Engineering Science and Equations

1 ENG1002 Sem 2 20 2 1 Fire Fighting Drone sections 1 to 3 Sample solution This simply presents the relevant content, engineering science and equations and results. This is NOT intended as an example of a Tech Analysis Report . Not all the detail as presented here w ere expected in the TAP assignment. Design Section 1 Payload and hovering time - Battery t ype , capacity, volume and mass etc 1.1 Battery Section 2 Table A : Battery Type Mass and volume Battery Type Energy Density, E D (kWh/ L ) Battery Capacity, B (Wh) 500 750 1000 1500 LiPo 0.5745 Volume, V B (m 3 ) 0.8 696 x10 - 3 1.3044 x10 - 3 1.7391 x10 - 3 2.60 97 x10 - 3 Volume, V B ( L ) 0.8 696 1.3044 1.7391 2.6097 Mass, m B (kg) 1.3044 1.9565 2.6087 3.9130 1.2 Gross Drone Mass M (kg) = m B + m F + m W where m F is the mass of the frame = 11. 2 kg and m W is the mass of water and retardant carried The density of water (and retardant) W = 1000 (kg/m 3 ) T he volume of water carried varies with the tank siz e V T m W = W * V T so M (kg) = ( 2.6109 x 10 - 3 B ) + m F + ( W * V T ) key combined equation Table B: Gross drone mass Gross Mass of drone with full tank (kg) Drone frame mass m F (kg) Battery Capacity B (Wh) Battery Mass m B (kg) Tank volume V T (L) 0 2.5 5 7.5 Mass of Water in full Tank m W (kg) 0 2.5 5 7.5 11.2 500 1.3044 12.504 15.004 17.504 20.004 11.2 750 1.9565 13.157 15.657 18.157 20.657 11.2 1000 2.6087 13.809 16.309 18.809 21.309 11.2 1500 3.9130 15.113 17.613 20.113 22.613 1.3 Hovering Time Given t H ( minutes) = where B is in battery capacity ( Wh ) , D is useable battery capacity 80%, M is gross drone mass (kg) PWR is power to weight ratio 55 (W/kg) t H ( minutes) = B (Wh) x 0.8 x 60 (min/hr) min/hr deduced from units required M (kg) x 55 (W/kg) 3 Table C: Hovering Times Hovering time t H ( min ) with full tank Battery Capacity B (Wh) Tank volume V T (L) 0 2.5 5 7.5 500 34.90 29.08 24.93 21.81 750 49.75 41.81 36.05 31.69 1000 63.20 53.51 46.40 40.96 1500 86.62 74.33 65.09 57.89 1.4 Hovering Time graph A similar graph could be presented with water volume on the X - axis instead. 1.5 Conclusions Shortest hover time (21.8 min) occurs for the smallest capacity battery when carrying 7.5 L of water and the longest time (86.6 min) occurs for the largest capacity battery with no load. 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00 0 500 1000 1500 2000 Flight Time (Hovering) - min Battery Capacity (kWh) Effect of Battery Capacity and Water Load on Flight Time of Hovering Drone 0 L 2.5 L 5 L 7.5 L 4 Design Section 2 Water Requirements 2.1 Deduce units of Cc Given the equation Amount of water ( Litres ) = Cc times the area of the fire (in square feet) (eqn 1) Let V (L) = Cc * A (ft 2 ) where Cc = 0.08 and is called the coverage coefficient The units of Cc can be found by solving for Cc Cc (?) = V (L) / A (ft 2 ) Hence units of Cc are L/ft 2 2.2 Equation 1 in SI units converti ng square metres to square feet by A (ft 2 ) = A (m 2 ) * 10.76 (ft 2 ) 1 (m 2 ) therefore V (L) = Cc (L/ft 2 ) * A (ft 2 ) = 0.08 (L ) * 10.76 5 (ft 2 ) * A (m 2 ) 1 (ft 2 ) 1 (m 2 ) V (L) = 0.8 6 12 (L ) * A (m 2 ) = 0.86 12 (L/m 2 ) * A (m 2 ) key equation 1 (m 2 ) 2.3 Fire Intensity Given With data taken from Figure 2 and using Table 4 in the Client Brief Table 1 : Fire behaviour and drone firefighting strategies . Fire Danger Flame Height (m) Intensity (kW/m) Significance Low 0 .0 - 0.5 0 - 50 Fire generally self - extinguish Medium 0.5 - 1.5 50 - 500 Drone attack possible High 1.5 - 3.0 500 - 2000 Fire too intense for drone Actually the highest intensity the drone should attempt is 455 kW/m due to the 10 % threshold. 