Numerical simulation of the slamming phenomenon of a wave-piercing trimaran in the presence of irregular waves under various seagoing modes

2019 ◽  
Vol 233 (4) ◽  
pp. 1198-1211
Author(s):  
Parviz Ghadimi ◽  
Amin Nazemian ◽  
Mohammad Sheikholeslami
Keyword(s):  
Vertical Velocity ◽  
Pressure Coefficient ◽  
Analytical Data ◽  
Water Entry ◽  
Irregular Waves ◽  
Maximum Pressure ◽  
Highly Nonlinear ◽  
Flare Region ◽  
Seakeeping Analysis ◽  
Bow Flare

Trimaran vessels have been of great interest to naval architects, due to their large deck space, low resistance at high speeds and stability. Meanwhile, determination of their slamming forces in the presence of highly nonlinear waves has always been a challenge for the structural designers. However, because of novelty and complexity of their hulls, there is insufficient information in this regard, which necessitates suitable effort in filling this gap. Accordingly, in this article, using Flow-3D, a commercial computational fluid dynamics code, seakeeping of a wave-piercing trimaran is simulated in the presence of irregular waves via standard Bretschneider spectrum in sea state 5 in various seagoing modes. These modes include two speeds and two waves with encountering angles of head sea and bow quartering sea. For validation purposes, seakeeping of a trimaran vessel and water entry of a wedge-shaped section are investigated and numerical results are compared against experimental and analytical data. Good compliance of the results confirms the accuracy of the proposed numerical model. In the slamming analysis of the considered trimaran, using the relative vertical velocity of the bow section from the seakeeping analysis, the water entry problem is investigated for the most severe slamming mode. Pressure distribution caused by water entry and instantaneous impact pressure, known as structural design pressure, is computed. The exerted slamming pressure on the bottom and bow flare region is determined to be 4300 and 2100 Pa, respectively. Results indicate that during slamming phenomenon, the maximum pressure exerted on the vessel’s floor occurs at the time of impact at which the pressure coefficient is 4.4. Accurate assessment of the vessel’s vertical velocity from the start of water entry until the water surface rise-up, and the utilized technique considered for slamming phenomenon in more realistic sea condition, can be considered as important features of this study.

An Approximate THD Theory for Journal Bearings

1990 ◽  
Vol 112 (2) ◽  
pp. 224-229 ◽  
Author(s):  
G. Gupta ◽  
C. R. Hammond ◽  
A. Z. Szeri
Keyword(s):  
Journal Bearing ◽  
Load Capacity ◽  
Pressure Coefficient ◽  
Journal Bearings ◽  
Maximum Pressure ◽  
Substantial Agreement ◽  
Interactive Mode ◽  
Lubricant Flow ◽  
Bearing Load ◽  
Sophisticated Model

The aim of this paper is to make available to the industrial designer results of the thermohydrodynamic theory of journal bearings, by providing a simplified, yet accurate model of journal bearing lubrication that can be implemented on a personal computer and be used in an interactive mode. The simplified THD theory we propose consists of two coupled ordinary differential equations for pressure and energy and an algebraic equation for viscosity, which are to be solved iteratively. Bearing load capacity, maximum bearing temperature, maximum pressure, coefficient of friction and lubricant flow rate calculated from this simplified theory compare well with results from a more sophisticated model. We also make comparisons with experimental data on full journal bearings, demonstrating substantial agreement between experiment and simplified theory.

SLAM CHARACTERISTICS OF A HIGH-SPEED WAVE PIERCING CATAMARAN IN IRREGULAR WAVES

2021 ◽  
Vol 156 (A1) ◽  
Author(s):  
B J French ◽  
G A Thomas ◽  
M R Davis
Keyword(s):  
Vertical Velocity ◽  
Significant Wave Height ◽  
High Speed ◽  
Irregular Waves ◽  
Two Dimensional ◽  
Towing Tank ◽  
Filling Height ◽  
Load Distributions ◽  
Poor Indicator ◽  
Wave Elevations

Slam characteristics of a 112m INCAT wave piercing catamaran in a range of realistic irregular sea conditions are presented in this paper. Towing tank testing of a 2.5 m hydroelastic segmented catamaran model was used to gather a database of slam events in irregular seas. The model was instrumented to measure motions, centrebow surface pressures and forces, encountered wave elevations and wave elevations within the bow area tunnel arches. From these measurements characteristics of the vessel slamming behaviour are examined: in particular relative vertical velocity, centrebow immersion, archway wave elevations and slam load distributions. A total of 2,098 slam events were identified over 22 different conditions, each containing about 80 to 100 slam events. The data, although inherently scattered, shows that encounter wave frequency and significant wave height are important parameters with regard to centrebow slamming. Relative vertical velocity was found to be a poor indicator of slam magnitude and slams were found to occur before the centrebow arch tunnel was completely filled, supporting the application of a two-dimensional filling height parameter as a slam indicator.

