Search for: All records

The shape design and optimization of bluff decks prone to aeroelastic phenomena require emulating the fluid-structure interaction parameters as a function of the body shape and the oscillation frequency. This is particularly relevant for long- and medium-span bridges equipped with single-box decks that are far from being considered streamlined and for other girder typologies such as traditional truss decks and modern twin- and multi-box decks. The success of aero-structural design frameworks, which are inherently iterative, relies on the efficient and accurate numerical evaluation of the wind-induced responses. This study proposes emulating the fluid-structure interaction parameters of bluff decks using surrogate modeling techniques to integrate them into aero-structural optimization frameworks. The surrogate is trained with data extracted from forced-vibration CFD simulations of a typical single-box girder to emulate the values of the flutter derivatives as a function of the deck shape and reduced velocity. The focus is on deck configurations ranging from streamlined to bluff cross-sections and on low reduced velocities to capture eventual aerodynamic nonlinearities. The girder cross-section geometry is tailored based on its buffeting performance. This design tool is fundamental to finding the optimum balance between the structural and aeroelastic requirements that drive the design of bluff deck bridges. 

Abstract Aero‐structural shape design and optimization of bridge decks rely on accurately estimating their self‐excited aeroelastic forces within the design domain. The inherent nonlinear features of bluff body aerodynamics and the high cost of wind tunnel tests and computational fluid dynamics (CFD) simulations make their emulation as a function of deck shape and reduced velocity challenging. State‐of‐the‐art methods address deck shape tailoring by interpolating discrete values of integrated flutter derivatives (FDs) in the frequency domain. Nevertheless, more sophisticated strategies can improve surrogate accuracy and potentially reduce the required number of samples. We propose a time domain emulation strategy harnessing temporal fusion transformers (TFTs) to predict the self‐excited forces time series before their integration into FDs. Emulating aeroelastic forces in the time domain permits the inclusion of time‐series amplitudes, frequencies, phases, and other properties in the training process, enabling a more solid learning strategy that is independent of the self‐excited forces modeling order and the inherent loss of information during the identification of FDs. TFTs' long‐ and short‐term context awareness, combined with their interpretability and enhanced ability to deal with static and time‐dependent covariates, make them an ideal choice for predicting unseen aeroelastic forces time series. The proposed TFT‐based metamodel offers a powerful technique for drastically improving the accuracy and versatility of wind‐resistant design optimization frameworks. 

Validation of CFD tornado wind field with experimental or field measurements is limited to comparison of tangential velocity profile at certain elevations above the ground level and few studies are based on comparison of pressure profile. However, important tornado vortex features such as touchdown swirl ratio (ST), core radius (rc), maximum tangential velocity (Vtmax), elevation of maximum tangential velocity (zc) and pressure distribution over a range of varying swirl ratios which strongly influences tornado forces on a building have not been accounted for validation of tornado wind field. In this study, important tornado vortex features are identified and validated with experimental measurements; the important tornado features obtained from the CFD model are found to be in reasonable agreement with experimental measurements. Besides, tornado chambers with different geometrical features (such as different outlet size and location and total heights) are used in different works of literature; however, the effect of variation of those key geometrical features on tornado wind field is not very well understood yet. So, in this work, the size of outlet and total height are systematically varied to study the effect on important tornado vortex parameters. Results indicate that reducing outlet diameter in a tornado chamber increases ST, Vtmax and zc and decreases rc. Similarly, increasing total height of tornado chamber decreases ST, Vtmax and rc whereas zc remains nearly constant. Overall, it is found that variation of outlet diameter has a stronger effect on tornado wind field than the variation in total height of tornado chamber. 

This is a summary paper 

In our earlier work (https://github.com/rpsuark/ASEE21-OpenFOAM-Introduction), it was reasoned that open-source software OpenFOAM would be a cost-effective and more accessible alternative for teaching Computational Fluid Dynamics (CFD) than commercial software. Commercial software like Ansys Fluent costs more than $10k per year for one user. The above-mentioned work models wind flow around a building for smooth flow, whereas extreme winds, which tend to be irregular, can cause various structural failures of buildings. These kinds of irregular wind flows are called turbulent flows. Thus, in this contribution, an additional three-week class module is provided for the ‘CFD for Wind Engineering’ class which includes hands-on material on modeling turbulent wind flow around a building using open-source software OpenFOAM and ParaView. To model the turbulence, Large Eddy Simulation (LES) is considered with a logarithmic inlet profile. To connect the log profile in a coarse grid, the law of the wall condition is also introduced in the OpenFOAM environment. To illustrate the application, the wind flow around a cubic building is considered. The current study’s case files and the extended report are provided at https://github.com/rpsuark/ASEE21-OpenFOAM-LES. 

To train future engineers and to equip them with necessary tools and skills for real-world problem solving, it is important to provide exposure to real-world problem solving by incorporating a software lab module while teaching engineering courses such as Computational Fluid Dynamics (CFD) and/or related Fluids courses. High cost of commercial software packages and limited number of licenses available for course instruction creates several challenges in incorporating commercial software packages in the instructional workflow. To circumvent such limitations, open-source software packages could be a good alternative as open-source software packages can be downloaded and used free of cost and thus provides a wider accessibility to students and practitioners. With the same motivation, in this contribution, an outline for implementing a two-week course module by incorporating open-source software in the instructional workflow is proposed and demonstrated by considering an example of wind flow around a building. The course module outlined in this work can also be extended to formulate a full-fledged CFD course for instructional purposes. Besides the information provided in this paper, authors have also shared an extended report based on current work and the relevant case files via Github repository (https://github.com/rpsuark/ASEE21-OpenFOAM-Introduction) for a hands on learning experience. With the help of information contained in this paper along with the extended report and uploaded case files, readers can install the open-source software packages - ‘OpenFOAM’ and ‘ParaView’, make their own simple case files, run simulations, and visualize the simulated results.