An efficient topology optimization method for fluid-structure problems was developed in an effort to determine the optimum flow channel route in a fuel cell bipolar plate from first principles. This study describes the derivation and solution of new mathematical equations for topology optimization combining a density-based algorithm, the interpolation method of moving asymptotes (MMA), and the incompressible Navier-Stokes equation with a term representing the chemical reaction between hydrogen and the catalyst. The present method is based on the finite element method with a newly developed reaction rate equation. In this model, a topology variable of 0 represents viscous flow, whereas a value of 1 indicates porous flow. The flow velocity and pressure were obtained from the Navier-Stokes equation and constraints and element matrices for sensitivity analyses during the optimization. MMA was utilized to calculate the optimum flow routes in the design domain. The influence of the key design parameter q and the pressure drop on the optimum topology were also investigated. The channel topology became smoother with decreasing q, and the number of channels increased with increasing pressure drop. 相似文献
This study compares the optimum designs of center pillar assembly with advanced high-strength steel (AHSS) to that of conventional
steel for crashworthiness and weight reduction in side impacts. A simplified side impact analysis method was used to simulate
the crash behavior of the center pillar assembly with efficient computing time. Thickness optimization aims to perform an
S-shaped deformation of the center pillar toward the cabin to reduce the injury level of a driver in a crash test. Center
pillar members were regarded as an assembly of parts that are fabricated with tailor-welded blanks, and the thickness of each
part was selected as a design variable. The thickness variables of parts that have significant effects on the deformation
mechanism were extracted as the main design variables for thickness optimization based on the results of a sensitivity analysis
with design of experiments. The optimization condition was constructed to induce an S-shaped deformation mode and reduce the
weight of the center pillar assembly. An optimum design was obtained after several iterations with response surface methodology
(RSM). Optimization was first performed with conventional steel and then with AHSS with the same procedure to optimize the
crashworthiness of the center pillar assembly. After thickness optimization, optimum designs were applied to the full vehicle
analysis to evaluate the validity of the optimization scheme with the simplified side impact analysis method. Then, the crashworthiness
of optimum designs with conventional steel and AHSS were compared using the full vehicle analysis. This comparison demonstrates
that AHSS can be more effectively utilized than conventional steel to obtain a lightweight design of an auto-body with enhanced
crashworthiness. 相似文献
The warm shrink fitting process is generally used to assemble automobile transmission parts (shafts/gears). However, this
process causes a deformation in the addendum and dedendum of the gear depending on the fitting interference and gear profile,
and this deformation causes additional noise and vibration between the gears. To address these problems, the warm shrink fitting
process is analyzed by considering the error in the dimensional deformation of the addendum and dedendum found when comparing
the results of a theoretical analysis and finite element analysis (FEA). A correction coefficient that reduces this error
is derived through an analysis of the difference in the cross-sectional area between the shapes used for the theoretical analysis
and that of the actual gear, and a closed-form equation to predict the dimensional deformation of the addendum and dedendum
is proposed. The FEA method is proposed to analyze the thermal-structural-thermal coupled field analysis of the warm shrink
fitting process (heating-fitting-cooling process). To verify the closed-form equation using the correction coefficient, measurements
are made of actual helical gears used in automobile transmissions. The results are in good agreement with those given by the
closed-form equation. 相似文献
A set of parametric stress analyses was carried out for two-planar tubular DKT-joints under different axial loading conditions.The analysis results were used to present general remarks on the effects of the geometrical parameters on stress concentration factors(SCFs) at the inner saddle,outer saddle,and crown positions on the central brace.Based on results of finite element(FE) analysis and through nonlinear regression analysis,a new set of SCF parametric equations was established for fatigue design purposes.An assessment study of equations was conducted against the experimental data and original SCF database.The satisfaction of acceptance criteria proposed by the UK Department of Energy(UK DoE) was also checked.Results of parametric study showed that highly remarkable differences exist between the SCF values in a multi-planar DKT-joint and the corresponding SCFs in an equivalent uni-planar KT-joint having the same geometrical properties.It can be clearly concluded from this observation that using the equations proposed for uni-planar KT-connections to compute the SCFs in multi-planar DKT-joints will lead to either considerably under-predicting or over-predicting results.Hence,it is necessary to develop SCF formulae specially designed for multi-planar DKT-joints.Good results of equation assessment according to UK DoE acceptance criteria,high values of correlation coefficients,and the satisfactory agreement between the predictions of the proposed equations and the experimental data guarantee the accuracy of the equations.Therefore,the developed equations can be reliably used for fatigue design of offshore structures. 相似文献
