Many porting systems for internal combustion engines have been tried and tested over the years, however the basic spring actuated
poppet valve system has prevailed over the last century. In the goal to lower engine output parasitic losses, a simple rotary
valve porting system design is proposed and analyzed. The proposed design concept takes into consideration and combines all
the prominent advantages of many ealier mutlitiple design variations over the past century. The inherent primary advantage
of such a rotary porting system is the elimination of reciprocating components, thus lowering vibration, and removal of highly
stiff springs which contribute to considerable system power loss. Comparable sized 3-D representations of both systems are
constructed in CAD (Computer Aided Design) software in order to run mechanical and fluid simulations to validate the efficiency
advantage of a rotary valve porting system. Using Pro/Engineer Mechanism Dynamics module, the minimum torque required to actuate
both systems at 2000 rpm and 3000 rpm is determined. Fluid simulations are performed using a commercial software CFDesign
V10. Volumetric flow rates are compared during the intake stroke as well as turbulence intensity factors which characterizes
a systems ability to properly mix the Air/Fuel mixture and the combustion efficiency. Some possible improvement on the rotary
geometry is suggested. 相似文献
Geographic Information Systems (GISs) are now being developed for urban transportation planning and modeling. Supporting other recent work, this paper demonstrates the combination of GIS and network-based, urban transportation planning (UTP) modeling software to create powerful tools for the analysis of policies and plans. Following a literature review and informal survey identifying GIS and UTP modeling software in use at transportation agencies, three applications of GIS for network modeling and relevant issues are discussed: 1) developing or modifying UTP models, 2) incorporating network data into a GIS framework, and 3) creating and using a high-speed interactive system suitable for providing near real-time alternatives and policy analysis. Some specific suggestions are made related to the use of two software products, and extensions to other platforms are noted. Conclusions allude to the potential of such systems while realistically pointing to the present difficulties and magnitude of effort that will be required. 相似文献
A summary of the seasonal development of the Northeast Water Polynya ice cover characteristics is presented. This is based primarily on satellite remote sensing observations, with some in situ measurements, including both new and published data. 相似文献
Summary Results of an experimental research program dealing with motorcycle and scooter tires are presented. Experimental tests were carried out by means of a rotating disk test machine, which is particularly suited to test tires in the presence of large camber angles. First, the capabilities of the rotating disk machine are discussed and results are compared with the ones obtained by means of other test machines. Then the properties of several motorcycle and scooter tires are presented and compared. The advantage of presenting results in terms of camber and sideslip stiffness is highlighted. The effect of tire working conditions (inflation pressure, load and temperature) is analyzed. Finally the measurement of tire torques is discussed and some results dealing with self-aligning, twisting and rolling resistance torques are presented. 相似文献
Over the past generation seaports have undergone a transformation from traditional cargo handling to logistical support centers and changed from bulk shipping and processing to high value-added management centers in an increasingly competitive global environment. Many have reorganized to become leaders of their region's economic development strategies. This paper reviews these changing roles and their impact on organizational issues. This organizational assessment is applied to the port of Kaohsiung and its envisioned role as a commercial hub and operations centre on the Pacific Rim. Issues such as split lines of responsibility, authority and jurisdiction across different levels of government are considered. Competing goals such as economic development, urban waterfront development, metropolitan urban structure, logistical integration, and infrastructure investment are discussed in this context. 相似文献
This paper deals with stochastic wave models and their influence on wave load modelling of marine structures. The need for more refined theories is underlined for some applications and an entirely new quadratic model for the wave elevation is outlined. Finally, a number of physical phenomena relevant to waves are illustrated which are likely to be important for marine structures and could, in the near future, require ad hoc modelling. 相似文献
Mean concentrations of the anthropogenic radioactive oceanographic tracers 99Tc, 90Sr and 137Cs have been measured as 0.005, 1.6 and 2.5 Bq m−3 in oceanic Northeast Atlantic surface water, east and northeast of the Azores, in 1992. This is, apparently, the first published value for fallout “background” 99Tc in oceanic Atlantic water.Comparison with older data indicates an observed half life for 90Sr and 137Cs in the northeast Atlantic surface water of 20 yr corresponding to a mean residence time of 80–100 yr for the stable elements.The observed 99Tc/90Sr ratio (3 × 10−3) in the Azores samples is 10 times higher than the theoretical fission yield decay corrected to 1992. This is in agreement with published data on rain water samples and may be characteristic for 1960's global fallout. Furthermore, the measured 137Cs/90Sr ratio is not significantly different from that observed for global fallout. There do not appear to be any additional significant sources of artificial radionuclides in this region. 相似文献
Weldability problems in jack-up rigs arise principally in leg construction where particularly high-strength steels (690 N mm−2 yield) are used for chords and racks. Attainment of mechanical properties is not usually difficult, although procedural trials are advisable.
Of potential fabrication problems, hydrogen cracking (heat-affected zones or weld metal) is of greatest concern, and consideration of solidification cracking is advisable. Lamellar tearing is not generally a problem with modern steels, and the risk of stress-relief cracking will be confined to the limited number of joints which can be heat-treated.
Fatigue cracking is probably the major cause of service failure of jack-up rigs, and the use of high-strength steels, which permits higher static stress limits, can exacerbate this problem. Hydrogen-induced stress corrosion can also occur, either due to cathodic polarisation or corrosion, particularly in the presence of H2S in foul sea-water. For this reason weld hardness limits need to be maintained. 相似文献