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Institute of Mechanics,
Chinese Academy of Sciences
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, Available online
, doi: 10.1016/j.taml.2018.05.002
Abstract:
Dropshafts are vertical structures widely used in urban drainage systems and buildings for water transportation. In this paper, a physical model study was conducted to investigate the air entrainment in the dropshaft under various flow regimes with and without air ventilation. Observed from the experiments, the air entrainment mechanisms varied with the water flow regimes in the dropshaft. When there was no water plug formed in the dropshaft, air could be supplied directly from downstream. Once the water plug was formed, while without venting, the air was replenished only from downstream intermittently and then in the form of large air bubble traveling upwards to the airspace at the top; while with venting, air was mainly replenished from the dropshaft top and no large air bubble was observed. The experimental results also showed that the amount of entrained air in the dropshaft with venting was greater than that without venting.
Dropshafts are vertical structures widely used in urban drainage systems and buildings for water transportation. In this paper, a physical model study was conducted to investigate the air entrainment in the dropshaft under various flow regimes with and without air ventilation. Observed from the experiments, the air entrainment mechanisms varied with the water flow regimes in the dropshaft. When there was no water plug formed in the dropshaft, air could be supplied directly from downstream. Once the water plug was formed, while without venting, the air was replenished only from downstream intermittently and then in the form of large air bubble traveling upwards to the airspace at the top; while with venting, air was mainly replenished from the dropshaft top and no large air bubble was observed. The experimental results also showed that the amount of entrained air in the dropshaft with venting was greater than that without venting.
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, doi: 10.1016/j.taml.2018.04.006
Abstract:
The bubbles rise up and burst at the free surface is a complex two-phase process. A free energy lattice Boltzmann method (LBM) model is adopted in this paper to study this phenomenon. The interface capturing technique of Zheng et al. [H.W. Zheng et al. J. Comput. Phys. 2006] is used to deal with the high density ratio problem. The Laplace law and the air-water interface capturing ability are validated for the multiphase model. The interaction between the single bubble or multiple bubbles and the free surface are studied by the multiphase model. The force acting on the bubble and the evolution of the free surface is studied. Meanwhile, effect of the initial distance between two adjacent bubbles on interaction effects of multiple bubbles is investigated as well.
The bubbles rise up and burst at the free surface is a complex two-phase process. A free energy lattice Boltzmann method (LBM) model is adopted in this paper to study this phenomenon. The interface capturing technique of Zheng et al. [H.W. Zheng et al. J. Comput. Phys. 2006] is used to deal with the high density ratio problem. The Laplace law and the air-water interface capturing ability are validated for the multiphase model. The interaction between the single bubble or multiple bubbles and the free surface are studied by the multiphase model. The force acting on the bubble and the evolution of the free surface is studied. Meanwhile, effect of the initial distance between two adjacent bubbles on interaction effects of multiple bubbles is investigated as well.
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, Available online
, doi: 10.1016/j.taml.2018.04.001
Abstract:
Numerous experimental evidences show that the grain size may significantly alter the yield strength of metals. Similarly, in \begin{document}$\gamma ' $\end{document} ![]()
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-strengthened nickel-based superalloys, the precipitate size also influences their yield strength. Then, how to describe such two kinds of size effects on the yield strength is a very practical challenge. In this study, according to experimental observations, a collinear micro-shear-bands model is proposed to explore these size effects on metal materials’ yield strength. An analytical solution for the simple model is derived. It reveals that the yield strength is a function of average grain-size or precipitate-size, which is able to reasonably explain size effects on yield strength. The typical example validation shows that the new relationship is not only able to precisely describe the grain-size effect in some cases, but also able to theoretically address the unexplained Hall-Petch relationship between the \begin{document}$\gamma ' $\end{document} ![]()
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precipitate size and the yield strength of nickel-based superalloys.
