Despite the prevalence and validity of the universal distinct element code(UDEC)in simulations in geotechnics domain,water-weakening process of rock models remains elusive.Prior research has made positive contribution...Despite the prevalence and validity of the universal distinct element code(UDEC)in simulations in geotechnics domain,water-weakening process of rock models remains elusive.Prior research has made positive contributions to a presupposed link between modelling parameters and saturation degree,Sr.Nevertheless,this effort presents inaccurate results and limited implications owing to the misleading interpretation,that is,devoid of the basic logic in UDEC that modelling parameters should be calibrated by tested macroscopic properties in contrast to a presupposed relation with Sr.To fill this gap,a new methodology is proposed by coupling a computationally efficient parametric study with the simulation of water-weakening mechanisms.More specifically,tested macroscopic properties with different Sr values are input into parametric relations to acquire initial modelling parameters that are sequentially calibrated and modulated until simulations are in line with geomechanical tests.Illustrative example reveals that numerical water-weakening effects on macroscopic properties,mechanical behaviours,and failure configurations are highly consistent with tested ones with noticeable computational expediency,implying the feasibility and simplicity of this methodology.Furthermore,with compatibility across various numerical models,the proposed methodology substantially extends the applicability of UDEC in simulating water-weakening geotechnical problems.展开更多
The buffeting performance of kilometer-level high-speed railway suspension bridges has a great impact on the smooth operation of high-speed trains.To investigate the buffeting performance of the structure significantl...The buffeting performance of kilometer-level high-speed railway suspension bridges has a great impact on the smooth operation of high-speed trains.To investigate the buffeting performance of the structure significantly different from traditional suspension bridges,the first long-span high-speed railway suspension bridge,Wufengshan Yangtze River Bridge(WYRB),is taken as a numerical example to demonstrate the effects of structural parameters and wind field parameters on the buffeting responses.Based on the design information,the spatial finite element model(FEM)of WYRB is established before testing its accuracy.The fluctuating wind fields are simulated via both classical and stochastic wave based spectral representation method(SRM).Finite element method is further taken to analyze the parametric sensitivity on wind induced buffeting responses in time domain.The results show that the vertical displacement is more sensitive to the changing dead load than the lateral and torsional ones.The larger stiffness of the main girder and the lower sag-to-span ratio are both helpful to reduce the buffeting responses.Wind spectrum and coherence function are key influencing factors to the responses so setting proper wind field parameters are essential in the wind-resistant design stage.The analytical results can provide references for wind resistance analysis and selection of structural and fluctuating wind field parameters for similar long-span high-speed railway suspension bridges.展开更多
An axisymmetrical unit cell model was used to represent a bimodal Al alloy that was composed of both nano-grained （NG） and coarse-grained （CG） aluminum. Effects of microstructural and materials parameters on tensi...An axisymmetrical unit cell model was used to represent a bimodal Al alloy that was composed of both nano-grained （NG） and coarse-grained （CG） aluminum. Effects of microstructural and materials parameters on tensile properties of bimodal AI alloy were investigated by finite element method （FEM）. The parameters analyzed included aspect ratios of CG Al and the unit cell, volume fraction of CG Al （VFCG）, and yield strength and strain hardening exponent of CG Al. Aspect ratios of CG Al and the unit cell have no significant influence on tensile stress-strain response of the bimodal Al alloy. This phenomenon derives from the similarity in elastic modulus and coefficient of thermal expansion between CG AI and NG Al. Conversely, tensile properties of bimodal Al alloy are extremely sensitive to VFCG, yield strength and strain hardening exponent of CG Al. Specifically, as VFCG increases, both yield strength and ultimate tensile strength （UTS） of the bimodal Al alloy decreases, while uniform strain of bimodal AI alloy increases. In addition, an increase in yield strength of CG Al results in an increase in both yield stress and UTS of bimodal AI alloy and a decrease in uniform strain of bimodal Al alloy. The lower capability in lowering the increase of stress concentration in NG Al due to a higher yield strength of CG Al causes the lower uniform strain of the bimodal AI alloy. When strain hardening exponent of CG Al increases, 0.2% yield stress, UTS, and uniform strain of the bimodal Al alloy increases. This can be attributed to the increased work-hardening ability of CG Al with a higher strain hardening exponent.展开更多
Loal flexibility of tubular joints has important effect on the static and dynamic behaviour of offshore platforms, therefore, the determination of it becomes an important research subject in the field of offshore engi...Loal flexibility of tubular joints has important effect on the static and dynamic behaviour of offshore platforms, therefore, the determination of it becomes an important research subject in the field of offshore engineering. In this paper, the local flexibility of TY-type tubular joints, which are widely used in offshore platforms, is calculated by using semi- analytical method. Based on the calculated results, parametric formulae for evaluating element in the local joint flexibility matrix of TY- type tubular joints are derived by regression. A test on PVC models of TY-type tubular joints to measure the local joint flexibility is also reported. A comparison of the results calculated from the parametric formulae presented in this paper with those measured from the model test shows that the parametric formulae are reliable. It is recommended that these formulae be used in the global structural analysis of offshore platforms.展开更多
In order to reduce the wheel profile wear of highspeed trains and extend the service life of wheels, a dynamic model for a high-speed vehicle was set up, in which the wheelset was regarded as flexible body, and the ac...In order to reduce the wheel profile wear of highspeed trains and extend the service life of wheels, a dynamic model for a high-speed vehicle was set up, in which the wheelset was regarded as flexible body, and the actual measured track irregularities and line conditions were considered. The wear depth of the wheel profile was calculated by the well-known Archard wear law. Through this model, the influence of the wheel profile, primary suspension stiffness, track gage, and rail cant on the wear of wheel profile were studied through multiple iterafive calculations. Numerical simulation results show that the type XP55 wheel profile has the smallest cumulative wear depth, and the type LM wheel profile has the largest wear depth. To reduce the wear of the wheel profile, the equivalent conicity of the wheel should not be too large or too small. On the other hand, a small primary vertical stiffness, a track gage around 1,435-1,438 mm, and a rail cant around 1：35-1：40 are beneficial for dynamic performance improvement and wheel wear alleviation.展开更多
