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"Ship propulsion Simulation methods."
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Marine propulsion simulation : methods and results
This book describes the main steps in developing a multi-physics simulation platform, representing the dynamics of a twin screw ship in six degrees of freedom. The interaction between the propulsion system and automation effects is also considered. The presented simulation methodology can be used in the preliminary ship design to analyse propulsion and control system action. Further applications can concern design optimization and crew training.
Book
Integrating Computational Fluid Dynamics for Maneuverability Prediction in Dual Full Rotary Propulsion Ships: A 4-DOF Mathematical Model Approach
To predict the maneuverability of a dual full rotary propulsion ship quickly and accurately, the integrated computational fluid dynamics (CFD) and mathematical model approach is performed to simulate the ship turning and zigzag tests, which are then compared and validated against a full-scale trial carried out under actual sea conditions. Initially, the RANS equations are solved, employing the Volume of Fluid (VOF) method to capture the free water surface, while a numerical simulation of the captive model test is conducted using the rigid body motion module. Secondly, hydrodynamic derivatives for the MMG model are obtained from the CFD simulations and empirical formula. Lastly, a four-degree-of-freedom mathematical model group (MMG) maneuvering model is proposed for the dual full rotary propulsion ship, incorporating full-scale simulations of turning and zigzag tests followed by a full-scale trial for comparative validation. The results indicate that the proposed method has a high accuracy in predicting the maneuverability of dual full-rotary propulsion ships, with an average error of less than 10% from the full-scale trial data (and within 5% for the tactical diameters in particular) in spite of the influence of environmental factors such as wind and waves. It provides experience in predicting the maneuverability of a full-scale ship during the ship design stage.
Journal Article
Simulation strategy of the full-scale ship resistance and propulsion performance
The ship powering performance can be predicted based on model tests or simulations. However, differences exist between the full-scale ship performance and extrapolated model data. Therefore, research on full-scale ship performance simulation has important scientific significance and engineering value. This study used the REGAL general cargo vessel to perform full-scale ship resistance and self-propulsion simulations for various grid numbers, time step sizes, and wall Y+ values and compared the calculation and empirical results. The resistance components, waveform, Courant-Friedrichs Lewy (CFL) number, pressure field, and wake flow field of various resistance simulation conditions were analysed. The wall Y+ value was observed to affect the capture of boundary layer flow, ship pressure field evolution, and waveform, which subsequently affect the ship resistance. A Y+ value within 200 was considered to be appropriate when simulating the powering performance of a full-scale ship. The waveform evolution was significantly affected by the time step size, which should meet the requirement that the CFL number on the free surface is less than 1. When simulating the self-propulsion of a full-scale ship based on sliding mesh, the CFL number on the interface should also be less than 1. Additionally, to obtain the correct propeller excitation force, it was recommended that the time step size be maintained below 1°/step (0.000076 L
PP
/v).
Journal Article
System Identification and Robust Control Method for Magnetic Bearings in Ship Propulsion Shaft Systems
In the field of rotating machinery, such as marine propulsion shafting, magnetic bearing-supported propulsion systems have garnered significant attention due to their non-mechanical contact advantages. To address the problem that the design of magnetic bearing controllers, based on theoretical models, neglects the dynamic characteristics of practical components like power amplifiers and displacement sensors, making it difficult to achieve ideal performance in practical applications, this paper proposes a control method for Hybrid Magnetic Bearings (HMBs) that combines a time-domain identification model with robust control. The method first models the power amplifier, HMB, and displacement sensor as an equivalent single system and obtains its high-precision transfer function model by performing system identification on its time-domain data using the least squares method. Based on this foundation, a PID controller is designed using the loop-shaping method to enhance the system’s robustness and control performance. Both simulations and experiments on an HMB test rig confirmed the controller’s effectiveness. The system showed excellent levitation, dynamic stability, and disturbance rejection, with experimental results closely matching simulations. The experimental results are consistent with the simulation results. This method provides a practical and feasible technical approach for enhancing the control performance of magnetic bearing-supported propulsion shafting.
