2022 Vol.12(1)

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Multiscale mechanics of noncovalent interface in graphene oxide layered nanocomposites
ZeZhou He, YinBo Zhu, HengAn Wu
Theoretical and Applied Mechanics Letters  12 (2022) 100304. doi: 10.1016/j.taml.2021.100304
[Abstract](315) [PDF 3176KB](6)
Noncovalent interfaces play a vital role in inelastic deformation and toughening mechanisms in layered nanocomposites due to their dynamical recoverability. When interfacial engineering is applied to design layered nanocomposites, shear-lag analysis is usually implemented to evaluate the capability of interfacial loading transfer. Here, we introduce a multiscale shear-lag model that correlates macroscale mechanical properties with the molecular mechanisms to quantify the effects of interfacial configuration in graphene oxide (GO) layered nanocomposites. By investigating the mechanical responses of commensurate and incommensurate interfaces, we identify that the commensurate interface exhibits a pronounced size effect due to the nucleation and propagation of interfacial defects, whereas the incommensurate interface displays uniform deformation. Our predictions are further validated through large-scale molecular dynamics simulations for GO layered nanocomposites. This work demonstrates how size effects and interfacial configurations can be exploited to fabricate layered nanocomposites with superior mechanical properties despite relying on weak noncovalent interfaces.
Capturing the baroclinic effect in non-Boussinesq gravity currents
Shengqi Zhang, Zhenhua Xia
Theoretical and Applied Mechanics Letters  12 (2022) 100313. doi: 10.1016/j.taml.2021.100313
[Abstract](272) [PDF 1658KB](5)
Direct numerical simulations of two-dimensional gravity currents with small and medium density variations are performed using different non-Boussinesq buoyancy approximations. Taking the full low-Machnumber approximation as the reference, the accuracy of several buoyancy terms are examined. It is found that all considered buoyancy terms performed well in the cases with small density variation. In the cases with medium density variation, the classical gravitational Boussinesq’s buoyancy term showed the lack of accuracy, and a simple correction did not make any improvement. In contrast, the recently introduced second-order buoyancy term showed a significantly higher accuracy. The present results and our previous derivations indicate that simple algebraic buoyancy approximations extended from the Boussinesq’s gravitational buoyancy are unlikely to achieve an accuracy beyond first order. Instead, it seems necessary to solve at least one extra Poisson equation for buoyancy terms to capture the higher-order baroclinic effect. An approximate analysis is also provided to show the leading term of the non-Boussinesq effect corresponding to gravity.
How far the wake of a wind farm can persist for?
Guodan Dong, Zhaobin Li, Jianhua Qin, Xiaolei Yang
Theoretical and Applied Mechanics Letters  12 (2022) 100314. doi: 10.1016/j.taml.2021.100314
[Abstract](336) [PDF 4045KB](14)
With the increased penetration of wind energy in our nation’s energy portfolio, wind farms are placed in a way close to each other. Thus, their wakes have to be fully considered in the design and operation of a wind farm. In this study, we investigate the wake of a wind farm using large-eddy simulation with wind turbine rotor modelled by the actuator disk model. The simulated results show that the wake of a wind farm can persist for a long distance in its downstream. For the considered wind farm layout, the velocity in the wake recovers 95% of that of the undisturbed inflow at 55 rotor diameters downstream from its last row, suggesting that the wake of a wind farm should be fully considered in the optimal design and operation for its downstream wind farms.
A universal bifurcation mechanism arising from progressive hydroelastic waves
Zhan Wang
Theoretical and Applied Mechanics Letters  12 (2022) 100315. doi: 10.1016/j.taml.2021.100315
[Abstract](255) [PDF 2111KB](4)
A unidirectional, weakly dispersive nonlinear model is proposed to describe the supercritical bifurcation arising from hydroelastic waves in deep water. This model equation, including quadratic, cubic, and quartic nonlinearities, is an extension of the famous Whitham equation. The coefficients of the nonlinear terms are chosen to match with the key properties of the full Euler equations, precisely, the associated cubic nonlinear Schrödinger equation and the amplitude of the solitary wave at the bifurcation point. It is shown that the supercritical bifurcation, rich with Stokes, solitary, generalized solitary, and dark solitary waves in the vicinity of the phase speed minimum, is a universal bifurcation mechanism. The newly developed model can capture the essential features near the bifurcation point and easily be generalized to other nonlinear wave problems in hydrodynamics.
A Lagrangian-based flame index for the transported probability density function method
Zhen Lu, Hua Zhou, Zhuyin Ren, Yue Yang, Hong G. Im
Theoretical and Applied Mechanics Letters  12 (2022) 100316. doi: 10.1016/j.taml.2021.100316
[Abstract](445) [PDF 905KB](9)
We propose a new flame index for the transported probability density function (PDF) method. The flame index uses mixing flux projections of Lagrangian particles on mixture fraction and progress variable directions as the metrics to identify the combustion mode, with the Burke-Schumann solution as a reference. A priori validation of the flame index is conducted with a series of constructed turbulent partially premixed reactors. It indicates that the proposed flame index is able to identify the combustion mode based on the subgrid mixing information. The flame index is then applied the large eddy simulation/PDF datasets of turbulent partially premixed jet flames. Results show that the flame index separate different combustion modes and extinction correctly. The proposed flame index provides a promising tool to analyze and model the partially premixed flames adaptively.
