Glider Performance Research Articles

Dynamics modeling of variable mass systems – a case study of an underwater inertia based propelled glider performance

Dynamics modeling of variable mass systems – a case study of an underwater inertia based propelled glider performance

Canard-configured underwater gliders lift enhancement investigation

ABSTRACT To enhance the lift performance of underwater gliders, this study investigates the application of the canard configuration. Initial experiments conducted in the towing tank confirm the feasibility of the canard configuration in enhancing lift on underwater gliders. Numerical simulations were conducted to determine the effects of canard shape and position on lift. The findings show that the canard vortex induces beneficial upwash, enhancing lift by facilitating flow separation and expanding the negative pressure region on the wing. Specifically, smaller canard sweep angles result in stronger canard vortices, increasing the impact of canards on the wings. A 45° canard sweep angle optimizes both lift and stability for underwater gliders. Positioning canards above and away from wings minimize adverse wake interactions with wing vortices, enhancing glider performance. Compared with the canard-off underwater glider, the lift-to-drag ratio of the canard-on underwater glider was improved by a maximum of 9.8%.

Advancing glider-based acoustic measurements of underwater-radiated ship noise.

Ocean gliders are versatile and efficient passive acoustic monitoring platforms in remote marine environments, but few studies have examined their potential to monitor ship underwater noise. This study investigates a Slocum glider's capability to assess ship noise compared to the ability of fixed observers. Trials were conducted in shallow coastal inlets and deep bays in Newfoundland, Canada, using a glider, hydrophone array, and single-moored system. The study focused on (1) the glider's self-noise signature, (2) range-depth-dependent propagation loss (PL) models, and (3) identifying the location of the vessel to the glider using glider acoustic measurements. The primary contributors to the glider's self-noise were the buoyancy pump and rudder. The pitch-motor noise coincided with the buoyancy pump activation and did not contribute to the glider self-noise in our experiments. PL models showed that seafloor bathymetry and sound speed profiles significantly impacted estimates compared to models assuming flat and range-independent profiles. The glider's performance in recording ship noise was superior to that of other platforms. Using its hydrophones, the glider could identify the bearing from the vessel, although a third hydrophone would improve reliability and provide range. The findings demonstrate that gliders can characterize noise and enhance our understanding of ocean sound sources.

Research on the Aerodynamic Characteristics of the Relationship between Lift-to-drag Ratio and Wing Shape of Gliders

A glider is a special type of aircraft without a power unit, which relies on the lift of airflow to resist weight. The characteristics of a glider are essential to its flight performance, which includes aspect ratio, sweepback, and taper ratio. Proper design of the wing shape can help achieve good performance, so research on these elements can be helpful. This paper aims to calculate the relationship between the aspect ratio and lift-drag coefficient which affects the performance of gliders. By calculation, this paper found out that high aspect ratio aircraft could generate more lift force and was optimum in designing gliders. Then an experiment with a paper plane was designed to show the impact of aspect ratio on glider performance. Then a paper airplane experiment was designed, and the changes in different aspect ratios were achieved by reshaping the wings of the paper airplane, while flight performance was estimated by the lift drag coefficient and descent angle of the glider. After data collection, calculation and analysis, different flight routes were recorded, and based on this, the lift drag coefficient and descent angle were calculated. The experimental results indicate that aspect ratio is one but not the only factor affecting the flight performance of gliders. Through theoretical analysis and experiments, this study verifies the basic mechanism of the influence of wing shape, especially aspect ratio, on glider flight, providing new ideas for improving glider performance.

