Download Wave powered autonomous surface vessels as components of

WAVE-POWERED AUTONMOUS SURFACE VESSELS
AS COMPONENTS OF OCEAN OBSERVING SYSTEMS
Roger Hine1 and Philip A. McGillivary2
1
2
Liquid Robotics Inc.
U.S. Coast Guard PACAREA Science Liaison
INTRODUCTION AND BACKGROUND
New and transformative technologies are required to meet the growing needs for ocean
observing systems internationally. A novel wave powered autonomous surface vehicle currently
under test and development in Hawaii has potential to enable new types of ocean observation as
well as cost savings over existing systems.
Marine environments are key components of national and international economies as an everincreasing percentage of the global populace depends on trade moving through international
ports. Security of ports, harbors, and maritime trade routes continues to be an important concern.
The importance of marine fisheries as a source of food and food security for many countries also
continues to increase, and changing climate and rainfall patterns are expected in the near-term to
further increase dependence on the sea for global protein supplies. However in many countries,
including the United States, there is a recognized crisis in policies for managing coastal, regional
and adjacent global marine ecosystems (Young et al., 2007). To a large degree this crisis stems
from a lack of data specific to the areas which must be managed in relation to the time-space
scales of ocean hydrodynamics and ocean climate responses critical for intelligent and
sustainable ocean management. This is true for developed nations throughout Europe and the
U.S., as well as for developing nations such as China (Prandle et al., 2005; Robinson and Brink,
2005; Li, 2006). A series of national and international plans have therefore been developed to put
in place a framework for ocean observing systems to address the need for improved spatial and
temporal data from the sea to improve understanding and management of the oceans (Ocean.US,
2002; UNESCO, 2003; Ocean Action Plan, 2004; U.S. Commission on Ocean Policy, 2004;
Ocean.US, 2006).
Within the international framework, Ocean.US was established under the US Global Ocean
Observing System (GOOS) management structure to coordinate efforts of nine federal agencies
tasked with various aspects of marine ecosystem management as part of the National Ocean
Partnership Program (NOPP). The charge for this organization was to develop the infrastructure
to provide information on marine ecosystems that would not only be useful for oceanographic,
ocean climate and scientific research, but also for operational ocean observations, which
generally require data in near-real time. The Ocean Observing Initiative (OOI) plan has as its
goal providing data for seven major purposes:
1) ocean climate studies;
2) maritime operations;
3) national security;
1
4)
5)
6)
7)
sustainable resource management;
preservation and restoration of marine systems;
natural hazard mitigation; and,
maintenance of public health (Ocean.US, 2002).
The science plan that has developed for the OOI calls for a network of fixed sensors that provide
near-real time data at high sampling rates, and mobile sensors with more restricted real-time data
telemetry capabilities (Ocean Research Interactive Observatory Networks [ORION], 2005). The
Science Summary Plan calls for a focus on the collection of ocean data to improve understanding
of ocean ecosystems in five key science areas:
1) ocean climate studies, including improving data on ocean and atmospheric fluxes of heat
and climate-critical gases such as CO2;
2) coastal dynamic studies, including improving data on conditions affecting fluxes of
nutrients, and biological responses of the coastal ocean ecosystem, including shifts in
species composition that affect fisheries and outbreaks of harmful algal blooms;
3) geodynamics, providing data on geological activity in the marine environment;
4) turbulent mixing and the biological responses to such mixing; and,
5) seafloor fluid-rock interactions (ORION, 2005).
The temporal and spatial scales for data collection in these five key science areas for the
proposed Ocean Observing Systems (OOSs) can be met partially by fixed data collection
systems, but also require mobile data collection platforms. To date progress has been made using
autonomous surface systems such as the GOOS drifters (http://www.aoml.noaa.gov/phod/dac/gdp.html), and
ARGO floats (http://www.argo.ucsd.edu/Acindex.html). These relatively inexpensive autonomous systems
have been supplemented in several spatially and temporally focused studies by more expensive,
and therefore more numerically limited glider and propeller driven autonomous underwater
vehicles (AUVs). Both kinds of vehicles have proven highly useful in focused studies where the
relatively long endurance (months or more) but limited speed (at 0.5 knot) capabilities of gliders
complements the higher speed (usually 2-4 knots) but shorter endurance (usually < a few weeks)
endurance of most propeller type AUVs. Development of solar-powered AUVs
(http://www.ausi.org/publications/SeaTechSolar.pdf) can improve the endurance of AUVs in environments
where extended periods of sunlight are an option, but cannot be relied on in all circumstances.
