Institute of Mechanics,
Chinese Academy of Sciences
2023 Vol.13(4)
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Theoretical and Applied Mechanics Letters 13 (2023) 100457.
doi: 10.1016/j.taml.2023.100457
Abstract:
Nonlinear and stochastic dynamics is essential and practical in almost all branches of natural science and engineering. It has been a central subject to understand various complex dynamics, such as random vibration, stochastic transition, synchronization, et al., in the areas of mechanical and aerospace engineering, physics and chemistry. For example, the stochastic resonance has been utilized effectively in mechanical fault diagnosis and weak signal detection. Naturally, many methods have been developed to get the stochastic responses, including stochastic averaging method, multiple scale method and path integral method, and so on. Theories of stochastic transition, including stochastic bifurcation, stochastic resonance and first passage process have been proposed to reveal the action mechanism of noises. Consequently, various applications have been found in mechanical, physical, and biological fields. However, the present framework, is far from revealing the underlying mechanisms and principles for many issues. It requires more attention to the non-Gaussian noise, high-dimensional systems, new combination with deep learning, and applications to frontier areas, to name but a few. Therefore, this special issue is organized to report the recent developments in nonlinear and stochastic dynamics, specially focusing on stochastic methods, stochastic dynamics and applications.
Nonlinear and stochastic dynamics is essential and practical in almost all branches of natural science and engineering. It has been a central subject to understand various complex dynamics, such as random vibration, stochastic transition, synchronization, et al., in the areas of mechanical and aerospace engineering, physics and chemistry. For example, the stochastic resonance has been utilized effectively in mechanical fault diagnosis and weak signal detection. Naturally, many methods have been developed to get the stochastic responses, including stochastic averaging method, multiple scale method and path integral method, and so on. Theories of stochastic transition, including stochastic bifurcation, stochastic resonance and first passage process have been proposed to reveal the action mechanism of noises. Consequently, various applications have been found in mechanical, physical, and biological fields. However, the present framework, is far from revealing the underlying mechanisms and principles for many issues. It requires more attention to the non-Gaussian noise, high-dimensional systems, new combination with deep learning, and applications to frontier areas, to name but a few. Therefore, this special issue is organized to report the recent developments in nonlinear and stochastic dynamics, specially focusing on stochastic methods, stochastic dynamics and applications.
Theoretical and Applied Mechanics Letters 13 (2023) 100440.
doi: 10.1016/j.taml.2023.100440
Abstract:
Dynamic Bayesian networks (DBNs) are commonly employed for structural digital twin modeling. At present, most researches only consider single damage mode tracking. It is not sufficient for a reusable spacecraft as various damage modes may occur during its service life. A reconfigurable DBN method is proposed in this paper. The structure of the DBN can be updated dynamically to describe the interactions between different damages. Two common damages (fatigue and bolt loosening) for a spacecraft structure are considered in a numerical example. The results show that the reconfigurable DBN can accurately predict the acceleration phenomenon of crack growth caused by bolt loosening while the DBN with time-invariant structure cannot, even with enough updates. The definition of interaction coefficients makes the reconfigurable DBN easy to track multiple damages and be extended to more complex problems. The method also has a good physical interpretability as the reconfiguration of DBN corresponds to a specific mechanism. Satisfactory predictions do not require precise knowledge of reconfiguration conditions, making the method more practical.
Dynamic Bayesian networks (DBNs) are commonly employed for structural digital twin modeling. At present, most researches only consider single damage mode tracking. It is not sufficient for a reusable spacecraft as various damage modes may occur during its service life. A reconfigurable DBN method is proposed in this paper. The structure of the DBN can be updated dynamically to describe the interactions between different damages. Two common damages (fatigue and bolt loosening) for a spacecraft structure are considered in a numerical example. The results show that the reconfigurable DBN can accurately predict the acceleration phenomenon of crack growth caused by bolt loosening while the DBN with time-invariant structure cannot, even with enough updates. The definition of interaction coefficients makes the reconfigurable DBN easy to track multiple damages and be extended to more complex problems. The method also has a good physical interpretability as the reconfiguration of DBN corresponds to a specific mechanism. Satisfactory predictions do not require precise knowledge of reconfiguration conditions, making the method more practical.
