Rough Tech Calcs

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Motor: The motor is responsible for deploying and retracting the flags which will alert swimmers to the presence of rip currents. The total torque the motor needs to produce is the torque required to retract the metal pole as well as the flag attached to it. The calculations below detail the amount of torque required to pull the metal pole and the flag. Torque needed to deploy pole: Two 304 stainless steel rods, 500mm in length will be welded together to form a 1m rod. The dimensions of each rod are 18 mm× 18 mm× 500 mm with a density of 8000 kg / m 3 [1] [2]. Using this the mass of each rod can be calculated. Rodmass = volume×density Rodmass = ( 0.018 × 0.018 × 0.5 ) × 8000 Rodmass = 1.296 kg The mass of the fabric which is attached to the steel rod also needs to be calculated as additional torque is needed to lift it. The material chosen for the flags is polyester due to its high strength and resistivity to tearing. The intended dimensions for the flag are 1 m× 1 m and given fabric weight of 130gsm (grams per square meter) the weight of each flag is: Flagmass = fabric GSM×area Flagmass = 130 × ( 1 × 1 ) Flagmass = 130 g Flagmass = 0.130 kg Since the length of the steel rod is 1m, the distance between the motor tip and the radius of rotation is also 1m. Using this radius length and the masses of the flag and steel pole, the torque required is: T = Fd T = mgd T =( m steel pole + m flag ) gd T =( 1.296 + 0.130 ) ( 9.81 ) ( 0.5 )

T = 6.995 Nm Two 12V geared motors will be used to raise and lower the flags in the case where a rip current is detected [3]. It produces 7 Nm of torque which is enough to raise and lower the flags. [1] Steel tube: https://www.ebay.com.au/itm/384234412773? chn=ps&_ul=AU&mkevt=1&mkcid=28 [2] 304 stainless steel density: https://www.google.com/search? q=304+stainless+steel+density&rlz=1C5CHFA_enAU950AU950&hl=en&biw=1440&bih=764& sxsrf=AB5stBiunqL4_L16ueP2JYu8LUmcE1- wyg:1691388972622&source=lnms&sa=X&ved=0ahUKEwi1zI738smAAxXatlYBHQnIAV4Q0p QJCIMH [3] Motor: https://ca.robotshop.com/products/12v-29rpm-geared-motors-w-7nm-torque-no-load- 33rpm-all-metal-gears Pitot tube: The pitot tubes play a key role in the rip detection module for Ripshark. Bernoulli’s principle states that the sum of the kinetic energy, potential energy and flow energy remains constant along a streamline. It is governed by the equation below as shown in figure 4 below [4]: static pressure + dynamic pressure + hydrostatic pressure = constant ( 1 ) P 1 + 1 2 ρV 1 2 + ρg h 1 = P 2 + 1 2 ρV 2 2 + ρgh 2 ( 2 ) where: P = static pressureat any point ∈ streamline ( Pa ) ρ = density of fluid acrossthe streamline ( kg / m 3 ) V = velocityof fluid at a given point ∈ the streamline ( m / s ) g = gravitational constant of Earth ( m / s 2 ) h = initialheight of streamlineabove ground level ( m ) The equation above can be re-arranged to determine the velocity of the fluid entering the pitot tube. The sum of the static pressure and the dynamic pressure is called the static pressure.

P stagnation = P static + P dynamic P stagnation = P 1 + 1 2 ρV 1 2 ( 3 ) Substituting equation (3) into equation (2) provides the formula for the fluid velocity at the opening of the pitot tube whilst assuming that the streamline occurs at constant height by which potential energy is equal to zero. P static + P dynamic + ρgh = P static + P dynamic + ρgh P stagnation + ρgh = P static + P dynamic + ρgh P stagnation = P static + P dynamic P stagnation = P 1 + 1 2 ρV 1 2 V 1 = √ 2 ( P stagnation − P 1 ) ρ ( 4 ) F igure 1. Pitot tube analysis [5] Equation 4 above states that the velocity of the waves can be measure effectively by the pitot tubes. Wave velocity is difficult to measure directly, however, the stagnation pressure is simple to measure as it is the pressure of the waves which hit the opening of the pitot tube. The static pressure is also calculated by the side tubes of the pitot tube. [4] Bernoulli’s equation: https://phys.libretexts.org/Bookshelves/University_Physics/Book %3A_University_Physics_(OpenStax)/Book%3A_University_Physics_I_-

