A lot of repeated work existed in the design of manufacturing process for similar parts, and many kinds of process knowledge which were not reused effectively contained in the historical process data. In these conditions, in order to reuse the typical process effectively and enhance design efficiency, typical process discovery was studied. The problem of typical process discovery was described firstly, the attributed directed graph was used to model the process. And the similarity between processes could be measured with the similarity between process cells and the similarity between process routes by the process model. Based on the process similarity, affinity propagation method was used to cluster the process. For the purpose of getting the effective clustering results and making sure the best number of clusters, the Silhouette index and the in-group proportion index were separately adopted in the clustering analysis. Finally, we have experimented the validity of the discovery algorithm by clustering typical process of machining process for satellite plate.
The coefficient of variation (CV) is an important quality parameter to measure the stability of the product quality. A variable two stage sampling plan based on the CV is developed in this paper when the quality characteristic follows normal distribution. The optimal plan parameters of the proposed variable two stage sampling plan are determined by minimizing the average sample number (ASN) using the two-point approach on the operating characteristic (OC) curve, and then tabulated for various combinations of acceptance quality level (AQL) and limiting quality level (LQL). The efficiency of the proposed variable two stage sampling plan is compared with the existing variable single sampling plan. The results show that the proposed plan has better performance than the single sampling plan in terms of ASN. Finally, the proposed plan is illustrated with a practical example.
In this paper we introduce a practical method to evaluate the reflectance of a layered turbid medium with a thin layer, which is not possible with the previous methods based on the diffusion theory. To this end, we employ two different reflectance models simultaneously. One is the newly improved 2-flux model for a thin layer and the other is the diffusion model for a thick layer. To combine the evaluation results from these two different models, we introduce a re-parameterization approach which makes these models compatible with each other. We verify that the proposed method yields robust performance by comparing with the Monte Carlo simulation. We also validate visual results and comparing the rendering time ours with other models.
Under growing concerns with sustainability in global and changing market, establishing a cooperative and competitive logistic is becoming a keen issue to provide manufacturing systems amenable to sales and operations planning. As a deployment for such practice, we have engaged in the various studies on logistics optimization. Especially, noticing that transportation cost and/or CO2 emission actually depend not only on distance but also loading weight (Weber basis), we have recently developed a few hybrid meta-heuristic methods for vehicle routing problems (VRP) and shown their effectiveness through numerical experiments. To the best of our knowledge, however, there exist no studies that take the Weber basis into account on VRP except for ours. As a hot interest in this area, we pay our attention on VRP with simultaneous pickup and delivery (VRPSPD). Then, this study attempts to extend the foregoing Weber basis study under single depot to multi-depot problem and intends to reveal some properties of VRPSPD. To work with such concerns, we have developed a novel hierarchical method comprised of a modified tabu search, a graph algorithm for the minimum cost flow problem and a Weber basis saving method. The proposed method is possible to solve various real world applications practically even with large problem sizes. Finally, the effectiveness of the proposed method is validated through numerical experiments taken place from various viewpoints to discuss about some peculiar features of VRPSPD.
In this study, we proposed two types of optimum trade-off charts considering mass variation for the design of a semi-active shock absorber and a passive shock absorber for landing gear. Each of these trade-off charts is formed from two curves indicating different types of data. Along one curve, the aircraft mass is constant, and shock absorbers having various dimensions are considered. Along the other curve, the aircraft mass varies from maximum to minimum values, and a specified shock absorber is considered. In order to generate optimum trade-off charts considering mass variation by means of a multi-objective optimization, we introduce a parameter related to the initial volume of gas inside the shock absorbers. We are able to establish and solve a multi-objective optimization problem and generate optimum trade-off charts considering mass variation. Using the optimum trade-off charts, we evaluate and compare the performance of semi-active and passive shock absorbers considering mass variation. It clearly demonstrates that the optimum trade-off charts are helpful in the design of landing gears for various aircrafts.
