In consideration of the effect of the internal flowing fluid and the external marine environmental condition on the vortex-induced vibration （VIV） of top tensioned riser （Till）, the differential equation is derive...In consideration of the effect of the internal flowing fluid and the external marine environmental condition on the vortex-induced vibration （VIV） of top tensioned riser （Till）, the differential equation is derived based on work-energy principles and the riser near wake dynamics is modeled by Facchinetti＇ s wake oscillator model. Then Galerkin＇ s finite element approximation is implemented to derive the nonlinear matrix equation of the coupled equations and file corresponding numerical programs are compiled which solve the coupled equations directly in the time domain. The comparison of the predicted results with the recent experimental results and the prediction of SHEAR7 is performed. The results show the validity of the proposed method on the prediction of VIV of deep water risers. The effect of internal flow on the dynamic characteristics and dynmnic response of the riser is analyzed and several valuable conelusions are drawn.展开更多
The fatigue life of top tensioned risers under vortex-induced vibrations (VIVs) with consideration of the effect of internal flowing fluid on the riser is analyzed in the time domain.The long-term stress histories of ...The fatigue life of top tensioned risers under vortex-induced vibrations (VIVs) with consideration of the effect of internal flowing fluid on the riser is analyzed in the time domain.The long-term stress histories of the riser under VIVs are calculated and the mean stresses,the number of stress cycles and amplitudes are determined by the rainflow counting method.The Palmgren-Miner rule for cumulative damage theory with a specified S-N curve is used to estimate the fatigue life of the riser.The corresponding numerical programs numerical simulation of vortex-induced vibrations (NSVIV) which can be used to calculate the VIV response and fatigue life of the riser are compiled.Finally the influences of the riser's parameters such as flexural rigidity,top tension and internal flow velocity on the fatigue life of the riser are analyzed in detail and some conclusions are drawn.展开更多
The bending stresses of top tensioned riser(TTR) under combined excitations of currents,random waves and vessel motions are presented in this paper,and the effect of the internal flowing fluid on the riser stresses is...The bending stresses of top tensioned riser(TTR) under combined excitations of currents,random waves and vessel motions are presented in this paper,and the effect of the internal flowing fluid on the riser stresses is also considered.The computation programs which are used to solve the differential equations in the time domain are compiled and the principal factors of concern including the angular movements at the upper and lower ends of the riser,lateral displacements and bending stresses are presented.Then the effects of current velocity,random wave,top tension,vessel mean offset,low frequency motion and internal flow velocity on the bending stresses of the riser are analyzed in detail.展开更多
The fluctuating furces of the fluid exerted on the top terrsioned riser （＇FIR） in the in-line and cross-flow directions are both modeled by van del Pol wake oscillator model and the nonlinear coupled dynamics of th...The fluctuating furces of the fluid exerted on the top terrsioned riser （＇FIR） in the in-line and cross-flow directions are both modeled by van del Pol wake oscillator model and the nonlinear coupled dynamics of the in-line and cross-flow vortex-induced vibrations （VIV） of the riser are analyzed in time domain in this papar. The numencal shnulation results of the riser＇s in-line and cross-flow displacements and curvatures are compared with experimental measurements and the comparison shows the validity of this method in modeling some main features of the riser＇s VIV. Finally, the effects of the riser＇s top tensions and internal flow velocities on the coupled vibrations of the riser are investigated.展开更多
