increase in lift is accompanied by a corresponding increase in drag so that the overall aerodynamic efficiency is at most marginally improved. Here, we discuss application of a custom optimized-design internal slot on a NACA 634-021 airfoil blade to allow ventilation of flow through the slot from the pressure side to the suction side of the blade, in support of delaying flow separation, and stall. Delaying flow separation, results in increase in lift and decrease in drag at significantly high angles of attack. Slot width and inclined angle were varied to determine the optimum configuration. Dynamic performance of the blade was investigated both numerically and experimentally, with angles of attack in the range 0 o ≤ AoA ≤ 30 o at a Reynolds number of 105. Lift and drag coefficients of the slotted airfoils predicted from the computational fluid dynamics (CFD) study correlate well with the corresponding coefficients determined via experiments. Experimental results show that a 58% increase in maximum lift coefficient and an 14% increase in maximum lift-to-drag ratio could be achieved with the optimum design case. Flow details obtained from the CFD study provide better insight into the underlying control mechanism of the internal slot. The findings could have significant implications for aeronautics and for improving capture of renewable energy from wind.

The combined effect of an internal slot in an airfoil and transverse leading-edge tubercles on its performance is studied. The internal slot allows flow ventilation from the pressure face to the su...

Underwater inflatable structures (UISs) are distributed in an initial folded state for ease of transportation and deployment. They are able to morph into their intended geometry upon arrival at their destination. This morphing/inflation process can be driven by hydrogel beads, which swell when they contact water. In this research, we study the physical characteristics of tubular UISs with different configurations (length, slenderness, beads density). We fabricated sets of tubular UISs with nylon sleeves filled with different amounts of hydrogel beads and built a flexural test platform mounted on the test tank for the bending experiment. This work provides the experimental Young’s modulus of the tubular UISs under elastic and plastic deformations, and also discusses how the different configurations contribute to the tubular UIS’s stiffness.

Autonomous recovery technology utilized by autonomous underwater vehicles (AUV) is facing enormous challenges resulting from rapid development. In this paper, the current research status of static and dynamic AUV docking is first introduced. Then two styles of underwater dynamic docking devices, captured-style and guided-style, are designed in accordance with two commonly used underwater docking devices. The two types of docking devices, focusing on their respective constitution characteristics, and working principles are introduced. The analysis is conducted on kinematics and movement stability. The two docking devices' dynamic characteristics are analyzed using computational fluid dynamics (CFD) software known as Star-CCM. The simulation results of the dynamic characteristics of the two docking devices are then compared. Finally, a preliminary lake test for the stable wing is carried out. Through the analysis of the two underwater dynamic docking devices' dynamic characteristics, we obtain conclusions: 1) the docking's stability is related to the relative position of hydrodynamic center point; 2) the relationship between the hydrodynamic characteristics of these two underwater docking devices and the velocity and attack angle is not exactly the same; 3) the velocity is an important factor affecting underwater dynamic docking or recycling an AUV.

With rising temperatures and complete melting of Arctic ice expected by 2050, an increasing interest in exploiting Arctic resources and protecting the Arctic from exploitation requires advanced technology be deployed to achieve long duration environmental monitoring and data collection. This will provide the necessary knowledge to guide the development of the Arctic in the coming decades. Here, we have concept designed and implemented for the first time an autonomous underwater morphing robot prototype known as First Arctic Under-ice Ocean Walking Laboratory (FAU-OWL) for long duration environmental monitoring and data collection in the Arctic. This underwater robot is capable of skiing or being anchored upside-down under a sheet of ice using buoyancy control in combination with suction cups and can travel long distances by morphing its legs into wings in order to glide as well as walk. In this paper, the detailed structure, working modes, energy supplement and equipped sensors were explained, and then the dynamics of FAU-OWL under different working modes was studied. Besides, the hydrodynamic characteristics of FAU-OWL were analyzed using computational fluid dynamics (CFD) software known as Star-CCM. Finally, the working principle of FAU-OWL under different working modes in combination with the test situation was described in detail.

The Underwater Inflatable Co-prime Sonar Array (UICSA) is a compact sonar array assembly that can be carried and deployed by autonomous vehicles. The UICSA morphs into a predetermined length to form the sensing node of a transformative underwater deployable network. This paper presents the design of UICSA's support structure and initial development of an embedded data logger. The UICSA employs hydrofoam as an infill in its inflatable support structure and the material's performance is validated using a set of lab tests. The data logger employs the Teensy board to synchronize multiple channels for recording. Performance of the data logger implemented with the UICSA is demonstrated through field deployment.

