Coupling flight mechanics and CFD - numerical simulation of shipborne rotors

This thesis demonstrates the use of Computational Fluid Dynamics (CFD) for the simulation of manoeuvring helicopters. Results are presented for the problem of shipborne operations, for which a literature survey showed that little work has been carried out. The CFD solver HMB2 was first validated using available experimental data for isolated ship wakes and helicopter loads at low advance ratios. A rotorcraft flight mechanics model was then developed and integrated into HMB2. The model includes a trimming method and a linearisation routine based on finite differences. The linear model of the aircraft can be used to estimate the controls applied by the pilot during a prescribed manoeuvre via the use of the SYCOS inverse-simulation method or via an LQR auto-pilot. The methods developed in the framework of this thesis include a general multi-body grid motion and an alternative formulation for earth-fixed frame of reference in the CFD. A study of the ship/rotor wake interaction was carried out using the actuator disc method that approximated the effect of the rotor, in a steady fashion and without resolving the flow around the blades. Various positions and thrust of the rotor were tested and the flowfield obtained via coupled simulations were compared with those obtained by super-imposing isolated rotor and ship flowfields. The results show that the superposition principle is not valid and leads to flowfields that have little to do with the real flow that is dominated by the interaction of helicopter and ship airwakes. The case of a rotor hovering in close proximity to a frigate deck was reproduced with fullyresolved blades, and the results shows a significant reduction of thrust due to the flow topology behind the hangar. The Helicopter Flight Mechanics (HFM) method was tested by simulating the aircraft response to a collective pilot input, using simplified models and coupled with CFD. Then, the coupled HFM/HMB2 method was used, in conjunction with the LQR auto-pilot, to simulate the phase of landing of a Sea King helicopter. Simulations were carried-out in free-air and above the frigate deck and the specified trajectories were followed adequately. Results for the ship landing show that the wake of the ship alters the obtained landing trajectory and that the current method captures some of the effects of the wake interaction

Preliminary Progress in Establishing Motion Fidelity Requirements for Maritime Rotorcraft Flight Simulators

The UK’s Royal Navy and Royal Fleet Auxiliary regularly perform launch and recovery operations of helicopters to and from their ships. These operations are carried out in challenging conditions such as confined ship deck space, irregular ship motion, sea spray and unsteady airflows, posing a high risk to the helicopter, ship and the crew. Together these elements form the Helicopter Ship Dynamic Interface (HSDI) environment (Ref. 1). To determine the limitations of the safe operability of helicopters to ships, a safety envelope is constructed through First-of Class Flight Trials (FOCFT) for every combination of helicopter/ship, to determine Ship Helicopter Operating Limits (SHOL) (Ref. 2), which detail the safe environmental conditions for launch and recovery operations. FOCFTs are performed at sea and are inevitably very expensive, which can typically take weeks to construct a SHOL envelope and very often the required wind and sea conditions may not be available, resulting in the development of a conservative SHOL (Ref. 3). Therefore, Modelling and Simulation (M&S) of the HSDI environment is being used to mitigate these risks, making SHOL testing safer, quicker and cost-effective and aims to inform the key test points of high uncertainty to test at sea (Ref. 4-6). The reliability of this support depends upon the identification of the fidelity requirements of the M&S elements, such as the motion and visual cueing, the flight dynamics model and the integration of unsteady airflow to represent the ship’s airwake (Ref. 5). Attempts have been made to assess the fidelity of the rotorcraft simulators (JSHIP (Ref. 5)), however, a standardized guideline to quantify the overall simulation fidelity is a challenge which is yet to be fully addressed (Ref. 7). The research presented in this paper is part of a project being carried out at the University of Liverpool, funded by QinetiQ and Dstl, which aims to achieve the following objective: “To undertake a structured examination of the M&S elements of the HSDI simulation environment to develop a new robust simulation fidelity matrix to support at sea flight trials.

Preliminary progress in establishing motion fidelity requirements for maritime rotorcraft flight simulators

Copyright © 2018 by AHS International, Inc. All rights reserved. The research presented in this paper is part of a project underway at the University of Liverpool (UoL) which aims to develop overall simulation fidelity requirements for maritime rotorcraft flight simulators. This requires a structured examination of individual Modelling and Simulation (M&S) elements, such as motion and visual cues, flight dynamics model and ship airwake integration. The paper reports the initial results of motion cueing research that has been conducted to assess and optimise the motion drive laws and determine high fidelity motion cueing for simulated shipboard operations. To do this, an objective technique, Vestibular Motion Perception Error (VMPE), has been developed. The technique was utilised to optimise the motion cues in UoL's Heliflight-R simulator for a simulated helicopter landing on an aircraft carrier in a turbulent environment. Four motion tuning sets were derived offline and experimentally tested. Results show the influence of different motion cues and airwake conditions on the pilot's overall self-motion perception, control strategy and task performance. It was found that high-fidelity motion cueing becomes more desirable for the pilot at higher airwake wind conditions, for which an 'Optimised' motion setting was obtained using the new technique, than at lower airwake turbulence conditions

