Accurate estimates of ductility demands on buckling-restrained braced frames(BRBFs)are crucial to performance-based design of BRBFs.An analytical study on the seismic behavior of BRBFs has been conducted at the ATLSS ...Accurate estimates of ductility demands on buckling-restrained braced frames(BRBFs)are crucial to performance-based design of BRBFs.An analytical study on the seismic behavior of BRBFs has been conducted at the ATLSS Center,Lehigh University to prepare for an upcoming experimental program.The analysis program DRAIN-2DX was used to model a one-bay,four-story prototype BRBF including material and geometric nonlinearities.The buckling- restrained brace(BRB)model incorporates both isotropic and kinematic hardening.Nonlinear static pushover and time- history analyses were performed on the prototype BRBF.Performance objectives for the BRBs were defined and used to evaluate the time-history analysis results.Particular emphasis was placed on global ductility demands and ductility demands on the BRBs.These demands were compared with anticipated ductility capacities.The analysis results,along with results from similar previous studies,are used to evaluate the BRBF design provisions that have been recommended for codification in the United States.The results show that BRB maximum ductility demands can be as high as 20 to 25.These demands significantly exceed those anticipated by the BRBF recommended provisions.Results from the static pushover and time- history analyses are used to demonstrate why the ductility demands exceed those anticipated by the recommended provisions. The BRB qualification testing protocol contained in the BRBF recommended provisions is shown to be inadequate because it requires only a maximum ductility demand of at most 7.5.Modifications to the testing protocol are recommended.展开更多
Development and testing of a serially multiplexed fiber optic sensor system is described.The sensor differs from conventional fiber optic acoustic systems,as it is capable of sensing AE emissions at several points alo...Development and testing of a serially multiplexed fiber optic sensor system is described.The sensor differs from conventional fiber optic acoustic systems,as it is capable of sensing AE emissions at several points along the length of a single fiber.Multiplexing provides for single channel detection of cracks and their locations in large structural systems. An algorithm was developed for signal recognition and tagging of the AE waveforms for detection of' crack locations,Labora- tory experiments on plain concrete beams and post-tensioned FRP tendons were pcrlormed to evaluate the crack detection capability of the sensor system.The acoustic emission sensor was able to detect initiation,growth and location of the cracks in concrete as well as in the FRP tendons.The AE system is potentially suitable lot applications involving health monitoring of structures following an earthquake.展开更多
Mechanical joints can have significant effects on the dynamics of assembled structures.However,the lack of efficacious predictive dynamic models tot joints hinders accurate prediction of their dynamic behavior.The goa...Mechanical joints can have significant effects on the dynamics of assembled structures.However,the lack of efficacious predictive dynamic models tot joints hinders accurate prediction of their dynamic behavior.The goal of our work is to develop physics-based,reduced-order,finite element models that are capable of replicating the effects of joints on vi- brating structures.The authors recently developed the so-called two-dimensional adjusted lwan beam element(2-D AIBE) to simulate the hysteretic behavior of bolted joints in 2-D beam structures.In this paper,2-D AIBE is extended to three-di- mensional cases by formulating a three-dimensional adjusted lwan beam element(3-D AIBE).hupulsive loading experi- ments are applied to a jointed frame structure and a beam structure containing the same joint.The frame is subjected to ex- citation out of plane so that the joint is under rotation and single axis bending.By assuming that the rotation in the joint is linear elastic,the parameters of the joint associated with bending in the flame are identified from acceleration responses of the jointed beam structure,using a multi-layer teed-torward neural network(MLFF).Numerieal simulation is then per- formed on the frame structure using the identified parameters.The good agreement between the simulated and experimental impulsive acceleration responses of the frame structure validates the efficacy of the presented 3-D AIBE,and indicates that the model can potentially be applied to more complex structural systems with joint parameters identified from a relatively simple structure.展开更多
