Mechanical Engineering conference papers
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Item Open Access Installation, Commissioning and Operation of the Atmospheric Boundary Layer Research Facility (ABLRF)(Australasian Fluid Mechanics Society, 2022) Emes, M.; Marano, M.; Jafari, A.; Arjomandi, M.; 23rd Australasian Fluid Mechanics Conference (4 Dec 2022 - 8 Dec 2022 : Sydney)This paper describes a recently installed and commissioned atmospheric boundary layer research facility (ABLRF) for high-fidelity field measurements of atmospheric turbulence and wind loads on structures. The goal is to characterise gust wind events and three-dimensional turbulence length scales, which are driving factors for dynamic effects such as torsional flutter and galloping on flexible structures, the turbulent transport and diffusion of dust and particle concentrations for heliostat mirror soiling, herbicide spray drift and propagation of pollutants in plumes. The ABLRF provides increased precision and resolution of near-surface turbulence data in the lowest 10 metres, with high-frequency measurements of the intensities and length scales of horizontal and vertical turbulence components. Preliminary analysis of mean wind velocity and turbulence data during a high-wind afternoon shows that the site is characterised by an open country terrain with logarithmic roughness height between 0.01 m and 0.03 m and friction velocity of 0.3 m/s.Item Metadata only Numerical study of effects of wind on the vertical fire spread with vertical/horizontal spandrel(Scientech Publisher LLC, 2022) Huang, Z.; Tian, Z.; Chen, X.; The 13th International Conference on Computational Methods (ICCM) (25 Jul 2022 - 28 Jul 2022 : virtual online)Due to the importance of preventing the vertical fire spreading along with buildings, two fire inhibition methods were raised by the National Construction Code clause [1] C2.6(a) including vertical spandrel of at least 900 mm high or horizontal spandrel of at least 1100 mm deep. This project aims to answer the research question of whether vertical spandrel of 900 mm and horizontal construction of 1100 mm are equivalent in performance in inhibiting the vertical fire spreading under the effects of wind using fire dynamics simulator (FDS) simulations. The geometry of the simulations is modified from experimental works conducted by Oleszkiewicz [2] by adding an air opening on the back wall. The preliminary results show that by slightly increasing the front wind (the wind direction is normal to the front opening of the building) from 0 m/s to 0.5 m/s, the radiation heat transfer from the flame to the above floor is increased slightly, however, further increasing the front wind speed will reduce the radiative heat flux on the above floor, due to the blocking effect of the front wind. When the front wind speed increases to above 4 m/s, the flame is blocked within the room. When the side wind (the wind direction is parallel to the front opening of the building) is introduced, there is a slight increase in heat flux for the wind speed of 1~4 m/s. Based on the preliminary simulation results, it is found that for the wind conditions, fire load and building structure investigated in the paper, the performance of the 900 mm vertical spandrel is lower than the horizontal spandrels even for the horizontal spandrel of 500 mm.Item Metadata only Design optimisation of a multi-mode wave energy converter(American Society of Mechanical Engineers (ASME), 2020) Sergiienko, N.Y.; Neshat, M.; Silva, L.S.P.D.; Alexander, B.; Wagner, M.; 39th International Conference on Ocean, Offshore and Arctic Engineering (OMAE) (3 Aug 2020 - 7 Aug 2020 : virtual online)A wave energy converter (WEC) similar to the CETO system developed by Carnegie Clean Energy is considered for design optimisation. This WEC is able to absorb power from heave, surge and pitch motion modes, making the optimisation problem nontrivial. The WEC dynamics is simulated using the spectral-domain model taking into account hydrodynamic forces, viscous drag, and power take-off forces. The design parameters for optimisation include the buoy radius, buoy height, tether inclination angles, and control variables (damping and stiffness). The WEC design is optimised for the wave climate at Albany test site in Western Australia considering unidirectional irregular waves. Two objective functions are considered: (i) maximisation of the annual average power output, and (ii) minimisation of the levelised cost of energy (LCoE) for a given sea site. The LCoE calculation is approximated as a ratio of the produced energy to the significant mass of the system that includes the mass of the buoy and anchor system. Six different heuristic optimisation methods are applied in order to evaluate and compare the performance of the best known evolutionary algorithms, a swarm intelligence technique and a numerical optimisation approach. The results demonstrate that if we are interested in maximising energy production without taking into account the cost of manufacturing such