pith. sign in

arxiv: 2606.17661 · v1 · pith:CWO7QAEKnew · submitted 2026-06-16 · ⚛️ physics.flu-dyn

Stability of Kirigami parachutes in effectively infinite numerical domains

Pith reviewed 2026-06-26 23:00 UTC · model grok-4.3

classification ⚛️ physics.flu-dyn
keywords kirigami parachutedynamic stabilityfluid dynamics simulationdeployment heightBiot-Savart boundary conditiondrag forcepermeabilityfalling disk
0
0 comments X

The pith

Kirigami parachutes achieve stable flight at deployment heights as small as half their radius.

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

The paper establishes that kirigami parachutes can descend stably even when their deployment height is only half the parachute radius, rapidly damping perturbations in simulations. It identifies that a deployment height roughly equal to the radius combines high drag with strong dynamic stability, while smaller heights cause tumbling through side-slip and rotation coupling. This finding supplies a concrete design rule for compact deployable parachutes. The result matters because it shows how permeability and lever-arm effects trade off during deployment to control both force magnitude and moment balance.

Core claim

The kirigami parachute achieves stable flight for deployment heights as small as half its radius, quickly damping out applied perturbations. For smaller deployments, the parachute tumbles due to side-slip and rotational coupling, as in falling disks. Deployments approximately equal to the radius offer high drag forces with strong dynamic stability, providing a simple design rule for deployable parachutes.

What carries the argument

The Biot-Savart far-field boundary condition, which reconstructs far-field velocity from interior vorticity to enable simulations whose dynamics vary less than 0.1 percent when the domain size is doubled.

If this is right

  • Linear forces on the parachute drop by a factor of 2 to 5 upon deployment because permeability increases.
  • Moments rise during deployment because the increased lever arm counterbalances the permeability change.
  • Deployments smaller than half the radius produce tumbling via side-slip and rotational coupling.
  • A deployment height approximately equal to the radius simultaneously maximizes drag and damping of perturbations.

Where Pith is reading between the lines

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

  • The identified design rule could be tested by manufacturing physical kirigami prototypes at the radius-scale deployment height and dropping them in still air.
  • The same boundary-condition approach might extend to other permeable falling bodies whose far-field flow must be treated without artificial walls.
  • Varying the cut pattern or sheet stiffness while holding deployment height at one radius would reveal how geometry modulates the observed stability threshold.

Load-bearing premise

The Biot-Savart far-field boundary condition produces dynamics that remain unchanged when the computational domain size is doubled, thereby representing an effectively infinite physical domain.

What would settle it

If doubling the computational domain again produces more than 0.1 percent change in the predicted descent velocity or rotation rate, the claim that the boundary condition represents an effectively infinite domain would be falsified.

Figures

Figures reproduced from arXiv: 2606.17661 by Gabriel D. Weymouth, Marin Lauber.