Computational fluid dynamics （CFD） modeling of the complex processes that occur within the burner of a gas turbine engine has become a critical step in the design process. However, due to computer limitations, it is...Computational fluid dynamics （CFD） modeling of the complex processes that occur within the burner of a gas turbine engine has become a critical step in the design process. However, due to computer limitations, it is very difficult to completely couple the fluid mechanics solver with the full combustion chemistry. Therefore, simplified chemistry models are required, and the topic of this research was to provide reduced chemistry models for CH4/O2 gas turbine flow fields to be integrated into CFD codes for the simulation of flow fields of natural gas-fueled burners. The reduction procedure for the CH4/O2 model utilized a response modeling technique wherein the full mechanism was solved over a range of temperatures, pressures, and mixture ratios to establish the response of a particular variable, namely the chemical reaction time. The conditions covered were between 1000 and 2500 K for temperature, 0.1 and 2 for equivalence ratio in air, and 0.1 and 50 atm for pressure. The kinetic time models in the form of ignition time correlations are given in Arrhenius-type formulas as functions of equivalence ratio, temperature, and pressure; or fuel-to-air ratio, temperature, and pressure. A single ignition time model was obtained for the entire range of conditions, and separate models for the low-temperature and high-temperature regions as well as for fuel-lean and rich cases were also derived. Predictions using the reduced model were verified using results from the full mechanism and empirical correlations from experiments. The models are intended for （but not limited to） use in CFD codes for flow field simulations of gas turbine combustors in which initial conditions and degree of mixedness of the fuel and air are key factors in achieving stable and robust combustion processes and acceptable emission levels. The chemical time model was utilized successfully in CFD simulations of a generic gas turbine combustor with four different cases with various levels of fuel-air premixing.展开更多
This paper focuses on propagating perturbed two-body motion using orbital elements combined with a novel integration technique.While previous studies show that Modified Chebyshev Picard Iteration(MCPI)is a powerful to...This paper focuses on propagating perturbed two-body motion using orbital elements combined with a novel integration technique.While previous studies show that Modified Chebyshev Picard Iteration(MCPI)is a powerful tool used to propagate position and velocity,the present results show that using orbital elements to propagate the state vector reduces the number of MCPI iterations and nodes required,which is especially useful for reducing the computation time when including computationally-intensive calculations such as Spherical Harmonic gravity,and it also converges for>5.5x as many revolutions using a single segment when compared with cartesian propagation.Results for the Classical Orbital Elements and the Modified Equinoctial Orbital Elements(the latter provides singularity-free solutions)show that state propagation using these variables is inherently well-suited to the propagation method chosen.Additional benefits are achieved using a segmentation scheme,while future expansion to the two-point boundary value problem is expected to increase the domain of convergence compared with the cartesian case.MCPI is an iterative numerical method used to solve linear and nonlinear,ordinary differential equations(ODEs).It is a fusion of orthogonal Chebyshev function approximation with Picard iteration that approximates a long-arc trajectory at every iteration.Previous studies have shown that it outperforms the state of the practice numerical integrators of ODEs in a serial computing environment;since MCPI is inherently massively parallelizable,this capability is expected to increase the computational efficiency of the method presented.展开更多
In this paper, a wavelet-fi ltered genetic-neuro-fuzzy(WGNF) control system design framework for response control of a highway bridge under various earthquake loads is discussed. The WGNF controller is developed by co...In this paper, a wavelet-fi ltered genetic-neuro-fuzzy(WGNF) control system design framework for response control of a highway bridge under various earthquake loads is discussed. The WGNF controller is developed by combining fuzzy logic, discrete wavelet transform, genetic algorithms, and neural networks for use as a control algorithm. To evaluate the performance of the WGNF algorithm, it is tested on a highway bridge equipped with hydraulic actuators. It controls the actuators installed on the abutments of the highway bridge structure. Various earthquakes used as input signals include an artifi cial earthquake, the El-Centro, Kobe, North Palm Springs, Turkey Bolu, Chi-Chi, and Northridge earthquakes. It is proved that the WGNF control system is effective in mitigating the vibration of the highway bridge under a variety of seismic excitation.展开更多
Acoustoelastic coupling occurs when a hollow structure’s in-vacuo mode aligns with an acoustic mode of the internal cavity.The impact of this coupling on the total dynamic response of the structure can be quite sever...Acoustoelastic coupling occurs when a hollow structure’s in-vacuo mode aligns with an acoustic mode of the internal cavity.The impact of this coupling on the total dynamic response of the structure can be quite severe depending on the similarity of the modal frequencies and shapes.Typically,acoustoelastic coupling is not a design feature,but rather an unintended result that must be remedied as modal tests of structures are often used to correlate or validate finite element models of the uncoupled structure.Here,however,a test structure is intentionally designed such that multiple structural and acoustic