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971.
Structural intensity characterization of composite laminates subjected to impact load 总被引:2,自引:0,他引:2
Structural intensity (SI) characterization of composite laminates subjected to impact load was dis-cussed. The SI pattern of the laminates which have different fiber orientations and boundary conditions wasanalyzed. The resultant forces and velocities of the laminates were calculated, and the structural intensity wasevaluated. The SI streamlines of carbon fiber reinforced epoxy composite laminates and the steel plates werediscussed. The results show that the SI streamlines of the graphite/epoxy laminates are different from that ofthe steel plates, and the SI streamlines are influenced by the boundaries, the stacking sequence of the compositelaminates. The change of the historical central displacement of the graphite/epoxy laminates is fasten thanthat of the steel plates. 相似文献
972.
A study of the mechanism of fences was given to reduce drag by means of theoretical analysis, numerical simulation and experimental research. A 3D mathematical model has been developed based on computational fluid dynamics software Phoenics that was capable of handling steady state, 3D flow to simulate the flow field around the truck. The experiment made in a low speed wind tunnel is used as references for validation. By analyzing the results of calculation and experiment, the flowing mechanism of the flow field around the container truck and the drag-reducing mechanism of #-shaped fences on the truck are unveiled, which provides theoretical guidance to the aerodynamic formation designing and amelioration. 相似文献
973.
Based on a shaking table experiment of 1 : 25 scale frame-shearwall structure model with steel transfer trusses, the dynamic characteristics, seismic responses in elastic and elastic-plastic phases with de- structive forms of the structure were studied. It was observed that cracks were developed with earthquake wave acceleration increasing, but no severe crack was developed in the structure during the experiment. In the seismic responses caused by artificial wave, site wave and E1 Centro wave, that caused by the artificial wave is the most intense one. Displacement angle between steel transfer trusses is large, which means the transfer stories might be weak. However, the seismic performance of the steel transfer trusses is good and the overall structure can satisfy seismic fortification requirements in the region of intensity 6. 相似文献
974.
Plain concrete plate and fiber concrete plate subjected to temperature drop load were analyzed on stochastic finite element method (FEM). It is found that fibers can enhance concrete ability to resist temperature drop load for improving concrete's fracture energy and deferring the crack process. It is found for concrete not to improve apparently its tensile strength and fracture energy is recommended to be its appraisal parameter. 相似文献
975.
A new approach was proposed to construct a performance-driven rectilinear Steiner tree with simultaneous buffer insertion and wiresizing optimization (PDRST/BW) under a higher order resistance-inductancecapacitance (RLC) delay model. This approach is based on the concept of sharing-buffer insertion and dynamic programming approach combined with a bottom-up rectilinear Steiner tree construction. The performances include the timing delay and the quality of signal waveform. The experimental results show that our proposed approach is scalable and obtains better performance than SP-tree and graph-RTBW approaches for the test signal nets. 相似文献
976.
Children’s mode choice for the school trip: the role of distance and school location in walking to school 总被引:2,自引:0,他引:2
Noreen C. McDonald 《Transportation》2008,35(1):23-35
Rising levels of childhood obesity in the United States and a 75% decline in the proportion of children walking to school
in the past 30 years have focused attention on school travel. This paper uses data from the US Department of Transportation’s
2001 National Household Travel Survey to analyze the factors affecting mode choice for elementary and middle school children.
The analysis shows that walk travel time is the most policy-relevant factor affecting the decision to walk to school with
an estimated direct elasticity of −0.75. If policymakers want to increase walking rates, these findings suggest that current
policies, such as Safe Routes to School, which do not affect the spatial distribution of schools and residences will not be
enough to change travel behavior. The final part of the paper uses the mode choice model to test how a land use strategy—community
schools—might affect walking to school. The results show that community schools have the potential to increase walking rates
but would require large changes from current land use, school, and transportation planning practices.
Noreen C. McDonald is an Assistant Professor at the University of North Carolina at Chapel Hill. Her research focuses on how the environment affects children’s travel behavior. 相似文献
Noreen C. McDonaldEmail: |
Noreen C. McDonald is an Assistant Professor at the University of North Carolina at Chapel Hill. Her research focuses on how the environment affects children’s travel behavior. 相似文献
977.
Galit Cohen-Blankshtain 《Transportation》2008,35(3):411-424
Transportation analysis emphasizes the necessity to internalize the transport externalities of car usage through taxation.
Yet taxation decisions are often made with non-transport goals in mind. In such cases, transport policies are made ‘by the
way.’ This paper examines such a case: Israel’s taxation policy on company cars. It shows that current taxation policies result
in increasing numbers of company cars and growing numbers of transport users who are not sensitive to the marginal cost of
car use and make excessive use of the car. As a result, a significant portion of Travel Demand Management (TDM) measures cannot
affect this group. The Israeli case of company car tax reform demonstrates the problematic effect of a policy that does not
take its overall consequences on other policy fields into account and thereby impairs efforts to reduce the negative impacts
of the transport system. Also, it demonstrates the importance of institutional aspects of transport policymaking.