Other surface autonomous vehicles have also recently been developed which can potentially play
a role in OOSs as well, including the Robo-kayak and the OASIS platform (Curcio, et al., 2006;
http://www.isd.gsfc.nasa.gov/Allhands/12-16-04/ASF.ppt), but their routine use remains to be fully evaluated.
For research in spatially limited areas where underwater moorings are present to receive data
from gliders and AUV vehicles via acoustic modems, near-real time data can be provided by
these arrangements. However for most regional and global ocean studies data telemetry for such
underwater vehicles is more restricted (ORION, 2005). Moreover, currently the deployment and
retrieval of gliders and AUVs usually involves the use of relatively expensive research vessels,
and to date has often included the additional cost of the loss of a certain portion of these
relatively expensive vehicles.
Plans for a network of OOSs that meet science needs of the ocean community are now well
developed, with a Conceptual Network Design (CND) plan and Conceptual Design Review
2
(CDR) completed in 2006 following a series of workshops addressing both OOS infrastructure
and costs requirements. However, one critical problem has arisen in that funding of the planned
OOSs has stalled at a small percentage of the estimated funding needed to deploy and maintain
the planned systems into the future. Insofar as the need for proceeding with a system of ocean
observatories is clearly critical for understanding climate, resource management, national
security and other concerns, a review of plans for proceeding with OOS deployment is ongoing.
This review is intended to re-evaluate costs and requirements with a goal of reducing costs as
long as six goals for the OOSs can still be met, namely that any cost-reducing methods:
1) involve new and transformative technology that provides interactive controls and realtime data;
2) new technologies must address priority research questions noted above;
3) new technologies must be useful at all three spatial scales, i.e. coastal, regional and
global;
4) new technologies must balance high risk and low risk components to provide a
reasonably high probability of success;
5) new technologies must balance fixed and mobile assets to avoid spatial or temporal
aliasing of data collection; and,
6) new technologies must be capital expenditures that reduce life cycle costs (ORION,
2005).
We here describe a new technology which meets all six of the ORION requirements for inclusion
as a component of ocean observing systems, providing continuous real-time data on the ocean
surface mixed layer.
WAVEGLIDER, A NEW AND TRANSFORMATIONAL TECHNOLOGY
Figure 1: An early wave glider prototype and one of the authors
3
Why a Wave Powered Vehicle?
A large range of ocean observing goals require light equipment to be positioned at the sea
surface for long durations. In many cases it is preferable to have a large number of small, low
cost, observing systems rather than a few large systems.
Without an anchor, keeping station at sea is fundamentally an energy problem. Currents and
weather effects will tend to pull a surface vehicle off target and energy is required to resist this.
Whether it is in batteries, fuel cells, or fuel tanks, energy stored on the vehicle will eventually
run out. The problem worsens as vehicle size decreases due to the increasing ratio of drag area
relative to the volume available for energy storage. Thus any small vehicle that is to
autonomously maintain station at the sea surface for indefinite duration must harvest energy
from the environment.
Wind, sun and wave energy are the three primary sources available for mechanical energy
harvesting at the ocean surface. Wind energy can be effectively converted to thrust through sails,
or rigid wings that function like sails. However a sailing vessel must tack to advance into the
wind, and this involves moving at high speeds relative to the water surface. As wind increases,
so do wind waves, and these waves will obstruct a small vehicle from moving effectively at high
speed. Solar power can be converted to electricity using commercial solar panels, but will be
unavailable when needed most; during prolonged storm periods. Worse, large solar panels
become a liability in these situations. Wave energy is ubiquitous in the ocean environment and
has the attractive attribute of increasing during storm periods when it will be needed most.
Harvesting Wave Energy
As a waves move horizontally across the water surface, the water itself moves in approximately
circular orbits. The diameter of the orbit decreases logarithmically with depth such that it is near
zero at a depth of approximately ½ the wave length. A vehicle with a component at the surface
and a component at depth can harness energy from this relative motion.
Figure 2. Wave Motion and WaveGlider. Water particles move in approximately circular orbits
of decreasing diameter as depth increases. The float will pull the glider upward with a rising
wave crest but the water around the glider will remain relatively stationary. (Items in figure not
to scale.)