modes are well-aligned,resulting in a coupled system that allows for an experimental investigation.First,coupling in the system is identified using a measure termed the magnification factor.Next,the structural-acoustic interaction is measured.Modifications to the system demonstrate the dependency of the coupling on changes in the mode shape and frequency proximity.This includes an investigation of several practical techniques used to decouple the system by altering the internal acoustic cavity,as well as the structure itself.These results show that acoustic absorption material effectively decoupled the structure while structural modifications,in their current form,proved unsuccessful.Readily available acoustic absorptive material was effective in reducing the coupled effects while presumably adding negligible mass or stiffness to the structure.展开更多
In the northeastern United States, whole-tree harvesting is widely used to supply fuel to biomass energy facilities, but questions remain regarding its long-term sustainability. We have previously reported findings in...In the northeastern United States, whole-tree harvesting is widely used to supply fuel to biomass energy facilities, but questions remain regarding its long-term sustainability. We have previously reported findings indicating no short-term decrease in forest productivity in whole-tree harvested sites when compared with similar conventionally (stem-only) harvested sites. Here we present additional results of the same study, but focus on the effect harvest treatment has on the species composition of the regenerating forest. Within northern hardwood forests in central New Hampshire and western Maine, regeneration surveys were conducted on four (4) small clearcuts in 2010 and twenty-nine (29) small clearcuts in 2011. The species and diameter of trees > 2 m in height were recorded within 1 m or 2 m-radius plots and used to calculate the biomass fraction of each species. The 2010 study additionally measured the density of trees 2 m in height and the diversity of understory non-tree species. Non-metric multidimensional scaling and multi-response permutation procedures were used to determine the effect of harvest treatment had on community-wide tree species composition. Potential differences were also examined on a species-by-species basis. Both analytic methods indicated no significant differences in species composition of tree species or understory communities. Within the limits of our data, we conclude that no significant effects of residue removal on species composition are observed within our sample of northern hardwood sites at this early stage of stand development.展开更多
Poplar alkaline peroxide mechanical pulp(APMP)was refined in a PFI mill at varied revolution and the properties of the refined fibers and the resulting hand sheets were tested.The raw poplar APMP fibers are stiff and ...Poplar alkaline peroxide mechanical pulp(APMP)was refined in a PFI mill at varied revolution and the properties of the refined fibers and the resulting hand sheets were tested.The raw poplar APMP fibers are stiff and have been detached from the lamella during APMP pulping process.During the refining process,the APMP fibers did not swell and fibrillate;they were easily broken and formed into fragments.The breaking length of formed hand sheets increased as the heating degree increased because lots of hydrogen bonds were formed between fibers and fine pieces.The tear strength of hand sheets first increased and then decreased as the beating degree changed from 17 to 70~SR.The maximum tear strength was achieved at 61~SR of the beating degree.These results indicated that the hydrogen bond between the fibers was the main factor influencing the tear index followed by the fiber length.Along with the increase of the beating degree,the sheet density increased while the opacity decreased.展开更多
The autonomous vehicles are the future of mobility across the globe and are expected to touch the lives of every person of all ages. But this comes with certain challenges regarding safety, reliability, cost, legal fr...The autonomous vehicles are the future of mobility across the globe and are expected to touch the lives of every person of all ages. But this comes with certain challenges regarding safety, reliability, cost, legal framework, regulations, etc. however, of all the concern safety and reliability are of utmost importance for researchers and engineers. The current research is focused on the movement of the autonomous vehicle in the work zone. The work zone is one of the most challenging areas for the autonomous vehicle to drive from. This is because the work zones are very dynamic, and all the construction activities are specific to the site condition and cannot always be predefined. The study provides a concept of how pavement marking can be used for smooth <span style="font-family:Verdana;">movement through the complicated work zone. In this study, various pav</span><span style="font-family:Verdana;">ement marking signs have been designed as a concept considering the standard colors and striping width being used in the Manual of Uniform Traffic control device (MUTCD). The study assumes that the movement of the autonomous vehicle will not be exclusive and that it will move with the driver driven vehicle. It is expected that autonomous vehicles will require special pavement marking and signage for smooth movement through the work zone. These pavement marking and signage will eventually become part of standard Traffic Control Plans (TCP) and Maintenance of Traffic Plans (MOT). The research aims to study the current research being done in this area and technology being used for detecting various pavement markings and signages.</span>展开更多
