Institute of Mechanics,
Chinese Academy of Sciences
2025 Vol.15(4)
Theoretical and Applied Mechanics Letters 15 (2025) 100504.
doi: 10.1016/j.taml.2024.100504
Abstract:
Generative adversarial network (GAN) models are widely used in mechanical designs. The aim in the airfoil shape design is to obtain shapes that exhibits the required aerodynamic performance, and conditional GAN is used for that aim. However, the output of GAN contains uncertainties. Additionally, the uncertainties of labels have not been quantified. This paper proposes an uncertainty quantification method to estimate the uncertainty of labels using Monte Carlo dropout. In addition, an uncertainty reduction method is proposed based on imbalanced training. The proposed method was evaluated for the airfoil generation task. The results indicated that the uncertainty was appropriately quantified and successfully reduced.
Generative adversarial network (GAN) models are widely used in mechanical designs. The aim in the airfoil shape design is to obtain shapes that exhibits the required aerodynamic performance, and conditional GAN is used for that aim. However, the output of GAN contains uncertainties. Additionally, the uncertainties of labels have not been quantified. This paper proposes an uncertainty quantification method to estimate the uncertainty of labels using Monte Carlo dropout. In addition, an uncertainty reduction method is proposed based on imbalanced training. The proposed method was evaluated for the airfoil generation task. The results indicated that the uncertainty was appropriately quantified and successfully reduced.
Theoretical and Applied Mechanics Letters 15 (2025) 100586.
doi: 10.1016/j.taml.2025.100586
Abstract:
The stability of supersonic inlets faces challenges due to various changes in flight conditions, and flow control methods that address shock wave/boundary layer interactions under only one set of conditions cannot meet developmental requirements. This paper proposes an adaptive bump control scheme and employs dynamic mesh technology for numerical simulation to investigate the unsteady control effects of adaptive bumps. The obtained results indicate that the use of moving bumps to control shock wave/boundary layer interactions is feasible. The adaptive control effects of five different bump speeds are evaluated. Within the range of bump speeds studied, the analysis of the flow field structure reveals the patterns of change in the separation zone area during the control process, as well as the relationship between the bump motion speed and the control effect on the separation zone. It is concluded that the moving bump endows the boundary layer with additional energy.
The stability of supersonic inlets faces challenges due to various changes in flight conditions, and flow control methods that address shock wave/boundary layer interactions under only one set of conditions cannot meet developmental requirements. This paper proposes an adaptive bump control scheme and employs dynamic mesh technology for numerical simulation to investigate the unsteady control effects of adaptive bumps. The obtained results indicate that the use of moving bumps to control shock wave/boundary layer interactions is feasible. The adaptive control effects of five different bump speeds are evaluated. Within the range of bump speeds studied, the analysis of the flow field structure reveals the patterns of change in the separation zone area during the control process, as well as the relationship between the bump motion speed and the control effect on the separation zone. It is concluded that the moving bump endows the boundary layer with additional energy.
Theoretical and Applied Mechanics Letters 15 (2025) 100588.
doi: 10.1016/j.taml.2025.100588
Abstract:
This study addresses the significant disparity in aerodynamic uplift forces experienced by single-strip high-speed pantographs under different operating directions. A systematic numerical investigation was conducted to evaluate the influence of key geometric parameters on aerodynamic characteristics, culminating in two targeted adjustment strategies. The reliability of the computational methodology was validated through comparative analysis, which revealed less than a 6% deviation in aerodynamic drag between the numerical simulations and wind tunnel tests. Aerodynamic decomposition revealed that the operating direction critically impacts the uplift force, which is governed by two factors: streamwise cross-strip positioning and the angular orientation of the arm hinge. These factors collectively determine the divergent aerodynamic responses of the panhead and frame during directional changes. By establishing a parametric database encompassing four strip-to-crossbar spacing configurations and six arm diameter variations, nonlinear response patterns of the uplift forces under different operating directions to geometric modifications were quantified. Both adjustment approaches, simultaneously reducing both streamwise and vertical strip-to-crossbar spacings to half of the original dimensions or increasing the upper arm spanwise diameter to 1.45 times and decreasing the lower arm spanwise diameter to 0.55 times the baseline values, successfully constrained aerodynamic uplift force deviations between operating directions within 3%.
