Aerodynamic performance of twin-box decks: a parametric study on gap width effects based on validated 2D URANS simulations

[Abstract:] 2D URANS simulations are conducted aiming to study the aerodynamic performance under smooth flow of twin-box decks depending on the gap distance between girders. The Stonecutters Bridge is taken as the reference geometry. In this parametric study, 14 gap to depth ratios in the range 0 ≤ G/D ≤ 9.70 are investigated, and for each geometry, 11 angles of attack in the range −10 ◦ ≤ α ≤ 10 ◦ are considered. Specific goals of this research have been: identification of the fundamental flow features, study of mean and fluctuating pressure coefficients distributions, identification of the vortex shedding mechanisms and general aerodynamic characterisation based on force coefficients. The numerical results provided herein are validated with wind tunnel data previously reported in the literature, finding a good agreement. A critical gap to depth ratio at G/D = 2.35, in terms of aerodynamic response, was identified, which is consistent with the value reported in the literature for a different bridge based on wind tunnel tests. The obtained set of data provide a general picture of the expected aerodynamic performance of a twin-box deck depending on the gap distance and could be of great value at the early design stage of long-span cable-supported bridges.Ministerio de Economía y Competitividad; BIA2016-76656-RMinisterio de Economía y Competitividad; BES-2014-068418Ministerio de Economía y Competitividad; BIA2013-41965-PXunta de Galicia; ED431C 2017/7

NUMERICAL AND EXPERIMENTAL CALCULATION OF ROLL AMPLITUDE EFFECT ON ROLL DAMPING

Roll motion is still a challenging problem in naval architecture and an adequate prediction of this physical phenomenon is important because of its undesirable effects such as capsizing. There are several methods using linear potential theory to predict roll motion, such as strip method, however, the accuracy of the calculated results lag behind the accuracy of other degrees of freedom due to viscosity. Viscosity have an important effect on roll damping, especially near resonance, and as it is known, it is not included in potential flow methods. Vortex shedding is the main physical phenomena in viscous damping of the roll motion and it affects the flow velocity around the bilge. This may lead to pressure increase or decrease on the hull. In the present study, roll damping of a forced rolling hull with bilge keels at different roll amplitudes was calculated numerically by using an Unsteady Reynolds-averaged Navier–Stokes (URANS) solver. For the purpose of validation, forced roll experiments were carried out and the results were plotted next to numerical results. The generated vortices around the hull and bilge keel were observed in the URANS calculations. In the case of large roll amplitude motion, the vortex shedding from the bilge keel interacts with the free surface and leads to decrease on roll damping

Verifikationsmethodik für die rechnerische Windtechnik Vorhersage von Windlasten an Tragwerken

In this thesis, a new credibility assessment framework is developed for computational wind engineering (CWE) simulations. The framework is mainly developed for testing code implementation correctness and estimation of the discretization uncertainty for eddy-resolving, and unsteady simulations. The framework is composed of two main milestones. First, a modular and flexible procedure for code verification is developed with the ability of testing black box codes. The code verification procedure focuses on the consistency of the code implementation and convergence of field variables. The procedure for code verification consists of analytical benchmarks, either exact or manufactured, with increasing complexity to test the implementation of each term in the Navier-Stokes equation. Second, the credibility assessment framework has a guideline for the quantification of discretization error/uncertainty. More precisely, guidelines are defined for solution verification. The discretization error/uncertainty estimation is based on Richardson Extrapolation approach. A solution biased uncertainty estimator is used to account for using unstructured grids, non-uniform refinement, and non-asymptotic solutions. The newly developed framework has a new definition for the measurement of grid size, handling simulation data with anomalous behavior, and for the safety factor definition in the uncertainty quantification of the discretization error. The assessment methodology is suited to both well- and ill-behaved sequences of simulations. The performance of the assessment methodology is checked with a glimpse on validation with experimental data. Finally, it can be concluded that the developed verification methodology is highly qualified to judge the quality of CWE simulations. Moreover, the generality and modularity of the framework makes it applicable to any software environment regardless of the discretization scheme. Consequently, the methodology encourages further research on the identification of the reliability of CWE simulations.In dieser Arbeit wird ein neues Rahmenwerk zur Glaubwürdigkeitsbewertung für rechnergestützte Windsimulationen (CWE) entwickelt. Der Rahmen wird hauptsächlich für die Prüfung der Korrektheit der Code-Implementierung und die Abschätzung der Diskretisierungsunsicherheit für wirbelauflösende und instationäre Simulationen entwickelt. Das Framework besteht aus zwei Hauptmeilensteinen. Erstens wird ein modulares und flexibles Verfahren zur Code-Verifikation entwickelt, das die Möglichkeit bietet, Black-Box-Codes zu testen. Das Code-Verifikationsverfahren konzentriert sich auf die Konsistenz der Code-Implementierung und die Konvergenz der Feldvariablen. Das Verfahren zur Codeverifizierung besteht aus analytischen Benchmarks, entweder exakt oder hergestellt, mit zunehmender Komplexität, um die Implementierung jedes Terms in der Navier-Stokes-Gleichung zu testen. Zweitens verfügt das Rahmenwerk zur Glaubwürdigkeitsbewertung über einen Leitfaden zur Quantifizierung von Diskretisierungsfehlern/Unsicherheiten. Genauer gesagt, werden Richtlinien für die Verifizierung der Lösung definiert. Die Schätzung des Diskretisierungsfehlers/der Unsicherheit basiert auf dem Richardson-Extrapolationsansatz. Ein lösungsverzerrter Unsicherheitsschätzer wird verwendet, um die Verwendung unstrukturierter Gitter, ungleichmäßiger Verfeinerung und nicht asymptotischer Lösungen zu berücksichtigen. Der neu entwickelte Rahmen hat eine neue Definition für die Messung der Gittergröße, die Behandlung von Simulationsdaten mit anomalem Verhalten und für die Definition des Sicherheitsfaktors bei der Unsicherheitsquantifizierung des Diskretisierungsfehlers. Die Bewertungsmethodik eignet sich sowohl für gut als auch für schlecht verhaltene Simulationsfolgen. Die Leistungsfähigkeit der Bewertungsmethodik wird mit einem Blick auf die Validierung mit experimentellen Daten überprüft. Abschließend kann festgestellt werden, dass die entwickelte Verifikationsmethodik hoch qualifiziert ist, um die Qualität von CWE-Simulationen zu beurteilen. Darüber hinaus macht die Allgemeingültigkeit und Modularität des Rahmens es für jede Softwareumgebung unabhängig vom Diskretisierungsschema anwendbar. Folglich fördert die Methodik weitere Forschungen zur Identifizierung der Zuverlässigkeit von CWE-Simulationen

