Shipboard Helicopter Research Articles

Inverse Kinematics Analysis of a 2-DOF Stabilized Platform using Simulink and Simscape

Abstract This paper presents a parallel manipulator with two universal-prismatic-universal (UPU)-type active limbs and one revolute-spherical (RS)-type passive limb which is used as a stabilizing platform based on the shipboard helicopter’s landing process and its kinematics are studied systematically. First, a 3D model of this stabilized platform is constructed, and its degrees of freedom are analyzed. Second, analytic formulas for solving the inverse kinematics and calculating the required lengths of each limb are derived and modeled using Simulink®. Third, a Simscape™ model is constructed for the proposed design, and finally, the comparison of the results between the two models is done.

Prediction of ship future motions at different predictable time scales for shipboard helicopter landing in regular and irregular waves

ABSTRACT Differing from the traditional helicopter landing on land, due to ship motions induced by actual waves, the landing safety of shipboard helicopter on vessels in waves deserves to be studied. To provide a judgment basis for the timing of shipboard helicopter landing, a hydrodynamic analysis method based on the Long-Short-Term Memory (LSTM) neural network is proposed to achieve the real-time prediction of ship motions in this study. Firstly, the hydrodynamic formulations based on potential flow theory for nonlinear ship motions in waves are presented. The implementation details of the LSTM neural networks are described. Secondly, the numerical verification study is carried out in regular and irregular waves, respectively. Furthermore, a destroyer model is employed to illustrate the proposed framework, and the results corresponding to the different time scales in waves are presented. Finally, the work of this paper is summarized and the certain conclusions are drawn.

Development and Flight Testing of Guidance, Navigation, Control, and Operator Interface for Shipboard Helicopter Operations

Unmanned Aircraft Systems (UASs) have become increasingly important assets for naval and maritime law enforcement operations. In response to the ever-increasing demand for autonomous systems, this paper presents a design, development, integration, and flight testing of an unmanned rotorcraft system capable of operating with a moving ship. The system was developed initially by playing back ship motion data in a simulation environment. Ship motion prediction, relative guidance, operator control interface, and landing flight management system were developed and tested against simulated sea state motion. The system was then flight tested using a 15-kg electric helicopter operating off a US Naval Academy’s yard patrol craft. The craft was instrumented with IMU and GPS for the craft’s own state estimation. The craft was also used as a moving-base station for Real-time Kinematic (RTK) relative positioning. The flight operation was done in the Chesapeake Bay. Autonomous capabilities including takeoff, landing, station-keeping, and maneuvering relative to a moving ship were successfully demonstrated.

Dynamic modeling and analysis of traction operation process for the shipboard helicopter

The traction operation of a shipboard helicopter on the deck is a complex force-coupling process involving multiple moving entities. To more efficiently simulate the traction process, this study introduces a dynamic model based on the independent modeling of moving subjects (IMMS) method. Initially, the forces on the tire and the articulation part are analyzed, followed by the separate establishment of dynamic models for the helicopter and tractor using the Lagrange equation. Considering the articulated states among the ship, helicopter, and tractor, and according to the active–passive relationships of each entity, a unified solution method is introduced to solve the motion equations sequentially. The model's reliability and real-time performance are subsequently assessed and validated, effectively simulating the helicopter's traction operation procedure. The results reveal that the IMMS dynamic model exhibits high reliability and requires, on average, only 0.5% of the CPU time compared to the conventional dynamic model. The IMMS approach will be useful in advancing research into the modeling of shipboard helicopter traction processes.

Numerical studies on the aeroelasticity of a shipboard helicopter rotor during engagement and disengagement with ship motions using CFD/CSD coupling approach