a system, the buoy should be built as large as possible (20 m radius and 30 m height). However, if we want the system that produces cheap energy, then the radius of the buoy should be approximately 11–14 m while the height should be as low as possible. These results coincide with the overall design that Carnegie Clean Energy has selected for its CETO 6 multi-moored unit. However, it should be noted that this study is not informed by them, so this can be seen as an independent validation of the design choices.Item Metadata only The ARES submarine project - A sandpit for industry digital transformation and workforce upskilling in Australia(2021) Fusil, E.; Submarine Institute of Australia (SIA) (8 Nov 2021 - 10 Nov 2021 : Adelaide Convention Centre, Adelaide SA)In 2020, the world tripped due to a virus which also impacted all Defence Shipbuilding programs. Dearth of resources, personnel, funding and jamming of our overseas connections disrupted the submarine world. How could those committed to developing the Australian sovereign capability keep moving forward? Imagination and innovation. Thanks to a Defence SA grant in 2020, a collaborative research team of Australian universities and industry partners had developed a feasibility study for ARES, the Australian Research and Experimental Submarine as a free running model. At the 2020 SIA Conference, the DST Chief scientist acknowledged the great work achieved by the ARES Team and the relevance of the topic to SEA1000 but the question became “where to from there and how do we secure future funding?”. This is why, building on the success of the project, we continued the development to the benefit of Defence but with a focus on two aspects of the eco-system: • Workforce upskilling, • Digital transformation. In other words: developing capability for the Defence industry from a people and tools perspective. In an era where the Industry 4.0 and digital twins are the buzz words, we have tried to put them into a real perspective by applying them to our project. The questions and challenges we have faced are about working together and in a consistent way: how can the software environment work and speak one voice? How do the people speak one voice or about the same submarine and deliver up to requirements? How can the food chain work efficiently from suppliers to production? And finally: what do the Customer and Primes want from Academia in that context?Item Open Access Exploring the Position of Humanitarian Engineering in Australia(Association for Engineering Education, 2023) Brown, N.; Smith, J.; Daniel, S.; Birzer, C.; Australasian Association for Engineering Education Conference (AAEE) (4 Dec 2022 - 7 Dec 2022 : Sydney, New South Wales)Context: The position of an engineering field, such as a discipline, specialisation, or area of practice, reflects the body of knowledge, skills and techniques required to practice. Humanitarian Engineering, which was recognised with a 6-digital Field of Research code in 2020, works within a range of contexts and communities where there are inherent power imbalances, and decisions and actions that affect immediate livelihoods and wellbeing. This can be considered similar to fields within Engineers Australia such as Amusement Rides and Devices (an area of practice) and Fire Safety (both an area of practice and technical society). These fields do not have large memberships, but are sufficiently specialised and high risk to require dedicated scrutiny. Humanitarian Engineering can be considered to warrant similar levels of enhanced scrutiny of its practice and education. Purpose: The Engineers Australia Humanitarian Engineering Community of Practice have devised a six-item agenda for the professionalisation of Humanitarian Engineering in Australia. This seeks to bring the same level of rigour, review, and recognition to Humanitarian Engineering as for any field, area of practice or discipline of engineering. This study set out to determine a broad consensus on the position of Humanitarian Engineering within existing frameworks in response to the agenda. Approach: The study adopted a modified Delphi method in which key stakeholders and representatives of Humanitarian Engineering education and practice in Australia were invited to a workshop to openly discuss and debate the position of Humanitarian Engineering in Australia. A pre-workshop survey established a starting point for discussion at a 2-hour workshop while a post-workshop survey identified and tested key insights and findings. Outcomes: A specific position on Humanitarian Engineering in Australia was not reached during the workshop. Rather, underlying assumptions were challenged and tested. Humanitarian Engineering was indeed considered to need higher levels of review and accountability, underpinned by key values and principles. A more specific set of next steps were identified in order to address unresolved questions and provide further analysis to support a potential position. Recommendations: Humanitarian Engineering education and practice should