Vaibhav Joshi

BITS Pilani, K K Birla Goa · Department of Mechanical Engineering

Locomotion of aquatic animals involves flapping of their body to generate lift and thrust. Through evolution, they have mastered their ability to move through complex environments in an energy-efficient manner. A crucial component of this movement is the ability to actively bend their bodies to generate maximum thrust. This motion is widely termed...

The current study investigates the flow dynamics around rigid flapping NACA0015 foils in tandem configuration at low Reynolds number. The effect of the heave amplitude of the upstream foil on the propulsive performance of the downstream foil is studied for heave amplitudes of 0.2-1 times the downstream foil chord length. The tandem foils are modell...

Biological locomotion, observed in the flexible wings of birds and insects, bodies and fins of aquatic mammals and fishes, consists of their ability to morph the wings/fins. The morphing capability holds significance in the ability of fishes to swim upstream without spending too much energy and that of birds to glide for extended periods of time. S...

In this study, we present two and three-dimensional numerical investigation to understand the combined effects of the non-dimensional heave amplitude varying from 0 to 1 and the pitch amplitude ranging from 0° to 30° on the propulsive performance for a single and tandem foil system at Reynolds number 1100 and reduced frequency 0.2. We initially pre...

Accuracy and numerical stability of nonlinear coupled fluid-elastic interaction simulations largely depends on the coupling and interface modeling algorithms. As part of the numerical coupling, the coupled solver requires to satisfy the kinematic and dynamic continuity conditions along the interface in addition to the fluid and structural dynamics...

Two-phase fluid-structure interactions are commonly observed phenomena in industries as well as daily life ranging from small-scale droplet interactions to large-scale ocean wave-current interaction with offshore marine structures. These applications involve complex multiscale and coupled nonlinear dynamics which can be quite challenging to predict...

Biological locomotion, observed in the flexible wings of birds and insects, bodies and fins of aquatic mammals and fishes, consists of their ability to morph the wings/fins. The morphing capability holds significance in the abilities of fishes to swim upstream without spending too much energy and that of birds to glide for extended periods of time....

In the previous chapter, we studied some of the basics of the finite element variational formulation for a transient convection-diffusion-reaction equation, which forms a canonical form for the nonlinear fluid-structure interaction equations.

In this chapter, we combine the balance laws of fluid and solid fields to formulate fluid-structure interactions.

Continuing the journey of the partitioned-type of coupling techniques, we focus on the modeling of turbulent effects in this chapter. These effects are predominant at high Reynolds numbers and are inherently chaotic and complex to capture by a numerical simulation. The closure problem for the turbulent flow can be broadly solved by three approaches...

This book is intended to provide a compilation of the state-of-the-art numerical methods for nonlinear fluid-structure interaction using the moving boundary Lagrangian-Eulerian formulation. Single and two-phase viscous incompressible fluid flows are considered with the increasing complexity of structures ranging from rigid-body, linear elastic and...

Before proceeding with the variational formulation of the fluid-structure coupled system, let us look at the convection-diffusion-reaction (CDR) equation which forms a canonical equation for any continuum transport system. The present chapter discusses the variational formulation and finite element technique applied to the CDR equation and reviews...

Interaction between interconnected multiple rigid or flexible bodies with the fluid can be found in engineering applications such as underwater robotics, helicopter rotor dynamics, offshore wind turbines and oil/gas platforms, bio-inspired flying vehicles, among others.

Two-phase fluid-structure interaction is omnipresent. It has applications from offshore pipelines carrying oil or gas [42, 195], marine vessels subjected to free-surface ocean waves, blood flow through arteries and veins, to multiphase flow inside heat exchangers.

This book aims at providing a survey of mathematical formulations and simulation techniques for fluid-structure interactions. As the name suggests, fluid-structure interactions involve the interplay of fluid flow and deformable/moving solid structures, aimed at understanding some physical phenomenon or designing an engineering device.

In this chapter, we deal with the first type of strategy in solving the fluid-structure interaction system, namely, monolithic techniques.

When a fluid flows past or inside a structure, loads exerted by the fluid tend to change the configuration of the structure by inducing deformations and/or displacements.

In the previous chapters, we formulated the finite element discretization of the fluid-structure interaction equations and looked into the monolithic type of coupling methods. An essential requirement of such a coupled system is the accurate description of the fluid–structure interface. In the monolithic technique, this feature is naturally taken c...

The present study investigates the mechanisms of wake-induced flow dynamics in tandem National Advisory Committee for Aeronautics 0015 flapping foils at low Reynolds number of Re = 1100. A moving mesh arbitrary Lagrangian–Eulerian framework is utilized to realize the prescribed flapping motion of the foils while solving the flow via incompressible...

Flapping hydrofoils in tandem configuration find applications in wave gliders, dragonfly, dorsal-tail fin interaction in fishes, among others. The flapping motion consists of a combination of heaving and pitching motion. This type of motion involves complex interaction of the vortices shed from the upstream hydrofoil with the downstream hydrofoil,...

In this paper, we present a numerical study on the transverse flow-induced vibration (FIV) of an elastically mounted sphere in the vicinity of a free surface at subcritical Reynolds numbers. We assess the interaction dynamics and the vibration characteristics of fully submerged and piercing spheres that are free to vibrate in the transverse directi...

