Numerical Simulation methods of RANS and LES have been widely used to simulate the velocity field induced by propellers. In order to combine advantages of quick computation time from RANS and ...detailed information from LES, this paper innovatively proposed a customized data-driven encoding-decoding network to achieve mapping from RANS results to LES results. Firstly, an encoding-decoding neural network model was constructed to extract features from RANS/LES for propeller wake. The extracted features with additional information concatenation during the encoding steps were then used to reconstruct the original samples and got a reconstruction error of 1%, which proved the effectiveness of feature extraction ability of the proposed model. The proposed model was then used to map directly from RANS to LES data with a better performance compared to traditional PCA feature extraction and mapping method. Afterwards, the proposed network was applied to two more RANS to LES mapping scenarios to validate the generalization ability. The model could map a coarse-grid RANS to LES of ship propeller with less than 9% MSE error. Similarly, mapped LES of nominal wake was 98% more alike the original LES samples than the RANS samples. As a result, the proposed model could be used either to extract features for potential feature-based performance prediction, or as a quicker method for detailed simulation for propeller wake and nominal wake, thus expedites the design process of ship design.
•Proposed a customized Encoding-Decoding network for feature extraction and mapping of simulated ship propeller wake field.•The feature extraction ability of the proposed network was better than PCA or SVD.•The proposed network could map from the RANS results to LES results of propeller wake with sufficient details in seconds, thus reduce the time for LES calculation.•The proposed network could map a coarse wake or a nominal wake with reasonable precision and robustness as well.
This paper evaluates the propeller wake characteristics of the benchmark ship propeller INSEAN E779A using large eddy simulations and identifies instability mechanisms that lead to wake breakdown. ...The effects of propeller blade loading on wake stability are considered by conducting simulations at different advance coefficients (J = 0.85, J = 0.65 and J = 0.45). The hydrodynamic results capture the propeller wake vortical structures and flow features from the onset and evolution of the instability to the far wake. The simulation results are verified and validated against experimental measurements from the literature. A new instability mechanism concerning mutual interaction among adjacent helical vortex sheets in the transition region is identified. Further, the formation of short wave instabilities in the vortex filaments is found to be initiated by the same mutual interactions among sheets. Lastly, it is shown that interaction of sheets with the preceding tip vortex induces the onset of tip vortical filaments breakup, mutual-interaction and long wave instability.
•Ship propeller wake geometry and flow field is described to new details using LES.•Gaps in fundamental physics related to wake instability mechanisms are identified.•A new phenomenon related to the helical vortex sheets interaction is observed.•It is shown that this interaction triggers the wake's transition to instability.•Sheets interaction with previously shed tip-vortex swells instabilities to wake end.
In the present paper, we study the hydrodynamic noise generated by a ship propeller in open sea conditions. We use Large Eddy Simulation for the hydrodynamic field whereas the acoustic field is ...reconstructed by applying the advective form of the Ffowcs-Williams and Hawkings equation. A dynamic Lagrangian model is adopted for the closure of the subgrid-scale stresses and a wall-layer model allows to skip the resolution of the viscous sub-layer. The acoustic equation is formulated in the integral form and solved through direct integration of the volume terms. The propeller herein considered is a benchmark case, whose fluid dynamic data are available in the literature. A grid of about 3 ×106 cells is able to reproduce accurately both integral quantities like thrust and torque over the propeller, and turbulence propagating downstream in the wake.
Different noise generation mechanisms are investigated separately. The linear terms give rise to a narrow-band noise spectrum, with a mean peak at the blade frequency and other peaks at frequencies multiple of the rotational one. The non-linear quadrupole term reveals a broad band noise spectrum; the shaft vortex provides the largest contribution to the non-linear part of the noise propagated in the far field.
•WLES gives accurate results, both for integral quantities and for turbulent field.•The advective FWH is solved using a direct volume integration.•The linear contribution gives narrow-band noise at the blade frequency.•The non-linear contribution is mainly associated with the shaft vortex.•The non-linear contribution gives broadband noise at low frequencies.
This paper explores the application of Physical-informed Neural Networks (PINNs) for reconstructing ship propeller wake fields, introducing a novel approach known as self-adaptive loss balanced ...physics-informed neural networks (LB-PINNs). It can enhance the accuracy of the reconstruction process by incorporating an adaptive weight to balance the loss term within the network. The initial sections of the paper present the foundational principles and framework of PINNs. To validate the efficacy of PINNs in solving partial differential equations, the well-known Burgers equation is applied and then these results with those obtained through LB-PINNs are compared. This comparative analysis highlights the superior performance of LB-PINNs in achieving accurate predictions. Moving forward, the open water characteristics of the KVLCC2 propeller are simulated by using computational fluid dynamics (CFD) software STAR CCM+, and the flow field information of the KVLCC2 propeller in open water is obtained. This simulation provides crucial flow field information, forming the basis for constructing a training sample set to train the neural network. The trained PINN and LB-PINN are used to infer approximate solutions of the governing equations at arbitrary time and space coordinates. The velocity and pressure distributions obtained by PINN and LB-PINN were compared with those simulated by STAR CCM+. The results confirm the applicability of both PINN and LB-PINN in the reconstruction of propeller wake fields, with LB-PINN demonstrating superior performance.
•A novel method for solving governing differential equations of fluid mechanics based on LB-PINN is introduced.•LB-PINN's adaptive weight balances the loss term, reducing mean square error by an order of magnitude compared to PINN.•Sparse numerical simulation data suffices for LB-PINN training, enabling ship propeller wake reconstruction.•Comparing flow field reconstructions using PINN, LB-PINN, and CFD shows LB-PINN's validity and accuracy.
