2021 Vol.35(3)
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2021, 35(3): 317-331.
doi: 10.1007/s13344-021-0030-3
Abstract:
Wave forces acting on a vertical cylinder at different locations on a slope beach in the near-shore region are investigated considering solitary waves as incoming waves. Based on the Reynolds-averaged Navier−Stokes equations and the k−\begin{document}$ {\textit{ɛ}}$\end{document} ![]()
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Wave forces acting on a vertical cylinder at different locations on a slope beach in the near-shore region are investigated considering solitary waves as incoming waves. Based on the Reynolds-averaged Navier−Stokes equations and the k−
2021, 35(3): 332-343.
doi: 10.1007/s13344-021-0031-2
Abstract:
The fish cage design requires accurate predictions of long-term extreme loads and responses. Compared with the time-consuming full long-term analysis method integrating all the probability distribution of the short-term extremes, the environmental contour method gains much attention in predicting the long-term extreme values due to the less computational effort. This paper investigates the long-term extreme response of a fish cage using the environmental contour method. The fish cage is numerically simulated based on the lumped-mass method and the curved beam theory. Based on the one-dimensional (1D) and two-dimensional (2D) environmental contour, the extreme responses, including the surge and heave motions, mooring force, and vertical bending of the floater, are predicted for different return periods and compared with the full long-term analysis results. Results indicate that the 1D method greatly underestimates the extreme values. The 2D environmental contour method with a higher percentile level, namely 90%, provides reasonable estimations and seems to be suitable for the long-term value analysis. Sensitivity studies show that the mooring arrangement and the bending stiffness have great effects on the bending moment and the mooring force and the mooring line pre-tension has minor effects on the fish cage response.
The fish cage design requires accurate predictions of long-term extreme loads and responses. Compared with the time-consuming full long-term analysis method integrating all the probability distribution of the short-term extremes, the environmental contour method gains much attention in predicting the long-term extreme values due to the less computational effort. This paper investigates the long-term extreme response of a fish cage using the environmental contour method. The fish cage is numerically simulated based on the lumped-mass method and the curved beam theory. Based on the one-dimensional (1D) and two-dimensional (2D) environmental contour, the extreme responses, including the surge and heave motions, mooring force, and vertical bending of the floater, are predicted for different return periods and compared with the full long-term analysis results. Results indicate that the 1D method greatly underestimates the extreme values. The 2D environmental contour method with a higher percentile level, namely 90%, provides reasonable estimations and seems to be suitable for the long-term value analysis. Sensitivity studies show that the mooring arrangement and the bending stiffness have great effects on the bending moment and the mooring force and the mooring line pre-tension has minor effects on the fish cage response.
2021, 35(3): 344-351.
doi: 10.1007/s13344-021-0032-1
Abstract:
Three blade-geometry optimization models derived along with assumptions from the blade element momentum (BEM) approach are studied by using a steady BEM code to improve a small horizontal-axis rotor of three blades that has been previously used in experiments. The base rotor blade has linear-radially varying chord length and pitch angle, while the other three models noted as Burton, Implicit and Hansen due to their references and characteristics yield blades of non-linearly varying chord length and pitch angle. The aim is to compare these rapid models and study how assumptions embedded in them affect performance and induction factors. It is found that the model that has the least assumptions (Hansen) and which considers the blade-profile drag in its optimization procedure yields the highest power coefficient, CP, at the optimal tip speed ratio (TSR), about 7% higher than the base one and also higher CP at high TSR. It produces an axial induction factor distribution along the blade that is closest to the 1D optimal value of 1/3. All optimized tangential induction-factor distributions along the blade closely vary as inverse to the square of the radial distance, while being mildly higher than the base distribution. It shows that sufficient swirl is necessary to increase power but at a level causing not too much energy loss in unnecessary swirl of the wake. At high TSR, all optimized rotors adversely produce higher thrust than the base one, but the one with most embedded assumptions (Burton) produces the highest thrust. Details of all three optimization models are given along with the distributions of the power, thrust, blade hydrodynamic efficiency and induction factors.