be subject to a high level of scrutiny to ensure appropriate education and practice. Regardless of a specific position and definition, further discussion and critique from within and outside engineering in Australia must continue.Item Metadata only New sensor development for hydrocyclone overflow particle cumulative percent passing size online monitoring - a preliminary experimental investigation under dry condition(The Australian Institute of Mining and Metallurgy, 2022) Tang, D.; Chen, L.; Yang, L.; Hu, E.; IMPC Asia PAcific 2022 (22 Aug 2022 - 24 Aug 2022 : Melbourne, Australia + Online); Batterham, R.Online monitoring of particles cumulative percent passing (PCPP) for a target size at hydrocyclone overflow, compared with traditional offline methods, provides PCPP feedback in real time, and is advantageous in enabling energy-efficient comminution, increasing downstream flotation efficiency, and improving upstream resource knowledge. However, existing online approaches are generally costly and bespoke, and some are sensitive to operational changes. Therefore, this study proposes a new low-cost alternative based on accelerometer measurement for online PCPP monitoring in the overflow of hydrocyclones and provides a preliminary experimental investigation under dry condition. The proposed method uses a sensing probe inserted into the overflow pipe of a hydrocyclone to receive particle impact from the incoming slurry, with accelerometers attached to the probe and mounting frame outside the pipe for particle-probe impact detection. As a preliminary investigation before studying particle-probe impact events in slurry, tests under dry condition without fluids were conducted using dry sand particles in free fall from a fixed height. Accelerometer measurements are analysed in both time and frequency domains through root-mean-square (RMS) and fast Fourier transform (FFT). Results show that accelerometer measurements are useful in estimating mass flow rates, which are correlated to the accelerometer output amplitude RMS values in time domain, in a non-linear mapping. Different particle size classes can be identified by examining the accelerometer output amplitude at a known mass flow rate. Different particle size classes feature their distinct signature frequencies (SFs) that can be examined via FFT and the SF is found to be independent of the mass flow rate. The results imply that any PCPP changes can be detected by the change in the accelerometer output amplitude as well as a shift in SF, which demonstrates the effectiveness of using accelerometers to gauge changes in PCPP. Based on the current findings in dry condition, future work will investigate particle-probe impact events in slurry.Item Metadata only Hybrid Transmission Line Kite Thread Removal Robot(VNU_HCM Press, 2021) Carlos, K.; Chen, N.; Hussain, F.; Liu, W.; Mourin, S.; Akmeliawati, R.; Chen, L.; International Conference on Intelligent Unmanned Systems (ICIUS) (25 Aug 2021 - 27 Aug 2021 : Ho Chi Minh City University of Technology, VNU-HCM, Vietnam)Robotic maintenance of high voltage transmission lines is becoming an increasingly feasible solution in providing a safer and more reliable alternative to manual maintenance. In particular, in areas of Indonesia, a significant majority of electrical faults are attributed to kite thread entanglements, and if not swiftly resolved, may cause significant power disruptions and blackouts. Due to the hazards associated with traditional manual removal methods, the paper proposes the preliminary design of a hybrid robot capable of remotely traversing the transmission lines and removing kite thread entanglements. A top-down system engineering approach is utilized in designing and building the robot. Furthermore, a functional analysis was performed to identify the user and system requirements of the robot that leads to the identification of its subsystems. A transmission line maintenance robot, equipped with a unique removal system with blades designed to fit onto varying transmission line sizes, has been designed and built for removing kite threads using a remotely-controlled drone. The proposed hybrid robot with its novel cutting mechanism provides an efficient and safe solution to remove kite threads entangled on transmission lines as it rolls along the lines.Item Metadata only Shallow water Submarine optimizations for signatures(DCN France, 2005) Fusil, E.; Undersea Defence Technology (UDT) (21 Jun 2005 - 23 Jun 2005 : Amsterdam)Originally stemming from the Cold War, theatres of operation have deeply changed for submarines. From deep waters to shallow waters, submarines have begun a natural evolution Submarines signatures and vulnerability had to adapt, therefore DCN has successfully developed design methods and tools to specify systems and subsystems in compliance with new objectives and strategies. These methods and tools enable not only to assess the signatures and vulnerability of nuclear and conventional submarines, but also arms DCN to take into account the theatre of operation (blue waters or shallow waters). Through this process, DCN is able to select the most suitable technologies and architectures to achieve the best performances, facing the various threats to be encountered. This paper will first present how the theatre of operation has an influence on DCN design choices with respect to these performances and then will give some examples related to acoustic discretion, target strength, vulnerability and electromagnetic signatures based on a conventional submarine design, all along through design tools.Item Metadata only Characterising the response of human heads during a simulated head-first impact(Australian & New Zealand Orthopaedic Research Society, 2021) Thompson-Bagshaw, D.; Quarrington, R.; Jones, C.; The 26th Annual Scientific Meeting of Australian & New Zealand Orthopaedic Research Society Conference (ANZORS) (5 Oct 2021 - 8 Oct 2021 : virtual online)Item Metadata only Characterising the response of human heads during a simulated head-first impact(Australian and New Zealand Society of Biomechanics, 2021) Thompson-Bagshaw, D.; Quarrington, R.; Jones, C.; The 12th Australasian Biomechanics Conference (ABC) (6 Dec 2021 - 7 Dec 2021 : virtual online, Adelaide, SA)Item Metadata only Innovative training and R&D in Subsea technologies and engineering at the University of Adelaide(Submarine Institute of Australia, 2019) Fusil, E.; SIA Submarine Science, Technology and Engineering Conference (SubSTEC5) (18 Nov 2019 - 21 Nov 2019 : Fremantle, Western Australia)Because now is the time to prepare the future, the University of Adelaide has invested in capability development to support the shipbuilding and allied industries in Australia: • From a workforce development first: reinvigorating the Masters of Maritime Engineering, the 2019 intake has seen 33 post-graduate students interested in that field. 10 students are also in a Dual Degree with ENSTA Bretagne of France. This is a new record since the creation of the MME in 2006. • From a R&D perspective as well: the Shipbuilding Hub for Integrated Engineering and Local Design has initiated a number of projects in R&D, including some with dual applications (civilian / military) in the Subsea environment. Whilst it is still early days to celebrate a new dawn, this paper intends to measure the practical progress made and to display the tangible achievements obtained by the University. Because the workforce ramp-up in the maritime domain will request to develop people rather than relocating or poaching skilled individuals, we intend to explore the options that could meet the expectations of Primes such as ASC, BAE and Naval Group, but also companies from allied industries, such as oil and gas or tier I or tier II subcontractors. Not following, but leading, the University of Adelaide has committed to the Maritime domain, and Subsea in particular, whilst focusing primarily on Naval Shipbuilding Plan with SEA1000, SEA5000 and SEA1180.Item Metadata only Stowing strategy for a heliostat field based on wind speed and direction(AIP Publishing, 2022) Emes, M.; Jafari, A.; Collins, M.; Wilbert, S.; Zarzalejo, L.; Siegrist, S.; Arjomandi, M.; International Conference on Concentrating Solar Power and Chemical Energy Systems (solarPACES) (28 Sep 2020 - 2 Oct 2020 : Virtual online); Richter, C.; Shultz, A.This paper investigates a stowing strategy of a heliostat field based on wind speed and direction, in terms of the potential benefit of additional energy collection through the partial stowing of heliostats within an azimuth angle range with reduced operating wind loads. Correlations of one-minute wind speed and DNI at a heliostat field site with the operating wind loads, based on the azimuth-elevation tracking angles of individual heliostats, were used to assess the increased operating time and collected thermal energy by the field. The results show that more than 23% of heliostats in the sector of the field with operating wind loads that are smaller than 50% of the stow loads can continue to operate during a high-wind period (e.g. 10 m/s). Adopting a stow strategy based on wind direction can increase the annual operating time of the heliostat field by 6% with increasing stow design wind speed from 6 m/s to 12 m/s. Furthermore, the stowing strategy based on wind direction to allow heliostats to continue to operate at wind speeds exceeding 10 m/s can achieve an additional 280 MWh of thermal energy collected by the heliostat field operation during time periods that would conventionally stow the entire field with 24 GWh of annual thermal energy captured.Item Open Access Laser ignition of iso-octane and n-heptane jets under compression-ignition conditions(Elsevier, 2022) Zhai, G.; Xing, S.; Yuen, A.C.Y.; Medwell, P.R.; Kook, S.; Yeoh, G.H.; Chan, Q.N.This work aims to investigate the effect of laser-induced plasma ignition (LI) on combustion behaviours of isooctane (a gasoline surrogate) at compression-ignition (CI) conditions. A high-energy laser was used to force the fuel ignition at a quiescent-steady environment inside an optically accessible constant-volume combustion chamber with 900 K ambient gas temperature, 22.8 kg∕m3 ambient gas density and 21 vol.