COMBINATION OF MESH DEFORMATION AND OVERSET GRID FOR SIMULATING UNSTEADY FLOW OF INSECT FLIGHT

2009 ◽  
Vol 23 (03) ◽  
pp. 525-528 ◽  
Author(s):  
TIANHANG XIAO ◽  
HAISONG ANG
Keyword(s):  
Insect Flight ◽  
Unsteady Flows ◽  
Flapping Wings ◽  
Mesh Deformation ◽  
Time Step ◽  
Overset Grids ◽  
Boundary Definition ◽  
Graph Mapping ◽  
Background Grid ◽  
Grid Cluster

As numerical simulation of unsteady flows due to moving boundaries such as flexible flapping-wings is difficult by conventional approaches, an effective strategy which combines mesh deformation based on Delaunay graph mapping and unstructured overset grids is proposed in this paper. A Delaunay graph is generated for each body-fitted grid cluster which overlaps or is embedded within an off-body background grid cluster. At each time step, the graph moves according to the wing's motion and deformation, and the grids move to new positions according to a one-to-one mapping between the graph and the grid. Then, intergrid-boundary definition is implemented automatically for computation.

A MULTI-TIME-STEP STRATEGY BASED ON AN OPTIMIZED TIME INTERPOLATION SCHEME FOR OVERSET GRIDS

2010 ◽  
Vol 18 (02) ◽  
pp. 131-148 ◽  
Author(s):  
DAKAI LIN ◽  
MIN JIANG ◽  
XIAODONG LI
Keyword(s):  
Numerical Stability ◽  
Grid Generation ◽  
Interpolation Scheme ◽  
Time Step ◽  
Overset Grids ◽  
Numerical Examples ◽  
Typical Time ◽  
Time Marching

A multi-time-step strategy for overset grids is proposed based on an optimized time interpolation scheme. Time interpolation is adopted in the vicinity of the interface between adjacent blocks, which are marching in time with different time steps satisfying the local numerical stability. There is no strict constraint on the ratio of mesh sizes between neighboring blocks, and it can alleviate the burden of the grid generation for multi-time-step marching methods. The optimized time interpolation scheme can be simply combined with the existing typical time marching schemes to achieve multi-time-step marching for overset grids. Some numerical examples are presented to demonstrate the feasibility and efficiency of the proposed strategy.

Four-Bar Linkage Mechanism for Insectlike Flapping Wings in Hover: Concept and an Outline of Its Realization

2005 ◽  
Vol 127 (4) ◽  
pp. 817-824 ◽  
Author(s):  
Rafał Z˙bikowski ◽  
Cezary Galin´ski ◽  
Christopher B. Pedersen
Keyword(s):  
Insect Flight ◽  
Micro Air Vehicles ◽  
Flapping Wing ◽  
Flapping Wings ◽  
Test Bed ◽  
Linkage Mechanism ◽  
Actual Design ◽  
Straight Line Mechanism ◽  
Four Bar Linkage ◽  
Air Vehicles

This paper describes the concept of a four-bar linkage mechanism for flapping wing micro air vehicles and outlines its design, implementation, and testing. Micro air vehicles (MAVs) are defined as flying vehicles ca. 150 mm in size (handheld), weighing 50–100 g, and are developed to reconnoiter in confined spaces (inside buildings, tunnels, etc.). For this application, insectlike flapping wings are an attractive solution and, hence, the need to realize the functionality of insect flight by engineering means. Insects fly by oscillating (plunging) and rotating (pitching) their wings through large angles, while sweeping them forward and backward. During this motion, the wing tip approximately traces a figure eight and the wing changes the angle of attack (pitching) significantly. The aim of the work described here was to design and build an insectlike flapping mechanism on a 150 mm scale. The main purpose was not only to construct a test bed for aeromechanical research on hover in this mode of flight, but also to provide a precursor design for a future flapping-wing MAV. The mechanical realization was to be based on a four-bar linkage combined with a spatial articulation. Two instances of idealized figure eights were considered: (i) Bernoulli’s lemniscate and (ii) Watt’s sextic. The former was found theoretically attractive, but impractical, while the latter was both theoretically and practically feasible. This led to a combination of Watt’s straight-line mechanism with a drive train utilizing a Geneva wheel and a spatial articulation. The actual design, implementation, and testing of this concept are briefly described at the end of the paper.