4
WaveGliders are comprised of two parts, a surface float and a submerged glider, connected by an
umbilical cable. As the float rises on the surface of the water it pulls the glider upwards. Fin
surfaces on the glider passively rotate to a positive angle of incidence so as to produce thrust. In
a second stage of motion, the float sinks down into a wave trough and allows the glider to lower
with it. The fin surfaces on the glider then rotate to a negative angle of incidence to produce
thrust again. Through both upward and downward motion stages the glider produces thrust. This
thrust generation is purely mechanical and continuous without the use of any electrical power or
control
Figure 3. Upward and downward motion phases
Aside from thrust generation, a second, perhaps equally significant, benefit arises from the two
part vehicle construction. This is the fact that the lower portion is sheltered from weather effects.
Storm winds will have a strong effect on small surface vehicles and will rapidly generate
currents in the very upper layers. These effects will be minimal slightly below the surface. The
submerged portion of a wave glider acts similarly to a sea anchor by keeping hold in the
relatively still waters below the surface. The result is that wave glider performance typically
improves as wind picks up. The increase in wave energy is more significant than the effects of
wind and surface currents on the float.
Vehicle Design
A wide variety of wing forms and vehicle architectures are possible and many have been tested.
They hold in common the basic distribution of components between float and glider.
While WaveGliders do not need electrical systems for propulsion, they do need them for
navigation, communication and sensor payload. Solar panels on the float provide a means of
5
charging batteries, although depending on payload and desired mission duration single charge
batteries may also be also a viable option. The float also supports communications and GPS
antennae. Iridium satellite communication is being used for primary command and control while
UHF is used for high bandwidth line of site transmissions such as hydrophone audio and still
image surveillance. A variety of different communications options can be supported.
The primary batteries are located in the glider where their weight is useful for generation of
thrust during the down stroke of the vehicle. A compass and the steering controller are also
located in the glider. The only actuator required in the system is used to drive the rudder for
steering control.
Payload may include a variety of observational equipment. Because they have no motor and no
propeller and because they have a portion of the vehicle already at depth, wave gliders make
good listening platforms. A connection for a hydrophone is placed at the tail of the glider. The
length of the hydrophone cable may be selected to achieve the desired depth and separation.
Cameras also may be placed at various locations on the vehicle. A look forward camera at the
back of the float shows the float, and birds resting on the float, as well as the area ahead. A look
down camera has been used to view the condition of the glider as well as the sea floor below.
Cameras mounted on the glider are suitable for observation of wildlife and fish counts.
WaveGlider prototypes have been developed to be portable by two people. They can be bundled
and shore launched and recovered by two people. Significantly larger sizes are also feasible and
may be desirable depending on payload and area of operation.
Development and Testing
Wave glider development and testing is being conducted by Liquid Robotics Inc. on the South
Kohala coast of the Big Island of Hawaii. The first operational prototypes were built in 2005 and
dozens of configurations have been tested. Multiple patent applications have been filed. A test
area for unattended glider operations is near a boat ramp and within kayak distance from shore.
Reliability and performance testing and continuous design improvement activities focus on
achieving demonstrable results in this and other test areas.
A web based user interface allows constant monitoring of location, status and sensor data. The
interface uses Google Maps to display position on a satellite image or map background. Users
can click on the map to create new waypoints and the gliders can be commanded to keep station
or to follow a waypoint course. Gliders also may be piloted remotely either with direct rudder
commands or desired heading commands.
A common operating mode is for the glider to follow a square course around four waypoints.
This reveals information about the glider performance as well as about environmental conditions.
Competing designs then may be raced around the course. Various design alterations are
evaluated empirically this way.
6
Figure 4. Screen capture of user interface showing 60 position reports from a WaveGlider on a
test course
Figure 5. Left: a glider was launched from shore and given command to proceed around the
square course. Right: A second glider that had been waiting off shore was commanded to race
the first on the same course. The relative performance was used to evaluate a design change.
APPLICATION TO OCEAN OBSERVING SYSTEMS
A number of capabilities which relate to OOS science areas are in formative stages of
development. For ocean climate observations, a payload may include two ultrasonic
anemometers at two and four meter heights to determine air-sea fluxes of heat and gases when
combined with an onboard atmospheric CO2 sensors (eg LiCOR CO2 sensor), and other marine
meteorology sensors. Such capabilities can be combined with water column thermistor chains or
7
small conductivity/temperature/depth (CTD) sensor packages which could be lowered through
the upper water column using existing low power technologies.
WaveGliders were originally developed and have been demonstrated with an acoustic
hydrophone used to monitor whale sound. This capability could be expanded for use in assisting
marine operations to provide data for whale collision avoidance along shipping and high speed
ferry routes by distribution of this data in real time via the National Automatic Identification
System (N-AIS) technology.
