Sea Trial Data Research Articles

Effect of incorrect sound velocity on synthetic aperture sonar resolution

Synthetic aperture sonar (SAS) is an imaging technique to produce centimeter resolution over hundreds-of-meter range on the sea floor, by constructing a virtual aperture whose length automatically adjusts itself for a given focusing range. SAS is near-field acoustic imaging, and this implies that the sound velocity should be accurately estimated for well focused imaging. Otherwise there will be image quality loss. However, sound velocity in the ocean varies with space and time, and there might also be measuring error of CTD (Conductivity, Temperature, and Depth) sensor, so sound velocity error has become one of the limiting factors to improve SAS resolution further. To characterize the effect of sound velocity error quantificationally, the practice SAS resolution is mode as the convolution of ideal seafloor reflectivity function and a phase error function in frequency domain, where the phase error is caused by incorrect sound velocity. Then the SAS resolution parameterized is calculated as a function of the sound velocity measuring error, or sound velocity gradient. It is shown that SAS azimuthally (along track) resolution loss, caused by sound velocity measurement error, increases linearly with detection range. Meanwhile the loss caused by sound velocity gradient increases squarely. It is simulated by considering the synthetic aperture data collection for a particular pixel, and results show that the point scatter response will defocus when the sound velocity measuring error is up to 1% at 200m range, or the sound velocity changes up to 2% over a typical gradient at 200m range, and be worse at a longer range. Furthermore, we demonstrate the influence of sound velocity errors on SAS imagery using a sea trial data and real CTD measurements at South China Sea. We evaluate the degradation in image quality with respect to sound velocity errors by using two plastic balls and a variable seafloor scene, and results also support the accuracy of theoretical conclusions above.

Assessment of multi-target distinguishing using deconvolved conventional beamforming

Multi-target distinguishing based on beamforming is a popular topic in array signal processing. Conventional beamforming as a frequently used method is robust but constrained by the Rayleigh limit. Deconvolved conventional beamforming is a better choice since point scattering function could be derived by deconvolution based on Lucy-Richardson, with narrower beam width and lower sidelobe levels. Besides, the robustness of the conventional beamforming is maintained. In this paper, a new method of combined deconvolved conventional beamforming with Dolph-Chebyshev weights is proposed. The proposed method could overcome the deficit of deconvolved conventional beamforming on low mainlobe of weak target caused by iteration. Firstly, principles of the method are given including conventional beamforming, deconvolved conventional beamforming and the proposed algorithm combined deconvolved conventional beamforming with Dolph-Chebyshev weights. Then, performance of the proposed method for bi-target signals with the equivalent strength, in terms of the effect of signal frequency on distinguishing performance of two closed spaced targets coexisted is analysed. For weak target detection existed strong interference, the superiority of the proposed algorithm is analysed. Finally, proposed method is validated with sea trial data of two ship target noise recorded by a 48-element array.

Research on reverberation characteristics analysis and suppression methods for active continuous detection

Compared with the traditional active detection with monopulse periodic emission mode, active continuous detection has the advantages of large emission duty ratio and continuous acquisition of process information. It can effectively overcome the disadvantages of high false alarm probability, poor environment adaptation ability and low detection efficiency in traditional active detection, so then improving the system detection ability. But active continuous detection is also facing more serious reverberation. In order to further improve capacity, the adaptable reverberation characteristics and detection methods are carried out in this paper. On the basis of theoretical modelling, the relationship between the characteristics of the active continuous detection reverberation and the signal form, the hydrological environment and the emission power are studied. The time frequency characteristics of reverberation and the attenuation law with distance of reverberation are mastered. A reverberation suppression method based on adaptive beamforming of sub-band steered minimum variance algorithm (SSMV) is studied for active continuous detection. Considering signal bandwidth and fast convergence, etc. The relationship between sub-array partition and reverberation suppression ability is analyzed. The validity of reverberation characteristic analysis is verified by simulation, the performance of the method of reverberation suppression is verified by sea trial data processing.