Figure 1
Figure 1. Figure 1: Isometric and downstream views of the kirigami parachutes with different deployment ratios, increasing from left to right in 𝐻 ∈ [0.5, 1.0, 2.0, 4.0]. The unsteady flow structures are visualized using isosurfaces of the 𝜆2-criterion with 𝜆2𝐿 2 /𝑈 2 = −0.02 at time 𝑡𝑈/𝐿 = 3. Kirigami, the art of cutting flat sheets into deployable 3D structures, has introduced a new class of falling porous structures with t… view at source ↗
Figure 2
Figure 2. Figure 2: Schematic of the computational domain 𝛺, its boundary 𝜕𝛺, and the immersed body B. The figure also shows the multilevel evaluation of the Biot-Savart integral for a boundary point 𝒙 over the nested subdomains D(1) ∪ D(2) ∪ D(3) ∪ D(4) = 𝛺. The 𝑙 = 2 domain half-width is shown, 𝑆 (2) , together with a schematic of the coarsening of the grid between the domains and the multilevel pooling P (3)→(4) . is the i… view at source ↗
Figure 3
Figure 3. Figure 3: (Left) Drag coefficient histories for deployment ratios 𝐻. The horizontal lines are the theoretical added-mass coefficient of a solid disk (𝐻 = 0, dotted) and the ring system Eq. 3.2 (𝐻 → ∞, dashed). (Center￾left) Variation of the initial added mass of a parachute with deployment 𝐻 = 1 for different numbers of rings 𝑁𝑟 and theoretical 𝐶11 limit (dotted). (Center-right) Measured linear and rotational added-… view at source ↗
Figure 4
Figure 4. Figure 4: Sensitivity of the kirigami parachute dynamics to the domain size. (Left) Trace, (center) force and moment coefficients, and (right) velocity and rotation angle during fall for different domains of 75M, 150M, and 200M cells, corresponding to the dotted, dashed and solid line, respectively. times the circumference, and the added inertia is half that value times the radius squared. 𝑚11,𝑖 ≈ 𝜌𝜋 𝑤 2 2 2𝜋 𝑟𝑖 +… view at source ↗
Figure 5
Figure 5. Figure 5: (Left) falling path, (center) vertical falling velocity and (right) the damping coefficient and terminal falling velocity of the kirigami parachute for different initial rotation angle 𝜃0 (line color) and deployment ratio 𝐻 (line thickness). The damping coefficient is obtained from a log-decrement test of 𝑢B,1 and the terminal falling velocity is the average of the last oscillation cycle. increases, the te… view at source ↗
Figure 6
Figure 6. Figure 6: Impulsively started circular cylinder at Re = 550 validation case. (Left) Vorticity field 𝜔𝐷/𝑈 at convective time 𝑡𝑈/𝐷 = 4 over the full 2𝐷 × 4𝐷 domain. (Right) Early time history of the drag coefficient 𝐶𝑑 = 𝐹𝑑/ 1 2 𝜌𝑈2𝐷 for various domain blockage ratios 𝐷/𝑊. The present Biot-Savart BCs match the theoretical and vortex-based methods even with 50% blockage [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Sphere flow vortex wake and drag coefficient at 𝑅𝑒 = 7400 with a resolution of 44 cells per radius. (Left) Instantaneous and time-averaged drag coefficients for three domains, where 𝐴 is the domain frontal area. The time-averaged drag is obtained by averaging the last 100 convective times. (Right) Wake visualised by using |𝜔|𝑅/𝑈 at time 𝑡𝑈/𝑅 = 53 for the entire 3.6𝐷 × 1.5𝐷 × 1.5𝐷 domain. We validate the FM… view at source ↗
read the original abstract

Kirigami, the art of cutting flat sheets into deployable 3D structures, has recently inspired a new class of parachutes which can deploy into a naturally stable inverted canopy. However, the dynamic mechanism, fluid forces, and geometrical parameters that grant this stability have not yet been clearly identified. In this paper, we use a novel Biot-Savart far-field boundary condition to perform prescribed acceleration and free-falling simulations in effectively infinite domains, tracking the descent of a parameterized kirigami parachute. The far-field velocity is reconstructed from the interior vorticity, resulting in less than 0.1% variation in the predicted dynamics as the domain size is doubled. We first show the linear forces drop 2-5 times as the parachute is deployed due to increased permeability, whereas the moments increase due the counterbalancing effect of the increased lever-arm. Next, we find that the kirigami parachute achieves stable flight for deployment heights as small as half its radius, quickly damping out applied perturbations. For smaller deployments, the parachute tumbles due to side-slip and rotational coupling, as in falling disks. These effectively unbounded simulations identify that deployments approximately equal to the radius offer high drag forces with strong dynamic stability, providing a simple design rule for deployable parachutes.

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 / 2 minor

Summary. The manuscript uses direct numerical simulations of kirigami parachutes with a Biot-Savart far-field boundary condition to model effectively infinite domains. It reports that linear forces drop 2-5 times with deployment due to increased permeability while moments increase due to lever-arm effects, that stable descent with rapid damping of perturbations occurs for deployment heights as small as R/2, and that deployments near the radius optimize both drag and dynamic stability, yielding a simple design rule.