Shot and step response measurements were carried out with inert bed and adsorption bed both under iso-thermal conditions.Parameter values were determined from a time domain analysis of the measured inputand response s...Shot and step response measurements were carried out with inert bed and adsorption bed both under iso-thermal conditions.Parameter values were determined from a time domain analysis of the measured inputand response signal.Sensitivity test in the parameter values showed that shot response measurements maygive more reliable parameter values than step measurements.Since Kubin[1]and Kucera[2]proposed a parameter estimation technique based on a moment methodfor adsorption system,attention has been focused on dynamic input-output measurements with variouspacked bed systems for the parameter estimation.The object of this work is to compare shot and step re-sponse measurements and see which measurement gives more reliable parameter values.展开更多
Commercial building sector accounts for 8% of the total electricity consumption in India. Cooling activities (HVAC) in commercial buildings consume 55% of the total energy utilized. Consequently, CO<sub>2</su...Commercial building sector accounts for 8% of the total electricity consumption in India. Cooling activities (HVAC) in commercial buildings consume 55% of the total energy utilized. Consequently, CO<sub>2</sub> emissions from conventional buildings in India were estimated to be 98 metric tonnes of CO<sub>2</sub> per million ft<sup>2</sup> in 2014. Solar thermal air conditioning can be the solution to these demands and can contribute to about 15% to 20% of India’s total oil consumption thereby reducing the dependence on fossil fuels. Hence, the main objective of the work is to model and simulate a solar absorption cooling system for GERMI office building located in Gandhinagar, Gujarat, India, using the transient simulation software ‘TRNSYS’. Cooling load estimation and comfort conditions required for the building were determined based on ASHRAE standards. Evacuated tube collectors were selected because of its market availability, ease of manufacturing and proven technology. Single effect absorption chiller was used because of its commercial availability. The effects of storage tank volume, collector area and collector slope were also investigated for parametric optimization. The results of the simulation and parametric analysis are analyzed and presented in the paper.展开更多
This paper aims to evaluate the stochastic response of steel columns subjected to blast loads using the modified single degree of freedom(MSDOF)method,which assessed towards the conventional single degree of freedom(S...This paper aims to evaluate the stochastic response of steel columns subjected to blast loads using the modified single degree of freedom(MSDOF)method,which assessed towards the conventional single degree of freedom(SDOF)and the experimentally validated Finite Element(FE)methods(LSDYNA).For this purpose,special atten-tion is given to calculating the response of H-shaped steel columns under blast.The damage amount is determined based on the support rotation criterion,which is expressed as a function of their maximum lateral mid-span dis-placement.To account for uncertainties in input parameters and obtain the failure probability,the Monte Carlo simulation(MCS)method is employed,complemented by the Latin Hypercube Sampling(LHS)method to reduce the number of simulations.A parametric analysis is hence performed to examine the effect of several input pa-rameters(including both deterministic and probabilistic parameters)on the probability of column damage as a function of support rotation.First,the MSDOF method confirms its higher accuracy in estimating the probability of column damage due to blast,compared to the conventional SDOF.The collected results also show that un-certainties of several input parameters have significant effects on the column behavior.In particular,geometric parameters(including cross-sectional characteristics,boundary conditions and column length)have major effect on the corresponding column response,in the same way of input blast load parameters and material properties.展开更多
This paper presents exact analytical solutions for a novel damped outrigger system, in which viscous dampers are vertically installed between perimeter columns and the core of a high-rise building. An improved analyti...This paper presents exact analytical solutions for a novel damped outrigger system, in which viscous dampers are vertically installed between perimeter columns and the core of a high-rise building. An improved analytical model is developed by modeling the effect of the damped outrigger as a general rotational spring acting on a Bernoulli-Euler beam. The equivalent rotational spring stiffness incorporating the combined effects of dampers and axial stiffness of perimeter columns is derived. The dynamic stiffness method(DSM) is applied to formulate the governing equation of the damped outrigger system. The accuracy and effi ciency are verifi ed in comparison with those obtained from compatibility equations and boundary equations. Parametric analysis of three non-dimensional factors is conducted to evaluate the infl uences of various factors, such as the stiffness ratio of the core to the beam, position of the damped outrigger, and the installed damping coeffi cient. Results show that the modal damping ratio is signifi cantly infl uenced by the stiffness ratio of the core to the column, and is more sensitive to damping than the position of the damped outrigger. The proposed analytical model in combination with DSM can be extended to the study of structures with more outriggers.展开更多
Numerical simulations are performed to investigate the effects of synthetic jet control on separation and stall over rotor airfoils. The preconditioned and unsteady Reynolds-averaged Navier–Stokes equations coupled w...Numerical simulations are performed to investigate the effects of synthetic jet control on separation and stall over rotor airfoils. The preconditioned and unsteady Reynolds-averaged Navier–Stokes equations coupled with a k x shear stream transport turbulence model are employed to accomplish the flowfield simulation of rotor airfoils under jet control. Additionally,a velocity boundary condition modeled by a sinusoidal function is developed to fulfill the perturbation effect of periodic jets. The validity of the present CFD procedure is evaluated by the simulated results of an isolated synthetic jet and the jet control case for airfoil NACA0015. Then, parametric analyses are conducted specifically for an OA213 rotor airfoil to investigate the effects of jet parameters（forcing frequency, jet location and momentum coefficient, jet direction, and distribution of jet arrays） on the control effect of the aerodynamic characteristics of a rotor airfoil. Preliminary results indicate that the efficiency of jet control can be improved with specific frequencies（the best lift-drag ratio at F＋= 2.0） and jet angles（40 or 75） when the jets are located near the separation point of the rotor airfoil. Furthermore, as a result of a suitable combination of jet arrays, the lift coefficient of the airfoil can be improved by nearly 100%, and the corresponding drag coefficient decreased by26.5% in comparison with the single point control case.展开更多
