Table Of ContentRINA
INTERNATIONAL CONFERENCE
ADVANCED MARINE MATERIALS:
TECHNOLOGY & APPLICATIONS
9 – 10 October 2003
© 2003: The Royal Institution of Naval Architects
The Institution is not, as a body, responsible for the
opinions expressed by the individual authors or
speakers
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Advanced Marine Materials: Technology & Applications, London, UK
CONTENTS
Challenges in Materials & Processes for Naval Applications *
Dr Jagath Mawella, MOD Sea Technology Group, UK
Ducted Propulsors with Steerable Outflow using Smart Materials
Technology
Todd Quackenbush & William Usab, Continuum Dynamics Inc, USA
B Carpenter, B&B Consultants, USA
Progress in Friction Stir Welding of Aluminium & Steel for Marine
Applications
R Johnson & P Threadgill, TWI Ltd, UK
Evaluation of Friction Stir Welded HSLA-65
Maria Posada, Naval Surface Warfare Centre, Carderock Division, USA
Et al
Adhesive Bonding in High Speed Craft – Weight Saving Technology
Gary Davidson, Revolution Design, Australia
The Use of Titanium in Naval Applications
John Fowler, Rolls-Royce Plc,UK
Titanium Alloy Ti-5111 for Naval Applications
E Czyryca, M Wells & K Tran, Naval Surface Warfare Center, USA
Creep & Cracking by Creep of a Submarine Heat Exchanger
Component Made of ASTM Pure Titanium Grade 4 & Grade 2
Thierry Millot, DCN Propulsion, France
Fatigue Properties of Laser Welded Steel Sandwich Panels
Janus Kozak, Gdansk University of Technology, Poland
Ultimate Strength Formulae for Aluminium Plates & Stiffened Panels
under Axial Compressive Loads
Jeom Kee Paik & Dong Hoon Lee, Pusan National University, Korea
Alexandre Duran, Pechiney Marine, France
Fatigue Life Characterisation of Hybrid Composite – Steel Joints
S Boyd, J Blake & R A Shenoi, University of Southampton, UK
J Mawella, MOD Sea Technology Group, UK
A Comparison Between a Chromate & a Non Chromate Surface
Treatment for Adhesive Bonding of a Carbon Fibre Composite to
Titanium Alloys
R Brown & P K Depa, University of Rhode Island, USA
W C Tucker, Naval Undersea Warfare Center - Newport, USA
© 2003: The Royal Institution of Naval Architects
Advanced Marine Materials: Technology & Applications, London, UK
Advances in Marine Composites & Marine Composite Sandwich *
Structures
Yapa Rajapakse, Programme Manager – Composites for Marine
Structures, Office of Naval Research, USA
Composite Blades in Marine Propulsors
C Kane & J Smith, QinetiQ, UK
An Evaluation of a Composite Module for the Improved Navy
Lighterage System (INLS)
Himat Garala, Naval Surface Warfare Centre, Carderock Division, USA
Composite Patch Repair of Steel Ships
J Dalzel-Job, J Sumpter & F Livingstone, QinetiQ, UK
Design, Verification & Forensic Correlation of Composite Yacht
Structures
Paul Miller, United States Naval Academy, USA
Investigation into Shock Loading Effects on Composite Structures
Sarah Mouring, United States Naval Academy, USA
L A Louca, Imperial College London, UK
The Nondestructive Inspection of a ½ Scale Corvette Hull Test Section
& a Royal Navy Archer Class Fast Patrol Craft Using the Structural
Irregularity and Damage Evaluation Routine
C Ratcliffe, United States Naval Academy, USA
R Crane, Naval Surface Warfare Center, Carderock Division, USA
Pipeworks Welding in Orbital A-TIG Process
F Cortial & J Richard, DCN Propulsion, France
Authors Contact Details
* Not available at time of publishing
© 2003: The Royal Institution of Naval Architects
Advanced Marine Materials: Technology & Applications, London, UK
DUCTED PROPULSORS WITH STEERABLE OUTFLOW USING SMART MATERIALS
TECHNOLOGY
T R Quackenbush and W J Usab, Jr., Continuum Dynamics, Inc., USA
B F Carpenter, B&B Consultants, USA
SUMMARY
The concept of a steerable ducted propulsor is an attractive prospect, and the extension of rapidly maturing smart
materials technology offers a way to achieve this goal. In particular, the development of Shape Memory Alloy (SMA)
actuation devices for underwater use has opened the way for a deformable 'Smart Duct'. This paper describes the
preliminary development of a ducted propeller with a deformable shroud that redirects the propeller wash to yield direct
steering force. The deformation is provided by a electrically-actuated nickel-titanium SMA cables. The potential
advantages of this steering control technology for naval applications include: enhanced low speed maneuvering for
submarines; reduction or elimination of conventional steering surfaces and of associated actuator noise; and elimination
of hydraulic actuation hardware in favor of all-electric components. The paper includes computational studies of
candidate Smart Duct designs, a description of relevant SMA actuator technology, and the results of model construction
for in-water testing.
