A highly stable and efficient spherical underwater robot with hybrid propulsion devices

Although the spherical underwater robot has the advantage of 0 radius for the turning locomotion, a variable radius of turning locomotion is also necessary for the path planning and obstacle avoidance of an underwater robot. This paper focused on the turning locomotion with variable radius for the forthgeneration spherical underwater robot (SUR IV) with the hybrid propulsion device. The hybrid propulsion device could be controlled by PWM signals to modify the thrust and linear velocity. The motion state of the turning locomotion was developed in different radius. The centripetal force of curve motion is also analyzed by Newton's first law. The relationship between the centripetal force and turning radius was proposed. In order to verify the turning locomotion with different turning radius, the experiment was carried out in the swimming pool. The experimental results show that the change of the turning radius can be achieved by adjusting the control input PWM signal of the main thruster and the assist thruster.

Aiming at multi robot cooperation application requirements of our small-scaled underwater spherical robots, a cooperative formation control system with static and dynamic target rounding up was proposed and studied in this paper. Considering the complex underwater environment and kinematic modeling of the robot, a simplified kinematic model of underwater spherical robot with horizontal and vertical motion was established. Given the environmental disturbances in practical underwater scenarios, an adaptive control algorithm was designed to control the underwater spherical robot, which has good robustness and adaptability. To handle the application requirement of static and dynamic target rounding up with multi robots, the path planning strategy of multi robot was proposed, the modeling of static and dynamic target rounding up was analyzed and optimized, and a controller based on linear quadratic regulator method was also designed to realize static/dynamic target rounding up with multi robots. In addition, underwater target rounding up experiments with two or three spherical robots were conducted to test the feasibility and performance of the proposed formation control system, and the experimental results confirmed the validity of the proposed system. This study may inspire future underwater multi robot cooperation that have properties of high efficiency, wide range and multi tasks and has low environmental interference of aquatic environments.

In this paper, a spherical underwater robot is proposed that uses six degree of freedom thrust allocator to determine the magnitude and the direction of thrust required for each water-jetted bilge pump thruster to create force and moment equilibrium. However, in order to ensure safe operation of the underwater robot it is equipped with redundant thruster configuration and therefore is over-actuated. Therefore, the choice of a particular solution for thrust allocation is found using an optimization process. In this work, the thrust allocation problem is formulated as an optimization problem, with an objective to minimize the total power consumption of the spherical underwater robot. A set of all physically realizable surge, sway and heave force for the i <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> thruster is called as its Attainable Thrust Region (ATR). Since the thrust force produced by each thruster is restricted to its ATR, the power consumption of underwater robot is determined by establishing a relationship between the power consumption and the thrust of an individual bilge pump. The formulated optimal thrust allocation problem is solved using Mincon (Sequential Quadratic Programming) and GA (Genetic Algorithm) optimization algorithm. The percentage savings in total power consumption for thruster system using the GA as compared to Mincon method is 33.82 %.

Underwater target acquisition and identification performed by manipulators having broad application prospects and value in the field of marine development. Conventional manipulators are too heavy to be used for small target objects and unsuitable for shallow sea working. In this paper, a bio-inspired Father–Son Underwater Robot System (FURS) is designed for underwater target object image acquisition and identification. Our spherical underwater robot (SUR), as the father underwater robot of the FURS, has the ability of strong dynamic balance and good maneuverability, can realize approach the target area quickly, and then cruise and surround the target object. A coiling mechanism was installed on SUR for the recycling and release of the son underwater robot. A Salamandra-inspired son underwater robot is used as the manipulator of the FURS, which is connected to the spherical underwater robot by a tether. The son underwater robot has multiple degrees of freedom and realizes both swimming and walking movement modes. The son underwater robot can move to underwater target objects. The vision system is installed to enable the FURS to acquire the image information of the target object with the aid of the camera, and also to identify the target object. Finally, verification experiments are conducted in an indoor water tank and outdoor swimming pool conditions to verify the effectiveness of the proposed in this paper.

While designing the power requirements of a ship, the most important factor to be considered is the ship resistance, or the sea drag forces acting on the ship. It is important to have an estimate of the ship resistance while designing the propulsion system since the power required to overcome the sea drag forces contribute to ‘losses’ in the propulsion system. There are three main methods to calculate ship resistance: Statistical methods like the Holtrop-Mennen (HM) method, numerical analysis or CFD (Computational Fluid Dynamics) simulations, and model testing, i.e. scaled model tests in towing tanks. At the start of the design stage, when only basic ship parameters are available, only statistical models like the HM method can be used. Numerical analysis/ CFD simulations and model tests can be performed only when the complete 3D design of the ship is completed. The present paper aims at predicting the calm water ship resistance using CFD simulations, using the Flow-3D software package. A case study of a roll-on/roll-off passenger (RoPax) ferry was investigated. Ship resistance was calculated at various ship speeds. Since the mesh affects the results in any CFD simulation, multiple meshes were used to check the mesh sensitivity. The results from the simulations were compared with the estimate from the HM method. The results from simulations agreed well with the HM method for low ship speeds. The difference in the results was considerably high compared to the HM method for higher ship speeds. The capability of Flow-3D to perform ship resistance analysis was demonstrated.