Against the background of analyzing coal wall stability in 14101 fully mechanized longwall top coal caving face in Majialiang coal mine,based on the torque equilibrium of the coal wall,shield support and the roof stra...Against the background of analyzing coal wall stability in 14101 fully mechanized longwall top coal caving face in Majialiang coal mine,based on the torque equilibrium of the coal wall,shield support and the roof strata,an elastic mechanics model was established to calculate the stress applied on the coal wall.The displacement method was used to obtain the stress and deformation distributions of the coal wall.This study also researched the influence of support resistance,protective pressure to the coal wall,fracture position of the main roof and mining height on the coal wall deformation.The following conclusions are drawn:(1) The shorter the distance from the longwall face,the greater the vertical compressive stress and horizontal tensile stress borne by the coal wall.The coal wall is prone to failure in the form of compressive-shear and tension;(2) With increasing support resistance,the revolution angle of the main roof decreases linearly.As the support resistance and protective force supplied by the face guard increases,the maximum deformation of the coal wall decreases linearly;(3) As the face approaches the fracture position of the main roof,coal wall horizontal deformation increases significantly,and the coal wall is prone to instability;and(4) The best mining height of 14101 longwall face is 3.0 m.展开更多
In this paper, mathematical models and dynamic analyses for both SDOF and MDOF structures isolated with dampers are established and performed, and a comprehensive computation method is provided. The shock absorbing ef...In this paper, mathematical models and dynamic analyses for both SDOF and MDOF structures isolated with dampers are established and performed, and a comprehensive computation method is provided. The shock absorbing effect is illustrated through an example of a two DOF damper-isolated system excited by sinusoidal waves and actual ground acceleration input recorded in earthquakes. It is shown that most of the responses of the structure with dampers reduce greatly near the resonant zone, but acceleration is enlarged in the lower or higher frequency zone; among various parameters, the influence of frictional coefficient n is the most significant, that of damping ratio of the dampers , is the second, and that of stiffness coefficient of the dampers k, is the slightest.展开更多
Recent research has shown that circular hollow section(CHS) joints may exhibit non-rigid behavior under axial load or bending. The non-rigid behavior significantly affects the mechanical performance of structures. Thi...Recent research has shown that circular hollow section(CHS) joints may exhibit non-rigid behavior under axial load or bending. The non-rigid behavior significantly affects the mechanical performance of structures. This paper is concerned with the parametric formulae for predicting axial stiffness of CHS X-joints while braces are in tension. The factors influencing the axial stiffness of CHS X-joints under brace axial tension are investigated,including the joint geometric parameters,the axial force of the chord,and bending moments of braces in two directions,etc. Effects of various parameters on axial stiffness of CHS X-joints are examined by systematic single-parameter nonlinear analysis using shell finite element methods. The analysis is implemented in a finite element code,ANSYS. The observed trends form the basis of the formulae for calculating the joint axial stiffness under brace axial tension by multivariate regression technique. In order to simplify the formulae,two non-dimensional variables are introduced. The proposed formulae can be used to calculate the joint axial stiffness in the design of single-layer steel tubular structures.展开更多
This paper presents the shear performance analysis of a heavy-duty universal hinged cast steel support with the largest bearing capacity. The effect of 9 parameters ( 52 specimens) ,i. e. height of the upper support,d...This paper presents the shear performance analysis of a heavy-duty universal hinged cast steel support with the largest bearing capacity. The effect of 9 parameters ( 52 specimens) ,i. e. height of the upper support,depth of the ring of the upper support,depth of the top plate of the bottom support,height of the ribs of the bottom support,depth of the ribs of the bottom support,bolt hole diameter,number of the ribs of the bowl,depth of the ribs of the bowl,and yield strength of the material,were analyzed with a 3-dimensional elastic-plastic finite element model in which the nonlinearities of geometry,material and contact were all considered. Analysis shows that height of the upper support,depth of the ring of the upper support and yield strength of the material have a great effect on the mechanical performance of the support. Height of the upper support has the largest effect on performance price ratio of the support,and the maximum effect can be up to 160% . Depth of the top plate of the bottom support,height of the ribs of the bottom support and depth of the ribs of the bottom support have a medium effect on performance price ratio of the support,and the effect is within the limit of 15% 19% .展开更多
To improve wind resistance capacity of cable-braced steel portal frames,a double-braced portal frame was proposed by adding two pre-stressed knee braces to a cable-braced portal frame. To study the reasonable range of...To improve wind resistance capacity of cable-braced steel portal frames,a double-braced portal frame was proposed by adding two pre-stressed knee braces to a cable-braced portal frame. To study the reasonable range of application and method of cable parameter determination for this novel structure,the influences of load condition, span, base constraint, and cable parameters on structural performance were investigated by using the finite element code SAP2000. The results show that pre-stressed knee braces can effectively resist both uplifted and lateral wind loads,so this cablestayed and knee-braced steel portal frame is suitable for large wind.When the vertical load is comparable with the wind load,this novel type of portal frames is suitable for a medium span( 21-48 m). The cables in the cable brace can be determined by structural vertical stiffness,and the cables in the knee brace can be designed as the same as those in the cable-stayed part for the reason that their cross sectional area has only a weak effect on the structure. If no cable fails,the pretension variation of the cable does not affect the stiffness of the portal frame. The cable in the cable brace,working together with the cables in the knee braces,can ease uneven distribution of internal force,and their pretensions can be determined according to actual engineering projects.展开更多