Numerous experimental evidences show that the grain size may significantly alter the yield strength of metals. Similarly, in
Uncorrected proof
, Available online
, doi: 10.1016/j.taml.2018.04.003
Abstract:
To reproduce the premature rupture process of metal sheet subjected to laser irradiation with subsonic airflow, which is an interesting phenomenon observed in the experiments given by Lawrence Livermore National Laboratory, a coupled numerical model considering the interaction and evolution of metal elastoplastic deformation and aerodynamic pressure profile is presented. With the thermal elastoplastic constitutive relationship and failure criterion, the simulated failure modes and dynamic rupture process are basically consistent with the experimental results, indicating plastic flow and multiple fracturing is the main failure mechanism. Compared with the case of non-airflow, subsonic airflow not only accelerates deformation, but also turns the bugle deformation, plastic strain and rupture mode into asymmetric.
To reproduce the premature rupture process of metal sheet subjected to laser irradiation with subsonic airflow, which is an interesting phenomenon observed in the experiments given by Lawrence Livermore National Laboratory, a coupled numerical model considering the interaction and evolution of metal elastoplastic deformation and aerodynamic pressure profile is presented. With the thermal elastoplastic constitutive relationship and failure criterion, the simulated failure modes and dynamic rupture process are basically consistent with the experimental results, indicating plastic flow and multiple fracturing is the main failure mechanism. Compared with the case of non-airflow, subsonic airflow not only accelerates deformation, but also turns the bugle deformation, plastic strain and rupture mode into asymmetric.
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, Available online
, doi: 10.1016/j.taml.2018.04.010
Abstract:
In a vast number of engineering fields like medicine, aerospace or robotics, materials are required to meet unusual performances that simple homogeneous materials are often not able to fulfil. Consequently, many efforts are currently devoted to develop future generations of materials with enhanced properties and unusual functionalities. In many instances, biological systems served as a source of inspiration, as in the case of cellular materials. Commonly observed in nature, cellular materials offer useful combinations of structural properties and low weight, yielding the possibility of coexistence of what used to be antagonistic physical properties within a single material. Due to their peculiar characteristics, they are very promising for engineering applications in a variety of industries including aerospace, automotive, marine and constructions. However, their use is conditional upon the development of appropriate constitutive models for revealing the complex relations between the microstructure's parameters and the macroscopic behavior. From this point of view, a great variety of analytical and numerical techniques have been proposed and exhaustively discussed in recent years. Noteworthy contributions, suggesting different assumptions and techniques are critically presented in this review paper.
In a vast number of engineering fields like medicine, aerospace or robotics, materials are required to meet unusual performances that simple homogeneous materials are often not able to fulfil. Consequently, many efforts are currently devoted to develop future generations of materials with enhanced properties and unusual functionalities. In many instances, biological systems served as a source of inspiration, as in the case of cellular materials. Commonly observed in nature, cellular materials offer useful combinations of structural properties and low weight, yielding the possibility of coexistence of what used to be antagonistic physical properties within a single material. Due to their peculiar characteristics, they are very promising for engineering applications in a variety of industries including aerospace, automotive, marine and constructions. However, their use is conditional upon the development of appropriate constitutive models for revealing the complex relations between the microstructure's parameters and the macroscopic behavior. From this point of view, a great variety of analytical and numerical techniques have been proposed and exhaustively discussed in recent years. Noteworthy contributions, suggesting different assumptions and techniques are critically presented in this review paper.
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, Available online
, doi: 10.1016/j.taml.2018.04.008
Abstract:
Stochastic dynamic analysis of the nonlinear system is an open research question which has drawn many scholars' attention for its importance and challenge. Fokker–Planck–Kolmogorov (FPK) equation is of great significance because of its theoretical strictness and computational accuracy. However, practical difficulties with the FPK method appear when the analysis of multi-degree-of-freedom (MDOF) with more general nonlinearity is required. In the present paper, by invoking the idea of equivalence of probability flux, the general high-dimensional FPK equation related to MDOF system is reduced to one-dimensional FPK equation. Then a cell renormalized method (CRM) which is based on the numerical reconstruction of the derived moments of FPK equation is introduced by coarsening the continuous state space into a discretized region of cells. Then the cell renormalized FPK (CR-FPK) equation is solved by difference method. Three numerical examples are illustrated and the effectiveness of proposed method is assessed and verified.