Performance Prediction of a 112m Wave-Piercing Catamaran

The prediction of power required to propel a high-speed catamaran involves the hydrodynamic interactions between the hull surface and the surrounding fluid that may be difficult to compute numerically. In this study model-scale experiments are used as a basis for comparison to full-scale sea trials data measured on a 112m Incat wave-piercing catamaran to predict the full-scale powering requirements from model-scale testing. By completing water jet shaft power measurements on an Incat vessel during sea trials, comparison of these results was made to model-scale test results to provide good correlation. The work demonstrates that the International Towing Tank Conference (ITTC) extrapolation techniques used provide a good basis for extrapolating the data from model-scale to full-scale to predict the power requirements for the full-scale catamaran vessel operating at high Froude Number with water jet propulsion. This provides a useful tool for future designers and researchers for determining the power requirements of a catamaran vessel through model tests.

Estimation of Hydrodynamic Coefficients from Results of Real Ship Sea Trials

Abstract This paper suggests an estimation method for ship’s hydrodynamic coefficients, which is based on the system identification method that calculates an optimum value in a mathematical way. For the purpose of modelling existing ships, this study collects real ship sea trial data as benchmarks. Prior to the optimization, a sensitivity analysis is carried out for easy and effective optimization. The simulation results using optimized coefficients agree well with corresponding benchmarks. Following this, with various trim and draught conditions, this study suggests new estimation formulas that concern all trim and draught conditions. Simulation results applying the estimation formulas are satisfactory in regard to a corresponding benchmark, compared to a result obtained by using an existing regression formula.

Deriving the absolute wave spectrum from an encountered distribution of wave energy spectral densities

The objective of ship motion-based wave spectrum estimation is to provide the distribution of wave energy densities in absolute domain. However, as a ship generally advances relative to the progressing waves, any spectrum estimate inherently dates back to the encounter domain and, consequently, the spectrum estimate must be transformed to absolute domain. In following sea conditions, spectrum transformation from encounter to absolute domain has no unique (mathematical) solution. This article presents an optimisation-based technique to carry out the particular transformation in following sea conditions. The optimisation relies on an object function established using (wave) spectral moments; calculated directly using the estimated encounter-wave spectrum on the one side and by using a parameterised wave spectrum valid in absolute domain on the other side. The simplicity of the transformation technique is a strength in itself as it leads to an insignificant computational effort in the transformation to absolute domain. Equally important, the specific technique proves capable to provide accurate results in the majority of cases, when comprehensive testings with numerically simulated data of following sea conditions are performed. Furthermore, the technique is tested successfully using experimental full-scale sea trials data.

Sequential inversion of self-noise using adaptive particle filter in shallow water.

The geoacoustic inversion based on a horizontal towed array sonar receiving tow-ship noise has demonstrated a promising technique for the parameter inversion in shallow water. In order to characterize the evolution of parameters in the time-varying environment, the adaptive particle filter for the sequential inversion is presented in this paper. The inversion problem is formulated as a dynamic and nonlinear process in the Bayesian framework, due to the fact that the self-noise is recorded sequentially in space and time. To deal with the interparameter correlations and time-varying noise process, the adaptive sequential importance sampling is carried out based on the estimated covariance matrix of parameters that is updated on-line. And the particles are proposed with an adaptive shift to handle the rapidly varying parameters. The tonal components at low frequencies of the self-noise are used in the inversion. The sequential inversion method is verified through the processing of both synthetic data and the sea-trial data in the shallow water environment. The results show that the adaptive particle filter method can achieve a more stable and accurate estimate than successively running global optimization algorithms and can do better than particle filter inversion in a rapidly varying environment.