An experimental study on water entry of a 3D bow-flare model with pitch angles

2021 ◽  
Vol 219 ◽  
pp. 108282
Author(s):  
Hang Xie ◽  
Xuefeng Wei ◽  
Fang Liu ◽  
Huilong Ren ◽  
Xinyu Liu ◽  
...  
Keyword(s):  
Experimental Study ◽  
Water Entry ◽  
Bow Flare ◽  
Flare Model

Numerical Analysis of a Surface Ship in Waves

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Shawn Aram
Keyword(s):  
Stokes Equations ◽  
Body Motion ◽  
Irregular Waves ◽  
Design Stage ◽  
Fluid Viscosity ◽  
Sea Waves ◽  
Added Resistance ◽  
Physical Mechanisms ◽  
Strip Theory ◽  
Seakeeping Analysis

Abstract Ship's resistance and engine power to sustain ship's speed in seaways are augmented due to complex non-linear interactions between the ship and the ambient sea (waves). Ship designers, in early design stage, use an ad hoc "sea margin" to account for the effects of seaways in selecting propeller and engine. A numerical tool capable of accurately predicting added resistance and power of a ship cruising in waves would greatly help select its powering (margin) requirement and determine the optimal operating point that can maximize the energy efficiency. For seakeeping analysis, strip theory-based methods have long been used. More recently, nonlinear time-domain three-dimensional (3D) panel methods have started being used widely. A more physics-based avenue to seakeeping analysis is offered by coupled solutions of two-phase unsteady Reynolds-Averaged Navier-Stokes equations and six degrees-of-freedom rigid-body motion (RBM) equations. The URANS approach also avails itself of including the effects of propulsors, either explicitly or approximately. By accounting for all the nonlinear effects in hydrodynamic forces and moments and the resulting ship motions, and the effects of fluid viscosity and turbulence, the coupled URANS-RBM method is believed not only able to predict added resistance and speed loss more accurately, but also to provide valuable insights into the physical mechanisms underlying added resistance and power. The objectives of this study are: (1) to validate a coupled URANS-RBM solver developed for high-fidelity prediction of added resistance, speed loss and added power on ships cruising in regular head sea and irregular waves, and (2) to conduct a detailed analysis of the interactions among ship hull, propeller and waves for a 1/49 scaled model of the ONR Tumblehome (ONRT) (Model 5613) in order to shed light on the physical mechanisms leading to added resistance, speed loss and added power. Figure 1 depicts the ONRT self-propellers with two 4-bladed propellers in regular waves. The main flow features such as the free surface, the hub vortices and blade-tip vortices from the propeller, as well as vortices generated by the sonar dome, shafts, shaft brackets and bilge keels are captured.

Particle Flow Simulation for Large Diameter Squat Silos Eccentric Discharge

2011 ◽  
Vol 99-100 ◽  
pp. 1106-1112
Author(s):  
Fang Yuan ◽  
Cheng Ying Dong ◽  
Yao Hui Song ◽  
Song Song Zhang
Keyword(s):  
Lateral Pressure ◽  
Large Diameter ◽  
Pressure Coefficient ◽  
Side Wall ◽  
Operating Conditions ◽  
Particle Flow ◽  
Scale Model ◽  
Maximum Pressure ◽  
Centrifuge Model Test ◽  
Eccentric Distance

The scale model of squat silo in large diameter was established with Particle Flow Code (PFC3D) in this paper. This scale model uses the centrifuge model test principle for reference and provides the field of gravity in the calculation of archetypal squat silo. When the silo filled with granules reaches static equilibrium state, record the static lateral pressure measurement values of its each column measured wall, followed by eccentric discharge simulation in different operating conditions, while monitoring the changes of Measured walls in five different directions during discharging granules, in order to analyze the influence of eccentric discharge on the lateral pressure of large diameter squat silos wall. Thus the following conclusion can be obtained: （1）Overpressure coefficient is close extensive between eccentric distance and far extensive between physical reference of storing material.（2）Under the same condition, the overpressure coefficient of same side wall will be minished with the increasing of discharge port.（3）For the same silo model, maximum pressure coefficient is related with eccentric distance, discharge port size and the position with the wall measured, and its value is greater than the calculated value of standard, because the overpressure coefficient calculation formula is only related with silo diameter and eccentric distance, and this is worth further discussion.