Stochastic dynamic analysis of the nonlinear system is an open research question which has drawn many scholars' attention for its importance and challenge. Fokker–Planck–Kolmogorov (FPK) equation is of great significance because of its theoretical strictness and computational accuracy. However, practical difficulties with the FPK method appear when the analysis of multi-degree-of-freedom (MDOF) with more general nonlinearity is required. In the present paper, by invoking the idea of equivalence of probability flux, the general high-dimensional FPK equation related to MDOF system is reduced to one-dimensional FPK equation. Then a cell renormalized method (CRM) which is based on the numerical reconstruction of the derived moments of FPK equation is introduced by coarsening the continuous state space into a discretized region of cells. Then the cell renormalized FPK (CR-FPK) equation is solved by difference method. Three numerical examples are illustrated and the effectiveness of proposed method is assessed and verified.
Uncorrected proof
, Available online
, doi: 10.1016/j.taml.2018.04.007
Abstract:
This work focuses on the study of the effect of hydrophobicity on the water flow in carbon nanotubes (CNTs) using a molecular dynamics (MD) approach for a wide range of potential applications such as water purification and high efficiency of nanofluid energy absorption systems (NEAS). The hydrophobicity between liquid water and surface of CNTs was characterized by interaction-energy-coefficient (IEC)—a parameter describing the energy interaction strength between water molecules and carbon atoms. It is shown that the static contact angles between water and carbon surface decrease from 155° to 44° when the values of IEC increase from 0.042 kJ/mol to 2.196 kJ/mol. In addition, the pressure drops in CNT became independent of IEC when the IEC value was higher than 1.192 kJ/mol for a given flow rate. It was found that the hydrophobicity of CNT surface has a significant impact on the pressure drop of water flow in the CNTs and MD method provides a quantitative evaluation of the impact.
This work focuses on the study of the effect of hydrophobicity on the water flow in carbon nanotubes (CNTs) using a molecular dynamics (MD) approach for a wide range of potential applications such as water purification and high efficiency of nanofluid energy absorption systems (NEAS). The hydrophobicity between liquid water and surface of CNTs was characterized by interaction-energy-coefficient (IEC)—a parameter describing the energy interaction strength between water molecules and carbon atoms. It is shown that the static contact angles between water and carbon surface decrease from 155° to 44° when the values of IEC increase from 0.042 kJ/mol to 2.196 kJ/mol. In addition, the pressure drops in CNT became independent of IEC when the IEC value was higher than 1.192 kJ/mol for a given flow rate. It was found that the hydrophobicity of CNT surface has a significant impact on the pressure drop of water flow in the CNTs and MD method provides a quantitative evaluation of the impact.
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Abstract:
This paper aims to investigate the hydrodynamic behavior of a tension leg platform (TLP) when the tendon connection angles are varied at 90°, 70°, 50°, and 30°. Three different types of loading conditions are applied to the TLP. Conditions include 100-year hurricane storm period, regular waves and no loading. The TLP displayed major response in the pitch degree of freedom. A maximum reduction of 14% in pitch rotation is achieved when 100-year hurricane storm conditions are applied to the TLP. This occurred in 0° loadings at 30° tendon connection angle as compared to 90° tendon connection angle. Reduction in pitch rotation is also achieved in the regular wave loadings. A maximum of 9% in pitch rotation is achieved during 0° wave loading at 30° tendon connection angle as compared to 90°. When the tendon connection angle is reduced from 90° to 30°, the natural frequency of the TLP increased both in pitch and yaw degrees of freedom by 2.55% and 2.4% respectively.