NOMENCLATURE achieving this goal. In particular, the development of
practical Shape Memory Alloy (SMA) actuation devices
D = propeller diameter, m for underwater use has opened the way for a deformable
J = advance ratio, V/nD 'Smart Duct'.
R = propeller radius, m
n = propeller rotation rate, 1/s Figure 1 depicts the overall concept of this system: a
V = onset flow speed, m/s ducted propeller with a deformable shroud that redirects
δ = duct trailing edge deflection angle, deg. the propeller wash to provide direct steering force. At
ρ = density, kg/m3 the same time, the induced flow over the duct generates
SMA Shape Memory Alloy substantial side forces that make this system more
effective in providing steering forces than vectored open
1. INTRODUCTION propellers at an equivalent slipstream deflection. As is
discussed below, the deformation is provided by an
Current systems for turning and maneuvering control for
electrically-actuated steel structure – embedded in
naval vessels have a range of limitations. For
flexible, hydrodynamically smooth sheathing - whose
submarines operating in a littoral environment enhanced
prime movers are a set of high strength nickel-titanium
turning capability at low forward speed is highly
SMA actuator cables.
desirable; improved maneuvering and performance
would also benefit the coming generation of Unmanned
Underwater Vehicles (UUVs). For surface combatants,
the ability to maneuver while minimizing or eliminating
cavitation-induced noise due to propeller wash
impingement on a rudder is a high priority. In all these
applications, development of technologies that minimize
the use of high-maintenance actuation (e.g., hydraulics)
in favor of electrical systems are an important long-term
priority for cost savings and for enabling new designs
that save space and weight and minimize hull
penetrations.
Ducted propulsors have been assuming a growing role in
naval combatants, and the concept of a steerable ducted
propulsor – one whose outflow can be redirected to
enhance low speed maneuvering and augment the
performance of (or replace) conventional rudders or
sternplanes – is an attractive prospect for addressing
these needs. However, mechanical implementation of
Figure 1: Side view of a notional Smart Duct propulsor,
such a concept through hydraulic or electro-mechanical
showing the undeflected (top) and deflected (bottom)
actuation would in many circumstances be prohibitively
duct shape. Propeller wake is indicated by the system of
difficult. The extension of rapidly maturing smart
vortex filaments trailing from the ducted propeller (not
materials technology, however, offers a realistic path to
shown).
© 2003: The Royal Institution of Naval Architects
Advanced Marine Materials: Technology & Applications, London, UK
The present paper is a summary of ongoing work whose steerable outflow to provide turning moment while
central objective is to design and build a Smart Duct garnering the hydroacoustic benefits of a ducted
technology demonstrator version suitable for in-water propulsor [4]. In the past, fixed-geometry ducts (Kort
testing at approximately 1/10th to 1/15th scale. Given the nozzles [5]) have most often been used to enhance the
prior work described below, this was judged to be the performance of heavily loaded propellers operating at
most appropriate focus for technology development at low speeds [6,7], though they are also used for a variety
this stage, since it would extend the existing database of of applications, including current ocean-going transports
engineering information about SMA devices for marine [8].