A new type of steel moment resisting frame with bottom flange friction devices （BFFDs） has been developed to provide self-centering capacity and energy dissipation, and to reduce permanent deformations under earthqu...A new type of steel moment resisting frame with bottom flange friction devices （BFFDs） has been developed to provide self-centering capacity and energy dissipation, and to reduce permanent deformations under earthquakes. This paper presents a numerical simulation of self-centering beam-column connections with BFFDs, in which the gap opening/closing at the beam-column interfaces is simulated by using pairs of zero-length elements with compression-only material properties, and the energy dissipation due to friction is simulated by using truss elements with specified hysteretic behavior. In particular, the effect of the friction bolt bearing against the slotted plate in the BFFDs was modeled, so that the increase in lateral force and the loss of friction force due to the bolt bearing could be taken into account. Parallel elastic-perfectly plastic gap （ElasticPPGap） materials in the Open System for Earthquake Engineering Simulation （OpenSees） were used with predefined gaps to specify the sequence that each bolt went into the bearing and the corresponding increase in bending stiffness. The MinMax material in OpenSees is used to specify the minimum and maximum values of strains of the ElasticPPGap materials. To consider the loss of friction force due to bok bearing, a number of parallel hysteretic materials were used, and the failure of these materials in sequence simulated the gradual loss of friction force. Analysis results obtained by using the proposed numerical model are discussed and compared with the test results under cyclic loadings and the seismic loading, respectively.展开更多
Stress Joint （SJ） plays a key role in the Top Tensioned Riser （TTR） system for deep water engineering. A preliminary design method of tapered SJ is proposed in the paper, which could help designers obtain accurate...Stress Joint （SJ） plays a key role in the Top Tensioned Riser （TTR） system for deep water engineering. A preliminary design method of tapered SJ is proposed in the paper, which could help designers obtain accurate design data. After a further sensitive analysis is carried out, the related parameters choice and control methods are recommended in the engineering practice. By taking the extreme environment conditions into consideration, the effects of bending stress reduction and curve control are analyzed, and the 3-D FE models are established by ABQOUS for numerical evaluation to verify the correctness of design results. At last, dynamic analysis and fatigue analysis, based on actual project, are carried out with designed stress joint. The analysis results prove the feasibility and guidance of this method in the practical engineering applications.展开更多
This paper (constituting Part B) addresses active interrogation for detecting Special Nuclear Materials (SN- Ms) and includes description of the transformational Tensioned Metastable Fluid Detector (TMFD) based method...This paper (constituting Part B) addresses active interrogation for detecting Special Nuclear Materials (SN- Ms) and includes description of the transformational Tensioned Metastable Fluid Detector (TMFD) based method for optimal monitoring. One of the greatest difficulties in detection of SNMs by active interrogation is the task of distinguishing between the probing particles and the secondary particles that indicate the presence of SNMs. The TMFD’s selective insensitivity and γ photon blindness features are advantageous for alleviating this problem. The working principle of the TMFD is discussed along with its applications for security. The experimental work to date involving detection of small quantities of uranium with conventional detectors is discussed along with results of fission neutron detection. Statistically significant detection was achieved within 5 minutes of counting to ascertain and measure conclusive evidence for the presence of a 55g sample of uranium containing 235U. Results of simulations of three active detection techniques utilizing a TMFD system are presented. The process for using the TMFD to discriminate active source particles using timing and energy are described. These simulations indicate that it should be possible to utilize the TMFD system for optimal neutron-based interrogation of SNMs.展开更多
After corrosion failure of post-tensioned tendons was identified in a Florida bridge in early 2011, laboratory tests were conducted in this study on extracted sections from the failed tendons to identify the grout pro...After corrosion failure of post-tensioned tendons was identified in a Florida bridge in early 2011, laboratory tests were conducted in this study on extracted sections from the failed tendons to identify the grout properties and makeup leading to the failure and also to elucidate the mechanism of corrosion. The initial steps in identification of PT tendons with a high propensity for corrosion initiation or damaged included a detailed visual inspection and identification of voids in the grout. Voids in tendon can be a result of bleed water formation or construction problems. General characteristics of the deficient grout and corrosion behavior of steel in the affected bridge gave a first approach to assessing grout deficiency and corrosion susceptibility. However, refinements in the understanding of the mechanisms causing grout segregation and the elucidation of the role of sulfates, oxygen content, and pore water pH in corrosion development are required.展开更多