This paper presents a forecasting method for product different size production method, which is for the customers and company has different size requirement on single product design, based on multi-attribute decision making (MADM). Because of the forecast product production factor is complicated, so that first step will filter out the evaluation criteria of wheelset design through practical experiences of focus group, seven professional product designers. After filter out, the evaluation criteria are including maneuverability, manufacturability, style, creativity, and cost. We proposed to use grey number design evaluation to solve forecast product production problem, to set weights for evaluation criteria, and to takes wheelset series of product design for example to verify the method. Grey number design evaluation mainly uses grey numbers to represent the ideas of customers and designers, and then uses Grey relational analysis to find out which factor is most needed by customers and forecast needs extra production among series of product design proposal. The prediction results assisted designer to choose the best alternative from single product proposals and serialized proposals.
Sliding friction is utilized in the vehicular friction clutch to provide some slippage for smooth shifting and standing-start which is associated with some undesired issues, such as wear and heating of plates, introduction of high non-linearity and significant frictional dissipation. In order to reduce heat generation and frictional dissipation during slipping phase, a novel concept of clutched train is proposed to substitute for friction clutch. The dynamics of clutched train is modeling and integrated into powertrain to estimate the effects of clutched train on longitudinal vehicle oscillations stimulated by the sudden change of accelerator pedal. Further, the engagement control of clutched train can be transplanted from the developed control algorithm of friction clutch due to their similar control-oriented models, and the influence on longitudinal vehicle oscillations aroused by clutched train engagement is investigated. Simulation results show that it can behave like the conventional clutch and satisfy the requirement of driving comfort with certain control algorithm. Finally, the frictional dissipation of clutched train engagement is evaluated and compared with friction clutch engagement.
In the fluid film lubrication of high speed turbomachinery, bearing performance plays a significant role in the dynamics of the rotor-bearing system. In this paper, a novel foil thrust bearing using multi-decked protuberant foils as supporting structure is developed and tested. Experimental bearing test rig using gas-driven high speed turbo-expander is set up to evaluate static loading characteristics of the bearing. Static stiffness, friction torque, nominal bearing clearance and axial vibration amplitude are discussed in the transient processes. Static loading characteristic of the bearing is evaluated based on the relationship between displacement and loading force. Test results indicate that this simply configured thrust bearing has a good prospect in high speed hydrodynamic lubrication.
A novel point contact gear drive with pinion circular arc teeth and gear parabolic curve teeth is proposed based on the application of two mismatched rack cutters. The rack cutter for generating a pinion is of normal circular arc profile, and the rack cutter for generating a gear is of normal parabolic curve profile which is tangent to the circular arc of the pinion. The number of contact points can be one or two by changing the design parameter of the parabolic curve. Equations of tooth surfaces are derived based on coordinate transformation and gear geometry theory. Computer program is developed to solve the tooth surface equations and establish the solid models. To find out the advantages and disadvantages of the proposed gear drives, the gear stress distribution and the contact deformation are investigated by using the finite element analysis. Three examples of the proposed gears and circular-arc gears are present to demonstrate the influence of the profile design parameters and the contact positions on the stress distribution. The result shows that the proposed gear drives can reduce 23.8%-35.3% contact stress or 23.2%-29.5% von Mises contact stress.
Job shop scheduling with the availability of more than one machine to perform an operation, also known as the flexible job shop scheduling problem, is computationally NP-hard. An efficient scheduling method is proposed here, using a genetic algorithm that incorporates heuristic rules. The scheduler's goal is to minimize mean tardiness. There are two types of decision making required: job selection and machine selection. Combinations of five job selection and five machine selection heuristics are examined. Numerical experiments show that the combination of Yoda et al.'s (SL/RPN)+SPT rule for job selection and Eguchi et al.'s (WINQ+RPT+PT)×PT rule for machine selection provide the best performance under different shop conditions when incorporated into the genetic algorithm. It is also found that applying genetic algorithm only for either job selection or machine selection can generate good schedules, depending on conditions.
With extensive application of foil gas journal bearings in high temperature conditions, the effect of increasing temperature on performance in the bearings have attracted more attention. High temperature can result in significant effects on static and dynamic characteristics and stability in foil gas journal bearings. In-depth understanding about thermal performance of foil bearings is in favor of structural optimization and developing more advanced foil bearings. This paper presents a short introduction about operational mechanisms and advantages of foil gas journal bearings firstly. Then, many works concerning thermal effects in foil gas journal bearings are detailedly reviewed. The problems that need to be improved or developed in the study of thermal effects of foil bearings are also presented, that is, accuracy and reliability of thermal predicting model, cooling methods and details of bearings and solid lubricant coatings which can be applied to a more wide temperature range.
