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761.
W. Perret R. Thater U. Alber C. Schwenk M. Rethmeier 《International Journal of Automotive Technology》2011,12(6):895-901
Fusion welding processes are widely used for joining metal structures, such as pipes, ships, and cars. In general, these joining
processes offer a very good compromise between reliability, safety, cost and maintenance which are important issues in the
current economical context. The negative heat effects of welding, i.e. distortions and residual stresses of the welded parts,
are well known and many researches in this field have already been done in the last decades in order to minimize them. On
the experimental side, many sophisticated procedures have become state of the art to deal with this problem. On the computational
side, the improvement of the simulation algorithms and the computing power enables the simulations of many physical phenomena
occurring during the welding process. The implementation of welding simulation techniques is nevertheless not an easy task
and often associated with expert knowledge which hinders their global application in an industrial environment. This paper
is focused on the industrial requirements of a welding simulation software with special respect to the needs of the automotive
industry. The necessary information to run a welding simulation and the expectations of a weld specialist without deep knowledge
in numerical methods are investigated. These expectations are tested on an automotive welded assembly with a commercially
available welding simulation software designed especially for the needs of the automotive industry. A welding experiment is
done and the measured temperature distributions and distortions serve as reference to validate the simulation results. The
result quality of the simulations of temperature fields and distortions is in best agreement with experimental data. The workflow
is well adapted for the considered industrial requirements and the time-tosolution as well as the computational costs are
acceptable, whereas the efficient calibration of the heat input model is still a point which will be further investigated
in current and future research works. 相似文献
762.
R. Dosthosseini A. Z. Kouzani F. Sheikholeslam 《International Journal of Automotive Technology》2011,12(6):943-950
Hybrid electric vehicles are powered by an electric system and an internal combustion engine. The components of a hybrid electric
vehicle need to be coordinated in an optimal manner to deliver the desired performance. This paper presents an approach based
on direct method for optimal power management in hybrid electric vehicles with inequality constraints. The approach consists
of reducing the optimal control problem to a set of algebraic equations by approximating the state variable which is the energy
of electric storage, and the control variable which is the power of fuel consumption. This approximation uses orthogonal functions
with unknown coefficients. In addition, the inequality constraints are converted to equal constraints. The advantage of the
developed method is that its computational complexity is less than that of dynamic and non-linear programming approaches.
Also, to use dynamic or non-linear programming, the problem should be discretized resulting in the loss of optimization accuracy.
The propsed method, on the other hand, does not require the discretization of the problem producing more accurate results.
An example is solved to demonstrate the accuracy of the proposed approach. The results of Haar wavelets, and Chebyshev and
Legendre polynomials are presented and discussed. 相似文献
763.
This paper presents the development and assessment of models to estimate pedestrian demand based on the level of pedestrian activity (high and low). As activity varies by the time of the day, temporal variations were evaluated by considering different time periods. Data collected at 128 low and 48 high pedestrian activity signalized intersections (a total of 176 signalized intersections) in the City of Charlotte, North Carolina were used to develop and assess the models using stepwise regression analysis through backward elimination of independent variables (includes demographic, land use, and network characteristics). The use of different buffer widths (proximal area) to extract these characteristics was also evaluated. Results, in general, show that pedestrian demand varied by the level of activity, explanatory variables extracted by buffer width, and time of the day. The estimates from the models could be used in transportation planning (identify required pedestrian facilities, resource allocation), safety, and operational analyses. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
764.
R. J. Allport 《运输评论》2013,33(4):365-384
This paper is concerned with the majority of developing nations who lack large resources for public sector projects. It questions the basis of much mass transit planning and attempts to put forward a more efficient way of reaching decisions. It calls extensively on experience of Metro Manila, capital of the Philippines, where an innovative system of metropolitan planning and administration is throwing a new light on ‘appropriate’ investment in such developing cities. Mass transit systems as currently conceived in such developing cities—fully segregated rail‐based systems—are unlikely to be affordable (at least for many years) and in consequence scarce resources should not be devoted to developing and evaluating them. Rather, the principal objective should be to provide low‐cost, affordable mass transit—affordable to governments and to passengers. This almost certainly points to road‐based systems, or predominantly at‐grade light rail transit (LRT) systems, which are usually regarded as ‘obviously unworkable’ in developing city environments. This judgement is questioned and it is suggested the potential of LRT to provide appropriate low‐cost mass transit is not being realized. An approach to determining its potential applicability is proposed. If feasible it should be evaluated against road‐based systems before decisions to implement new mass transit systems are taken. While circumstances vary between countries the central message of this paper—that public sector resources have a very high opportunity cost which make all but the lowest‐cost mass transit systems very difficult to justify—will hold in all but the higher‐income developing economies. 相似文献
765.
R. L. Mackett 《运输规划与技术》2013,36(4):233-247
In this paper, the application of a model representing the impact of interaction between transport costs and the location of housing, population, job employment, shopping and land is described. Two particular uses of the model are considered. Firstly, the effects of changing transport costs upon people of different social status in terms of money and time spent on travelling are examined and compared with results based upon the assumption that the location of population and employment are not responsive to changes in transport cost, as in the conventional transport demand model. Secondly, the effects of six land use‐transport policy sets are examined in terms of the impact upon urban morphology, and the opportunities and travel behaviour of the three social groups. The effects are also compared with the objectives of the strategies. 相似文献
766.