Underwater Inflatable Co-Prime Sonar Array (UICSA) is a compact sonar array assembly that can be deployed in the ocean then morph into a predetermined length to work. As a sonar array, it is critical to reduce the structural deflection and maintain sensor spacing under external forces like ocean currents. The array, like the mooring system, is affected by ocean currents. In this paper, we conduct the numerical study of the morphed UICSA made of different materials in different current conditions using OrcaFlex. The results can evaluate the performance of different UICSA systems and determine the optimal UICSA design.

The hole erosion test (HET) is commonly used to study the occurrence of internal soil erosion when water concentrated leaks occur. This erosion is known as “piping” in soil mechanics. Piping erosion is invisible and occurs randomly within the soil body. Therefore, to gain a better understanding of how piping erosion develops, it would be helpful to utilize a viewable HET design in which the dynamics of the piping hole can be observed directly. In this note, a new HET apparatus is presented that can be used to observe the development of piping erosion and to monitor the dynamic pressure condition during the hole erosion process. A preliminary model test was carried out based on the new viewable HET apparatus and “pressure heads” monitoring technique. The results successfully verified the performance of the proposed apparatus and experimental methods during the process of hole erosion, indicating that the hole shape changes during continuous erosion and is not fully symmetrical because of the initial profile of the hole. The internal hole becomes increasingly curved when subjected to continuous piping flow. Test results agree with the numerical simulation reported in 2015 by Riha and Jandora, who considered the effect of the hole entrance shape.

The towing system has a wide range of applications including aircraft launch, aerial refueling, underwater docking, and submarine topography detection. Based on aerial refueling technology, an underwater towing system for recovering an Autonomous Underwater Vehicle (AUV) is designed in this paper, which consists of one steel rod, one cable and one stable wing. First, the mechanical structure of the towing system is introduced and three steel rod models are selected. Next, the stability of the towing system is analyzed, and the numerical simulation software Star-CCM is used to study the influence of different shapes, velocities, and installation angles on the hydrodynamic characteristics of the steel rod. After the force analysis of the steel rod and the cable, the deflection of the steel rod and the vibration of the cable are studied. Through the analysis of the towing system, when the hydrodynamic center point F is located behind the center of gravity G, the towing system is more stable, the drag and lateral force of model c are smaller than that of model a and model b, and the relationship between the drag of the steel rod with the installation angle is obtained. Some other very significant conclusions are also drawn which guide the design of the towing system.

Numerical simulations are conducted to investigate the effect of an augmentation channel on the performance of a straight-blade vertical-axis turbine. The flow field is simulated with a commercial software FLUENT, in which the finite volume method is used to solve Reynolds averaged Navier-Stokes equations and the SST k-ω turbulence model. The rotation of the rotor is simulated by solving a rotation motion equation. A comparison between a standalone turbine in a free, open stream versus one in an augmentation channel is drawn, with discussion regarding variation of hydrodynamic torques on the blade and rotor, the power and torque output by the shaft, and the rotational speed. The comparison reveals that for a turbine in a channel, the fluctuations of hydrodynamic torques and rotational speed are dramatically reduced, and the power output is more than 30% higher than that of the standalone turbine.

The three-dimensional scour beneath a partially-buried pipeline in regular waves was visualized using a miniature camera installed in a transparent pipeline. The scour mechanism was analyzed based on the results. Scour development was observed to start at the upstream edge of the span shoulder when the flow in the span headed downstream. The nearby sediment scoured quickly, and a new scour front formed, which can be attributed to the deflected flow entering the scour hole. The new scour front retreated gradually. The end of the original scour front deformed and moved downstream, probably due to the enhanced seepage flow near the edge of the span shoulder. After that, the new scour front extended to the downstream interface of the sediment and the pipeline, and continued to retreat until the first half of the scour process ended. In the second half of the scour process, the sediment transportation occurred in a similar but mirror-imaged manner. The scour hole propagation rate was also determined based on visualization. The results show that the scour hole propagation rate under a pipeline decreases with an increasing pipeline embedment ratio and rises with the KC (Keulegan–Carpenter) number, which is similar to the result of a previous study.