% O2 concentration. A diesel surrogate (n-heptane) was tested at a lower charge temperature of 735 K to offset its higher fuel reactivity than the iso-octane, such that the flames of both fuels can have a similar lift-off length. Forced laser ignition was introduced either before or after the natural autoignition timing of the fuels. The laser was focused at the jet axis 15 mm and 30 mm from the nozzle. High-speed schlieren imaging, heat release analysis and flame luminosity measurement were applied to the flames. The high-speed schlieren imaging was used to monitor the flame structure evolution of the natural ignition and LI cases. Due to laser ignition, the flame lift-off lengths decrease, with which the uncertainties in the lift-off distances reduce by more than 80%. The laser-affected flame bases return back to the natural flame base locations. The uncertainties in the lift-off lengths also increase, as the flame stabilisation locations approach the natural lift-off distances. Under the test conditions of this work, the rates at which the iso-octane flames shift downstream are slower than the n-heptane cases. The heat release rate profiles show high heat release from the flames following the LI events, before transitioning to lower steady values. The flame luminosity measurements indicate a strong correlation between the LI affected lift-off length and increased soot formation. The luminosity levels decrease as the flame base shifts downstream over time.Item Metadata only Aeroacoustic performance of cylinders with a circumferential varying porous coating(American Institute of Aeronautics and Astronautics, 2020) Arcondoulis, E.J.G.; Liu, Y.; Geyer, T.F.; Sedaghatizadeh, N.; Arjomandi, M.; AIAA Aviation Forum (15 Jun 2020 - 19 Jun 2020 : virtual online)The vortex shedding tone magnitude of a cylinder in uniform flow can be suppressed by applying a porous coating. The mechanism for the vortex shedding tone suppression is not fully understood, nor is the optimal porous coating to achieve maximum tone suppression. Understanding the internal flow field of Porous Coated Cylinder (PCC) can provide a deeper understanding of the interaction of the porous media and the development of the external flow field and therefore lead to the improved designs of PCCs. This paper presents a flow visualization test conducted in a water tunnel at The University of Adelaide that reveals the internal flow field of a Structured PCC (SPCC). The results of these experiments were then used to design SPCCs that possess two different porosities along the cylinder circumference which were then tested in a small anechoic wind tunnel at Brandenburg Technical University Cottbus - Senftenber using two microphone arc arrays and a hot-wire anemometry probe in the wake and separated shear layer. Each SPCC revealed two tones and a high frequency broadband contribution, yet each tone magnitude was weaker than the equivalent bare cylinder shedding tone and presented decreased overall sound pressure levels. Applying a more densely spaced porous region on the cylinder windward side resulted in stronger higher frequency broadband contributions yet when placed on the cylinder leeward side negligible changes in the acoustic spectrum were recorded. By investigating the coherence between the flow and acoustic signals stronger evidence was gathered to suggest that the higher frequency tone is generated by localized flow behavior in the separated shear layer. Using time-averaged profiles in the wake revealed that the SPCC with uniform porosity around its circumference has the lowest drag coefficient and the cylinder with denser porous spacing on the windward side has the highest drag coefficient.Item Metadata only Temperature measurements by laser-induced phosphorescence: Effect of laser flux variation(Monash University, 2015) Kueh, K.C.Y.; Lau, T.; Nathan, G.; Alwahabi, Z.; 7th Australian Conference on Laser Diagnostics in Fluid Mechanics and Combustion (9 Dec 2015 - 11 Dec 2015 : Melbourne)Laser-induced Phosphorescence technique (LIP) was applied to non-intrusive temperature measurements of a hot plate coated with ZnO:Zn. The dependence of the emission intensity ratio of two wavelength ranges on the temperature was evaluated. A non-linear relationship at temperatures below 600K was found. The effect of the laser flux on the accuracy of the LIP temperature measurement was investigated. It was found that a 10% increase of laser flux, in the range of 2-14 mJcm-2, results in a 2% change in the computed temperature, centred around 600K.Item Metadata only Effect of flapping-frequency on attitude estimation of a tailless flapping-Wing micro air vehicle(Australian Robotics and Automation Association (ARAA), 2020) Cartwright, J.; Foster-Hall, W.; Tam, W.; Vinod, H.; Akmeliawati, R.; Australasian Conference on Robotics and Automation (ACRA) (8 Dec 2020 - 10 Dec 2020 : virtual online)It is well