Based on curve fitting of coefficients of three component forces of the Messina Straits Bridge, and the previously proposed semi-analytical expressions of flutter derivatives of flexible structure, the change of flutt...Based on curve fitting of coefficients of three component forces of the Messina Straits Bridge, and the previously proposed semi-analytical expressions of flutter derivatives of flexible structure, the change of flutter derivatives of slender bridge cross-section with respect to its aerodynamic center, rotational speed and angle variation is studied using a parametric method. The calculated results are compared with the measured ones, and expressions of flutter derivatives of the Messina Straits Bridge are derived. The intrinsic relationships existing in flutter derivatives are validated again. It is shown that the influence of the rotational speed on flutter derivatives is not negligible. Therefore, it provides an additional semi-analytical approach for analyzing flutter derivatives of the bridge with streamlined cross-section to get its aerodynamic information.展开更多
Relationships between flutter derivatives of slender bridge are investigated based on our previously proposed semi-analytical flutter derivatives of flexible structure. The intrinsic relations are validated with test ...Relationships between flutter derivatives of slender bridge are investigated based on our previously proposed semi-analytical flutter derivatives of flexible structure. The intrinsic relations are validated with test data of flutter derivatives of two bridges. Changes in flutter derivatives with the aerodynamic center, rotation speed, and angle variation are also studied by using a parametric method. The results show correctness of the proposed expressions of flutter derivatives given by authors in Ref. [1], and indicate that certain relations exist between these derivatives. It is also shown that semi-analytical flutter derivatives are applicable to bridges with a streamlined cross-section.展开更多
Tension cables are easily prone to generating varied vibrations under the action of external loads, which adversely affects the safety of bridges. Therefore, it is necessary to take effective measures to suppress the ...Tension cables are easily prone to generating varied vibrations under the action of external loads, which adversely affects the safety of bridges. Therefore, it is necessary to take effective measures to suppress the vibrations of tension cables. Cable end dampers are widely used in vibration reduction for cable-stayed bridges due to their convenient installation and low costs. However, the previous studies on the tension cable-viscous damper systems mostly adopt the linear method, and the weakening effect of the flexibility of mounting brackets on the damper vibration reduction is not sufficiently taken into account. Therefore, this paper adopts the improved Kelvin model to conduct the derivation, solution, and parametric analysis of vibration equations for the stay cable-nonlinear viscous damper systems. The results of parametric analysis show that the maximum modal damping ratio that can be obtained by cables and the corresponding optimal damping coefficient of dampers are correlated with the damping nonlinear coefficient α, stiffness nonlinear coefficient β, vibration order n, installation position a/L, and stiffness coefficient μ, etc.;among them, n damping nonlinear coefficient α and stiffness nonlinear coefficient β are the key parameters that affect the parameter design of dampers, where damping nonlinear coefficient α mainly controls the optimal damping coefficient and stiffness nonlinear coefficient β mainly controls the maximum damping ratio. Based on the parametric analysis, the design principles of dampers and value requirements of key parameters under different vibration suppression objectives are presented.展开更多
This paper proposes a theoretical study of a cold storage system in a CO2 （carbon dioxide） MT （medium temperature） plant for supermarkets application. The aim of this plant strategy is that in the daily hours the ...This paper proposes a theoretical study of a cold storage system in a CO2 （carbon dioxide） MT （medium temperature） plant for supermarkets application. The aim of this plant strategy is that in the daily hours the storage can export heat form the refrigerant outcoming the gas cooler/condenser whereas during the nightly hours it can be maintained cooled by this latter before its incoming into the evaporator. Besides, the storage can be used for reducing the energy peak consumption, permitting to size the plant on a lower energy target, and it can influence the choice of the optimisation logic of the plant controller, in this work a model for a MT CO2 transcritical/subcritical cycle, able to manage the transient due to the changes of loads and external conditions, is proposed to take into account the evolution with time in a fixed time step. A parametrical analysis has been conduced for understanding the optimal design of the plant. A seasonal analysis is considered too, for understanding the cold storage benefits in different periods of year.展开更多
In recent years,the escalation in accidental explosions has emerged as a formidable threat to tunnel infrastructures.Therefore,it is of great significance to conduct a dynamic performance analysis of the tunnels,to im...In recent years,the escalation in accidental explosions has emerged as a formidable threat to tunnel infrastructures.Therefore,it is of great significance to conduct a dynamic performance analysis of the tunnels,to improve the safety and maintain the functionality of underground transport hubs.To this end,this study proposes a dynamic performance assessment framework to assess the extent of damage of shallow buried circular tunnels under explosion hazards.First,the nonlinear dynamic finite element numerical model of soil-tunnel interaction system under explosion hazard was established and validated.Then,based on the validated numerical model,an explosion intensity(EI)considering both explosion equivalent and relative distance was used to further analyze the dynamic response characteristics under typical explosion conditions.Finally,this study further explored the influence of the integrity and strength of the surrounding soil,concrete strength,lining thickness,rebar strength,and rebar rate on the tunnel dynamic performance.Our results show that the dynamic performance assessment framework proposed for shallow circular tunnels fully integrates the coupling effects of explosion equivalent and distance,and is able to accurately measure the degree of damage sustained by these structures under different EI.This work contributes to designing and managing tunnels and underground transport networks based on dynamic performance,thereby facilitating decision-making and efficient allocation of resources by consultants,operators,and stakeholders.展开更多
基金supported by the National Natural Science Foundation of China under Grant Nos.41977249 and 42090052the China Scholarship Council under file No.202204910040.