The presence of friction generators1 such as bus-stops,intersections,petrol pumps and pedestrian crossings,etc.significantly influences the speed of traffic stream.Among all the friction generators,understanding the i...The presence of friction generators1 such as bus-stops,intersections,petrol pumps and pedestrian crossings,etc.significantly influences the speed of traffic stream.Among all the friction generators,understanding the impact of bus-stops is particularly important from planning and modeling perspective in the Indian context.Therefore,this study presents a methodology to quantify the impact of bus-stops on the speed of other motorized vehicles(the total motorized vehicle fleet minus the buses)under heterogeneous traffic conditions.The methodology was validated on the typical urban arterials in Delhi,India.Two types of data,location of bus-stops and speed profiles of motorized vehicles,were collected by GPS and V-box respectively.These two data sets were mapped and merged using ArcGIS.To understand the nature of traffic stream near bus-stops,‘influence regions’of bus-stops were extracted.Later,characteristic parameters such as lengths of the influence regions and average speeds in the influence regions were computed.Finally,95%confidence intervals of these characteristic parameters were obtained and regression analysis was performed to quantify the impact of bus-stops on the speed of motorized vehicles.The results of study suggest that the influence region of bus-stops on the corridors investigated varies from 140–170 meters and average speed of motorized vehicles in the influence region is reduced by 26–38%of the free flow speed.These findings can better inform planners about the speeds used in traffic flow and travel demand modeling under heterogeneous conditions by helping them in accounting for the speed-reducing impacts of busstops.Moreover,transit planners may also consider the magnitudes and characteristics of the influence regions of bus-stops while determining their locations along the corridor to minimize their adverse impacts on the speed of other motorized vehicles.展开更多
In order to better predict the traffic states on freeways and make management decisions,a hybrid model of support vector machine(SVM)and K-nearest neighbor(KNN)is proposed for shortterm freeway exiting volume predicti...In order to better predict the traffic states on freeways and make management decisions,a hybrid model of support vector machine(SVM)and K-nearest neighbor(KNN)is proposed for shortterm freeway exiting volume prediction.First,a historical data set is built by using the freeway toll data.The abnormal toll records,such as records that have same entry and exit station,illogical time record and abnormal travel speed,are excluded by data quality control.Based on the historical dataset,it is found that the exiting volume has periodical variation over time which provides the basis of the short-term prediction.Then,the historical data set is cross-classified into twelves groups based on the day of week and time of day.The prediction has been done for each group.Finally,the prediction is accomplished by the hybrid-model of SVM and KNN.The exiting volumes of previous time periods are used as the feature vector for KNN and SVM.Besides,a dynamic weight is adopted for the prediction of current time period based on the latest prediction accuracy of KNN and SVM.The model results indicate that the proposed algorithm is feasible and accurate.The Mean Absolute Percentage Error is under 10%.When comparing with the results of single KNN or SVM method,the results show that the combination of KNN and SVM can improve the reliability of the prediction significantly.The proposed method can be implemented in the on-line application of exiting volume prediction,which is able to consider different vehicle types.展开更多
Young driver crashes are over represented in any country’s crash statistics.This problem is more acute in developing countries where the law enforcement is not strict and the licensing structure is not well developed...Young driver crashes are over represented in any country’s crash statistics.This problem is more acute in developing countries where the law enforcement is not strict and the licensing structure is not well developed.According to World Health Organization(WHO)road crashes are the single greatest cause of death for men aged 15-29 years old.More than 8500 young drivers die each year in the Organization for Economic Co-operation and Development(OECD)countries and the death rates for young drivers are doubled than the older aged drivers.Young driver crashes and deaths cause great economic,social cost on individuals,families and societies.Many research studies have been conducted to find out the causes of crash and deaths.These found that the conventional youth training schemes help young learner to develop their driving skills and knowledge,meanwhile they do not help to gain real road driving experience.Research