Large grid simulations of surface combatant flow at straight-ahead and static drift conditions

2016 ◽  
Vol 30 (5) ◽  
pp. 356-362
Author(s):  
Shanti Bhushan ◽  
Hyunse Yoon ◽  
Frederick Stern
Keyword(s):  
Surface Combatant ◽  
Drift Conditions ◽  
Straight Ahead ◽  
Large Grid

Scalability studies and large grid computations for surface combatant using CFDShip-Iowa

2011 ◽  
Vol 25 (4) ◽  
pp. 466-487 ◽  
Author(s):  
Shanti Bhushan ◽  
Pablo Carrica ◽  
Jianming Yang ◽  
Frederick Stern
Keyword(s):  
Free Surface ◽  
Message Passing Interface ◽  
Free Surface Flows ◽  
Processing Unit ◽  
Mean Flow ◽  
Time Step ◽  
Vortical Structures ◽  
Cpu Time ◽  
Surface Combatant ◽  
Straight Ahead

Scalability studies and computations using the largest grids to date for free-surface flows are performed using message-passing interface (MPI)-based CFDShip-Iowa toolbox curvilinear (V4) and Cartesian (V6) grid solvers on Navy high-performance computing systems. Both solvers show good strong scalability up to 2048 processors, with V6 showing somewhat better performance than V4. V6 also outperforms V4 in terms of the memory requirements and central processing unit (CPU) time per time-step per grid point. The explicit solvers show better scalability than the implicit solvers, but the latter allows larger time-step sizes, resulting in a lower total CPU time. The multi-grid HYPRE solver shows better scalability than the portable, extensible toolkit for scientific computation solver. The main scalability bottleneck is identified to be the pressure Poisson solver. The memory bandwidth test suggests that further scalability improvements could be obtained by using hybrid MPI/open multi-processing (OpenMP) parallelization. V4-detached eddy simulation (DES) on a 300 M grid for the surface combatant model DTMB 5415 in the straight-ahead condition provides a plausible description of the vortical structures and mean flow patterns observed in the experiments. However, the vortex strengths are over predicted and the turbulence is not resolved. V4-DESs on up to 250 M grids for DTMB 5415 at 20° static drift angle significantly improve the forces and moment predictions compared to the coarse grid unsteady Reynolds averaged Navier–Stokes, due to the improved resolved turbulence predictions. The simulations provide detailed resolution of the free-surface and breaking pattern and vortical and turbulent structures, which will guide planned experiments. V6 simulations on up to 276 M grids for DTMB 5415 in the straight-ahead condition predict diffused vortical structures due to poor wall-layer predictions. This could be due to the limitations of the wall-function implementation for the immersed boundary method.

Numerical Simulation of Viscous Flows Around a Surface Combatant Model at Different Drift Angles Using Overset Grids

2020 ◽  
pp. 2041015
Author(s):  
Jianhua Wang ◽  
Zhenghao Liu ◽  
Decheng Wan
Keyword(s):  
Flow Field ◽  
Viscous Flows ◽  
Wave Pattern ◽  
Resistance Coefficient ◽  
Current Approach ◽  
Ship Hull ◽  
Wake Region ◽  
Hydrodynamic Derivatives ◽  
Surface Combatant ◽  
Straight Ahead

Viscous flows around ship hull is of great complexity, and when the ship is advancing with drift angles, the flow field can be more complicated. In this paper, the viscous flow field around an obliquely towed surface combatant DTMB 5512 is computed using the unsteady Reynolds-averaged Navier–Stokes (URANS) method. The numerical simulations are carried out by the in-house CFD solver naoe-FOAM-SJTU, which is developed on the open source platform OpenFOAM. To refine local grids and simulate dynamic ship motions, the overset grid approach is applied. Grid convergence study is first performed at straight-ahead towed condition with three sets of grid number and the results show monotonically convergence. Six different drift angles for the DTMB 5512 model at Froude number of 0.28 are simulated and the predicted hydrodynamic forces and flow field are presented. During the simulation, the ship hull is free to trim and sinkage at a free surface environment. As for straight-ahead towed condition, the total resistance coefficient and flow field, i.e., wave pattern and wake region, between this work and the experiment are compared. Both force coefficients and flow field show good agreement with the available experimental data. For oblique towed conditions, the lateral force, yaw moment and the derived hydrodynamic derivatives are also presented and compared with the experimental results. The variation of wave pattern and wake region at different drift angles are presented and analyzed. The results show that the current approach can be an effective tool to predict the viscous flows and hydrodynamic loads for oblique towed ships.

