Nelson Chen’s research while affiliated with Northwestern University and other places

What is this page?


This page lists works of an author who doesn't have a ResearchGate profile or hasn't added the works to their profile yet. It is automatically generated from public (personal) data to further our legitimate goal of comprehensive and accurate scientific recordkeeping. If you are this author and want this page removed, please let us know.

Publications (16)


S1 Fig
  • Data
  • File available

June 2017

·

10 Reads

Nishant Nangia

·

·

Nelson Chen

·

[...]

·

Neelesh A. Patankar

Correlation between different Reynolds numbers. The swimming–speed Reynolds number Re vs. Relat (⚫; blue), Relat,L (♦; purple), and Rewave (◼; red) for the swimmers considered in [4], along with the lines of best fit. The best fit lines are given by log Re = 1.803 + 1.340log Relat, log Re = −0.4058 + 1.2306log Relat,L, and log Re = −1.450 + 1.083log Rewave. (EPS)

Download


S10 Fig

June 2017

·

8 Reads

Qualitative analysis of the velocity mechanism. Mid–sheet (z = −0.05 cm) contours of axial fluid velocity for a stationary sheet simulation for various snapshots in time. Black dots represent the Lagrangian points of the undulating body. The plate has L = 1.0 cm, h = 0.1 cm, f = 3 Hz, a = 0.05 cm with (a) & (b) SW = 13.33, (c) & (d) SW = 10, (e) & (f) SW = 5. (EPS)



S4 Fig

June 2017

·

12 Reads

Dimensionless axial force data from Fig 7. Dimensionless axial propulsive force F^ vs. specific wavelength for additional small–sheet simulations in which (a) frequency and (b) amplitude were varied. These data represent cases where (a) 2.53 ≤ Relat ≤ 10.11 and (b) 0.28 ≤ Relat ≤ 10.16. Data are available in S2 Data. (EPS)



S7 Fig

June 2017

·

8 Reads

Momentum transfer by an undulatory swimmer. At the front of the swimmer, the body sucks stationary fluid with negligible momentum min and accelerates it downstream. This ejected fluid is often manifested as a wake with momentum mwake∼ℳwave(λf). Finally, this wake eventually dissipates further downstream as it loses momentum. (TIFF)


S6 Fig

June 2017

·

8 Reads

Dimensionless axial force data from Fig 9. Dimensionless axial propulsive force F^ generated by a stationary undulating sheet with prescribed anguilliform (▲) and carangiform (⚫) amplitude profiles plotted against specific wavelength. These data represent cases where Relat = 4.49. Data are available in S2 Data. (EPS)



Observed St and SW ranges from meta–analysis data of body/caudal fin swimmers
The Strouhal number (top) and specific wavelength (bottom) for the species considered in this study. Data points represent average values, x ¯ i where x ∈ {St, SW}, of individual species and error bars indicate ± one s.d. from the species mean. Dashed lines represent St = 0.3 and SW = 10. Distinction is made between anguilliform and non–anguilliform swimmers. Data labeled as Ambystoma mexicanum and Ambystoma mexicanum young are from adult and larval axolotl, respectively. All observations of Clupea harengus and Danio rerio came from anguilliform larvae. For some species, the error bars are not visible at this scale, while for others, only one observation is recorded and no error bars are available; see Table 1 for more details. The data are available in S1 Data.
Variability in St as a function of Relat and AR
Intraspecies mean Strouhal number vs. (a) lateral Reynolds number, and (b) aspect ratio for observed non-anguilliform(⚫) and anguilliform(▲) swimmers. Of these, orange (green) points represent swimmers with (without) well–defined caudal fins. Error bars indicate ± one s.d. from the species mean. For some species, the error bars are not visible at this scale, while for others, only one observation is recorded and no error bars are available; see Table 1 for more details. Data are available in S1 Data and Table 1.
Variability in SW and OSW as a function of Relat and AR
Intraspecies mean specific wavelength vs. (a) lateral Reynolds number, (b) aspect ratio for observed non-anguilliform(⚫) and anguilliform(▲) swimmers. Of these, orange (green) points represent swimmers with (without) well–defined caudal fins. Red crosses (×) represent the optimal specific wavelength for simulations done in the present study. Blue asterisks (*) represent the optimal specific wavelengths for robotic undulating sheets reported in [11, 12]. Error bars indicate ± one s.d. from the species mean. For some species, the error bars are not visible at this scale, while for others, only one observation is recorded and no error bars are available; see Table 1 for more details. Data are available in S1 Data and Table 1.
Measured swimming speed and force from undulating sheet simulations
(a) Axial swimming speed and propulsive force computed from free–swimming (green) and translation–locked (black) simulations of rectangular sheets plotted against the specific wavelength. In free–swimming simulations, the forward swimming speed of the undulating plate was an output parameter of the simulation. Simulations were carried out at a lateral Reynolds number Relat = 4.49, with corresponding swimming–speed Reynolds number range 1.8 × 10¹ < Re < 1.51 × 10². Data are available in S2 Data. (b) Evolution of axial Fx and heave forces Fz over time for a translation–locked, undulating sheet simulation with SW = 13.33. The oscillation in Fz is a signature of the linear recoil effect on the swimmer. The sway force Fy is not shown because the kinematics of the swimmer’s undulation lead to large Fy values, although it also oscillates about a mean value. (c) Evolution of U in each coordinate direction over time for a self–propelled, undulating sheet simulation with SW = 13.33. The oscillation of the heave velocity Uz about 0 is not easily visible at this scale.
Measured propulsive force from low Relat undulating sheet simulations
The axial propulsive force generated by a stationary undulating sheet plotted against specific wavelength. In both cases (a) & (b), plate span was varied. These data represent cases where Relat < 1 × 10². Data are available in S2 Data.

+9

Optimal specific wavelength for maximum thrust production in undulatory propulsion

June 2017

·

384 Reads

·

32 Citations

What wavelengths do undulatory swimmers use during propulsion? In this work we find that a wide range of body/caudal fin (BCF) swimmers, from larval zebrafish and herring to fully–grown eels, use specific wavelength (ratio of wavelength to tail amplitude of undulation) values that fall within a relatively narrow range. The possible emergence of this constraint is interrogated using numerical simulations of fluid–structure interaction. Based on these, it was found that there is an optimal specific wavelength (OSW) that maximizes the swimming speed and thrust generated by an undulatory swimmer. The observed values of specific wavelength for BCF animals are relatively close to this OSW. The mechanisms underlying the maximum propulsive thrust for BCF swimmers are quantified and are found to be consistent with the mechanisms hypothesized in prior work. The adherence to an optimal value of specific wavelength in most natural hydrodynamic propulsors gives rise to empirical design criteria for man–made propulsors.


Citations (1)


... Since its introduction, the IB method has emerged as a powerful tool for modeling biological FSI problems, with applications spanning from animal locomotion [4][5][6][7][8][9][10][11] to cardiac mechanics. [12][13][14][15][16][17][18] Because the IB method discretizes the structural and Eulerian degrees of freedom separately, it avoids the difficulties of grid generation associated with body-fitted approaches. ...

Reference:

Local Divergence-Free Immersed Finite Element-Difference Method Using Composite B-Splines
Optimal specific wavelength for maximum thrust production in undulatory propulsion