When the shipboard helicopter rotor engages and disengages on a ship deck, due to the influence of wind-over-deck environment and ship airwake, the heterogeneity of rotor airload is large. This large heterogeneity leads to the fluctuation of blade deflection which changes the aerodynamic forces and causes danger of over deflection. To investigate the aeroelasticity of a rotor blade and find the rule of deflection and the deformed blade aerodynamic force in the rotor/ship coupling flow field, we establish a loose computational fluid dynamics/computational structural dynamics (CFD/CSD) coupling model. This coupling model simulates the aeroelastic characteristics of the shipboard helicopter rotor during engagement and disengagement with ship motions. In the simulation, the CFD solver is based on Reynolds-averaged Navier-Stokes (RANS) equations and the CSD solver is based on the moderate deflection beam model. We compare the results with the experimental data and verify the effectiveness of the simulation. Through the analysis of the flow field, blade deflection, and aerodynamic forces under various wind-over-deck conditions at different positions, we find in certain cases, that the elastic deflection has a significant impaction the blade aerodynamic force. As the wind direction anglesincrease, the rotor blade is more likely to have a large negative elastic twist deflection, causing drop of aerodynamic forces and danger of over deflection.

A multi-objective optimization problem research for amphibious operational mission of shipboard helicopters

Airborne landing with shipboard helicopters gradually replaces surface landing to dominate joint amphibious operations. A problem with shipboard helicopter mission planning is conducted in the context of amphibious operations. First, the typical missions of shipborne helicopters in amphibious operations are analyzed. An Amphibious Operational Mission Planning Model for Shipboard Helicopters (AOMPMSH) is established, with the objectives of minimizing the completion time of the amphibious campaign and minimizing troop and helicopter losses, taking the available operational resources and the order of the mission sub-phases into account. Then, a simulation-based amphibious operations effectiveness assessment model is constructed to calculate the optimization objectives of AOMPMSH by simulating the campaign development with an amphibious objective area situation transfer model and simulating the engagement process with a modified Lanchester model. A reference point based multi-objective optimization algorithm is designed to solve the proposed AOMPMSH. The population iteration mechanism employs an initial population generation method and a local search method to solve the problem of vast definition space. The population ranking selection mechanism employs a population distribution based reference point generation method to solve the problem of population irregular distribution. Finally, a simulation case with the background of a battalion-scaled amphibious campaign is presented. The calculation results verify the rationality of the proposed model and the superiority of the designed algorithm and have some reference value for the operational applications of shipboard helicopters in amphibious operations.

Research on Reliability Growth of Shock Absorption System in Rapid Secure Device of Shipboard Helicopter

Research on Reliability Growth of Shock Absorption System in Rapid Secure Device of Shipboard Helicopter

Supporting shipboard helicopter flight testing with simulation and metrics for predicting pilot workload

Shipboard helicopter operations are much more challenging and complex than land-based operations due to many factors associated with the presence of the ship. To determine those conditions in which safe operations may occur, a First of Class Flight Trial (FOCFT) is conducted for every new ship–helicopter pair. This trial results in a Ship–Helicopter Operating Limit (SHOL) envelope that is used to document operational limits for regular operations. Conducting a FOCFT is a, expensive, and time-consuming task that requires testing all aspects of operations. Modeling and simulation efforts to support shipboard helicopter operations have been ongoing internationally for many years with the intention of de-risking FOCFT and introducing efficiency into the testing process. Canada will be accepting several new ship classes into its fleet over the next two decades. In support of FOCFT for these new ships, modeling and simulation tools are being developed by the National Research Council (NRC) Canada and Defence Research and Development Canada (DRDC) and significant advancements have occurred in the past decade. As part of this work, NRC and DRDC now use a framework and analysis approach that is intended to standardize SHOL testing with the use of modeling and simulation. This paper introduces that framework and gives details on the modeling and simulation tools that can be used to reduce risk and increase efficiency for Canada’s upcoming FOCFTs.

Study on the Tooth Profile Parameters Design Method of Crown Gear Coupling for Helicopter Tail Folding Device

Shipboard helicopter folding technology can increase the number of helicopters parked on board aircraft carriers. Crown gear coupling is the trend in helicopter tail rotor folding technology due to its ability to automatically and quickly engage and disengage helicopter tail rotors. This paper presents a method for the design of tooth parameters for crown gear coupling for folding devices. The model of the relationship between tooth shape parameters and angular displacement of the crown gear coupling and the model of the relationship between angular displacement and shaft line angle of the crown gear coupling were established, respectively, and the basic parameters of tooth shape and modified parameters of the crown gear coupling were designed. The correctness of the design method of the tooth parameters of the crown gear coupling for the folding device was also verified through motion simulation. The results of the study provide a theoretical basis for the design and optimization of crown gear couplings for folding devices.