Maritime protection of critical infrastructure assets in the Campeche Sound

Following the 9/11 terrorist events in the United States, the Mexican Navy developed strategies designed to prevent similar attacks on the strategic facilities located in the Campeche Sound in the Gulf of Mexico. The Sound is of great economic importance because more than 83 percent of the petroleum produced in Mexico is extracted from that area. This also makes it a key potential target for international terrorists. This research analyzed and evaluated the Mexican Navy's allocation of surveillance and interdiction resources assigned to the Campeche Sound. The data was obtained via an agent-based simulation, implemented through the use of the software program Map Aware Non-uniform Automata (MANA). The simulation model includes the presence of terrorist boats attacking oil platforms, the Navy resources in the area, service-provider ships in the Sound, and fishing boats that often penetrate into the Sound's exclusion and prevention zones. From the study is concluded that: the most important threat factor in the scenarios is the speed of the enemy boats; and, with its broad surveillance and communication capabilities, the HAWKEYE is the most important navy resource in the area. The results also provide an operational guide to allocate the Navy units in the Campeche Sound.http://archive.org/details/maritimeprotecti109451745Approved for public release; distribution is unlimited

Motion Fidelity Requirements for Helicopter-Ship Operations in Maritime Rotorcraft Flight Simulators

The research presented in this paper is part of a longer-term project to develop overall fidelity requirements for simulated helicopter shipboard operations to inform and support First of Class Flight Trials. The paper reports the results of motion cueing assessment and optimisation research, conducted in a six-degree-of-freedom motion flight simulator, to develop simulator motion drive laws capable of providing high fidelity motion cueing for simulated shipboard operations. To do this, a novel objective technique, Vestibular Motion Perception Error (VMPE), has been developed. The technique was utilised to optimise the motion cues for simulated helicopter landings on a naval single-spot destroyer at different wind and sea-state conditions. New simulator motion tuning sets were derived offline and then tested experimentally to compare the objective VMPE predictions with subjective assessments from a test pilot. Results show the influence of different motion cues, airwake conditions and ship motion states on the pilot’s overall perception of self-motion, control strategy, task performance and workload. It was found that high-fidelity motion cueing becomes more desirable for the pilot at higher wind conditions and sea states, for which an ‘Optimised’ motion setting was obtained using the new technique. Moreover, the use of an ‘Optimised’ motion setting generated by the VMPE methodology resulted in reduced pilot workload, leading to improved simulated maritime helicopter operational capability. The technique provides a rational methodology for motion tuning which could be applied in training and engineering simulators

Sea state from monoscopic ocean video in real environments

Video of the ocean surface is used as a means for estimating useful information about the scene. A methodology is first introduced for approximating the pixel to metre scale from high-scale videos of the ocean, such as from an aeroplane. Radar images are used for testing. The temporal and spatial domains are associated through the phase modulation of waves, and a process is introduced that selects the waves with the highest energy to be used for estimating the pixel scale. The spatial information is then used with the calculated pixel scale for approximating the sea state. Due to the difficulty of obtaining high-scale videos, a methodology is then introduced that uses the temporal variation from video, and specifically time series of pixel intensities. It aims to isolate and utilise the temporal variation of the wave field from all other video elements, such as environmental brightness fluctuations. The methodology utilises the Kalman filter and the least squares approximate solution for providing an uncalibrated video amplitude spectrum. A method is proposed for scaling this spectrum to metres with the use of an empirical model of the ocean. The significant wave height is estimated from the calibrated video amplitude spectrum. Videos of the ocean in real environments from a shipborne camera and a tower are used for testing. In both sets of data, in situ buoy information is used solely for validation. The next technique aims to approximate the sea state from the same kind of data, namely videos of the ocean in real environments, without calibrating a video amplitude spectrum. The proposed methodology tracks the principal component of the movement of water in the video, which is speculated to be associated with the dominant frequency of the ocean. To accomplish this, the singular spectrum analysis algorithm and the extended Kalman filter are used. Then, the shape of an empirical spectrum is utilised in order to translate the dominant frequency output into a significant wave height estimation. The problem of not using ocean theory associated with a particular empirical energy spectrum for calibration is examined in the next methodology. A secondary oscillatory component from the singular spectrum analysis algorithm is identified with the incorporation of the extended Kalman filter. Ocean theory involving the equilibrium range of oceans is used for calibration. The shipborne videos are used for testing the behaviour of the techniques for approximately the same sea state of 3.1m to 3.4m of significant wave height. The tower videos are used for testing the techniques for a variety of sea states ranging between 0.5m and 3.6m of significant wave height. From all methodologies, the maximum observed values of root mean square error 0.37m and of mean absolute percentage error 18% suggest that the work is promising at estimating these states

