US20130032078A1

US20130032078A1 - Sea Glider

Info

Publication number: US20130032078A1
Application number: US13/542,727
Authority: US
Inventors: Christopher R. Yahnker; Robert Eugene Hughes; Marc Jeremy Hoffman; Amber Kardes
Original assignee: iRobot Corp
Current assignee: iRobot Corp
Priority date: 2011-07-15
Filing date: 2012-07-06
Publication date: 2013-02-07
Also published as: WO2013012568A1

Abstract

A sea glider that includes a pressure hull and fore and aft fairings encapsulating the pressure hull. At least one of the fore and aft fairings defines an Ogive profile.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This U.S. patent application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/508,385, filed on Jul. 15, 2011, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

This disclosure relates to sea gliders.

BACKGROUND

Sea gliders travel through water with extremely modest energy requirements using changes in buoyancy for thrust coupled with a stable, low-drag, hydrodynamic shape. Sea gliders are generally deep diving UUVs that may measure temperature, salinity, and other quantities in the ocean, sending back data using global satellite telemetry. Sea gliders can collect physical, chemical and biological oceanographic data and performs a variety of missions for researchers and military planners.

SUMMARY

A sea glider having fairings the define an Ogive profile accommodate a relatively increased payload capacity, as compared to fairings defining other profiles, thus allowing the sea glider to carry relatively more and larger sensors. The fairings provide a relatively larger overall length of the sea glider and the profile of an aft fairing defines a convex shape, adding payload volume. These two features combined give the fairings a 650% increase in the volumetric payload capacity of the sea glider, as compared to a typical sea glider. Moreover, the fairings provide a reduction in total drag by as much as 25%, as compared to a typical sea glider, which can improve endurance of the sea glider (since less thrust is required to propel the sea glider).
One aspect of the disclosure provides a sea glider that includes a pressure hull and fore and aft fairings encapsulating the pressure hull. At least one of the fore and aft fairings defines an Ogive profile.
Implementations of the disclosure may include one or more of the following features. In some implementations, the sea glider includes a straight section joint connecting the fore fairing to the aft fairing. The aft fairing may define a convex shape. Moreover, the fore and aft fairings may comprise fiberglass (e.g., fiberglass composite) and/or each have a wall thickness of between about 2 mm and about 12 mm.
In some implementations, the sea glider includes right and left wings disposed opposite of each other on the aft fairing, a rudder disposed on the aft fairing, and an antenna disposed on the aft fairing. The sea glider may include a flooded payload section disposed aft of the pressure hull and at least partially enclosed by the aft fairing. A bladder system may be housed by the payload section for altering a buoyancy of the sea glider. The sea glider may include a controller in communication with at least one of the bladder system, a rudder disposed on the aft fairing, and an antenna. The rudder may be movable and/or removable from the sea glider. In some examples, the controller executes a Kalman filter for predicting water currents. In additional examples, the controller executes waypoint navigation by using a depth averaged current navigation algorithm.
Another aspect of the disclosure provides a sea glider body that includes fore and aft fairings for encapsulating a pressure hull. At least one of the fore and aft fairings defines an Ogive profile. A straight section defined between the fore and aft fairings has a length of about 200 mm. The fore and aft fairings have a combined overall length of between about 1.8 meters and about 2.0 meters.
In some implementations, the fore and aft fairings comprise fiberglass (e.g., fiberglass composite) and/or each have a wall thickness of between about 2 mm and about 12 mm. The aft fairing may define a convex shape. The fore fairing may define approximately 75 mm of the straight section and the aft fairing may define the remaining portion of the straight section. The sea glider body may include a flooded payload section at least partially enclosed by the aft fairing.
In yet another aspect, a sea glider includes a pressure hull and fore and aft fairings encapsulating the pressure hull. The fore and aft fairings each define an Ogive profile. The sea glider includes right and left wings disposed opposite of each other on the aft fairing, a rudder disposed on the aft fairing, an antenna disposed on the aft fairing, and a bladder system disposed in a flooded payload section disposed aft of the pressure hull and at least partially defined by the aft fairing. The bladder system alters a buoyancy of the sea glider. The sea glider also includes a controller in communication with at least one of the bladder system, the rudder, and the antenna.
In some implementations, the fore and aft fairings together define a straight section about a joint connecting the fairings. The fore and aft fairings may have a combined overall length of between about 1.8 meters and about 2.0 meters and the straight section may have a length of about 200 mm. In some examples, the fore fairing defines approximately 75 mm of the straight section and the aft fairing defines the remaining portion of the straight section. The aft fairing may define a convex shape. The fore and aft fairings may each comprise fiberglass (e.g., fiberglass composite) and/or have a wall thickness of between about 2 mm and about 12 mm.
In some instances, the controller executes a Kalman filter for predicting water currents. In addition or alternatively, the controller may execute waypoint navigation by using a depth averaged current navigation algorithm.
The details of one or more implementations of the disclosure are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a front perspective view of an exemplary sea glider.