In order to reduce the damage of ordinary gravity dam impacted by boulders in debris flow,a blocks-combined dam based practical project is proposed.The dynamic response of the proposed dam under impact load is investi...In order to reduce the damage of ordinary gravity dam impacted by boulders in debris flow,a blocks-combined dam based practical project is proposed.The dynamic response of the proposed dam under impact load is investigated by using ABAQUS finite element software.Considering the impact velocity and impact height,the anti-impact performance of blocks-combined dam is discussed in terms of deformation,displacement,impact force,acceleration,and energy,and is compared with that of ordinary dam.Results show that the displacement,impact force and acceleration of dam increase with the increase of impact velocity and height.The impact energy of blocks-combined dam is mainly absorbed and consumed by the friction between the component interfaces,which is related to the location of impact point.Compared with the ordinary gravity dam,the blocks-combined dam has better impact resistance to boulders in debris flow.展开更多
The purpose of the paper is to calculate the equivalent mechanics parameters of reinforced surroundings, which is based on the assume that the reinforcement of bolts is equivalent to the improvement of mechanics param...The purpose of the paper is to calculate the equivalent mechanics parameters of reinforced surroundings, which is based on the assume that the reinforcement of bolts is equivalent to the improvement of mechanics parameters of surroundings and combines with site engineering practice. Use numerical simulation analysis to study the reinforcement mechanism of full length bolts, thus to provide theoretical bases for bolting design.展开更多
Single-walled carbon nanotubes(SWCNTs)are receiving immense research attention due to their tremendous thermal,electrical,structural and mechanical properties.In this paper,an exact solution of the dynamic response of...Single-walled carbon nanotubes(SWCNTs)are receiving immense research attention due to their tremendous thermal,electrical,structural and mechanical properties.In this paper,an exact solution of the dynamic response of SWCNT with a moving uniformly distributed load is presented.The SWCNT is modelled via the theories of Bernoulli-Euler-thermal elasticity mechanics and solved using Integral transforms.The developed closed-form solution in the present work is compared with existing results and excellent agreements are established.The parametric studies show that as the magnitude of the pressure distribution at the surface increases,the deflection associated with the single walled nanotube increases at any mode whilst a corresponding increase in temperature and foundation parameter have an attenuating effect on deflection.Moreover,an increase in the Winkler parameter,as well as a decrease in the SWCNT mass increases its frequency of vibration.Furthermore,an increase in the speed of the external agent decreases the total external pressure as a result of the removal of dead loads.The present work is envisaged to improve the application of SWCNT as nanodevices for structural,electrical and mechanical systems.展开更多
The paper analyses quantitatively the anchoring effect of tensioned bolts on surrounding rock strength, and defines two concepts: one is the surrounding rock strength increased amount Δτ13 and the other is the stren...The paper analyses quantitatively the anchoring effect of tensioned bolts on surrounding rock strength, and defines two concepts: one is the surrounding rock strength increased amount Δτ13 and the other is the strength influence factor k. The anchoring effect of tensioned bolts is considered to increase a strength increased amount Δτ13 where Δτ13 is the product k and ten-sioned load p, i. e. Δτ13 = kp, where k is a function of two variables x and y. The distribu-tive properties both Δτ13 and k are also discussed in the paper, obtaining some useful results for designing bolting support parameters.展开更多
