Ordered zigzag wrinkles, or herringbones, arising from surface instability in biaxially compressed thin films on soft substrates offer significant potential for diverse engineering applications. In this study, we experimentally investigated the formation of herringbone patterns in silicon dioxide (SiO₂) thin films bonded to poly(dimethylsiloxane) (PDMS) substrates. Specifically, we examined how the biaxial pre-strain ratio, defined as the ratio of pre-strain applied to the substrate in the second direction to that applied in the first orthogonal direction prior to film formation, and the film thickness influence herringbone geometry. Under equi-biaxial pre-strain ratio, the films developed herringbones with jog angles of approximately 80°, and the wavelength, amplitude, and length of these patterns showed a nearly linear dependence on film thickness. When the biaxial pre-strain ratio was varied from 0.67 to 1.50, the jog angle was tuned from 40°to 100°. Surface roughness analysis showed that the arithmetical mean height ranged from 0.13 to 0.30 μm depending on both film thickness and biaxial pre-strain ratio. These findings provide insights into controlling herringbone formation in SiO₂ films and offer design guidelines for engineered surfaces with tailored morphological features.

A local stress approach, employing failure conditions derived from notched round-bar tensile tests has successfully traced the ductile crack propagation in compact tension (CT) specimens. The failure condition is expressed using the failure stress index (FSI), which is a linear sum of equivalent and mean stresses. Material failure occurs when the FSI reaches a specific limit. The limit FSI, applicable to high-stress triaxiality ranges—particularly in the crack frontal region—was established based on the failure conditions observed at the center of the notched cross-section of round-bar specimens from two steel grades. We utilized the Gurson–Tvergaard–Needleman (GTN) model, incorporating a stress-controlled void nucleation term, as a framework to implement the limit FSI. The model can induce intense void nucleation and growth occurring just before failure, leading to final material failure. The model faithfully replicated the failure process of the notched round-bar specimens of two steel grades. Key model parameters include the void nucleation stress, and the correction coefficient related to the limit FSI, reducing the need to adjust other void growth parameters such as the initial void fraction. Ultimately, the model effectively traced the ductile crack propagation in CT specimens of two steel grades. A critical aspect of the analysis was the emergence of an FSI concentration zone ahead of the crack tip, termed the process zone. This zone indicates that void nucleation initiates not at the crack tip itself but within its frontal region. Additionally, scanning-electron-microscope examination of fracture surfaces revealed that similar fracture processes play in both notched round-bar and CT specimens. These findings reinforce the applicability of the limit FSI in predicting microscopic failures in the frontal region of mode I ductile cracks.

Directed energy deposition-arc (DED-Arc) is a promising additive manufacturing technique for efficiently and cost-effectively producing large-scale, complex aluminum exterior members. However, achieving uniform thickness in structures fabricated by DED-Arc remains challenging due to heat accumulation and other process-related factors. This study aimed to suppress thickness variation in aluminum components fabricated by DED-Arc by using a deposition strategy incorporating interpass temperature control, and further evaluated their structural performance. Interpass temperature control regulates the temperature between deposition layers to reduce heat buildup, leading to a more consistent material deposition and reduced variation in thickness. In addition, the geometric accuracy, tensile strength, and compressive strength of aluminum stub column specimens produced using this approach were evaluated. Compression tests were conducted on specimens with and without thickness variation to assess the impact of thickness variation on buckling performance. This approach helps predict the design strength based on the width-to-thickness ratio, regardless of the variation in thickness. Furthermore, a buckling mode transition, indicating a shift in the deformation pattern under compressive loads, was observed at a width-to-thickness ratio of approximately 12.5, offering insights into the structural stability of these components. This study demonstrates that combining a DED-Arc process incorporating interpass temperature control with a width-to-thickness ratio-based evaluation enables the fabrication of structurally reliable aluminum components, even in the presence of thickness variation.

