OCEN 201Introduction to Ocean &

Coastal Engineering

Instruments & MeasurementsJun Zhang

Jun-zhang@tamu.edu

Measurements   (Laboratory & Field)• Laboratory Measurements: 1. Under well-controlled conditions or environments ,

they are easier to be conducted than the corresponding Field Measurements.

2. They are cheaper and more “accurate”. 3. In view of coastal and ocean engineering, the sizes of

the models used in laboratory measurements are much smaller than those of their prototypes. Hence, essential similarity laws must be followed.

4. It is not likely to follow all essential similarity laws in model tests, certain assumptions must be made. Therefore, Laboratory Measurements cannot totally replace the related Field Measurements.   

• Field Measurements

1. They are difficult to be conducted because of harsh environments (e.g. rough seas and high wind speed in a hurricane).

2. They are usually very expensive and may not be accurate.

3. It is necessary to conduct Field Measurements in order to examine the validity of the assumptions (such as the neglect of certain similarity laws) made in the related Laboratory Measurements.   

• Similarity Laws (Chapter 9)1. Geometric Similarity (model and prototype are

geometrically similar); that is, the corresponding ratios of their dimensions are the same.

2. Kinematic Similarity 3. Dynamic Similarity. (matching non-dimensional

coeff. between model & prototype)4. Important non-dimensional coefficients - Reynolds # (viscous)** - Froude # (gravity)** - Euler # (pressure)* - Mach # (compressibility or elasticity) - Weber # (surface tension) Table 10-3 PP354 (old version pp267)   

Measurements  & Intstruments 

1. Survey: water depth & beach contour (Lidar, sonar & traditional survey instruments)

2. Force or pressure (strain gage, load cell & pressure transducer)

3. Wave elevation (wave gage*, indirect measurements: pressure transducer, velocimetry, LDV, ADV & PIV)

4. Velocity (LDV, ADV & PIV, electro-magnetic meter)

5. Accelerations: Accelerometer

Measurements  & Intstruments  (continue)

5. Movement or deformation (optical tracking system, PIV)

6. Wind velocity

7. Temperature

8. Salinity

9. Density

10. Sea Gilder

Wave Gage (Capacity* & Resistance)

Directional Wave Gages

Principles of Strain Gages

Pressure Transducers

For the information about LDV & PIV and Their Applications see the supplement materials

Facilities for Ocean & Coastal Related Lab M.

1. Wave Basins (Deepwater & Shallow water Basin: OTRC wave Basin & Hayens Coastal Lab Basin)-Directional wave generation

- Current generation (Nozzle type) - Wind generation

2. Wave Flume (1-D wave Basin, CLAB 109,) - Unidirectional wave generation - Current generation - Wind generation

Facilities for Ocean & Coastal Related Lab M.

3. Dredging loop (Hynes coastal lab)- Current generation- Towing Carriage

Description

Overview

• AUV / UUV• Self-regulated

buoyancy• Propelled by battery

power• Propelled by ocean’s

thermal energy• New technology!

History

• Preliminary designs (1986)

• Test runs: Florida, New York (1991)

• Result: the “Slocum” glider

• Scripps / Woods Hole: “Spray”

• APL-UW: “Seaglider”

• Slocum “Thermal Glider” (2005)

Vehicle Control

• Driving force: lift provided by wings

• Pitch/roll: internal weight shift

• Onboard computers

• Surface GPS fixes

• Pressure sensors

• Tilt sensors

• Magnetic compasses

Slocum, Spray, and Seaglider

Webb Research “Slocum”

• Weight: 52 kg• Diameter: 21.3 cm• Length: 1.5 m• Speed: 40 cm/s• Depth: 4 – 200 m • Endurance: 30 days• Range: 1500 km• Alkaline batteries

Webb Research “Slocum”

Webb’s “Thermal Glider”

• Weight: 60 kg• Diameter: 21.3 cm• Length: 1.5 m• Speed: 40 cm/s• Depth: 4 – 2000 m• Endurance: 5 years! • Range: 40000 km• Environmental power

Webb’s “Thermal Glider”

Scripps/Woods Hole “Spray”

• Weight: 52 kg• Diameter: 20 cm• Length: 2 m• Speed: 25 cm/s• Depth: 1500 m• Endurance: 815 cycles • Range: 4700 km• Lithium cells

Scripps/Woods Hole “Spray”

APL-UW “Seaglider”

• Weight: 52 kg• Diameter: 30 cm• Length: 1.8 m• Speed: 25 cm/s• Depth: 1000 m• Endurance: 650 cycles • Range: 4600 km• Lithium cells

APL-UW “Seaglider”

Design

Early Field Trials

• Wakulla Springs, Florida

• Straight flight, dives, turns

• Navigation and data relays

• Telemetry recorded

• Maneuvering parameters

• Instabilities found

Test Dive Profile

Design Solutions

• Increase glide speed

• Decrease pitch/heading oscillations

• Increase stall resistance

• Revise autopilot algorithms

• Swept wings

• Antenna moved to nose

Test Results, Conclusions

• Glide slope ratio similar to Space Shuttle• Energy expended at bottom of dive cycle• Decrease dive cycles = less energy• How do we decrease cycles?• *Lower glide speeds* • Longer endurance • Greater range

Applications

Current Uses

• Slocum: shallow water, short range• Spray/Seaglider: deeper, longer dives• Take measurements

-temperature

-conductivity (salinity)

-currents

-chlorophyll fluorescence

-optical backscatter

Current Uses

• Seaglider:

-physical, chemical oceanography

-tactical oceanography

-underwater Reconnaissance

-communications gateway

-navigation aid

Dive Profile

Dive Profile

Spray: La Jolla 2001

• Underwater canyon, 3 km width

• 11 day mission

• Maintained synthetic mooring

• Plotted wave, current propagation

Monterey 2003

• 10 Slocums and 5 Sprays

• Sample 100 square-km area

• Use networking to forecast conditions

• Example of large-scale team usage

Monterey 2003

Spray: Gulf Stream 2004

• New England to Bermuda• First crossing of the Gulf Stream

Seaglider: TASWEX-04

• Navy ASW exercise, East China Sea• Battlespace assessment• Tactical remote sensing• Mission successful

Future Uses

• ONR: Liberdade XRay

• USN “PLUSNet” program

• Largest glider

• Hydrodynamic efficiency

• Acoustics, electric field sensors

• 1-3 kt cruise, 1200-1500 km range

Liberdade XRay

Economics