文摘Despite the prevalence and validity of the universal distinct element code(UDEC)in simulations in geotechnics domain,water-weakening process of rock models remains elusive.Prior research has made positive contributions to a presupposed link between modelling parameters and saturation degree,Sr.Nevertheless,this effort presents inaccurate results and limited implications owing to the misleading interpretation,that is,devoid of the basic logic in UDEC that modelling parameters should be calibrated by tested macroscopic properties in contrast to a presupposed relation with Sr.To fill this gap,a new methodology is proposed by coupling a computationally efficient parametric study with the simulation of water-weakening mechanisms.More specifically,tested macroscopic properties with different Sr values are input into parametric relations to acquire initial modelling parameters that are sequentially calibrated and modulated until simulations are in line with geomechanical tests.Illustrative example reveals that numerical water-weakening effects on macroscopic properties,mechanical behaviours,and failure configurations are highly consistent with tested ones with noticeable computational expediency,implying the feasibility and simplicity of this methodology.Furthermore,with compatibility across various numerical models,the proposed methodology substantially extends the applicability of UDEC in simulating water-weakening geotechnical problems.
基金Projects(51908125,51978155) supported by the National Natural Science Foundation of ChinaProject(W03070080)supported by the National Ten Thousand Talent Program for Young Top-notch Talents,China+1 种基金Project(BK20190359)supported by the Natural Science Foundation of Jiangsu Province,ChinaProject(BE2018120) supported by the Key Research and Development Plan of Jiangsu Province,China。
文摘The buffeting performance of kilometer-level high-speed railway suspension bridges has a great impact on the smooth operation of high-speed trains.To investigate the buffeting performance of the structure significantly different from traditional suspension bridges,the first long-span high-speed railway suspension bridge,Wufengshan Yangtze River Bridge(WYRB),is taken as a numerical example to demonstrate the effects of structural parameters and wind field parameters on the buffeting responses.Based on the design information,the spatial finite element model(FEM)of WYRB is established before testing its accuracy.The fluctuating wind fields are simulated via both classical and stochastic wave based spectral representation method(SRM).Finite element method is further taken to analyze the parametric sensitivity on wind induced buffeting responses in time domain.The results show that the vertical displacement is more sensitive to the changing dead load than the lateral and torsional ones.The larger stiffness of the main girder and the lower sag-to-span ratio are both helpful to reduce the buffeting responses.Wind spectrum and coherence function are key influencing factors to the responses so setting proper wind field parameters are essential in the wind-resistant design stage.The analytical results can provide references for wind resistance analysis and selection of structural and fluctuating wind field parameters for similar long-span high-speed railway suspension bridges.
基金supported by the Office of Naval Re-search, contract N00014-03-C-0163, monitored by Rod Pe-terson.
文摘An axisymmetrical unit cell model was used to represent a bimodal Al alloy that was composed of both nano-grained （NG） and coarse-grained （CG） aluminum. Effects of microstructural and materials parameters on tensile properties of bimodal AI alloy were investigated by finite element method （FEM）. The parameters analyzed included aspect ratios of CG Al and the unit cell, volume fraction of CG Al （VFCG）, and yield strength and strain hardening exponent of CG Al. Aspect ratios of CG Al and the unit cell have no significant influence on tensile stress-strain response of the bimodal Al alloy. This phenomenon derives from the similarity in elastic modulus and coefficient of thermal expansion between CG AI and NG Al. Conversely, tensile properties of bimodal Al alloy are extremely sensitive to VFCG, yield strength and strain hardening exponent of CG Al. Specifically, as VFCG increases, both yield strength and ultimate tensile strength （UTS） of the bimodal Al alloy decreases, while uniform strain of bimodal AI alloy increases. In addition, an increase in yield strength of CG Al results in an increase in both yield stress and UTS of bimodal AI alloy and a decrease in uniform strain of bimodal Al alloy. The lower capability in lowering the increase of stress concentration in NG Al due to a higher yield strength of CG Al causes the lower uniform strain of the bimodal AI alloy. When strain hardening exponent of CG Al increases, 0.2% yield stress, UTS, and uniform strain of the bimodal Al alloy increases. This can be attributed to the increased work-hardening ability of CG Al with a higher strain hardening exponent.
文摘Loal flexibility of tubular joints has important effect on the static and dynamic behaviour of offshore platforms, therefore, the determination of it becomes an important research subject in the field of offshore engineering. In this paper, the local flexibility of TY-type tubular joints, which are widely used in offshore platforms, is calculated by using semi- analytical method. Based on the calculated results, parametric formulae for evaluating element in the local joint flexibility matrix of TY- type tubular joints are derived by regression. A test on PVC models of TY-type tubular joints to measure the local joint flexibility is also reported. A comparison of the results calculated from the parametric formulae presented in this paper with those measured from the model test shows that the parametric formulae are reliable. It is recommended that these formulae be used in the global structural analysis of offshore platforms.