Review of research on Arctic sea ice physics based on the Chinese National Arctic Research Expedition

China launched its Arctic research program and organized the first Chinese National Arctic Research Expedition (CHINARE-Arctic) in 1999. By 2016, six further expeditions had been conducted using the R/V Xuelong. The main region of the expeditions has focused on the Pacific sector of the Arctic Ocean for sea ice observations. The expeditions have used icebreaker, helicopter, boat, floe, and buoy platforms to perform these observations. Some new technologies have been developed, in particular, the underway auto-observing system for sea ice thickness using an electromagnetic instrument. The long-term measurement systems, e.g., the sea ice mass balance buoy, allow observations to extend from summer to winter. Some international cooperation projects have been involved in CHINARE-Arctic, especially the “Developing Arctic Modeling and Observing Capabilities for Long-Term Environmental Studies” project funded by the European Union during the International Polar Year. Arctic sea ice observations have been used to verify remote sensing products, identify changes in Arctic sea ice, optimize the parameterizations of sea ice physical processes, and assess the accessibility of ice-covered waters, especially around the Northeast Passage. Recommendations are provided as guidance to future CHINARE-Arctic projects. For example, a standardized operation system of sea ice observations should be contracted, and the observations of sea ice dynamics should be enhanced. The upcoming launch of a new Chinese icebreaker will allow increased ship time in support of future CHINARE Arctic oceanographic investigations

Aeronautical engineering: A continuing bibliography with indexes (supplement 284)

This bibliography lists 974 reports, articles, and other documents introduced into the NASA scientific and technical information system in Oct. 1992. The coverage includes documents on design, construction, evaluation, testing, operation, and performance of aircraft (including aircraft engines) and associated components, equipment, and systems. It also includes research and development in aerodynamics, aeronautics, and ground support equipment for aeronautical vehicles

The Validation and Application of CFD-generated Aircraft Carrier Airwakes for Flight Simulation

This thesis describes an extensive experimental and computational study of the air flow over the UK Royal Navy's Queen Elizabeth Class (QEC) aircraft carriers, including how the air flow will affect aircraft flying operations, particularly rotorcraft. Maritime fixed- and rotary-wing aircraft routinely perform launch and recovery manoeuvres to and from ships at sea, often in challenging environmental conditions. Pilots performing such manoeuvres must contend with ship motion, sea spray, and an unsteady airwake generated by the air flow shedding off the ship’s superstructure. The main aim of the research was to investigate the use of modelling and simulation to improve understanding of the flying environment over the flight deck of the QEC. The unsteady air flow over the QEC was created using Computational Fluid Dynamics (CFD) and incorporated into flight simulators at the University of Liverpool (UoL) and at BAE Systems, Warton. Experimental data to confirm the validity of the computed air flow was obtained from a small-scale experiment in which a 1.4 m long (1:200) scale model of the QEC was submerged in a water channel and Acoustic Doppler Velocimetry (ADV) was used to measure the unsteady flow around the ship. The results show generally very good agreement between the model-scale experiment and CFD. Piloted flight simulation trials were conducted using the UoL’s HELIFLIGHT-R full-motion flight simulator in which a test pilot conducted simulated deck landings of a representative Sikorsky SH-60B Seahawk helicopter to the flight deck of the QEC under a range of wind conditions. Results for aircraft performance and pilot workload are presented. These trials demonstrated how flight simulation could be used to support flight trials and helicopter clearance activities, but also notes that real-world trials data are needed to compare with the simulations before the techniques can be beneficially deployed. A non-piloted simulation technique was also deployed in which the unsteady forces and moments imposed by the air flow onto the helicopter fuselage were quantified; the results were correlated with the pilot workload ratings from the piloted simulation trials. The results have demonstrated how modelling and simulation can be effectively used to inform real-world flight trials. The simulations reaffirmed how important it is that helicopter flight models respond to the very different velocity components that are imposed on different parts of the aircraft by the highly unsteady three-dimensional air flow. Fixed-wing flight models, however, are not typically designed to capture the unsteady moments created during hover in a highly turbulent flow at low speeds. A new aerodynamic model of a fixed-wing aircraft has been developed which uses strip theory to create the overall forces and moments acting on the aircraft when hovering in a ship airwake. The results show the effect of the QEC airwakes on a hovering fixed-wing aircraft and provide recommendations for the number of strips required to accurately capture the effect of the flow