FIG. 2 is a top perspective view of an exemplary sea glider.

FIG. 3 is a side view of an exemplary sea glider.

FIG. 4 is a graphical view of a tangent Ogive profile.

FIG. 5 is a side view of first and second exemplary sea gliders.

FIG. 6 is a graphical view of results of an exemplary computational fluid dynamics analysis of a sea glider.

FIGS. 7A is a graphical view of fluid flow over a sea glider having fairings defining non-Ogive profiles.

FIGS. 7B is a graphical view of fluid flow over a sea glider having fairings defining Ogive profiles.

FIG. 8 is a graphical view of horizontal versus vertical speed of a sea glider in water.

FIG. 9 is a graphical view of metrics of a sea glider model having fairings defining an Ogive profile

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

A sea glider can be used to expand hydrographic observations at significantly less cost than using ships or moorings. The sea glider can be used to monitor environmental conditions in and around polar icecaps, study the impacts of deep-sea accidents, and record and track marine mammals from Alaska to Hawaii, for example.
Referring to FIGS. 1-3, in some implementations, a sea glider 100 includes a pressure hull 110 (e.g., anodized aluminum shell) surrounded by a glider body 120 having fore and aft fairings 120 a, 120 b. The fairings 120 a, 120 b can each have an external surface 122 a, 122 b defining a smooth and hydrodynamic shaped that allow seawater to pass between an inner surface 124 a, 124 b of the fairing 120 a, 120 b and the outer surface 112 of the pressure hull 110. A flooded payload section 130 can be disposed aft of the pressure hull 110 and at least partially enclosed by the aft fairing 120 b. The fairings 120 a, 120 b accommodate a flooded payload section 130 having payload capacity to house a bladder system 140 to increase and decrease the buoyancy of the sea glider 100 and/or provide sensor payload capacity. For example, the payload section 130 may house a global positioning sensor (GPS), current profilers, PAR sensors, and acoustic modems, and/or a Glider Payload CTD 180 (GPCTD) (available from Sea-Bird Electronics, Inc. of 13431 NE 20th Street, Bellevue, Wash. 98005). The glider payload CTD (GPCTD) measures conductivity, temperature, and pressure, and dissolved oxygen of the sea water.
In the examples shown, the sea glider 100 includes right and left wings 150 a, 150 b (e.g., having a combined wing span of about 1 meter), a rudder 152, and an antenna 160 (e.g., about 1 meter long) disposed on the aft fairing 120 b for iridium satellite data telemetry, for example. Each of the components can be used for navigation of the sea glider 100 in water. The rudder 152 may be movable and/or removable from the sea glider 100. The sea glider 100 may include a controller 105 in communication with one or more of the bladder system 140, the right and left wings 150 a, 150 b, the rudder 152, the antenna 160, a battery 190 (e.g., lithium), and any sensors housed by the payload section 130. The controller 105 may include at least includes a programmable or preprogrammed digital data processor, e.g., a microprocessor, for performing program steps, algorithms and/or mathematical and logical operations as may be required. Moreover, the controller 105 may include digital data memory in communication with the data processor for storing program steps and other digital data therein. In some examples, the controller 105 includes one or more clock elements for generating timing signals, 256 MB Compact Flash memory, 8 serial data channels, 4 frequency channels, 12 channels 12-bit A/D, and/or 5 digital outputs. For guidance control, the controller 105 may execute a navigation routine that uses dead reckoning between GPS fixes using pitch, roll, and heading. The navigation routine may use a Kalman filter prediction for mean and oscillatory currents. Moreover, in some examples, the navigation routine uses a bathymetry map for surface to near-bottom dives.