Three blade-geometry optimization models derived along with assumptions from the blade element momentum (BEM) approach are studied by using a steady BEM code to improve a small horizontal-axis rotor of three blades that has been previously used in experiments. The base rotor blade has linear-radially varying chord length and pitch angle, while the other three models noted as Burton, Implicit and Hansen due to their references and characteristics yield blades of non-linearly varying chord length and pitch angle. The aim is to compare these rapid models and study how assumptions embedded in them affect performance and induction factors. It is found that the model that has the least assumptions (Hansen) and which considers the blade-profile drag in its optimization procedure yields the highest power coefficient, CP, at the optimal tip speed ratio (TSR), about 7% higher than the base one and also higher CP at high TSR. It produces an axial induction factor distribution along the blade that is closest to the 1D optimal value of 1/3. All optimized tangential induction-factor distributions along the blade closely vary as inverse to the square of the radial distance, while being mildly higher than the base distribution. It shows that sufficient swirl is necessary to increase power but at a level causing not too much energy loss in unnecessary swirl of the wake. At high TSR, all optimized rotors adversely produce higher thrust than the base one, but the one with most embedded assumptions (Burton) produces the highest thrust. Details of all three optimization models are given along with the distributions of the power, thrust, blade hydrodynamic efficiency and induction factors.
2021, 35(3): 352-360.
doi: 10.1007/s13344-021-0038-8
Abstract:
The low side friction of piles in coral sand results in the low bearing capacity of foundations. In this paper, expansive concrete pile is utilized to improve the bearing capacity of pile foundations in coral sand. Both model tests and numerical simulation are performed to reveal the bearing mechanism of expansive concrete pile in coral sand. Results showed that the lateral earth pressure near pile increases obviously and the side friction of piles is improved, after adding expansion agent to the concrete. The horizontal linear expansion is 1.11% and the bearing capacity increased 41% for the pile, when 25% expansion agent is added. Results in finite element numerical simulation also show that ultimate bearing capacity increases with the increase of the linear expansion ratio. Besides, the area for obvious increase in side friction is below the surface of soil about three times the pile diameter, and the expansion leads to a high side friction sharing of the pile. Therefore, the cast-in-place expansive concrete pile is effective in improving the bearing capacity of piles in coral sand.
The low side friction of piles in coral sand results in the low bearing capacity of foundations. In this paper, expansive concrete pile is utilized to improve the bearing capacity of pile foundations in coral sand. Both model tests and numerical simulation are performed to reveal the bearing mechanism of expansive concrete pile in coral sand. Results showed that the lateral earth pressure near pile increases obviously and the side friction of piles is improved, after adding expansion agent to the concrete. The horizontal linear expansion is 1.11% and the bearing capacity increased 41% for the pile, when 25% expansion agent is added. Results in finite element numerical simulation also show that ultimate bearing capacity increases with the increase of the linear expansion ratio. Besides, the area for obvious increase in side friction is below the surface of soil about three times the pile diameter, and the expansion leads to a high side friction sharing of the pile. Therefore, the cast-in-place expansive concrete pile is effective in improving the bearing capacity of piles in coral sand.
Very Large Eddy Simulation of Cavitation from Inception to Sheet/Cloud Regimes by A Multiscale Model
2021, 35(3): 361-371.
doi: 10.1007/s13344-021-0033-0
Abstract:
The cavitating flow in different regimes has the intricate flow structure with multiple time and space scales. The present work develops a multiscale model by coupling the volume of fluid (VOF) method and a discrete bubble model (DBM), to simulate the cavitating flow in a convergent-divergent test section. The Schnerr−Sauer cavitation model is used to calculate the mass transfer rate to obtain the macroscale phase structure, and the simplified Rayleigh−Plesset equation is applied to simulate the growing and collapsing of discrete bubbles. An algorithm for bridging between the macroscale cavities and microscale bubbles is also developed to achieve the multiscale simulation. For the flow field, the very large eddy simulation (VLES) approach is applied. Conditions from inception to sheet/cloud cavitation regimes are taken into account and simulations are conducted. Compared with the experimental observations, it is shown that the cavitation inception, bubble clouds formation and glass cavity generation are all well represented, indicating that the proposed VOF-DBM model is a promising approach to accurately and comprehensively reveal the multiscale phase field induced by cavitation.
