A bearing capacity evaluation for the surface strip foundation on a working platform modelled on a twolayered substrate is considered in the study.The upper layer is assumed as man-made and wellcontrolled and thus non...A bearing capacity evaluation for the surface strip foundation on a working platform modelled on a twolayered substrate is considered in the study.The upper layer is assumed as man-made and wellcontrolled and thus non-variable.The lower layer modelling natural cohesive soil is subjected to spatial variability of undrained shear strength.The random failure mechanism method(RFMM)is used to evaluate the bearing capacity.This approach employs a kinematic assessment of the critical load and incorporates the averaging of three-dimensional(3 D)random field along dissipation surfaces that result from the failure mechanism geometry.A novel version of the approach considering an additional linear trend of undrained shear strength in the spatially variable layer is proposed.The high efficiency of the RFMM algorithm is preserved.The influences of foundation length,trend slope in the spatially variable layer,fluctuation scales,and thickness of the homogenous sand layer on the resulting bearing capacity evaluations are analysed.Moreover,for selected cases,verification of the RFMM based assessment obtained using random finite difference method(RFDM)based on 3 D analysis is provided.Two types of analyses are performed using RFDM based on associated and non-associated flow rules.For associated flow rule which corresponds to RFMM,the RFMM is conservative and efficient and thus it seems preferable.However,if RFDM employs non-associated flow rule(much lower dilation angle for sand layer),the efficient RFMM is no longer conservative.For this situation,a combined approach that improves the efficiency of the numerical method is suggested.展开更多
A coupled electromechanical dynamic model for a working platform supported by an active magneticguide(AMG)is set up according to the special stiffness and damping theory of maglev system and theunique vibration of the...A coupled electromechanical dynamic model for a working platform supported by an active magneticguide(AMG)is set up according to the special stiffness and damping theory of maglev system and theunique vibration of the working platform for a machine tool.The dynamic characteristics of a workingplatform supported by an AMG are studied using different groups of control parameters.Results show thatthe dynamic characteristics of the platform system,such as critical vibration frequency,vibration modeand so on,can be improved by adjusting the control parameters.This research offers theoretical supportfor ultra-high-speed and ultra-precise machine working platform designs,including the structure of plat-forms,the design of electromagnets,and the establishment of the control parameters.展开更多
Rigid model of the aerial work platform and hydraulic model of the oscillating mechanism were established with ADAMS. The simulation of two parameters, cy-linder force and oil chamber pressure, was carried out. The si...Rigid model of the aerial work platform and hydraulic model of the oscillating mechanism were established with ADAMS. The simulation of two parameters, cy-linder force and oil chamber pressure, was carried out. The simulation result is useful to the design of the oscillating mechanism.展开更多
This paper proposes a new machining method for part s using group technology suitable for workshop condition in China. The method divi des the parts of each product into similar kinds according to their features, an d...This paper proposes a new machining method for part s using group technology suitable for workshop condition in China. The method divi des the parts of each product into similar kinds according to their features, an d installs each kind of parts on different working platforms. The working platfo rm, as a unit, is designed to be flexible and is interchangeable. It can be hung and fitted to the CNC working table. By changing the platforms in turn, nearly all the parts of one product can be processed with one CNC machine, and can be s ent directly to an assembly shop. Thus the number of management links is reduced and the production rate is increased. Several working platforms may be needed w hen several different types of parts are being processed. However, to reduce pro duction costs, it is necessary to limit the similarity coefficient of part class ification. The feature-coding classification is better for processing parts wit h this method. A practical classification code made by the author is for plastic injection machines. As an example, ten numbers (0～9) are used to express the d i fferent functions and the main features of the parts in the first code-rank. An insufficient classification may be offset by applying cut store and adjusting f unctions to the processing program in the CNC machine center, thereby allowing a set of parts which are not completely similar to be processed on a single worki ng platform. Before a set of parts with incompletely similar features is machine d on a working platform, it is necessary to plan reasonable technological proces s, for which we adopted an optimum method aimed to shorten the working period so as to increase production rate. The fixture planning for this processing method is also discussed in this paper. Modular fixture is recommended for mounting a set of parts on a working platform. In general, modular fixture has a basic boar d and a set of disassemble locating and clamping elements. Because the working p latform can be used directly as the main locating datum, it is unnecessary to de sign another basic board. However, if a working platform is to be used for diffe rent sets of parts, it is better to design it as a dowel-pin series basic board .展开更多
The Lima call for climate action adopted at the Lima Climate Conference on Climate Change specifies that the principles of the United Nations Framework Convention on Climate Change,including the principle of common bu...The Lima call for climate action adopted at the Lima Climate Conference on Climate Change specifies that the principles of the United Nations Framework Convention on Climate Change,including the principle of common but differentiated responsibilities,shall apply to the new climate agreement to be adopted at the Paris Conference on Climate Change in 2015.Decisions on other heavily debated items,including the intended nationally determined contributions,were also made at the Lima Conference.The significant achievements in Lima and the positive momentum have laid a solid foundation for the adoption of a new climate agreement in the Paris Climate Conference.Four measures are proposed for China to meet great challenges in addressing climate change beyond 2020,including early formulation and issuance of a climate change law,establishment of a greenhouse gas emission trading scheme,promotion of advanced climate technology investments,and further international engagement for climate change.展开更多