applications and would also go far toward establishing
the feasibility of their use in practical turning control Clearly, however, providing a robust hardware
systems. As will be seen, the test articles being fabricated mechanism for controlling outflow from such ducted
here are intended to be demonstrators rather than propeller systems presents a challenge. Using
engineering prototypes, the development of such a scaled conventional mechanical actuation devices to control
prototype being beyond the scope of the present work. flaps or otherwise vary the outflow would likely be
The concepts being developed and the status of model prohibitively complex and bulky for such applications, as
fabrication and demonstration will be described well as, inviting excessive drag penalties and premature
following a review of prior work. separation. As has been demonstrated in a variety of
applications in recent years (and outlined below), smart
materials-driven actuation devices can produce very high
2. OVERVIEW OF PRIOR TECHNOLOGY
force actuation in modest volumes that are competitive in
power requirements with conventional alternatives (e.g.,
Current-generation steering control for submarines and
Refs. [8-20]). In recent years, the applications for this
other submersibles in general requires the use of
technology have included more challenging high-force
hydraulic rams to drive control surfaces (e.g., rudders
aeronautical applications (e.g., inlet shaping for transonic
and sternplanes) via conventional mechanical
fighter aircraft [16]) as well as marine roles[19].
attachments. The forces required are large and the drive
machinery for control surface mechanisms are not only
heavy (which contributes to generally undesirable For the present Smart Duct application, SMAs represent
constraints on vehicle c.g. placement), but also occupies the best alternative among smart material actuators.
substantial portions of scarce volume in the aft Consider, for example, the review of smart material
engineering sections and necessitates numerous candidates by Crawley [21] from which the material
penetrations of the pressure hull. Also, present control performance data in Table is drawn. Most of the
surfaces can provide substantial steering forces at low materials considered have limited strain capability.
speed, but can lose effectiveness as the submarine SMAs, on the other hand, offer a very high strain
maneuvers and angular rates build up [1,2]. capability (up to 5-8%), which leads to the potential for
large amplitude motion with greatly reduced volume,
weight and moving parts relative to competing concepts.
Recent submarine propulsor design has evolved to
Furthermore, their high elastic modulus suggests SMA
include the routine use of ducted propellers
actuators can provide a high ratio of force to volume that
configurations. These ducts represent lifting surfaces
makes them well suited to the challenges of providing
that could potentially generate very large hydrodynamic
high force actuation in confined spaces. Also, when
forces to augment or possibly replace more conventional
properly implemented, SMA-based actuators can be
surfaces, should the option become available of making
engineered with sufficient bandwidth to allow closed-
the hydrodynamic forces involved controllable. Clearly,
loop control for the marine and aeronautical applications
to realize this possibility it becomes necessary to devise
listed above, while taking full advantage of their other
methods to address the challenging engineering issue of
benefits and ease of activation.
how to create a steerable duct and redirect the outflow of
these propulsors.
Material PZT G- PMN Terfenol Nitinol
Devices based on ‘smart’ materials technology are a 1195 DZ (NiTi)
particularly promising way to enable this approach to Actuation Piezo- Electro- Magneto- Shape
steering control. Such devices offer high-authority mechanism ceramic strictor strictor memory
control for a variable geometry ducted propeller,
alloy
reducing or bypassing the need for conventional rudders.
εmax, 350 500 580 8500
Regarding other applications, steering control for current
µstrain
naval surface vessels typically rely on conventional
E, GPa 62 117 48 28(m);90(a)
rudder surfaces, deflected in the slipstream of open
propellers. Such surfaces are subject to a variety of Bandwidth High High Moderate Low
problems [3], including separation at large angles of (note: m = martensitic, a = austenitic)
attack and cavitation at high forward speed or high
Table 1: Comparison of various ‘smart’ material
loading. Shrouded or ducted propellers with controllable
properties [21].
outflow could greatly relieve such problems, providing
© 2003: The Royal Institution of Naval Architects
Advanced Marine Materials: Technology & Applications, London, UK
The most practical shape memory materials are alloys of water at 20 kts. An initial demonstration of this system
nickel, titanium, and copper (though in some cases took place in the NASA/Langley Transonic Dynamics
alternate alloys or optimized doping can enhance selected Tunnel in April 2000; in these tests, an SMA-actuated
material properties). SMAs exist in one of two stable cowling was tested at flow speeds up to Mach 0.7.