Numerical Investigation of Sub-Iteration Criterions for Unsteady Flow Computations with Dual-Time Method

2013 ◽  
Vol 432 ◽  
pp. 189-195
Author(s):  
Guang Ning Li ◽  
Min Xu
Keyword(s):  
Unsteady Flow ◽  
Unsteady Flows ◽  
Numerical Results ◽  
Iteration Step ◽  
Convergence Criterion ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Physical Time ◽  
New Criterion

The convergence of sub-iteration with the dual-time method is very important for the prediction of unsteady flow field. The influence of sub-iteration step number, criterion of sub-iteration convergence and the choice of physical time step size on the calculation results are discussed by solving of the two-dimensional unsteady Euler equations. A new convergence criterion (named residual criterion) of sub-iteration for unsteady flows is proposed, and the unsteady flow test case AGARD-CT5 is calculated to verify the new criterion. The results show that, with the same criterion of sub-iteration, the results from different physical time step sizes are in agreement with each other. The difference between the experiment data and the numerical results are small, and if the sub-iteration criterion used is reasonable and small enough, the dependence of numerical results of unsteady flows on the physical time step will be decreased as possible. The new criterion of sub-iteration for dual-time step unsteady calculations can be used for engineering problem.

Numerical Solution of Incompressible Unsteady Flows in Turbomachinery

2000 ◽  
Vol 123 (3) ◽  
pp. 680-685 ◽  
Author(s):  
L. He ◽  
K. Sato
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Unsteady Flows ◽  
Navier Stokes ◽  
Time Step ◽  
Navier Stokes Equations ◽  
Flow Solver ◽  
Time Stepping ◽  
Incompressible Viscous Flow ◽  
Dual Time Stepping

A three-dimensional incompressible viscous flow solver of the thin-layer Navier-Stokes equations was developed for the unsteady turbomachinery flow computations. The solution algorithm for the unsteady flows combines the dual time stepping technique with the artificial compressibility approach for solving the incompressible unsteady flow governing equations. For time accurate calculations, subiterations are introduced by marching the equations in the pseudo-time to fully recover the incompressible continuity equation at each real time step, accelerated with a multi-grid technique. Computations of test cases show satisfactory agreements with corresponding theoretical and experimental results, demonstrating the validity and applicability of the present method to unsteady incompressible turbomachinery flows.

scholarly journals Reliable Shape Optimization of Structures Subjected to Transient Dynamic Loading Using Genetic Algorithms

2005 ◽  
Vol 12 (6) ◽  
pp. 407-424 ◽  
Author(s):  
Sabyasachi Chand ◽  
Anjan Dutta
Keyword(s):  
Genetic Algorithm ◽  
Finite Element ◽  
Genetic Algorithms ◽  
Shape Optimization ◽  
Analysis Tool ◽  
Time Step ◽  
Transient Dynamic ◽  
Boundary Definition ◽  
Automatic Mesh ◽  
Shape Changes

This paper presents a reliable method of solution of two dimensional shape optimization problems subjected to transient dynamic loads using Genetic Algorithms. Boundary curves undergoing shape changes have been represented by B-splines. Automatic mesh generation and adaptive finite element analysis modules are integrated with Genetic algorithm code to carry out the shape optimization. Both space and time discretization errors are evaluated and appropriate finite element mesh and time step values as obtained iteratively are adopted for accurate dynamic response. Two demonstration problems have been solved, which show convergence to the optimal solution with number of generations. The boundary curve undergoing shape optimization shows smooth shape changes. The combinations of automatic mesh generator with proper boundary definition capabilities, analysis tool with error estimation and Genetic algorithm as optimization engine have been observed to behave as a satisfactory shape optimization environment to deal with real engineering problems.