This study addresses the significant disparity in aerodynamic uplift forces experienced by single-strip high-speed pantographs under different operating directions. A systematic numerical investigation was conducted to evaluate the influence of key geometric parameters on aerodynamic characteristics, culminating in two targeted adjustment strategies. The reliability of the computational methodology was validated through comparative analysis, which revealed less than a 6% deviation in aerodynamic drag between the numerical simulations and wind tunnel tests. Aerodynamic decomposition revealed that the operating direction critically impacts the uplift force, which is governed by two factors: streamwise cross-strip positioning and the angular orientation of the arm hinge. These factors collectively determine the divergent aerodynamic responses of the panhead and frame during directional changes. By establishing a parametric database encompassing four strip-to-crossbar spacing configurations and six arm diameter variations, nonlinear response patterns of the uplift forces under different operating directions to geometric modifications were quantified. Both adjustment approaches, simultaneously reducing both streamwise and vertical strip-to-crossbar spacings to half of the original dimensions or increasing the upper arm spanwise diameter to 1.45 times and decreasing the lower arm spanwise diameter to 0.55 times the baseline values, successfully constrained aerodynamic uplift force deviations between operating directions within 3%.
Theoretical and Applied Mechanics Letters 15 (2025) 100589.
doi: 10.1016/j.taml.2025.100589
Abstract:
Understanding the phase behavior of hydrocarbons and their mixtures, especially under confinement, is crucial for the extraction of shale oil and gas. In this study, we employed molecular dynamics simulations to investigate the phase behaviors of three typical hydrocarbons (methane, pentane, and octane) in the bulk phase and in nanopores. We find that the confinement effect can alter the phase behavior of a single-component hydrocarbon. For the mixture of methane and octane in nanopores, a rather high proportion of methane could inhibit the capillary condensation of octane. We also studied the influence of phase behavior on the recovery dynamics of hydrocarbon mixtures from blind nanopores of different sizes at different gas-oil ratios. The capillary condensation of the heavy hydrocarbon components in the nanopore throat could hinder the transport of light. These findings increase the understanding of the occurrence states of shale oil and gas and their migration through nanopore throats, providing practical guidance for shale oil and gas development.
Understanding the phase behavior of hydrocarbons and their mixtures, especially under confinement, is crucial for the extraction of shale oil and gas. In this study, we employed molecular dynamics simulations to investigate the phase behaviors of three typical hydrocarbons (methane, pentane, and octane) in the bulk phase and in nanopores. We find that the confinement effect can alter the phase behavior of a single-component hydrocarbon. For the mixture of methane and octane in nanopores, a rather high proportion of methane could inhibit the capillary condensation of octane. We also studied the influence of phase behavior on the recovery dynamics of hydrocarbon mixtures from blind nanopores of different sizes at different gas-oil ratios. The capillary condensation of the heavy hydrocarbon components in the nanopore throat could hinder the transport of light. These findings increase the understanding of the occurrence states of shale oil and gas and their migration through nanopore throats, providing practical guidance for shale oil and gas development.
Theoretical and Applied Mechanics Letters 15 (2025) 100590.
doi: 10.1016/j.taml.2025.100590
Abstract:
Many animal and plant tissues, such as adipose tissue and fruits, can be taken as liquid-saturated soft composites, which have densely packed pores that are filled with liquid. Typically, when the pore dimensions are sufficiently small (at the micro- or nanoscale), surface effects significantly influence the mechanical properties of the material. To characterize the thermomechanical properties critical for animals and plants, we propose an idealized cubic closed-cell model in which liquid compressibility and surface stress (i.e., surface moduli and residual surface stress) are considered. Analytical solutions of the model are then employed to quantify how the surface stress, porosity, and liquid bulk modulus affect the effective Young’s modulus, effective Poisson ratio, and effective coefficient of thermal expansion (CTE) of the liquid-saturated soft composite. An increase in residual surface stress reduces both the effective modulus and effective CTE, whereas increasing the surface moduli result in a greater effective modulus and reduced effective CTE. The results provide critical insights into how surface effects govern the macroscopic thermomechanical behavior of liquid-saturated soft composites with small pores.