Experimental investigations into the effect of at-sea conditions on ship airwake characteristics

Shipboard helicopter operations are significantly impacted by the characteristics of the ship airwake which depend on environmental conditions in addition to the ship superstructure. In this paper, the effect of free stream turbulence, wind speed and ship motion on the airwake frequency spectra of two 1:50 scaled ships with stern flight-decks was investigated using wind tunnel testing. Results from a full-scale sea trial are also presented. Using both the wind tunnel and the sea trial data in ship motion conditions corresponding to medium sea states, results showed the ship motion energy was transmitted to the ship airwake at the motion frequencies. For single-frequency ship motions, the energy transfer occurred at the motion frequency only, whereas for more realistic at-sea ship motions with a range of frequency components the energy was transferred at a broadband of frequencies corresponding to the motion frequency range. The way in which realistic motion component effects combine at sea and the amount of energy added to the airwake in realistic conditions is presented. The impact of incoming atmospheric turbulence was also examined.

Simulation Experiment Analysis and Verification of Ship Resonance for Shipboard Helicopter

According to the dynamic characteristics of shipboard helicopter landing, the time-domain load of ship movement on the fuselage under complex sea conditions, the nonlinear dynamic characteristics of rotor damper, and the influence of rotor blade flapping movement and aerodynamic force are considered. The fuselage, rotor lagging damper, blade flapping and lagging movement and aerodynamic model are modeled separately as sub-models, and then the subsystems are integrated according to mechanical principles to finally establish the ship resonance analysis model of helicopter. The method for simulation experiment of ship resonance is put forward. The whole process of ship resonance experiment is dynamically demonstrated by digital simulation technology, which simulates the excitation load on the fuselage caused by the rise and fall and rolling movement of the ship. Actually simulates the lifting collective pitch and conducts periodic excitation by disturbing the control stick. Based on the transient response of the time-domain simulation dynamic system under disturbance, the stability of ship resonance is analyzed. The accuracy of the simulation method is verified through project cases, and the simulation experiment analysis techniques for accurately predicting the unstable boundary of ship resonance are mastered, which provides design and analysis means instead of the experiment that cannot be carried out in model development.

The NATO generic destroyer – a shared geometry for collaborative research into modelling and simulation of shipboard helicopter launch and recovery

The helicopter-ship dynamic interface is the environment above the landing deck of a ship where a helicopter pilot has to control the aircraft while contending with a moving deck and an unsteady airflow known as the ship airwake. Research into understanding this environment has included modelling the airwake using wind tunnel studies and Computational Fluid Dynamics, and has often used the Simple Frigate Shape (SFS), a generic ship geometry representative of a naval frigate. This paper reviews the contribution that the SFS has made to research into the helicopter-ship dynamic interface, and introduces a new ship geometry for future research. The new ship, developed within a NATO Research Task Group, is the NATO Generic Destroyer (NATO-GD), a concept ship with a simplified geometry that is more representative of a modern helicopter-enabled combat ship with a stealthy superstructure. As well as introducing the NATO-GD as a common platform for research, the paper also introduces a number of ship motion profiles to encourage new research that will include the effect of ship motion on the airwake. It is anticipated that future research on a common ship, with prescribed motion and adopting a common helicopter will lead to improved or new modelling methodologies.

Comparative assessment of URANS, SAS and DES turbulence modeling in the predictions of massively separated ship airwake characteristics

An early assessment of the ship airwake characteristics is one of the most challenging tasks associated with the designing of vessels. The design of warship superstructures has traditionally followed the basic polyhedron shape (box type structures) to achieve the desired stealth capability. However, presence of such a box shape bluff superstructure generates massively separated airwake over the ship helodeck region. This airwake results into complex flow phenomena which carry strong velocity gradients in space and time, along with widely varying turbulence length scales. Under such conditions, the launch and recovery of a shipboard helicopter operations are very hazardous. Thus, an accurate assessment of the resultant ship airwake flow phenomena at early design stages is desirable.We present a comparative time-accurate assessment study in order to gain a better understanding of the capability of the Unsteady Reynolds-Averaged Navier-Stokes (URANS), the Scale-Adaptive Simulation (SAS) and the Detached Eddy Simulation (DES) turbulence models in predicting turbulent ship airwake characteristics. Detailed comparisons are conducted with respect to the in-house experimental data. Results show that the DES and SAS produce nearly similar trends of the mean flow properties when compared to the experimental results. However, comparisons of velocity spectra indicate that SAS can resolve the dominant large-scale turbulent flow structures with less computational burden. Further, this study also attempts to compare the variation of mean flow quantities with steady RANS approach in order to quantify the percentage variation between the predictions of the steady and unsteady turbulence modelling approach.