基金the support of the National Natural Science Foundation of China (No. 51005189)the National Key Technology R&D Program of China (2009BAG12A01)
文摘In order to reduce the wheel profile wear of highspeed trains and extend the service life of wheels, a dynamic model for a high-speed vehicle was set up, in which the wheelset was regarded as flexible body, and the actual measured track irregularities and line conditions were considered. The wear depth of the wheel profile was calculated by the well-known Archard wear law. Through this model, the influence of the wheel profile, primary suspension stiffness, track gage, and rail cant on the wear of wheel profile were studied through multiple iterafive calculations. Numerical simulation results show that the type XP55 wheel profile has the smallest cumulative wear depth, and the type LM wheel profile has the largest wear depth. To reduce the wear of the wheel profile, the equivalent conicity of the wheel should not be too large or too small. On the other hand, a small primary vertical stiffness, a track gage around 1,435-1,438 mm, and a rail cant around 1：35-1：40 are beneficial for dynamic performance improvement and wheel wear alleviation.
文摘Shot and step response measurements were carried out with inert bed and adsorption bed both under iso-thermal conditions.Parameter values were determined from a time domain analysis of the measured inputand response signal.Sensitivity test in the parameter values showed that shot response measurements maygive more reliable parameter values than step measurements.Since Kubin[1]and Kucera[2]proposed a parameter estimation technique based on a moment methodfor adsorption system,attention has been focused on dynamic input-output measurements with variouspacked bed systems for the parameter estimation.The object of this work is to compare shot and step re-sponse measurements and see which measurement gives more reliable parameter values.
文摘Commercial building sector accounts for 8% of the total electricity consumption in India. Cooling activities (HVAC) in commercial buildings consume 55% of the total energy utilized. Consequently, CO<sub>2</sub> emissions from conventional buildings in India were estimated to be 98 metric tonnes of CO<sub>2</sub> per million ft<sup>2</sup> in 2014. Solar thermal air conditioning can be the solution to these demands and can contribute to about 15% to 20% of India’s total oil consumption thereby reducing the dependence on fossil fuels. Hence, the main objective of the work is to model and simulate a solar absorption cooling system for GERMI office building located in Gandhinagar, Gujarat, India, using the transient simulation software ‘TRNSYS’. Cooling load estimation and comfort conditions required for the building were determined based on ASHRAE standards. Evacuated tube collectors were selected because of its market availability, ease of manufacturing and proven technology. Single effect absorption chiller was used because of its commercial availability. The effects of storage tank volume, collector area and collector slope were also investigated for parametric optimization. The results of the simulation and parametric analysis are analyzed and presented in the paper.
文摘This paper aims to evaluate the stochastic response of steel columns subjected to blast loads using the modified single degree of freedom(MSDOF)method,which assessed towards the conventional single degree of freedom(SDOF)and the experimentally validated Finite Element(FE)methods(LSDYNA).For this purpose,special atten-tion is given to calculating the response of H-shaped steel columns under blast.The damage amount is determined based on the support rotation criterion,which is expressed as a function of their maximum lateral mid-span dis-placement.To account for uncertainties in input parameters and obtain the failure probability,the Monte Carlo simulation(MCS)method is employed,complemented by the Latin Hypercube Sampling(LHS)method to reduce the number of simulations.A parametric analysis is hence performed to examine the effect of several input pa-rameters(including both deterministic and probabilistic parameters)on the probability of column damage as a function of support rotation.First,the MSDOF method confirms its higher accuracy in estimating the probability of column damage due to blast,compared to the conventional SDOF.The collected results also show that un-certainties of several input parameters have significant effects on the column behavior.In particular,geometric parameters(including cross-sectional characteristics,boundary conditions and column length)have major effect on the corresponding column response,in the same way of input blast load parameters and material properties.
基金973 Program under Grant under Grant No.2012CB723304It was partially supported by the Major Research Plan of the National Natural Science Foundation of China under Grant No.91315301-07+2 种基金in part by Program for Changjiang Scholars and Innovative Research Team in University under Grant No.IRT13057the Ministry of Education Program for New Century Excellent Talents in University under Grant No.NCET-11-0914the Guangzhou Ram Scholar Program Grant No.10A032D
文摘This paper presents exact analytical solutions for a novel damped outrigger system, in which viscous dampers are vertically installed between perimeter columns and the core of a high-rise building. An improved analytical model is developed by modeling the effect of the damped outrigger as a general rotational spring acting on a Bernoulli-Euler beam. The equivalent rotational spring stiffness incorporating the combined effects of dampers and axial stiffness of perimeter columns is derived. The dynamic stiffness method(DSM) is applied to formulate the governing equation of the damped outrigger system. The accuracy and effi ciency are verifi ed in comparison with those obtained from compatibility equations and boundary equations. Parametric analysis of three non-dimensional factors is conducted to evaluate the infl uences of various factors, such as the stiffness ratio of the core to the beam, position of the damped outrigger, and the installed damping coeffi cient. Results show that the modal damping ratio is signifi cantly infl uenced by the stiffness ratio of the core to the column, and is more sensitive to damping than the position of the damped outrigger. The proposed analytical model in combination with DSM can be extended to the study of structures with more outriggers.
