aerodynamic analysis of drag reduction devices on the underbody for saab

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Page 1: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 1/88

 

 

 

 

 

 

 

 

 

 

Page 2: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 2/88

Page 3: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 3/88

 

 

 

 

 

 

 

 

 

 

Page 4: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 4/88

 

 

 

   

 

 

 

 

 

 

 

 

 

 

 

Page 5: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 5/88

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

       

     

 

 

 

 

 

 

 

 

 

 

 

Page 6: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 6/88

 

Page 7: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 7/88

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 8: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 8/88

 

 

 

 

 

 

 

         

 

     

     

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 9: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 9/88

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

     

     

     

     

     

 

 

  y+  

   

 

C d      

 

C l      

 

C  p          

  C  p             

     

  V         

  V         

  V         

C m    

  C d      

  C l      

  C  p             

     

  V         

  V         

  V         

C m    

 

Page 10: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 10/88

 

         

         

 

       

   

  V         

 

             

 

 

τ ω  

 

     

 

 

 

     

 

     

     

   

  C  p           

  C  p          

  C  p        

 

     

       

 

10◦  

 

 

 

Af   

 

 

 

     

     

     

     

 

         

 

 

 

Page 11: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 11/88

 

     

   

   

 

     

     

 

 

     

 

 

 

 

Page 12: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 12/88

 

Af   

m2

C d   

C l   

C m   

C  p   

c p    [J/kg · K ]

ρ  

kg/m3

F A    [N ]

F D    [N ]

F G    [N ]

F L    [N ]

F R    [N ]

g  

m/s2

k

   [W/K  · m]

 p    [P a]

T     [K ]

U     [m/s]

V     [m/s]

µ    [kg/m · s]

Φ   

y+   

 

   

   

   

   

   

 

Page 13: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 13/88

 

 

 

 

 

 

 

 

 

 

 

     

 

 

 

 

 

 

 

 

 

 

 

 

 

 

         

 

 

 

 

 

   

 

Page 14: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 14/88

 

 

   

   

   

   

   

 

 

 

         

 

 

 

   

     

 

 

         

 

 

   

   

   

   

 

Page 15: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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Page 16: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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Page 17: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 17/88

 

 

   

 

 

 

         

   

   

 

 

 

Ma  = 0.3  ≈ 100 [m/s] 

   

Continuity equation :  ∂u

∂x +

 ∂ v

∂y +

 ∂ w

∂z  = 0  

      2nd

   

 

ρgx −  ∂p∂x  +  µ

∂ 2u∂x2  +   ∂ 2u

∂y2  +   ∂ 2u∂z2

 =  ρ du

dt

ρgy −  ∂p∂y  +  µ ∂ 2v

∂x2  +   ∂ 2v∂y2  +   ∂ 2v

∂z2 =  ρ dvdt

ρgz −  ∂p∂z  + µ

∂ 2w∂x2   +   ∂ 2w

∂y2   +   ∂ 2w∂z2

 =  ρ dw

dt

 

      1st  

ρc pdT 

dt  = k∇2T  + Φ  

ρ =  densityt =  time

 p =  pressureµ =  static viscosity

g =  gravity constant

c p  =  specific heat capacityT   = temperaturek =  coefficient of thermal conductivity

Φ = viscous dissipation f unction

 

 

     

   

 

Page 18: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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F X  = F A + F R + F G + F D  =  ma + f R mg cosα + mg sinα + 12 ρC DAf U 2  

 

 

     

 

 

 

   

 

Page 19: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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0 20 40 60 80 100 120 140 1600

100

200

300

400

500

600

700

800

Speed [km/h]

   R  e  s   i  s   t  a  n  c  e   [   N   ]

 Aerodynamic drag vs. Rolling resistance

 Aerodynamic dragRolling resistance

 

  (F D)          

 

 

       

 

 

 

 

     

 

   

 p1 + ρV  21

2  = p2 +

 ρV  222

 

 p =  static pressure

ρV  2

2  = dynamic pressure

 

 

 

 

 

 

   

 

Page 20: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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C d =  F 

D1

2ρU 2A

 

 

ρ =  air density

  U  = f reestream velocity

  F D  =  drag force  

  A =  frontal area  

 

 

 

  (F L)  

 

C l =  F L1

2ρU 2A

 

 

      C  p  

 C  p

  C  p  

  C  p    C  p  

 

C  p  = p − p∞1

2ρV  2

  =  p − p∞

dynamic pressure  

  p∞    p

 

 

 

 

 

 

 

 

     

Re = ρU l

µ  

 

 

   

 

Page 21: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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dpdx

 < 0  

 

 