Combined numerical and experimental simulations of unsteady ship airwakes

To aid pilot training for shipboard helicopter operations, computational fluid dynamics (CFD) is increasingly being performed to model ship airwakes. The calculated velocity field data are exported to the flight simulator as look-up tables. In the Canadian context, work to expand ship airwake simulation capabilities for future use in flight simulators is currently being done using the open-source OpenFOAM. The current paper reports on the progress of this work using the simple frigate shape 2 (SFS2), which is a highly simplified ship geometry, to validate the method for low-sea-state (also referenced to as static) cases. By employing delayed detached eddy simulations (DDES), OpenFOAM was able to compute the unsteady ship airwakes well compared to experimental data and other references. After validation, OpenFOAM was applied to the Canadian Patrol Frigate (CPF), a more representative example of a naval vessel. Hybrid structured and unstructured grids were used because of the complexity of the CPF geometry. The agreement between the computed and the experimental results for the static CPF was reasonable, which built a solid foundation supporting further development of simulation for the CPF in motion.

Aeroelastic analysis of a shipboard helicopter rotor with ship motions during engagement and disengagement operations

An aeroelastic simulation of a shipboard helicopter rotor with ship motions during engagement and disengagement operations is investigated to explore the coupled dynamic behavior between the rotor and the ship. A finite element analysis based on a moderate deflection beam model is employed to capture the flap, lag and torsion deflections of the rotor blade. The ship is treated as a six-degree-of-freedom rigid body. By using the Hamiltonʼs principle, system equations of motion are derived based on the generalized force formulation. The responses agree well with the test data of the rotor blade droop stop impact and the transient aeroelastic response of the shipboard teetering model rotor. Parametric investigations illustrate that the ship pitch motion has significant influence on the maximum negative displacement of the blade tip. Additional over 25% increase of the tip deflection can be introduced by the ship pitch motion. The aerodynamic and inertial couplings between the ship motion and the rotor have significantly nonlinear influence on the transient aeroelastic response. Both terms should be taken into account in the coupled helicopter–ship dynamics model.

Development and Experimental Validation of a Shipboard Helicopter On-Deck Maneuvering Simulation

Routine shipboard helicopter operation on many classes of ships requires that helicopters be maneuvered and traversed along the ship deck using installed helicopter securing and handling equipment. This paper describes the derivation, implementation, and validation of a four-degrees-of-freedom mathematical model for predicting and analyzing the behavior of shipboard aircraft under the influence of external aircraft handling forces. The resulting model is suitable both for engineering analysis and training applications. The helicopter model includes the coupled dynamics of the aircraft, landing gear, and optionally steerable or castorable auxiliary wheel assembly. Detailed tire modeling addresses the transient development and release of tire deflection and cornering forces related to yawed and unyawed relaxation lengths as well as direct application of forces by the handling system. Verification and both qualitative and full-scale experimental validation of the model, performed using a number of simple maneuvers to validate specific aspects of the simulation, are discussed. It is shown that the resulting HeliMan simulation captures the underlying dynamics of the shipboard helicopter maneuvering process. Full-scale validation data show that in many cases the simulation is able to reproduce closely the measured data. The effect of tire side loading on longitudinal rolling resistance has been identified as a shortcoming of existing rolling tire models and the most probable cause for differences that exist between simulated and measured results in some validation cases. Nomenclature A = vector representing the accelerations for the two bodies