The cavitating flow in different regimes has the intricate flow structure with multiple time and space scales. The present work develops a multiscale model by coupling the volume of fluid (VOF) method and a discrete bubble model (DBM), to simulate the cavitating flow in a convergent-divergent test section. The Schnerr−Sauer cavitation model is used to calculate the mass transfer rate to obtain the macroscale phase structure, and the simplified Rayleigh−Plesset equation is applied to simulate the growing and collapsing of discrete bubbles. An algorithm for bridging between the macroscale cavities and microscale bubbles is also developed to achieve the multiscale simulation. For the flow field, the very large eddy simulation (VLES) approach is applied. Conditions from inception to sheet/cloud cavitation regimes are taken into account and simulations are conducted. Compared with the experimental observations, it is shown that the cavitation inception, bubble clouds formation and glass cavity generation are all well represented, indicating that the proposed VOF-DBM model is a promising approach to accurately and comprehensively reveal the multiscale phase field induced by cavitation.
2021, 35(3): 372-383.
doi: 10.1007/s13344-021-0034-z
Abstract:
In recent decades, path planning for unmanned surface vehicles (USVs) in complex environments, such as harbours and coastlines, has become an important concern. The existing algorithms for real-time path planning for USVs are either too slow at replanning or unreliable in changing environments with multiple dynamic obstacles. In this study, we developed a novel path planning method based on the D* lite algorithm for real-time path planning of USVs in complex environments. The proposed method has the following advantages: (1) the computational time for replanning is reduced significantly owing to the use of an incremental algorithm and a new method for modelling dynamic obstacles; (2) a constrained artificial potential field method is employed to enhance the safety of the planned paths; and (3) the method is practical in terms of vehicle performance. The performance of the proposed method was evaluated through simulations and compared with those of existing algorithms. The simulation results confirmed the efficiency of the method for real-time path planning of USVs in complex environments.
In recent decades, path planning for unmanned surface vehicles (USVs) in complex environments, such as harbours and coastlines, has become an important concern. The existing algorithms for real-time path planning for USVs are either too slow at replanning or unreliable in changing environments with multiple dynamic obstacles. In this study, we developed a novel path planning method based on the D* lite algorithm for real-time path planning of USVs in complex environments. The proposed method has the following advantages: (1) the computational time for replanning is reduced significantly owing to the use of an incremental algorithm and a new method for modelling dynamic obstacles; (2) a constrained artificial potential field method is employed to enhance the safety of the planned paths; and (3) the method is practical in terms of vehicle performance. The performance of the proposed method was evaluated through simulations and compared with those of existing algorithms. The simulation results confirmed the efficiency of the method for real-time path planning of USVs in complex environments.
2021, 35(3): 384-397.
doi: 10.1007/s13344-021-0035-y
Abstract:
In the present study, the dynamics of the tendon system of a tension-leg platform (TLP) is investigated through the absolute nodal coordinate formulation (ANCF). Based on the energy conversion principle, the stiffness, generalized elastic force, external load and mass matrices of the element are deduced to perform the element assembling by using the finite element method. Then the motion equation of the tendon/riser is established. In this study, the TLP in the International Ship Structures Committee (ISSC) model under the first and second wave forces is considered as the case study. The simulation is performed in the MATLAB environment. Moreover, the accuracy and reliability of the programs are verified for cases of beam model with theoretical solutions. It is found that the motion response of tendons is affected by the TLP movement and environmental load, simultaneously. Then, the motion response is calculated using the SESAM software and exported as the boundary of ANCF tendons. Finally, the static and dynamic characteristics of the four tendons of ISSC TLP are analyzed systematically by the ANCF method. Performed analysis proves the effectiveness and feasibility of the ANCF method. It is concluded that the proposed method is a powerful scheme for calculating the dynamics of tendon/riser in the field of ocean engineering.