Journal Article
Application of virtual disk propulsion model for self-propelled surface ship in regular head wave
The advanced numerical methods with new model and scheme, to reduce the requirements of the computation times and computer resources for seakeeping predictions, are urgent according to the International Towing Tank Conference seakeeping committee. In the present study, different propulsion models are used to implement the seakeeping performance simulations of a self-propelled surface ship sailing in waves. Both the accuracy and the computational cost are investigated. Four different propulsion models for self-propelled surface ship simulation including the discretized propeller model, the descriptive body-force method, the Osaka University method and the modified Osaka University method were studied. Uncertainty analyses are conducted separately for hull, propeller in calm water and ship motions in waves. Numerical simulations in calm water and waves are carried out to obtain the ship attitudes, resistance, motion responses and added resistance. Self-propulsion simulations in calm water and waves are performed to obtain the propeller rotation speed, the ship motions and the speed loss. Four wavelengths (
λ
/
L
pp
=
0.65
,
0.85
,
1.15
,
1.95
) of regular head waves with a wave steepness of 1/60 are considered according to the benchmark case of the Tokyo 2015 Computational Fluid Dynamics Workshop. The self-propulsion simulation results of the thrust, torque, ship motions and speed loss using different propulsion models have been compared to each other. It can be found that all the differences of speed loss are less than 2% and these of heave and pitch amplitudes are less than 6.13%. The modified Osaka University method, which provides numerical results closest to those of the discretized propeller model, is an alternative method for ship self-propulsion simulations in waves.
Journal Article
Simulation of a Hybrid Propulsion System on Tugboats Operating in the Strait of Istanbul
The implementation of hybrid propulsion systems in vessels has gained prominence due to their significant advantages in energy efficiency and their reduction in harmful emissions, particularly during low engine load operations. This study evaluates hybrid propulsion system applications in two different tugboats, focusing on fuel consumption and engine load across eight distinct operational scenarios, including Istanbul Strait crossings and towing and pushing manoeuvres. The scenarios incorporate asynchronous electric motors with varying power ratings, lead-acid and lithium iron phosphate batteries with distinct storage capacities, and photovoltaic panels of different sizes. The highest fuel savings of 72.4% were recorded in the second scenario, which involved only towing and pushing operations using lithium iron phosphate batteries. In contrast, the lowest fuel savings of 5.2% were observed in the sixth scenario, focused on a strait crossing operation employing lead-acid batteries. Although integrating larger-scale batteries into hybrid propulsion systems is vital for extended ship operations, their adoption is often limited by space and weight constraints, particularly on tugboats. Nevertheless, ongoing advancements in hybrid system technologies are expected to enable the integration of larger, more efficient systems, thereby enhancing fuel-saving potential.
Journal Article
Effects of non-sinusoidal pitching motion on the propulsion performance of an oscillating foil
Numerical simulations have been used in this paper to study the propulsion device of a wave glider based on an oscillating hydrofoil, in which the profile of the pitching and heaving motion have been prescribed for the sake of simplicity. A grid model for a two-dimensional NACA0012 hydrofoil was built by using the dynamic and moving mesh technology of the Computational Fluid Dynamics (CFD) software FLUENT and the corresponding mathematical model has also been established. First, for the sinusoidal pitching, the effects of the pitching amplitude and the reduced frequency were investigated. As the reduced frequency increased, both the mean output power coefficient and the optimal pitching amplitude increased. Then non-sinusoidal pitching was studied, with a gradual change from a sinusoid to a square wave as the value of β was increased from 1. It was found that when the pitching amplitude was small, the trapezoidal pitching profile could indeed improve the mean output power coefficient of the flapping foil. However, when the pitching amplitude was larger than the optimal value, the non-sinusoidal pitching motion negatively contributed to the propulsion performance. Finally, the overall results suggested that a trapezoidal-like pitching profile was effective for the oscillating foil of a wave glider when the pitching amplitude was less than the optimal value.