In this paper, a spherical underwater robot uses optimal thrust allocator to determine the magnitude and the direction of thrust required for each water-jetted bilge pump thruster to create force and moment equilibrium. However, in order to ensure safe operation of the underwater robot it is equipped with redundant thruster configuration and therefore is over-actuated. Therefore, the choice of a particular solution for thrust allocation is found using an optimization process. In this work, the thrust allocation problem is formulated as an optimization problem, with an objective to minimize the total power consumption of the spherical underwater robot. The power consumption of underwater robot depends on the thrust generated by each bilge pump. The relationship between the power consumption and the thrust of the bilge pump is established using experimental data. The formulated optimal thrust allocation problem is solved using Mincon (Sequential Quadratic Programming) and SA (Simulated Annealing) optimization algorithm. The percentage savings in total power consumption for thruster system using the SA method as compared to Mincon method is 50.6 %.

Considering the complicated disturbance in underwater circumstance, usually it is difficult to solve the control problem when the robot changes its motion state or it is subject to ocean currents, its performance deteriorates since the fixed set of parameters is no longer valid for the new conditions. Thus, in this paper, an auto-tune PID (Proportional + Integral + Derivative)-like controller based on Neural Networks is applied to our amphibious spherical underwater robot, which has a great advantage on processing online for the robot due to their nonlinear dynamics. The Neural Networks (NN) plays the role of automatically estimating the suitable set of PID gains that achieves stability of the system. The NN adjusts online the controller gains that attain the smaller position tracking error. The performance of the NN-based controller is investigated in ADAMS and MATLAB cooperative simulation. The velocity of the spherical robot can be controlled to precisely track desired trajectory in body-fixed coordinate system. Additionally, real time experiments on our underwater spherical robot are conducted to show the effectiveness of the algorithm.

In the navigation of underwater robots, large ocean current disturbance often causes significant tracking errors. To better resist ocean current disturbance, the hydrodynamic characteristics of the spherical underwater robot are studied, and a model predictive control strategy based on adaptive model parameters is proposed, according to these characteristics. Firstly, the hydrodynamic characteristics of the robot under static water and constant flow disturbance were obtained and analyzed by the computational fluid dynamics method. Then, the dynamic models of the robot under different disturbances could be calculated from the data obtained, based on the least square method. Finally, an adaptive model predictive control (AMPC) strategy, with an ocean current observer, was designed, based on the dynamic models. When the current disturbance velocity was twice the robot velocity, the proposed strategy reduced the tracking error by 39% and 42% in X and Y directions, respectively. In addition, the hydrodynamic characteristics were verified by experiments.

A normally-open thermally-actuated microvalve was designed (using microfabrication/soft-lithography techniques involving 3D Printed molds), assembled and tested. The motivation of the research work is to develop an array of microvalves for precise delivery of water to individual plants in a field (with the goal of developing smart irrigation systems for high value cash-crops in the agricultural sector). It is currently impossible to control application of irrigation-water at the level of a single plant. If such a capability were practically available on farms, the result would be a step change in precision agriculture, such that the output of every plant in a farm field could be optimized (i.e., food-water-energy nexus in sustainability applications). The aim of this study is to develop and test a microfluidic system (consisting of a microvalve array) that could be controlled, capillary by capillary, to deliver the needed amount of water to individual plants in a large field. Two types of test fluids were leveraged for thermo-hydraulic actuation of the microvalves developed in this study: (a) Design-I: using air, and (b) Design-II: using Phase Change Material (PCM). The PCM used in this study is PureTemp29. The proposed approach enabled a simple and cheap design for microvalves that can be manufactured easily and are robust to weather conditions (e.g., when exposed to the elements in orchards and open fields). Other advantages include: safe and reliable operation; low power consumption; can tolerate anomalous pressure loads/fluctuations; simple actuation; affords easy control schemes; is amenable for remote control; provides long-term reliability (life-cycle duration estimated to be 3∼5 years); can be mass produced and is low maintenance (possibly requiring no maintenance over the life time of operation). The microvalve consists of two layers: a flow layer and a control layer. The control layer is heated from below and contains a microfluidic chamber with a flexible polymeric thin-membrane (200 microns in thickness) on top. The device is microfabricated from Poly-Di-Methyl-Siloxane (PDMS) using soft lithography techniques (using a 3D Printed mold). The control chamber contains either air (thermo-pneumatic actuation) or PCM (thermo-hydraulic actuation involving repeated melting/freezing of PCM). The flow layer contains the flow channel (inlet and outlet ports, horizontal section and valve seat). The experimental results from testing the efficacy of the two types of micro-valves show a 60% reduction (for thermo-pneumatic actuation using air) and 40% reduction (for thermo-hydraulic actuation using PCM) in water flow rates for similar actuation conditions (i.e., heater temperature values). PCM design is expected to consume less power (lower OPEX) for long-term actuation but may have slower actuation speed and have higher manufacturing costs (CAPEX). Air actuation design is expected to consume more power (higher OPEX) for longer-term operation but may have faster actuation speeds and lower manufacturing costs (CAPEX). Computational Fluid Dynamics (CFD) simulations were performed to investigate the effect of flowing water (in the microfluidic channel) on the average absolute pressure and temperature of air in the actuation chamber. The CFD simulations were performed using a commercial tool (Ansys™ 2019R1®). The results from the CFD simulations are presented in this study.