Hybrid autonomous underwater vehicles (AUVs) use internal actuators, e.g., tunnel thruster, moving mass, and ballast chamber, for yaw and pitch steering. Unlike control surfaces, internal actuators perform independently of relative flows around AUVs, thus suitable for missions which require excellent low-speed maneuverability. This research focuses on an investigation into the control design of an REMUS AUV using internal actuators to steer its heading direction. It has been shown that an internal moving mass together with a tunnel thruster is capable of providing actuations to serve the purpose. However, our analysis indicates that a coupling between roll and pitch motion causes the internal actuators to oscillate if depth-plane motion is neglected when deriving control laws for the internal actuators. We present a novel control strategy by taking advantage of the cross-coupling effect when designing the heading autopilot system with internal actuators. The effectiveness and robustness of the proposed design are validated by simulation results.

For ocean pollution emergencies, decision-makers need to quickly know the location of the pollutant for quick assessment and response strategies. In this study, an integrated operational forecasting model coupling a non-Fickian particle-tracking diffusion model based on fractional Brownian motion and geographic information system (GIS) has been developed to implement an operating system for pollutant drift forecasting. The software was developed in C# and C++ language using ArcGIS Engine functions which provides improved visualization and user-friendly and automatic tools for simulation in a geographically referenced environment. The capabilities and effectiveness of the developed software were illustrated by predicting red tide drift through calibration with field observations. This visualized operational forecasting software provides a quick and easy deployable tool for decision-makers in quick response to emergency ocean pollution events. A fBm particle-tracking model for forecasting pollutant drift was presented.A GIS-based software coupled with the pollutant dispersion model was developed.The model was well calibrated by field observations.The software provides a quick, visualization and easy deployable tool for drift simulation.The prediction of red tide drift was presented to demonstrate application of software.

Hydrodynamic and morphological processes become more complex with large spatial variations after tidal barrier building and estuary restoration. Using a process-based model, responses in the estuary to a two-phase restoration measure in the Shuanglong Estuary are investigated. Numerical modeling indicates that tide-asymmetry in the barraged estuary is the primary factor that determines responses of morphology. After partial absence of tidal flats (first-phase restoration), flood tide-asymmetry is switched to ebb tide-asymmetry in the lower unrestored reach. This induces lower estuary erosion via increased tidal prism, though it is enhanced in the upper widened-deepened restored reach leading to severe siltation. After full restoration (second-phase restoration), current velocities are significantly increased with reduced flood tide-asymmetry. A quantitative comparison of the impact of the cross-sectional profile to net sediment transport shows that a switch from flood-dominated estuary to ebb-dominated estuary can be caused by reshaping the tidal flat which may reduce flood tide-asymmetry. The sediment flushing efficiency after the estuary restoration is further investigated in different sluice discharges with regards to two floodgate operations. Low sluice discharge during ebb tides increases the sediment flushing efficiency, but continuous high sluice discharge contributes to significant improvement of sediment flushing capacity and reduction of flushing duration. We conclude to prevent the flushed sediment from re-deposition into the estuary, a larger flushing capacity discharge released in a short period is required after the second-phase restoration in the Shuanglong Estuary.

Underwater Inflatable Co-prime Sonar Array (UICSA) is a compact array assembly, which upon deployment in the ocean expands to its predetermined length and acquires sensing data. The UICSA employs an inflatable array support structure, which can be compressed into a compact package. The employed the sparse array configuration – co-prime array also reduces the number of sensors typically required for a uniform linear configuration. With the “two-way compression”, storing, handling, and transporting the compactly designed UICSA system is convenient, particularly for the autonomous vehicles with limited payload space. In this paper, we propose four designs of UICSA based on different support structure constructions. We fabricated the prototypes and deployed them in an acoustic test tank. The experimental data were analyzed to evaluate the system performance. The results validate the capability of the UICSA for direction finding and also reveal that the underwater inflatable structure as a platform can have broad prospects in the ocean-related applications.

We consider underwater target detection by using a novel active, self-contained and rapidly deployable underwater inflatable co-prime sonar array (UICSA). In particular, we measure the received signal strength (RSS) and angle-of-arrival (AoA) of acoustic signals reflected by an underwater target. Measurements from different positions of the transmitter with respect to the UICSA are organized in a three mode real-valued tensor. Then, the conformity of each entry with respect to all other data points in the tensor is calculated based on recursively refined calculations of $L_{1}$ -norm tensor subspaces. Conformity values are then used for the detection of an underwater target. We evaluate the data conformity of RSS and AoA recordings acquired from the testbed deployment of a seven-element UICSA prototype and three underwater acoustic transmitters at Florida Atlantic University. We show for the first time that conformity evaluation over multi-modal data measurements can accurately detect the presence of an underwater target.

