An official website of the United States government
Abstract We present a new computational fluid dynamics approach for simulating two‐phase flow in hybrid systems containing solid‐free regions and deformable porous matrices. Our approach is based on the derivation of a unique set of volume‐averaged partial differential equations that asymptotically approach the Navier‐Stokes Volume‐of‐Fluid equations in solid‐free regions and multiphase Biot Theory in porous regions. The resulting equations extend our recently developed Darcy‐Brinkman‐Biot framework to multiphase flow. Through careful consideration of interfacial dynamics (relative permeability and capillary effects) and extensive benchmarking, we show that the resulting model accurately captures the strong two‐way coupling that is often exhibited between multiple fluids and deformable porous media. Thus, it can be used to represent flow‐induced material deformation (swelling, compression) and failure (cracking, fracturing). The model's open‐source numerical implementation,hybridBiotInterFoam, effectively marks the extension of computational fluid mechanics into modeling multiscale multiphase flow in deformable porous systems. The versatility of the solver is illustrated through applications related to material failure in poroelastic coastal barriers and surface deformation due to fluid injection in poro‐visco‐plastic systems.
more »
« less
Flow Supervision for Deformable NeRF
In this paper we present a new method for deformable NeRF that can directly use optical flow as supervision. We overcome the major challenge with respect to the computationally inefficiency of enforcing the flow constraints to the backward deformation field, used by deformable NeRFs. Specifically, we show that inverting the backward deformation function is actually not needed for computing scene flows between frames. This insight dramatically simplifies the problem, as one is no longer constrained to deformation functions that can be analytically inverted. Instead, thanks to the weak assumptions required by our derivation based on the inverse function theorem, our approach can be extended to a broad class of commonly used backward deformation field. We present results on monocular novel view synthesis with rapid object motion, and demonstrate significant improvements over baselines without flow supervision.
more »
« less
- Award ID(s):
- 1925281
- PAR ID:
- 10482402
- Publisher / Repository:
- IEEE
- Date Published:
- ISBN:
- 979-8-3503-0129-8
- Page Range / eLocation ID:
- 21128 to 21137
- Format(s):
- Medium: X
- Location:
- Vancouver, BC, Canada
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The interaction between deformable surfaces and oscillatory driving is known to produce complex secondary time-averaged flows due to inertial and elastic nonlinearities. Here, we revisit the problem of oscillatory flow in a cylindrical tube with a deformable wall, and analyse it under a long-wave theory for small deformations, but for arbitrary Womersley numbers. We find that the oscillatory pressure does not vary linearly along the length of a deformable channel, but instead decays exponentially with spatial oscillations. We show that this decay occurs over an elasto-visco-inertial length scale that depends on the material properties of the fluid and the elastic walls, the geometry of the system, and the frequency of the oscillatory flow, but is independent of the amplitude of deformation. Inertial and geometric nonlinearities associated with the elastic deformation of the channel drive a time-averaged secondary flow. We quantify the flow using numerical solutions of the perturbation theory, and gain insight by developing analytic approximations. The theory identifies a complex non-monotonic dependence of the time-averaged flux on the elastic compliance and inertia, including a reversal of the flow. Finally, we show that our analytic theory is in excellent quantitative agreement with the three-dimensional direct numerical simulations of Pandeet al.(Phys. Rev. Fluids, vol. 8, no. 12, 2023, 124102).more » « less
-
null (Ed.)We present an experimental investigation of the acceleration statistics and the added mass tensor of deformable gas bubbles in turbulence. By simultaneously tracking both bubbles and their surrounding flow in three dimensions, we find two independent ways of estimating the bubble acceleration: either directly measured from three-dimensional bubble trajectories or indirectly calculated from the bubble's equation of motion. When such an equation is projected onto the bubble frame, the added-mass coefficient becomes a diagonal tensor with three elements being linked to the standard deviation of bubble acceleration along three bubble principal axes. This constraint aids in experimentally determining the added mass coefficient tensor. The obtained trend of $$C_A$$ seems to agree with Lamb's potential flow solutions for spheroids, suggesting that the added-mass force on deformable bubbles can be modelled using spheroids with the same geometry and orientation. In addition, the probability density function of the relative orientation between the semi-major axis of deformed bubbles and the slip acceleration in turbulence is shown. A surprising finding is that the bubble orientation, indicated by the bubble's major axis, is not random in turbulence but rather is preferentially aligned with the slip acceleration. The degree of this alignment increases as bubbles deform more. Because accelerating along the major axis of a more deformed bubble entails reduced added mass, the acceleration standard deviation of deformable bubbles increases as a function of the bubble aspect ratio.more » « less
-
null (Ed.)A phenomenological model is proposed to describe the deformation and orientation dynamics of finite-sized bubbles in both quiescent and turbulent aqueous media. This model extends and generalizes a previous work that is limited to only the viscous deformation of neutrally buoyant droplets, conducted by Maffettone & Minale ( J. Non-Newtonian Fluid Mech. , vol. 78, 1998, pp. 227–241), into a high Reynolds number regime where the bubble deformation is dominated by flow inertia. By deliberately dividing flow inertia into contributions from the slip velocity and velocity gradients, a new formulation for bubble deformation is constructed and validated against two experiments designed to capture the deformation and orientation dynamics of bubbles simultaneously with two types of surrounding flows. The relative importance of each deformation mechanism is measured by its respective dimensionless coefficient, which can be isolated and evaluated independently through several experimental constraints without multi-variable fitting, and the results agree with the model predictions well. The acquired coefficients imply that bubbles reorient through body rotation as they rise in water at rest but through deformation along a different direction in turbulence. Finally, we provide suggestions on how to implement the proposed framework for characterizing the dynamics of deformable bubbles/drops in simulations.more » « less
-
Deformable microchannels emulate a key characteristic of soft biological systems and flexible engineering devices: the flow-induced deformation of the conduit due to slow viscous flow within. Elucidating the two-way coupling between oscillatory flow and deformation of a three-dimensional (3-D) rectangular channel is crucial for designing lab-on-a-chip and organ-on-a-chip microsystems and eventually understanding flow–structure instabilities that can enhance mixing and transport. To this end, we determine the axial variations of the primary flow, pressure and deformation for Newtonian fluids in the canonical geometry of a slender (long) and shallow (wide) 3-D rectangular channel with a deformable top wall under the assumption of weak compliance and without restriction on the oscillation frequency (i.e. on the Womersley number). Unlike rigid conduits, the pressure distribution is not linear with the axial coordinate. To validate this prediction, we design a polydimethylsiloxane-based experimental platform with a speaker-based flow-generation apparatus and a pressure acquisition system with multiple ports along the axial length of the channel. The experimental measurements show good agreement with the predicted pressure profiles across a wide range of the key dimensionless quantities: the Womersley number, the compliance number and the elastoviscous number. Finally, we explore how the nonlinear flow–deformation coupling leads to self-induced streaming (rectification of the oscillatory flow). Following Zhang and Rallabandi (J. Fluid Mech., vol. 996, 2024, p. A16), we develop a theory for the cycle-averaged pressure based on the primary problem’s solution, and we validate the predictions for the axial distribution of the streaming pressure against the experimental measurements.more » « less