Low back pain is a major medical problem frequently encountered in the field of occupational health, and lumber support belts are often used for the prevention and treatment of low back pain. This study investigated the effect of width (60, 90, 120, and 150 mm) and thickness (1, 2, 3, and 4 layers) of lumber support belts on the physical workload of the low back in order to optimize these lumber support belt parameters and thus minimize workload. Subjects performed a bandage-wrapping task with and without the use of a lumber support belt. The trunk segment was divided into 3 areas: the chest, abdomen, and pelvis. The chest, abdominal, and pelvic angles were measured, and the L5/S1 compression force was estimated. In addition, subjective scores of perceived abdominal discomfort and perceived difficulty of the bandage-wrapping task were measured. We found that the use of a lumber support belt during this task decreased the abdominal angle and increased the chest and pelvic angles while reducing the L5/S1 compression force. A wider lumber support belt increases compression forces, perceived discomfort, and perceived difficulty of the task, whereas a thicker lumber support belt increases perceived discomfort. Optimization results showed that a 60-mm-wide, 3-layer lumber support belt is the most effective in reducing the workload of the low back during a task involving trunk flexion.
In the present study, a human ankle joint pushing mechanism with a brace structure was developed, and the force balance relationship of the proposed system to avoid pain at sites other than the ankle joint was evaluated. The proposed system uses the brace structure to prevent the movement of the geometric arrangement of the ankle joint and the device rotational axis when pressure is applied to the foot. The results of experiments revealed that the proposed brace mechanism did not change the position of the ankle joint when a force was applied to the foot so that pain could be avoided. The proposed mechanism will be useful for developing a device for the purpose of applying large forces to the ankle joint.
A pretension design method is proposed for the cablenet system of large span cable-beam structure. This method can improve computational efficiency of pretension design under influence of beams’ deformations. In this method, cablenet system is divided into two parts-inner cablenet and edge cablenet. Inner cablenet is a pure cablenet area, its optimal pretension distribution can be easily found by using balance matrix analysis method. Edge cablenet is the other cablenet area connected with beams, and for this cablenet system, an iterative calculation combined with balance matrix analysis method and nonlinear finite element method is used to calculate its reasonable pretension distributions. In the iteration process, the shape of edge cablenet is iteratively updated according to displacements of connection joints between edge cablenet and beams, and based on these shape changes, pretension distributions of edge cablenet is recalculated iteratively. And by using this method, influence of beams’ deformations can be added to cablenet pretension design. Because above complicated iterative calculation is just limited to the edge cablenet, scale of nonlinear finite element calculation in the iteration will be much smaller than calculation for the whole cable-beam structure, and the efficiency and accuracy of this calculation can be also improved at the same time. At last, this method is programmed for a numerical example, and the results indicate that the method is feasible.
In order to solve the time-varying bending bearing capacity of orthogonal curve-face gear, we proposed the calculation and test method of bending stress of gear tooth root. Using the spatial engagement theory and gear carrying capacity theory, the parametric equations of pitch curve and pressure angle on the pitch curve of orthogonal curve-face gear were derived, and the algorithm of equivalent tooth form factor and equivalent stress correction factor was obtained. Force condition in the meshing process of orthogonal curve-face gear was analyzed. The variation of principal curvature and force of orthogonal curve-face gear was achieved. Using the simplification algorithm of regarding the orthogonal curve-face gear pair as equivalent non-circular gear rack, the calculation method of bending stress of orthogonal curve-face gear was acquired, and the impact of basic structure parameter of gear pair on bending stress was analyzed. Using five-axis CNC machining to process the entity. Experimental of orthogonal curve-face gear using strain gauges was carried out to justify the correction of the theory. Comparing the theoretical calculation and experimental results, the variation laws was similar, and then the calculation method of bending strength of orthogonal curve-face gear was verified.