shows that the lack of driving experience,higher order perception and maturity increase young driver crash exposure.To this end,Graduated Driver Licensing System(GDLS)have been developed.GDLS helps young drivers to focus on road driving experience and it divided the whole licensing process into different phases.It also helps the young drivers to get supervised driving experience which help them to accumulate driving hours to get the provisional license.The GDLS helps not only in gaining experience in driving but also in developing the higher order perception(hazard perception)which is very much needed during driving.This paper discusses a number of driver’s licensing systems and training programs and highlights the need for a licensing system that focus not only on the development of better hazard perception and understanding the road environment for young drivers but also on some other factors that affect road safety.It is argued that the consultation of community concerning the development of a licensing system is essential to minimize road crashes in the youth group as it would guarantee that the young drivers are fully aware of various driving risk factors at training stage rather than the practicing stage.展开更多
文摘Accurate estimates of ductility demands on buckling-restrained braced frames(BRBFs)are crucial to performance-based design of BRBFs.An analytical study on the seismic behavior of BRBFs has been conducted at the ATLSS Center,Lehigh University to prepare for an upcoming experimental program.The analysis program DRAIN-2DX was used to model a one-bay,four-story prototype BRBF including material and geometric nonlinearities.The buckling- restrained brace(BRB)model incorporates both isotropic and kinematic hardening.Nonlinear static pushover and time- history analyses were performed on the prototype BRBF.Performance objectives for the BRBs were defined and used to evaluate the time-history analysis results.Particular emphasis was placed on global ductility demands and ductility demands on the BRBs.These demands were compared with anticipated ductility capacities.The analysis results,along with results from similar previous studies,are used to evaluate the BRBF design provisions that have been recommended for codification in the United States.The results show that BRB maximum ductility demands can be as high as 20 to 25.These demands significantly exceed those anticipated by the BRBF recommended provisions.Results from the static pushover and time- history analyses are used to demonstrate why the ductility demands exceed those anticipated by the recommended provisions. The BRB qualification testing protocol contained in the BRBF recommended provisions is shown to be inadequate because it requires only a maximum ductility demand of at most 7.5.Modifications to the testing protocol are recommended.
基金National Science Foundation,Grant number CMS-9900338
文摘Development and testing of a serially multiplexed fiber optic sensor system is described.The sensor differs from conventional fiber optic acoustic systems,as it is capable of sensing AE emissions at several points along the length of a single fiber.Multiplexing provides for single channel detection of cracks and their locations in large structural systems. An algorithm was developed for signal recognition and tagging of the AE waveforms for detection of' crack locations,Labora- tory experiments on plain concrete beams and post-tensioned FRP tendons were pcrlormed to evaluate the crack detection capability of the sensor system.The acoustic emission sensor was able to detect initiation,growth and location of the cracks in concrete as well as in the FRP tendons.The AE system is potentially suitable lot applications involving health monitoring of structures following an earthquake.
文摘Mechanical joints can have significant effects on the dynamics of assembled structures.However,the lack of efficacious predictive dynamic models tot joints hinders accurate prediction of their dynamic behavior.The goal of our work is to develop physics-based,reduced-order,finite element models that are capable of replicating the effects of joints on vi- brating structures.The authors recently developed the so-called two-dimensional adjusted lwan beam element(2-D AIBE) to simulate the hysteretic behavior of bolted joints in 2-D beam structures.In this paper,2-D AIBE is extended to three-di- mensional cases by formulating a three-dimensional adjusted lwan beam element(3-D AIBE).hupulsive loading experi- ments are applied to a jointed frame structure and a beam structure containing the same joint.The frame is subjected to ex- citation out of plane so that the joint is under rotation and single axis bending.By assuming that the rotation in the joint is linear elastic,the parameters of the joint associated with bending in the flame are identified from acceleration responses of the jointed beam structure,using a multi-layer teed-torward neural network(MLFF).Numerieal simulation is then per- formed on the frame structure using the identified parameters.The good agreement between the simulated and experimental impulsive acceleration responses of the frame structure validates the efficacy of the presented 3-D AIBE,and indicates that the model can potentially be applied to more complex structural systems with joint parameters identified from a relatively simple structure.