The present study examines an OpenFOAM-based LES analysis from the viewpoints of inviscid energy conservation and viscous turbulence decay. The Smagorinsky model is employed as the sub-grid scale (SGS) model, and a two-dimensional periodic analytical solution and a three-dimensional periodic Taylor-Green vortex (TGV) are employed to represent inviscid flows. The analytical relationship for the kinetic energy K, dK/dt = 0, with t as the dimensionless time, is utilized to validate the OpenFOAM results. For the viscous flow case, the TGV flow in a three-dimensional periodic cubic domain is adopted, and its turbulence kinetic energy distribution is compared with that obtained by a spectral method to examine the analysis. The OpenFOAM-based analysis exhibits energy conservation error in flows that should ideally conserve energy. For the two-dimensional flow, this error decreases with increasing grid resolution N. However, in the three-dimensional flow, the error does not improve even with higher N. In the three-dimensional TGV flow, the turbulence kinetic energy predicted by OpenFOAM exhibits a strong agreement with that from the spectral method when a standard constant value of the Smagorinsky model is employed and the mesh is sufficiently refined. Conversely, for a condition of relatively coarse mesh, the decay characteristics of turbulent kinetic energy deviate from those of the spectral method, and a higher constant value of the Smagorinsky model than the default value becomes necessary to reproduce comparable results. These results suggests that even in LES simulations where highly accurate conservation laws are not satisfied, adjusting the model constants so that the predicted values match experimental or numerical reference data can improve the apparent reliability of the turbulent kinetic energy in the decaying turbulence.

In this study, we derived a motorcycle riding simulation model reproducing the steering input forms of Bruschetta et al. (2020) and Picotti et al. (2024), where the plant model input is the steering angle and the path-following controller (rider model) input is the steering rate, based on the riding simulation model of Hatakeyama et al. (2024b). For this purpose, a plant model was derived by modifying that of Hatakeyama et al. (2024a) and changing the steering torque input to steering angle input. Additionally, by removing the equation corresponding to the steering dynamics of the internal model of the path-following controller derived by Hatakeyama et al. (2024b), the steering torque input was changed to a steering rate input. Using the modified riding simulation model, along with the riding simulation model of Hatakeyama et al. (2024b), which adopted a steering input form where both the plant model and the path-following controller take the steering torque as the input, riding simulations were conducted under identical conditions. By keeping the model structure, controller weights, and solver of the nonlinear model predictive control identical, except for differences related to the steering input form, it was possible to focus the analysis on the impact of the steering input form on riding simulation performance. The riding simulation demonstrated that, in the simulation model with a steering input form where the plant model and path-following controller take the steering angle and rate as the inputs, the lack of steering dynamics resulted in excessive oscillations in the control input or even divergence of the response. This shows that in motorcycle model-based development, the response does not reflect reality unless the input to the plant model and path-following controller is the steering torque, as reported by Hatakeyama et al. (2024b).

This paper derives the topological derivative of structural eigenvalues based on the partial differential equations of time-harmonic elastodynamics and their weak form, with the goal of achieving topology optimization of structural eigenvalues. To compute the topological derivative, it is first necessary to obtain the eigenvalues and eigenvectors of the structure. Traditional directmethods compute all eigenvalues and eigenvectors in a single step, which require substantial computational effort in finite element analysis. Engineering applications typically focus only on a subset of the lower order modes, so computing the full spectrum leads to unnecessary computational cost. To address this, we present a novel approach based on the Fast Fourier Transform (FFT) of the time-domain response of structure to obtain the first few eigenvalues and eigenvectors. This method significantly reduces computational costs. In the numerical examples for topology optimization, we employed a Level Set Method based on the reaction-diffusion equation to update the optimization variables. The results demonstrate that the new topological derivative and time-domain response analysis effectively achieve the optimization of structural eigenvalues.

