Static softening characteristics and static recrystallization kinetics of aluminum alloy A6082 after hot deformation

The static softening behavior of aluminum alloy A6082 was investigated by interrupted hot tests conducted on Gleeble-1500 simulator at deformation temperatures from 573 to 773 K and strain rates from 0.1 to 10 s⁻¹, with a pre-strain from 0.3 to 0.7 and variable inter-pass delay times. The offset method was applied to convert the changes in flow stress between two passes to static softening fraction. The microstructural changes were characterized by the quantitative metallography of quenched specimens. The results showed both static softening and static recrystallization curves exhibited a simple sigmoidal shape; the static softening is related to the static recrystallization in a nonlinear manner with 50% static recrystallized volume fraction corresponding to 80% static softening fraction; an increase in temperature, strain rate or pre-strain yields a decrease in the time for 50% static recrysallized volume fraction, on which the temperature has the most remarkable influence; Si and Mn additions accelerate the process of static recrystallization. Finally, the equations of static recrystallization kinetics of this alloy were developed with a good agreement between the predicted and experimental results.     

Four-degree-of-freedom course stability of an air cushion vehicle

A four-degree-of-freedom mathematical model was established to investigate the course stability of an air cushion vehicle (ACV). The forces of aerodynamic,propeller and rudder were obtained by wind tunnel experiments. A series of constrained model experiments with horizontal-planar-motion-mechanism (HPMM) were conducted to determine the hydrodynamics. The ACV's course stability was analyzed by using Hurwitz deter-mination method with differential equation of perturbation,and the four-degree-of-freedom cours...     

Research of interaction force coefficients based on model test in loading condition

It is very difficult,for the component-type ship mathematical model,to estimate the interaction force coefficients among the hull,propeller and rudder. Some coefficients such as wake fraction and flow straightening coefficient were studied from the model tests in diffierent loading conditions and the normal force of rudder was tested in captive model tests to obtain the coefficients. From these results of the tests,the flow straightening coefficients increase with the increase of trims or drafts. Similarly,...     

Improvement of collaborative optimization

This paper presents a new improved collaborative optimization (CO) model that provides solution capabilities for multiobjective multidisciplinary optimization problems. Reasons that cause computational difficulties in CO algorithm are firstly analyzed. Then a new system level objective function is advised to minimize relative value between the collaborative objective function and single disciplinary objective function. And it eliminates the effect of dimensions and magnitude orders among objectives. A new s...     

Real-time life-cycle modular design method based on game theory for jack-up

AbstractTo study an entity the entire jack-up performs as a total system with close interdependency and high level of integration of a myriad of subsystems supporting each individual function.All subsystems should be arranged in regular geometric space with clear regional division according to their respective functions.The "building block"such as arrangement makes it feasible to apply modular design method while the integration and conflicts among subsystems offer an arena for game theoretic analysis.All the contradictions between subsystems should be resolved bye the designer.Here we present a game theoretic analysis methodology,which based on the basic principles of game theory,through the establishment of matrix-mode game models to describe and analyze engineering design tasks.By using this method the optimization process in various fields of expertise can be effectively coordinated and controlled,and the parallel design patterns can be achieved to some extent.Taking account of the impact of commercial or technical activities in platform’s life cycle,time line is considered in the early stage of design process which provides more convenience for effcient upgrade and reconfiguration.Some second-hand three-legged jack-up upgrade design process is used as an example to illustrate the utility of the method.     

Identification of grinding wheel wear signature by a wavelet packet decomposition method

Grinding is known as the most complicated material removal process and the method for monitoring the grinding wheel wear has its own characteristics comparing with the approaches for detecting the wear on regular cutting tools. Research efforts were made to develop the wheel wear monitoring system due to its significance in grinding process. This paper presents a novel method for identification of grinding wheel wear signature by combination of wavelet packet decomposition (WPD) based energies. The distinctive feature of the method is that it takes advantage of the combinational information of the decomposed frequency components based on the WPD so the extracted features can be customized according to the specific monitored object to get better diagnosis effects. Experiments are researched on monitoring of grinding wheel wear states under different machining conditions. The results show that the energy ratio extracted from the measured vibration signals is consistent with the grinding wheel wear condition evaluated by experiment and the further extracted feature ratio can be used in prediction of wheel wear condition.     

Comparison of gas particle flow prediction from large eddy simulation and Reynolds-averaging Navier-Stokes modeling

In order to account for the effect of particle existence on gas-particle turbulence flow in large-eddy simulation (LES), a new gas-particle turbulent kinetic energy subgrid-scale (SGS) turbulence model is established, and the effect of particle wake is also considered in gas turbulent kinetic energy SGS turbulence model. Simulation of gas-particle turbulence flow in backward-facing step is carried out by LES using present model and by unified second-order moment (USM) model. The prediction statistical results including mean velocity and fluctuation velocity by LES using present model are in reasonable agreement with the experimental results. It is shown that present model is with higher calculating accuracy than USM model, which indicates that the turbulent kinetic energy SGS turbulence model is suitable.     

Position control for asymmetrical hydraulic cylinder system using a single on/off valve

A single on/off valve is used to carry out the position control of the asymmetrical hydraulic cylinder. The influence of the nominal flow rate on the positional accuracy of piston is investigated and the proximate formula for calculating the nominal flow rate of on/off valve is introduced. The system structure proposed in this paper could avoid cavitation and hyper pressure in two chambers to some extent. The simulation results indicated that the control method in this paper could satisfy the expected control requirements.     

Subjective well-being related to satisfaction with daily travel

Previous research demonstrates an impact on subjective well-being (SWB) of affect associated with routine performance of out-of-home activities. A primary aim of the present study is to investigate whether satisfaction with daily travel has a positive impact on SWB, either directly or indirectly through facilitating the performance of out-of-home activities. A secondary aim is to determine whether emotional-symbolic or instrumental reasons for car use results in higher satisfaction with daily travel than other travel modes. A survey of a population-based sample of 1,330 Swedish citizens included measures of car access and use, satisfaction with daily travel, satisfaction with performance of out-of-home routine activities, and affective and cognitive SWB. The results confirmed that the effect on affective and cognitive SWB of satisfaction with daily travel is both direct and indirect via satisfaction with performance of activities. Percent weekly car use had a small effect on satisfaction with daily travel and on affective SWB, although fully mediating the effect of satisfaction with performance of the activities. This suggests that car use plays a minor role for satisfaction with daily travel and its effect on SWB. This role may be larger if investigated after a forced reduced car use.     

Modelling the dynamics of bus use in a changing travel environment using panel data

Panel data offers the potential to represent the influence on travel choices of changing circumstances, past history and persistent individual differences (unobserved heterogeneity). A four-wave panel survey collected data on the travel choices of residents before and after the introduction of a new bus rapid transit service. The data shows gradual changes to bus use over the four waves, implying time was required for residents to become aware of the new service and to adapt to it. Ordered response models are estimated for bus use over the survey period. The results show that the influence of level of service (LOS) is underestimated if unobserved heterogeneity is not taken into account. The delayed response to the new service is able to be well represented by including LOS as a lagged variable. Current bus use is found to be conditioned on past bus use, but with additional influence of lagged LOS and unobserved heterogeneity. It is shown how different model specifications generate different evolution patterns with the most realistic predictions arising from a model which takes into account lagged responses to change in LOS and unobserved heterogeneity. The paper demonstrates the feasibility of developing panel data models that can be applied to forecasting the effect of interventions in the travel environment. Longer panels—encompassing periods of both stability and change—are required to support future efforts at modelling travel choice dynamics.