Theoretical and Applied Mechanics Letters 13 (2023) 100452.
doi: 10.1016/j.taml.2023.100452
Abstract:
Ocean thermal energy conversion (OTEC) is a process of generating electricity by exploiting the temperature difference between warm surface seawater and cold deep seawater. Due to the high static and dynamic pressures that are caused by seawater circulation, the stiffened panel that constitutes a seawater tank may undergo a reduction in ultimate strength. The current paper investigates the design of stiffening systems for OTEC seawater tanks by examining the effects of stiffening parameters such as stiffener sizes and span-over-bay ratio for the applied combined loadings of lateral and transverse pressure by fluid motion and axial compression due to global bending moment. The ultimate strength calculation was conducted by using the non-linear finite element method via the commercial software known as ABAQUS. The stress and deformation distribution due to pressure loads was computed in the first step and then brought to the second step, in which the axial compression was applied. The effects of pressure on the ultimate strength of the stiffener were investigated for representative stiffened panels, and the significance of the stiffener parameters was assessed by using the sensitivity analysis method. As a result, the ultimate strength was reduced by approximately 1.5% for the span-over-bay ratio of 3 and by 7% for the span-over-bay ratio of 6.
Ocean thermal energy conversion (OTEC) is a process of generating electricity by exploiting the temperature difference between warm surface seawater and cold deep seawater. Due to the high static and dynamic pressures that are caused by seawater circulation, the stiffened panel that constitutes a seawater tank may undergo a reduction in ultimate strength. The current paper investigates the design of stiffening systems for OTEC seawater tanks by examining the effects of stiffening parameters such as stiffener sizes and span-over-bay ratio for the applied combined loadings of lateral and transverse pressure by fluid motion and axial compression due to global bending moment. The ultimate strength calculation was conducted by using the non-linear finite element method via the commercial software known as ABAQUS. The stress and deformation distribution due to pressure loads was computed in the first step and then brought to the second step, in which the axial compression was applied. The effects of pressure on the ultimate strength of the stiffener were investigated for representative stiffened panels, and the significance of the stiffener parameters was assessed by using the sensitivity analysis method. As a result, the ultimate strength was reduced by approximately 1.5% for the span-over-bay ratio of 3 and by 7% for the span-over-bay ratio of 6.
Theoretical and Applied Mechanics Letters 13 (2023) 100453.
doi: 10.1016/j.taml.2023.100453
Abstract:
Buckling and postbuckling characteristics of laminated graphene-enhanced composite (GEC) truncated conical shells exposed to torsion under temperature conditions using finite element method (FEM) simulation are presented in this study. In the thickness direction, the GEC layers of the conical shell are ordered in a piece-wise arrangement of functionally graded (FG) distribution, with each layer containing a variable volume fraction for graphene reinforcement. To calculate the properties of temperaturedependent material of GEC layers, the extended Halpin-Tsai micromechanical framework is used. The FEM model is verified via comparing the current results obtained with the theoretical estimates for homogeneous, laminated cylindrical, and conical shells, the FEM model is validated. The computational results show that a piece-wise FG graphene volume fraction distribution can improve the torque of critical buckling and torsional postbuckling strength. Also, the geometric parameters have a critical impact on the stability of the conical shell. However, a temperature rise can reduce the crucial torsional buckling torque as well as the GEC laminated truncated conical shell’s postbuckling strength.
Buckling and postbuckling characteristics of laminated graphene-enhanced composite (GEC) truncated conical shells exposed to torsion under temperature conditions using finite element method (FEM) simulation are presented in this study. In the thickness direction, the GEC layers of the conical shell are ordered in a piece-wise arrangement of functionally graded (FG) distribution, with each layer containing a variable volume fraction for graphene reinforcement. To calculate the properties of temperaturedependent material of GEC layers, the extended Halpin-Tsai micromechanical framework is used. The FEM model is verified via comparing the current results obtained with the theoretical estimates for homogeneous, laminated cylindrical, and conical shells, the FEM model is validated. The computational results show that a piece-wise FG graphene volume fraction distribution can improve the torque of critical buckling and torsional postbuckling strength. Also, the geometric parameters have a critical impact on the stability of the conical shell. However, a temperature rise can reduce the crucial torsional buckling torque as well as the GEC laminated truncated conical shell’s postbuckling strength.