This paper presents visible experimental results of three-dimensional scour beneath pipelines. A miniature camera installed inside a transparent pipeline was used to observe the scour propa...

A geotextile mattress with sloping curtain (GMSC) was introduced to protect underwater pipelines from scour in steady currents. GMSC is a newly developed countermeasure against river and es...

Sea level changes in the Yangtze River Estuary (YRE) as a result of river discharge are investigated based on the monthly averaged river discharge from 1950 to 2011 at the Datong station. Quantification of the sea level contribution is made by model computed results and the sea level rates reported by the China Sea Level Bulletin (CSLB). The coastal modeling tool, MIKE21, is used to establish a depth-averaged hydrodynamic model covering the YRE and Hangzhou Bay. The model is validated with the measured data. Multi-year monthly river discharges are statistically calculated based on the monthly river discharges at Datong station from 1950 to 2011. The four characteristic discharges (frequency of 75%, 50% and 25%, and multi-year monthly) and month-averaged river discharge from 1950 to 2011 are used to study the seasonal and long-term changes of sea level. The computed sea level at the Dajishan and Lvsi stations are used to study the multi-time scale structure of periodic variation in different time scale of river discharge series. The results reveal that (1) the sea level rises as the river discharge increases, and its amplification decreases from upstream to the offshore. (2) The sea level amplification on the south coast is greater than that on the north coast. When river discharge increases by 20,000 m 3 /s, the sea level will increase by 0.005–0.010 m in most of Hangzhou Bay. (3) The sea level at the Dajishan station, influenced by river discharge, increased 0.178 mm/y from 1980 to 2011. Correspondingly, the sea level rose at a rate of 2.6–3.0 mm/y during the same period. These values were provided by the CSLB. The increase in sea level (1980–2011) at the Dajishan station caused by river discharge is 6.8–8.9% of the total increase in sea level. (4) The 19–20 year dominant nodal cycle of sea level at the Dajishan and Lvsi stations is in accord with 18.6 year nodal cycle of main tidal constituents on Chinese coasts. It implies that the sea-level change period on the coast of the Yangtze River is mainly controlled by tides.

Designs of hybrid autonomous underwater vehicles (AUVs), which use internal actuators instead of control surfaces to steer, have emerged recently in the ocean engineering community. This paper focuses on the heading autopilot design for a REMUS AUV by using an internal moving mass. A nonlinear dynamical system is first derived which describes the horizontal-plane motion of the vehicle coupled with an internal moving mass. It is shown that a displacement of the internal mass in the sway direction can affect the flow of the dynamical system in phase space. Using displacement as the system input, a LQR controller is designed to stabilize the heading angle of the vehicle by taking advantage of the position and inertia of the internal moving mass. The linear controller cannot deal with large perturbations due to the constraints on the maximum displacement and movement speed of the internal moving mass. Consequently, a tunnel thruster is added to the design in order to address the problem. A nonlinear full-state feedback law is derived based on backstepping and Lyapunov redesign technique to control the displacement of the internal mass and the force exerted by the tunnel thruster. Simulation results demonstrate the effectiveness of the proposed design.

This paper visualizes the onset of scour under a pipeline in regular waves and studies the mechanism in this process. After the test started, the sand particles near the downstream mudline began to oscillate periodically, probably due to the distribution pattern of the seepage hydraulic gradient under the pipeline as well as asymmetric waves. As the wave height gradually increased, the sand under the pipeline began to oscillate at increasing amplitude and the coverage of oscillation extended upstream. Some sand rushed out from the bottom of the pipeline, and the sand oscillated almost symmetrically around the bottom line of the pipeline thereafter. The oscillation amplitude of the sand particles continued to rise, probably due to a decrease in the seepage path under the pipeline and loosened sediment in the oscillation. The scour onset occurred after more sand rushed out from under the pipeline. The visualization results reproduced the delay in the scour onset reported previously, and related the delay to the aforementioned increase in sediment oscillation amplitude. This visualization can improve the understanding of the scour onset mechanism, and can serve as a guide to further investigate the critical conditions of scour onset and scour control countermeasures for offshore structures.