Multi-objective optimization and driving mechanism design for controllable wings of underwater gliders

Recently, underwater glider has become an effective tool for long-term ocean exploration. Controllable wing technology, which can improve comprehensive performance of underwater glider, has received widespread attention. This paper mainly proposes a multi-objective optimization based design method of controllable wings for underwater gliders. First, controllable wing configuration parameters are determined, specifically including wing span and sweep angle here. Then, hydrodynamic equations, containing controllable wing configuration parameters, are obtained by CFD simulation and quartic polynomial fitting. On this basis, the glider performance analysis model, quantitatively evaluating voyage velocity, static stability and energy consumption, are derived, and multi-objective optimization model of wing configuration parameters is established. Meanwhile, the relationship between controllable wing configuration parameters and the glider comprehensive performance is discussed. Especially, surrogate model technology is introduced into optimization calculation process to improve optimization efficiency. And non-dominated sorting genetic algorithm II is employed to obtain Pareto optimal set, which will make design objectives of driving mechanism of controllable wings clearer. Based on multi-objective optimization results and linkage synthesis method, a novel driving mechanism of controllable wings is designed, and corresponding principle prototype is manufactured. Besides, the motion characteristic, sealing and locking methods of the design scheme are also discussed.

Fabrication of UiTM’s Energy Glider

Glider is a fixed-wing aircraft which does not depend on the engine. A glider can fly for an extended period depending on the design and area of the lifting surface. Just like any other aircrafts, the design of wings is crucial to produce lift force to keep aircraft in the air. Gliders have long wings and is designed to be lightweight which allows it to have a high lift-to-drag ratio (L/D) to glide at a long distance. The maximum lift-to-drag ratio, 〖(L/D〗_max) can indicate how far the glider will glide as it is one of the most important performance parameters. This project aims to design, build, and fly an energy glider. Prior on the design of the energy glider, statistical analysis has been done by comparing data from many studies to aid in determining the initial values of the glider. Then, the general design of the energy glider has been decided during the preliminary design. To support the design decision made, ANSYS Fluent software has been used to study flow of air over KFm-5A aerofoil profile which has been chosen during the early stages of design. The model of the energy glider was then designed in CATIA V5 software with a wingspan of 1.52 m and fuselage length of 0.69 m. Lastly, flight test was conducted to achieve the project’s objective. During the flight test, the glider reached a ceiling height of approximately 300 m and obtained a velocity of 144 km/h. The analysis of the glider performance will be used as an aircraft data for future research.

A hybrid polynomial-based optimization method for underwater gliders with parameter uncertainty

As a type of enduring platform for ocean exploration, underwater glider usually contains some uncertain parameters in actual engineering applications, which are related to manufacturing errors, assembly errors, and sensor measurement errors. Uncertain parameters will make the glider performance show uncertain characteristics, so it is necessary to consider their effects in the design optimization process for an underwater glider. In this paper, a hybrid polynomial-based optimization method is proposed to solve optimization problems of underwater gliders with parameter uncertainty. The hybrid polynomial consists of power function terms and trigonometric function terms, and it is used for fitting surrogate models of the glider dynamic models. The fitted surrogate models are used for quickly calculating the performance evaluation parameters of underwater gliders. Specifically, power function terms and trigonometric function terms correspond to optimization design variables and uncertain parameters, respectively. The hybrid polynomial method covers the convenience of the traditional response surface method and the advantage of the Chebyshev polynomial in interval analysis. Based on surrogate models and interval analysis, we can estimate boundary functions of performance evaluation parameters, and they are employed to construct optimization objective functions. Then, the optimization iteration calculation can be carried out. Here, the proposed method is used for determining the optimal control parameter values of the Petrel-II glider with the uncertainty of some configuration and measurement parameters. The optimization objectives are to minimize the specific energy consumption and maximize the average advance velocity simultaneously. Finally, some laws of the glider performance are summarized.

Multidisciplinary optimization-based path planning for underwater gliders executing multi-point exploration missions

The underwater glider is an energy-saving autonomous observation platform for long-term ocean exploration missions. In this paper, we carry out theoretical research to solve the path planning problem for multi-point exploration missions of underwater gliders. First, performance evaluation models of the glider are established, including the dynamic model, the voyage range and velocity models, and the energy consumption and utilization rate models. Based on the performance evaluation models, a path planning method is proposed to determine the optimal path that can make the glider complete the multi-point exploration mission by consuming less energy and time. The path planning method consists of three steps. In the first step, the surrogate models of performance evaluation parameters are obtained by using the polynomial functions to fit the dynamic simulation results. In the second step, the multi-objective optimization algorithms and the surrogate models are used for determining the control parameter values that can maximize the glider energy utilization rate and voyage velocity simultaneously. Then, under the given path, the correlation between the glider performance and the number of profiles is studied. In the third step of the path planning method, we establish an optimization objective function by using the energy consumption and time consumption of the glider motion. Meanwhile, the path planning problem is regarded as a traveling salesman problem, and it is solved by using the genetic algorithm. Finally, several numerical cases are given to demonstrate the proposed path planning method. The research work can provide certain theoretical guidance for the actual application of underwater gliders.