Significance. If the domain-independence and stability results hold, the work supplies a concrete, falsifiable design guideline for deployable parachutes and demonstrates a parameter-free numerical tool for unbounded flows. The direct time-marching approach without fitted parameters or self-referential equations is a methodological strength.

major comments (1)
  1. [Abstract] Abstract: the claim that the Biot-Savart reconstruction produces <0.1% variation when the domain is doubled does not identify the monitored observable (vertical velocity, lateral force, angular velocity, or perturbation damping rate). Because the central stability conclusion (stable flight for heights ≥ R/2) requires that small-amplitude dynamics are free of residual boundary effects, this omission is load-bearing for the result.
minor comments (2)
  1. The manuscript would benefit from explicit mesh-refinement and time-step studies reported alongside the stability metrics (damping time constants) rather than only mean descent speed.
  2. Notation for deployment height (relative to radius R) and the precise definition of the Biot-Savart far-field velocity reconstruction should be stated once in the methods before being used in the results.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their constructive comment on the abstract and for recognizing the methodological strengths of the Biot-Savart approach. We address the single major comment below and will revise the manuscript accordingly.

read point-by-point responses
  1. Referee: [Abstract] Abstract: the claim that the Biot-Savart reconstruction produces <0.1% variation when the domain is doubled does not identify the monitored observable (vertical velocity, lateral force, angular velocity, or perturbation damping rate). Because the central stability conclusion (stable flight for heights ≥ R/2) requires that small-amplitude dynamics are free of residual boundary effects, this omission is load-bearing for the result.

    Authors: We agree that the abstract should explicitly name the observables used to quantify the <0.1% variation. In the full manuscript the domain-doubling test was performed on the vertical descent velocity, the lateral force components, the angular velocity, and the exponential damping rates of applied perturbations; these quantities were monitored because they directly govern the stability conclusions. We will revise the abstract to state that the monitored observables are the descent velocity, lateral forces, angular velocities, and perturbation damping rates, thereby making the domain-independence claim fully transparent for the small-amplitude dynamics. revision: yes

Circularity Check

0 steps flagged

No significant circularity; results from direct numerical simulation

full rationale

The paper reports outcomes from time-marching fluid simulations of kirigami parachute dynamics under a Biot-Savart far-field boundary condition. The <0.1% variation statement is an empirical domain-size check on the numerical method, not a derivation that reduces to its own inputs. No load-bearing claims involve fitted parameters renamed as predictions, self-definitional equations, or self-citation chains that substitute for independent evidence. The stability and force results are simulation outputs, not tautological restatements of the method.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The work rests on standard incompressible flow assumptions and the validity of the Biot-Savart reconstruction for unbounded domains; no new physical entities or fitted constants are introduced in the abstract.

axioms (1)
  • standard math Incompressible Navier-Stokes equations govern the flow around the parachute
    Implicit background assumption for all fluid simulations described.

pith-pipeline@v0.9.1-grok · 5755 in / 1234 out tokens · 38014 ms · 2026-06-26T23:00:53.972062+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

72 extracted references · 59 canonical work pages

  1. [1]

    2015 , journal =

    Lee, Injae and Choi, Haecheon , pages =. 2015 , journal =. doi:10.1016/j.jcp.2014.09.028 , issn =

  2. [2]

    2008 , journal =

    Colonius, Tim and Taira, Kunihiko , number =. 2008 , journal =. doi:10.1016/j.cma.2007.08.014 , issn =

  3. [3]

    and Weymouth, Gabriel D

    Maertens, Audrey P. and Weymouth, Gabriel D. , pages =. 2015 , journal =. doi:10.1016/j.cma.2014.09.007 , issn =

  4. [4]

    Immersed boundary methods

    Mittal, Rajat and Iaccarino, Gianluca , number =. 2005 , journal =. doi:10.1146/annurev.fluid.37.061903.175743 , issn =

  5. [5]

    and Limbert, Georges , month =

    Lauber, Marin and Weymouth, Gabriel D. and Limbert, Georges , month =. 2022 , journal =. doi:10.1016/J.JCP.2022.111076 , issn =