Underwater pipelines are vital to the oil industry. Extending the service life of these pipelines is a key issue in improving the sustainability of oil transportation. A geotextile mattress with floating plate (GMFP) is a novel and sustainable countermeasure for scour and erosion control and is herein introduced to protect a partially buried pipeline from local scour in steady currents. A series of experiments was designed to verify the protection capabilities of the GMFP and investigate its parametric effects on protection. The average seepage hydraulic gradient under the pipeline was adopted to depict the protection effects of the GMFP, and was calculated with the pore pressure readings under the pipeline. The test results show that the GMFP is capable of protecting a pipeline from the onset of local scour in a unidirectional current. The average seepage hydraulic gradient below the pipeline decreases remarkably after a GMFP is installed. The average hydraulic gradient shows a descending trend with increased sloping angle &alpha, when 0.64 &lt, sin&alpha, &lt, 0.77. The hydraulic gradient hits a nadir at sin&alpha, = 0.77 and climbs with the increasing sloping angle when sin&alpha, &gt, 0.82. The hydraulic gradient ascends when the bottom opening ratio &delta, increases from 0.167 to 0.231, due to the decreased intensity of the bottom vortex. The hydraulic gradient drops with a rising plate height, except for a fluctuation at Hp = 0.12 m. An approximate negative correlation is found between the obstruction height of the floating plate and the average hydraulic gradient under the pipeline. This could be partially attributed to the extension and amplification of the bottom vortex on the leeside of the pipeline due to the increased plate obstruction height.

Inflatable structures offer advantages such as lightweight, compact, and cost-efficient. As such, underwater inflatable structures (UISs) can be advantageous in many marine applications. The UISs are initially folded into a compact package which is dropped from the surface of the ocean to reach an underwater destination and morph into its inflated form. Relying on UISs, we've designed an Underwater Inflatable Co-prime Sonar Array (UICSA) prototype. In this paper, we investigate the physical design of the UISs to support the UICSA. A UICSA prototype is constructed to evaluate the morphing performance and deployment procedures. The experiments results and the design considerations are presented.

In many scientific and defense surveillance missions, reducing the size, weight, and power (SWaP) of sensing systems is critical to accomplishing the intended objectives. At the backend, compressive sensing (CS) has been widely adopted to maintain the signal fidelity with less measurements, thereby reducing the hardware complexity. On the other hand, SWaP reduction can also be achieved with intelligent mechanical design. In this paper, we discuss a novel system concept, namely, Underwater Inflatable Co-prime Sonar Array (UICSA), which provides SWaP compression on two fronts. First, the sonar array is implemented as an inflatable structure, also referred to as a deployable structure, which is a folded package with compact stowed dimension. The folded package can be detached from a carrying platform and it can morph into its final structure form at the destination. Second, a sparse array configuration, namely, a co-prime array, is employed, which can resolve a much higher number of sources compared to a conventional uniform half-wavelength spaced array for a given number of sensors. The integration of these two concepts leads to a simulatenous reduction in the stowed dimension of the sonar array and the number of employed hydrophones. We describe the development of a UICSA prototype and provide underwater source direction-of-arrival estimates obtained using initial datasets acquired with the developed prototype.

The resistance of an open-channel flow under the influence of bending deformation of submerged flexible vegetation canopy was experimentally studied in an indoor water flume. Altogether, 27...

A series of indoor experiment were carried out to investigate the optimal placement of a new type of wave energy converter, the tilt-ladder-breakwater (TLB). The TLB is a Chinese patented device that transforms the wave energy into current energy to create electricity. The main part of this device is a breakwater with its wave-ward front-wall composing of tilt ladders. The tilt ladders are used to beak waves and guide the current into their low end to provide concentrated energy for the generation of electric power. This device is simple and low-cost in construction and high efficient in power-generation. It has great application prosperity in coastal areas. For the purpose of obtaining an optimal orientation of TLB, a series of experimental tests were carried out. The concentrated current forces (𝐹) at the low end of tilt ladders were measured. The results show that the incident wave angle (𝜃) has significant effect on current force. In all the tests, 𝐹 reaches maximum at 35°- 45° incident wave conditions. For 𝜃 45°, 𝐹 is decreasing with the increasing of 𝜃. Aiming at obtaining the highest efficiency of energy transforming from wave into current for electric-powergeneration, it is determined that the optimal angle between TLB and the incident wave is in the range of [35° − 45°].