Numerical Solution of 3-D Water Entry Problems With a Constrained Interpolation Profile Method

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Qingyong Yang ◽  
Wei Qiu
Keyword(s):  
Numerical Solutions ◽  
Stokes Equations ◽  
Type Equation ◽  
Water Entry ◽  
Navier Stokes ◽  
Time Step ◽  
Constrained Interpolation ◽  
Navier Stokes Equations ◽  
Highly Nonlinear ◽  
Calm Water

This paper presents the numerical solutions of slamming problems for 3D bodies entering calm water with vertical and oblique velocities. The highly nonlinear water entry problems are governed by the Navier-Stokes equations and were solved by a constrained interpolation profile (CIP)-based finite difference method on a fixed Cartesian grid. In the computation, the 3D CIP method was employed for the advection calculations and a pressure-based algorithm was applied for the nonadvection calculations. The solid body and the free surface interfaces were captured by density functions. For the pressure computation, a Poisson-type equation was solved at each time step by using the conjugate gradient iterative method. Validation studies were carried out for a 3D wedge, a cusped body vertically entering calm water, and the oblique entry of a sphere into calm water. The predicted hydrodynamic forces on the wedge, the cusped body, and the sphere were compared with experimental data.

A Numerical Study on the Performance of Fixed Oscillating Water Column Wave Energy Converter at Steep Waves

2016 ◽  
Author(s):  
Morteza Anbarsooz ◽  
Ali Faramarzi ◽  
Amirmahdi Ghasemi
Keyword(s):  
Wave Height ◽  
Wave Energy ◽  
Nonlinear Waves ◽  
Numerical Study ◽  
Wave Length ◽  
Analytical Data ◽  
Absorption Efficiency ◽  
Numerical Results ◽  
Highly Nonlinear ◽  
Steep Waves

In the current study, a fully nonlinear two-dimensional numerical wave tank is developed using the commercial CFD software, Ansys Fluent 15.0, in order to study the absorption characteristics of an OWC at linear and highly nonlinear steep waves. The two-phase Volume-Of-Fluid (VOF) method is employed to predict the water free surface evolution. The numerical results are first validated against the available analytical data in the literature. The good agreement between the numerical results and those of analytics, revealed the capability of the developed numerical tank to study the performance of the OWC. Next, the simulations are performed for strongly nonlinear waves, up to the wave steepness of 0.069 (H/L=0.069), where H is the wave height and L is the wave length. The optimum pneumatic damping of the air turbine at such strongly steep and nonlinear waves is determined. Results show that the absorption efficiency of the OWC decreases considerably as the wave height increases. Moreover, the maximum wave energy absorption efficiency for the highly nonlinear waves occurs at a pneumatic damping coefficient lower than that of the linear theory.

ANALYSIS OF THE WATER IMPACT OF SYMMETRIC WEDGES WITH A MULTI- MATERIAL EULERIAN FORMULATION

2021 ◽  
Vol 154 (A4) ◽  
Author(s):  
S Wang ◽  
C Guedes Soares
Keyword(s):  
Pressure Distribution ◽  
Impact Velocity ◽  
Pressure Coefficient ◽  
Time History ◽  
Maximum Pressure ◽  
Vertical Force ◽  
Force Coefficient ◽  
Explicit Finite Element ◽  
Eulerian Formulation ◽  
The Impact

The two-dimensional hydrodynamic problem of a symmetric wedge vertically impacting in calm water is analysed by using an explicit finite element method based on a multi-material Eulerian formulation. The slam-induced loads on wedges with different deadrise angle at a constant velocity are calculated, including pressure distribution, maximum pressure coefficient, force coefficient and time history of vertical force, which are compared with available theoretical and analytical results. The time evolution of pressure distribution and free surface elevation are presented. Furthermore, the effects of impact velocity are investigated. It shows that this method is capable of predicting the local slamming loads, and as well assessing the effects of the deadrise angle and the impact velocity on the slamming pressure for the wedge-shape section.

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