Roof challenge
DESIGN OF ROOF
Objective
To design the car roof and its bows with reinforcements and ditch area by using siemens NX cad software.
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. It helps designing the aerodynamics of the car. Roof has bows and reinforcements inorder to withstand the load while driving or at stance. There are two considerations for desiging the roof. They are Heat distortion criteria and snowed condition.
Roof Design
Front Roof Rail
Bow I
Reinforced center roof rail
Bow II
Rear Roof Rail
Roof
All Bows
Roof Assembly
Moment of Inertia
Bow I
Reinforced Centre
Bow II
Calculations
1.Heat Distortion Criteria
At particular temperature the roof tends to elongate or bend at specified load. By providing the bows and reinforcements this can be controlled. Bow prediction formula as follows
By using this formula bow position is idenfied whether it satisfies the condition or not.
| BOW | RX | RY | R | L | l | t | R^2/t | W | OK/NG |
| FR & I | 5733.95 | 2405.07 | 3388.75 | 2030.35 | 371.26 | 0.75 | 15311500 | 1.524154 | ok |
| I & CTR | 4963.22 | 6233.17 | 5526.17 | 2030.35 | 460.84 | 0.75 | 40718117 | 2.092715 | ok |
| CTR & II | 3915.62 | 10687.21 | 5731.36 | 2030.35 | 460.91 | 0.75 | 43798015 | 2.14977 | ok |
| II & RR | 3198.96 | 15140.71 | 5281.94 | 2030.35 | 353.33 | 0.75 | 37198532 | 1.909341 | ok |
2. Snowed Criteria
When the static load applied on roof it tends to bend inside. If the load is removed then the roof should come back to its original state. This can be achived by providing bow because it provides load carrying capacity to the roof.
| BOWs | t | Ly | Lx | ly | Y | My | α | S | Rx | Ry | ly * t^2 | [(Rx + Ry)/2]^2 | Qr | OK/NG |
| FR & I | 0.75 | 2030.35 | 1107.58 | 3645 | 460.89 | 723348.4 | 0.887356 | 499.395 | 3426.72 | 2095.38 | 2050.313 | 7623397.103 | 60.69173882 | ok |
| I & CTR | 0.75 | 2030.35 | 1065.76 | 17747 | 537.9 | 802788.9 | 0.911843 | 537.95 | 2407.82 | 6135.94 | 9982.688 | 18248958.73 | 111.5185998 | ok |
| CTR & II | 0.75 | 2030.35 | 1044.63 | 37749 | 538 | 802884.3 | 0.876149 | 499.59 | 6331.65 | 11383.15 | 21233.81 | 78453534.76 | 61.83349181 | ok |
| III & RR | 0.75 | 2030.35 | 461.19 | 5438.95 | 17141.19 |
Conclusion
Thus the roof is designed and the calculations are made for Heat and snow conditions. And the results obtained are found normal.