基金supported by a University Turbine Systems Research grant from the South Carolina Institute for Energy Studies, contract number 04-01-SR114
文摘Computational fluid dynamics （CFD） modeling of the complex processes that occur within the burner of a gas turbine engine has become a critical step in the design process. However, due to computer limitations, it is very difficult to completely couple the fluid mechanics solver with the full combustion chemistry. Therefore, simplified chemistry models are required, and the topic of this research was to provide reduced chemistry models for CH4/O2 gas turbine flow fields to be integrated into CFD codes for the simulation of flow fields of natural gas-fueled burners. The reduction procedure for the CH4/O2 model utilized a response modeling technique wherein the full mechanism was solved over a range of temperatures, pressures, and mixture ratios to establish the response of a particular variable, namely the chemical reaction time. The conditions covered were between 1000 and 2500 K for temperature, 0.1 and 2 for equivalence ratio in air, and 0.1 and 50 atm for pressure. The kinetic time models in the form of ignition time correlations are given in Arrhenius-type formulas as functions of equivalence ratio, temperature, and pressure; or fuel-to-air ratio, temperature, and pressure. A single ignition time model was obtained for the entire range of conditions, and separate models for the low-temperature and high-temperature regions as well as for fuel-lean and rich cases were also derived. Predictions using the reduced model were verified using results from the full mechanism and empirical correlations from experiments. The models are intended for （but not limited to） use in CFD codes for flow field simulations of gas turbine combustors in which initial conditions and degree of mixedness of the fuel and air are key factors in achieving stable and robust combustion processes and acceptable emission levels. The chemical time model was utilized successfully in CFD simulations of a generic gas turbine combustor with four different cases with various levels of fuel-air premixing.
文摘This paper focuses on propagating perturbed two-body motion using orbital elements combined with a novel integration technique.While previous studies show that Modified Chebyshev Picard Iteration(MCPI)is a powerful tool used to propagate position and velocity,the present results show that using orbital elements to propagate the state vector reduces the number of MCPI iterations and nodes required,which is especially useful for reducing the computation time when including computationally-intensive calculations such as Spherical Harmonic gravity,and it also converges for>5.5x as many revolutions using a single segment when compared with cartesian propagation.Results for the Classical Orbital Elements and the Modified Equinoctial Orbital Elements(the latter provides singularity-free solutions)show that state propagation using these variables is inherently well-suited to the propagation method chosen.Additional benefits are achieved using a segmentation scheme,while future expansion to the two-point boundary value problem is expected to increase the domain of convergence compared with the cartesian case.MCPI is an iterative numerical method used to solve linear and nonlinear,ordinary differential equations(ODEs).It is a fusion of orthogonal Chebyshev function approximation with Picard iteration that approximates a long-arc trajectory at every iteration.Previous studies have shown that it outperforms the state of the practice numerical integrators of ODEs in a serial computing environment;since MCPI is inherently massively parallelizable,this capability is expected to increase the computational efficiency of the method presented.
基金MOF(Ministry of Oceans and Fisheries)and a Grant(12-RTIPB01)from Regional Technology Innovation Program funded by MOLIT(Ministry of Land,Infrastructure and Transport)of Korean government
文摘In this paper, a wavelet-fi ltered genetic-neuro-fuzzy(WGNF) control system design framework for response control of a highway bridge under various earthquake loads is discussed. The WGNF controller is developed by combining fuzzy logic, discrete wavelet transform, genetic algorithms, and neural networks for use as a control algorithm. To evaluate the performance of the WGNF algorithm, it is tested on a highway bridge equipped with hydraulic actuators. It controls the actuators installed on the abutments of the highway bridge structure. Various earthquakes used as input signals include an artifi cial earthquake, the El-Centro, Kobe, North Palm Springs, Turkey Bolu, Chi-Chi, and Northridge earthquakes. It is proved that the WGNF control system is effective in mitigating the vibration of the highway bridge under a variety of seismic excitation.