Many animal and plant tissues, such as adipose tissue and fruits, can be taken as liquid-saturated soft composites, which have densely packed pores that are filled with liquid. Typically, when the pore dimensions are sufficiently small (at the micro- or nanoscale), surface effects significantly influence the mechanical properties of the material. To characterize the thermomechanical properties critical for animals and plants, we propose an idealized cubic closed-cell model in which liquid compressibility and surface stress (i.e., surface moduli and residual surface stress) are considered. Analytical solutions of the model are then employed to quantify how the surface stress, porosity, and liquid bulk modulus affect the effective Young’s modulus, effective Poisson ratio, and effective coefficient of thermal expansion (CTE) of the liquid-saturated soft composite. An increase in residual surface stress reduces both the effective modulus and effective CTE, whereas increasing the surface moduli result in a greater effective modulus and reduced effective CTE. The results provide critical insights into how surface effects govern the macroscopic thermomechanical behavior of liquid-saturated soft composites with small pores.
Theoretical and Applied Mechanics Letters 15 (2025) 100591.
doi: 10.1016/j.taml.2025.100591
Abstract:
An efficient, diversified, and low-dimensional airfoil parameterization method is critical to airfoil aerodynamic optimization design. This paper proposes a supersonic airfoil parameterization method based on a bijective cycle generative adversarial network (Bicycle-GAN), whose performance is compared with that of the conditional variational autoencoder (cVAE) based parameterization method in terms of parsimony, flawlessness, intuitiveness, and physicality. In all four aspects, the Bicycle-GAN-based parameterization method is superior to the cVAE-based parameterization method. Combined with multifidelity Gaussian process regression (MFGPR) surrogate model and a Bayesian optimization algorithm, a Bicycle-GAN-based optimization framework is established for the aerodynamic performance optimization of airfoils immersed in supersonic flow, which is compared with the cVAE-based optimization method in terms of optimized efficiency and effectiveness. The MFGPR surrogate model is established using low-fidelity aerodynamic data obtained from supersonic thin-airfoil theory and high-fidelity aerodynamic data obtained from steady CFD simulation. For both supersonic conditions, the CFD simulation costs are reduced by >20% compared with those of the cVAE-based optimization, and better optimization results are obtained through the Bicycle-GAN model. The optimization results for this supersonic flow point to a sharper leading edge, a smaller camber and thickness with a flatter lower surface, and a maximum thickness at 50% chord length. The advantages of the Bicycle-GAN and MFGPR models are comprehensively demonstrated in terms of airfoil generation characteristics, surrogate model prediction accuracy and optimization efficiency.
An efficient, diversified, and low-dimensional airfoil parameterization method is critical to airfoil aerodynamic optimization design. This paper proposes a supersonic airfoil parameterization method based on a bijective cycle generative adversarial network (Bicycle-GAN), whose performance is compared with that of the conditional variational autoencoder (cVAE) based parameterization method in terms of parsimony, flawlessness, intuitiveness, and physicality. In all four aspects, the Bicycle-GAN-based parameterization method is superior to the cVAE-based parameterization method. Combined with multifidelity Gaussian process regression (MFGPR) surrogate model and a Bayesian optimization algorithm, a Bicycle-GAN-based optimization framework is established for the aerodynamic performance optimization of airfoils immersed in supersonic flow, which is compared with the cVAE-based optimization method in terms of optimized efficiency and effectiveness. The MFGPR surrogate model is established using low-fidelity aerodynamic data obtained from supersonic thin-airfoil theory and high-fidelity aerodynamic data obtained from steady CFD simulation. For both supersonic conditions, the CFD simulation costs are reduced by >20% compared with those of the cVAE-based optimization, and better optimization results are obtained through the Bicycle-GAN model. The optimization results for this supersonic flow point to a sharper leading edge, a smaller camber and thickness with a flatter lower surface, and a maximum thickness at 50% chord length. The advantages of the Bicycle-GAN and MFGPR models are comprehensively demonstrated in terms of airfoil generation characteristics, surrogate model prediction accuracy and optimization efficiency.