Theoretical and Applied Mechanics Letters 13 (2023) 100454.
doi: 10.1016/j.taml.2023.100454
Abstract:
This work compares the threshold applied to the swirling strength as well as the vortex orientation statistics in the total and fluctuating velocity fields using direct numerical simulations of compressible and incompressible turbulent channel flows. It is concluded that the difference in the swirling strength for vortex identification is minimal in the logarithmic region such that these two situations share the same threshold. Regarding the vortex orientation, the inclination angle remains similar. However, as the wall-normal distance increases, a more and more obvious distinction is noticed for its orientation with respect to the spanwise (z) direction. It is mainly due to their intrinsic differences and attendant contrasting preference for the vortex identification, i.e., vortices rotating in the -z direction for the total velocity field and in the z direction for the fluctuating one. These observations function as a reasonable explanation for various remarks in previous studies.
This work compares the threshold applied to the swirling strength as well as the vortex orientation statistics in the total and fluctuating velocity fields using direct numerical simulations of compressible and incompressible turbulent channel flows. It is concluded that the difference in the swirling strength for vortex identification is minimal in the logarithmic region such that these two situations share the same threshold. Regarding the vortex orientation, the inclination angle remains similar. However, as the wall-normal distance increases, a more and more obvious distinction is noticed for its orientation with respect to the spanwise (z) direction. It is mainly due to their intrinsic differences and attendant contrasting preference for the vortex identification, i.e., vortices rotating in the -z direction for the total velocity field and in the z direction for the fluctuating one. These observations function as a reasonable explanation for various remarks in previous studies.
Theoretical and Applied Mechanics Letters 13 (2023) 100467.
doi: 10.1016/j.taml.2023.100467
Abstract:
We provide the capillary pressure curves pc(s) as a function of the effective saturation s based on the theoretical framework of upscaling unsaturated flows in vertically heterogeneous porous layers proposed recently (Z. Zheng, Journal of Fluid Mechanics, 950, A17, 2022). Based on the assumption of vertical gravitational-capillary equilibrium, the saturation distribution and profile shape of the invading fluid can be obtained by solving a nonlinear integral-differential equation. The capillary pressure curves pc(s) can then be constructed by systematically varying the injection rate. Together with the relative permeability curves krn(s) that are already obtained. One can now provide quick estimates on the overall behaviours of interfacial and unsaturated flows in vertically-heterogeneous porous layers.
We provide the capillary pressure curves pc(s) as a function of the effective saturation s based on the theoretical framework of upscaling unsaturated flows in vertically heterogeneous porous layers proposed recently (Z. Zheng, Journal of Fluid Mechanics, 950, A17, 2022). Based on the assumption of vertical gravitational-capillary equilibrium, the saturation distribution and profile shape of the invading fluid can be obtained by solving a nonlinear integral-differential equation. The capillary pressure curves pc(s) can then be constructed by systematically varying the injection rate. Together with the relative permeability curves krn(s) that are already obtained. One can now provide quick estimates on the overall behaviours of interfacial and unsaturated flows in vertically-heterogeneous porous layers.
Theoretical and Applied Mechanics Letters 13 (2023) 100451.
doi: 10.1016/j.taml.2023.100451
Abstract:
Advancements in uncrewed aircrafts and communications technologies have led to a wave of interest and investment in unmanned aircraft systems (UASs) and urban air mobility (UAM) vehicles over the past decade. To support this emerging aviation application, concepts for UAS/UAM traffic management (UTM) systems have been explored. Accurately characterizing and predicting the microscale weather conditions, winds in particular, will be critical to safe and efficient operations of the small UASs/UAM aircrafts within the UTM. This study implements a reduced order data assimilation approach to reduce discrepancies between the predicted urban wind speed with computational fluid dynamics (CFD) Reynolds-averaged Navier Stokes (RANS) model with real-world, limited and sparse observations. The developed data assimilation system is UrbanDA. These observations are simulated using a large eddy simulation (LES). The data assimilation approach is based on the time-independent variational framework and uses space reduction to reduce the memory cost of the process. This approach leads to error reduction throughout the simulated domain and the reconstructed field is different than the initial guess by ingesting wind speeds at sensor locations and hence taking into account flow unsteadiness in a time when only the mean flow quantities are resolved. Different locations where wind sensors can be installed are discussed in terms of their impact on the resulting wind field. It is shown that near-wall locations, near turbulence generation areas with high wind speeds have the highest impact. Approximating the model error with its principal mode provides a better agreement with the truth and the hazardous areas for UAS navigation increases by more than 10% as wind hazards resulting from buildings wakes are better simulated through this process.