文摘Acoustoelastic coupling occurs when a hollow structure’s in-vacuo mode aligns with an acoustic mode of the internal cavity.The impact of this coupling on the total dynamic response of the structure can be quite severe depending on the similarity of the modal frequencies and shapes.Typically,acoustoelastic coupling is not a design feature,but rather an unintended result that must be remedied as modal tests of structures are often used to correlate or validate finite element models of the uncoupled structure.Here,however,a test structure is intentionally designed such that multiple structural and acoustic modes are well-aligned,resulting in a coupled system that allows for an experimental investigation.First,coupling in the system is identified using a measure termed the magnification factor.Next,the structural-acoustic interaction is measured.Modifications to the system demonstrate the dependency of the coupling on changes in the mode shape and frequency proximity.This includes an investigation of several practical techniques used to decouple the system by altering the internal acoustic cavity,as well as the structure itself.These results show that acoustic absorption material effectively decoupled the structure while structural modifications,in their current form,proved unsuccessful.Readily available acoustic absorptive material was effective in reducing the coupled effects while presumably adding negligible mass or stiffness to the structure.
文摘In the northeastern United States, whole-tree harvesting is widely used to supply fuel to biomass energy facilities, but questions remain regarding its long-term sustainability. We have previously reported findings indicating no short-term decrease in forest productivity in whole-tree harvested sites when compared with similar conventionally (stem-only) harvested sites. Here we present additional results of the same study, but focus on the effect harvest treatment has on the species composition of the regenerating forest. Within northern hardwood forests in central New Hampshire and western Maine, regeneration surveys were conducted on four (4) small clearcuts in 2010 and twenty-nine (29) small clearcuts in 2011. The species and diameter of trees > 2 m in height were recorded within 1 m or 2 m-radius plots and used to calculate the biomass fraction of each species. The 2010 study additionally measured the density of trees 2 m in height and the diversity of understory non-tree species. Non-metric multidimensional scaling and multi-response permutation procedures were used to determine the effect of harvest treatment had on community-wide tree species composition. Potential differences were also examined on a species-by-species basis. Both analytic methods indicated no significant differences in species composition of tree species or understory communities. Within the limits of our data, we conclude that no significant effects of residue removal on species composition are observed within our sample of northern hardwood sites at this early stage of stand development.
文摘Poplar alkaline peroxide mechanical pulp(APMP)was refined in a PFI mill at varied revolution and the properties of the refined fibers and the resulting hand sheets were tested.The raw poplar APMP fibers are stiff and have been detached from the lamella during APMP pulping process.During the refining process,the APMP fibers did not swell and fibrillate;they were easily broken and formed into fragments.The breaking length of formed hand sheets increased as the heating degree increased because lots of hydrogen bonds were formed between fibers and fine pieces.The tear strength of hand sheets first increased and then decreased as the beating degree changed from 17 to 70~SR.The maximum tear strength was achieved at 61~SR of the beating degree.These results indicated that the hydrogen bond between the fibers was the main factor influencing the tear index followed by the fiber length.Along with the increase of the beating degree,the sheet density increased while the opacity decreased.