The fairings 120 a, 120 b define a hydrodynamic shape while optionally providing removable hatch cover(s) 170 for accessing the payload section 130. The payload capacity of sea glider 100 is a function of both mass and volume, and directly affects the maximum change in buoyancy that the vehicle can achieve resulting in the desired thrust. During fairing development, a number of different profiles for the fairings 120 a, 120 b were analyzed for increasing the payload volume without adversely affecting the hydrodynamics of the sea glider 100. In some implementations, the fairings 120 a, 120 b define an Ogive profile, which provides advantageous hydrodynamic results. The basic equations for an Ogive profile can be modified to define the shape and size used by the sea glider 100. Specifically, the end conditions can be chosen so that the shape is tangent to the fore fairing 120 a and an antenna mount 162.
FIG. 4 graphically illustrates a tangent Ogive profile. The profile of this shape is formed by a segment of a circle such that the joint 126 is tangent to the curve of the fairing at its base; and the base of the fairing is on the radius of the circle. The radius of the circle that forms the Ogive is called the Ogive Radius p and it is related to the length and base radius of the fairing as expressed by the following formula.
$\begin{matrix} ρ = \frac{R^{2} + L^{2}}{2 R} & (1) \end{matrix}$
The radius y at any point x, as x varies from 0 to L is:
y=√{square root over (ρ²−(L−x)²)}+R−ρ (2)
The fairing length, L, may be equal to, or less than the Ogive Radius p. The fore and/or aft fairings 120 a, 120 b may define tangent Ogive profiles. Moreover, the fore fairing 120 a may define a spherically blunted tangent Ogive.
Referring to FIG. 5, while a sea glider 10 having fairings defining non-Ogive profiles can house a payload mass of approximately 2 kg in water with a useable payload volume of approximately 3,200 cm^{3, fairings 120} a, 120 b defining an Ogive profile can accommodate a payload section 130 that can house approximately 4 kg in water and provide a useable payload volume of over 21,000 cm^3.
Referring again to FIG. 3, to provide a relatively low weight sea glider 100, the fairings 120 a, 120 b may be constructed of fiberglass (e.g., a fiberglass composite) and have a wall thickness T of between about 2 mm and about 12 mm. In some examples, the fairings 120 a, 120 b are made of a fiberglass composite that includes syntactic foam and fiberglass. Other composites are possible as well, such as, but not limited to, a composite of fiberglass, carbon fiber, and/or syntactic foam. An overall length L_Allof sea glider 100 (without an antenna) may be between about 1.8 meters and about 2.0 meters.
The sea glider 100 may include a fairing joint 126 joining the first and second fairings 120 a, 120 b. The fairing joint 126 may be configured as a straight section having a length L_Jof about a 200 mm (8 inches). The straight section fairing joint 126 allows for a relatively larger payload section 130 while not having any significant impact on drag on the sea glider 100, since a parallel section on torpedo shaped bodies of revolution with a length to diameter ratio of 6:1 to 11:1 have minimal effect on total drag and cost less to manufacture than complex curves. Approximately 75 mm (3 inches) of the straight section fairing joint 126 may be added to the fore fairing 120 a. The remaining 125 mm (5 inches) of the straight section fairing joint 126 may be added to the aft fairing 120 b.
The hatch cover(s) 170 extend to match the length extensions for the fairings 120 a, 120 b, to enable full access to the flooded payload section 130 and to increase the available space for mounting sensors. The aft fairing 120 b defines a convex shape, rather than a typical concave shape, which allows the sea glider 100 to accommodates a relative larger payload section 130, by significantly increases the payload volume by increasing the flooded space. The increased volume provides greater clearance for the bladder 140, cables, and tubing that reside in the flooded payload section 130. It also allows for the mounting of relatively larger sensors, GPCTD 180, echo sounders, and/or an Acoustic Doppler Current Profiler (ADCP) inside the flooded payload section 130.
