Fog billboard + calculations

Last crawled date: 1 year, 10 months ago

During developing this project the main aim was to provide reliable and effective work of Fog Billboard (FB) at any weather conditions and without interference of specialists as for its adjusting and repair. F.B. will be maximally effective and reliable at minimal cost and minimal time for its construction. Maximally effective use is 1 m3 of space.
I hope I’ve managed to do it.
And I hope you will appreciate it.

Fog Billboard is a hybrid structure of net which includes all advantages of cylindrical and cubic methods of stretching net. FB consists of a small collector of fog, overall dimensions 2x2x2m. There is metal net (21.3 m2) outside the collector. Thanks to concave system of a stretch it most effectively directs a stream of damp air on net, at any speed of wind and its direction, it doesn’t need rotary mechanism. The frame with ease can stand direct wind 70 mph, with the maximum tension 6MN/sq.m. 0.7 mm shifting is possible. The system can be adjusted within 1.5m - 3m over the level of land. FB weighs 177 kg. The structure can be assembled with the only key S22.

At first I decided to see how fog behaves passing through usual net. Using much smaller copy of FB I simulated wind stream at a flat net. If air stream is direct the results of the experiment are excellent, but if the wind is angular the stream passed by. I also compared the areas of nets at dimensions 1x1x1m. If the area is flat, it has 1m2. This structure of net is very simple, but not very effective.

The next step was the space structures.
At cubic structure area is 4m2. At direct steam of wind, fog stream crossed through construction and contacted with net several times. But if the wind stream in cube center is angular there is stagnation area of air. It doesn’t give chance to normal passing of new damp air.
Cylindrical structure has smaller area of net (3.14 m2) and bigger streamlining. Fog doesn’t pass through the net, and flows round it rolling from edges. Therefore fog contacts with net once.

Later I decided to unite these 2 structures. The idea “Fog billboard” was born in such a way. At direct stream of air the main stream is directed by the structure to its corners. Part of fog settles there and the part of fog goes further to angular area, still the part of fog passed central and goes to rear area. At angular stream of air, which will be mainly present at real weather conditions, 90% of fog goes to net and several times contacts with the net (at “entrance” and “exit”) in such a way the best intake of moisture is reached. Inside the net the maximum circulation of damp air gives the best supply of new moisture. The area of this net is 4.4 m2.

Frame
Having chosen the structure of net, I came over to modeling of frame. As the basic bearing component I took the square aluminum shape of 40x4 mm from an alloy 5052-H38 or similar. I tested some cross-sections and stopped at the square variant (more at render). Characteristics of this material are similar to steel but it is nearly 3 times lighter. Calculation of frame strength was made considering coefficient of effective cross section of net k=0.25 and the weight of all additional “equipment” (see renders). The frame is fixed by screwing it with 4 screws into the land and fastening of the design base with nuts. The top angular points are fixed with cables. Different angles of wind give different tension, the maximum value 6 MN/m2 and 0.7 mm shifting. It don’t exceed material fluidity limit and has huge of safety. It is possible to tell for sure it will stand 11balls wind of the various directions and rushes.

Height adjustment
Adjustment of frame height is carried out with a jack using partly remade Hi-Lift system which is used in the jacks of the same name product from “High-Lift Jack Company”. The person swinging a handle 0.5 m length can raise the frame to the height 1.5m - 3m with 50 mm step. In contrast to the jack the remade system has mobile element – lath. The construction is fixed with removable bolt D24.

Net
The weight of net is about 30 kg. The net has flexible polymeric fringing with the sealed metal holes for fixing. At the top it is fixed with tension springs. They are responsible for a stretch of a net and partially decrease wind gust. At bottom it is fastened with corresponding hooks. The net goes beyond the lower fringing in order that the end of net was closer as possible to the bottom of a tube, it minimizes losses of water which flows down on the net to a collector.

Collecting of water
The system of water drainage consists of polymeric tubes. Water goes from four angular points with system 4 in 1. Then the drain hose can be brought to a tank-collector or directly to the house where water is necessary provided that the house is lower than the collector of fog. The hoses are fixed with clamps. I refused to use cap nuts – if such nut is damaged to replace it will be problematic, especially in those areas where there is no fresh water. To replace clamp is much simpler and cheaper. 4 pre filters are used in system They prevent flowing of foliage and dirt into hoses.

It seems to me that’s all!

Good luck to all!