“Push-and-pull”efficient structures have been inconceivable between XVIII centuries.It is because of the incapacity of obtain an efficient behaviour of tensioned material.Since XVIII centuries,architecture developed...“Push-and-pull”efficient structures have been inconceivable between XVIII centuries.It is because of the incapacity of obtain an efficient behaviour of tensioned material.Since XVIII centuries,architecture developed some structural knowledge generating novel structural forms in the architecture and engineering that were not known before.Tensegrities and tensioned structures were studied due to the knowledge of geometry and tension.Some investigations about tensegrities and tensioned structures have been developed since that moment.Tensegrities are bar and cable structures that work only in compression or tension efforts.Bars and cables are balanced,but in appearance the growth is disorderly.Most of deployable structures are based on tensegrity systems.The research is focused in presenting a summary of tensegrities and tensioned architectures that have been used in the structural design of novel patterns.The research of adequate materials to tension efforts will be crucial in this study.The investigation presents an important state of the art that provides technical solutions to apply on novel architectures based on tensegrities and tensioned structures.The research is useful to produce the current constructive solutions based on these constructive systems.展开更多
基金supported by the National High Technology Research and Development Program of China(863 Program,Grant No.2006AA09Z356 and No.2007AA09Z313)
文摘In consideration of the effect of the internal flowing fluid and the external marine environmental condition on the vortex-induced vibration （VIV） of top tensioned riser （Till）, the differential equation is derived based on work-energy principles and the riser near wake dynamics is modeled by Facchinetti＇ s wake oscillator model. Then Galerkin＇ s finite element approximation is implemented to derive the nonlinear matrix equation of the coupled equations and file corresponding numerical programs are compiled which solve the coupled equations directly in the time domain. The comparison of the predicted results with the recent experimental results and the prediction of SHEAR7 is performed. The results show the validity of the proposed method on the prediction of VIV of deep water risers. The effect of internal flow on the dynamic characteristics and dynmnic response of the riser is analyzed and several valuable conelusions are drawn.
基金supported by the High Technology Research and Development Program of China (863 Program,Grant Nos.2006AA09Z356 and 2007AA09Z313)
文摘The fatigue life of top tensioned risers under vortex-induced vibrations (VIVs) with consideration of the effect of internal flowing fluid on the riser is analyzed in the time domain.The long-term stress histories of the riser under VIVs are calculated and the mean stresses,the number of stress cycles and amplitudes are determined by the rainflow counting method.The Palmgren-Miner rule for cumulative damage theory with a specified S-N curve is used to estimate the fatigue life of the riser.The corresponding numerical programs numerical simulation of vortex-induced vibrations (NSVIV) which can be used to calculate the VIV response and fatigue life of the riser are compiled.Finally the influences of the riser's parameters such as flexural rigidity,top tension and internal flow velocity on the fatigue life of the riser are analyzed in detail and some conclusions are drawn.
基金supported by the High Technology Research and Development Program of China (863 Program, Grant Nos SQ2009AA09Z3487852 and 2007AA09Z313)
文摘The bending stresses of top tensioned riser(TTR) under combined excitations of currents,random waves and vessel motions are presented in this paper,and the effect of the internal flowing fluid on the riser stresses is also considered.The computation programs which are used to solve the differential equations in the time domain are compiled and the principal factors of concern including the angular movements at the upper and lower ends of the riser,lateral displacements and bending stresses are presented.Then the effects of current velocity,random wave,top tension,vessel mean offset,low frequency motion and internal flow velocity on the bending stresses of the riser are analyzed in detail.
基金supported by the High Technology Research and Development Program of China (863 Pro-gram, Grant No.2010AA09Z303)the Key Project of National Natural Science Foundation of China (Grant No.50739004)
文摘The fluctuating furces of the fluid exerted on the top terrsioned riser （＇FIR） in the in-line and cross-flow directions are both modeled by van del Pol wake oscillator model and the nonlinear coupled dynamics of the in-line and cross-flow vortex-induced vibrations （VIV） of the riser are analyzed in time domain in this papar. The numencal shnulation results of the riser＇s in-line and cross-flow displacements and curvatures are compared with experimental measurements and the comparison shows the validity of this method in modeling some main features of the riser＇s VIV. Finally, the effects of the riser＇s top tensions and internal flow velocities on the coupled vibrations of the riser are investigated.