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_Mechanics_Sound_Oscillations_and_Waves_(OpenStax)/14%3A_Fluid_Mechanics/14.08% 3A_Bernoullis_Equation#:~:text=p1%2B12%CF%81,follow%20it%20along%20its%20path [5] Figure 1 source: https://makersportal.com/blog/2019/02/06/arduino-pitot-tube-wind- speed-theory-and-experiment [] Pitot tube to buy: https://www.kogan.com/au/buy/drx-f1912930-px4-differential-airspeed-pitot-tube-pitot- tube-airspeedometer-sensor-and-tube-11357191733284/? utm_source=google&utm_medium=product_listing_ads&gclid=Cj0KCQjwrMKmBhCJARIsAH uEAPRYzvJvczMidoAZn5r9vCLgQzr70cB8vCH7e9oeFr-Nqyfd_y9Y5fAaAv2iEALw_wcB Arduino board and MPXV7002DP pressure sensor: The MPXV7002DP pressure sensor converts the pressure measurements made by the pitot tube and converts them into a velocity measurement. The pitot tube had two output ports, one carried the stagnation pressure whilst the other tube carried the static pressure. The pressure sensor contains two input ports receive the stagnation and static pressures. It then computes the velocity of the fluid entering the pitot tubes and transmits it to the Arduino Uno board. The pressure sensor requires 2.5V and 2.5A of current and a total power of: P = VI P = 2.5 ( 2.5 ) P = 6.25 W

Since four pitot tubes are going to be used, four pressure sensors also must be used to calculate wave velocity across all directions. The Arduino Uno board will receive input velocity values from all four pressure sensors simultaneously and will run them through a code. This velocity values from all four pressure sensors are fed into the code and compared against the threshold wave velocity. If any velocity reading exceeds the threshold velocity measurement, the code will then find which pressure sensor the reading came from and raise the flag in that direction. This is shown by the pseudocode of the program below. Figure 2. Arduino Code analysing velocity readings [] [6] Pressure sensor: https://www.ebay.com.au/itm/403821743753? chn=ps&_ul=AU&_trkparms=ispr%3D1&amdata=enc %3A1LFGj7Xo5QamVza1lwpclmg42&norover=1&mkevt=1&mkrid=705-139619-5960- 0&mkcid=2&mkscid=101&itemid=403821743753&targetid=1598469863278&device=c&mkt ype=pla&googleloc=9071742&poi=&campaignid=19657035767&mkgroupid=143201283022 &rlsatarget=pla- 1598469863278&abcId=9305369&merchantid=494542554&gclid=Cj0KCQjwk96lBhDHARIsA EKO4xboj97_fhAoTfE8xrJ1x1kh446RrfGCQ5leJffYefy_c1YgsYFzIFkaAnguEALw_wcB

[7] Figure 2 source: https://makersportal.com/blog/2019/02/06/arduino-pitot-tube-wind-speed-theory-and- experiment [] Arduino to buy: https://core-electronics.com.au/arduino-uno-r3.html? gclid=Cj0KCQjwrMKmBhCJARIsAHuEAPQhZGPo9grl8ItEiNGGzacq2tAUptzCQv5XKM0dzPzD9h IUuyUNjNkaAq0SEALw_wcB Charge controller and inverter: A charge controller limits the rate at which current is added to the battery or removed from it [8]. It is an electrical component which has to be added to the electrical system on the buoy to ensure that a build-up of charge or voltage doesn’t occur which could trigger a fire. When the batteries storage capacity is full, the charge controller turns off the flow of current in the electrical circuit. This prevents a build-up of charge ensuring there is no overheating in the wires. The selected charge controller limits the intake/out-take of charge to 30A and voltage to 24V ensuring a safe and controlled amount of energy transfer across the system. An inverter is another component which will be required as it converts DC current generated by the solar panels to AC current to be used in the system and stored in the battery [10]. AC current flows in both directions in an electric circuit and has the voltage constantly flip from positive to negative producing a clean sine wave. A sinusoidal wave signal is preferred as it can be transferred across wires limited energy dissipation and can also be transformed into higher or lower voltages easily [11]. The inverter selected for Ripshark operates at 240V and 600W/1200W and since each solar panel produce 1050W of power the inverter will convert all power generated into AC current (MOVE THIS SENETENCE TO SOLAR PANEL SECTION). [8] How a charge controller works/ why its needed: https://www.morningstarcorp.com/faq/how-does-solar-charge-controller-work/#:~:text=The %20charge%20controller%20regulates%20the,of%20charge%20without%20getting %20overcharged . [9] Charge controller: https://www.amazon.com.au/Upgraded-Controller-Intelligent-Multi-Function- Adjustable/dp/B0BN52PWJT/ref=asc_df_B0BN52PWJT/?tag=googleshopdsk- 22&linkCode=df0&hvadid=341774438116&hvpos=&hvnetw=g&hvrand=7349935978441973 881&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9071742&hvt argid=pla-1973645854484&psc=1 [10] How does an inverter work: https://www.energy.gov/eere/solar/solar-integration-inverters-and-grid-services- basics#:~:text=An%20inverter%20is%20one%20of,which%20the%20electrical%20grid %20uses . [11] AC vs DC: https://learn.sparkfun.com/tutorials/alternating-current-ac-vs-direct-current-dc/all