Computational Fluid Dynamics (CFD) may be used for determining the shape and size of the fairings 120 a, 120 b. CFD enables the import of various 3D CAD geometry for fairing shapes, wings, and sensors and analysis of those components in a virtual flow tank. Using CFD, profiles at different pitch angles and velocities were analyzed to build up a comparison of hydrodynamic performance. FIG. 6 illustrates an exemplary CFD analysis of the sea glider 100. The CFD model provided direct estimates of the drag, lift forces, and moments that act upon the vehicle during operation. This data was used to compare and contrast different flow shapes and profiles. In addition, the results allowed observation of critical factors such as turbulence intensity and boundary layer separation that are difficult to witness in laboratory testing or detect in real world applications.
FIG. 7A illustrates the flow over sea glider fairings 120 a, 120 b of a sea glider 10 having a non-Ogive profile and a concave profile for the aft fairing 120 b, and gives an approximation of where a boundary layer breaks and flow transitions from laminar to turbulent. The colors represent the predicted degree of turbulence, with lighter colors showing increasing levels of turbulence; darker regions represent little to no turbulence and lighter regions are highly turbulent flow. Similar to testing a model in a flow tank, the virtual vehicle was held stationary and pitched at different angles of attack to visualize the flow while calculating the resulting forces and moments acting on the vehicle (FIG. 4). In FIG. 7A, the boundary layer breaks around the joint 126 between the fore and aft fairings 120 a, 120 b. This sets up a turbulent layer over the back of the sea glider 10 where sensors protrude from the hatch covers. It also creates a condition where roughly 40% of the rudder 152 is in the turbulent wake of the sea glider 10 resulting in decreased control authority.
FIG. 7B illustrates flow over the fairings 120 a, 120 b of a sea glider 100 defining an Ogive shape. In this design, the boundary layer separation point is moved aft by approximately 25 cm (10 inches) with respect to the other sea glider 10 and creates a relatively smaller turbulent region. Based on a number of analyses run with different attack angles and flow velocities, the reduction in total vehicle drag due to the reduced turbulence is as much as 25%. This reduction in drag may result in extended endurance for the sea glider 100.
A combination of simulation runs can be used to determine the hydrodynamic coefficients for lift HD_A, profile drag HD_B, and induced drag HD_C. These coefficients may be the initial sea glider control inputs and can be used by sea glider control algorithms for navigation, stall angle calculations, and glide slope calculations, each executable on the controller 105. FIG. 8 depicts a plot of the sea glider performance model for a set of hydrodynamic coefficients HD_A, HD_B, HD_C computed from the CFD results.
In FIG. 8, the MAX_BUOY line amidst the dark cluster of points on the bottom of the plot represents the stall angle and the Glide Slope line is the desired glide slope. The space between the stall angle and glide slope defines valid operating points for horizontal and vertical velocities depending on the desired thrust and the maximum buoyancy of the sea glider 100. The greater the separation between the stall angle and glider slope, the wider the variety of options that is available to the pilot when operating the sea glider 100 to maximize efficiency and endurance. A small amount of asymmetry may have a significant impact on the control of the sea glider 100.
FIG. 9 graphically illustrates parameters of a sea glider model having valid solutions for hydrodynamic coefficients.
The sea glider 100 may use waypoint navigation by executing a Depth Averaged Current (DAC) navigation algorithm on the controller 105. As the sea glider 100 moves through the water between waypoints, it is pushed by currents. As a part of its navigation algorithms, the sea glider 100 attempts to compensate for the currents by adjusting its target such that the currents will push the sea glider 100 towards the desired waypoint. In some implementations, the navigational control algorithm uses a Kalman filter to estimate the currents. In additional implementations, the navigation model uses depth-averaged current (DAC) calculations specific to the hydrodynamics of the sea glider 100. This DAC algorithm reduces the processor time required to calculate a navigational heading and results in a power savings that can lead to an increase in overall duration for a long-term mission.
A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.