Hydrodynamic Analysis of Fluid Obstruction Around Different Geometric Bodies

The aim of this paper is to conduct a hydrodynamic analysis of fluid flow around different geometric bodies on the laboratory physical model HM 133 of the Gunt Company from Hamburg and to show the formation of boundary layer and separation points on the observed bodies. The paper covers the field of real fluid dynamics which includes a description of laminar and turbulent flow together with a Reynolds number. A detailed representation of the boundary layer, its characteristics, and its structure are included. The body models in the paper used on the HM 133 physical model were an oblong straight body and cylindrical bodies with 6 mm, 12 mm, 18 mm, and 24 mm in diameter. The research was conducted in the Hydrotechnical Laboratory of the Faculty of Civil Engineering, University of Rijeka. Hydrodynamic analyses were made based on the tested body models on the physical model HM 133 together with the analyses on the numerical models performed using the ANSYS Fluent software

An Accurate Finite Element Method for the Numerical Solution of Isothermal and Incompressible Flow of Viscous Fluid

Despite its numerical challenges, finite element method is used to compute viscous fluid flow. A consensus on the cause of numerical problems has been reached; however, general algorithms—allowing a robust and accurate simulation for any process—are still missing. Either a very high computational cost is necessary for a direct numerical solution (DNS) or some limiting procedure is used by adding artificial dissipation to the system. These stabilization methods are useful; however, they are often applied relative to the element size such that a local monotonous convergence is challenging to acquire. We need a computational strategy for solving viscous fluid flow using solely the balance equations. In this work, we present a general procedure solving fluid mechanics problems without use of any stabilization or splitting schemes. Hence, its generalization to multiphysics applications is straightforward. We discuss emerging numerical problems and present the methodology rigorously. Implementation is achieved by using open-source packages and the accuracy as well as the robustness is demonstrated by comparing results to the closed-form solutions and also by solving well-known benchmarking problems

How to Control Hydrodynamic Force on Fluidic Pinball via Deep Reinforcement Learning

Deep reinforcement learning (DRL) for fluidic pinball, three individually rotating cylinders in the uniform flow arranged in an equilaterally triangular configuration, can learn the efficient flow control strategies due to the validity of self-learning and data-driven state estimation for complex fluid dynamic problems. In this work, we present a DRL-based real-time feedback strategy to control the hydrodynamic force on fluidic pinball, i.e., force extremum and tracking, from cylinders' rotation. By adequately designing reward functions and encoding historical observations, and after automatic learning of thousands of iterations, the DRL-based control was shown to make reasonable and valid control decisions in nonparametric control parameter space, which is comparable to and even better than the optimal policy found through lengthy brute-force searching. Subsequently, one of these results was analyzed by a machine learning model that enabled us to shed light on the basis of decision-making and physical mechanisms of the force tracking process. The finding from this work can control hydrodynamic force on the operation of fluidic pinball system and potentially pave the way for exploring efficient active flow control strategies in other complex fluid dynamic problems

Stabilization Trajectory and Recovery System for High Altitude Weather Balloon Payloads (S.T.A.R.)