This paper aims to investigate the hydrodynamic behavior of a tension leg platform (TLP) when the tendon connection angles are varied at 90°, 70°, 50°, and 30°. Three different types of loading conditions are applied to the TLP. Conditions include 100-year hurricane storm period, regular waves and no loading. The TLP displayed major response in the pitch degree of freedom. A maximum reduction of 14% in pitch rotation is achieved when 100-year hurricane storm conditions are applied to the TLP. This occurred in 0° loadings at 30° tendon connection angle as compared to 90° tendon connection angle. Reduction in pitch rotation is also achieved in the regular wave loadings. A maximum of 9% in pitch rotation is achieved during 0° wave loading at 30° tendon connection angle as compared to 90°. When the tendon connection angle is reduced from 90° to 30°, the natural frequency of the TLP increased both in pitch and yaw degrees of freedom by 2.55% and 2.4% respectively.
Uncorrected proof
, Available online
, doi: 10.1016/j.taml.2018.04.004
Abstract:
The principle and 1:3 internal resonance of a rectangular thin plate in a transverse magnetic field is investigated. Based on the magneto-elastic vibration equation and electromagnetic force expressions of the thin plates, the nonlinear magneto-elastic vibration differential equations of rectangular plates under external excitation in a transverse magnetic field are derived. For a rectangular plate with one side fixed and three other sides simply supported, the two-degree-of-freedom nonlinear Duffing vibration differen-tial equations are proposed by the method of Galerkin. The method of multiple scales is adopted to solve the model equations and obtain four first-order ordinary differential equations governing modulation of the amplitudes and phase angles involved via the first-order or the second-order primary-internal reso-nances. With a numerical example, the amplitude frequency response curves, time history responses, phase portraits and Poincare maps of the first two order vibration modes via principle-internal resonance are respectively captured. And the effects of external excitation amplitudes, magnetic field intensities and thicknesses on the vibration of system are discussed. The results show that the response is dominated by the low mode when principle-internal resonance occurs. The internal resonance provides a mechanism for transferring energy from a high mode to a low mode.
The principle and 1:3 internal resonance of a rectangular thin plate in a transverse magnetic field is investigated. Based on the magneto-elastic vibration equation and electromagnetic force expressions of the thin plates, the nonlinear magneto-elastic vibration differential equations of rectangular plates under external excitation in a transverse magnetic field are derived. For a rectangular plate with one side fixed and three other sides simply supported, the two-degree-of-freedom nonlinear Duffing vibration differen-tial equations are proposed by the method of Galerkin. The method of multiple scales is adopted to solve the model equations and obtain four first-order ordinary differential equations governing modulation of the amplitudes and phase angles involved via the first-order or the second-order primary-internal reso-nances. With a numerical example, the amplitude frequency response curves, time history responses, phase portraits and Poincare maps of the first two order vibration modes via principle-internal resonance are respectively captured. And the effects of external excitation amplitudes, magnetic field intensities and thicknesses on the vibration of system are discussed. The results show that the response is dominated by the low mode when principle-internal resonance occurs. The internal resonance provides a mechanism for transferring energy from a high mode to a low mode.
Uncorrected proof
, Available online
, doi: 10.1016/j.taml.2018.04.002
Abstract:
Numerical simulations using volume of fluid (VOF) method are performed to study the impact of liquid-to-gas density ratio on the trajectory of nonturbulent liquid jets in gaseous crossflows. In this paper, large eddy simulation (LES) turbulence model is coupled with the VOF method to describe the turbulence effects accurately. In addition, dynamic adaptive mesh refinement method with two refinement levels is applied to refine the size of the cells located at gas-liquid interface. Density ratio is changed from 10 to 5000 while other nondimensional numbers are kept constant. Large density ratios are considered in this paper since they are common in many practical applications such as solution precursor/suspension plasma sprays. Our simulations show that the penetration height, especially in the farfield, increases as the density ratio increases. A general correlation for the jet trajectory, which can be used for a wide range of density ratios, is developed based on our simulation results.
Numerical simulations using volume of fluid (VOF) method are performed to study the impact of liquid-to-gas density ratio on the trajectory of nonturbulent liquid jets in gaseous crossflows. In this paper, large eddy simulation (LES) turbulence model is coupled with the VOF method to describe the turbulence effects accurately. In addition, dynamic adaptive mesh refinement method with two refinement levels is applied to refine the size of the cells located at gas-liquid interface. Density ratio is changed from 10 to 5000 while other nondimensional numbers are kept constant. Large density ratios are considered in this paper since they are common in many practical applications such as solution precursor/suspension plasma sprays. Our simulations show that the penetration height, especially in the farfield, increases as the density ratio increases. A general correlation for the jet trajectory, which can be used for a wide range of density ratios, is developed based on our simulation results.