In the present study, the dynamics of the tendon system of a tension-leg platform (TLP) is investigated through the absolute nodal coordinate formulation (ANCF). Based on the energy conversion principle, the stiffness, generalized elastic force, external load and mass matrices of the element are deduced to perform the element assembling by using the finite element method. Then the motion equation of the tendon/riser is established. In this study, the TLP in the International Ship Structures Committee (ISSC) model under the first and second wave forces is considered as the case study. The simulation is performed in the MATLAB environment. Moreover, the accuracy and reliability of the programs are verified for cases of beam model with theoretical solutions. It is found that the motion response of tendons is affected by the TLP movement and environmental load, simultaneously. Then, the motion response is calculated using the SESAM software and exported as the boundary of ANCF tendons. Finally, the static and dynamic characteristics of the four tendons of ISSC TLP are analyzed systematically by the ANCF method. Performed analysis proves the effectiveness and feasibility of the ANCF method. It is concluded that the proposed method is a powerful scheme for calculating the dynamics of tendon/riser in the field of ocean engineering.
2021, 35(3): 398-409.
doi: 10.1007/s13344-021-0036-x
Abstract:
Influences of topographic variations of the offshore fringing reef on the harbor oscillations excited by incident N-waves with different amplitudes and waveform types are studied for the first time. Both the propagation of the N-waves over the reef and the subsequently-induced harbor oscillations are simulated by a Boussinesq-type numerical model, FUNWAVE-TVD. The present study concentrates on revealing the influences of the plane reef-face slope, the reef-face profile shape and the lagoon width on the maximum runup, the wave energy distribution and the total wave energy within the harbor. It shows that both the wave energy distribution uniformity and the total wave energy gradually increase with decreasing reef-face slope. The profile shape of the reef face suffering leading-elevation N-waves (LEN waves) has a negligible impact on the wave energy distribution uniformity, while for leading-depression N-waves (LDN waves), the latter gradually decreases with the mean water depth over the reef face. The total wave energy always first increases and then decreases with the mean water depth over the reef face. In general, the total wave energy first sharply decreases and then slightly increases with the lagoon width, regardless of the reef-face width and the incident waveform type. The maximum runup subjected to the LEN waves decreases monotonously with the lagoon width. However, for the LDN waves, its changing trend with the lagoon width relies on the incident wave amplitude.
Influences of topographic variations of the offshore fringing reef on the harbor oscillations excited by incident N-waves with different amplitudes and waveform types are studied for the first time. Both the propagation of the N-waves over the reef and the subsequently-induced harbor oscillations are simulated by a Boussinesq-type numerical model, FUNWAVE-TVD. The present study concentrates on revealing the influences of the plane reef-face slope, the reef-face profile shape and the lagoon width on the maximum runup, the wave energy distribution and the total wave energy within the harbor. It shows that both the wave energy distribution uniformity and the total wave energy gradually increase with decreasing reef-face slope. The profile shape of the reef face suffering leading-elevation N-waves (LEN waves) has a negligible impact on the wave energy distribution uniformity, while for leading-depression N-waves (LDN waves), the latter gradually decreases with the mean water depth over the reef face. The total wave energy always first increases and then decreases with the mean water depth over the reef face. In general, the total wave energy first sharply decreases and then slightly increases with the lagoon width, regardless of the reef-face width and the incident waveform type. The maximum runup subjected to the LEN waves decreases monotonously with the lagoon width. However, for the LDN waves, its changing trend with the lagoon width relies on the incident wave amplitude.
2021, 35(3): 410-421.
doi: 10.1007/s13344-021-0037-9
Abstract:
The nonlinear dynamic response induced by the wave-current interaction on a deepwater steep wave riser (SWR) is numerically investigated based on a three-dimensional (3D) time-domain finite element method (FEM). The governing equation considering internal flow is established in the global coordinate system. The whole SWR consists of three segments: the decline segment, buoyancy segment and hang-off segment, in which the buoyancy segment is wrapped by several buoyancy modules in the middle section, leading to the arch bend and sag bend. A Newmark-β iterative scheme is adopted for the accurate analysis to solve the governing equation and update the dynamic response at each time step. The proposed method is verified through the published results for the dynamic response of steel catenary riser (SCR) and static configuration of steel lazy wave riser (SLWR). Simulations are executed to study the influence of wave height, current velocity/direction, internal flow density/velocity and top-end pressure on the tension, configuration and bending moment of the SWR. The results indicate that the influence of the current on the configuration and mechanical behavior of the SWR is greater than that of the wave, especially in the middle section. With increasing current velocity, the suspending height of the middle section drops, meanwhile, its bending moment decreases accordingly, but the tension increases significantly. For a fixed external load, the increasing internal flow density induces the amplification of the tension at the hang-off segment and the mitigation at the decline segment, while the opposite trend occurs at the bending moment.
