Accelerometers

Three types of accelerometers are used, viz. Endevco model 2262A-25, Endevco model 2262A-200, and Sundstrand model QA-700. The Endevco accelerometers are rugged, fluid damped transducers of the piezoresistive type. The output range of model 2262A-25 is ± 25 g, and of model 2262A-200 ± 200 g. Both models are light weight (28 gram), high-sensitivity (20 mV/g and 2.5 mV/g respectively at 100 Hz). The static acceleration limit is 250 g for model 2262A-25 and 1000 g for model 2262A-200. The frequency range of model 2262A-25 is from 0 to 650 Hz and of model 2262A-200 from 0 to 1800 Hz. Detailed technical data can be found at www.endevco.com.

The integral electronics in the Sundstrand accelerometers develop an acceleration-proportional output current providing both static and dynamic acceleration measurements. They have an output range of ± 30 g and a maximum bias of 8-10~3 g. The static acceleration limit is 250 g. The Sundstrand accelerometers weigh 46 grams. Detailed technical data can be found at www.inertialsensor.com.

The high-sensitivity of both the Endevco and Sundstrand accelerometers is ideal for obtaining good signal-to-noise ratio even when the response amplitudes are low.

F.4.1 Accelerometer mounting

For an accelerometer to generate accurate and useful data, it must be properly coupled to the system under investigation. This means that the mounting must be rigid over the frequency range of interest to avoid distortion of the frequency response of the measurement. The natural frequency of an accelerometer, when mounted, is dependent on the stiffness of the coupling method. This requires a proper selection of the accelerometer mounting technique to be applied as well as thorough surface preparation. The following mounting methods are commonly used:

• Adhesives (e.g. hot glue, double-back tape, and cyanoacrylate);

• Magnetic adapters.

The key question is which mounting method is most suited for the intended purpose. The recommended mounting method is that used for calibration [177]. Issues that must be considered include: weight of the accelerometer, required bandwidth of the measurement, amplitude anticipated, type of mounting surface, and whether or not a mounting surface may be altered.

When possible, the best method is to mount an accelerometer with a stud since no adhesive is as stiff as a mounting stud. Cyanoacrylate instant adhesives have the widest frequency range and the broadest temperature limits of the adhesive-mount options for accelerometers weighing less than 10 grams, but attachment on rough surfaces is difficult and removal is time consuming [178]. Double back tape and hot glue are viable alternatives when removal time is an important issue. Hot glue is the preferred method of attachment for systems having hard to reach areas. Magnetic mounting is convenient and easily accomplished for accelerometers weighing over 50 grams. This method, however, reduces the usable bandwidth.

In our case it was not allowed to tap holes into the tower and rotor blades for a stud mount. We have decided to mount the accelerometers on the blades with hot glue (for easy attachment and removal) and to mount the accelerometers on the tower with double-back tape.

F.4.2 Accelerometer positions

The accelerometer positions are listed in Table F.1. The tower postions are measured with respect to the ground level, the blade postions are measured with respect to the blade tips.

Accelerometers

Tag

Position

Tower/Blade

Orientation

Type

A-01

0.00

Tower

- (x)

QA-700

A-02

12.66

Tower

- (x)

QA-700

A-03

21.80

Tower

- (x)

QA-700

A-04

36.00

Tower

- (x)

QA-700

A-05

44.38

Tower

- (x)

QA-700

A-06

13.75

Blade A

L1 (z)

2262A-25

A-07

13.75

Blade A

D1 (x)

2262A-25

A-08

7.75

Blade A

L1 (z)

2262A-200

A-09

7.75

Blade A

D1 (x)

2262A-200

A-10

7.75

Blade A

D2 (x)

2262A-200

A-11

1.75

Blade A

L1 (z)

2262A-200

A-12

1.75

Blade A

D1 (x)

2262A-200

A-13

1.75

Blade A

D2 (x)

2262A-200

A-14

1.75

Blade B

L1 (z)

2262A-200

A-15

1.75

Blade B

D1 (x)

2262A-200

A-16

1.75

Blade B

D2 (x)

2262A-200

A-17

1.75

Blade C

L1 (z)

2262A-200

A-18

1.75

Blade C

D1 (x)

2262A-25

A-19

1.75

Blade C

D2 (x)

2262A-25

Table F.1: Accelerometer positions on both the tower (w.r.t. ground level) and the rotor blades (w.r.t. blade tip). During the parked modal test, blade A is pointing upwards (i.e. at 12 o'clock position) while blade B and C are numbered anti-clockwise (rotation about x-axis).

The orientation of the rotor blade accelerometers is shown in Fig. F.5. The "L1" accelerometers are placed at the rotor blade nose. The "D1" accelerometers are placed on the rib, while the "D2" accelerometers are placed midway the "D1" accelerometers and the tail.

Figure F.5: Orientation of the accelerometers mounted on the rotor blades.

Appendix G

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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