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arxiv: 2106.16052 · v1 · submitted 2021-06-30 · 🧮 math.NA · cs.NA

Backward Euler method for the equations of motion arising in Oldroyd model of order one with nonsmooth initial data

Pith reviewed 2026-05-24 13:21 UTC · model grok-4.3

classification 🧮 math.NA cs.NA
keywords Oldroyd modelbackward Euler methodfinite element discretizationa priori error estimatesviscoelastic fluidsnonsmooth initial datauniform in time
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The pith

The backward Euler finite element method for the Oldroyd model achieves optimal L2 error estimates that are uniform in time for nonsmooth initial data under a uniqueness condition.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper develops and analyzes a numerical scheme for the equations describing viscoelastic fluid motion in the Oldroyd model of order one in two dimensions. It uses backward Euler stepping in time together with finite element approximation in space, for cases where the forcing is time-independent or bounded in time. The discrete solutions are shown to stay bounded in the Dirichlet norm for all time. Optimal error bounds in the L2 norm are proved for problems starting from nonsmooth data, and these bounds do not grow with time provided the continuous problem has unique solutions.

Core claim

For the 2D Oldroyd model of viscoelastic fluids of order one, the backward Euler method with finite element discretization in space yields discrete solutions that are bounded uniformly in time in the Dirichlet norm. Optimal a priori error estimates in the L2 norm are derived for nonsmooth initial data, and these estimates remain uniform in time when the uniqueness condition holds for the continuous problem.

What carries the argument

Backward Euler time discretization combined with finite element spatial discretization applied to the Oldroyd viscoelastic fluid equations.

If this is right

  • The discrete solutions remain bounded in the Dirichlet norm uniformly in time.
  • Optimal L2-norm error estimates are obtained for nonsmooth initial data.
  • These error estimates are uniform in time under the uniqueness assumption.
  • Numerical results confirm the theoretical predictions.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The method could be applied to long-time integration of viscoelastic flows without accumulating errors over time.
  • Similar uniform estimates might be possible for other time discretizations if they preserve the structure used here.
  • Extensions to three dimensions would require establishing the uniqueness condition first.

Load-bearing premise

The continuous Oldroyd problem satisfies a uniqueness condition.

What would settle it

A numerical experiment where the L2 error grows without bound as time increases, for a case with nonsmooth initial data where uniqueness is known to hold.

Figures

Figures reproduced from arXiv: 2106.16052 by Amiya K. Pani, Bikram Bir, Deepjyoti Goswami.

Figure 1
Figure 1. Figure 1: Velocity and pressure errors based on P2-P0 element for [PITH_FULL_IMAGE:figures/full_fig_p024_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Velocity and pressure errors based on MINI element for E [PITH_FULL_IMAGE:figures/full_fig_p025_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Velocity and pressure errors based on P2-P0 element for [PITH_FULL_IMAGE:figures/full_fig_p026_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Velocity and pressure errors based on MINI element for E [PITH_FULL_IMAGE:figures/full_fig_p026_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Velocity errors in L 2 - norm with respect to time for Example 7.2. For the example 7.2, the numerical results are shown for final time T = 10, 20, 30, 40 and 50 with µ = 1, γ = 0.1, δ = 1, k = 0.1 and h = 2−i , i = 2, 3, . . . , 6. We represent the errors and the convergence rates for the velocity in L 2 -norm for P2-P0 and MINI-elements in [PITH_FULL_IMAGE:figures/full_fig_p026_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Uniform in time errors for P2-P0 element (left) and MINI ele [PITH_FULL_IMAGE:figures/full_fig_p027_6.png] view at source ↗
read the original abstract

In this paper, a backward Euler method combined with finite element discretization in spatial direction is discussed for the equations of motion arising in the $2D$ Oldroyd model of viscoelastic fluids of order one with the forcing term independent of time or in $L^{\infty}$ in time. It is shown that the estimates of the discrete solution in Dirichlet norm is bounded uniformly in time. Optimal {\it a priori} error estimate in $\textbf{L}^2$-norm is derived for the discrete problem with non-smooth initial data. This estimate is shown to be uniform in time, under the assumption of uniqueness condition. Finally, we present some numerical results to validate our theoretical results.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 0 minor

Summary. The manuscript analyzes a backward Euler finite-element discretization of the 2D Oldroyd model of order one. It proves that the discrete solution remains bounded uniformly in time in the Dirichlet norm when the forcing is time-independent or merely L^∞ in time. Under an additional uniqueness assumption on the continuous problem, it derives an optimal a priori L² error estimate that is also uniform in time, even for nonsmooth initial data, and supplies numerical experiments to illustrate the theory.

Significance. If the uniqueness condition can be justified for the stated data classes, the uniform-in-time L² error bound would constitute a useful advance in the numerical analysis of viscoelastic flows, extending existing results to nonsmooth data while controlling the growth of the error constant.

major comments (1)
  1. [Abstract] Abstract: The claim of a uniform-in-time optimal L² error estimate is obtained only after invoking an unproven uniqueness condition on the continuous Oldroyd system. No proof or reference is supplied showing that this condition holds for the 2-D model with L^∞-in-time forcing and nonsmooth initial data; without it the Gronwall argument produces a time-dependent factor that may grow, undermining the uniformity assertion.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the careful reading and for highlighting the role of the uniqueness assumption. We respond to the major comment below.

read point-by-point responses
  1. Referee: [Abstract] Abstract: The claim of a uniform-in-time optimal L² error estimate is obtained only after invoking an unproven uniqueness condition on the continuous Oldroyd system. No proof or reference is supplied showing that this condition holds for the 2-D model with L^∞-in-time forcing and nonsmooth initial data; without it the Gronwall argument produces a time-dependent factor that may grow, undermining the uniformity assertion.

    Authors: We agree that the uniform-in-time L² error bound is conditional on the uniqueness assumption for the continuous problem. The manuscript already states this explicitly both in the abstract and in the body of the paper. Establishing uniqueness for the 2-D Oldroyd model of order one with merely L^∞-in-time forcing and nonsmooth initial data is a difficult open question in the analysis of viscoelastic flows and lies outside the scope of the present numerical-analysis work. Similar conditional error estimates under a uniqueness hypothesis appear in the literature on the Navier–Stokes equations and related viscoelastic models. Without the assumption the Gronwall factor may indeed grow, which is why the result is stated conditionally. We will revise the abstract to emphasize the conditional character more prominently. revision: yes

Circularity Check

0 steps flagged

No circularity; error estimates derived under explicit external assumption

full rationale

The provided abstract and description show a standard mathematical derivation of a priori L2 error estimates for a backward Euler FEM discretization of the 2D Oldroyd system. The uniform-in-time bound is obtained under an explicitly stated assumption of uniqueness for the continuous problem; this is a hypothesis, not a result derived inside the paper. No self-definitional steps, fitted inputs renamed as predictions, self-citation chains, or ansatzes appear in the text. The analysis is self-contained as a proof under stated conditions, consistent with the default expectation for theoretical papers.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The analysis depends on standard PDE theory plus one model-specific assumption; no free parameters or invented entities are mentioned.

axioms (1)
  • domain assumption Uniqueness condition for the continuous Oldroyd problem
    Explicitly invoked in the abstract to obtain the uniform-in-time error estimate.

pith-pipeline@v0.9.0 · 5651 in / 1156 out tokens · 22288 ms · 2026-05-24T13:21:34.767924+00:00 · methodology

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