crystalline phases: a high temperature 'austenite' and a
low temperature 'martensite'. The austenitic phase has a These tests not only produced the full system
conventional stress-strain curve with a higher linear functionality desired (achieving 11 deg. of angular travel
modulus of elasticity while the martensitic phase exhibits on the cowling) but also demonstrated actuation using
a stress plateau between two yield points (Figure 2). extremely high force bundled SMA assemblies. These
Transition between the austenite and martensite phases actuators were very large (~2 m. long) (Figure 3b) and
can be triggered by applied stress, but it is more typically composed of 34 1.75mm dia. wires and offer 7.5 cm of
accomplished through temperature change. NiTi alloys deflection, as well as, 27000 N of actuation force (or
are good conductors, so direct ohmic heating is a popular roughly 800 N/wire). This type of exceptionally high
and robust way to control the shape memory effect. force device is the product of rapidly advancing SMA
Phase transformation temperatures ranging from 40 deg. materials processing and design work; it also indicates
C to 150 deg. C are available, depending on the that the high actuation forces required for naval
particular alloy used; the martensite phase for most SMA applications of SMA actuators are within the reach of
materials typically occurs at room temperature. The current technology.
maximum recovery strain for conventional NiTi (one of
the most common SMAs) is approximately 8 percent,
though reducing this level of strain will increase cycle
life substantially; 3%-4% strain levels are sustainable for
long-term cyclic operation. SMAs are good choices for
applications that call for steady or low-frequency (up to
0.5 Hz) cyclic actuation.
Austenite (high temperature)
D
C
Stress
a) front view of Smart Inlet
B
A
Martensite (low temperature)
Strain b) overall view of SMA cable bundle
Figure 3: Experimental large-scale SMA systems
Figure 2: Stress/strain characteristics of a typical
demonstrated in recent wind tunnel tests.
thermally activated SMA in its martensite and austenite
phases during cyclic loading: A = onset of twinned The potential of SMA technology for use in actuation of
martensite deformation; B = end of twinned martensitic marine control surfaces has been recognized for some
regime; C = plastic deformation region; D = initiation of time. One example was the development and test of a
return to austenite state. Conformal Control Surface (CCS) in 1992-93, as
described in MacLean et al. [10]. The CCS was
Recent projects have established a substantial base of envisioned as a candidate for use on torpedoes or small
engineering data and device performance using SMA submersibles, and the prototype involved the use of SMA
actuation, including: extensive materials testing (e.g., wires embedded in a flexible foil, with the wires oriented
wire stress/strain analysis, repeatability, sensitivity to such that their actuation would produce large tip
thermal environment); generation of aero/thermo/elastic deformations and substantial lift coefficients. Water
models for airfoil and hydrofoil deflection with tunnel testing of a small (600 cm2) CCS device at
embedded actuators; integration studies for candidate NUWC Newport confirmed its ability to achieve large
actuator designs, as well as results from benchtop, wind deflections at flow rates up to approximately 10 kts.
tunnel, and water tunnel testing of prototypes. One such Other recent projects have tested SMA-actuated
project was the design and testing of an SMA-actuated geometry control devices specifically tailored for high-
inlet shaping system for a full scale F-15 inlet (Ref. 13). force, high-deflection marine applications. One of these
This system of complementary SMA-based actuators began as an DARPA/ONR-sponsored element of the
(Figure 3) is designed to operate in air at essentially the SAMPSON program, the Tab Assisted Control (TAC)
same dynamic pressure (~40 KPa) as that experienced in effort, which is developing and demonstrating SMA-
© 2003: The Royal Institution of Naval Architects
Advanced Marine Materials: Technology & Applications, London, UK
driven tab devices to assist the operation of submarine 3. SMART DUCT DESIGN
sternplanes [19].
3.1 HYDRODYNAMIC DESIGN
Another marine application – one particularly pertinent
to this project – emerged from prior work by the present A first step in design of a Smart Duct demonstrator was
authors on the design of prototype deformable hydrofoils to assess the deflection requirement for adequate side
that would be cyclically deflected to accelerate the (turning) force generation. Modeling for this was
breakup of submarine wakes [9,10,12,20]. Figure 4 conducted with a well-validated potential flow model of
shows a small scale (7.5 cm span) model of a deformable duct/propeller performance developed over the past 10
cross-section employing a NACA 0012 contour; the foil years for both aeronautical and marine applications,
shown here used embedded 0.50 mm diameter SMA denoted the Fast Panel/Vortex for FPV model [22-25]. It
wires and achieved the design goal of repeatable, large was validated for both isolated ducts and combined
amplitude deflections in water under dynamic pressure duct/propeller systems using data from [26-28].
loadings up to 13.5 KPa. A large-span version of this
device was developed for testing in a 0.9 m diameter A reasonable target for Smart Duct performance would
water tunnel (Figure 4c). be for it to match or exceed the turning force available
from existing conventional rudder systems. For typical
current systems, the rudder side force for full deflection
is roughly twice the thrust necessary for self-propulsion.