基金National Natural Science Foundation of China Under Grant No. 51078075a grant from Southeast University (No. 3205000502)the financial support from the State Key Lab of Subtropical Building Science, South China University of Technology under Grant No. 2010KB05
文摘A new type of steel moment resisting frame with bottom flange friction devices （BFFDs） has been developed to provide self-centering capacity and energy dissipation, and to reduce permanent deformations under earthquakes. This paper presents a numerical simulation of self-centering beam-column connections with BFFDs, in which the gap opening/closing at the beam-column interfaces is simulated by using pairs of zero-length elements with compression-only material properties, and the energy dissipation due to friction is simulated by using truss elements with specified hysteretic behavior. In particular, the effect of the friction bolt bearing against the slotted plate in the BFFDs was modeled, so that the increase in lateral force and the loss of friction force due to the bolt bearing could be taken into account. Parallel elastic-perfectly plastic gap （ElasticPPGap） materials in the Open System for Earthquake Engineering Simulation （OpenSees） were used with predefined gaps to specify the sequence that each bolt went into the bearing and the corresponding increase in bending stiffness. The MinMax material in OpenSees is used to specify the minimum and maximum values of strains of the ElasticPPGap materials. To consider the loss of friction force due to bok bearing, a number of parallel hysteretic materials were used, and the failure of these materials in sequence simulated the gradual loss of friction force. Analysis results obtained by using the proposed numerical model are discussed and compared with the test results under cyclic loadings and the seismic loading, respectively.
基金supported by the National High Technology Research and Development Program of China (863 Program,Grant No. 2008AA09A105-04)
文摘Stress Joint （SJ） plays a key role in the Top Tensioned Riser （TTR） system for deep water engineering. A preliminary design method of tapered SJ is proposed in the paper, which could help designers obtain accurate design data. After a further sensitive analysis is carried out, the related parameters choice and control methods are recommended in the engineering practice. By taking the extreme environment conditions into consideration, the effects of bending stress reduction and curve control are analyzed, and the 3-D FE models are established by ABQOUS for numerical evaluation to verify the correctness of design results. At last, dynamic analysis and fatigue analysis, based on actual project, are carried out with designed stress joint. The analysis results prove the feasibility and guidance of this method in the practical engineering applications.
文摘This paper (constituting Part B) addresses active interrogation for detecting Special Nuclear Materials (SN- Ms) and includes description of the transformational Tensioned Metastable Fluid Detector (TMFD) based method for optimal monitoring. One of the greatest difficulties in detection of SNMs by active interrogation is the task of distinguishing between the probing particles and the secondary particles that indicate the presence of SNMs. The TMFD’s selective insensitivity and γ photon blindness features are advantageous for alleviating this problem. The working principle of the TMFD is discussed along with its applications for security. The experimental work to date involving detection of small quantities of uranium with conventional detectors is discussed along with results of fission neutron detection. Statistically significant detection was achieved within 5 minutes of counting to ascertain and measure conclusive evidence for the presence of a 55g sample of uranium containing 235U. Results of simulations of three active detection techniques utilizing a TMFD system are presented. The process for using the TMFD to discriminate active source particles using timing and energy are described. These simulations indicate that it should be possible to utilize the TMFD system for optimal neutron-based interrogation of SNMs.
文摘After corrosion failure of post-tensioned tendons was identified in a Florida bridge in early 2011, laboratory tests were conducted in this study on extracted sections from the failed tendons to identify the grout properties and makeup leading to the failure and also to elucidate the mechanism of corrosion. The initial steps in identification of PT tendons with a high propensity for corrosion initiation or damaged included a detailed visual inspection and identification of voids in the grout. Voids in tendon can be a result of bleed water formation or construction problems. General characteristics of the deficient grout and corrosion behavior of steel in the affected bridge gave a first approach to assessing grout deficiency and corrosion susceptibility. However, refinements in the understanding of the mechanisms causing grout segregation and the elucidation of the role of sulfates, oxygen content, and pore water pH in corrosion development are required.
