Roof challenge
Roof Design
Introduction
An automobile roof or car top is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements. Because the earliest automobiles were designed in an era of horse-drawn carriages, early automobile roofs used similar materials and designs.
Objective:
- The main objective of this project is to understand the design process to design the roof & to understand calculation behind it with flanges & reinforcements like ditch area,front roof rails,bow roofs,central roof rail & rear roof rail
- For curvature study on roof perform the calculations for heat distortion & snow load criteria for determining that bow roofs are at correct positions.
Types of Reinforcements that the car has are:
- Front Roof Rail
- Bow Roofs
- Central Roof Rail
- Rear Roof Rail
Front roof Rail master section reference image
Rear roof rail master section reference image
Front Roof Rail
Bow Roof 1
Central Roof Rail
Bow roof 2
Rear Roof Rail
Caculations
Bow–roof prediction Formula
W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68
Judgment Condition
OK< 2.7
Where
L = Roof Length in X-Direction[mm](Roof dimension in 0-Y)
R = Roof curvature
R = 2(Rx*Ry)/(Rx+Ry)
Rx = X curvature
Ry = Y curvature
t = Roof plate thickness [mm]
l = Bow Roof Span [mm]
|
Bows Position |
Rx |
Ry |
R |
I |
L |
t |
(R^2)/t
|
W |
OK/NG |
|
FRR & BR1 |
2612.1 |
3258.9 |
2899.8 |
258.3 |
2058.5 |
0.65 |
12937479.6 |
1.404 |
OK |
|
BR1 & CRR |
4590.2 |
7447.3 |
5679.6 |
305.4 |
2058.5 |
0.65 |
49628934.3 |
2.135 |
OK |
|
CRR & BR2 |
3741.2 |
11737.3 |
5673.9 |
307.7 |
2058.5 |
0.65 |
49527924.62 |
2.135 |
OK |
|
BR2 & RRR |
3098 |
15361 |
5156.2 |
247.8 |
2058.5 |
0.65 |
40902877.12 |
1.910 |
OK |
Snow Load Criteria
Snow load Prediction formula:
Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]
Note: The Qr value given over here is correct. There was a typo error in the formula given in the video.
Where
α = My x Lx2 x 10-12 , My = Y(Ly-Y)
Judgment condition
Qr ≥ 3.1
250 ≤ s ≤ 380
t = Roof plate thickness [mm]
Ly = Distance between the front and rear roof Rails on the Vehicle along with 0Y[mm]
Length of Roof panel with the center point between Roof rail Front /Rear as the front and rear reference point.
Lx = Distance between the Left and Right end of the roof on the Roof BOW [mm]
The width of the roof panel is exposed on the surface.
Y = Distance front Front Roof Rail to Roof BOW[mm]
s = Distance for which Roof BOW bears divided load [mm]
s = L1/2 + L2/2
Iy = Geometrical moment of inertia of Roof BOW (Y cross-section )[mm4]
Rx = Lateral direction curvature radius of roof panel Y cross-section on Roof BOW [mm]
Roof panel curvature Radius of the Length Lx in Front view
Ry = Longitudinal Direction curvature radius of the Roof panel X cross-section on Roof BOW [mm]
Roof panel X curvature radius of length s in Side view
|
Bow Position |
Iy |
α |
Lx |
Ly |
Y |
My |
S |
Rx |
Ry |
t |
Qr |
Det |
|
FRR & BR1 |
19145.7 |
0.88 |
1143.6 |
1901.7 |
476.7 |
679411.5 |
483.9 |
2817.6 |
1402.3 |
0.65 |
4.26 |
OK |
|
BR1 & CRR |
20621.2 |
0.81 |
1093.8 |
1901.7 |
471.5 |
674463.3 |
494.8 |
3151.2 |
4405 |
0.65 |
1.52 |
OK |
|
CRR & BR2 |
23093.4 |
0.77 |
1067.6 |
1901.7 |
473.0 |
675879.8 |
460.5 |
3636.8 |
8496.9 |
0.65 |
7.47 |
OK |
Views of the Roof:
Isometric
Front
Top
Bottom
Left
Conclusion: