Based on the dynamic loading(1-100 s^(-1)) experiments under different temperatures(223-298 K) and stress states, uniaxial and biaxial strength criterion of a Hydroxyl-terminated polybutadiene(HTPB)based composite sol...Based on the dynamic loading(1-100 s^(-1)) experiments under different temperatures(223-298 K) and stress states, uniaxial and biaxial strength criterion of a Hydroxyl-terminated polybutadiene(HTPB)based composite solid propellant were further investigated. These experiments were conducted through the use of a new uniaxial INSTRON testing machine, different new designed gripping apparatus and samples with different configurations. According to the test results, dynamic uniaxial tensile strength criterion of the propellant was directly constructed with the master curve of the uniaxial maximum tensile stress. Whereas, a new method was proposed to determine the dynamic uniaxial compressive strength of the propellant in this study. Then uniaxial compressive strength criterion of the propellant was constructed based on the related master curve. Moreover, it found that the uniaxial tensilecompressive strength ratio of the propellant is more sensitive to loading temperature under the test conditions. The value of this parameter is about 0.4 at room temperature, and it reduces to 0.2-0.3 at low temperatures. Finally, the theoretical biaxial strength criterion of HTPB propellant under dynamic loading was constructed with the unified strength theory, the uniaxial strength and the typical biaxial tensile strength. In addition, the theoretical limit lines of the principal stress plane for the propellant under dynamic loading at different temperatures were further plotted, and the scope of the limit line increases with decreasing temperature.展开更多
Based on the theory of impact dynamics, the motion equations for a mooring line-floating body system before and after impact loading are established with consideration of the viscoelastic property of mooring lines. Th...Based on the theory of impact dynamics, the motion equations for a mooring line-floating body system before and after impact loading are established with consideration of the viscoelastic property of mooring lines. The factors that influence the taut-slack conditions of a mooring system are analyzed through classifying the taut-slack regions, which are defined by non-dimensional ratios of displacement, frequency, and damping of the system. The mooring system of Jip spar platform is analyzed, and the snap tension characteristics of mooring lines are given. The factors that influence the maximum tension in mooring lines, including the mass of the floating body, length of mooring lines, frequency and amplitude of external excitation, and pretension in mooting lines, are also analyzed through computing the dynamic response of system and parametric study. It is shown that the maximum tension increases with the increasing mass of the floating body, external excitation and pretension. Also, it is found that the influence of the non-dimensional ratio of damping increases with the increase of the pretension in mooring lines.展开更多
This study presents a practical design strategy for a large-size Submerged Floating Tunnel(SFT)under different target environments through global-performance simulations.A coupled time-domain simulation model for SFT ...This study presents a practical design strategy for a large-size Submerged Floating Tunnel(SFT)under different target environments through global-performance simulations.A coupled time-domain simulation model for SFT is established to check hydro-elastic behaviors under the design random wave and earthquake excitations.The tunnel and mooring lines are modeled with a finite-element line model based on a series of lumped masses connected by axial,bending,and torsional springs,and thus the dynamic/structural deformability of the entire SFT is fully considered.The dummy-connection-mass method and constraint boundary conditions are employed to connect the tunnel and mooring lines in a convenient manner.Wave-and earthquake-induced hydrodynamic forces are evaluated by the Morison equation at instantaneous node positions.Several wave and earthquake conditions are selected to evaluate its global performance and sensitivity at different system parameters.Different BuoyancyWeight Ratios(BWRs),submergence depths,and tunnel lengths(and mooring intervals)are chosen to establish a design strategy for reducing the maximum mooring tension.Both static and dynamic tensions are critical to find an acceptable design depending on the given target environmental condition.BWR plays a crucial role in preventing snap loading,and the corresponding static tension is a primary factor if the environmental condition is mild.The tunnel length can significantly be extended by reducing BWR when environmental force is not that substantial.Dynamic tension becomes important in harsh environmental conditions,for which high BWR and short mooring interval are required.It is underscored that the wet natural frequencies with mooring are located away from the spectral peaks of design waves or earthquakes.展开更多
The major objective of this research was to discuss the effects of loading rate on the flexural-tension properties and uniaxial compressive strength of micro-surfacing mixture using three-point bending test and uniaxi...The major objective of this research was to discuss the effects of loading rate on the flexural-tension properties and uniaxial compressive strength of micro-surfacing mixture using three-point bending test and uniaxial compressive test respectively. As a preventive maintenance surface treatment on asphalt pavement, micro-surfacing was formed on the basis of the ISSA recommendation of an optimum micro-surfacing design. Tests were conducted over a wide range of temperature to investigate the difference of properties from low loading rate to a relatively high loading rate. Three-point bending test was used to study the flexural strength, strain and modulus of micro-surfacing mixture, and uniaxial compressive test was carried out to obtain the relationship between strength and the loading rate as well as temperature. The experimental results showed that flexural strength at high loading rate was larger than that at low loading rate. The flexural strength difference between low and high loading rate enlarged when the temperature rose. The flexural strain at high loading rate increased compared with results of the low loading rate. Results of the flexural modulus revealed that micro-surfacing mixture exhibited better anti-cracking characteristic at low temperature when given a relatively low loading rate. Results of uniaxial compressive test revealed that the strength difference of micro-surfacing among different loading rates increased with the increase of temperature. The logarithm relationship between the strength and loading rate over a wide range of temperature was obtained to compare the experimental and predicted values, which resulting in a reasonable consistency.展开更多
基金financial support of the National 973 Program in China (No. 61338)the National Funds in China (Nos.11772352, 61407200203 and 51328050101)
文摘Based on the dynamic loading(1-100 s^(-1)) experiments under different temperatures(223-298 K) and stress states, uniaxial and biaxial strength criterion of a Hydroxyl-terminated polybutadiene(HTPB)based composite solid propellant were further investigated. These experiments were conducted through the use of a new uniaxial INSTRON testing machine, different new designed gripping apparatus and samples with different configurations. According to the test results, dynamic uniaxial tensile strength criterion of the propellant was directly constructed with the master curve of the uniaxial maximum tensile stress. Whereas, a new method was proposed to determine the dynamic uniaxial compressive strength of the propellant in this study. Then uniaxial compressive strength criterion of the propellant was constructed based on the related master curve. Moreover, it found that the uniaxial tensilecompressive strength ratio of the propellant is more sensitive to loading temperature under the test conditions. The value of this parameter is about 0.4 at room temperature, and it reduces to 0.2-0.3 at low temperatures. Finally, the theoretical biaxial strength criterion of HTPB propellant under dynamic loading was constructed with the unified strength theory, the uniaxial strength and the typical biaxial tensile strength. In addition, the theoretical limit lines of the principal stress plane for the propellant under dynamic loading at different temperatures were further plotted, and the scope of the limit line increases with decreasing temperature.
基金supported by the National Natural Science Foundation of China (Grant Nos .50679051 and 50639030) the National High Technology Research and Development Program of China (863 Program, Grant No.2007AA09Z304)
文摘Based on the theory of impact dynamics, the motion equations for a mooring line-floating body system before and after impact loading are established with consideration of the viscoelastic property of mooring lines. The factors that influence the taut-slack conditions of a mooring system are analyzed through classifying the taut-slack regions, which are defined by non-dimensional ratios of displacement, frequency, and damping of the system. The mooring system of Jip spar platform is analyzed, and the snap tension characteristics of mooring lines are given. The factors that influence the maximum tension in mooring lines, including the mass of the floating body, length of mooring lines, frequency and amplitude of external excitation, and pretension in mooting lines, are also analyzed through computing the dynamic response of system and parametric study. It is shown that the maximum tension increases with the increasing mass of the floating body, external excitation and pretension. Also, it is found that the influence of the non-dimensional ratio of damping increases with the increase of the pretension in mooring lines.
基金This work was supported by the National Research Foundation of Korea(NRF)Grant funded by the Korean Government(MSIT)(No.2017R1A5A1014883).
文摘This study presents a practical design strategy for a large-size Submerged Floating Tunnel(SFT)under different target environments through global-performance simulations.A coupled time-domain simulation model for SFT is established to check hydro-elastic behaviors under the design random wave and earthquake excitations.The tunnel and mooring lines are modeled with a finite-element line model based on a series of lumped masses connected by axial,bending,and torsional springs,and thus the dynamic/structural deformability of the entire SFT is fully considered.The dummy-connection-mass method and constraint boundary conditions are employed to connect the tunnel and mooring lines in a convenient manner.Wave-and earthquake-induced hydrodynamic forces are evaluated by the Morison equation at instantaneous node positions.Several wave and earthquake conditions are selected to evaluate its global performance and sensitivity at different system parameters.Different BuoyancyWeight Ratios(BWRs),submergence depths,and tunnel lengths(and mooring intervals)are chosen to establish a design strategy for reducing the maximum mooring tension.Both static and dynamic tensions are critical to find an acceptable design depending on the given target environmental condition.BWR plays a crucial role in preventing snap loading,and the corresponding static tension is a primary factor if the environmental condition is mild.The tunnel length can significantly be extended by reducing BWR when environmental force is not that substantial.Dynamic tension becomes important in harsh environmental conditions,for which high BWR and short mooring interval are required.It is underscored that the wet natural frequencies with mooring are located away from the spectral peaks of design waves or earthquakes.
文摘The major objective of this research was to discuss the effects of loading rate on the flexural-tension properties and uniaxial compressive strength of micro-surfacing mixture using three-point bending test and uniaxial compressive test respectively. As a preventive maintenance surface treatment on asphalt pavement, micro-surfacing was formed on the basis of the ISSA recommendation of an optimum micro-surfacing design. Tests were conducted over a wide range of temperature to investigate the difference of properties from low loading rate to a relatively high loading rate. Three-point bending test was used to study the flexural strength, strain and modulus of micro-surfacing mixture, and uniaxial compressive test was carried out to obtain the relationship between strength and the loading rate as well as temperature. The experimental results showed that flexural strength at high loading rate was larger than that at low loading rate. The flexural strength difference between low and high loading rate enlarged when the temperature rose. The flexural strain at high loading rate increased compared with results of the low loading rate. Results of the flexural modulus revealed that micro-surfacing mixture exhibited better anti-cracking characteristic at low temperature when given a relatively low loading rate. Results of uniaxial compressive test revealed that the strength difference of micro-surfacing among different loading rates increased with the increase of temperature. The logarithm relationship between the strength and loading rate over a wide range of temperature was obtained to compare the experimental and predicted values, which resulting in a reasonable consistency.