To quantify the goals for side force, consider that a
typical drag coefficient for steady, self-propelled motion
along the submarine longitudinal axis is roughly 0.12
based on frontal area and dynamic pressure. This defines
a) neutral shape
the net axial thrust that the propulsor must deliver, and,
by extension, the dimensional force requirements for a
candidate Smart Duct.
The duct geometry selected for use in the present studies
involves the an aspect ratio 1.0 duct with a cross section
based on an airfoil with a relatively flat lower surface
b) downward deflection
and an upper surface adapted from an NACA 0011
profile. The design selected was chosen to provide: a
relatively constant-diameter (neutral) cross section;
benign leading and trailing edge separation behavior; and
adequate thickness to accommodate likely sizes of
deflectable ring hardware and appropriate fairings.
Figure 5 shows the geometry in use in the present design,
as depicted by the FPV flow model.
c ) oblique view of a 68 cm span hydrofoil installed in
the 0.9 m water tunnel.
Figure 4: Test articles used for benchtop and water tunnel
experiments on an SMA-actuated deformable hydrofoil.
Tests were conducted in the fall of 1998 in the NSWC
Carderock Variable Pressure Cavitation Channel (VPCC)
at flow speeds up to 5.2 m/s (13.5 KPa dynamic
pressure). The large trailing edge deflection and force
amplitudes were demonstrated over four days of
experimentation in the VPCC, featuring large numbers of
cycles of essentially continuous, repeatable deflection
performance. The ability of this type of SMA-based
actuator to achieve large-amplitude deflections in a high Figure 5: Side views of isolated ducts for undeflected
force marine environment was a key milestone, and deflected cases (top); side and oblique views of a
suggesting the possibility of scaling up this type of SMA- duct+propeller combination (bottom). (Note: the wake
based control system to provide continuous deformation of only one propeller blade is shown in this view).
control of duct geometry for a Smart Duct design.
© 2003: The Royal Institution of Naval Architects
Advanced Marine Materials: Technology & Applications, London, UK
A first set of calculations studied the effect of RPM (normalized by a reference speed) with thrust operating
variation at low speed with a deflected duct. The at self-propulsion levels. Figure 6b shows the absolute
calculations assumed a representative three-bladed levels thrust and side force, indicating that the ratio of
propeller with solidity and pitch similar to existing side force to self-propulsion thrust in these cases is well
designs. However, since the results are similar to those over the target value of 2.0. Results also indicate that
obtained in early studies using actuator disk models, they the side force resulting from the trailing edge deflection
are not considered sensitive to details of propeller design. is roughly equal to Tsin δ; for the trailing edge deflection
The results in terms of side force vs. RPM are given in angle of 20 deg., sin δ is 0.34, suggesting that a side
Figure 6a; they have been corrected for the nonzero force of approximately 30 percent of self-propulsion
forward speed by subtracting a constant force of 9000 N thrust will arise from flow redirection.
to account for the effective lift of an isolated duct at 2
kts. fps with a deflected trailing edge at 20 deg. As is While this deflection does not necessarily represent the
evident, the side force generated can be substantial, up to optimal design or the maximum achievable side force, it
90,000 N for high RPM levels (this case corresponds to a indicates that a 20 deg. trailing edge deflection meets the
300,000 N and so represents a large overthrust case). desired steering force goal. Additional studies are
This illustrates the potential of the Smart Duct to underway using representative submarine hull shapes to
generate substantial side forces at very low speeds. assess likely installation effects.
1 105
3.2 MECHANICAL DESIGN
8 104 Early conceptual design work on Smart Duct actuation
centered on developing the two classes of concepts to
N)
orce ( 6 104 esifmfeiclat rt hine ditus cets dseenflteiacltsio tno, tih.ee. ,a an tbaegaomni sdte aflcetuctaitoino nc odnecsiegpnt
F
e shown in Figures 3 and 4 and a sliding ring concept that
d
cted Si 4 104 rise pmreoseren tso fa pao t“esnotliiadl lys tbaeten”e fiacpiaplr odaecpha rtbuarsee. d Tohne feolramsteicr
e
orr deformation of a composite beam, while the latter has a
C
mechanical character and promises higher deflections for
2 104
an equivalent size. Test and development work led to
selection of the sliding ring concept, whose
implementation is now described.