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[12] Inverter: https://www.amazon.com.au/GIANTZ-Inverter-12V-240V-Camping- Caravan/dp/B07BLP2664/ref=asc_df_B07BLP2664/?tag=googleshopdsk- 22&linkCode=df0&hvadid=341793271862&hvpos=&hvnetw=g&hvrand=6532070688137792 008&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9071742&hvt argid=pla-675706699381&psc=1 Solar panels: The solar panels are the only source through which electrical energy will be generated on the buoy. EXPLAIN HOW SOLAR PANELS WORK IN SUMMARY. The selected solar panels generate 350W of power each. To reach the required amount of power for the electrical components on the buoy, 3 solar panels will be used to generate a total of 1050W of power. Table 1 below details the energy requirements for each component and the quantity required, table 2 details the energy generated from the solar panels and table 3 outlines the amount of energy remaining after the electrical components receive the energy they need. From observation of table 3, 7.857kWh off energy remains in the battery to be stored. This is a large amount of energy which is not being used, however, it is necessary to take this precaution as there will be days where sufficient sunlight is not present at the beach. The calculations below outline the number of days the buoy can be powered solely of the battery. Battery: On the buoy, the solar panels will generate electrical energy which will be transferred to the battery. Each electrical component will be wired such that they draw energy from the battery instead of using it straight from the solar panels. By doing so the wiring between each electrical component will be much simpler, reducing the risk of wire entanglement which poses the hazard of wires overheating due to energy dissipation. The battery has a capacity voltage capacity of 14.4V at 250A of current which can store 3.6kW of power. [13] Battery: https://itechworld.com.au/products/100ah-12v-lithium-ion-battery-slim- lifepo4-deep-cycle-camping-rv-solar-itech100a? variant=41121209221275¤cy=AUD&utm_medium=product_sync&utm_source=googl e&utm_content=sag_organic&utm_campaign=sag_organic&srsltid=ASuE1wSwzbx0nEZk8yab A6-7T0rAd45kpueNaB4SOWZ2GZxMNhwyG9S6zWY Energy needed per day = power consumed×operatingtime Considering a fully sunny day the operating time will be 14 hours. Energy needed per day = 0.169 ( 14 ) Energy needed per day = 2.366 kWh Energy generated per day = power generated×operating time

Energy generated per day = 0.7 ( 14 ) Energy generated per day = 9.8 kWh Energy remaing after consumption = Energy generated − energyneeded Energy remainingafter consumption = 9.8 − 2.366 Energy remainingafter consumption = 7.434 kWh Since the battery can store 50.4 kWh of energy the buoy can be powered from the battery for: No.of days batteryused without genergy generation = 50.4 7.434 N o.of daysbattery used without genergy generation = 6.7 days Rounding down for safe measure gives 6 days on which the buoy can be powered of a fully stored battery. Table 1. Energy requirements per electrical component Part Volage (V) Current (A) Power (kW) Time (h) Consumption (kWh) Quantity Motor 12 3.5 0.042 6 0.252 2 Pitot tube - - - 14 - 4 Arduino 0.020 14 0.28 1 Charge controller 5 2.5 0.0125 14 0.175 1 Pressure sensor 5.25 0.1 0.00525 14 0.0074 4 Inverter 15 2.1 0.0315 14 0.441 1 Total 0.169 - 1.43 15 Table 2. Energy generated by solar panels Part Voltage (V) Current (A) Power (kW) Time (h) Consumption (kWh) Quantity Solar Panels - - 0.350 14 4.9 2 Total 76 44 0.700 - 9.8 2 Table 3. Energy remaining after electrical component consumption Part Power (W) Consumption (kWh) Quantity All electric components 715.6 1.943 15 Solar panels 700 9.8 4 Power left 684.4 7.857 19

Table 4. Battery storage capacity Voltage (V) Current (A) Power (kW) Time (h) Storage (kWh) Battery 14.4 250 3.6 14 50.4 Material: High density polyethylene (HDPE) is the material which will be used to manufacture the exterior of the buoy. HDPE was chosen due to its low density of 960 kg / m 3 which is lower than the density of water ensuring it will float [14]. Its other qualities include low moisture absorption, high resistance to corrosion and it being easy to weld [15]. The surface area of the buoy must be determined to know how many kilograms of HDPE is required. [14] HDPE density: https://plasticseurope.org/plastics-explained/a-large-family/polyolefins/#:~:text=The %20density%20of%20HDPE%20can,and%20tensile%20strength%20than%20LDPE . [15] HDPE properties: https://www.curbellplastics.com/materials/plastics/hdpe/ [16] Cost of HDPE: https://businessanalytiq.com/procurementanalytics/index/hdpe-price-index/ Part Quantity Cost per component ($) Motor 2 72.90 Pitot tube 4 133.00 Arduino 1 45.50 Charge controller 1 13.99 Pressure sensor 4 140.91 Inverter 1 60.95 Battery 1 251.00 Total 14 1612.85

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