Parametric bandwidth synthesis for active sonar

This talk presents an unconventional range processing technique applicable to linear FM pulsed and continuous active sonar. Parametric bandwidth synthesis (BWS) involves performing linear-predictive extrapolation using a low-order parametric autoregressive (AR) model to extend the bandwidth of received sonar returns. Synthetically increasing the bandwidth of echoes results in improved range resolution and greater pulse compression gain compared to standard matched filtering. It should be noted that despite the resolution improvement, BWS does not improve ranging accuracy beyond that of the transmitted signal. Using a low-order AR model for BWS enhances specular target returns and discrete scatterers, while not enhancing diffuse multipath, reverberation, and noise returns. BWS performance was verified in simulation and with sea trial data from the Littoral Continuous Active Sonar 2015 (LCAS-15) experiment. Processed results confirm that BWS improves range resolution of the echo repeater target, while suppressing multipath, diffuse reverberation, and noise. Analysis of the practical limits of BWS are also included.This talk presents an unconventional range processing technique applicable to linear FM pulsed and continuous active sonar. Parametric bandwidth synthesis (BWS) involves performing linear-predictive extrapolation using a low-order parametric autoregressive (AR) model to extend the bandwidth of received sonar returns. Synthetically increasing the bandwidth of echoes results in improved range resolution and greater pulse compression gain compared to standard matched filtering. It should be noted that despite the resolution improvement, BWS does not improve ranging accuracy beyond that of the transmitted signal. Using a low-order AR model for BWS enhances specular target returns and discrete scatterers, while not enhancing diffuse multipath, reverberation, and noise returns. BWS performance was verified in simulation and with sea trial data from the Littoral Continuous Active Sonar 2015 (LCAS-15) experiment. Processed results confirm that BWS improves range resolution of the echo repeater target, while suppr...

Numerical study of propulsion system performance during ship acceleration

Ship acceleration manoeuvre is important in terms of safety and engine performance. Head seaways are one of the most challenging conditions for the ship propulsion. A detailed simulation of the propulsion system's transient response during dynamic acceleration in harsh conditions can result in a thorough investigation of the engine performance, a better management of control system and the monitoring of engine limiters application in real conditions. For the overall propulsion system performance assessment during ship acceleration, a computational tool has been developed that consists of a number of sub-systems for the simulation of engine, turbocharger, propeller components and their interaction. The developed tool has been first validated against available shop and sea trials data and subsequently it has been tested for the simulation of propulsion system performance during acceleration in dynamic conditions. Based on the simulation results, a sensitivity analysis has been performed for the investigation of the governor control unit limiters that apply on the engine during acceleration. As a result, the effect of engine governor limiters on the overall engine and hydrodynamic performance of the ship during acceleration is quantified and discussed.

Multi-Sensor, Adjustable-Period Integrated Navigation Method Based on Multi-Stage Signal Trigger for Underwater Vehicles

For underwater vehicle navigation sensors, the output signal periods are different and time-varying. This would result in the decline of precision, and even wrong results. To deal with the problem, this paper puts forward a multi-sensor, adjustable-period integrated navigation method based on multi-stage signal trigger. This method considers the valid signals of a Doppler Velocity Log (DVL) as the trigger signals of a Dead-Reckoning (DR) navigation program. It also considers the valid signals of an acoustic positioning sensor as the trigger signals of the integrated navigation program. In this method, it can adjust the filtering period in real time. According to the time label of signals, this method actualises the time-space alignment of sensors. Then it conducts DR navigation and integrated navigation. The method can not only utilise the valid signals of each sensor sufficiently but also fuses the data based on time-space alignment efficiently. Sea trial data shows that when the output signal periods are certain, navigation precision of the method in this paper is better than a non-adjustable-period filtering method. Moreover, in poor conditions, it can also attain a high precision.

Propulsion control strategies for ship emergency manoeuvres

This work deals with the propulsion control aspects relating to some of the most critical emergency manoeuvres of a ship: slam start and crash stop. In these particular situations a very important role is played by the automation system that has to manage the whole propulsive chain (i.e. main engine, mechanical transmission and propeller) in a safe and efficient way. With regard to this, a simulation based design methodology is adopted to develop and test new control schemes for ship propulsion. The proposed control layout is applicable to any type of propulsion systems equipped with controllable pitch propellers, since it is mainly based on the automatic adjustment of the propeller pitch. Thus the desired performance requirements are met through adaptive control strategies able to address the complex issues of slam start, crash stop and similar stressful manoeuvres. The adaptivity of the automation process to several critical propulsive conditions reduces significantly the number of the control parameters to be estimated, as recently demonstrated by the automation design of a new twin-screw ship. For this application, the comparison between simulation results and sea trials data is finally shown for validation design purposes.