Advancements in uncrewed aircrafts and communications technologies have led to a wave of interest and investment in unmanned aircraft systems (UASs) and urban air mobility (UAM) vehicles over the past decade. To support this emerging aviation application, concepts for UAS/UAM traffic management (UTM) systems have been explored. Accurately characterizing and predicting the microscale weather conditions, winds in particular, will be critical to safe and efficient operations of the small UASs/UAM aircrafts within the UTM. This study implements a reduced order data assimilation approach to reduce discrepancies between the predicted urban wind speed with computational fluid dynamics (CFD) Reynolds-averaged Navier Stokes (RANS) model with real-world, limited and sparse observations. The developed data assimilation system is UrbanDA. These observations are simulated using a large eddy simulation (LES). The data assimilation approach is based on the time-independent variational framework and uses space reduction to reduce the memory cost of the process. This approach leads to error reduction throughout the simulated domain and the reconstructed field is different than the initial guess by ingesting wind speeds at sensor locations and hence taking into account flow unsteadiness in a time when only the mean flow quantities are resolved. Different locations where wind sensors can be installed are discussed in terms of their impact on the resulting wind field. It is shown that near-wall locations, near turbulence generation areas with high wind speeds have the highest impact. Approximating the model error with its principal mode provides a better agreement with the truth and the hazardous areas for UAS navigation increases by more than 10% as wind hazards resulting from buildings wakes are better simulated through this process.
Theoretical and Applied Mechanics Letters 13 (2023) 100458.
doi: 10.1016/j.taml.2023.100458
Abstract:
The aim of this study is the numerical analysis of the melting process of the phase change material (PCM) in a spiral coil. The space between the inner tube and outer shell is filled with RT-50 as PCM. Moreover, the hybrid nanofluid (with a carbon component) flows through the inner tube. The novelty of this work is to use different configurations of fin and different percentage of hybrid nanoparticles (SWCNTs-CuO) on the PCM melting process. In the numerical model created by ANSYS-Fluent, the effect of various inlet temperatures is investigated. The results indicate that the extended surface created by extra fin has a dominant effect on melting time, so by adding the third fin, the melting time is reduced by 39.24%. The next most influential factor in PCM melting is the inlet temperature of the working fluid, so that 10°C increment of temperature result in the PCM melting time decreased by 35.41%.
The aim of this study is the numerical analysis of the melting process of the phase change material (PCM) in a spiral coil. The space between the inner tube and outer shell is filled with RT-50 as PCM. Moreover, the hybrid nanofluid (with a carbon component) flows through the inner tube. The novelty of this work is to use different configurations of fin and different percentage of hybrid nanoparticles (SWCNTs-CuO) on the PCM melting process. In the numerical model created by ANSYS-Fluent, the effect of various inlet temperatures is investigated. The results indicate that the extended surface created by extra fin has a dominant effect on melting time, so by adding the third fin, the melting time is reduced by 39.24%. The next most influential factor in PCM melting is the inlet temperature of the working fluid, so that 10°C increment of temperature result in the PCM melting time decreased by 35.41%.