Of the 657,000 global balloon launches each year, only 20% of payloads are recovered, leading to unsustainable business and environmental practices. This paper details the development and evaluation of the S.T.A.R. (Stabilization, Trajectory, and Recovery) system, which increases the recovery rate of weather balloon sensors by enabling ideal landing conditions. System testing concludes that S.T.A.R. is capable of housing weather sensors in a fully controllable glider capable of targeted landing. If properly scaled up and redesigned for mass production, the S.T.A.R. system increases weather-sensing equipment recovery for weather-reporting institutions around the world. Although the featured iterations consist of basswood, carbon fiber spars, and 3D-printed parts, future iterations should be made primarily of foam for expedited manufacturing. This additionally allows for a lightweight and uniform cylindrical body to reduce drag

Simulations of propelling and energy harvesting articulated bodies via vortex particle-mesh methods

The emergence and understanding of new design paradigms that exploit flow induced mechanical instabilities for propulsion or energy harvesting demands robust and accurate flow structure interaction numerical models. In this context, we develop a novel two dimensional algorithm that combines a Vortex Particle-Mesh (VPM) method and a Multi-Body System (MBS) solver for the simulation of passive and actuated structures in fluids. The hydrodynamic forces and torques are recovered through an innovative approach which crucially complements and extends the projection and penalization approach of Coquerelle et al. and Gazzola et al. The resulting method avoids time consuming computation of the stresses at the wall to recover the force distribution on the surface of complex deforming shapes. This feature distinguishes the proposed approach from other VPM formulations. The methodology was verified against a number of benchmark results ranging from the sedimentation of a 2D cylinder to a passive three segmented structure in the wake of a cylinder. We then showcase the capabilities of this method through the study of an energy harvesting structure where the stocking process is modeled by the use of damping elements

Computational fluid dynamics modelling of pipeline on-bottom stability.

Subsea pipelines are subjected to wave and steady current loads which cause pipeline stability problems. Current knowledge and understanding on the pipeline on-bottom stability is based on the research programmes from the 1980s such as the Pipeline Stability Design Project (PIPESTAB) and American Gas Association (AGA) in Joint Industry Project. These projects have mainly provided information regarding hydrodynamic loads on pipeline and soil resistance in isolation. In reality, the pipeline stability problem is much more complex involving hydrodynamic loadings, pipeline response, soil resistance, embedment and pipe-soil-fluid interaction. In this thesis Computational Fluid Dynamics (CFD) modelling is used to investigate and establish the interrelationship between fluid (hydrodynamics), pipe (subsea pipeline), and soil (seabed). The effect of soil types, soil resistance, soil porosity and soil unit weight on embedment was examined. The overall pipeline stability alongside pipeline diameter and weight and hydrodynamic effect on both soil (resulting in scouring) and pipeline was also investigated. The use of CFD provided a better understanding of the complex physical processes of fluid-pipe-soil interaction. The results show that the magnitude of passive resistance is on the average eight times that of lateral resistance. Thus passive resistance is of greater significance for subsea pipeline stability design hence the reason why Coulombs friction theory is considered as conservative for stability design analysis, as it ignores passive resistance and underestimates lateral resistance. Previous works (such as that carried out by Lyons and DNV) concluded that soil resistance should be determined by considering Coulombs friction based on lateral resistance and passive resistance due to pipeline embedment, but the significance of passive resistance in pipeline stability and its variation in sand and clay soils have not be established as shown in this thesis. The results for soil porosity show that increase in pipeline stability with increasing porosity is due to increased soil liquefaction which increases soil resistance. The pipe-soil interaction model by Wagner et al. established the effect of soil porosity on lateral soil resistance but did not attribute it to soil liquefaction. Results showed that the effect of pipeline diameter and weight vary with soil type; for sand, pipeline diameter showed a greater influence on embedment with a 110% increase in embedment (considering combined effect of diameter and weight) and a 65% decrease in embedment when normalised with diameter. While pipeline weight showed a greater influence on embedment in clay with a 410% increase. The work of Gao et al. did not completely establish the combined effect of pipeline diameter and weight and soil type on stability. Results also show that pipeline instability is due to a combination of pipeline displacement due to vortex shedding and scouring effect with increasing velocity. As scoring progresses, maximum embedment is reached at the point of highest velocity. The conclusion of this thesis is that designing for optimum subsea pipeline stability without adopting an overly conservative approach requires taking into consideration the following; combined effect of hydrodynamics of fluid flow on soil type and properties, and the pipeline, and the resultant scour effect leading to pipeline embedment. These results were validated against previous experimental and analytical work of Gao et al, Brennodden et al and Griffiths