In order to achieve safe navigation, it is important to be able to understand and calculate the effects of an external force on the maneuvering behavior of a ship. This paper analyzes the course stability and yaw motion of a ship traveling under steady wind conditions. A course stability criterion and approximate formulae for the yaw motion in steady wind, including the aero/hydrodynamic force derivatives for the ship, are derived. To confirm the reliability of the criterion and formulae, they were used to investigate a pure car carrier in steady wind. The results of this investigation revealed that course instability appears in the head and following wind directions, mainly under the influence of aerodynamic derivatives with respect to the yaw restoring forces. However, this course instability can be reduced by applying steering control. For winds ranging from head winds to beam winds, yaw oscillation appears when the period is relatively long and the damping is small. The analytical formulae derived here can be used to gain a better understanding of ship maneuvering behavior in steady wind. 相似文献
Intensive microstructure sampling over the southern slope of the Cycladic Plateau found very weak mixing in the pycnocline, centered on a thin minimum of diapycnal diffusivity with Kρ=1.5×10−6 m2 s− 1. Below the pycnocline, Kρ increased exponentially in the bottom 200 m, reaching 1 × 10− 4 m2 s− 1 a few meters above the bottom. Near-bottom mixing was most intense where the bottom slope equaled the characteristic slope of the semi-diurnal internal tide. This suggests internal wave scattering and/or generation at the bottom, a conclusion supported by near-bottom dissipation rates increasing following rising winds and with intensifying internal waves. Several pinnacles on the slope were local mixing hotspots. Signatures included a vertical line of strong mixing in a pinnacle's wake, an hydraulic jump or lee wave over a downstream side of the summit, and a ‘beam’ sloping upward at the near-inertial characteristic slope. Because dissipation rate averages were dominated by strong turbulence, ?/νN2 > 100, the effect on Kρ of alternate mixing efficiencies proposed for this range of turbulent intensity is explored. 相似文献
Previous choice studies have proposed a way to condition the utility of each alternative in a choice set on experience with the alternatives accumulated over previous periods, defined either as a mode used or not in a most recent trip, or the mode chosen in their most recent trip and the number of similar one-way trips made during the last week. The paper found that the overall statistical performance of the mixed logit model improved significantly, suggesting that this conditioning idea has merit. Experience was treated as an exogenous influence linked to the scale of the random component, and to that extent it captures some amount of the heterogeneity in unobserved effects, purging them of potential endogeneity. The current paper continues to investigate the matter of endogeneity versus exogeneity. The proposed approach implements the control function method through the experience conditioning feature in a choice model. We develop two choice models, both using stated preference data. The paper extends the received contribution in that we allow for the endogenous variable to have an impact on the attributes through a two stage method, called the Multiple Indicator Solution, originally implemented in a different context and for a single (quality) attribute, in which stage two is the popular control function method. In the first stage, the entire utility expression associated with all observed attributes is conditioned on the prior experience with an alternative. Hence, we are capturing possible correlates associated with each and every attribute and not just one selected attribute. We find evidence of potential endogeneity. The purging exercise however, results in both statistical similarities and differences in time and cost choice elasticities and mean estimates of the value of travel time savings. We are able to identify a very practical method to correct for possible endogeneity under experience conditioning that will encourage researchers and practitioners to use such an approach in more advanced non-linear discrete choice models as a matter of routine.
ABSTRACTThe impacts of air transport on the economy arise both directly, via activity in the aviation sector; and indirectly, via increased spending and wider economic benefits associated with improved access to resources, markets, technology and economic mass. Economic activity, in turn, supports and generates demand for air transport. Despite its potential importance, the reciprocal nature of the causal relationship between air transport and economic performance has remained somewhat understudied. This paper provides a synthesis review of the channels the aviation sector interacts with regional economy. The review focuses on quantitative studies that contribute to the state-of-the-art understandings of the causality. We find that the reciprocal causal relationship is more likely to prevail in less developed economies. For more developed economies, only one direction of the causality is recognised, which runs from air transport to economic growth. Especially substantial is the effect of airline enplanement on service-related employment. The reverse direction of the relationship is, however, not as significant as believed in a causal sense within the developed world. Therefore, cautions need to be taken when applying income elasticities (such as the elasticity of air passenger demand with respect to GDP) in air travel demand forecasting, which implicitly assumes that economic growth causally leads to air traffic increment. Based on the fundamental links between air transport and economic growth, some typical imperfections and inefficiencies in aviation markets are discussed and promising avenues for future research are proposed. 相似文献