  6. [6]

    and Sani, Robert L

    Gresho, Philip M. and Sani, Robert L. , number =. 1987 , journal =. doi:10.1002/fld.1650071008 , issn =

  7. [7]

    Fernando, J. N. and Weymouth, Gabriel D. and Rival, D. E. , pages =. 2020 , journal =. doi:10.1016/j.jfluidstructs.2019.102835 , issn =

  8. [8]

    , pages =

    Peskin, Charles S. , pages =. 2010 , journal =. doi:10.1017/cbo9780511550140.007 , issn =

  9. [9]

    2007 , journal =

    Taira, Kunihiko and Colonius, Tim , number =. 2007 , journal =. doi:10.1016/j.jcp.2007.03.005 , issn =

  10. [10]

    1967 , journal =

    Chorin, Alexandre Joel , number =. 1967 , journal =. doi:10.1016/0045-7930(73)90010-8 , issn =

  11. [11]

    and Marichal, Y

    Gillis, T. and Marichal, Y. and Winckelmans, G. and Chatelain, P. , month =. 2019 , journal =. doi:10.1016/J.JCP.2019.05.033 , issn =

  12. [12]

    1999 , booktitle =

    Cheng, H and Greengard, L and Rokhlin, V , pages =. 1999 , booktitle =

  13. [13]

    1987 , journal =

    Greencard, L and Rokhlin, V , pages =. 1987 , journal =

  14. [14]

    2017 , journal =

    Liska, Sebastian and Colonius, Tim , month =. 2017 , journal =. doi:10.1016/j.jcp.2016.11.034 , issn =

  15. [15]

    2016 , journal =

    Liska, Sebastian and Colonius, Tim , pages =. 2016 , journal =. doi:10.1016/j.jcp.2016.04.023 , keywords =

  16. [16]

    2020 , journal =

    Dorschner, Benedikt and Yu, Ke and Mengaldo, Gianmarco and Colonius, Tim , month =. 2020 , journal =. doi:10.1016/j.jcp.2020.109270 , issn =

  17. [17]

    and Martinsson, P

    Gillman, A. and Martinsson, P. G. , month =. 2014 , journal =. doi:10.1016/J.CAM.2013.09.003 , issn =

  18. [18]

    doi:10.1016/j.jcp.2009.12.035 , keywords =

    2010 , author =. doi:10.1016/j.jcp.2009.12.035 , keywords =

  19. [19]

    2004 , journal =

    Ying, Lexing and Biros, George and Zorin, Denis , number =. 2004 , journal =. doi:10.1016/j.jcp.2003.11.021 , issn =

  20. [20]

    2006 , journal =

    Mccorquodale, Peter and Colella, Phillip and Balls, Gregory T and Baden, Scott B , volume =. 2006 , journal =

  21. [21]

    2014 , journal =

    Liska, Sebastian and Colonius, Tim , month =. 2014 , journal =. doi:10.1016/j.jcp.2014.07.048 , issn =

  22. [22]

    2018 , journal =

    Cummins, Cathal and Seale, Madeleine and Macente, Alice and Certini, Daniele and Mastropaolo, Enrico and Viola, Ignazio Maria and Nakayama, Naomi , number =. 2018 , journal =. doi:10.1038/s41586-018-0604-2 , issn =

  23. [23]

    2002 , journal =

    Colonius, Tim and Ran, Hongyu , number =. 2002 , journal =. doi:10.1006/JCPH.2002.7161 , issn =

  24. [24]

    and Duponcheel, M

    Billuart, P. and Duponcheel, M. and Winckelmans, G. and Chatelain, P. , month =. 2023 , journal =. doi:10.1016/j.jcp.2022.111726 , issn =

  25. [25]

    Combustion and Flame , keywords =

    Hou, Wei and Colonius, Tim , month =. 2024 , journal =. doi:10.1016/J.JCP.2024.113370 , issn =

  26. [26]

    2008 , journal =

    Miller, G H , pages =. 2008 , journal =. doi:10.1016/j.jcp.2008.05.005 , keywords =

  27. [27]

    and Pesavento, U

    Andersen, A. and Pesavento, U. and Wang, Z. Jane , month =. 2005 , journal =. doi:10.1017/S0022112005005847 , issn =