The aim of this paper is to examine the effect of wind on the thermal diffusion characteristics of floating production storage and offloading (FSPO) topside models subject to fire. It is motivated by the need to identify the fire loads on FPSO topsides, taking into account the effects of wind speed and direction. The results of an experimental and numerical study undertaken for these purposes are reported here. This paper is part of Phase II of the joint industry project on explosion and fire engineering of FPSOs (EFEF JIP) [1]. An experiment was performed on a 1/14-scale FPSO topside model using a wind tunnel test facility. The locations of the heat source of the fire were varied, as were the speed and direction of the wind, and the temperature distribution was measured. Computational fluid dynamics (CFD) simulations using the ANSYS CFX program were performed on the test model, with the results obtained compared with the experimental results. It is concluded that wind has a significant effect on the thermal diffusion characteristics of the test model and that the CFD simulations are in good agreement with the experimental results. The insights developed in this study will be very useful for the fire engineering of FPSO topsides.

Wind tunnel experiments and Computational Fluid Dynamics (CFD) simulations are used to analyze natural ventilation in a sawtooth roof building. A 1:10 scale model is tested in an atmospheric boundary layer wind tunnel. The CFD simulations are performed with Ansys CFX software. The aim of this study is to evaluate the reliability of CFD simulation in predicting pressure data at opening height in a sawtooth roof building with wind tunnel data. The model is evaluated for prevailing wind in five directions: 0 and 45° (air extractor sheds), 90° (neutral situation) and 135 and 180° (air collector sheds). The computational grid resolution shows that the inclusion of prisms and the increase of the grid refinement in the building’s surface cause insignificant differences in Cp (wind pressure coefficient). In general, the error values below 10% indicate a good agreement between CFD simulations and wind tunnel data.

Abstract. Ultrasonic anemometers mounted on rotary-wing drones have the potential to provide a cost-efficient alternative to the classical meteorological mast-mounted counterpart for atmospheric boundary layer research. However, the propeller-induced flow may degrade the accuracy of free-stream wind velocity measurements by wind sensors mounted on drones – a fact that needs to be investigated for optimal sensor placement. Computational fluid dynamics (CFD) simulations are an alternative to experiments for studying characteristics of the propeller-induced flow but require validation. Therefore, we performed an experiment using three short-range continuous-wave Doppler lidars (light detection and ranging; DTU WindScanners) to measure the complex and turbulent three-dimensional wind field around a hovering drone at low ambient wind speeds. Good agreement is found between experimental results and those obtained using CFD simulations under similar conditions. Both methods conclude that the disturbance zone (defined as a relative deviation from the mean free-stream velocity by more than 1 %) on a horizontal plane located at 1 D (rotor diameter D of 0.71 m) below the drone extends about 2.8 D upstream from the drone center for the horizontal wind velocity and more than 7 D for the vertical wind velocity. By comparing wind velocities along horizontal lines in the upstream direction, we find that the velocity difference between the two methods is ≤ 0.1 m s−1 (less than a 4 % difference relative to the free-stream velocity) in most cases. Both the plane and line scan results validate the reliability of the simulations. Furthermore, simulations of flow patterns in a vertical plane at the ambient speed of 1.3 m s−1 indicate that it is difficult to accurately measure the vertical wind component with less than a 1 % distortion using drone-mounted sonic anemometers.