Continuity  :  ∂u

∂x +

 ∂ v

∂y  = 0  

Momentum along wall :  ∂u

∂x +  v

∂u

∂y  ≈ U 

 dU 

dx  +

 1

ρ

∂τ 

∂y  

 

  u   =   v   = 0  

∂τ 

∂y

wall

=  µ∂ 2u

∂y2

wall

= −ρU  dU 

dx  =

  dp

dx  

 

 

 

xs  

 

τ w   = 0  

 

 

 

   

 

 

   

 

Page 22: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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 φ  

 

 

30◦  

 

 

 

 

 

    γ,

 

 

     

 

 

   

γ,  

     

   

 

Page 24: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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h2

h1

 

  θ

 

 

 

 

 

     

     

 

 

 

   

 

Page 26: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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C diffuserD   = tanθ

−C diffuser

L

 

 

 

C  pd

C  pd = p2 − p1

1

2ρU 2

1

 

 

 

 

 

 

 

 

 

 

 

           

 

 

   

 

Page 27: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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ρgx −  dpdx +  µ d2u

dx2  +   d2udy2  +   d2u

dz2  =  ρ dudt

ρgy −  dpdy  +  µ

d2vdx2  +   d2v

dy2  +   d2vdz2

 =  ρ dv

dt

ρgz −  dpdz  + µ

d2wdx2   +   d2w

dy2   +   d2wdz2

 =  ρ dw

dt

 

   

∂ρ

∂t  +

 ∂ (ρu)

∂x  +

 ∂ (ρv)

∂y  +

 ∂ (ρw)

∂z  = 0  

∂u

∂x

 + ∂ v

∂y

 + ∂ w

∂z

  = 0  

u, v, w & p

 

 

   

   

u =  1

T ˆ 

0

u dt  

 p = ¯ p + p

u = u + u

v = v + v

w = w + w

 

   

 

Page 28: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

http://slidepdf.com/reader/full/aerodynamic-analysis-of-drag-reduction-devices-on-the-underbody-for-saab 28/88

 

       

∂ u

∂x +

 ∂ v

∂y +

 ∂  w

∂z  = 0  

ρgx − ∂  p

∂x +

  ∂ 

∂x

µ

∂ u

∂x − ρu2

+

  ∂ 

∂y

µ

∂ u

∂y − ρuv

+

  ∂ 

∂z

µ

∂ u

∂z − ρuw

 =  ρ

du

dt  

 ρuv      

     

 

 

 

 

 

 

     

 

k  −    

  k  −  

 

 

  k −      

µt  

k      k  

   

   

k =u2 + v2 + w2

1/2  

 

k −  

 

k−     

    k −    

    k−  

 

µt =  Cµρk2

 

ρuv   k −  

   

 

Page 29: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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− ρu

iu

j  = µt

∂ui∂xj

+  ∂ uj∂xi

− 23

ρk + µt ∂ui

∂xi

δ ij  

 

 

 

 

 

 

 

 

         

     

y+

 

y+ = yu∗

ν   

u∗ = 0.05U   

 

u∗

  ν   

  y  

 

  y+ = 1  

 

y+

       

 

 

   

 

Page 30: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

8/12/2019 Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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Page 31: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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y+  

 

 

 

   

 

Page 32: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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  1    

 

 

 

   

 

Page 35: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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        Af   

 

 

Af  

 

m2  

m  

m  

   

 

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 S 1,√ 

 

  S 2,√ 

  S 3,√ 

  S 4,√ 

  S 5,√ 

  S 6,√ 

 

  S 7,√ 

 

  S 8,√ 

 

  S 9,√ 

 

  S 10,√ 

 

  S 11,√ 

 

  S 12,√ 

 

  S 13,√ 

 

  S 14,√ 

 

 

 W 1,√ 

 

  W 2,√ 

  W 3,√ 

  W 4,√ 

  W 5√ 

  W 6,√ 

  W 7,√ 

  W 8,√ 

  W 9,√ 

  W 10,√ 

  W 11,√ 

  W 12,√ 

 

  W 13,√ 

 

  W 14,√ 

 

  W 15,√ 

 

  W 16,√ 

 

  W 17,√ 

 

 

     

 

 

 

         

 

 

 

k − ε  

   

 

Page 41: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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C d      

  C l  

   

   

 

Page 42: Aerodynamic Analysis of Drag Reduction Devices on the Underbody for SAAB

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      C  p  

 

  C  p  

 

 

         

 

 

 

   

  C d  

 

 

 

 

y+  

y+  

 

   

 

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y+

 

 

y+  

 

 

y+  

 

y+  

 

 

   

 

0 5 10 15 20 25 30 35 400

0.05

0.1

0.15

0.2

0.25

Velocitymagnitude [m/s]

   Z  −  c  o  o  r   d   i  n  a   t  e   [  m   ]