基金supported by the National Natural Science Foundation of China (No. 11272150)
文摘Numerical simulations are performed to investigate the effects of synthetic jet control on separation and stall over rotor airfoils. The preconditioned and unsteady Reynolds-averaged Navier–Stokes equations coupled with a k x shear stream transport turbulence model are employed to accomplish the flowfield simulation of rotor airfoils under jet control. Additionally,a velocity boundary condition modeled by a sinusoidal function is developed to fulfill the perturbation effect of periodic jets. The validity of the present CFD procedure is evaluated by the simulated results of an isolated synthetic jet and the jet control case for airfoil NACA0015. Then, parametric analyses are conducted specifically for an OA213 rotor airfoil to investigate the effects of jet parameters（forcing frequency, jet location and momentum coefficient, jet direction, and distribution of jet arrays） on the control effect of the aerodynamic characteristics of a rotor airfoil. Preliminary results indicate that the efficiency of jet control can be improved with specific frequencies（the best lift-drag ratio at F＋= 2.0） and jet angles（40 or 75） when the jets are located near the separation point of the rotor airfoil. Furthermore, as a result of a suitable combination of jet arrays, the lift coefficient of the airfoil can be improved by nearly 100%, and the corresponding drag coefficient decreased by26.5% in comparison with the single point control case.
基金provided by the Priority Academic Program Development of Jiangsu Higher Education Institutions,the Graduate Students of Jiangsu Province Innovation Program (No.CXZZ13_0948)the National Natural Science Foundation of China (No.51304202)the Natural Science Foundation of Jiangsu Province (No.BK20130190)
文摘Against the background of analyzing coal wall stability in 14101 fully mechanized longwall top coal caving face in Majialiang coal mine,based on the torque equilibrium of the coal wall,shield support and the roof strata,an elastic mechanics model was established to calculate the stress applied on the coal wall.The displacement method was used to obtain the stress and deformation distributions of the coal wall.This study also researched the influence of support resistance,protective pressure to the coal wall,fracture position of the main roof and mining height on the coal wall deformation.The following conclusions are drawn:(1) The shorter the distance from the longwall face,the greater the vertical compressive stress and horizontal tensile stress borne by the coal wall.The coal wall is prone to failure in the form of compressive-shear and tension;(2) With increasing support resistance,the revolution angle of the main roof decreases linearly.As the support resistance and protective force supplied by the face guard increases,the maximum deformation of the coal wall decreases linearly;(3) As the face approaches the fracture position of the main roof,coal wall horizontal deformation increases significantly,and the coal wall is prone to instability;and(4) The best mining height of 14101 longwall face is 3.0 m.
文摘In this paper, mathematical models and dynamic analyses for both SDOF and MDOF structures isolated with dampers are established and performed, and a comprehensive computation method is provided. The shock absorbing effect is illustrated through an example of a two DOF damper-isolated system excited by sinusoidal waves and actual ground acceleration input recorded in earthquakes. It is shown that most of the responses of the structure with dampers reduce greatly near the resonant zone, but acceleration is enlarged in the lower or higher frequency zone; among various parameters, the influence of frictional coefficient n is the most significant, that of damping ratio of the dampers , is the second, and that of stiffness coefficient of the dampers k, is the slightest.
文摘Recent research has shown that circular hollow section(CHS) joints may exhibit non-rigid behavior under axial load or bending. The non-rigid behavior significantly affects the mechanical performance of structures. This paper is concerned with the parametric formulae for predicting axial stiffness of CHS X-joints while braces are in tension. The factors influencing the axial stiffness of CHS X-joints under brace axial tension are investigated,including the joint geometric parameters,the axial force of the chord,and bending moments of braces in two directions,etc. Effects of various parameters on axial stiffness of CHS X-joints are examined by systematic single-parameter nonlinear analysis using shell finite element methods. The analysis is implemented in a finite element code,ANSYS. The observed trends form the basis of the formulae for calculating the joint axial stiffness under brace axial tension by multivariate regression technique. In order to simplify the formulae,two non-dimensional variables are introduced. The proposed formulae can be used to calculate the joint axial stiffness in the design of single-layer steel tubular structures.
基金Sponsored by the National Natural Science Foundation of China( Grant No. 50878066)the National Key Technology R&D Program during the 11th Five-Year Plan Period of China( Grant No. 2006BAJ01B02)
文摘This paper presents the shear performance analysis of a heavy-duty universal hinged cast steel support with the largest bearing capacity. The effect of 9 parameters ( 52 specimens) ,i. e. height of the upper support,depth of the ring of the upper support,depth of the top plate of the bottom support,height of the ribs of the bottom support,depth of the ribs of the bottom support,bolt hole diameter,number of the ribs of the bowl,depth of the ribs of the bowl,and yield strength of the material,were analyzed with a 3-dimensional elastic-plastic finite element model in which the nonlinearities of geometry,material and contact were all considered. Analysis shows that height of the upper support,depth of the ring of the upper support and yield strength of the material have a great effect on the mechanical performance of the support. Height of the upper support has the largest effect on performance price ratio of the support,and the maximum effect can be up to 160% . Depth of the top plate of the bottom support,height of the ribs of the bottom support and depth of the ribs of the bottom support have a medium effect on performance price ratio of the support,and the effect is within the limit of 15% 19% .