Uncorrected proof
, Available online
, doi: 10.1016/j.taml.2018.04.005
Abstract:
The potential for harvesting energy from a flexible delta wing using a piezoelectric bimorph is experimentally investigated. Different configurations of the proposed harvesting system were tested in a wind tunnel over a broad range of airspeeds. In addition to evaluating the level of harvested power, an analysis is performed to extract critical aspects for the relation between speed, flexibility, geometry and the potential power that can be harvested from a clamped, cantilevered flexible delta wing at low angles of attack and low speeds. This analysis provides an insight into parameters that impact energy harvesting from flexible membranes or elements.
The potential for harvesting energy from a flexible delta wing using a piezoelectric bimorph is experimentally investigated. Different configurations of the proposed harvesting system were tested in a wind tunnel over a broad range of airspeeds. In addition to evaluating the level of harvested power, an analysis is performed to extract critical aspects for the relation between speed, flexibility, geometry and the potential power that can be harvested from a clamped, cantilevered flexible delta wing at low angles of attack and low speeds. This analysis provides an insight into parameters that impact energy harvesting from flexible membranes or elements.
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2018, 8(3): 143-146.
doi: 10.1016/j.taml.2018.03.006
Abstract:
We review the previous attempts of rational subgrid-scale (SGS) modelling by employing the Kolmogorov equation of filtered quantities. Aiming at explaining and solving the underlying problems in these models, we also introduce the recent methodological investigations for the rational SGS modelling technique by defining the terms of assumption and restriction. These methodological works are expected to provide instructive criterions for not only the rational SGS modelling, but also other types of SGS modelling practices.
We review the previous attempts of rational subgrid-scale (SGS) modelling by employing the Kolmogorov equation of filtered quantities. Aiming at explaining and solving the underlying problems in these models, we also introduce the recent methodological investigations for the rational SGS modelling technique by defining the terms of assumption and restriction. These methodological works are expected to provide instructive criterions for not only the rational SGS modelling, but also other types of SGS modelling practices.
2018, 8(3): 153-159.
doi: 10.1016/j.taml.2018.03.002
Abstract:
Storm surge along the China's Zhe-Min coast is addressed using the tightly coupled surge model of ADCIRC+SWAN. In this study, we primarily focus on the effects of surge-tide interaction and wave set-up/set-down. And the influences of intensity and landing moment of tropical cyclone (TC) are also presented. The results show that: water elevation without considering tide-surge interaction tends to be underestimated/overestimated when TC lands during astronomical low/high tide; tide-surge coupling effect is more pronounced north of TC track (more than 0.7 m in our cases); irrelevant to TC's intensity, wave set-up south of TC track is negligible because the depth-related wave breaking doesn't occur in water body blown towards open seas.
Storm surge along the China's Zhe-Min coast is addressed using the tightly coupled surge model of ADCIRC+SWAN. In this study, we primarily focus on the effects of surge-tide interaction and wave set-up/set-down. And the influences of intensity and landing moment of tropical cyclone (TC) are also presented. The results show that: water elevation without considering tide-surge interaction tends to be underestimated/overestimated when TC lands during astronomical low/high tide; tide-surge coupling effect is more pronounced north of TC track (more than 0.7 m in our cases); irrelevant to TC's intensity, wave set-up south of TC track is negligible because the depth-related wave breaking doesn't occur in water body blown towards open seas.