This paper discusses the combined influence of building morphology and trees on air pollutant concentrations in the Marylebone neighbourhood (central London). Computational Fluid Dynamics (CFD) simulations are performed with OpenFOAM using the k-ε model. Aerodynamic and deposition effects of Platanus acerifolia trees are considered. While aerodynamic effects are treated as typically done in the literature, i.e. as a porous media, for the deposition an enhanced model with an additional sink term was implemented. CFD results are compared with UK AURN (Automatic Urban and Rural Network) station concentrations. Several meteorological conditions are analysed based on London City Airport weather station data, with attention to prevailing winds.CFD simulations show that trees trap air pollution by up to about 7% at the Marylebone monitoring station in the spring, autumn and summer seasons, suggesting that the aerodynamic effects are similar over the different leaf seasons. Aerodynamic effects are more important at lower wind speeds causing little turbulent dispersion. Deposition effects are found to be 4 times less important with reductions of up to about 2%, with more deposition in summer due to a greater leaf area density. Furthermore, for winds parallel to Marylebone Road, the aerodynamic effects decrease concentrations suggesting that in such cases trees could be considered as a mitigation measures. This is different from perpendicular winds for which trees exacerbate trapping, as found in previous studies. The analysis of concentration levels obtained from CFD simulations across the whole street confirms a beneficial aerodynamic dispersive effect of trees of 0.7% in summer time for all wind directions averaged at a wind speed of 5m/s (yearly average wind speed observed in the area). Results highlight the need to account for both aerodynamic and dispersion effects of trees in CFD modelling to achieve a comprehensive evaluation and help city planners with a sustainable design of trees in urban environments.

This study examines the aerodynamic performance of a NACA 4412 airfoil that is covered with denticles, comparing it to a smooth NACA 4412 airfoil. The aim was to assess the lift-to-drag ratio of the airfoil utilizing biomimetic surfaces inspired by the dermal denticles of Isurus oxyrinchus. To achieve this, the airfoils were subjected to testing in a wind tunnel. Both the denticles-covered and smooth airfoils, measuring 355 by 184 mm, were equipped with 27 pressure taps distributed across three spanwise sections: the leading edge, upper surface, and lower surface. Nine flexible tubes were connected to pressure sensors for each row of static taps. Wind tunnel tests were conducted at various angles of attack (AOAs), ranging from −10.8° to 16.2° with an increment of 1.8°. Testing was carried out at wind speeds of 3, 6, and 9 m/s. Computational fluid dynamics (CFD) simulations were conducted on the smooth airfoil under identical conditions to validate the wind tunnel testing setup. The lift and drag coefficients were derived from the recorded static pressures. A comparison between the aerodynamic coefficients obtained from experiments and CFD simulations indicated that higher wind speeds are preferable for wind tunnel testing as they yield more consistent results. When examining the aerodynamic coefficients of the smooth airfoil compared to the denticle-covered airfoil, it was found that the latter generally produced higher lift and drag, resulting in a lower lift-to-drag ratio across different angles of attack and wind speeds. Specifically, at 3 m/s, the denticle-covered airfoil exhibited better lift at most AOAs, higher drag at certain AOAs, and improved lift-to-drag ratios. At wind speeds of 6 and 9 m/s, the denticle-covered airfoil demonstrated higher lift for all tested AOAs and increased drag for several AOAs, yet it consistently had lower lift-to-drag ratios. These findings point to the potential benefits of utilizing the denticle-covered NACA 4412 airfoil due to its enhanced lift characteristics at lower wind speeds. Further research is warranted to quantify the differences between the airfoil types.

Considerable progress has been achieved in recent decades in understanding the phenomena related to the onset of condensation in steam flows, both experimentally and especially numerically. Nevertheless, there is still a certain disagreement between the different numerical models used. Unfortunately, the available experimental validation data are not sufficiently detailed to allow for proper validation of computational fluid dynamics (CFD) simulations. Therefore, this paper presents new experimental data for condensing steam flows, acquired in a supersonic nozzle according to Barschdorff, at the Institute of Thermal Turbomachinery Laboratory (ITSM) at the University of Stuttgart. A steady inlet pressure of approximately 784 mbar was set for three inlet temperatures down to 100.2 ∘C. Condensation onset is accurately captured across the nozzle, using down to 1 mm spatial resolution for both pneumatic and light spectra measurements. CFD simulations were performed using the commercial solver ANSYS CFX. The droplet diameters are numerically overestimated by approximately a factor of 1.5. Disagreement has been found between original Barschdorff’s experiments and measurements at ITSM. However, there is a good agreement in terms of the pressure distribution along the nozzle axis between experimental and numerical results. The reproducibility of the results is excellent.