基金financially supported by the National Natural Science Foundation of China(Grant No.51379015,51579013)the Fundamental Research Funds for the Central Universities,Excellent doctoral dissertation cultivation project of Chang’an University+2 种基金the Fundamental Research Funds for the Central Universities,Chang’an University(CHD)(Grant No.300102289303)Natural National Science FoundationFundamental Research Funds for the Central Universities for the financial support。
文摘In order to reduce the damage of ordinary gravity dam impacted by boulders in debris flow,a blocks-combined dam based practical project is proposed.The dynamic response of the proposed dam under impact load is investigated by using ABAQUS finite element software.Considering the impact velocity and impact height,the anti-impact performance of blocks-combined dam is discussed in terms of deformation,displacement,impact force,acceleration,and energy,and is compared with that of ordinary dam.Results show that the displacement,impact force and acceleration of dam increase with the increase of impact velocity and height.The impact energy of blocks-combined dam is mainly absorbed and consumed by the friction between the component interfaces,which is related to the location of impact point.Compared with the ordinary gravity dam,the blocks-combined dam has better impact resistance to boulders in debris flow.
文摘The purpose of the paper is to calculate the equivalent mechanics parameters of reinforced surroundings, which is based on the assume that the reinforcement of bolts is equivalent to the improvement of mechanics parameters of surroundings and combines with site engineering practice. Use numerical simulation analysis to study the reinforcement mechanism of full length bolts, thus to provide theoretical bases for bolting design.
文摘Single-walled carbon nanotubes(SWCNTs)are receiving immense research attention due to their tremendous thermal,electrical,structural and mechanical properties.In this paper,an exact solution of the dynamic response of SWCNT with a moving uniformly distributed load is presented.The SWCNT is modelled via the theories of Bernoulli-Euler-thermal elasticity mechanics and solved using Integral transforms.The developed closed-form solution in the present work is compared with existing results and excellent agreements are established.The parametric studies show that as the magnitude of the pressure distribution at the surface increases,the deflection associated with the single walled nanotube increases at any mode whilst a corresponding increase in temperature and foundation parameter have an attenuating effect on deflection.Moreover,an increase in the Winkler parameter,as well as a decrease in the SWCNT mass increases its frequency of vibration.Furthermore,an increase in the speed of the external agent decreases the total external pressure as a result of the removal of dead loads.The present work is envisaged to improve the application of SWCNT as nanodevices for structural,electrical and mechanical systems.
文摘The paper analyses quantitatively the anchoring effect of tensioned bolts on surrounding rock strength, and defines two concepts: one is the surrounding rock strength increased amount Δτ13 and the other is the strength influence factor k. The anchoring effect of tensioned bolts is considered to increase a strength increased amount Δτ13 where Δτ13 is the product k and ten-sioned load p, i. e. Δτ13 = kp, where k is a function of two variables x and y. The distribu-tive properties both Δτ13 and k are also discussed in the paper, obtaining some useful results for designing bolting support parameters.
文摘“Push-and-pull”efficient structures have been inconceivable between XVIII centuries.It is because of the incapacity of obtain an efficient behaviour of tensioned material.Since XVIII centuries,architecture developed some structural knowledge generating novel structural forms in the architecture and engineering that were not known before.Tensegrities and tensioned structures were studied due to the knowledge of geometry and tension.Some investigations about tensegrities and tensioned structures have been developed since that moment.Tensegrities are bar and cable structures that work only in compression or tension efforts.Bars and cables are balanced,but in appearance the growth is disorderly.Most of deployable structures are based on tensegrity systems.The research is focused in presenting a summary of tensegrities and tensioned architectures that have been used in the structural design of novel patterns.The research of adequate materials to tension efforts will be crucial in this study.The investigation presents an important state of the art that provides technical solutions to apply on novel architectures based on tensegrities and tensioned structures.The research is useful to produce the current constructive solutions based on these constructive systems.