Cohen-Blankshtain is a lecturer at the department of Geography and School of Public Policy at the Hebrew University. Her research interests include urban policy, transport and ICT policy and participation process in public policy. 相似文献
Galit Cohen-BlankshtainEmail: |
Cohen-Blankshtain is a lecturer at the department of Geography and School of Public Policy at the Hebrew University. Her research interests include urban policy, transport and ICT policy and participation process in public policy. 相似文献
978.
An analysis on long term emission benefits of a government vehicle fleet replacement plan in northern illinois 总被引:1,自引:1,他引:0
There have been a number of studies of the effectiveness of vehicle scrappage programs, which offer incentives to accelerated
scrappage of older vehicles often thought to be high emitters. These programs are voluntary and aimed at replacement of household
vehicles. In contrast, there is a gap in knowledge related to the emissions benefits of government fleet replacement (retirement)
programs. In this study, the efficacy of a fleet replacement program for a local government agency in Northern Illinois, the
Forest Preserve of DuPage County (FPDC), is examined using a probabilistic vehicle survival model that accounts for time-varying
covariates such as vehicle age and gasoline price. The vehicle lifetime operating emissions are calculated based on the estimated
vehicle survival probabilities from the survival model and compared with those derived using the EPA default fleet used in
MOBILE6 and the fleet represented by the Oak Ridge National Laboratory (ORNL) survival curve. The results suggest that while
there may be short term emission benefits of the FPDC fleet replacement plan, the long-term emission benefits are highly sensitive
to economic factors (e.g., future gasoline price) and exhibit a decreasing trend. This indicates that an adaptive multi-stage
replacement strategy as opposed to a fixed one is preferable to achieve optimal cost effectiveness.
Dr. Jie Lin (Jane) is an assistant professor in Department of Civil and Materials Engineering and a researcher with the Institute for Environmental Science and Policy at University of Illinois at Chicago. Her current research is focused on transportation sustainability through holistic modeling of energy consumption and emissions associated with private, freight, and public transportation activities. Dr. Cynthia Chen is an assistant professor in the civil engineering department at City College of New York. Her research expertise and interests cover travel behavior analysis, land use and transportation, transportation safety, and environmental analysis. Dr. Deb Niemeier is a professor at UC Davis and her current research focus is on the nexus between transportation, land use and climate change, particularly how land use and transportation decisions affect energy consumption and contribute to climate change. She is considered an expert on transportation-air quality modeling and policy and sustainability. 相似文献
Debbie A. NiemeierEmail: |
Dr. Jie Lin (Jane) is an assistant professor in Department of Civil and Materials Engineering and a researcher with the Institute for Environmental Science and Policy at University of Illinois at Chicago. Her current research is focused on transportation sustainability through holistic modeling of energy consumption and emissions associated with private, freight, and public transportation activities. Dr. Cynthia Chen is an assistant professor in the civil engineering department at City College of New York. Her research expertise and interests cover travel behavior analysis, land use and transportation, transportation safety, and environmental analysis. Dr. Deb Niemeier is a professor at UC Davis and her current research focus is on the nexus between transportation, land use and climate change, particularly how land use and transportation decisions affect energy consumption and contribute to climate change. She is considered an expert on transportation-air quality modeling and policy and sustainability. 相似文献
979.
980.
Abhra Roy Chowdhury Wang Xue Manasa Ranjan Behera S. K. Panda 《Journal of Marine Science and Technology》2016,21(1):102-114
This paper investigates the hydrodynamic characteristics of the rectilinear motion of a robotic fish underwater vehicle. This 2-joint, 3-link multibody vehicle model is biologically inspired by a body caudal fin carangiform fish propulsion mechanism. Navier–Stokes equations are used to compute the unsteady flow fields generated due to the interaction between the vehicle and the surrounding incompressible and Newtonian fluid (water) environment. The NACA 0014 airfoil aerodynamic profile has been designed to boost the swimming efficiency by reducing drag as the vehicle undergoes an undulatory/oscillatory motion. Using the Lighthill slender body model, a traveling wave mathematical function is defined to undulate the robotic fish posterior (caudal) region while the motion tracking is carried out by dynamic meshing technique. The results obtained show that though the net lift force approaches to zero, the net thrust or negative drag coefficient maintains a finite value dependent on kinematic parameters like tail beat frequency (TBF) and amplitude span (AS) at a given propulsive wavelength and the forward velocity of the vehicle. The results reveal the effects of TBF and AS on the coefficient of drag friction and the thrust force. Drag coefficients obtained from the simulations are compared and validated with the experimental results. The hydrodynamic results are found to be similar to the kinematic study results and suggest that TBF and AS play the most effective roles in the bioinspired propulsion technique. Relation of these parameters with propelling thrust force and forward velocity is also in conjunction over a given range of TBF and AS values. 相似文献