scholarly journals Assessment of Statistical and Hybrid LES Turbulence Closures for Surface Combatant DTMB5415 at 20° Static Drift Condition

2015 ◽  
Author(s):  
Michel Visonneau ◽  
Emmanuel Guilmineau ◽  
Jeroen Wackers ◽  
GanBo Deng ◽  
Patrick Queutey
Keyword(s):  
Free Surface ◽  
Flow Analysis ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Vortical Structures ◽  
Turbulence Closures ◽  
Surface Combatant ◽  
Drift Conditions ◽  
Vehicle Technologies ◽  
Cfd Method

This paper provides detailed validation of the complex free-surface flow around the surface combatant DTMB5415 at 20° static drift conditions. Particular emphasis is being placed on the onset and progression of the various vortical structures created at the sonar dome, at the free-surface and around bilge keels in conditions where free-surface breaking may occur. A detailed analysis of this complex free-surface flow is conducted on grids which are dynamically refined to capture the vortical structures. Local comparisons with recent experiments performed at the Iowa Institute of Hydraulic Research (IIHR) during a joint NATO-AVT (Advanced Vehicle Technologies) collaboration are used to perform detailed flow analysis and draw some conclusions about the actual potentialities of advanced Computation Fluid Dynamics (CFD) method in terms of physical and numerical modeling.

Gaze behavior of pre-adolescent children afflicted with Asperger Syndrome

2013 ◽  
Vol 9 (2) ◽  
pp. 173-186 ◽  
Author(s):  
Mari Wiklund
Keyword(s):  
Asperger Syndrome ◽  
Conversation Analysis ◽  
High Functioning Autism ◽  
Eye Contact ◽  
Nonverbal Behaviors ◽  
Gaze Behavior ◽  
High Functioning ◽  
The Gaze ◽  
In The Beginning ◽  
Straight Ahead

Asperger syndrome (AS) is a form of high-functioning autism characterized by qualitative impairment in social interaction. People afflicted with AS typically have abnormal nonverbal behaviors which are often manifested by avoiding eye contact. Gaze constitutes an important interactional resource, and an AS person’s tendency to avoid eye contact may affect the fluidity of conversations and cause misunderstandings. For this reason, it is important to know the precise ways in which this avoidance is done, and in what ways it affects the interaction. The objective of this article is to describe the gaze behavior of preadolescent AS children in institutional multiparty conversations. Methodologically, the study is based on conversation analysis and a multimodal study of interaction. The findings show that three main patterns are used for avoiding eye contact: 1) fixing one’s gaze straight ahead; 2) letting one’s gaze wander around; and 3) looking at one’s own hands when speaking. The informants of this study do not look at the interlocutors at all in the beginning or the middle of their turn. However, sometimes they turn to look at the interlocutors at the end of their turn. This proves that these children are able to use gaze as a source of feedback. When listening, looking at the speaker also seems to be easier for them than looking at the listeners when speaking.

Postural Preparation to Making a Step: Is There a “Motor Program” for Postural Preparation?

2007 ◽  
Vol 23 (4) ◽  
pp. 261-274 ◽  
Author(s):  
Adriana M. Degani ◽  
Alessander Danna-Dos-Santos ◽  
Mark L. Latash
Keyword(s):  
Reaction Time ◽  
Simple Reaction Time ◽  
Center Of Pressure ◽  
Motor Program ◽  
Whole Body ◽  
Single Motor ◽  
Simple Reaction ◽  
Specific Manner ◽  
Young Subjects ◽  
Straight Ahead

We tested the hypothesis that a sequence of mechanical events occurs preceding a step that scales in time and magnitude as a whole in a task-specific manner, and is a reflection of a “motor program.” Young subjects made a step under three speed instructions and four tasks: stepping straight ahead, down a stair, up a stair, and over an obstacle. Larger center-of-pressure (COP) and force adjustments in the anteriorposterior direction and smaller COP and force adjustments in the mediolateral direction were seen during stepping forward and down a stair, as compared with the tasks of stepping up a stair and over an obstacle. These differences were accentuated during stepping under the simple reaction time instruction. These results speak against the hypothesis of a single motor program that would underlie postural preparation to stepping. They are more compatible with the reference configuration hypothesis of whole-body actions.

Sign in / Sign up

Export Citation Format

Share Document