Design and validation of an unmanned surface vehicle simulation model

In this paper we present a multiphysics simulation model of Halcyon, an autonomous unmanned surface vehicle (USV). The simulation model presented in this paper has been developed to rapidly progress the design, development and validation of Halcyon’s autonomy management system, particularly in challenging sea conditions. Using simulation for this purpose enables extensive testing across the full environmental operating envelope of the vessel, hence greatly reducing the need for real-world sea-trials. The simulator is comprised of a novel and comprehensive sea-surface wave environment model, a six degree of freedom nonlinear unified seakeeping and manoeuvring boat dynamics model, an actuation dynamics model, an autopilot and an interface with an autonomy management system. Results are presented that show good agreement between real-world and simulated sea-trials data.

Optimal trim control of a high-speed craft by trim tabs/interceptors Part I: Pitch and surge coupled dynamic modelling using sea trial data

A pitch and surge coupled dynamic model of a high-speed craft is not available for dynamic trim control applications in the literature. The existing fluid-structure interaction models of a high-speed craft are not adequate for simulations and control applications, since they require a great deal of computation time, for example more than 20–40s depending on a vessel particulars. Hence, in this work, we aimed to obtain a dynamic model of a high-speed craft for surge and pitch motions. Then the obtained model will be utilized to design an automatic controller which adjust the command signal on a high-speed craft to increase fuel efficiency, safety and comfort of passengers in a vessel. The coupled pitch and surge motion of a high-speed craft with trim tabs/interceptors was modelled by using full scale sea trial data. The linear parametric modelling using System Identification (SI) Methods and Artificial Neural Network (ANN) modelling were carried out and the comparisons of both the training and validation results are given. High correlation coefficients and low average values of absolute errors in surge and pitch dynamics were obtained by using ANN Method. The ANN model can be improved for further control designs on a marine vessel's operations.

On-board measurement techniques to quantify underwater radiated noise level

Cavitating ship propellers are known to be the dominant noise source contributing significantly to the underwater radiated noise (URN) level. Innovative measurement methods using on-board devices need to be further investigated as they offer a serious alternative to traditional methods in terms of cost-efficiency and practicality. This exploratory study combined simultaneous on- and off-board noise and vibration measurements with cavitation views captured by digital photography and high speed cameras.Comprehensive full-scale trials were conducted on Newcastle University’s research vessel, The Princess Royal, in the framework of the FP7-EU project SONIC. On-board data were captured from multiple measurement systems (including. hull pressure sensors, accelerometers, optical devices, shaft strain gauges) provided by SONIC project partners CETENA, Wärtsilä , University of Southampton and Newcastle University. A new semi-empirical correlation method based on cavitating propeller pressure fluctuation and the URN level was established. Results offer clear evidence of successfully estimating URN with on-board measurements up to the middle frequency region where the blade passing fundamental and low harmonic frequencies occur. These illuminating insights reported in this paper provide valuable benchmark sea trial data in full scale.

잔향 환경에 강인한 능동 소나 펄스의 분해능 특성 연구

ABSTRACT: Many researches for improving detection performance in the reverberation environment have been conducted in active sonar systems. Especially the type of active pulse makes an impact on the detection performance in the reverberation environment. Thus, this paper describes the detection performance of PTFM (Pulse Trains of Frequency Modulated waveform), Costas, and Geometric Comb pulses which are known for their outstanding performance against the reverberation. Sea trial data of those pulses was analyzed and it was figured out that the range resolution of PTFM pulse was deteriorated by its sub-pulses. Costas pulse showed performance degradations of the doppler resolution by multipath signals. Geometric Comb pulse showed the best doppler resolution.Keywords: Active sonar, PTFM, Costas, Geometric comb, Range resolution, Doppler resolution PACS numbers: 43.60.Bf, 43.30.Vh†Corresponding author: Eui Cheol Jeong (jec528@add.re.kr) P. O. Box 18, Jinhae-gu, Changwon, Gyeongnam 51678, Republicof Korea(Tel: 82-55-540-6537, Fax: 82-55-542-3737)