0
0 20 40 60 80 100 120 140 160
RPM
Early feasibility studies for the Smart Duct [8] indicated
a) side force as a function of RPM at 2 kts. forward speed
a key aspect of a successful design would be to preserve
a circular interior cross-section of the duct geometry
3 105 when deflected, since such designs minimize the
generation of unsteady loading that could contribute to
vibration or radiated noise. One concept that would
2.5 105
Side Force (N)
allow maintenance of a circular cross-section is shown in
Thrust (N)
Figure 7, which depicts neutral and deflected conditions
2 105 of a candidate the conceptual ‘sliding ring’ design [Note:
this design is shown in structural skeleton form, without
N)
e (1.5 105 the taper and hydrodynamic fairing that would be used in
c
or actual applications]. This concept entails using
F
azimuthally oriented SMA actuators that provide
1 105
differential sliding motion between adjacent ring
segments; the sliding interface between segments can
5 104 provide substantial flow turning, given an adequate
number of ring segments. Ring diameter and stacking is
adjusted to conform to the hydrodynamic shape of the
0
0.2 0.4 0.6 0.8 1 1.2 duct in its neutral position. Each ring is allowed to slide
V/V
ref between it neighbor using slots milled into mating
b) side force and self-propulsion thrust cases over a surfaces at 0 and 180 degree clocking locations. Pins
range of forward speeds. that ride in each slot are rigidly attached only to one of
the neighboring rings such that an equal amount of
Figure 6: Predicted Smart Duct performance. relative motion is realized.
A second set of results was generated for a ducted This mechanism provides a progressive increase in
propeller system at a range of forward speeds overall duct deflection as each ring is translated. At
© 2003: The Royal Institution of Naval Architects
Advanced Marine Materials: Technology & Applications, London, UK
model scale, the rings are retained in the longitude sliding surfaces and interlocking features. In addition,
direction using spring washers and snap ring type shape memory wire termination blocks and electrical
keepers placed over the pins. Insulated shape memory egress features were constructed and access holes drilled.
wires positioned along each ring circumference are SMA wire bundles (composed here of two .38 mm
terminated at each pin location. To achieve bi- NiTiCu wires) were inserted and wiring and control
directional motion two independent sets of shape mechanisms were developed for actuation of the
memory wire of length π times the duct radius (πR) are individual rings.
required for each ring. As such each ring can move
approximately 2.0 to 2.5% of πR significantly more than
Digital actuation similar to that anticipated for the final
that which can be achieved in the beam deflection test 1/12th scale article has been added making this model
concept. In order to maintain desirable fluid flow near
fully functional for benchtop testing. This
the surface, ring thickness should be minimized to reduce
implementation features a "two way" shape memory
the effects of “steps” on both the outside internal
implementation, with mechanical springs providing
surfaces. This is done, however, at the expense of
pretensioning and sets of SMA wires installed in each
increased part count and wire egress complexity. Further
ring to supply the force to translate the ring stack. ‘Dry’
since the rings are retained at pinned joints they must be
benchtop tests indicated achievement of the goal of 0.5
sufficiently thick to resist bending loads induced by non-
cm displacement per ring. Given the individual ring
uniform flow-induced loading. thickness of 1.27 cm, the local slope between rings was
atan (0.5/1.27) = 21 deg.; this indicates that the goal of
Counting pins Slot 20 deg. angular deflection was achieved.
SMA
The next step in testing this article was to attach it to a
actuators
12" O.D. front duct fairing for ‘wet’ testing in the CDI
low speed flow tank (Figure 8). Because the operating
Direction
flow speed of the facility is 0.75 m/s, this did not expose
of motion
the model to high dynamic pressures. However, model
experiences a convective cooling environment
significantly more representative of realistic conditions
than the initial static tests. Figure 8 shows the model in
Rear view its neutral (unpowered) position as well as in its fully
deflected position.
Actuation causes
rings to slip
Side view
Figure 7: Schematic of sliding rings concept for
maintaining circular duct cross-section.