Underwater deployable structures are known as Ocean Morphing Structures, which can be compacted and transported by underwater robots then morph into the final form upon arrival. The underwater deployable structures are made of waterproof fabrics to provide a lightweight, compact solution for the underwater application. This paper focuses on the fabric materials strength used for the ocean morphing structures’ fabrication. The material of Polyethylene Terephthalate (PET) film and the glued seams are tested in dry and wet conditions. This work provides the experimental study of the physical strength for the effect of fabrication direction, fabric thickness and application environment.

Rigid flow deflectors are usually used on water flow beds to protect engineering structures such as breakwater in coasts and to regulate flow routes in open channels. To reduce its side-effects, i.e., local scour at the toe of deflectors, a flexible flow deflector is proposed, and the corresponding local scour was investigated in this study. A flume experiment was conducted to investigate local scour. To show the advantage of flexible deflectors, a control experimental test was also conducted using a traditional rigid deflector under the same blockage area configuration and the same flow conditions. The flow field near the flexible deflector was also measured to reveal the local flow field. The results show that the bed-scour develops near the toe edges of both flexible and rigid deflectors, but the maximum and averaged scour depths for the flexible deflector are smaller. This advantage of flexible deflector in scour depth is mainly caused by its prone posture, which induces the upward stretching and enlarging horizontally rotating vortex and the upward shifted vertically rotating vortex. The former dissipates more turbulent energy and the latter results in smaller bed shear stress, which lead to smaller scour depth directly. In addition, the up- and down-swaying movement of the flexible deflector can also assistant to dissipate more turbulent energy, thereby damping the intense of the horseshoe vortices and thus weakening scour depth as well. The results of this study provide an elementary understanding on the mechanisms of a flexible flow structure and an alternative deflector-device to reduce scour depth.

Plants in natural water flow can improve water quality by adhering and absorbing the fine suspended sediments. Dense plants usually form an additional permeable bottom boundary for the water flow over it. In the flow layer above dense plants, the flow velocity generally presents a zero-plane-displacement and roughness-height double modified semi-logarithmic profile. In addition, the second order shear turbulent moment (or the Reynolds stress) are different from that found in non-vegetated flow. As a result, the turbulent momentum diffusivity of flow and thus the diffusivity of sediment will shift, which will cause the vertical profile of suspended sediment and the corresponding Rouse formula deform. A set of physical experiments with three different diameters of fine suspended sediments was conducted in an indoor water flume. These experiments investigated a new distribution pattern of suspended sediment and the correspondingly deformed Rouse formula in the flow layer over the dense plants. Experimental results showed that above the dense plants, the shear turbulent momentum of flow presented a plant-height modified negative linear profile, which has been proposed by a previous study, and the vertical distribution of fine suspended sediments presented an equilibrium pattern. Based on the plant-modified profiles of flow velocity and the shear turbulent momentum a new zero-plane and plant-height double modified Rouse formula were analytically derived. This double-parameter modified Rouse formula agrees well with the measured profile of suspended sediment concentration experimentally observed in the present study. By adjusting the Prandtl&ndash, Schmidt number, i.e., the ratio of sediment diffusivity to flow diffusivity, the double-parameter modified Rouse formula can be applied to submerged dense plant occupied flow.

Underwater docking is currently a key technology for supplementing energy and self-recovery of autonomous underwater vehicles(AUVs). Three types of docking methods are introduced first. The captured-rod docking method is selected for this research effort, and its mechanical properties are analyzed. A Remus100 and a captured-rod with a radius of 50 mm are used to simulate the dynamic underwater docking and collision processes. The theoretical model analysis of deformation and collision of the captured-rod is carried out. Finally, a portable AUV is tested for collisions under different conditions. Through simulation and test, we found that there is a Karman vortex behind the captured-rod. When Remus100 approaches the captured-rod and the distance between them is less than a certain value, the captured-rod's wake will have an influence on the forces on the Remus100. The degree of influence positively correlates with the current's velocity. The lateral and vertical forces on the Remus100 are more susceptible to the captured-rod's wake, and are affected by the captured-rod's wake earlier. The collision force increases as the collision velocity increases, but the collision time is the opposite. We analyze and compare the results obtained by simulations, tests and theoretical model.