Journal Article
A Review of Research on the Vacuum Plume
Chemical and electrical thrusters are generally utilized to control the attitude and orbit of spacecraft in aerospace. When they are firing, the exhaust expands into the vacuum environment, known as the vacuum plume. The plume flow can collide with spacecraft surfaces due to sufficient expansion, exerting adverse effects on the spacecraft, such as heating load, force/torque, contamination, and sputtering. Therefore, it is vital to investigate the vacuum plume to ensure the function and safety of the spacecraft. This review introduces the ground test and numerical simulation methods of the vacuum plume for chemical and electrical thrusters. The vacuum environment, invasive, and non-invasive (optical) measurements of the ground test are concluded. Numerical simulation of plume flow and its effects is exampled. The hybrid CFD-DSMC (computational fluid dynamics and direct simulation Monte Carlo) algorithm is employed to simulate the gas plume flow spanning continuum and transitional and free molecular flow regimes for chemical thrusters. By contrast, the PIC-DSMC (particle-in-cell plus direct simulation Monte Carlo) algorithm is used for the plasma plume flow containing charged particles exhausted by electrical thrusters. Moreover, the topics of fast prediction of the vacuum plume, plume–surface interaction, and plume–Lunar/Mars regolith interaction are proposed for future research.
Journal Article
Research on the Detection Method of Excessive Spark in Ship DC Motors Based on Wavelet Analysis
In order to analyze and solve the problem of excessive commutation spark of DC motor in ship electric propulsion system, which leads to a decrease in output power and low torque, this paper first establishes a mathematical model of the ship DC motor, builds its simulation model based on the mathematical model, and conducts simulation verification. Secondly, the Cassie arc model is introduced to model the commutation spark, and the Cassie arc model is connected in series in the armature winding of the DC motor to achieve virtual injection of excessive spark fault of the DC motor. Finally, the Fourier transform and wavelet analysis are used to process the data of the armature winding current and excitation current of the DC motor. The simulation results show that when an arc fault occurs in the DC motor, the ripple coefficient of the armature current and excitation current will increase, and the high-frequency component will increase. DB8 is an adopted wavelet function that decomposes the armature current and excitation current six times, and calculates the energy changes before and after the fault of each decomposed signal layer. It is found that without considering the approximate components, the D4 layer wavelet energy of the armature current and excitation current has the largest proportion in the detail components. The D1, D2, and D3 layers’ wavelet decomposition signals of the armature current and excitation current have significant energy changes; that is, the energy increase in the middle and high frequency parts exceeds 20%, and the D3 layer wavelet decomposition signal has the largest energy change, exceeding 40%. This can be used as a fault characteristic quantity to determine whether the DC motor has a large spark fault. This study can provide reference and guidance for online detection technology of excessive sparks in ship DC motors.
Journal Article
Numerical Research on Hull–Propeller–Rudder–Ice Interaction of Full-Scale Polar Transport Ship in Brash Ice Channel
A strong nonlinear ice load has a significant impact on the resistance and power demand of polar transport ships under different drafts in brash ice channels. In this study, the CFD-DEM coupling method is used to investigate the self-propulsion performance of a full-scale polar transport ship in brash ice channels. The interactions between the full-scale polar transport ship, propeller, rudder, and brash ice are effectively simulated. First, the hydrodynamic performance of an open-water propeller is tested, and it is found that the numerical errors of efficiency and the experimental result are less than 8%. Then, the ice resistance, total thrust, effective power, delivered power, and propulsive efficiency of the polar transport ship under different draft conditions are studied, and the results are in good agreement with those of the self-propulsion model tests in the brash ice channel. Through a numerical simulation of self-propulsion in the brash ice channel, self-propulsion points under different drafts and brash ice thicknesses are obtained. It is found that the propeller rotation speed is closely related to the draft depth. Finally, experiments and numerical simulations of the total ice resistance are carried out under different brash ice thicknesses, and the results are consistent with those of the empirical formulas. The accuracy of the three empirical formulas under different drafts is compared. This research work determines the resistance, power demand, and propulsive efficiency of a polar transport ship under given ice conditions and speeds, as well as the self-propulsion points under different ice thicknesses. It is of great significance for the control of ships in polar navigation.
Journal Article