known that the amount of lift generated by the flapping motion of an insect-mimicking Flapping Wing Micro Air Vehicle (FW-MAV) depends on its flapping frequency. However, the effect of flapping frequency on attitude estimation and control of a FW-MAV platform is hardly explored and thus, warrants investigation. In this paper, we propose attitude estimation and control of FWMAV via measured flapping frequency of a tailless KUBeetle-S model developed at Konkuk University that uses a rack-pinion mechanism to emulate the high amplitude flapping motion of a beetle. Pitch, roll and yaw moments are generated using the Stroke Plane Change (SPC) and Trailing Edge Control (TEC) mechanisms. A telemetry system was developed to provide an interface to view real time attitude data and enable post-processing and analysis in MATLAB. Moving average, complementary and Kalman filters were applied to examine the signal in both the time and frequency domain. A novel approach to estimate flapping frequency of FW-MAVs using data from an onboard accelerometer is presented. This method has the potential to allow for direct control of the flapping frequency and by doing so reduce weight and increase the manoeuvrability of the platform.Item Metadata only Modelling motion instabilities of a submerged wave energy converter(IWWWFB, 2019) Rijnsdorp, D.; Orszaghova, J.; Skene, D.; Wolgamot, H.; Rafiee, A.; International Workshop of Water Waves and Floating Bodies (IWWWFB) (7 Apr 2019 - 10 Apr 2019 : Newcastle, Australia)Item Metadata only Real-time prediction of unidirectional irregular waves(IWWWFB, 2019) Skene, D.; Wolgamot, H.; Geldard, J.; Taylor, P.; Draper, S.; International Workshop of Water Waves and Floating Bodies (IWWWFB) (7 Apr 2019 - 10 Apr 2019 : Newcastle, Australia)Item Open Access A summary of experimental studies on heliostat wind loads in a turbulent atmospheric boundary layer(AIP Publishing, 2020) Arjomandi, M.; Emes, M.; Jafari, A.; Yu, J.; Ghanadi, F.; Kelso, R.; Cazzolato, B.; Coventry, J.; Collins, M.; Solar Power and Chemical Energy Systems Annual Conference (SolarPACES) (1 Oct 2019 - 4 Oct 2019 : Daegu, South Korea); Richter, C.The aerodynamic loads on heliostats have been investigated through an extensive range of experimental studies at the University of Adelaide in association with the Australian Solar Thermal Research Institute (ASTRI). Applied modelling techniques using spires and roughness elements were adopted for generation and characterisation of the temporal and spatial turbulence fluctuations, matching those in the lower region of the atmospheric boundary layer (ABL) where full-scale heliostats are positioned. Heliostat wind loads were found to be highly dependent on the critical scaling parameters of the heliostat and the turbulence intensities and scales in the ABL flow. The peak drag and lift coefficients on heliostats followed a similar variation with elevation and azimuth angles to those previously reported in the literature at a similar turbulence intensity. However, the current study revealed a linear increase of the peak drag and lift coefficients on heliostats in operating and stow positions with a parameter defined by the product of the turbulence intensity and the ratio of the turbulence length scales to the heliostat chord length.Item Open Access An experimental investigation of unsteady pressure distribution on tandem heliostats(AIP Publishing, 2020) Jafari, A.; Emes, M.; Cazzolato, B.; Ghanadi, F.; Arjomandi, M.; Solar Power and Chemical Energy Systems Annual Conference (SolarPACES) (1 Oct 2019 - 4 Oct 2019 : Daegu, South Korea); Richter, C.The unsteady surface pressure distribution on heliostats in a tandem arrangement is investigated in this experimental study. The differential pressure on the panel of a heliostat model is measured for a range of gaps between the two tandem heliostats, varying from 1 to 7 times the chord length dimension of the panel. The heliostat models are placed in a simulated turbulent atmospheric boundary layer in the University of Adelaide wind tunnel. The measured surface pressures are analysed and compared with those of a single heliostat, at three elevation angles of 30°, 60° and 90°. The results showed that the peak pressure distribution on the tandem heliostat differs significantly from the single heliostat. Regions of large-magnitude pressure occur near the edges of the panel at smaller gap ratios. Large unsteady variations of the position of the centre of pressure are found for the tandem heliostat at gap ratios equal to and less than 5, which lead to an increase of the hinge moment relative to the single heliostat. The peak hinge moment coefficient on a tandem heliostat is found to be 40% and 70% larger than the coefficient on the single heliostat at elevation angles of 30° and 60°, respectively. The results therefore indicate the importance of the unsteady wind loads in different rows of a field for the design of heliostats as they vary significantly from the loads on a single heliostat dependent on the field arrangement.