Autonomous straightening and traversing of shipboard helicopters

AbstractThis paper describes an investigation into autonomous shipboard helicopter maneuvering and traversing operations using the Aircraft/Ship Integrated Secure and Traverse (ASIST) recovery and handling system developed by Indal Technologies, Inc. The ASIST system continuously monitors the aircraft's position and orientation and provides a means of actuation to maneuver the helicopter on deck. This allows the possibility for completely autonomous aircraft securing, maneuvering, and traversing capability. An autonomous maneuvering algorithm offers the potential for automatically selecting the optimal maneuvering sequence and executing it with greater efficiency and reliability than can be achieved by a human operator. The proposed method takes advantage of the position and orientation of the helicopter measured by the existing Helicopter Position Sensing Equipment thereby not requiring additional sensors on the actual helicopter. The paper presents the development and validation of the autonomous straightening and traversing algorithms using a nonlinear on‐deck helicopter maneuvering simulation and the Carleton Experimental Shipboard Helicopter Interface Platform.

Simulation of Pilot Workload for a Helicopter Operating in a Turbulent Ship Airwake

This article describes a recent study in helicopter/ship dynamic interface simulation to examine pilot workload in the presence of a ship's airwake. The flight dynamics model represents a UH-60 helicopter and is based on the GENHEL software. This flight model has been updated to include a high-order dynamic inflow model and gust penetration effects of the time-varying ship airwake. The airwake model is derived from time-accurate computational fluid dynamics (CFD) solutions and provides an appropriately detailed level of fidelity to capture its effect on pilot workload. To simulate pilot control inputs for shipboard approach operations, an optimal control model of the human pilot is developed. The pilot model can be easily tuned to achieve different tracking performances, based on a desired crossover frequency, in each control axis and is designed to operate over a range of airspeeds using a simple gain scheduling algorithm. The pilot model is used to predict pilot workload for shipboard approaches in two different wind-over-deck conditions. Validation studies are conducted using both time and frequency domain analyses. The pilot control input autospectra predicted from the simulation model are compared to those of flight test data from the Joint Shipboard Helicopter Integration Process program. The paper also discusses the application of a stochastic airwake model for more efficient simulation. This new airwake model is derived from the simulation with the full CFD airwake by extracting an equivalent six-dimensional gust vector. The spectral properties of the gust components are then analysed, and shaping filters are designed to simulate the gusts when driven by white noise. It is proposed that the stochastic gust model can be used to optimize the automatic flight control system in order to improve disturbance rejection properties of the aircraft.

What Comes Down Must Go Up: Training Shipboard Helicopter Signaling Skills

This paper discusses the findings from a project to develop a low-cost, effective training solution for shipboard helicopter signaling skills. We identified training objectives, explored training/simulation concepts, identified signal task training requirements, and demonstrated a prototype concept. The training solution includes an innovative prototype Hand Signal Recognition System that utilizes computer vision, a personal computer, a video camera, image acquisition and processing software, and a decision-making algorithm to recognize hand signals in support of signal task training for the Navy Landing Signal Enlisted (LSE) position. The training solution is practical for LSE signal training at the schoolhouse, capable of being deployed aboard ship with some constraints, and cost-effective. The training techniques and hand signal recognition technology developed in this project, and the lessons learned about training shipboard signaling skills, are useful to a variety of training and human factors professionals. The training and technology are relevant to a variety of applications such as emergency medical evacuation, search and rescue, oil platform operations, and shipboard control of unmanned aerial vehicles.

Joint Shipboard Helicopter Operations: Human Factors Issues and Challenges

As part of the US military's Joint Force initiative, non-Navy helicopters are increasingly required to conduct operations on Navy ships. Consequently, shipboard helicopter interoperability has become a requirement for all the military forces. Key shipboard helicopter operations include: landings and takeoffs, launch and recovery support activities, ordnance handling, refueling, and external load operations. These operations involve a variety of helicopter types from the different services on all aviation-capable Navy ships, in different sea states, and under changing visibility and environmental conditions. The requirement for shipboard helicopter interoperability involves several unique human factors issues and poses many challenges. In this paper, we discuss the major issues and challenges as they relate to three broad categories: procedures, training, and compatibility. We identify areas where human factors specialists can make significant contributions to improve the effectiveness and safety of shipboard helicopter operations. In addition, we identify opportunities for future research.