Claims

1. A sea glider comprising:

a pressure hull; and

fore and aft fairings encapsulating the pressure hull;

wherein at least one of the fore and aft fairings defines an Ogive profile.

2. The sea glider of claim 1, further comprising a straight section joint connecting the fore fairing to the aft fairing.

3. The sea glider of claim 1, wherein the aft fairing defines a convex shape.

4. The sea glider of claim 1, wherein the fore and aft fairings comprise fiberglass.

5. The sea glider of claim 4, wherein the fore and aft fairings each have a wall thickness of between about 2 mm and about 12 mm.

6. The sea glider of claim 1, further comprising:

right and left wings disposed opposite of each other on the aft fairing;

a rudder disposed on the aft fairing; and

an antenna disposed on the aft fairing.

7. The sea glider of claim 1, further comprising a flooded payload section disposed aft of the pressure hull and at least partially enclosed by the aft fairing.

8. The sea glider of claim 7, further comprising a bladder system housed by the payload section for altering a buoyancy of the sea glider.

9. The sea glider of claim 8, further comprising a controller in communication with at least one of the bladder system, a removable rudder disposed on the aft fairing, and an antenna.

10. The sea glider of claim 9, wherein the controller executes a Kalman filter for predicting water currents.

11. The sea glider of claim 9, wherein the controller executes waypoint navigation by using a depth averaged current navigation algorithm.

12. A sea glider body comprising:

fore and aft fairings for encapsulating a pressure hull, at least one of the fore and aft fairings defines an Ogive profile;

a straight section defined between the fore and aft fairings, the straight section having a length of about 200 mm;

wherein the fore and aft fairings have a combined overall length of between about 1.8 meters and about 2.0 meters.

13. The sea glider body of claim 12, wherein the fore and aft fairings comprise fiberglass.

14. The sea glider body of claim 13, wherein the fore and aft fairings each have a wall thickness of between about 2 mm and about 12 mm.

15. The sea glider body of claim 12, wherein the aft fairing defines a convex shape.

16. The sea glider body of claim 12, wherein the fore fairing defines approximately 75 mm of the straight section and the aft fairing defines the remaining portion of the straight section.

17. The sea glider body of claim 12, further comprising a flooded payload section at least partially enclosed by the aft fairing.

18. A sea glider comprising:

a pressure hull;

fore and aft fairings encapsulating the pressure hull, the fore and aft fairings each defining an Ogive profile;

right and left wings disposed opposite of each other on the aft fairing;

a rudder disposed on the aft fairing;

an antenna disposed on the aft fairing;

a bladder system disposed in a flooded payload section disposed aft of the pressure hull and at least partially defined by the aft fairing, the bladder system altering a buoyancy of the sea glider; and

a controller in communication with at least one of the bladder system, the rudder, and the antenna.

19. The sea glider of claim 18, wherein the fore and aft fairings together define a straight section about a joint connecting the fairings.

20. The sea glider of claim 19, wherein the fore and aft fairings have a combined overall length of between about 1.8 meters and about 2.0 meters and the straight section has a length of about 200 mm.

21. The sea glider of claim 20, wherein the fore fairing defines approximately 75 mm of the straight section and the aft fairing defines the remaining portion of the straight section.

22. The sea glider of claim 18, wherein the aft fairing defines a convex shape.

23. The sea glider of claim 18, wherein the fore and aft fairings comprise fiberglass.

24. The sea glider of claim 23, wherein the fore and aft fairings each have a wall thickness of between about 2 mm and about 12 mm.

25. The sea glider of claim 18, wherein the controller executes a Kalman filter for predicting water currents.

26. The sea glider of claim 18, wherein the controller executes waypoint navigation by using a depth averaged current navigation algorithm.