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Fuzzy flexible fibers attached to biological surfaces can reduce drag and influence fluid flow by altering their shape, an intriguing phenomenon that has garnered increasing attention. The complexity of fluid–structure interaction problems leads to highly nonlinear equations that describe this issue. Existing analytical solutions, such as perturbation methods and series expansion techniques, still do not perfectly align with experimental observations. To address this problem, this study explores numerical approaches. By introducing the method of homotopy transformation, we first tackle the convergence difficulties associated with the classical Newton–Raphson iterative method due to the a priori selection of initial values. Second, numerical results indicate that the proposed method aligns with experimental results across all velocity distributions, confirming previous conjectures regarding the −1/2 scaling rate at higher velocities. The developed homotopy numerical algorithm is compared with the shooting method provided by the MAPLE software, demonstrating superior convergence and computational results compared to existing numerical methods. Finally, we further investigate the deformation of elastic fibers under very large loads. The proposed method exhibits excellent convergence properties and can be utilized to explore numerical solutions for nonlinear equations, particularly in fluid–structure interaction problems, providing insights for future scientific exploration and engineering applications. [ABSTRACT FROM AUTHOR]

The foldcore of an origami structure made up of rigid triangular units is suggested. This foldcore has two stable states: contraction and expansion. The suggested foldcore's peak stress, average stress, and densification strain were numerically analyzed at different cutting heights and varied parameters n, and the damage modes were analyzed. Finally, the impact of strain rate on the proposed foldcore's structural response and energy absorption capacity is investigated. The contraction stable state foldcore with a cutting 1/5 height was discovered to have the best energy absorption capacity. Increasing n improves its energy absorption performance, but decreases its dense strain. [ABSTRACT FROM AUTHOR]

The shear stress generated by wall turbulence is the main cause of wall friction resistance in turbulent flow through pipes. This paper investigates the impact of inserting rest periods (regions of constant Reynolds number) within the pulsating operating cycle of velocity on the fully turbulent flow at large time-averaged Reynolds numbers, using the large eddy simulation (LES) method. The study aims to explore the effect of increasing rest periods within pulsations on drag resistance. The dimensionless shear stress and drag reduction rates during different time periods of rest were analyzed. Numerical simulation results indicate that the pulsating velocity operation mode does not necessarily lead to drag reduction; it may even result in increased resistance. Inserting rest periods within the pulsation cycle can achieve drag reduction effects, with the maximum drag reduction rate reaching 21.8%. This paper utilizes large eddy simulation (LES) to compare and validate the feasibility of LES for pipe pulsating operation modes against experimental results and direct numerical simulation (DNS) results from the literature, providing a rationale and proof of concept for further in-depth studies on other pipe pulsating flows. [ABSTRACT FROM AUTHOR]

In nature and engineering applications, flexible fiber beds covering biological surfaces can play a role in reducing resistance. These fibers deform under the action of fluids, and this deformation affects the fluid flow state, forming a complex fluid–solid interaction phenomenon. To quantitatively analyze these issues, the physical model is simplified. We focus on the deformation of a soft hair bed caused by Stokes flow. Additionally, we study the deformation of a single hair under Stokes flow in greater detail. The deformation problem of an elastic single fiber in a channel caused by Stokes flow can be described by a nonlinear integral equation. We have obtained a new series solution, which has been compared with the previous perturbation method to verify the accuracy and effectiveness of the series solution. Meanwhile, we have further provided an extended form of flexible fiber deformation through experimental fitting. This fluid–solid interaction problem involves multiple fields and is very important in many natural and engineering systems. The research in this paper can not only help us better understand complex phenomena in nature but also delve into the interaction mechanism between fluids and solids, providing a theoretical basis for future scientific research and engineering applications. [ABSTRACT FROM AUTHOR]

The study of laminar unsteady boundary layer flows is essential for understanding the transition from laminar to turbulent flow, as well as the origins of turbulence. However, finding solutions to this phenomenon poses significant challenges. In this study, we introduce a novel method that employs a similarity transformation to convert the two-dimensional unsteady laminar boundary layer equations into a single partial differential equation with constant coefficients. By applying this transformation, we successfully derive similarity solutions for flat plate boundary layer flow, expressed in terms of Kummer functions. For convergent boundary layer flow, we derive an approximate analytical solution that includes both shock wave and soliton wave solutions. The superposition of these solutions provides evidence for the existence of solitons or soliton-like coherent structures (SCS) within boundary layers. Additionally, this paper explores two- and three-dimensional laminar flows, as well as three-dimensional turbulent flow equations, revealing that they all incorporate third-order derivatives with respect to spatial coordinates. This finding suggests that all viscous fluid motions have the potential to exhibit solitons/like coherent structures (SCS). [ABSTRACT FROM AUTHOR]

The nested tube system is a cost-efficient energy absorbing device that is particularly crucial for applications with constrained squeeze zones and space. Using the triple continuous nested tube (TCNT) method for nesting is quite useful. The single-stage mode and two-stage mode are its two distinctive force–displacement curve forms. In this study, finite element models suitable for TCNT structures were developed using Abaqus software, and several control groups were constructed according to different initial collapse loads. Through an in-depth analysis of each component of the TCNT, it is discovered that the stiffness competition between the two inner rings is the primary factor contributing to the step-like mechanical response. The TCNT system comprehensively outperforms the conventional single ring design for specific energy absorption (SEA). The prediction equation regarding the initial collapse load of this system is also discussed in this paper. Since the relative errors of the theoretical and numerical solutions are more concentrated, the accuracy can be increased by the amplification factor. The final polynomial fit equation obtained gives a glimpse of the full force–displacement curve. [ABSTRACT FROM AUTHOR]

The woven structure made of naturally curved (in-plane) ribbons has smooth geometry and fewer geometric imperfections, but there is no study of its buckling mechanical properties under vertical loads. The aim of this paper is to investigate buckling mechanical properties of spherical woven structures. Three spherical woven structures with different ribbon types and six new spherical woven structures with different ribbon widths and thicknesses were designed and the quasi-static vertical compression tests were carried out. The buckling load of spherical woven structures were studied by nonlinear finite element and ring buckling theory. Results indicate that the failure mode of the spherical weave structure under vertical loading can be divided into two stages, where a flat contact region forms between the spherical weave structure and the rigid plate and inward dimple of ribbons. Spherical weave structures using naturally curved (in-plane) ribbon weaving have better buckling stability than those woven with straight ribbon. Based on theoretical and finite element analysis, we propose a buckling load equation and buckling correction factor equation for the new spherical weave structure under vertical compression load. The formula is validated and has good agreement with the test results, which could help to design the stability of spherical weave structures with in-plane ribbons. [ABSTRACT FROM AUTHOR]