A rotating piston engine with electric generator in serial hybrid propulsion system for use in light aircraft

Analysis of the possibility of using a rotary engine based electric generator to propell a powered sailplane. The paper presents analysis of utilising Wankel type enine as a power input for an electric generator in the motor glider propulsion system. This generator would be a part of the propulsion system of a hybrid motor glider using the AOS 71 motor glider airframe. In the research, the rotational characteristics of the LCR 407ti wankel engine were determined experimentally. Driving torque run, power and fuel consumption were determined as a function of engine speed. The obtained results are presented in diagrams. The conceptual diagram of the hybrid drive is presented. The electric generator was selected and its effectiveness, as well as the effectiveness of entire propulsion system was assessed from the motor glider's performance point of view. Basing on the research conducted, conclusions were drawn and there were indicated the objectives and directions of further research on hybrid propulsion with specific aerodynamic and mass limitations of the aircraft

Underwater Glider Propulsion Systems VBS Part 1: VBS Sizing and Glider Performance Analysis

The Variable Buoyancy System (VBS) is a critical device in the operation of underwater gliders that should be properly sized to achieve the required vehicle propulsion; safety within the operating range; and adequate efficiency at the nominal depth rating. The VBS budget volume depends mainly on the glider hydrodynamics and the main operating states of the vehicle. A method is proposed with analytical equations to analyze the performance of underwater gliders and to estimate the resultant velocities of the vehicle as a function of the buoyancy change and the glider angle. The method is validated to analyze the glider performance of underwater gliders and is essential to get the main design requirement for the propulsion system: the VBS budget volume. The paper presents the application of the method to obtain the VBS sizing for an academic glider; a comparison with the historical hydrodynamic data of the Slocum glider; the results of the glider performance study; and the development of the characteristic charts necessary to evaluate the performance of the vehicle and its flight parameters.

Glider performance analysis and intermediate-fidelity modelling of underwater vehicles

This paper analyses the transit performance of state-of-the-art underwater vehicles and presents an intermediate-fidelity steady-state flight mechanics model for qualitative performance assessment of underwater vehicles. Focusing on the comparison of underwater gliders and propeller-driven AUVs, a simple glide metric is presented and the transit performance of the legacy underwater gliders Slocum, Spray and Seaglider as well as propeller-modified versions thereof is evaluated. The evaluation is based on various data sets from wind tunnel tests and Computational Fluid Dynamics (CFD) studies, and shows that for the respective hull shapes gliding locomotion proves more efficient in ideal conditions. However, biofouling conditions inflict a double penalty on glider performance, rendering gliders inferior to propeller-driven vehicles. The Slocum data set is used to validate a steady-state flight mechanics model for qualitative performance prediction. It is shown that even simplistic models based on semi-empirical and analytical expressions can be successfully used for design optimization through parametrization. Being computationally efficient, the model can be a useful tool for design engineers in early design phases. The model is used to evaluate the effects of wing span on gliding efficiency, indicating that the current design of the Slocum glider is near-optimal.