The nonlinear dynamic response induced by the wave-current interaction on a deepwater steep wave riser (SWR) is numerically investigated based on a three-dimensional (3D) time-domain finite element method (FEM). The governing equation considering internal flow is established in the global coordinate system. The whole SWR consists of three segments: the decline segment, buoyancy segment and hang-off segment, in which the buoyancy segment is wrapped by several buoyancy modules in the middle section, leading to the arch bend and sag bend. A Newmark-β iterative scheme is adopted for the accurate analysis to solve the governing equation and update the dynamic response at each time step. The proposed method is verified through the published results for the dynamic response of steel catenary riser (SCR) and static configuration of steel lazy wave riser (SLWR). Simulations are executed to study the influence of wave height, current velocity/direction, internal flow density/velocity and top-end pressure on the tension, configuration and bending moment of the SWR. The results indicate that the influence of the current on the configuration and mechanical behavior of the SWR is greater than that of the wave, especially in the middle section. With increasing current velocity, the suspending height of the middle section drops, meanwhile, its bending moment decreases accordingly, but the tension increases significantly. For a fixed external load, the increasing internal flow density induces the amplification of the tension at the hang-off segment and the mitigation at the decline segment, while the opposite trend occurs at the bending moment.
2021, 35(3): 422-431.
doi: 10.1007/s13344-021-0039-7
Abstract:
A piggyback pipeline consists of two pipes such that the secondary line rides on the main pipe with a fixed distance between two pipes in length. The novel strategy is utilized in offshore areas instead of a single flow line. In this regard, there are only a handful of experimental and numerical studies investigating the effect of scour below a piggyback pipeline under steady current. Hence, this study focuses on examining the influential factors on scouring due to steady current including the pipe diameter and the gap between pipes through numerical simulations and experimental tests. Accordingly, at the first phase of the research, a single pipe was established and tested in laboratory to compare the results with those of an empirical equation. After finishing experimental verifications, piggyback pipelines were also assembled to study the scouring under steady current conditions. It was concluded that by increasing the gap distance between the pipes, the maximum scour depth decreases; however, an increase in the small pipe’s diameter results in a larger maximum scour depth. Secondly, numerical simulations were carried out using the FLOW-3D software which was found to be a suitable tool for the numerical investigation of this study. Finally, the numerical results have been compared with the corresponding experimental data and a relatively good agreement was achieved between them.
A piggyback pipeline consists of two pipes such that the secondary line rides on the main pipe with a fixed distance between two pipes in length. The novel strategy is utilized in offshore areas instead of a single flow line. In this regard, there are only a handful of experimental and numerical studies investigating the effect of scour below a piggyback pipeline under steady current. Hence, this study focuses on examining the influential factors on scouring due to steady current including the pipe diameter and the gap between pipes through numerical simulations and experimental tests. Accordingly, at the first phase of the research, a single pipe was established and tested in laboratory to compare the results with those of an empirical equation. After finishing experimental verifications, piggyback pipelines were also assembled to study the scouring under steady current conditions. It was concluded that by increasing the gap distance between the pipes, the maximum scour depth decreases; however, an increase in the small pipe’s diameter results in a larger maximum scour depth. Secondly, numerical simulations were carried out using the FLOW-3D software which was found to be a suitable tool for the numerical investigation of this study. Finally, the numerical results have been compared with the corresponding experimental data and a relatively good agreement was achieved between them.
2021, 35(3): 432-442.
doi: 10.1007/s13344-021-0040-1
Abstract:
To study the distribution characteristics and similarity laws of nuclei under different pressures, based on the self-designed decompression chamber and the acoustic measuring system, the size distributions of nuclei in the degassed tap water under negative ambient pressures were measured. A number density distribution function of nuclei based on the modified Weibull distribution function was proposed and verified by the experimental measurement results and some published data of nuclei size distribution. Based on this nuclei number density distribution function, the similarity law of the nuclei size distribution was analyzed: in the scale experiment, the value of exponential in the similarity law of the nuclei number density should be determined by the nuclei size distribution of the water in the prototype experiment and the actual nuclei size distribution of the water in the model experiment. And a precondition is that the nuclei size distributions are similar.
