A Fast Method to Predict the Cavitation Volume on Two-Dimensional Sections

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Zhibo Zeng ◽  
Gert Kuiper
Keyword(s):  
Pressure Fluctuations ◽  
Prediction Method ◽  
Fast Method ◽  
Two Dimensional ◽  
Fast Calculation ◽  
Wake Field ◽  
Marine Propellers ◽  
Sheet Cavitation ◽  
Blade Section ◽  
Dimensional Section

The paper presents a simplified prediction method to estimate cavitation-induced pressure fluctuations by marine propellers in a nonuniform wake field. It is realized by a very fast calculation of the cavitation volume variation. The sheet cavitation volume is represented by the cavitation area in a two-dimensional section, which is the vapor area inside the cavity contour. The variation of the cavitation area on a two-dimensional blade section has been simplified to a relation in quasi-steady condition with only a limited number of nondimensional parameters. This results in a fast method to predict the cavitation area of a blade section passing a wake peak, using a precalculated database. Application of this method to the prediction of cavitation-induced pressure fluctuations shows to be effective. This makes optimization of propeller sections for minimum cavitation-induced pressure fluctuations feasible.

Application of a Boundary Element Method in the Prediction of Unsteady Blade Sheet and Developed Tip Vortex Cavitation on Marine Propellers

2004 ◽  
Vol 48 (01) ◽  
pp. 15-30
Author(s):  
Hanseong Lee ◽  
Spyros A. Kinnas
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Pressure Fluctuations ◽  
Ship Hull ◽  
Tip Vortex ◽  
Tip Vortex Cavitation ◽  
Marine Propellers ◽  
Sheet Cavitation ◽  
Numerical Predictions ◽  
Element Method

Most marine propellers operate in nonaxisymmetric inflows, and thus their blades are often subject to an unsteady flow field. In recent years, due to increasing demands for faster and larger displacement ships, the presence of blade sheet and tip vortex cavitation has become very common. Developed tip vortex cavitation, which often appears together with blade sheet cavitation, is known to be one of the main sources of propeller-induced pressure fluctuations on the ship hull. The prediction of developed tip vortex cavity as well as blade sheet cavity is thus quite important in the assessment of the propeller performance and the corresponding pressure fluctuations on the ship hull. A boundary element method is employed to model the fully unsteady blade sheet (partial or supercavitating) and developed tip vortex cavitation on propeller blades. The extent and size of the cavity is determined by satisfying both the dynamic and the kinematic boundary conditions on the cavity surface. The numerical behavior of the method is investigated for a two-dimensional tip vortex cavity, a three-dimensional hydrofoil, and a marine propeller subjected to nonaxisymmetric inflow. Comparisons of numerical predictions with experimental measurements are presented.

scholarly journals An Adjoint Optimization Prediction Method for Partially Cavitating Hydrofoils

2021 ◽  
Vol 9 (9) ◽  
pp. 976
Author(s):  
Dimitra Anevlavi ◽  
Kostas Belibassakis
Keyword(s):  
Prediction Method ◽  
Cavitation Number ◽  
Cavity Shape ◽  
Marine Propellers ◽  
Sheet Cavitation ◽  
Hydrokinetic Turbines ◽  
Design Variables ◽  
Gradient Based ◽  
Lifting Surfaces ◽  
Continuous Adjoint

Much work has been done over the past years to obtain a better understanding, predict and alleviate the effects of cavitation on the performance of lifting surfaces for hydrokinetic turbines and marine propellers. Lifting-surface sheet cavitation, when addressed as a free-streamline problem, can be predicted up to a desirable degree of accuracy using numerical methods under the assumptions of ideal flow. Typically, a potential solver is used in conjunction with geometric criteria to determine the cavity shape, while an iterative scheme ensures that all boundary conditions are satisfied. In this work, we propose a new prediction model for the case of partially cavitating hydrofoils in a steady flow that treats the free-streamline problem as an inverse problem. The objective function is based on the assumption that on the cavity boundary, the pressure remains constant and is evaluated at each optimization cycle using a source-vorticity BEM solver. The attached cavity is parametrized using B-splines, and the control points are included in the design variables along with the cavitation number. The sensitivities required for the gradient-based optimization are derived using the continuous adjoint method. The proposed numerical scheme is compared against other methods for the NACA 16-series hydrofoils and is found to predict well both the cavity shape and cavitation number for a given cavity length.

