Session Abstracts:
Graduate Student Researcher
Missouri University of Science and Technology
High Fidelity Direct Numerical Simulations of Intense Wave-Wall Impacts
Co-Authors: Wouter Mostert (University of Oxford), Gaurav Savant (USACE Coastal and Hydraulics Laboratory), Daoru Han (Missouri University of Science and Technology), and Guirong Yan (Missouri University of Science and Technology)
Abstract: The effects of wave-wall impacts are important considerations for the design of structures and other infrastructure in coastal communities which may face flooding due to hurricane-induced storm surge. This has not been properly considered in the current building codes. The analysis of wave impacts presents a challenging numerical problem as their effects are sensitive to the wave shape just before impact (Hu et al. 2017, J. Fluids and Struct., 75). This situation is also made more numerically difficult due to the possibility of substantial air entrainment in the overturning wave just before impact (Peregrine & Thais 1996, J. Fluid Mech., 325). To address these challenges, we present two-dimensional direct numerical simulations of solitary gravity waves which impact a vertical wall. The wave traverses a bathymetry which includes an initially uniform depth that transitions to a uniform slope beach ramp before finally shoaling and breaking on a flooded beach of uniform depth before impacting the vertical wall. The beach slope, initial wave amplitude, and wall location are varied such that distinct types of breaker impacts are simulated, including plunging, flip-through, and bore types. Impact pressure profiles along the wall are determined and compared against various analytical predictions and standards. The effects of the local breaking parameters on the wave impact type and their relation to the impact pressure profile are also explored.
Postdoctoral Scholar
Western University
The implications of CFD mesh design on building wind loads
Co-Authors: Girma Bitsuamlak (Western University)
Abstract: Mesh design in Computational Fluid Dynamics (CFD) is a critical yet challenging aspect that significantly influences the accuracy of simulations, particularly in assessing wind loads on buildings. This study aims to establish relationships between the physical requirements of wind loading and CFD meshing parameters, focusing on optimizing mesh design for accurate and efficient simulations.
A key contribution of this research in the approaching region of the computational domain is the proposal of a method to determine the mesh size based on the maximum reduced frequency that needs to be resolved for cladding loads. This relationship ensures that the mesh is adequately refined to capture the necessary physical phenomena without excessive computational cost.
In the region near the bluff body, we introduce the concept of effective viscosity to enhance the fidelity of the simulations. Specifically, for Large Eddy Simulation (LES), a new definition of effective viscosity is proposed, grounded in the sub-grid scale viscosity. This approach aims to better represent the turbulent flow characteristics close to the structure, which are crucial for accurate wind load predictions.
The study is supplemented with examples demonstrating the application of these relationships in practical CFD simulations. The findings underscore the importance of carefully tailored mesh design, highlighting how these proposed relationships can guide the development of efficient meshes that achieve a balance between computational resources and simulation accuracy.
Postdoctoral Scholar
University of Texas Arlington
Assessing Hydrodynamic Impact of Debris Accumulation on Bridges Using Computational Fluid Dynamics Modeling
Co-Authors: Michelle Hummel (University of Texas Arlington)
Abstract: Stream crossing bridges are susceptible to debris blockages, which can cause upstream flooding and increase hydrodynamic forces. Additionally, the accumulation of debris around bridge piers presents considerable risks to both structural integrity and hydraulic performance. This study employs advanced Computational Fluid Dynamics (CFD) modeling techniques, utilizing OpenFOAM, to investigate the impacts of various debris shapes on bridge hydrodynamics. The simulations used two types of debris: flat plate debris, consisting of smaller items like grass, leaves, and paper that get tangled with tree branches and form a flat surface against a bridge, and wedge-shaped debris, which builds up in a streamlined form upstream of bridges. Simulations were run on the Stampede2 HPC system at the Texas Advanced Computing Center (TACC). The results demonstrate that debris significantly alters flow patterns, generating dynamic forces that compromise bridge stability. Notably, flat plate debris on the upstream side of the bridge increases drag force by 46% compared to no-debris conditions. Additionally, wedge-shaped debris substantially increases the overturning moment, posing a risk of bridge overturning. These findings underscore the critical importance of strategic debris management for bridge safety and functionality, providing quantitative insights into how different debris shapes affect hydrodynamic forces and informing robust design criteria and effective countermeasures. The simulation data offer valuable guidelines for engineers to develop enhanced protective strategies against debris-related hydrodynamic impacts.