Topology optimization for fluid–structure interaction problems considering heat transfer performance
Theoretical and Applied Mechanics Letters 15 (2025) 100592.
doi: 10.1016/j.taml.2025.100592
Abstract:
Effectively controlling the deformation and temperature of heated structures is crucial for achieving high-performance active cooling through fluid flow. In this study, the topology optimization design of structures considering fluid–structure interactions and heat transfer performance was investigated, and then optimized designs of two-dimensional/three-dimensional cooling impingement systems obtained using the proposed method were obtained. In the optimization model, the objective function was constructed as a weighted combination of the mechanical deformations at specific locations and the average temperature within the designated solid channel structures. Additionally, explicit functional interpolation models were introduced to establish connections between the thermal, fluid, and solid properties, along with the element densities. In the analysis model, the strongly coupled structural mechanical deformation and fluid velocity field were analyzed via a dynamic-grid-based finite element model with a Winslow elliptic smoother to automatically track the fluid–structure interface during the process of optimization. To solve the optimization problems, the globally convergent moving asymptotic optimizer method was used to adjust the design variables on the basis of the sensitivity analysis. A demonstration of the efficacy of the proposed algorithm is provided through the presentation of several optimization examples. Furthermore, two- and three-dimensional cooling impingement systems were designed with the proposed method.
Effectively controlling the deformation and temperature of heated structures is crucial for achieving high-performance active cooling through fluid flow. In this study, the topology optimization design of structures considering fluid–structure interactions and heat transfer performance was investigated, and then optimized designs of two-dimensional/three-dimensional cooling impingement systems obtained using the proposed method were obtained. In the optimization model, the objective function was constructed as a weighted combination of the mechanical deformations at specific locations and the average temperature within the designated solid channel structures. Additionally, explicit functional interpolation models were introduced to establish connections between the thermal, fluid, and solid properties, along with the element densities. In the analysis model, the strongly coupled structural mechanical deformation and fluid velocity field were analyzed via a dynamic-grid-based finite element model with a Winslow elliptic smoother to automatically track the fluid–structure interface during the process of optimization. To solve the optimization problems, the globally convergent moving asymptotic optimizer method was used to adjust the design variables on the basis of the sensitivity analysis. A demonstration of the efficacy of the proposed algorithm is provided through the presentation of several optimization examples. Furthermore, two- and three-dimensional cooling impingement systems were designed with the proposed method.
Theoretical and Applied Mechanics Letters 15 (2025) 100593.
doi: 10.1016/j.taml.2025.100593
Abstract:
All-solid-state lithium metal batteries (ASSLMBs) are widely recognized as promising next-generation energy storage technologies that offer significant advantages in terms of safety and energy density. However, the long-term cycling stability of these batteries is often compromised by interfacial failures driven by coupled mechanical and diffusion effects. This study presents a probabilistic failure prediction model that quantifies interfacial damage and capacity loss in composite electrodes under the coupled influence of mechanical-diffusion-induced processes. We first develop a pseudo3D (P3D) interface failure model for a binary particle system to evaluate interfacial failure during the critical delithiation process. The P3D model is validated through mechanical‒diffusion coupled simulations. Additionally, for multiparticle composite electrode films with heterogeneous particle sizes, we identify a key structural factor that governs the failure of the particle‒solid electrolyte interface, which follows a three-parameter Burr distribution. Building on this, we develop a probabilistic model to predict the capacity fade in multiporject composite films. This work provides a comprehensive understanding of the critical geometric factors that influence interfacial stability, offering valuable theoretical insights and practical guidance for the rapid assessment, optimization, and enhancement of cycling stability in ASSLMBs.
All-solid-state lithium metal batteries (ASSLMBs) are widely recognized as promising next-generation energy storage technologies that offer significant advantages in terms of safety and energy density. However, the long-term cycling stability of these batteries is often compromised by interfacial failures driven by coupled mechanical and diffusion effects. This study presents a probabilistic failure prediction model that quantifies interfacial damage and capacity loss in composite electrodes under the coupled influence of mechanical-diffusion-induced processes. We first develop a pseudo3D (P3D) interface failure model for a binary particle system to evaluate interfacial failure during the critical delithiation process. The P3D model is validated through mechanical‒diffusion coupled simulations. Additionally, for multiparticle composite electrode films with heterogeneous particle sizes, we identify a key structural factor that governs the failure of the particle‒solid electrolyte interface, which follows a three-parameter Burr distribution. Building on this, we develop a probabilistic model to predict the capacity fade in multiporject composite films. This work provides a comprehensive understanding of the critical geometric factors that influence interfacial stability, offering valuable theoretical insights and practical guidance for the rapid assessment, optimization, and enhancement of cycling stability in ASSLMBs.