4. DEMONSTRATOR FABRICATION AND
TESTING
a) neutral position
As noted above, the ultimate goal of current experimental
activity is construction and test of a Smart Duct
technology demonstrator at roughly 1/12th scale (38 cm
dia.) for water tunnel testing at up to 10 kts. forward
speed. A preliminary step in implementation and testing
of the overall concept, though, involved construction of a
roughly 1/14th scale benchtop demonstrator (30 cm OD,
25 cm ID). This benchtop model of the sliding disk
section is was constructed to verify segment to segment
displacement magnitude and structural stiffness. Digital
actuation similar to that anticipated for the final test
article was added to make model fully functional. A first
step involved machining four ring segments from acrylic
sheet with the appropriate geometry defining the outside
diameter, tracks for shape memory wire placement, b) fully deflected
© 2003: The Royal Institution of Naval Architects
Advanced Marine Materials: Technology & Applications, London, UK
Figure 8: Representative snapshots of in-water testing of the deflection of the trailing edge of the actuated rings.
the 30 cm diameter Smart Duct model (without trailing To have a smoothly faired yet flexible ring stack, the
edge fairing and sheathing). flexible sheath is attached in tension during installation
via restraining plates on the leading and trailing edges of
During several test cycles, repeatable actuation up to the the flexible duct region; this installation ensures against
design level of 20 deg. (equivalent to a total trailing buckling or puckering in the surface when deflected.
edge displacement of 1.8 cm in this truncated model)
were achieved. The side force on this ~1/14th scale After final modifications currently underway, the model
model (as measured by the strain gauge balance shown in Figure 10 will be used in in-water testing at the
supporting the test article) was 4.4 N during each of these U.S. Navy Carderock 0.9m water tunnel in October
runs. This scales up to roughly 125 lbs. for the final 2003. The test matrix currently entails an initial series of
~1/12th scale water tunnel model operating at its top runs without a propeller over a range of speeds from 2 to
design speed of 10 kts, matching closely the values 10 kts and at angles of attack from 0 to 25 deg.
predicted for the latter without a propeller present. Objectives of this first phase of the test include
establishing side force and drag generated by the model
These preliminary tests established the mechanical as well as its power requirements, response time,
suitability of the sliding ring mechanism as well as its repeatability of motion, and amplitude of deflection
capability for (limited) operation immersed in water. [note: variable power control applied to the rings will be
However, the final implementation requires a smooth used to generate a more smoothly increasing deflection
hydrodynamic fairing as well as watertight sheathing to pattern than the full-amplitude deflection shown in
protect the SMA actuation hardware from the long-term Figure 10].
adverse effects of water exposure (particularly in a salt
water environment). As currently envisioned, the front fairing 30 cm ID
completed structure of the Smart Duct water tunnel
demonstrator will be composed of: first, a rigid fairing
(with a smooth airfoil shape) comprising roughly the first
1/2 of the duct length, combined with a rigid support
stand; second, the active duct section, sheathed to present
a smooth interior and exterior surface; and, third, a
passively deflecting tapered section bringing the duct
cross-section to a hydrodynamically acceptable
termination. A non-powered mock-up of this
configuration – shown in Figure 9 - has been constructed
to illustrate the overall concept, though with the
hydrodynamic sheathing absent to illustrate the movable ring stack powered ring stack
mechanical detail of the structure. (10 6mm rings , passive (10 13mm rings
move with aftmost SMA simulating SMA-
Construction of the powered water tunnel demonstrator is rings) actuated components)
nearing completeion, as is shown in Figure 10.
Proceeding from leading edge to trailing edge, the Figure 9: Non-powered mockup of the complete Smart
elements of the model are as follows. The rigid front Duct demonstrator.
fairing has an overall length of 19 cm, and is itself
composed of two components: a front lip section 3.8 cm
long and a constant-diameter "barrel" section 15.25 cm
long and 4.1 cm in thickness. The front lip is a hardened
urethane plastic, cast into a custom shape with a
modified 3:1 elliptical cross-section on the inner surface
to maintain a favorable pressure gradient for turning flow
into the duct at angle of attack. This front lip is joined
via a screw attachment to the barrel section, which itself
is constructed from three segments of 5 cm long by 39.4
cm O.D. /31.1 cm I.D. sections of PVC plastic.
These sections are in turn bolted to a 5 cm long
aluminum center interface section which will connect the
model to the tunnel balance. This interface section
serves as the mount for the 13 cm long SMA-actuated
ring stack coated by the ~ 2 mm flexible rubber
sheathing. The final 3" of the duct is a stack of
contracting aluminum rings mounted to passively follow
© 2003: The Royal Institution of Naval Architects