Boundary Layer on diffuser 

5 degreesdiffuser xy−cord: (5.0;0)

 

0 5 10 15 20 25 30 35 401.455

1.46

1.465

1.47

1.475

1.48

Velocity magnitude [m/s]

   Z  −  c  o  o  r   d   i  n  a   t  e   [  m   ]

Boundary Layer on roof 

 

 

 

 

 

 

        

 

   

 

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C d    

 

C l  

C l    

 

 C  p      

        

 

 

   

 

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C  p        

 

    

 

    C  p  

   

C  p  

   

C  p  

 

C  p           

  C  p  

     

   

 

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V       

     

     

V       

     

 

 

       

 

   

           

V       

 

 

   

 

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C m  

 

C m  

 

C m    

 

     

C d      

         

  C d  

     

       

   

 

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C d    

 

C l  

           

C d  

C l    

 

 

C  p  

           

 

           

   

 

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V       

     

 

     

 

   

 

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V       

 

   

V         

 

 

     

 

 

 

 

   

 

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C m  

 

 

C d  

 

 

   

 

   

   

   

   

 

 

 

 

 

   

 

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  8◦       5◦    

 

     

     

 

 

 

 

 

 

   

 

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  ± 

  ±  

 

 

 

         

 

 

 

 

 

 

 

 

   

 

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V       

 

     

 

 

 

 

 

     

 

   

 

   

   

   

 

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τ ω

 

 

 

   

 

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C  p    8◦

 

 

 

 

 

 

 

 

 

 

   

 

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C  p  

 

 

 

   

 

 

 

 

 

 

 

 

 

 

   

 

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C d    

   

[%]  

 

C d    

   

[%]  

   

 

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  C d

   

 

   

 

   

     

 

 

 

 

 

   

       

    

   

   

 

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  C d  

 

 

 

 

 

k − ω      

 

         

 

 

 

 

 

 

 

 

 

 

 

 

 

   

 

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C  p         

C  p        

   

 

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C  p      

 

 

   

   

 

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 −  

 

 

 −  

 −    −    −    −  

  −    −   −  

 

 −  

 −    −    −    −    −  

 

 

−  

  −  

  −  

  −  

 

 −    −    −    −  

  −  

 −    −    −    −  

  −  

 

 

 −    −    −  

 −    −    −  

 −    −    −    −  

 

 

−  

  −  

  −  

  −  

 −    −    −  

 

 −    −    −    −  

 −    −    −  

 

 

 

 −    −    −    −    −    −  

  −  

 −    −    −    −    −    −  

  −  

 −    −    −    −    −  

 

−  

  −  

   

 

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  −  

 

−  

  −  

  −  

  −  

  −  

 −    −  

  −  

 −    −    −    −    −    −  

 −    −  

  −  

 

 −    −    −    −    −    −  

  −  

 −    −    −    −    −    −  

  −  

 −    −    −    −    −  

 −    −  

  −  

 −    −    −    −    −  

 −    −  

  −  

 −    −    −    −    −    −  

 −    −  

  −  

 

 −    −    −    −  

 −    −    −  

 −    −    −  

 −    −    −  

 −    −    −  

 −    −    −    −    −    −    −  

 −    −    −    −    −    −  

 −    −    −    −    −    −    −  

 −    −    −    −    −    −  

  −  

 −    −    −   −    −    −    −    −    −  

 −    −  

  −   −   −    −  

 

 −    −    −    −    −     −  

 −    −    −    −    −     −  

 −    −    −    −    −     −  

 −    −    −    −    −     −  

 −    −    −    −    −     −  

 −    −    −    −    −     −  

   

 

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 −    −    −    −    −     −  

 

−  

  −  

  − 

 −  

  −  

  −  

 −    −    −    −    −     −  

 −    −    −    −    −     −  

 −    −    −    −    −     −  

 −    −    −    −    −     −  

 

 −  

 −  

 −  

 

 −  

 −  

 −    −  

 

 −    −     −     −     

 −  

 −    −     −     −     

 −  

 −    −     −     −     

 −  

 −  

 −    −    −  

  −   −    −     −    −   −    −     −    −    −    −     −    −   −    −     − 

  −   −    −     −    −   −    −     −    −    −    −     −    −   −    −     − 

  −   −    −     −    −   −    −     −    −    −    −     −    −   −    −     −  

 −    −    −  

 

 −   −    −  

  −  

  −  

 

 −    −  

 −    −  

  −  

 

 −  

 

 

   

 

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  −  

  −  

  −  

 

 

 

 −    −  

 −    −  

 

 −    −  

 

  −    −    −  

 

 −    −  

  −  

  −  

  −  

  −  

 −    −  

 −    −  

  −  

 −  

 −