To study the distribution characteristics and similarity laws of nuclei under different pressures, based on the self-designed decompression chamber and the acoustic measuring system, the size distributions of nuclei in the degassed tap water under negative ambient pressures were measured. A number density distribution function of nuclei based on the modified Weibull distribution function was proposed and verified by the experimental measurement results and some published data of nuclei size distribution. Based on this nuclei number density distribution function, the similarity law of the nuclei size distribution was analyzed: in the scale experiment, the value of exponential in the similarity law of the nuclei number density should be determined by the nuclei size distribution of the water in the prototype experiment and the actual nuclei size distribution of the water in the model experiment. And a precondition is that the nuclei size distributions are similar.
2021, 35(3): 443-453.
doi: 10.1007/s13344-021-0041-0
Abstract:
A structure scheme of a pile-based breakwater with integrated oscillating water column (OWC) energy conversion chamber was proposed, and four structure forms had been designed. Based on the physical test, the variations of the reflected wave height, the transmitted wave height, the air velocity at the outlet of the chamber, the air pressure and the wave height in the air chamber were studied under the conditions of different wave heights, periods, with or without elliptical front wall and the baffles on both sides of the chamber. Moreover, based on the results, the changes and relationship between the wave-eliminating effect and energy conversion effect of the scheme were analyzed. In general, it turns out, the transmission coefficients of the four structure forms are kept below 0.5. Furthermore, the transmission coefficients of the structural forms G2, G3, and G4 were all smaller than 0.4, and it is only 0.1 at its smallest. Thereinto, in general, the structure form G4 has the best wave-eliminating and energy conversion performance. At the same time, when the wave steepness is 0.066, the energy conversion and wave dissipation effect of the four structure forms is the best. The research results could be provided as the reference for the design structure selection of pile-based breakwater with integrated OWC energy conversion chamber.
A structure scheme of a pile-based breakwater with integrated oscillating water column (OWC) energy conversion chamber was proposed, and four structure forms had been designed. Based on the physical test, the variations of the reflected wave height, the transmitted wave height, the air velocity at the outlet of the chamber, the air pressure and the wave height in the air chamber were studied under the conditions of different wave heights, periods, with or without elliptical front wall and the baffles on both sides of the chamber. Moreover, based on the results, the changes and relationship between the wave-eliminating effect and energy conversion effect of the scheme were analyzed. In general, it turns out, the transmission coefficients of the four structure forms are kept below 0.5. Furthermore, the transmission coefficients of the structural forms G2, G3, and G4 were all smaller than 0.4, and it is only 0.1 at its smallest. Thereinto, in general, the structure form G4 has the best wave-eliminating and energy conversion performance. At the same time, when the wave steepness is 0.066, the energy conversion and wave dissipation effect of the four structure forms is the best. The research results could be provided as the reference for the design structure selection of pile-based breakwater with integrated OWC energy conversion chamber.
2021, 35(3): 454-464.
doi: 10.1007/s13344-021-0042-z
Abstract:
The double-body heave wave energy converter (WEC) is one of the most conducive devices to absorb the wave energy from relative motion while the law of which is not well understood. This paper makes an in-depth study on this wave energy converter, by means of the combination of theoretical analysis and physical model experiment. The hydrodynamic characteristics and energy capture of the double-buoy under constant and linear Power Take-Off (PTO) damping are investigated. Influences of absolute mass and mass ratio are discussed in the theoretical model. Relative displacement amplitude and average power output are tested in the experiment to analyze the effect of the wave period and outer buoy’s mass, while the capture width ratio (CWR) is also calculated. Results show that the wave period and mass of the buoys have a significant effect on the converter. Different forms of PTO damping have no influence on the optimal wave period and mass ratio of this device. It is recommended to select the double-buoy converter with a mass ratio of 0.80 and to place it in an area with the frequent wave period close to the natural period of the outer buoy to achieve the optimal energy capture.
