**3.1.3 Influencing factors analysis**

The orthogonal experimental table L18(37) and the simulation results are shown in table5.

The trend charts were shown as Figure 6 and Figure 7. The /*L D* increase with the growth of chord and aspect ratio, and decrease with the growth of backswept,it has little relationship with the location of the wings. The *l* α ′ increase as chord and backswept increase when the wings is located after the hydrodynamic center, which means the stability increase as chord and backswept raise. The stability gets higher as the wing location becomes father away from behind the center of the body.

The ranges of chord, aspect ratio, backswept and distance of the wings is separately 2.448, 1.077, 1.303 and 0.312 for the *L*/*D*, which was gained by the range method. It is shows that the effects significance series for glide efficiency is chord, backswept, aspect ratio and the location of wings. The chord was dramatic for the index *L*/*D* at the significance level 0.10 and 0.05 adopted by the range method.

In like manner, the range of chord, aspect ratio, backswept and distance of the wings is separately 0.051, 0.037, 0.095 and 0.031 for the *l* α ′ , which was gained by the range method. It is shows that the effects significance series for glide stability is backswept, chord, aspect ratio and the location of wings. The backswept was dramatic for the index *l* α ′ at the significance level 0.10 and 0.05 adopted by the range method.


Hydrodynamic Characteristics of the Main Parts of a Hybrid-Driven Underwater Glider PETREL 45

Table 5. Orthogonal experimental table and the results

Fig. 6. L/D tendency chart

44 Autonomous Underwater Vehicles

level chord(mm) aspect ratio backswept (°) distance(mm) 1 100 6 20 100 2 150 8 40 0 3 200 10 60 -100

The design of the wing will generate important impacts on glide efficiency and glide stability of the vehicle. The lift to drag ratio *L D* is chosen for measurement of the glide efficiency, the bigger values correspond to the more efficient gliding. The inverse of *L/D* expresses the glide slope [7, 19]. Existing oceanographic gliders are designed for static stability in steady glides, and the static stability can be measured by the non-dimensional

> *lll* α α

*l ML*

*l* 0 α

The orthogonal experimental table L18(37) and the simulation results are shown in table5. The trend charts were shown as Figure 6 and Figure 7. The /*L D* increase with the growth of chord and aspect ratio, and decrease with the growth of backswept,it has little

moment induced by incremental angle of attack makes the vehicle to turn to the original

α α

> , the moment induced by incremental angle of attack makes the angle of attack

α

when the wings is located after the hydrodynamic center, which means the stability increase as chord and backswept raise. The stability gets higher as the wing location becomes father

The ranges of chord, aspect ratio, backswept and distance of the wings is separately 2.448, 1.077, 1.303 and 0.312 for the *L*/*D*, which was gained by the range method. It is shows that the effects significance series for glide efficiency is chord, backswept, aspect ratio and the location of wings. The chord was dramatic for the index *L*/*D* at the significance level 0.10

In like manner, the range of chord, aspect ratio, backswept and distance of the wings is

It is shows that the effects significance series for glide stability is backswept, chord, aspect

ratio and the location of wings. The backswept was dramatic for the index *l*

α

α= −

and is the Lift induced by the angle of attack

α

<sup>=</sup> / (7)

is the hydrodynamic moment induced by angle of

= ; It is called static stability while '

α

/ (8)

′ increase as chord and backswept increase

′ , which was gained by the range method.

. It is static instability

*l* 0 α< , the

α

′ at the

Table 4. Orthogonal experimental table

*l* α

'

become bigger; It is neutral stability while '

relationship with the location of the wings. The *l*

away from behind the center of the body.

and 0.05 adopted by the range method.

separately 0.051, 0.037, 0.095 and 0.031 for the *l*

significance level 0.10 and 0.05 adopted by the range method.

Here, *l* is the vehicle length, *M*

**3.1.3 Influencing factors analysis** 

, the equations are[20~21]:

**3.1.2 Analysis indexes** 

hydrodynamic lever '

attackα , *L*α

while '

state.

*l* 0 α

Hydrodynamic Characteristics of the Main Parts of a Hybrid-Driven Underwater Glider PETREL 47

0 2 4 6 8 10 12 14 16 18 20 angle of attack α(°)

> model 1 model 2 model 3 model 4

2 4 6 8 10 12 14 16 18 20 angle of attack α(°)

′ and angle of attack

model 1 model 2 model 3 model 4

Fig. 8. The pressure distribution chart of model 3

1.33×10<sup>2</sup> 7.82×10<sup>1</sup> 2.35×10 -1.75×101 -5.85×101 -9.96×101 1 41×10<sup>2</sup>

Fig. 9. The relationship between *L*/*D* and angle of attack


α

Static Stability Coefficient

Fig. 10. The relationship between *l*

 *l*

*α'*

Lift-to-Drag Ratio L/D

Fig. 7. *l* α′ Tendency chart

It is well known that the chord and aspect ratio of the wings should be increased, and the backswept decreased for the higher glide efficiency when PETREL is operated in the gilde mode. Simutaneously, the backswept of the wings should be increased and the wings should be moved backward father behind the center of the vehicle for the higher stability. It indicates that the effects from the increment of the backswept of the wings are inversed in increasing the glide efficiency and the stability. The backswept of the wings should be determined in terms of other capability indexes of the underwater vehicle.