Towards multi-fidelity simulation of flows around an underwater vehicle with appendages and propeller
Zhideng Zhou, Zhaobin Li, Guowei He, Xiaolei Yang
Theoretical and Applied Mechanics Letters  12 (2022) 100318. doi: 10.1016/j.taml.2021.100318
[Abstract](719) [PDF 2422KB](18)
Flow around a real-life underwater vehicle often happens at a high Reynolds number with flow structures at different scales from the boundary layer around a blade to that around the hull. This poses a great challenge for large-eddy simulation of an underwater vehicle aiming at resolving all relevant flow scales. In this work, we propose to model the hull with appendages using the immersed boundary method, and model the propeller using the actuator disk model without resolving the geometry of the blade. The proposed method is then applied to simulate the flow around Defense Advanced Research Projects Agency (DARPA) suboff. An overall acceptable agreement is obtained for the pressure and friction coefficients. Complex flow features are observed in the near wake of suboff. In the far wake, the core region is featured by a jet because of the actuator disk, surrounded by an annular region with velocity deficit due to the body of suboff.
Simulation and prediction of membrane fusion dynamics
Zhi Zheng, Shouqin Lü, Mian Long
Theoretical and Applied Mechanics Letters  12 (2022) 100321. doi: 10.1016/j.taml.2022.100321
[Abstract](586) [PDF 1211KB](13)
Membrane fusion is an important process by which biological membranes perform their life activities. Simulations show that the membrane fusion process happens mainly through three pathways, where the Stalk-Pore hypothesis, in which two membranes come into close contact to form a stalk to a hemifusion intermediate, and then the fusion pore opens to achieve completely fusion, is widely accepted, and there exist two free energy barriers that break the current structural steady state for lipid rearrangement. Factors of lipid composition, mechanical environment, protein and ion have regulatory roles in the membrane fusion process by effecting membrane curvature structurally and the free energy barriers from energetic perspective. Meanwhile, many theoretical models, represented by the Helfrich model, have been proposed to predict the membrane fusion process. In this paper, we review the research process of membrane fusion and mainly introduce the dynamics of membrane fusion, regulation factors and typical theoretical models.
Numerical model and hydrodynamic performance of tuna finlets
Jun-Duo Zhang, Wei-Xi Huang
Theoretical and Applied Mechanics Letters  12 (2022) 100322. doi: 10.1016/j.taml.2022.100322
[Abstract](290) [PDF 2642KB](7)
Finlets, a series of small individual triangular fins located along the dorsal and ventral midlines of the body, are remarkable specializations of tuna and other scombrid fishes capable of high-speed swimming. In this study, a symmetric model containing nine finlets of tuna is proposed to overcome the limitation of measurement without losing authenticity. Hydrodynamic performance along with three-dimensional flow structures obtained by direct numerical simulation are demonstrated to disclose the underlying hydrodynamics mechanism of finlets. Complex interactions of leading-edge vortices (LEVs), trialing-edge vortices (TEVs), tip vortices (TVs) and root vortices (RVs) are observed from the three-dimensional vortical structures around the finlets. Two more cases consisting of the 3rd to 9th (without the first two) and the 3rd to 7th (without the first two and the last two) finlets are also simulated to examine the effects of the first two and the last two finlets.
Sampling Moiré method for full-field deformation measurement: A brief review
Qinghua Wang, Shien Ri
Theoretical and Applied Mechanics Letters  12 (2022) 100327. doi: 10.1016/j.taml.2022.100327
[Abstract](310) [PDF 2546KB](5)
The sampling Moiré (SM) method is one of the vision-based non-contact deformation measurement methods, which is a powerful tool for structural health monitoring and elucidation of damage mechanisms of materials. In this review, the basic principle of the SM method for measuring the twodimensional displacement and strain distributions is introduced. When the grid is not a standard orthogonal grating and cracks exist on the specimen surface, the measurement methods are also stated. Two of the most typical application examples are described in detail. One is the dynamic deflection measurement of a large-scale concrete bridge, and the other is the residual thermal strain measurement of small-scale flip chip packages. Several further development points of this method are pointed out. The SM method is expected to be used for deformation measurement of various structures and materials for residual stress evaluation, crack location prediction, and crack growth evaluation on broad scales.
Editorial of 10-years Anniversary of Theoretical and Applied Mechanics Letters
J. C. Li
Theoretical and Applied Mechanics Letters  12 (2022) 100328. doi: 10.1016/j.taml.2022.100328
[Abstract](241) [PDF 263KB](5)
It has been ten years since 2011 when the first issue of Theoretical and Applied Mechanics Letters (TAML) came out. To date, TAML has published over 700 articles and 30 special issues covering a broad range of topics in mechanics. Such great achievements are even not possible without the continued dedication and support from authors, reviewers and editors. At this very special moment, I would like to express my sincere thanks to all of you, and hope you will continue to devote your time and efforts to the further advances of TAML.