This paper provides semi-analytical spectral methods for efficiently analyzing three-dimensional non-axisymmetric sound fields within axisymmetric cavities subject to arbitrary boundary conditions. By expanding the velocity potential using Fourier series in the circumferential direction, the problem is reduced to a set of two-dimensional equations. The introduction of generalized curvilinear coordinates enables the application of spectral methods to irregular axisymmetric domains, overcoming the limitations of conventional spectral methods restricted to regular geometries. Two types of spectral methods―the spectral collocation method and the spectral nodal Galerkin method―are formulated and applied to sound field analyses in cylindrical and kettledrum-shaped cavities. Numerical results demonstrate that the proposed methods achieve high accuracy with a small number of unknowns. Among the proposed approaches, the nodal Galerkin method exhibits the fastest convergence and highest accuracy.

This study developed a Message-Passing-Interface-based dynamic load balancing algorithm with four execution orders for the parallel parametric study of nonlinear finite element analyses. The dynamic load balancing algorithm is based on the master–worker method. The execution orders are descending and ascending orders for the number of nodes and for the number of incremental steps. In particular, Execution Orders A and B are the node-major step-minor descending order and the step-major node-minor descending order, respectively. These methods were applied to two numerical examples of finite-deformation elastic–plastic problems, namely, a compact tension specimen and a notched cylinder. The dynamic load balancing algorithm with Execution Order B was the fastest in the first numerical example, whereas that with Execution Order A was the fastest in the second. However, the differences between the results for Execution Orders A and B were slight in both numerical examples. Hence, both Execution Orders A and B are able to achieve practically short total computational time. The speedups from the static load balancing algorithm to the dynamic one for the two numerical examples were 1.54 and 1.37, respectively. The speedups from the ascending execution order to the descending execution order were 1.24 and 1.29, respectively. The results demonstrated that both dynamic load balancing and an appropriate execution order are necessary to reduce the load imbalance and thereby achieve short total computational time.

This study presents the development and validation of a vibration model for an infant-stroller system. A theoretical framework was constructed to capture the dynamic interactions between the stroller structure and an infant model, in which joints were represented using spring-damper elements. Model validation was performed by comparing frequency response characteristics obtained from numerical simulations under sinusoidal excitation (5 mm amplitude, 0.1-10 Hz) with those measured on a random uneven road surface, as well as by comparing transient responses to a single-wavelength, inverted cosine-shaped bump (12 mm in height and 60 mm in width). Simulation results showed general agreement with experimental data, confirming the model’s fidelity. A parametric case study was conducted to investigate the effect of stroller center of gravity (CoG) on infant vibration exposure. Forward CoG shifts increased vertical accelerations of the seat, head, and torso, particularly during bump traversal, due to enhanced pitch motion. Conversely, placing the CoG near the infant’s seating position mitigated anterior-posterior vibration amplification. These findings suggest that the proposed model enables predictive analysis of how stroller configuration affects infant dynamic response. The framework may serve as a practical tool for optimizing stroller design parameters to improve comfort and safety. Future work will incorporate seat-contact effects, age-related anthropometric variation, and optimization-based parameter identification.

Deployable wings reduce storage volume when an aircraft is not in flight. Although deployable wing structures have been extensively researched, very few such structures with high storage efficiency and stiffness have been put into practical use. To overcome this issue, we propose applying a convex boom and bellows structure, a lightweight, stiff, and simple structure widely used in deployable space structures, to the spars and ribs of the main structure of a deployable wing. The feasibility of a deployable wing main structure consisting of a convex boom and bellows-type ribs is verified. The structural characteristics of specimens of the proposed deployable wing main structure are evaluated through analysis and experiments. The proposed deployable wing main structure has high storage efficiency and stiffness. When the number of spars of the convex boom was increased from one to two and the cross-sectional thickness of the bellows-type ribs was increased from 2.0 to 3.0 mm, the bending stiffness per unit mass increased by 38.1% and the torsional stiffness per unit mass increased by 97.1%. The structural evaluation results demonstrate that not only the convex boom but also the bellows-type ribs significantly contribute to the structural stiffness of the deployable wing, and the feasibility of the proposed deployable wing main structure.