Roof challenge

Aim:

• To create a roof of the car with Bow roofs,Centre roof rail,Front & Rear roof rail and calculating the section modulus of it and to create reinforcements,check for Draft analysis. Do a curvature study on the roof and perform calculations to determine the position of the Bow-roof.

Introduction:

• What is roof in car?

The roof of a car or other vehicle is the top part of it, which protects passengers or goods from the weather,dust and avoiding the open condition of the car.

• Types of roofs in car?

Convertible roofs.

Hardtops.

Sunroofs.

T-tops.

Targa tops

Vinyl roofs.

• What are the Reinforcement required in designing a Roof ?

The above fig shows a roof of the car and basically to design a roof it needs reinforcement i.e. to strenghten the part,So for a SUV model,long vehicle passenger,sedan,etc requires as follows

1. Front Roof Rail

2. Bow Roof rail

3. Centre Roof rail

4. Rear Roof rail

• Why do we need Roof rails in car?

1. Mostly all car ensure safety for the passengers,so while taking a roof part it saves passenger from the direct sunlight,protects them from the dust,mud and other impurites occur in driving.

2. Not all the time we can say that the car can be driven without any crash or accidents,so lets have an example a car is traveling in the highway with the speed of 120kmph and suddenly an obstacle i.e. a person crosses the road,So due to this a driverturns the vehicle away from the person which lead to rollover the car and cause the car upside down,So there if a roof is strong enough the person will survive or he may die.

3. So for these ffactors we need to ensure that the roof is strong enough to withstand the load.

NOTE:

1. For small commercial cars like Maruti swift,VOlswagen polo,Hyundai i20,etc requires only front roof rail ,centre roof rail and rear roof rail.
2. For long vehcile like suvs,Scorpio,Kia carnival,Fortuner,etc requires additional bow roofs.
3. The roof should have certian length in front as well as rear for the vision of the person that should not block the view and to sustain loads and impact on the roof.The below fig shows an example.

Procedure:

Given input as class A suface and for references the cross section of the bow roofs,Real roof,Front roof rail are given.From these input we need to create a reinforcement and adding the thickness to the surface to convert as an solid model.

Front Roof Rail:

• Extract the surface from the input and offset the surface to respective depth and then trim the sheet with the help of an boundry line i.e. offseted from the front roof edge line and join the gap using studio surface option and then sew it add relative face blends at the corners.
• Add additional reinforcement like emboss by creating a sketch and project it to the surface and then emboos it at certain depth.

Bow Roof Rail:

• It is same as that of creating a front roof rail but here the depth clearance should be 5mm gap and attach the roof corners by offseting it fromt he main surface to a value of 1.7mm and remove the excess part by triming option.
• The thickess of the Bow roof rail is 1mm
• In this model there are 2 Bow roof rails are added for additional strength.

Centre Roof Rail:

• For centre roof rail is taken as major area in roof because the load will act on the centre of the roof so to withstand the load the centre roof rail is deisgned with additional reinforcement and the load will act in roll over condition of car.
• The same procedure of front roof rail is used by offsetting the surface and triming the boundries and join them by using studio surface option.

Rear Roof Rail:

• Rear roof rail as different parameters followed it as backdoor pivoting area were the backdoor hinge action is taken account in the Rear roof rail and creating the rear roof rail is same as that of front roof rail.

Bow Roof Calaculation:

1. Heat Distortion Calculation:

W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [ 1.10x10^(-3) x l] - 2.68

Judgement Condition : OK< 2.7> 3.1

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]

Procedure for Heat Distortion calculation:

• First draw a line at center of the object and create a line b/w each roof rail i.e. Draw a line @ centre of front roof rail to bow roof rail-01 and continue these step for other roof rails.
• The below fig shows an caluclation procedure from the model and draw the line 100mm each from the centre of the line.
• For calculating I bow roof span= measure the distance b/w the two roof rails(Front to bow-01,bow-01 to centre, etc.)
• Then project the points to the roof outer panel and join the points with arc so that we get the value of RX and RY

• After calculating the heat distortion that all the roof rails are in okay condition that it can withstand the heat distotion on the roof.

2. Snow Load calculation:

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)

Judgement 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 reference point of the front and the rear.

Lx = Distance between the Left and Right end of the roof on the Roof BOW [mm]

Width of the roof panel 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

• For calculating the snow load it is same as that of heat distortion calculation,but here we nedd to calculate the 2 lengths b/w the roof rails and need to calculate the section modulus of the roof rails.
• Create the points and project the points in outer panel and join the points by arc and measure it for Rx and Ry values.

• As the calculation shows that the Bow roof -01 and 02 are not satisfying the laod criteria so the modification should be done o these areas by Increasing the area and the green color reprsents the mid roof rail is satisfying the load criteria.

Section Modulus calculation:

S=I/Y

Draft analysis:

Front Roof rail

Bow roof rail-01 and center Roof rail

Bow roof rail-02 and Rear roof rail

Views:

Conclusion:

• Learned about the roof rail modelling and necessary of rails in roof and learned the load calculation of heat distortion and the snow load for designing the roof and done the section modulus of the roof rails to ensure that the roof rails are meeting the conditions.
• In snow load criteria improvement is required.
• The draft analysis is okay for the roof conditions.