文摘The autonomous vehicles are the future of mobility across the globe and are expected to touch the lives of every person of all ages. But this comes with certain challenges regarding safety, reliability, cost, legal framework, regulations, etc. however, of all the concern safety and reliability are of utmost importance for researchers and engineers. The current research is focused on the movement of the autonomous vehicle in the work zone. The work zone is one of the most challenging areas for the autonomous vehicle to drive from. This is because the work zones are very dynamic, and all the construction activities are specific to the site condition and cannot always be predefined. The study provides a concept of how pavement marking can be used for smooth <span style="font-family:Verdana;">movement through the complicated work zone. In this study, various pav</span><span style="font-family:Verdana;">ement marking signs have been designed as a concept considering the standard colors and striping width being used in the Manual of Uniform Traffic control device (MUTCD). The study assumes that the movement of the autonomous vehicle will not be exclusive and that it will move with the driver driven vehicle. It is expected that autonomous vehicles will require special pavement marking and signage for smooth movement through the work zone. These pavement marking and signage will eventually become part of standard Traffic Control Plans (TCP) and Maintenance of Traffic Plans (MOT). The research aims to study the current research being done in this area and technology being used for detecting various pavement markings and signages.</span>
文摘The presence of friction generators1 such as bus-stops,intersections,petrol pumps and pedestrian crossings,etc.significantly influences the speed of traffic stream.Among all the friction generators,understanding the impact of bus-stops is particularly important from planning and modeling perspective in the Indian context.Therefore,this study presents a methodology to quantify the impact of bus-stops on the speed of other motorized vehicles(the total motorized vehicle fleet minus the buses)under heterogeneous traffic conditions.The methodology was validated on the typical urban arterials in Delhi,India.Two types of data,location of bus-stops and speed profiles of motorized vehicles,were collected by GPS and V-box respectively.These two data sets were mapped and merged using ArcGIS.To understand the nature of traffic stream near bus-stops,‘influence regions’of bus-stops were extracted.Later,characteristic parameters such as lengths of the influence regions and average speeds in the influence regions were computed.Finally,95%confidence intervals of these characteristic parameters were obtained and regression analysis was performed to quantify the impact of bus-stops on the speed of motorized vehicles.The results of study suggest that the influence region of bus-stops on the corridors investigated varies from 140–170 meters and average speed of motorized vehicles in the influence region is reduced by 26–38%of the free flow speed.These findings can better inform planners about the speeds used in traffic flow and travel demand modeling under heterogeneous conditions by helping them in accounting for the speed-reducing impacts of busstops.Moreover,transit planners may also consider the magnitudes and characteristics of the influence regions of bus-stops while determining their locations along the corridor to minimize their adverse impacts on the speed of other motorized vehicles.
文摘In order to better predict the traffic states on freeways and make management decisions,a hybrid model of support vector machine(SVM)and K-nearest neighbor(KNN)is proposed for shortterm freeway exiting volume prediction.First,a historical data set is built by using the freeway toll data.The abnormal toll records,such as records that have same entry and exit station,illogical time record and abnormal travel speed,are excluded by data quality control.Based on the historical dataset,it is found that the exiting volume has periodical variation over time which provides the basis of the short-term prediction.Then,the historical data set is cross-classified into twelves groups based on the day of week and time of day.The prediction has been done for each group.Finally,the prediction is accomplished by the hybrid-model of SVM and KNN.The exiting volumes of previous time periods are used as the feature vector for KNN and SVM.Besides,a dynamic weight is adopted for the prediction of current time period based on the latest prediction accuracy of KNN and SVM.The model results indicate that the proposed algorithm is feasible and accurate.The Mean Absolute Percentage Error is under 10%.When comparing with the results of single KNN or SVM method,the results show that the combination of KNN and SVM can improve the reliability of the prediction significantly.The proposed method can be implemented in the on-line application of exiting volume prediction,which is able to consider different vehicle types.
文摘Young driver crashes are over represented in any country’s crash statistics.This problem is more acute in developing countries where the law enforcement is not strict and the licensing structure is not well developed.According to World Health Organization(WHO)road crashes are the single greatest cause of death for men aged 15-29 years old.More than 8500 young drivers die each year in the Organization for Economic Co-operation and Development(OECD)countries and the death rates for young drivers are doubled than the older aged drivers.Young driver crashes and deaths cause great economic,social cost on individuals,families and societies.Many research studies have been conducted to find out the causes of crash and deaths.These found that the conventional youth training schemes help young learner to develop their driving skills and knowledge,meanwhile they do not help to gain real road driving experience.Research shows that the lack of driving experience,higher order perception and maturity increase young driver crash exposure.To this end,Graduated Driver Licensing System(GDLS)have been developed.GDLS helps young drivers to focus on road driving experience and it divided the whole licensing process into different phases.It also helps the young drivers to get supervised driving experience which help them to accumulate driving hours to get the provisional license.The GDLS helps not only in gaining experience in driving but also in developing the higher order perception(hazard perception)which is very much needed during driving.This paper discusses a number of driver’s licensing systems and training programs and highlights the need for a licensing system that focus not only on the development of better hazard perception and understanding the road environment for young drivers but also on some other factors that affect road safety.It is argued that the consultation of community concerning the development of a licensing system is essential to minimize road crashes in the youth group as it would guarantee that the young drivers are fully aware of various driving risk factors at training stage rather than the practicing stage.