Application of Particle Filter using TA Bearing Measurements

Background/Objectives: An Algorithm, the Particle filter, is proposed for implementing the bearings only Torpedo Motion Analysis (TMA). The required density of the state vector is represented as a set of random samples, which are updated and propagated by the algorithm. The method is not restricted by assumptions of linearity or Gaussian noise. Methods/Statistical analysis: The particle filter is combined with Modified Gain Bearings Only Extended Kalman Filter and the results are compared with that of Extended Kalman Filter or Unscented Kalman Filters. Findings: Almost similar performance is obtained. The algorithm is applied to track a torpedo using measurements available from towed array. Application/Improvements: The results in simulation mode and with sea trial data are presented.

Method for determining initial position of dead reckoning system of underwater vehicle

According to the characteristics of underwater navigation sensors,the method for determining the initial position based on dead reckoning( DR) trajectory translation strategy in the initial period of position was proposed to improve the accuracy of the initial position of DR system. This method combined the features of DR system and hydroacoustic navigation system,and got the optimal trajectory under the constraints of certain movement trends by translating DR trajectory to calculate the initial position. One real sea trial data was used to analyze this method. The results show that the position error of this method is 60. 2% and 77. 2%of the error of the average method and the least squares fitting method. The application of this method can reduce the position error of DR system and improve the stability of DR / hydroacoustic integrated navigation system.

A Multi-Model EKF Integrated Navigation Algorithm for Deep Water AUV

A novel integrated navigation algorithm, multi-model EKF (Extended Kalman Filter) integrated navigation algorithm, is presented in this paper for the deep water autonomous underwater vehicle. When a deep water vehicle is performing tasks in the deep sea, the navigation error will accumulate over time, if it relies solely on its own inertial navigation system. In order to get a more accurate position for the deep water vehicle online, an integrated navigation system is constructed by adding the acoustic navigation system. And because it is difficult to establish the kinematic model and the measurement model accurately for the deep water vehicle in the underwater environment, we propose the Multi-model EKF integrated navigation algorithm, and estimate the measurement errors of beacons online. Then we can estimate the position of the deep water vehicle more accurately. The new algorithm has been tested by both analyses and field experiment data (the lake and sea trial data), and results show that the multi-model EKF integrated navigation algorithm proposed in this paper significantly improves the navigation accuracy for the deep water vehicle.

Underwater terrain positioning method based on least squares estimation for AUV

To achieve accurate positioning of autonomous underwater vehicles, an appropriate underwater terrain database storage format for underwater terrain-matching positioning is established using multi-beam data as underwater terrainmatching data. An underwater terrain interpolation error compensation method based on fractional Brownian motion is proposed for defects of normal terrain interpolation, and an underwater terrain-matching positioning method based on least squares estimation (LSE) is proposed for correlation analysis of topographic features. The Fisher method is introduced as a secondary criterion for pseudo localization appearing in a topographic features flat area, effectively reducing the impact of pseudo positioning points on matching accuracy and improving the positioning accuracy of terrain flat areas. Simulation experiments based on electronic chart and multi-beam sea trial data show that drift errors of an inertial navigation system can be corrected effectively using the proposed method. The positioning accuracy and practicality are high, satisfying the requirement of underwater accurate positioning.

선박용 디젤 기관의 순간 각속도와 토크 변동에 관한 연구

The demand for shipboard energy management is expected to gradually increase based on ship energy efficiency management plans (SEEMPs), which have been in use since January 1, 2013. Therefore, the fuel consumption of the main engine, which occupies the greatest portion of the energy used, along with elements related to the engine power, should be strictly monitored. There are many different methods for indicating the engine power. However, this study performed an experiment to monitor the status of a ship’s engine power in real time using an encoder and a proximate switch, which are economical to purchase and easy to install. In the experiment, the angular velocity during one cycle of a two-stroke low-speed engine was measured, and the measured data were converted to the torque fluctuation. The angular velocity during an abnormal firing condition in the cylinder was also measured, and the torque fluctuation as a result of a misfire was considered. The results were compared with sea trial data to determine the reliability. In this study, the status of the engine power was determined using the torque fluctuation of the main engine in an operating ship.