Dai Zhou

Partitioned subiterative coupling schemes for aeroelasticity using combined interface boundary condition method

The combined interface boundary condition (CIBC) method has been recently proposed for fluid–structure interaction. The CIBC method employs a Gauss–Seidel-like procedure to transform traditional interface conditions into velocity and traction corrections whose effect is controlled by a dimensional parameter. However, the original CIBC method has to invoke the uncorrected traction when forming the traction correction. This process limits its application to fluid–rigid body interaction. To repair this drawback, a new formulation of the CIBC method has been developed by using a new coupling parameter. The reconstruction is simple and the structural traction is removed completely. Two partitioned subiterative coupling versions of the CIBC method are developed. The first scheme is an implicit strategy while the second one is a semi-implicit strategy. Iterative loops are actualised by the fixed-point algorithm with Aitken accelerator. The obtained results agree with the well-documented data, and some famous flow phenomena have been successfully detected.

Laminar Flow Patterns Around Three Side-By-Side Arranged Circular Cylinders Using Semi-Implicit Three-Step Taylor-Characteristic-Based-Split (3-TCBS) Algorithm

Abstract One limitation of the classical characteristic-based-split (CBS) algorithm is that its computational time step is relatively small because it is an explicit scheme with conditional stability. We present in this paper a semi-implicit form of a three-step Taylor-characteristic-based-split (3-TCBS) Galerkin fmite element (FE) method in the framework of incremental projection method to numerically solve incompressible fluid flow problems. First, the velocities are semi-implicitly estimated by a three-step process. The computational code is then verified by using the benchmark problems of lid-driven cavity and of flow around a fixed circular cylinder at Reynolds numbers in the laminar regime. Comparisons between the current method and the classical CBS algorithm show that the present 3- TCBS scheme can provide a larger time step with more accurate results. Then, this method is employed to investigate the problem of laminar flow over three cylinders which are arranged side-by-side. The Reynolds numbers range from 40 to 160 and the spacing ratios were set as 1.2, 1.4, 1.6, 1.8, 2.2, 2.5, 3.2, and 4.0. Eight different wake patterns were systematically categorized and their relationships with the Reynolds number and spacing ratio are presented.

Wake-Induced Vibrations of a Circular Cylinder behind a Stationary Square Cylinder Using a Semi-Implicit Characteristic-Based Split Scheme

AbstractThis study develops a semi-implicit characteristic-based-split (SI-CBS) finite-element algorithm under the framework of the fractional step method to cope with the vortex-induced vibration (VIV) problem. The authors present a modified linear spring analogy algorithm for successful updating of the grid deformation. They verify the computational code against two benchmark problems. One is the VIV of an elastically mounted cylinder with transverse oscillation at R=150. The other is the transversely wake-induced vibration (WIV) of a circular cylinder by a stationary one. The authors conduct a two-dimensional (2D) numerical investigation on the problem of laminar flow over a two-cylinder system, which consists of a front stationary square cylinder and a rear two-degree-of-freedom (2-DOF) circular cylinder in a tandem arrangement. They find that the Reynolds number and reduced velocities play key roles in the WIVs of the circular cylinder. In addition to the wake patterns 2S, 2P, and P+S, the authors ob...

Numerical Simulation of Fluctuating Wind Effects on an Offshore Deck Structure

The offshore structures that play a vital role in oil and gas extraction are always under complicated environmental conditions such as the random wind loads. The structural dynamic response under the harsh wind is still an important issue for the safety and reliable design of offshore structures. This study conducts an investigation to analyze the wind-induced structural response of a typical offshore deck structure. An accurate and efficient mixture simulation method is developed to simulate the fluctuating wind speed, which is then introduced as the boundary condition into numerical wind tunnel tests. Large eddy simulation (LES) is utilized to obtain the time series of wind pressures on the structural surfaces and to determine the worst working condition. Finally, the wind-induced structural responses are calculated by ANSYS Parametric Design Language (APDL). The numerically predicted wind pressures are found to be consistent with the existing experimental data, demonstrating the feasibility of the proposed methods. The wind-induced displacements have the certain periodicity and change steadily. The stresses at the top of the derrick and connections between deck and derrick are relatively larger. These methods as well as the numerical examples are expected to provide references for the wind-resistant design of the offshore structures.