2018, 8(3): 164-170.
doi: 10.1016/j.taml.2018.03.004
Abstract:
A thermal magnification device is proposed by using effective thermal conductivity. Different from transformation optics method, the magnification design is realized analytically by enforcing equality of effective thermal conductivity on the magnification device and the reference case in specified domains. The validity of theoretical analysis is checked by numerical simulation results, which demonstrates the magnifying effects of the proposed design. The device only needs isotropic and homogeneous materials that are easy to obtain in nature. It is also shown that the obtained magnifying conditions are the same as those derived by separation of variables. But the proposed method proves more flexible for multilayered materials and simpler for non-spherical objects under non-uniform thermal fields. It can also be extended to other fields and applications governed by Laplace equation.
A thermal magnification device is proposed by using effective thermal conductivity. Different from transformation optics method, the magnification design is realized analytically by enforcing equality of effective thermal conductivity on the magnification device and the reference case in specified domains. The validity of theoretical analysis is checked by numerical simulation results, which demonstrates the magnifying effects of the proposed design. The device only needs isotropic and homogeneous materials that are easy to obtain in nature. It is also shown that the obtained magnifying conditions are the same as those derived by separation of variables. But the proposed method proves more flexible for multilayered materials and simpler for non-spherical objects under non-uniform thermal fields. It can also be extended to other fields and applications governed by Laplace equation.
2018, 8(3): 171-183.
doi: 10.1016/j.taml.2018.03.005
Abstract:
In this study, laminar convective heat transfer over two heated wall-mounted cubes is investigated. Two cubes, which are under constant heat flux, are placed in different tandem and staggered arrangements on a base plate. This problem is studied for different streamwise and spanwise distances between two cubes in different Renolds number (Re), by using finite-volume method. Effects of these parameters are considered on flow and heat transfer characteristics. The results show that the temperature distribution is strongly dependent on flow structure and varies with any change of flow pattern in different arrangements of cubes. In addition, it is observed that the drag coefficient, which is influenced more by pressure forces, in staggered arrangement, is greater than tandem arrangement. Results show that by increasing the spanwise distance the amount of mean Nusselt number (Nu) of Cube 2 becomes the same as Cube 1.
In this study, laminar convective heat transfer over two heated wall-mounted cubes is investigated. Two cubes, which are under constant heat flux, are placed in different tandem and staggered arrangements on a base plate. This problem is studied for different streamwise and spanwise distances between two cubes in different Renolds number (Re), by using finite-volume method. Effects of these parameters are considered on flow and heat transfer characteristics. The results show that the temperature distribution is strongly dependent on flow structure and varies with any change of flow pattern in different arrangements of cubes. In addition, it is observed that the drag coefficient, which is influenced more by pressure forces, in staggered arrangement, is greater than tandem arrangement. Results show that by increasing the spanwise distance the amount of mean Nusselt number (Nu) of Cube 2 becomes the same as Cube 1.
2018, 8(3): 184-192.
doi: 10.1016/j.taml.2018.03.007
Abstract:
A theoretical analysis is presented to predict the nonlinear thermo-structural response of metallic sandwich panels with truss cores under through-thickness gradient temperature field, which is a common service condition for metallic thermal protection system (TPS). The in-plane temperature distribution is assumed to be uniform, and through-thickness temperature field is determined by heat conduction. Two typical conditions are analyzed: nonlinear thermal bending in fixed inside surface temperature, and thermal post-buckling in fixed temperature difference between two surfaces. Temperature-dependent mechanical properties are considered, and gradient shear stiffness and bending stiffness due to non-uniform temperature is included. Results indicate that the temperature-dependent material properties obviously affect bending resistance; however, the effect is negligible on post-buckling behavior. Influences of geometric parameters on the thermo-structural behavior of the sandwich panel according to the present theoretical model are discussed.
A theoretical analysis is presented to predict the nonlinear thermo-structural response of metallic sandwich panels with truss cores under through-thickness gradient temperature field, which is a common service condition for metallic thermal protection system (TPS). The in-plane temperature distribution is assumed to be uniform, and through-thickness temperature field is determined by heat conduction. Two typical conditions are analyzed: nonlinear thermal bending in fixed inside surface temperature, and thermal post-buckling in fixed temperature difference between two surfaces. Temperature-dependent mechanical properties are considered, and gradient shear stiffness and bending stiffness due to non-uniform temperature is included. Results indicate that the temperature-dependent material properties obviously affect bending resistance; however, the effect is negligible on post-buckling behavior. Influences of geometric parameters on the thermo-structural behavior of the sandwich panel according to the present theoretical model are discussed.