Associate Professor
Louisiana State University
Quantifying Combined Wind-wave Loads on Offshore Wind Turbines
Co-Authors: Tianqi Ma
Abstract: Wind-wave interactions impose wind forcing on wave surface and wave effects on turbulent wind structures, which essentially influences the wind-wave loading on structures. Existing research treats the wind and wave loading separately and ignores their interactions. The present study aims to characterize the coupled wind-wave loading on offshore wind turbines. A high-fidelity two-phase model is developed to simulate highly turbulent wind-wave fields based on the open-source program OpenFOAM. A numerical case study is conducted to simulate the combined wind-wave loading on offshore wind turbines under operational and extreme conditions. Under operational conditions, the wind-wave coupling effect on the combined loading is minimal. However, under extreme conditions, the coupled wind-wave fields lead to an increase in the average aerodynamic loading and a significant amplification of the fluctuation in the aerodynamic loading. Specifically, the maximum bending moment Fy at both the tower bottom and the monopile bottom experiences an increase of around 6%. Furthermore, the wind-wave coupling effect is evident in the standard deviation of the aerodynamic loading at the tower bottom. The standard deviation of the shear force at the tower bottom increases by up to 45%. Also, the standard deviation of the bending moment at the tower bottom increases by approximately 27%. This study reveals the importance of considering the wind-wave coupling effect under extreme conditions, which provides valuable insights into the planning and design of offshore wind turbines.
Professor
University of Notre Dame
Drone-base Photogrammetry for the simulation of Wind Field and Associated loads on Buildings in Urban Clusters
Co-Authors: Donglian Gu (University of Science and Technology Beijing), Ning Zhang (University of Science and Technology Beijing), and Zhen Xu (University of Science and Technology Beijing)
Abstract: Accurate and efficient simulation of wind fields around buildings and the resulting wind loads in urban environments is crucial for environmental, architectural, and structural engineering applications. The typical process for conducting CFD (Computational Fluid Dynamics) simulations of wind effects on building clusters involves acquiring the geometric model of the buildings, generating a mesh of the geometry, and solving for relevant quantities. However, relying on urban building databases or simplified geometric models, such as footprint extrusion or image-based 3D reconstruction using oblique angle photography and voxelization, often leads to computational challenges and compromises in accuracy.
This study addresses these limitations by introducing a novel workflow that utilizes drone-based photogrammetry, deep learning, and geometric complexity quantification to create highly detailed 3D models of real building clusters. These models are then used to generate a mesh for CFD simulations, enabling more accurate predictions of urban wind fields and wind loads on individual buildings.
The proposed method was validated through simulations of three real-world building clusters. Compared to traditional footprint extrusion models, it achieved a 29.2% reduction in error for large eddy simulation (LES) cases and a 17.6% reduction for steady Reynolds-averaged Navier-Stokes (RANS) equations cases. Additionally, it improved computational efficiency by 33.7% in LES simulations compared to oblique photography-based models. This approach offers a balanced solution for urban wind flow simulations, providing a high level of accuracy and efficiency, and has the potential to complement wind tunnel studies with enhanced sensing capabilities of flow and pressure fields.
Postdoctoral Scholar
UC Berkeley
Towards developing a comprehensive aerodynamic database for low-rise buildings using CFD: validation against wind tunnel data
Co-Authors: Xinlong Du (University of California Berkeley), Christopher Alegbeleye (University of Delaware), Catherine Gorlé (Stanford University), Adam Zsarnoczay (Stanford University), Frank McKenna (University of California Berkeley), Rachel Davidson (University of Delaware), Ertugrul, Taciroglu (UCLA), and Matthew DeJong (University of California Berkeley)
Abstract: Wind-induced damage to low-rise buildings is a leading cause of property loss annually. Traditionally, boundary layer wind tunnel experiments have been the primary method for assessing wind loads on these structures. More recently, with the abundance of high-performance computing, computational fluid dynamics (CFD) promises considerable potential for simulating wind effects on structures, overcoming many of the limitations associated with wind tunnel testing. This study investigates the application of Large Eddy Simulation (LES) for predicting wind loads on low-rise buildings, aiming to develop a comprehensive aerodynamic database that encompasses various building archetypes and exposure conditions. For creating the computational models, the CFD-based workflow implemented in the NHERI-SimCenter/WE-UQ tools is adopted. The first part of the study tackles key challenges in computational wind load evaluation, such as accurate modeling of natural wind turbulence and separated flows around buildings. Then, results from the LES model are validated against boundary layer wind tunnel measurements for different building archetypes and multiple wind directions. The comparison shows that both the approaching wind field and the predicted cladding loads are in satisfactory agreement with the wind tunnel data. Overall, this study highlights the importance of thoroughly validated CFD workflows for accurate assessment of wind loads on low-rise buildings.