  28. [28]

    2002 , journal =

    Martinsson, Per-Gunnar and Rodin, Gregory J , number =. 2002 , journal =

  29. [29]

    Weymouth, G. D. , pages =. 2014 , journal =. doi:10.1017/JFM.2014.42 , issn =

  30. [30]

    2008 , journal =

    Cocle, Roger and Winckelmans, Grégoire and Daeninck, Goéric , number =. 2008 , journal =. doi:10.1016/j.jcp.2007.10.010 , issn =

  31. [31]

    1976 , journal =

    Lackner, K , pages =. 1976 , journal =

  32. [32]

    2019 , journal =

    Kavouklis, Chris and Colella, Phillip , number =. 2019 , journal =. doi:10.2140/CAMCOS.2019.14.1 , issn =

  33. [33]

    , month =

    Weymouth, Gabriel D. , month =. 2022 , journal =. doi:10.1016/J.COMPFLUID.2022.105620 , issn =

  34. [34]

    1993 , journal =

    Chen, Yen Ming and ou, Yuh Roung and ou, Yuh Roung , number =. 1993 , journal =. doi:10.1017/S0022112093001867 , issn =

  35. [35]

    and Oliva, Assensi , month =

    Rodriguez, Ivette and Borell, Ricard and Lehmkuhl, Oriol and Perez Segarra, Carlos D. and Oliva, Assensi , month =. 2011 , journal =. doi:10.1017/jfm.2011.136 , issn =

  36. [36]

    and Tummers, M

    Reijtenbagh, J. and Tummers, M. J. and Westerweel, J. , number =. 2023 , journal =. doi:10.1103/PhysRevLett.130.174001 , issn =

  37. [37]

    Jane , number =

    Wang, Z. Jane , number =. 1999 , journal =. doi:10.1006/JCPH.1999.6289 , issn =

  38. [38]

    2000 , journal =

    Shusser, Michael and Gharib, Morteza , pages =. 2000 , journal =

  39. [39]

    2013 , journal =

    Auguste, Franck and Magnaudet, Jacques and Fabre, David , pages =. 2013 , journal =. doi:10.1017/JFM.2012.602 , issn =

  40. [40]

    2022 , journal =

    Marzin, Tom and Le Hay, Kerian and De Langre, Emmanuel and Ramananarivo, Sophie , number =. 2022 , journal =. doi:10.1103/PhysRevFluids.7.023906 , issn =

  41. [41]

    and Zadpoor, Amir A

    Callens, Sebastien J.P. and Zadpoor, Amir A. , number =. 2018 , journal =. doi:10.1016/J.MATTOD.2017.10.004 , issn =

  42. [42]

    1984 , journal =

    Morton, B R , pages =. 1984 , journal =. doi:10.1080/03091928408230368 , issn =

  43. [43]

    , number =

    Yang, Yi and Vella, Katherine and Holmes, Douglas P. , number =. 2021 , journal =. doi:10.1126/SCIROBOTICS.ABD6426 , issn =

  44. [44]

    1995 , journal =

    Koumoutsakos, P and Leonard, A , pages =. 1995 , journal =

  45. [45]

    Scott and Kanso, Eva , month =

    Vincent, Lionel and Shambaugh, W. Scott and Kanso, Eva , month =. 2016 , journal =. doi:10.1017/JFM.2016.432 , issn =

  46. [46]

    Carleton, A. G. and Modarres-Sadeghi, Y. , month =. 2024 , journal =. doi:10.1016/J.EML.2024.102198 , issn =

  47. [47]

    and Melancon, David , number =

    Lamoureux, Danick and Fillion, Jérémi and Ramananarivo, Sophie and Gosselin, Frédérick P. and Melancon, David , number =. 2025 , journal =. doi:10.1038/s41586-025-09515-9 , issn =

  48. [48]

    , number =

    Wang, Chengjie and Eldredge, Jeff D. , number =. 2013 , journal =. doi:10.1007/s00162-012-0279-5 , issn =

  49. [49]