2018, 8(3): 193-196.
doi: 10.1016/j.taml.2018.03.008
Abstract:
Fluid-structure-interaction (FSI) phenomenon is common in science and engineering. The fluid involved in an FSI problem may be non-Newtonian such as blood. A popular framework for FSI problems is Peskin’s immersed boundary (IB) method. However, most of the IB formulations are based on Newtonian fluids. In this letter, we report an extension of the IB framework to FSI involving Oldroyd-B and FENE-P fluids in three dimensions using the lattice Boltzmann approach. The new method is tested on two FSI model problems. Numerical experiments show that the method is conditionally stable and convergent with the first order of accuracy.
Fluid-structure-interaction (FSI) phenomenon is common in science and engineering. The fluid involved in an FSI problem may be non-Newtonian such as blood. A popular framework for FSI problems is Peskin’s immersed boundary (IB) method. However, most of the IB formulations are based on Newtonian fluids. In this letter, we report an extension of the IB framework to FSI involving Oldroyd-B and FENE-P fluids in three dimensions using the lattice Boltzmann approach. The new method is tested on two FSI model problems. Numerical experiments show that the method is conditionally stable and convergent with the first order of accuracy.
2018, 8(3): 197-200.
doi: 10.1016/j.taml.2018.03.009
Abstract:
Internal solitary waves have been found to disintegrate into a series of solitons over variable bathymetry, with important applications for offshore engineering. Considering realistic background stratification in the South China Sea, internal solitary waves propagating over a step are studied here. By assuming disintegrated solitons propagate independently, a theoretical model, namely a triangular temporal-distribution law based on the Korteweg–de Vries theory, is proposed to describe the fission process of internal solitary waves undergoing disintegration. A parameter is then introduced to quantify the accuracy of the theoretical model. The results indicate that the triangular law predicts the fission process better for a longer travelling distance and a larger amplitude of internal solitary waves.
Internal solitary waves have been found to disintegrate into a series of solitons over variable bathymetry, with important applications for offshore engineering. Considering realistic background stratification in the South China Sea, internal solitary waves propagating over a step are studied here. By assuming disintegrated solitons propagate independently, a theoretical model, namely a triangular temporal-distribution law based on the Korteweg–de Vries theory, is proposed to describe the fission process of internal solitary waves undergoing disintegration. A parameter is then introduced to quantify the accuracy of the theoretical model. The results indicate that the triangular law predicts the fission process better for a longer travelling distance and a larger amplitude of internal solitary waves.
2018, 8(3): 201-207.
doi: 10.1016/j.taml.2018.03.010
Abstract:
Distributed leading-edge (LE) roughness could have significant impact on the aerodynamic performance of a low-Reynolds-number (low-Re) airfoil, which has not yet been fully understood. In the present study, experiments were conducted to study the effects of distributed hemispherical roughness with different sizes and distribution patterns on the performance of a GA (W)-1 airfoil. Surface pressure and particle image velocimetry (PIV) measurements were performed under various incident angles and different Re numbers. Significant reduction in lift and increase in drag were found for all cases with the LE roughness applied. Compared with the distribution pattern, the roughness height was found to be a more significant factor in determining the lift reduction and altering stall behaviors. It is also found while the larger roughness advances the aerodynamic stall, the smaller roughness tends to prevent deep stall at high incident angles. PIV results also suggest that staggered distribution pattern induces higher fluctuations in the wake flow than the aligned pattern does. Results imply that distributed LE roughness with large element sizes are particularly detrimental to aerodynamic performances, while those with small element sizes could potentially serve as a passive control mechanism to alleviate deep stall conditions at high incident angles.