Internal tide energy flux over a ridge measured by a co-located ocean glider and moored acoustic Doppler current profiler

Abstract. Internal tide energy flux is an important diagnostic for the study of energy pathways in the ocean, from large-scale input by the surface tide to small-scale dissipation by turbulent mixing. Accurate calculation of energy flux requires repeated full-depth measurements of both potential density (ρ) and horizontal current velocity (u) over at least a tidal cycle and over several weeks to resolve the internal spring–neap cycle. Typically, these observations are made using full-depth oceanographic moorings that are vulnerable to being “fished out” by commercial trawlers when deployed on continental shelves and slopes. Here we test an alternative approach to minimize these risks, with u measured by a low-frequency acoustic Doppler current profiler (ADCP) moored near the seabed and ρ measured by an autonomous ocean glider holding station by the ADCP. The method is used to measure the semidiurnal internal tide radiating from the Wyville Thomson Ridge in the North Atlantic. The observed energy flux (4.2±0.2 kW m−1) compares favourably with historic observations and a previous numerical model study. Error in the energy flux calculation due to imperfect co-location of the glider and ADCP is estimated by subsampling potential density in an idealized internal tide field along pseudorandomly distributed glider paths. The error is considered acceptable (<10 %) if all the glider data are contained within a “watch circle” with a diameter smaller than 1∕8 the mode-1 horizontal wavelength of the internal tide. Energy flux is biased low because the glider samples density with a broad range of phase shifts, resulting in underestimation of vertical isopycnal displacement and available potential energy. The negative bias increases with increasing watch circle diameter. If watch circle diameter is larger than 1∕8 the mode-1 horizontal wavelength, the negative bias is more than 3 % and all realizations within the 95 % confidence interval are underestimates. Over the Wyville Thomson Ridge, where the semidiurnal mode-1 horizontal wavelength is ≈100 km and all the glider dives are within a 5 km diameter watch circle, the observed energy flux is estimated to have a negative bias of only 0.4 % and an error of less than 3 % at the 95 % confidence limit. With typical glider performance, we expect energy flux error due to imperfect co-location to be <10 % in most mid-latitude shelf slope regions.

Performance of an Ocean Buoyancy Glider in a Coastal Region: Application to the Gulf of Mexico Hypoxic Zone

AbstractThe Gulf of Mexico Coastal Hypoxia Glider Experiment was designed to assess the feasibility of using ocean glider technology in the coastal hypoxic zone of the northern Gulf of Mexico in Summer/Fall 2014. The objectives were (1) to coordinate and operate multiple autonomous buoyancy ocean gliders in depths less than 50 m and (2) to determine how close to the bottom gliders can reliably reach without making contact. Strong vertical and horizontal stratification gradients, strong coastal currents, and the low-oxygen conditions that occur within the lower water column characterize the coastal area of the northern Gulf of Mexico. These environmental conditions combine with the presence of more than 5,000 surface piercing oil/gas structures to make piloting and navigation in the region challenging. We quantify glider performance to assess the usefulness of buoyancy gliders to address the National Oceanic and Atmospheric Administration Action Plan goal to monitor the spatial extent, duration, and severity of the Gulf hypoxic zone. We find that the gliders, despite the operational challenges, were consistently able to travel from the surface to the oxygen-depleted depths of subpycnocline waters, that is, within 2 m of the ocean bottom. Our assessment is that gliders are able to provide real-time observations suitable to monitor coastal hypoxia.

The design and implementation of ocean ambient noise acquisition system based on the underwater glider

Ocean ambient noise (OAN) is the background noise of the ocean,which is considered as the interference for the underwater acoustic equipment,on the other hand,it can be used to invert the parameters of the ocean environment. It is important to acquire and study the spatial temporal characteristics of ocean ambient noise. As a new type of underwater detection platform,underwater glider's performance is suitable to acquire the ocean ambient noise. This paper designed and realized an OAN acquisition system (OANAS),which is mounted on the Underwater glider. The system mainly includes two parts,the deepwater hydrophone array and the acquisition system. This design uses the ADI's BF518,the AD73360 and the uClinux to make the acquisition system have high speed,low power consumption and low noise abilities,it can also sample eighteen underwater signal roads synchronously and meet the requirement of the system. The data memorized is proved effective,the system is proved to be stable and meet the design requirement through the test which the OANAS mounted on the Hybrid Underwater Glider in the National Ocean Technology Center.