Theoretical and Applied Mechanics Letters 13 (2023) 100460.
doi: 10.1016/j.taml.2023.100460
Abstract:
In order to develop a anchoring operation simulation system and improve safety during anchoring operations, a relatively accurate mathematical model of anchoring operations needs to be established. In this paper, the stress condition of anchor chain under environmental and subsea geological conditions is further studied and the stress condition of anchor chain is analyzed based on the previous research. In this paper, a quasi-static model based on catenary method is used as the basis of dynamic analysis, and the dynamic model of anchor chain is established based on the concentrated mass method, which fully considers the influence of anchor chain weight, hydrodynamic force, ocean current and interaction with the seabed. The fourth-order Runge Kutta method was used to solve the model numerically, and a calculation procedure was developed. The accuracy of the model was verified by comparing the calculated results with the experimental results, indicating that the constructed anchor chain dynamics model has a high accuracy.
In order to develop a anchoring operation simulation system and improve safety during anchoring operations, a relatively accurate mathematical model of anchoring operations needs to be established. In this paper, the stress condition of anchor chain under environmental and subsea geological conditions is further studied and the stress condition of anchor chain is analyzed based on the previous research. In this paper, a quasi-static model based on catenary method is used as the basis of dynamic analysis, and the dynamic model of anchor chain is established based on the concentrated mass method, which fully considers the influence of anchor chain weight, hydrodynamic force, ocean current and interaction with the seabed. The fourth-order Runge Kutta method was used to solve the model numerically, and a calculation procedure was developed. The accuracy of the model was verified by comparing the calculated results with the experimental results, indicating that the constructed anchor chain dynamics model has a high accuracy.
Theoretical and Applied Mechanics Letters 13 (2023) 100461.
doi: 10.1016/j.taml.2023.100461
Abstract:
In this paper, we propose an finite element approach based on classical plate theory to investigate the dynamic stability of a layered composite plate subject to nonlinear aerodynamic load. This study considers the influence of temperature, nonlinear geometry, and nonlinear aerodynamic load on composite plate structures simultaneously. Specifically, the present work conduct comparison the results of the critical pressure value between the nonlinear aerodynamic load and the linear aerodynamic load, thereby pointing out some necessary cases which must consider the nonlinearity of aerodynamic load for calculating the aerospace structures. We determine the critical pressure value and vibrational amplitude response of the plate by means of calculation. The outcomes of our calculations can be useful in designing and repairing body shells and wings of aircraft equipment.
In this paper, we propose an finite element approach based on classical plate theory to investigate the dynamic stability of a layered composite plate subject to nonlinear aerodynamic load. This study considers the influence of temperature, nonlinear geometry, and nonlinear aerodynamic load on composite plate structures simultaneously. Specifically, the present work conduct comparison the results of the critical pressure value between the nonlinear aerodynamic load and the linear aerodynamic load, thereby pointing out some necessary cases which must consider the nonlinearity of aerodynamic load for calculating the aerospace structures. We determine the critical pressure value and vibrational amplitude response of the plate by means of calculation. The outcomes of our calculations can be useful in designing and repairing body shells and wings of aircraft equipment.
Theoretical and Applied Mechanics Letters 13 (2023) 100466.
doi: 10.1016/j.taml.2023.100466
Abstract:
In a T-shaped mixer, the two liquid streams in the inlet channels meet each other at the T-junction, and their liquid-liquid contacting face exhibits planar, swirling folds and the folds breaking to be chaos and turbulence, as the Reynolds number increases. The characteristic mixing scenario attracts long-time attention, given these mixings are of fundamental importance in fluid physics and also have been successfully used in engineering applications. The experimental and numerical studies of flow features and mixing characteristics in T-mixers are overviewed in this manuscript. This review introduces the experimental and numerical techniques in the studies, the flow and mixing characteristics in the corresponding regimes and application examples of the T-mixers at last, aiming at introducing fundamentals to researchers with initial interests on this topic.
In a T-shaped mixer, the two liquid streams in the inlet channels meet each other at the T-junction, and their liquid-liquid contacting face exhibits planar, swirling folds and the folds breaking to be chaos and turbulence, as the Reynolds number increases. The characteristic mixing scenario attracts long-time attention, given these mixings are of fundamental importance in fluid physics and also have been successfully used in engineering applications. The experimental and numerical studies of flow features and mixing characteristics in T-mixers are overviewed in this manuscript. This review introduces the experimental and numerical techniques in the studies, the flow and mixing characteristics in the corresponding regimes and application examples of the T-mixers at last, aiming at introducing fundamentals to researchers with initial interests on this topic.
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