Theoretical and Applied Mechanics Letters 15 (2025) 100595.
doi: 10.1016/j.taml.2025.100595
Abstract:
Bistable beams, with their characteristic recoverable elastic large deformations, are widely utilized in reversible deformation designs. However, analytical modeling of bistable beams under third-order mode deformation remains a challenge. For example, theoretical research on bistable beams in existing energy-consuming materials has focused mainly on the deformation process of the second-order mode. To address this challenge, the present work establishes an analytical model for the deformation process of a bistable beam from the first-order mode to the third-order mode via the elliptic integral method. Additionally, judgment conditions for identifying the critical points of modal transitions are provided. Second, the analytical model allows for the calculation of the maximum instability force and the unstable equilibrium position when third-order mode deformation occurs in the bistable beam during the snap-through process. The unstable equilibrium position of the bistable beam during third-order mode deformation is significantly lower than the positions of the two fixed ends. The validity of the analytical model was confirmed through experiments and finite element modeling. In the compression experiments of bistable beams with identical dimensional parameters presented in the present work, the work done by the external force during the third-order mode deformation process is 2 times that of the second-order mode deformation process. This will provide a completely new approach for the design of energy-consuming materials based on bistable beams.
Bistable beams, with their characteristic recoverable elastic large deformations, are widely utilized in reversible deformation designs. However, analytical modeling of bistable beams under third-order mode deformation remains a challenge. For example, theoretical research on bistable beams in existing energy-consuming materials has focused mainly on the deformation process of the second-order mode. To address this challenge, the present work establishes an analytical model for the deformation process of a bistable beam from the first-order mode to the third-order mode via the elliptic integral method. Additionally, judgment conditions for identifying the critical points of modal transitions are provided. Second, the analytical model allows for the calculation of the maximum instability force and the unstable equilibrium position when third-order mode deformation occurs in the bistable beam during the snap-through process. The unstable equilibrium position of the bistable beam during third-order mode deformation is significantly lower than the positions of the two fixed ends. The validity of the analytical model was confirmed through experiments and finite element modeling. In the compression experiments of bistable beams with identical dimensional parameters presented in the present work, the work done by the external force during the third-order mode deformation process is 2 times that of the second-order mode deformation process. This will provide a completely new approach for the design of energy-consuming materials based on bistable beams.
Theoretical and Applied Mechanics Letters 15 (2025) 100596.
doi: 10.1016/j.taml.2025.100596
Abstract:
This paper investigates the ventilated cavity phenomena of a symmetric body under specific conditions, focusing on the factors affecting the vortex structure. The ventilated cavitating flow development process is simulated with a homogeneous free surface model combined with a filter-based turbulence model. The results show the characteristics of the pressure pulse and the bubble shedding around the axisymmetric body. A quasiperiodic pressure pulse occurs at the middle of the body. In addition, three main types of vortices occur in ventilated partial cavitation: large-scale cloud vortices, U-type vortices, and small-scale vortices. Further analysis revealed that the cavities and vortex structures have similar influencing factors. The vorticity transport equation is applied to analyze the main factors influencing the vortex. The results indicate that fluid density primarily affects large-scale cloud vortices, the velocity gradient plays a dominant role in U-type vortices, and fluid angular velocity is the main influencing factor for small-scale vortices.
This paper investigates the ventilated cavity phenomena of a symmetric body under specific conditions, focusing on the factors affecting the vortex structure. The ventilated cavitating flow development process is simulated with a homogeneous free surface model combined with a filter-based turbulence model. The results show the characteristics of the pressure pulse and the bubble shedding around the axisymmetric body. A quasiperiodic pressure pulse occurs at the middle of the body. In addition, three main types of vortices occur in ventilated partial cavitation: large-scale cloud vortices, U-type vortices, and small-scale vortices. Further analysis revealed that the cavities and vortex structures have similar influencing factors. The vorticity transport equation is applied to analyze the main factors influencing the vortex. The results indicate that fluid density primarily affects large-scale cloud vortices, the velocity gradient plays a dominant role in U-type vortices, and fluid angular velocity is the main influencing factor for small-scale vortices.
Theoretical and Applied Mechanics Letters 15 (2025) 100587.
doi: 10.1016/j.taml.2025.100587
Abstract:
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