Elements of Underwater Glider Performance and Stability

AbstractUnderwater gliders are winged autonomous underwater vehicles (AUVs) that can be deployed for months at a time and travel thousands of kilometers. As with any vehicle, different applications impose different mission requirements that impact vehicle design. We investigate the relationship between a glider’s geometry and its performance and stability characteristics. Because our aim is to identify general trends rather than perform a detailed design optimization, we consider a generic glider shape: a cylindrical hull with trapezoidal wings. Geometric parameters of interest include the fineness ratio of the hull, the wing position and shape, and the position and size of the vertical stabilizer. We describe the results of parametric studies for steady wings-level flight, both at minimum glide angle and at maximum horizontal speed, as well as for steady turning flight. We describe the variation in required lung capacity and maximum lift-to-drag ratio corresponding to a given vehicle size and speed; we also consider range and endurance, given some initial supply of energy for propulsion. We investigate how the turning performance varies with wing and vertical stabilizer configuration. To support this analysis, we consider the glider as an 8-degree-of-freedom multibody system (a rigid body with a cylindrically actuated internal moving mass) and develop approximate expressions for turning flight in terms of geometry and control parameters. Moving from performance to stability and recognizing that a glider’s motion is well described in terms of small perturbations from wings-level equilibrium, we study stability as an eigenvalue problem for a rigid (actuators-fixed) flight vehicle. We present a number of root locus plots in terms of various geometric parameters that illuminate the design tradeoff between stability and control authority.

Optimization of displacement and gliding path and improvement of performance for an underwater thermal glider

The underwater thermal glider utilizes ocean thermal energy to change its buoyancy, which enables it to ascend and descend. A Phase Change Material (PCM) as the working fluid inside the thermal engine tubes is sensitive to the surrounding seawater temperature, whose effects are different with the various displacements and gliding angles of the glider. In this paper, the effects of the displacement and the gliding angle on the performance of the thermal engine were studied numerically and experimentally. On this basis, the ways to eliminate the negative effect of a thermocline on the performance of the thermal engine were obtained. The results show that the displacement and gliding angle affect the transition time of the PCM. There exist the threshold values of the displacement and gliding angle for the normal work of thermal engine. There are two means of eliminating the negative effect of a thermocline on the performance of the thermal engine and improving glider performance: one is to increase the displacement, and the other is to decrease the absolute value of the gliding angle. There is also another better way to improve glider performance.

Optimal patterns of glider dynamic soaring

AbstractThis paper presents optimal patterns of glider dynamic soaring utilizing wind gradients. A set of three‐dimensional point‐mass equations of motion is used and basic glider performance parameters are identified through normalizations of these equations. In particular, a single parameter is defined that represents the combined effects of air density, glider wing loading, and wind gradient slope. Glider dynamic soaring flights are formulated as non‐linear optimal control problems and three performance indices are considered. In the first formulation, the completion time of one cycle of dynamic soaring is minimized subject to glider equations of motion, limitations on glider flights, and appropriate terminal constraints that enforce a periodic dynamic soaring flight. In the second formulation, the final altitude after one cycle of dynamic soaring is maximized subject to similar constraints. In the third formulation, the least required wind gradient slope that can sustain an energy‐neutral dynamic soaring flight is determined. Different terminal constraints are used to produce basic, travelling, and loiter dynamic soaring patterns. These optimal control problems are converted into parameter optimization via a collocation approach and solved numerically with the software NPSOL. Different patterns of glider dynamic soaring are compared in terms of cycle completion time and altitude‐increasing capability. Effects of wind gradient slope and wind profile non‐linearity on dynamic soaring patterns are examined. Copyright © 2004 John Wiley & Sons, Ltd.

Aerodynamics of Pteranodon

A computer program originally designed to test glider performance was adapted and used to study the flight behaviour of Pteranodon. A drag polar was determined for the membranous wing, giving a cambered plate profile. Results of the program described the straight flight performance, the turning ability and circling within thermals. Pteranodon was found to have a very low sinking speed, a similar lift/drag ratio to gliding birds, to be capable of staying aloft at extremely low speeds and a very small turning circle. The stress involved while turning was calculated and found to be low. It is suggested that a change from settled light-wind weather to more turbulent conditions could have brought about the extinction of this highly specialized animal.