基金Fund of Jiangsu Province Key Laboratory of Structure Engineering,China(No.ZD1302)
文摘To improve wind resistance capacity of cable-braced steel portal frames,a double-braced portal frame was proposed by adding two pre-stressed knee braces to a cable-braced portal frame. To study the reasonable range of application and method of cable parameter determination for this novel structure,the influences of load condition, span, base constraint, and cable parameters on structural performance were investigated by using the finite element code SAP2000. The results show that pre-stressed knee braces can effectively resist both uplifted and lateral wind loads,so this cablestayed and knee-braced steel portal frame is suitable for large wind.When the vertical load is comparable with the wind load,this novel type of portal frames is suitable for a medium span( 21-48 m). The cables in the cable brace can be determined by structural vertical stiffness,and the cables in the knee brace can be designed as the same as those in the cable-stayed part for the reason that their cross sectional area has only a weak effect on the structure. If no cable fails,the pretension variation of the cable does not affect the stiffness of the portal frame. The cable in the cable brace,working together with the cables in the knee braces,can ease uneven distribution of internal force,and their pretensions can be determined according to actual engineering projects.
文摘Based on curve fitting of coefficients of three component forces of the Messina Straits Bridge, and the previously proposed semi-analytical expressions of flutter derivatives of flexible structure, the change of flutter derivatives of slender bridge cross-section with respect to its aerodynamic center, rotational speed and angle variation is studied using a parametric method. The calculated results are compared with the measured ones, and expressions of flutter derivatives of the Messina Straits Bridge are derived. The intrinsic relationships existing in flutter derivatives are validated again. It is shown that the influence of the rotational speed on flutter derivatives is not negligible. Therefore, it provides an additional semi-analytical approach for analyzing flutter derivatives of the bridge with streamlined cross-section to get its aerodynamic information.
文摘Relationships between flutter derivatives of slender bridge are investigated based on our previously proposed semi-analytical flutter derivatives of flexible structure. The intrinsic relations are validated with test data of flutter derivatives of two bridges. Changes in flutter derivatives with the aerodynamic center, rotation speed, and angle variation are also studied by using a parametric method. The results show correctness of the proposed expressions of flutter derivatives given by authors in Ref. [1], and indicate that certain relations exist between these derivatives. It is also shown that semi-analytical flutter derivatives are applicable to bridges with a streamlined cross-section.
文摘Tension cables are easily prone to generating varied vibrations under the action of external loads, which adversely affects the safety of bridges. Therefore, it is necessary to take effective measures to suppress the vibrations of tension cables. Cable end dampers are widely used in vibration reduction for cable-stayed bridges due to their convenient installation and low costs. However, the previous studies on the tension cable-viscous damper systems mostly adopt the linear method, and the weakening effect of the flexibility of mounting brackets on the damper vibration reduction is not sufficiently taken into account. Therefore, this paper adopts the improved Kelvin model to conduct the derivation, solution, and parametric analysis of vibration equations for the stay cable-nonlinear viscous damper systems. The results of parametric analysis show that the maximum modal damping ratio that can be obtained by cables and the corresponding optimal damping coefficient of dampers are correlated with the damping nonlinear coefficient α, stiffness nonlinear coefficient β, vibration order n, installation position a/L, and stiffness coefficient μ, etc.;among them, n damping nonlinear coefficient α and stiffness nonlinear coefficient β are the key parameters that affect the parameter design of dampers, where damping nonlinear coefficient α mainly controls the optimal damping coefficient and stiffness nonlinear coefficient β mainly controls the maximum damping ratio. Based on the parametric analysis, the design principles of dampers and value requirements of key parameters under different vibration suppression objectives are presented.
文摘This paper proposes a theoretical study of a cold storage system in a CO2 （carbon dioxide） MT （medium temperature） plant for supermarkets application. The aim of this plant strategy is that in the daily hours the storage can export heat form the refrigerant outcoming the gas cooler/condenser whereas during the nightly hours it can be maintained cooled by this latter before its incoming into the evaporator. Besides, the storage can be used for reducing the energy peak consumption, permitting to size the plant on a lower energy target, and it can influence the choice of the optimisation logic of the plant controller, in this work a model for a MT CO2 transcritical/subcritical cycle, able to manage the transient due to the changes of loads and external conditions, is proposed to take into account the evolution with time in a fixed time step. A parametrical analysis has been conduced for understanding the optimal design of the plant. A seasonal analysis is considered too, for understanding the cold storage benefits in different periods of year.
基金Project(22dz1201202)supported by the Shanghai Science and Technology Committee Program,ChinaProjects(52108381,52090082)supported by the National Natural Science Foundation of China+1 种基金Project(2023QNRC001)supported by the Young Elite Scientists Sponsorship Program by CAST,ChinaProject(TSY2022QT161)supported by the Damage Database for Urban Rail Transit Underground Structures and Resilience Evaluation Algorithm Research。
文摘In recent years,the escalation in accidental explosions has emerged as a formidable threat to tunnel infrastructures.Therefore,it is of great significance to conduct a dynamic performance analysis of the tunnels,to improve the safety and maintain the functionality of underground transport hubs.To this end,this study proposes a dynamic performance assessment framework to assess the extent of damage of shallow buried circular tunnels under explosion hazards.First,the nonlinear dynamic finite element numerical model of soil-tunnel interaction system under explosion hazard was established and validated.Then,based on the validated numerical model,an explosion intensity(EI)considering both explosion equivalent and relative distance was used to further analyze the dynamic response characteristics under typical explosion conditions.Finally,this study further explored the influence of the integrity and strength of the surrounding soil,concrete strength,lining thickness,rebar strength,and rebar rate on the tunnel dynamic performance.Our results show that the dynamic performance assessment framework proposed for shallow circular tunnels fully integrates the coupling effects of explosion equivalent and distance,and is able to accurately measure the degree of damage sustained by these structures under different EI.This work contributes to designing and managing tunnels and underground transport networks based on dynamic performance,thereby facilitating decision-making and efficient allocation of resources by consultants,operators,and stakeholders.