We present a finite element based variational interface-preserving and conservative phase-field formulation for the modeling of incompressible two-phase flows with surface tension dynamics. The preservation of the hyperbolic tangent interface profile of the convective Allen-Cahn phase-field formulation relies on a novel time-dependent mobility mode...

We present a three-dimensional (3D) partitioned aeroelastic formulation for a flexible multibody system interacting with incompressible turbulent fluid flow. While the incompressible Navier-Stokes system is discretized using a stabilized Petrov-Galerkin procedure, the multibody structural system consists of a generic interaction of multiple compone...

Flow-structure interactions of submerged or floating bodies can lead to undesired behavior in many marine and offshore engineering applications. In this paper, we consider a complex nonlinear dynamical system of unsteady wake flow interacting with a freely moving tugboat in open water. To meet the operational demands of compact, agile, and high pow...

We present a finite element based variational interface-preserving and conservative phase-field formulation for the modeling of incompressible two-phase flows with surface tension dynamics. The preservation of the hyperbolic tangent interface profile of the convective Allen-Cahn phase-field formulation relies on a novel time-dependent mobility mode...

We present a numerical study on the transverse flow-induced vibration (FIV) of an elastically mounted sphere in the vicinity of a free surface at subcritical Reynolds numbers. To begin, We verify and analyze the mode transitions and the motion trajectories of a fully submerged sphere vibrating freely in all directions for the Reynolds number up to...

In this paper, we study the aeroelastic behavior of a hovering bat using a three-dimensional variational fluid-flexible multibody framework. The aeroelastic framework consists of solving the coupled nonlinear interactions of flexible multiple components of the bat wing with the unsteady aerodynamics. To begin, we carry out the mesh convergence and...

Fluctuating wave force on a bluff body is of great significance in many offshore and marine engineering applications. We present a Convolutional Neural Network (CNN) based data-driven computing to predict the unsteady wave forces on bluff bodies due to the free-surface wave motion. For the full-order modeling and high-fidelity data generation, the...

Precise position and motion control of offshore vessels is often challenging, especially in harsh environment due to highly nonlinear dynamic loads from free-surface ocean waves and currents. In addition, coupled nonlinear effects of risers and mooring cables connected to the vessel can lead to unexpected responses, thus justifying the significance...

In this paper, we present an adaptive variational procedure for unstructured meshes to capture fluid-fluid interfaces in two-phase flows. The two phases are modeled by the phase-field finite element formulation, which involves the conservative Allen-Cahn equation coupled with the incompressible Navier-Stokes equations. The positivity preserving var...

We present a novel partitioned iterative formulation for modeling of fluid-structure interaction in two-phase flows. The variational formulation consists of a stable and robust integration of three blocks of differential equations, viz., incompressible viscous fluid, a rigid or flexible structure and two-phase indicator field. The fluid-fluid inter...

We present a three-dimensional (3D) common-refinement method for non-matching meshes between discrete non-overlapping subdomains of incompressible fluid and nonlinear hyperelastic structure. To begin, we first investigate the accuracy of common-refinement method (CRM) to satisfy traction equilibrium condition along the fluid-elastic interface with...

This paper is concerned with the partitioned iterative formulation to simulate the fluid-structure interaction of a nonlinear multibody system in an incompressible turbulent flow. The proposed formulation relies on a three-dimensional (3D) incompressible turbulent flow solver, a nonlinear monolithic elastic structural solver for constrained flexibl...

We present an adaptive variational procedure for unstructured meshes to capture the fluid-fluid interface in two-phase flows. The two phases are modeled by the phase-field finite element formulation involving the conservative Allen-Cahn equation coupled with the incompressible Navier-Stokes equations. The positivity preserving variational formulati...

We present a positivity preserving variational scheme for the phase-field modeling of incompressible two-phase flows with high density ratio and using meshes of arbitrary topology. The variational finite element technique relies on the Allen-Cahn phase-field equation for capturing the phase interface on a fixed mesh with a mass conservative and ene...

We present a bounded and positivity preserving variational (PPV) method for the turbulence transport equation of Spalart–Allmaras based delayed detached eddy simulation (DDES). We employ the developed solver to simulate the vortex-induced vibration of a slender flexible riser immersed in a turbulent flow. The fluid-structure interface problem is so...

Due to the complexity involved in the vortex-induced vibration (VIV) of long offshore risers, the fundamental understanding of the coupled kinematics and dynamics of the standing and traveling waves is not well established. In the present contribution, a systematic numerical study on slender flexible riser immersed in a turbulent flow is performed...

A positivity preserving variational (PPV) procedure is proposed to solve the convection–diffusion–reaction (CDR) equation. Through the generalization of stabilized finite element methods, the present variational technique offers minimal phase and amplitude errors for different regimes associated with convection, diffusion and reaction effects. With...

A group of circular cylinders exists in many engineering practices, such as offshore drilling riser system. Due to the interference between the riser main tube and auxiliary lines, the hydrodynamic forces acting on the riser system is much different from those on a single circular cylinder. It is very rare in the publication and still not certain i...

When a riser array system is subjected to a uniform flow, an unstable flow-induced vibration commonly occurs among cylinders, generally called fluid-elastic instability. It can cause long-term or short-term damage to the riser array system. A numerical investigation has been performed in the present study. Generally, flow-induced vibrations include...