MECH2400 9400 Assignment B Swivelling Cable Tether System Design Due
Friday the 8th of October (Week 8) 11:59pm through CANVAS Problem
Summary: There is an identified need to acquire reliable but cost
effective low to medium altitude meteorological data (atmospheric
pressure, temperature, humidity and wind speed) on Western Australia’s
north western coastline (Figure 1.0). The region of interest is bounded
by Carnarvon through to just north of Port Hedland (a distance of
approximately 1000kms) on Australia’s west coast. The coastal region has
the highest wind rating and has been classified as Region D – severe
cyclonic (Figure 2.0). The data is required to serve as part of an early
an early warning system for incoming cyclones. Figure 1.0 Figure 2.0
Scope: It is planned to install ten, Tethered Weather Balloons (TWB)
separated by a distance of 100km from each other as the methodology to
obtain the necessary data. The TWB will carry a payload of approximately
20kg which is comprised of; sensors to measure; air pressure, wind
speed, temperature and humidity. A solenoid valve that is connected to
each TWB to enable to release of Helium gas for lowering the TWB (as a
safety mechanism when wind speed reaches 25.0m/s or for servicing).
Additional electronic components include; high capacity Li-Po batteries,
a GPS system to track the TWB in the event of it disconnecting from its
tether, a 3 axis accelerometer to measure speed and acceleration, an
inertial measurement unit to measure attitude, a small on-board CPU with
RAM and an SSD, a cable harness and a long range Wi-Fi antenna. The
components will be housed in an industrial shock proof case. The TWBs
will have the ability to collaboratively send and receive data to each
other as a method to enable the sending of the required data to the main
meteorological bases at Carnarvon and Port Hedland on a regular hourly
basis (to minimise battery usage) or on a per minute basis if an urgent
need arises. The TWBs are to operate at a fixed altitude of 1000m. The
operation of the TWB system is designed to be unattended with a
projected life of 10 to 20 years. Six monthly service intervals to
replenish the Helium gas, replace Li-Po batteries and inspect and
replace any faulty electronics or mechanical components is part of the
maintenance schedule. Data: Balloon Data: Balloon diameter (DB) = 25.0m
(assume the balloon is perfectly spherical in shape at all times)
Balloon volume (VB) = (1.333 * π * (0.5 * DB)3) Balloon altitude (HB) =
1000.0m Balloon payload (Bp) = 20kg (assume the mass of balloon is
negligible) Density of Helium gas (ρHe) = 0.174kg/m3 Density of air
(ρair) = 1.29kg/m3 Acceleration due to gravity (ag) = 9.81m/s2 Helium
Balloon Lifting Force (FL) = VB *(ρair - ρHe) * ag Wind Speed Drag Force
Data: Maximum allowable wind speed velocity (vmax) = 25.0m/s Balloon
area (AB) = 0.25 * π * DB2 Drag Coefficient of Sphere (cd) = 0.5 Drag
Force (Fd) = cd * 0.5 * ρair * v2max * AB Cable Data: A galvanised wire
cable with a 6 x 24 construction (as shown in Figure 3.0) available from
Bullivants (order code 110176) has been selected as the preferred
choice as it has higher resistance to corrosion. The cable is assumed to
be in a taunt (non-sagging) state at all times. Figure 3.0 Diameter of
cable = 26mm Mean Breaking Force (MBF) = 304kN Approximate mass per
linear length (kg/100m) = 215kg End connections: End connections are to
be of a, ‘closed swage socket’ style as defined in AS2759 – 2004 and
illustrated in Figure 4.0 in Third Angle Projection below. No exact
dimensions are available for the end connection but may be scaled to
suit based on the wire cable diameter. Figure 4.0 Your Task: With
reference to the Problem Summary, Scope and Data provided, your main
requirement for Assignment B focuses on the mechanical design and stress
analysis of a Swivelling Cable Tether System (SCTS) to provide an
anchored support for the TWB that differs in design from the ‘Cable
Tensioning System’ presented in Assignment 1B and illustrated in Figures
5.0 and 5.1. Under the effects of wind, the SCTS is to be able to
rotate on at least two axis (similar to a mechanism). Figure 5.0 Figure
5.1 Cable Tensioning System (Courtesy of Dr. Thai Nguyen) Concrete
Support Data: A concrete foundation approximately 3.0m in length, 3.0m
in width and 3.0m in depth has been secured deeply below ground level
with protruding studs to ensure that your SCTS has a secure mounting
point. A sample image of a typical concrete slab that connects to a
mechanical post is shown in Figure 6.0 below. Figure 6.0 Assignment B
Requirements: In a report format which includes; title page, contents
page, conclusions/insights and references to APA 7th or Harvard,
consider the following three criteria: 1. Conceptualisation / Creativity
(5%) Using methods of Creativity, conceptualise at least two distinct,
original designs for your SCTS. Discuss in detail which Creativity
methods (or combinations of) you used (approximately 300 words including
images) to come up with your designs. Develop a Trade-off table to
analyse which of these two potential designs is the most feasible. You
may wish to discuss these two designs with other students in terms of
arriving at weighting values. Explain your reasoning for; selecting
certain criteria, arriving at weightings and the scores you allocated
for each of the two designs (approximately 300 words). 2. Basic Stress
Analysis (15%) The stress analysis is to be carried out on your final
selection of SCTS from Point 1 above. There are two cases that need to
be analysed: Case 1: The case of no wind any direction acting on the TWB
i.e. the TWB is direct above your final SCTS. Case 2: The case of when
the wind velocity is acting along only one axis of your final SCTS in
its swivelled position. Perform stress analysis as outlined below on the
main components of your final SCTS design to ensure that the TWB is
safely secured in place. 1. Carry out basic stress analysis of the major
load carrying members including the fasteners used. Any mild or
stainless steel may be used and fasteners of any diameter, grade or
style may be used. 2. You will also need to define the threaded mounting
studs shown in Figure 6.0 that connect the concrete base to your SCTS
design (in terms of: quantity, arrangement, diameter, grade, length and
nuts plus washers required). You are not required to design the grade of
concrete needed or how the threaded studs are connected to the
concrete. 3. A factor of safety (F of S) of 2.0 is to be used on all
stressed components of your SCTS design. 4. Include all FBDs, SF
Diagrams, BM Diagrams and deflection in key points. Use standard
equations, do not derive equations from first principles. 5. Your SCTS
must be able to be easily pulled apart. Consequently, welding is not be
used as a method of joining major components together. 6. No Finite
Element Analysis (FEA) is to be used in this assignment. 3. Engineering
Drawings (5%) Draw an Assembly Drawing of your final assembled SCTS with
some basic overall dimensions and a parts list. Use drawing sheets of
size A2, A1 or A0 size. You are not required to produce detail drawings
for your design in this assignment. Submit your Assignment B into the
CANVAS portal as a single PDF file named using your student number e.g.
496394428.pdf. THIS ASSIGNMENT SHOULD TAKE AN AVERAGE STUDENT
APPROXIMATELY 20 HOURS TO COMPLETE The author would like to extend
thanks to Prof. Steve Armfield and A/Prof. KC Wong for their advice and
support in the drafting of this assignment. Paul Briozzo 13/09/2021