scholarly journals An information theoretic approach to link prediction in multiplex networks

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Seyed Hossein Jafari ◽  
Amir Mahdi Abdolhosseini-Qomi ◽  
Masoud Asadpour ◽  
Maseud Rahgozar ◽  
Naser Yazdani
Keyword(s):  
Real World ◽  
Link Prediction ◽  
Large Scale ◽  
Similarity Measures ◽  
Prediction Method ◽  
General Purpose ◽  
Fast Method ◽  
Theoretic Approach ◽  
Multiplex Networks ◽  
Wide Range

AbstractThe entities of real-world networks are connected via different types of connections (i.e., layers). The task of link prediction in multiplex networks is about finding missing connections based on both intra-layer and inter-layer correlations. Our observations confirm that in a wide range of real-world multiplex networks, from social to biological and technological, a positive correlation exists between connection probability in one layer and similarity in other layers. Accordingly, a similarity-based automatic general-purpose multiplex link prediction method—SimBins—is devised that quantifies the amount of connection uncertainty based on observed inter-layer correlations in a multiplex network. Moreover, SimBins enhances the prediction quality in the target layer by incorporating the effect of link overlap across layers. Applying SimBins to various datasets from diverse domains, our findings indicate that SimBins outperforms the compared methods (both baseline and state-of-the-art methods) in most instances when predicting links. Furthermore, it is discussed that SimBins imposes minor computational overhead to the base similarity measures making it a potentially fast method, suitable for large-scale multiplex networks.

Electronic structure and photocatalytic band offset of few-layer GeP2

2017 ◽  
Vol 5 (42) ◽  
pp. 22146-22155 ◽  
Author(s):  
Fazel Shojaei ◽  
Jae Ryang Hahn ◽  
Hong Seok Kang
Keyword(s):  
Crystal Structure ◽  
Electronic Structure ◽  
Structure Prediction ◽  
Prediction Method ◽  
Group Iv ◽  
Band Offset ◽  
Two Dimensional ◽  
Crystal Structure Prediction ◽  
T Phase ◽  
Structure Prediction Method

Based on a sophisticated crystal structure prediction method, we propose two-dimensional (2D) GeP2in the tetragonal (T) phase never observed for other group IV–V compounds.

A Nonlinear Method for Predicting Unsteady Sheet Cavitation on Marine Propellers

1983 ◽  
Vol 27 (01) ◽  
pp. 56-74
Author(s):  
Frederick Stern ◽  
William S. Vorus
Keyword(s):  
Complete Solution ◽  
Near Field ◽  
Fluid Velocity ◽  
Far Field ◽  
Static Potential ◽  
Nonlinear Method ◽  
Slender Body Theory ◽  
Marine Propellers ◽  
Sheet Cavitation ◽  
Dynamic Potential

A method is presented which provides a basis for predicting the nonlinear dynamic behavior of unsteady propeller sheet cavitation. The method separates the fluid velocity potential boundary-value problem into two parts, static and dynamic, which are solved sequentially in a forward time stepping procedure. The static potential problem is for the cavity fixed instantaneously relative to the propeller and the propeller translating through the nonuniform wake field. This problem can be solved by standard methods. The dynamic potential represents the instantaneous reaction of the cavity to the static potential field and thus predicts the cavity's deformation and motion relative to the blade. A solution is obtained for the dynamic potential by using the concepts of slender-body theory to define near-and far-field potentials which are matched to form the complete solution. In the far field, the cavity is represented by a three-dimensional spanwise line distribution of sources. In the near field, the cavity is approximated at each cross section as a semi-ellipse with unknown axes a(t), b(t), and position l(t) along the chord of the foil section. Conditions are derived that determine (a, b, l) by minimizing the square error in satisfying the dynamic boundary condition. These conditions yield the equations of motion of the cavity in the form of three coupled nonlinear second-order ordinary differential equations with time as the independent variable. The theory is presented for the general foil and not specifically for propellers. However, the method incorporates features in its formulation which facilitate its application to marine propellers. The method is demonstrated by using the steady noncavitating potential for the two-dimensional half-body as an approximation to the static potential. Both fixed and unsteady cavities are calculated. The unsteady cavities are calculated by varying the hydrostatic pressure in the half-body pressure field sinusoidally.

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