The dynamic analysis of underwater towed systems is challenging considering complex flow disturbances such as ship propeller wakes. This paper proposed a new fully-coupled three-dimensional ...hydrodynamic model for the dynamic analysis of an underwater towed system under complex flow disturbances. The hydrodynamic characteristics of the towed vehicle and the flow field behind the towing ship and propeller were simulated using computational fluid dynamics (CFD). The fluid forces on the towing cable were determined by combining the Morison formula and the CFD method. A dynamic analysis of an underwater towed system in a towing ship propeller wake under typical uncontrolled towing and depth regulation operations was conducted. The simulation results indicated that the proposed method was reasonable. Moreover, the time-averaged position and posture of the underwater towed system and its hydrodynamic characteristics vary with the rotation rate of the ship propeller in uncontrolled towing operation under a fixed towing speed. Furthermore, the fluid forces on the towing system and the cable tension in the depth regulation operation changed more drastically than in the uncontrolled towing operation. The proposed method can be easily extended to simulate other marine cable systems.
•A hydrodynamic model for dynamic analysis of underwater towed system under complex flow disturbances was proposed.•Real-time three-dimensional dynamic responses of underwater towed system in ship propeller wakes were investigated.•The proposed method was demonstrated using towing experiments.•The control system exhibits robust nature in ship propeller wakes.
Acoustic analysis of ship propeller using CFD Sravani, Vemuri; Srinivas Prasad, S.; Ravi Teja, M. ...
International journal of ambient energy,
12/31/2022, Volume:
43, Issue:
1
Journal Article
Peer reviewed
The acoustic levels generated by ship propeller are very much important in the design and development of the propeller from stealth technology point of view. The KCS SVA 1193 model of propeller ...geometry has been taken from the literature. The complex 3D geometry of the propeller is created using CATIAV5. The propeller geometry, surrounded by the sea water, has been considered by creating the fluid domain around the propeller. The acoustic levels, generated by the propeller, are computed using commercial software package ANSYS FLUENT. The unstructured mesh is generated in the fluid domain. The k-∈ standard turbulence model is selected to capture the viscous effects. The velocity at the inlet, pressure at outlet and moving frame of reference boundary conditions are used for computational analysis. Broadband noise model is used to capture the effects of the acoustic waves. The thrust and torque have been estimated for the chosen propeller. In this analysis, the acoustic power level of the propeller is captured and the non-dimensional coefficients are calculated.
•Detected VIV-induced structural resonance, a main cause of ship propeller damage.•Proposed a CNN-based detection algorithm using vibration signals inside the hull.•Generated large data with the same ...pattern as measurement data using mode superposition.•Verified with test data from a test rig and ship vibration measurement data.
Vortex-induced vibration (VIV) resulting lock-in phenomenon which is the vibration frequency of the structure immersed in a fluid is locked in its resonance frequencies within a flow speed range is a potential cause of vibration fatigue and/or singing of the propellers of large merchant ships. A deep learning-based indirect VIV detection algorithm that works by vibration measurement data of a hull structure instead of a propeller during the sea trial phase is proposed in this study. RPM-frequency representations of the vibration signal by stacking the vibration frequency spectrum relative to various propeller RPM's, so-called waterfall chart of 2-dimensional data like an image, are measured and fed into the proposed convolutional neural network (CNN) architecture for VIV detection i.e. VIV frequency and RPM range. To generate the large data set, artificial data looks real, for learning, a method based on the modal superposition method instead of time-consuming fluid-structure interaction analysis is proposed. 10k set data for training, 1k set for hyper-parameter tuning, and 1k set for the test were generated. After the training, it showed a diagnosis success rate of 82% for the test set. To test the proposed VIV detection algorithm, investigations were carried out in a laboratory on a small-scale ship propulsion system designed in such a way that the vortex shedding frequency and the underwater natural frequency match each other. The proposed VIV detection algorithm was tested using the structural vibration signals measured at stationary structures in the air instead of the rotating propeller immersed in water. Lastly, the validity of the proposed algorithm was tested using the structural vibration signal measured at the hull structure of a crude oil carrier in which a propeller singing occurred during her sea trial.
Maritime transport is the most energy-effective mode to move large amounts of goods around the world. Hauling cargo via waterway produces an enormous quantity of greenhouse gas emissions. Vessel fuel ...efficiency directly influences ship emissions by affecting the amount of burnt fuel. Optimizing ships operating in waves rather than in calm water conditions could decrease the fuel consumption of vessels. In particular, ship propellers are traditionally designed neglecting dynamic conditions such as time-varying wake distribution and propulsion factors, propeller speed fluctuations, ship motions, and speed loss.
The effect of waves on the propeller performance can be evaluated using both a quasi-steady and a fully-unsteady approach. The former is a fast computational approximation method based on the assumption that the ratio of propeller angular frequency to wave encounter frequency is sufficiently large. The latter provides a complete representation of the propeller dynamics, but it is computationally expensive.
The purpose of this paper is to compare the propeller performance in the presence of waves using the quasi-steady and the fully unsteady approach. This analysis is performed by observing the differences in unsteady propeller forces, cavitation volume, and hull pressure pulses between the two approaches. The full-scale KVLCC2 propeller is utilized for the investigation.
Results show a good agreement between the quasi-steady and the fully-unsteady approach in the prediction of the temporal mean and the fluctuation amplitude of KT and KQ, the cavity volume variation, and the hull pressure pulses. Therefore, for the considered operating conditions, the quasi-steady approach can be used to compute the propeller performance in waves.