The double-body heave wave energy converter (WEC) is one of the most conducive devices to absorb the wave energy from relative motion while the law of which is not well understood. This paper makes an in-depth study on this wave energy converter, by means of the combination of theoretical analysis and physical model experiment. The hydrodynamic characteristics and energy capture of the double-buoy under constant and linear Power Take-Off (PTO) damping are investigated. Influences of absolute mass and mass ratio are discussed in the theoretical model. Relative displacement amplitude and average power output are tested in the experiment to analyze the effect of the wave period and outer buoy’s mass, while the capture width ratio (CWR) is also calculated. Results show that the wave period and mass of the buoys have a significant effect on the converter. Different forms of PTO damping have no influence on the optimal wave period and mass ratio of this device. It is recommended to select the double-buoy converter with a mass ratio of 0.80 and to place it in an area with the frequent wave period close to the natural period of the outer buoy to achieve the optimal energy capture.
2021, 35(3): 465-474.
doi: 10.1007/s13344-021-0043-y
Abstract:
Owing to different influence factors of foundation soil, the initial stress state of the soil under various working conditions is complex. To simulate this situation, in this paper, a series of tests on undisturbed soft clay under pure principal stress axis rotation were carried out by using the hollow cylinder apparatus (HCA). The influence of initial consolidation angle ζ (the angle between the vertical direction and direction of the applied load in consolidation) and intermediate principal stress coefficient b on pore water pressure accumulation of undisturbed soft clay were mainly studied. The test results show that, during pure principal stress axis rotation, the pore water pressure accumulation of the undisturbed soft clay fluctuates and increases with the rotation of the major principal stress; the values of major principal stress angles α, corresponding to the peak value of the pore water pressure in a certain cycle, are different with different initial consolidation angles; the pore water pressure accumulation of soft clay is greatly affected by the intermediate principal stress coefficient b. With the fixed initial consolidation angle ζ, the variation trend of the maximum pore water pressure for each cycle is appropriately the same with different b values. With the increase of cycles, the difference value of pore water pressure between b = 0 and b = 1 in each cycle increases gradually with different initial consolidation angles ζ. While with different initial consolidation angles ζ, the increase of the pore water pressure when b increases from 0 to 0.5 is different with that when b increases from 0.5 to 1; the variation of maximum pore water pressure with ζ is significantly affected by the value of b; the value of maximum pore water pressure increases with the cycle number increases under all test conditions, but the growth rate decreases gradually. And the variation of maximum pore water pressure with the cycle number N is obviously influenced by both ζ and b.
Owing to different influence factors of foundation soil, the initial stress state of the soil under various working conditions is complex. To simulate this situation, in this paper, a series of tests on undisturbed soft clay under pure principal stress axis rotation were carried out by using the hollow cylinder apparatus (HCA). The influence of initial consolidation angle ζ (the angle between the vertical direction and direction of the applied load in consolidation) and intermediate principal stress coefficient b on pore water pressure accumulation of undisturbed soft clay were mainly studied. The test results show that, during pure principal stress axis rotation, the pore water pressure accumulation of the undisturbed soft clay fluctuates and increases with the rotation of the major principal stress; the values of major principal stress angles α, corresponding to the peak value of the pore water pressure in a certain cycle, are different with different initial consolidation angles; the pore water pressure accumulation of soft clay is greatly affected by the intermediate principal stress coefficient b. With the fixed initial consolidation angle ζ, the variation trend of the maximum pore water pressure for each cycle is appropriately the same with different b values. With the increase of cycles, the difference value of pore water pressure between b = 0 and b = 1 in each cycle increases gradually with different initial consolidation angles ζ. While with different initial consolidation angles ζ, the increase of the pore water pressure when b increases from 0 to 0.5 is different with that when b increases from 0.5 to 1; the variation of maximum pore water pressure with ζ is significantly affected by the value of b; the value of maximum pore water pressure increases with the cycle number increases under all test conditions, but the growth rate decreases gradually. And the variation of maximum pore water pressure with the cycle number N is obviously influenced by both ζ and b.
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