SPS TURBULENT MODELING OF HIGH SPEED TRANSOM STERN FLOW

Transom stern flow is a complicated fluid flow phenomenon especially at high speed regime. Therefore, various authors have studied the transom stern flow, both numerically and experimentally. Smoothed Particle Hydrodynamics method can be considered as a good choice for simulation of nonlinear physics related to the transom flow. Accordingly, SPH as a meshless, Lagrangian, and particle method is presented in this article and SPS turbulent model is also included for more accurate solution. For density modification, a second order density filter scheme is employed. For validation of numerical setup, several draft based Froude numbers are considered and it is shown that SPH solution is in good agreement with available experimental data. Furthermore, three longitudinal Froude number are investigated for high speed transom flow simulation. High speed cases are compared with Savitsky’s formula and it is observed that at high speeds, SPH solutions are also reasonable

SPS TURBULENT MODELING OF HIGH SPEED TRANSOM STERN FLOW

Transom stern flow is a complicated fluid flow phenomenon especially at high speed regime. Therefore, various authors have studied the transom stern flow, both numerically and experimentally. Smoothed Particle Hydrodynamics method can be considered as a good choice for simulation of nonlinear physics related to the transom flow. Accordingly, SPH as a meshless, Lagrangian, and particle method is presented in this article and SPS turbulent model is also included for more accurate solution. For density modification, a second order density filter scheme is employed. For validation of numerical setup, several draft based Froude numbers are considered and it is shown that SPH solution is in good agreement with available experimental data. Furthermore, three longitudinal Froude number are investigated for high speed transom flow simulation. High speed cases are compared with Savitsky’s formula and it is observed that at high speeds, SPH solutions are also reasonable

Calm-water performance of a boat with two swept steps at high-speeds: Laboratory measurements and mathematical modeling

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An attempt to predict planing hull motions using machine learning methods

Designing a high-speed craft for better seakeeping in waves can contribute significantly to higher safety and human comfort. Early in the design process, mathematical models such as the 2D+T method are commonly used, while high-fidelity computational fluid dynamics (CFD) and experimental models are used later in the process. Some of the limitations of such models are that they are not fast enough to be used in the ship's system for real-time monitoring or to develop a digital twin. Recently, machine learning methods have demonstrated great promise in building surrogate models from data. These methods include deep learning and recurrent neural network (RNN). In this paper, a systematic investigation of the network architectures and the used optimizers to train the network is presented. Adam, Adagrad, RMSprob and SGD are investigated in training the network. To train the model almost 35000 data points were collected for Fridsma hull operating in 18 regular waves using a 2D+T model. The result showed that gated recurrent unit (GRU) outperformed long short-term memory (LSTM) and RNN in predicting the heave motion. Also, one hidden layer with 5 neurons was enough to achieve mean absolute error of 0.000298 and to predict unseen waves when trained with more than 24000 data points.QC 20230811</p

Calm Water Performance of Hard-Chine Vessels in Semi-Planing and Planing Regimes

In the current paper, a mathematical model is developed for performance prediction of hard-chin boats which can be used in both semi-planing and planing regimes. The proposed model bases on the 2D+T theory and implements pressure distributions over the length of the hull in order to compute the forces. To determine the forces in the semi-planing range, a function is proposed for the non-dimensional length at which the transom effect appears. Three drag components, which are: frictional drag, induced drag, and spray drag, are considered in the computations performed using an iterative method to satisfy two equilibrium equations. The validity of the proposed method is verified by comparing the predicted trim angle and resistance against the available experimental data. Based on this comparison, it is observed that the proposed method reveals satisfying accuracy in both semi-planing and planing regimes. The method is then used to study variation of hydrodynamic and hydrostatic forces as the hull makes a transition from the semi-planing regime to the planing regime. In addition, different components of the resistance are analyzed

Hydrodynamic characteristics of tunneled planing hulls in calm water

Tunneled planing hull is a special design of high speed craft which can reduce the frictional resistance to achieve higher velocities in high speeds. But, at lower speeds tunnels may lead to increase hull resistance. Therefore, tunneled planing hull design is an important issue which should be conducted with full prior information. In this study, a tunneled planing hull has numerically been studied in details using Star-CCM+ software. These simulations are based on Finite Volume Method (FVM) solution of Reynolds Averaged Navier-Stokes Equations (RANSE). Also, Volume of Fluid (VOF) method has been employed to obtain free surface variations, accurately. Morphing mesh approach has also been implemented to be able to simulate tunneled planing hull in two degrees of freedom in heave and pitch directions. Presented numerical setup has been validated by comparison of computed trim angle and hull resistant against the experimental results which have been presented by previous researchers. Afterwards, various physical phenomena around the considered tunneled planing hull as well as different physical parameters such as skin friction distribution, details of wetted surface area (total wetted surface, tunnel wetted surface, spray angle, keel and chain wetted length), shear and pressure drag, pressure distribution, wake pattern, and stream lines have been discussed, thoroughly. In this paper a new parameter as tunneled efficiency has been introduced based on obtained results. Tunnel efficiency shows appropriate speed range of planing hulls for using tunnel advantages in drag reduction. Presented results help designers to find new insight about the hydrodynamics of tunneled planing hulls.QC 20220324</p