Other possible uses for marine operations relating to shipping and fisheries are the capability of
WaveGliders to be used as either fixed or mobile communications nodes to extend the range and
reduce the cost of communications between ships and the shore, or between ships. These
communication node capabilities can similarly prove useful for national security purposes, which
can additionally make use of the capability of WaveGliders to acoustically detect ships or divers
in restricted areas.
WaveGliders may be particularly well suited to mapping applications, especially in remote areas.
An acoustic bathymetry system may be supported to provide seafloor maps in remote areas. A
similar system may be used for detection of suspicious objects in ship channels, as well as
mapping shipping channels in port and harbors for bottom obstructions that may occur as a result
of natural hazards such as tsunami or hurricane storm surge.
For management of resources, preservation of marine ecosystems and maintaining public health,
WaveGliders will be developed for monitoring of coastal pollution, and can be used in future for
monitoring of water quality associated with offshore aquaculture facilities. The possibility also
exists in the near future of including sensors on WaveGliders that detect harmful algal blooms,
human and fish disease microorganisms. WaveGliders are already being developed for wider use
in detection, tracking and preservation of protected marine mammals. Further, as noted above,
WaveGlider acoustic detection systems can monitor vessel activities in marine protected areas to
ensure conservation.
CONCLUSION
The novel energy harvesting and station keeping technology being demonstrated by Liquid
Robotics in Hawaii represents an important new platform with cost saving capabilities that have
not been available previously to the scientific community. With continuous surface presence,
wave powered autonomous surface vehicles can offer unrestricted real-time data capabilities and
blur the boundaries between traditional fixed and mobile assets. Small and low cost vehicles
make redundant use practical to decrease mission risks and ensure continuous coverage. The
ability to be remotely deployed from ship or shore, travel long distances to a mission area, and to
return to port for maintenance significantly reduces operating costs associated with other systems
that require expensive ship time. WaveGliders represent a new and transformative technology
that is likely to play an important enabling role for achieving international ocean observing
system goals.
8
REFERENCES
Curcio, J.A., P.A. McGillivary, K. Fall, A. Maffei, K. Schwehr, B. Twiggs, C. Kitts and P.
Ballou. 2006. Self-positioning smart buoys, the “Unbouy” solution: logistic considerations using
autonomous surface craft technology and improved communications infrastructure. Proceedings
Marine Technology Society, Boston, 2006, 4pp.. (Online)
Li, H. 2006. The impacts and implications of the legal framework for sea use planning and
management in China. Ocean and Coastal Management 49(9-10):717-726.
Ocean.US. 2002. Building Consensus: Toward an Integrated and Sustained Ocean Observing
System, Ocean.US Publication No.1, 174pp. (www.ocean.us/documents/)
Oceans.US. 2002. Promoting and facilitating an integrated and sustained ocean observing
system. (www.ocean.us.net)
Ibid., 2006. The First U.S. Integrated Ocean Observation System Development Plan. Ocean.US
Publication No.9, 86pp. (www.ocean.us/documents)
Ocean Research Interactive Observatory Networks [ORION]. 2005. Ocean Observatories
Initiative Science Plan Summary. Revealing the Secrets of Our Ocean Planet. 9pp.
(www.orionprogram.org)
Ibid., 2006. News from the Program Office. ORION Newsletter 3(2):1-2. (www.orionprogram.org)
Prandle, D., H. Los, T. Pohlman, Y-H. de Roeck, and T. Stipa. 2005. Modeling in coastal and
shelf seas – European challenges. European Marine Board Position Paper 7, 28pp.
Robinson, A.R. and K. Brink. 2005. The Sea: The Global Coastal Ocean: Multiscale
Interdisciplinary Processes. Harvard University Press, Boston, Mass..
UNESCO. 2003. The Integrated Strategic Plan for the Coastal Module of the Global Ocean
Observing System. GOOS Report No. 125, 190pp. (http://ioc.unesco.org/goos/docs/doclist.htm)
U.S. Commission on Ocean Policy. 2004. An Ocean Blueprint for the 21st Century: Final Report
of the U.S. Commission on Ocean Policy. ww.oceancommission.gov/documents/welcome.html
Young, O.R., G. Osherenko, J. Eckstrom, L.B. Crowder, J. Ogden, J.A. Wilson, J.C. Day, F.
Douvere. C.N. Ehler, K.L. McLeod, B.S. Halpern, and R. Peach. 2007. Solving the crisis in
ocean governance. Place-based management of marine ecosystems. Environment 49(4):20-32.
WaveGlider is a trademark of Liquid Robotics Inc. Patent Pending
All trademarks are the property of their respective owners.
9