Distributed leading-edge (LE) roughness could have significant impact on the aerodynamic performance of a low-Reynolds-number (low-Re) airfoil, which has not yet been fully understood. In the present study, experiments were conducted to study the effects of distributed hemispherical roughness with different sizes and distribution patterns on the performance of a GA (W)-1 airfoil. Surface pressure and particle image velocimetry (PIV) measurements were performed under various incident angles and different Re numbers. Significant reduction in lift and increase in drag were found for all cases with the LE roughness applied. Compared with the distribution pattern, the roughness height was found to be a more significant factor in determining the lift reduction and altering stall behaviors. It is also found while the larger roughness advances the aerodynamic stall, the smaller roughness tends to prevent deep stall at high incident angles. PIV results also suggest that staggered distribution pattern induces higher fluctuations in the wake flow than the aligned pattern does. Results imply that distributed LE roughness with large element sizes are particularly detrimental to aerodynamic performances, while those with small element sizes could potentially serve as a passive control mechanism to alleviate deep stall conditions at high incident angles.
2018, 8(3): 147-152.
doi: 10.1016/j.taml.2018.03.001
Abstract:
Jellyfish are easily carried by ocean currents, yet most studies on jellyfish focus on the kinematics in a quiescent fluid. In this experimental and theoretical study, we focus on rowing jellyfish, those that partially contract their bells and paddle in a relaxed manner. We film six species of rowing jellyfish in a range of background flow speeds at the Georgia Aquarium. Each species has a unique contraction frequency, which is independent of both the body orientation and the background flow speed. Our mathematical model reveals that jellyfish contract to offset their sinking. This behavior is invariant: Despite the background flow conditions, jellyfish contract as if they are oriented upright in a quiescent fluid. Our study suggests that jellyfish operate in open-loop without feedback from their environment.
Jellyfish are easily carried by ocean currents, yet most studies on jellyfish focus on the kinematics in a quiescent fluid. In this experimental and theoretical study, we focus on rowing jellyfish, those that partially contract their bells and paddle in a relaxed manner. We film six species of rowing jellyfish in a range of background flow speeds at the Georgia Aquarium. Each species has a unique contraction frequency, which is independent of both the body orientation and the background flow speed. Our mathematical model reveals that jellyfish contract to offset their sinking. This behavior is invariant: Despite the background flow conditions, jellyfish contract as if they are oriented upright in a quiescent fluid. Our study suggests that jellyfish operate in open-loop without feedback from their environment.
2018, 8(3): 160-163.
doi: 10.1016/j.taml.2018.03.003
Abstract:
Based on nonlocal thermoelastic theory, this article studies the reflection of waves in nanometer semi-conductor media. Firstly, the governing equations are established based on coupled nonlocal elasticity theory, plasma diffusion equation, and moving equation. Then, using the harmonic method, the solution of the dissipation equation and the analytic expression of the reflection coefficient rate are obtained. Finally, the influences of nonlocal parameters on wave velocities are showed graphically. It is found that after the introduction of nonlocal effect, the phase and group velocities all show the attenuation, and as the frequency increases, the nonlocal parameter is bigger, and the decay rate is faster. The reflection coefficient rate varies greatly with different theories, with different reflection coefficient rates depending on the incident angle.
Based on nonlocal thermoelastic theory, this article studies the reflection of waves in nanometer semi-conductor media. Firstly, the governing equations are established based on coupled nonlocal elasticity theory, plasma diffusion equation, and moving equation. Then, using the harmonic method, the solution of the dissipation equation and the analytic expression of the reflection coefficient rate are obtained. Finally, the influences of nonlocal parameters on wave velocities are showed graphically. It is found that after the introduction of nonlocal effect, the phase and group velocities all show the attenuation, and as the frequency increases, the nonlocal parameter is bigger, and the decay rate is faster. The reflection coefficient rate varies greatly with different theories, with different reflection coefficient rates depending on the incident angle.
2018, 8(3): 143-146
doi: 10.1016/j.taml.2018.03.006
2018, 8(3): 147-152
doi: 10.1016/j.taml.2018.03.001
2018, 8(2): 137-141
doi: 10.1016/j.taml.2018.02.010
2018, 8(3): 197-200
doi: 10.1016/j.taml.2018.03.009