Computation of Multi-Passage Cascade Flows With Overset and Deforming Grids

1997 ◽  
Author(s):  
Ismail H. Tuncer ◽  
Wolfgang Sanz
Keyword(s):  
Moving Boundary ◽  
Grid Method ◽  
Navier Stokes ◽  
Computational Results ◽  
Compressor Cascade ◽  
Overset Grid ◽  
Overset Grids ◽  
Overset Grid Method ◽  
Background Grid ◽  
Good Agreement

An overset grid method is applied to the solution of single and multi-passage cascade flows with a compressible Navier-Stokes solver. C-type grids around individual blades are overset onto a Cartesian background grid. Overset grids are allowed to move in time relative to each other as prescribed by the oscillatory plunging motion. The overset grid method uses a simple, robust numerical algorithm to localize moving boundary points and to interpolate solution variables across intergrid boundaries. Computational results and comparisons with single/staggered, deforming grid solutions are presented for in- and out-of-phase multi-passage flows through a compressor cascade. Very good agreement is obtained against the deforming grid solutions.

Investigation of Periodic Boundary Conditions in Multipassage Cascade Flows Using Overset Grids

1999 ◽  
Vol 121 (2) ◽  
pp. 341-347 ◽  
Author(s):  
I. H. Tuncer ◽  
S. Weber ◽  
W. Sanz
Keyword(s):  
Solution Method ◽  
Grid Method ◽  
Navier Stokes ◽  
Flow Conditions ◽  
Compressor Cascade ◽  
Overset Grid ◽  
Overset Grids ◽  
Single Passage ◽  
Overset Grid Method ◽  
Background Grid

A Navier–Stokes solution method with overset grids is applied to unsteady multipassage cascade flows, and the unsteady blade loadings are compared against the single-passage solutions with the direct store interblade boundary condition. In the overset grid solutions, the multipassage domain is discretized with O-type grids around each blade and a rectangular background grid. Blade grids are allowed to move in time relative to the background grid, as prescribed by the oscillatory plunging motion. The overset grid method uses a simple, robust numerical algorithm to localize moving intergrid boundary points and to interpolate solution variables across grids. Computational results are presented for two and four-passage, subsonic and transonic flows through a turbine and a compressor cascade. The overset grid solutions over the multipassage periodic domains agree well with the single-passage solutions and the experimental data. It is concluded that the time linearization error introduced by the direct store approach is negligible in the range of flow conditions studied.

Gridless Adaptive Method for Simulating Unsteady Flows with Moving Shocks

2012 ◽  
Vol 271-272 ◽  
pp. 948-952
Author(s):  
Sai Hu Pu
Keyword(s):  
High Resolution ◽  
Numerical Test ◽  
Unsteady Flows ◽  
Adaptive Method ◽  
Test Cases ◽  
Computational Domain ◽  
Local Pressure ◽  
Time Step ◽  
Physical Features ◽  
Cloud Of Points

In this paper, the gridless adaptive method is extended to simulate unsteady flows with moving shocks. In order to capture physical features like moving shocks with local high resolution, a technique of dynamic cloud of points is achieved by adopting clouds refinement and clouds coarsening procedures during the evolution of the unsteady flows. The regions for clouds refinement and clouds coarsening are determined at every time step by an indicator, which is defined as a function of the local pressure gradient. Once the regions of cloud of points to be adjusted are located by the indicator, the clouds refinement is carried out by introducing new points based on the existing structure of cloud of points, and the clouds coarsening procedure is also implemented simultaneously in order to control the size of the points distributed in the whole computational domain. The numerical test cases show that the gridless adaptive method presented can capture moving shocks with high resolution successfully in both inviscid and viscous test cases.

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