    2004 , journal =

    Colonius, Tim , pages =. 2004 , journal =. doi:10.1146/annurev.fluid.36.050802.121930 , issn =

  50. [50]

    2022 , journal =

    Yu, Ke and Dorschner, Benedikt and Colonius, Tim , month =. 2022 , journal =. doi:10.1016/j.jcp.2021.110845 , issn =

  51. [51]

    1997 , journal =

    Rennich, Steven C and Lele, Sanjiva K , pages =. 1997 , journal =

  52. [52]

    Grosch, C. E. and Orzag, S. A. , pages =. 1977 , journal =

  53. [53]

    1998 , journal =

    Tsynkov, Semyon V , pages =. 1998 , journal =

  54. [54]

    Calderon, D. E. and Cleaver, D. J. and Gursul, I. and Wang, Z. , number =. 2014 , journal =. doi:10.1063/1.4891256/258599 , issn =

  55. [55]

    1995 , journal =

    JEong, Jinhee and Hussain, Fazle , pages =. 1995 , journal =. doi:10.1017/S0022112095000462 , issn =

  56. [56]

    , month =

    Beckers, Diederik and Eldredge, Jeff D. , month =. 2022 , journal =. doi:10.1017/jfm.2022.238 , issn =

  57. [57]

    2025 , journal =

    Bose, Chandan and Bruce, Callum and Viola, Ignazio Maria , number =. 2025 , journal =. doi:10.1007/S00162-025-00740-6 , issn =

  58. [58]

    and Limbert, Georges , number =

    Lauber, Marin and Weymouth, Gabriel D. and Limbert, Georges , number =. 2023 , journal =. doi:10.1098/RSIF.2023.0466 , issn =

  59. [59]

    Sani, R. L. and Gresho, P. M. , number =. 1994 , journal =. doi:10.1002/FLD.1650181006 , issn =

  60. [60]

    2026 , journal =

    Carleton, Adrian and Modarres-Sadeghi, Yahya , month =. 2026 , journal =. doi:10.1016/J.JFLUIDSTRUCTS.2026.104590 , issn =

  61. [61]

    , month =

    Lamoureux, Danick and Ramananarivo, Sophie and Melancon, David and Gosselin, Frédérick P. , month =. 2025 , journal =. doi:10.1016/J.EML.2024.102271 , issn =

  62. [62]

    2022 , journal =

    L. 2022 , journal =. doi:10.1103/PhysRevD.106.124021 , issn =

  63. [63]

    2009 , journal =

    Fong, William and Darve, Eric , number =. 2009 , journal =. doi:10.1016/j.jcp.2009.08.031 , issn =

  64. [64]

    1976 , booktitle =

    Chadwick, Edmund , pages =. 1976 , booktitle =

  65. [65]

    Collins, W. M. and Dennis, S. C.R. , number =. 1973 , journal =. doi:10.1093/QJMAM/26.1.53 , issn =

  66. [66]

    1977 , journal =

    Jamb, R A , pages =. 1977 , journal =

  67. [67]

    and Anderson, R

    Higuchi, H. and Anderson, R. W. and Zhang, J. , number =. 1996 , journal =. doi:10.2514/3.13204 , issn =

  68. [68]

    Godoy-Diana, R and Aider, J. L. and Wesfreid, J. E. , pages =. 2008 , journal =

  69. [69]

    2015 , journal =

    Marichal, Y and Chatelain, P and Winckelmans, G , pages =. 2015 , journal =. doi:10.1016/j.piutam.2015.11.010 , issn =

  70. [70]

    and Pesavento, U

    Andersen, A. and Pesavento, U. and Wang, Z. Jane , month =. 2005 , journal =. doi:10.1017/S002211200500594X , issn =

  71. [71]

    2006 , journal =

    Yun, Giwoong and Kim, Dongjoo and Choi, Haecheon , number =. 2006 , journal =. doi:10.1063/1.2166454 , issn =

  72. [72]

    Weymouth and Bernat Font

    Weymouth, Gabriel D. and Font, Bernat , month =. 2025 , journal =. doi:10.1016/J.CPC.2025.109748 , issn =