文摘A bearing capacity evaluation for the surface strip foundation on a working platform modelled on a twolayered substrate is considered in the study.The upper layer is assumed as man-made and wellcontrolled and thus non-variable.The lower layer modelling natural cohesive soil is subjected to spatial variability of undrained shear strength.The random failure mechanism method(RFMM)is used to evaluate the bearing capacity.This approach employs a kinematic assessment of the critical load and incorporates the averaging of three-dimensional(3 D)random field along dissipation surfaces that result from the failure mechanism geometry.A novel version of the approach considering an additional linear trend of undrained shear strength in the spatially variable layer is proposed.The high efficiency of the RFMM algorithm is preserved.The influences of foundation length,trend slope in the spatially variable layer,fluctuation scales,and thickness of the homogenous sand layer on the resulting bearing capacity evaluations are analysed.Moreover,for selected cases,verification of the RFMM based assessment obtained using random finite difference method(RFDM)based on 3 D analysis is provided.Two types of analyses are performed using RFDM based on associated and non-associated flow rules.For associated flow rule which corresponds to RFMM,the RFMM is conservative and efficient and thus it seems preferable.However,if RFDM employs non-associated flow rule(much lower dilation angle for sand layer),the efficient RFMM is no longer conservative.For this situation,a combined approach that improves the efficiency of the numerical method is suggested.
基金the National High Technology Research and Development Program of China(No2001AA423310)
文摘A coupled electromechanical dynamic model for a working platform supported by an active magneticguide(AMG)is set up according to the special stiffness and damping theory of maglev system and theunique vibration of the working platform for a machine tool.The dynamic characteristics of a workingplatform supported by an AMG are studied using different groups of control parameters.Results show thatthe dynamic characteristics of the platform system,such as critical vibration frequency,vibration modeand so on,can be improved by adjusting the control parameters.This research offers theoretical supportfor ultra-high-speed and ultra-precise machine working platform designs,including the structure of plat-forms,the design of electromagnets,and the establishment of the control parameters.
文摘Rigid model of the aerial work platform and hydraulic model of the oscillating mechanism were established with ADAMS. The simulation of two parameters, cy-linder force and oil chamber pressure, was carried out. The simulation result is useful to the design of the oscillating mechanism.
文摘This paper proposes a new machining method for part s using group technology suitable for workshop condition in China. The method divi des the parts of each product into similar kinds according to their features, an d installs each kind of parts on different working platforms. The working platfo rm, as a unit, is designed to be flexible and is interchangeable. It can be hung and fitted to the CNC working table. By changing the platforms in turn, nearly all the parts of one product can be processed with one CNC machine, and can be s ent directly to an assembly shop. Thus the number of management links is reduced and the production rate is increased. Several working platforms may be needed w hen several different types of parts are being processed. However, to reduce pro duction costs, it is necessary to limit the similarity coefficient of part class ification. The feature-coding classification is better for processing parts wit h this method. A practical classification code made by the author is for plastic injection machines. As an example, ten numbers (0～9) are used to express the d i fferent functions and the main features of the parts in the first code-rank. An insufficient classification may be offset by applying cut store and adjusting f unctions to the processing program in the CNC machine center, thereby allowing a set of parts which are not completely similar to be processed on a single worki ng platform. Before a set of parts with incompletely similar features is machine d on a working platform, it is necessary to plan reasonable technological proces s, for which we adopted an optimum method aimed to shorten the working period so as to increase production rate. The fixture planning for this processing method is also discussed in this paper. Modular fixture is recommended for mounting a set of parts on a working platform. In general, modular fixture has a basic boar d and a set of disassemble locating and clamping elements. Because the working p latform can be used directly as the main locating datum, it is unnecessary to de sign another basic board. However, if a working platform is to be used for diffe rent sets of parts, it is better to design it as a dowel-pin series basic board .
文摘The Lima call for climate action adopted at the Lima Climate Conference on Climate Change specifies that the principles of the United Nations Framework Convention on Climate Change,including the principle of common but differentiated responsibilities,shall apply to the new climate agreement to be adopted at the Paris Conference on Climate Change in 2015.Decisions on other heavily debated items,including the intended nationally determined contributions,were also made at the Lima Conference.The significant achievements in Lima and the positive momentum have laid a solid foundation for the adoption of a new climate agreement in the Paris Climate Conference.Four measures are proposed for China to meet great challenges in addressing climate change beyond 2020,including early formulation and issuance of a climate change law,establishment of a greenhouse gas emission trading scheme,promotion of advanced climate technology investments,and further international engagement for climate change.