L. Bouillaut O. François P. Aknin R. Donat S. Bondeux S. Dubois 《Recherche - Transports - Sécurité》2011,27(4):241-257
This article deals with a generic approach called VirMaLab (virtual maintenance laboratory) for reliabilitybased maintenance modeling for complex systems (with multi-components and multi-states). Based on the probabilistic graphical models formalism (also known as Bayesian networks), this stochastic approach takes into account both the degradation process of the considered system (an original semi-Markovian model is proposed) and maintenance strategies (from diagnosis factors to all kinds of maintenance actions). For complete decision support tools, cost parameters should also be considered (maintenance actions, unavailability of the system, running, etc.). In this article, two applications of this approach to rail maintenance are introduced. The first one focuses on the optimization of the compromise refurbishment/repairing of central part of the RER A line. The second one focuses on the comparison and evaluation of various maintenance strategies in the modernization of the command control systems of Paris metro lines. 相似文献
767.
Children are an often overlooked and understudied population group, whose travel needs are responsible for a significant number
of trips made by a household. In addition, children’s travel and activity participation during the post-school period have
direct implication for adults’ activity-travel patterns. A better understanding of children’s after school activity-travel
patterns and the linkages between parents and children’s activity-travel needs is necessary for accurate prediction and forecasting
of activity-based travel demand modeling systems. In this paper, data from the 2002 Child Development Supplement of the Panel
Study of Income Dynamics is used to undertake a comprehensive assessment of the post-school out-of-home activity-location
engagement patterns of children aged 5–17 years. Specifically, this research effort utilizes a multinomial logit model to
analyze children’s post-school location patterns, and employs a multiple discrete–continuous extreme value model to study
the propensity of children to participate in, and allocate time to, multiple activity episode purpose-location types during
the after-school period. The results show that a wide variety of demographic, attitudinal, environmental, and others’ activity-travel
pattern characteristics impact children’s after school activity engagement patterns. 相似文献
768.
Abdul Rawoof Pinjari Ram M. Pendyala Chandra R. Bhat Paul A. Waddell 《Transportation》2011,38(6):933-958
The integrated modeling of land use and transportation choices involves analyzing a continuum of choices that characterize
people’s lifestyles across temporal scales. This includes long-term choices such as residential and work location choices
that affect land-use, medium-term choices such as vehicle ownership, and short-term choices such as travel mode choice that
affect travel demand. Prior research in this area has been limited by the complexities associated with the development of
integrated model systems that combine the long-, medium- and short-term choices into a unified analytical framework. This
paper presents an integrated simultaneous multi-dimensional choice model of residential location, auto ownership, bicycle
ownership, and commute tour mode choices using a mixed multidimensional choice modeling methodology. Model estimation results
using the San Francisco Bay Area highlight a series of interdependencies among the multi-dimensional choice processes. The
interdependencies include: (1) self-selection effects due to observed and unobserved factors, where households locate based
on lifestyle and mobility preferences, (2) endogeneity effects, where any one choice dimension is not exogenous to another,
but is endogenous to the system as a whole, (3) correlated error structures, where common unobserved factors significantly
and simultaneously impact multiple choice dimensions, and (4) unobserved heterogeneity, where decision-makers show significant
variation in sensitivity to explanatory variables due to unobserved factors. From a policy standpoint, to be able to forecast
the “true” causal influence of activity-travel environment changes on residential location, auto/bicycle ownership, and commute
mode choices, it is necessary to capture the above-identified interdependencies by jointly modeling the multiple choice dimensions
in an integrated framework. 相似文献
769.
This paper introduces a new procedure to forecast the future O/D demand. It is a hybrid of logit and Fratar model. The hybrid model has the long run, policy sensitive, characteristic of a logit model, calibrated at sector‐level with little/no zero O/D cells. This feature, joint with a Fratar‐type operation at zonal level within a sector, gives a better performance to this model than either of the two types of the models alone. The performance of the hybrid model is contrasted with a neural network model, and shows encouraging results in a real case. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
770.
The maximum approximate composite marginal likelihood (MACML) estimation of multinomial probit-based unordered response choice models 总被引:1,自引:0,他引:1
Chandra R. Bhat 《Transportation Research Part B: Methodological》2011,45(7):923-939
The likelihood functions of multinomial probit (MNP)-based choice models entail the evaluation of analytically-intractable integrals. As a result, such models are usually estimated using maximum simulated likelihood (MSL) techniques. Unfortunately, for many practical situations, the computational cost to ensure good asymptotic MSL estimator properties can be prohibitive and practically infeasible as the number of dimensions of integration rises. In this paper, we introduce a maximum approximate composite marginal likelihood (MACML) estimation approach for MNP models that can be applied using simple optimization software for likelihood estimation. It also represents a conceptually and pedagogically simpler procedure relative to simulation techniques, and has the advantage of substantial computational time efficiency relative to the MSL approach. The paper provides a “blueprint” for the MACML estimation for a wide variety of MNP models. 相似文献