2.4 Amount of Water needed at each site Area to be extinguished A(m 2 ) = * (D/2) 2 and V (L) = 0.8612 (L/m 2 ) * A (m 2 ) Table D: Water Volumes Site Flame height, H (m) Flame base, D (m) Flame length, F L (m) Fire intensity (kW/m) = 3*(10*F L ) 2 Attempt to extinguish? (Yes/No) Why? Target Area , A (m 2 ) Water Volume, V (L) A 0.1 0 0.1 0 0.1118 3.75 No - Fire generally self - ex tinguish 0.0079 0.0068 B 0.94 1.11 1.0916 357.4 9 Yes - Moderate 0.967 7 0.83 33 D 1.15 1.10 1.275 487. 5 No - within the 10% threshold 0.9 503 0.81 84 E 0.83 0.65 0.8914 238.3 6 Yes - Moderate 0.331 8 0.285 8 G 1.13 0.84 1.2055 435.9 9 Yes - Moderate 0.55 42 0.477 3 The green coloured rows indicate fires that the drone is to attempt to extinguish 1.5964 (L) 5 2.5 Total Amount of Water needed to be carried with 2.5 safety factor The total of water for all sites * 2.5 V T OT (L) = 1.5964 (L) * 2.5 = 3.991 L 2.6 Conclusions Sites A and D are to be excluded from the fire fighting. To fight fires at sites B, E and G t he required volume of water (& retardant) is 4 L , S o the drone must carry a tank capable of holding at least 4 L, hence only the 5 L and 7.5 L tanks are suitable . Design Section 3 Drone Flight Time 3 .1 Distances between waypoints Given the equation for the distance between waypoints of Using data from table 5. Table 2 : Waypoints. Assume constant altitude of 20 m. (start) A B C D E F G Grid X - location (m) 145 122 344 650 470 330 130 Grid Y - location (m) 500 66 230 64 980 850 1115 The total distance around the flight path may be calculated as the sum of the distances between the waypoints A - B, B - C, C - D, D - E, E - F, F - G, G - A. Waypoint x - loc (m) y - loc (m) x,y - dist (m) cumul ative _dist ance (m) A 145 500 B 122 66 434.6 434.6 C 344 230 276.0 710.6 D 650 64 348.1 1058.7 E 470 980 933.5 1992.3 F 330 850 191.0 2183.3 G 130 1115 332.0 2515.3 A 145 500 615.2 3130.5 3.2 Range and required aerial surveillance time Total distance d = 3130.5 m Applying wind factor c W = 1.25 Range R = 3913.1 m Traveling at an average speed of v av = 2.5 m/s The required aerial surveillance flight time t R = 3913.1 (m) / 2.5 (m/s) = 1,565 sec = 26.09 min 6 3.3 Comparison of Aerial surveillance flight time and the required aerial surveillance time Aerial surveillanc e flight time t S = 0.75 x t H and utilising calculations from Table C from section 1.3 having already eliminated tanks sizes below 5 L . Table C : Hovering Times (copied from above) Hovering time t H (min) with full tank Battery Capacity B (Wh) Tank volume V T (L) 0 2.5 5 7.5 500 34.90 29.08 24.93 21.81 750 49.75 41.81 36.05 31.69 1000 63.20 53.51 46.40 40.96 1500 86.62 74.33 65.09 57.89 Table E: Aerial surveillance flight time Aerial surveillance flight time t S (min) with full tank Battery Capacity B (Wh) Tank volume V T (L) 5 7.5 500 18.7 16.4 750 27.0 23.8 1000 34.8 30.7 1500 48.8 43.4 3.4 & 3.5 Identify acceptable battery capacity and water tank options & Conclusions Only the Batteries and Tank Volume op t ions shown in green in Table E above are capable of achieving a flight time greater than th e required flight time of 26.09 min. Although combination for B = 750 Wh and a 7.5 L tank would be able to achieve the required Aerial surveillance flight time if carrying le ss than 5 L.