A study on bullock carts. Part 1. Engineering analysis of the two-wheel bullock cart design

An engineering analysis of the design of two-wheel bullock carts has been carried out with the aid of a mathematical model. Non-dimensional expressions for the pull and the neck load have been developed. In the first instance, the cart is assumed to be cruising at constant velocity on a terrain with the effective coefficient of rolling friction varying over a wide range (0.001 to 0.5) and the gradient varying between +0.2 to −0.2. Subsequently, the effect of inertia force due to an acceleration parallel to the ground is studied. In the light of this analysis, two modifications to the design of the cart have been proposed and the relative merits of the current designs and the proposed designs are discussed.     

A study on bullock carts. Part 2. Experimental study of forces in a bullock cart

A strain gauge load cell with separate bridges for measurement of the pull and the bending moment in the plane containing the net neck load and pull was developed and fixed in the longitudinal member of an experimental cart. A cart fitted first with pneumatic wheels and then with steel-rimmed wooden wheels was tested on three terrains—tar road, mud road and grassy terrain. Pull vs time and moment vs time records were obtained in each test and analysed. It is found that the bullocks pull the cart rather discontinuously at the low velocities at which these carts normally operate. On the tar road and the grassy terrain, the mean static coefficient of friction is significantly higher for the cart with steelrimmed wooden wheels. The dynamic frictional resistance of the terrain for the cart with steel-rimmed wooden wheels is lower than for the cart with pneumatic wheels so long as the wheels do not dig or sink into the terrain. The fluctuation in the neck load is lower in the cart fitted with pneumatic wheels. Also, the ground-induced low-amplitude high-frequency vibratory load content in the neck load is lower in the cart with pneumatic wheels.     

Low speed vehicle passenger ejection restraint effectiveness

Current golf carts and LSV's (Low Speed Vehicles) produce a significant number of passenger ejections during sharp turns. These LSV's do not typically possess seatbelts, but do provide outboard bench seat hip restraints that also serve as handholds. However, many current restraint designs appear incapable of preventing passenger ejections due to their low height and inefficient handhold position. Alternative handhold and hip restraint designs may improve passenger safety. Accordingly, this paper examines minimum size requirements for hip restraints to prevent passenger ejection during sharp turns and evaluates the effectiveness of a handhold mounted at the center of the bench seat. In this study, a simulation of a turning cart supplies the dynamic input to a biomechanical model of an adult male seated in a golf cart. Various restraint combinations are considered, both with and without the central handhold, to determine the likelihood of passenger ejection. It is shown that only the largest restraint geometries prevent passenger ejection. Adequate hip restraints should be much larger than current designs and a central handhold should be provided. In this way, golf cart and LSV manufacturers could reduce passenger ejections and improve fleet safety by incorporating recommendations provided herein.     

Recursive annealing: A computational model for machine design

We propose a model for optimally directed conceptual design of machines in which the transformation of function to form occurs iteratively along an abstraction continuum. An algorithm called FFREADA is introduced as a computational implementation of the model. FFREADA is a grammar-based optimizing design algorithm that uses recursive simulated annealing to generate optimally directed designs. During FFREADA's design process, the mapping of function to form is accomplished using an abstraction grammar production system and a predefined library of function and form entities. FFREADA also has a random design generation mode that can be used to record data to characterize the space of design solutions. FFREADA is demonstrated by designing an idealized power supply using a variety of performance objectives. Results show the algorithm able to explore and record information about a tractably infinite design space before converging to the optimal design.     

基于一物多用思想下的儿童推车设计研究

目的基于一物多用的设计思想,发现扩大儿童推车使用功能的设计方法,以延长其生命周期和使用范围。方法通过时间和空间两个设计方向,进行设计方法总结和实践探讨。将儿童推车和儿童三轮车进行设计整合,以延长其使用时间;将儿童推车、婴儿床以及婴儿摇篮三者有机结合,以延长其使用范围。结论一物多用的设计思想能够有效延长产品的生命周期和使用范围,通过对时间和空间两个维度的设计方法进行探索,不仅为儿童推车的绿色设计提供了理论和实践支撑,而且还为其他产品的通用性设计提供了借鉴案例。     

Ejection of a rear facing,golf cart passenger

The following report details the findings of a series of experiments and simulations performed on a commercially available, shuttle style golf cart during several maneuvers involving rapid accelerations of the vehicle. It is determined that the current set of passive restraints on these types of golf carts are not adequate in preventing ejection of a rear facing passenger during rapid accelerations in the forward and lateral directions. Experimental data and simulations show that a hip restraint must be a minimum of 13 in. above the seat in order to secure a rear facing passenger during sharp turns, compared to the current restraint height of 5 in. Furthermore, it is determined that a restraint directly in front of the rear facing passenger is necessary to prevent ejection. In addressing these issues, golf cart manufacturers could greatly reduce the likelihood of injury due to ejection of a rear facing, golf cart passenger.     

Graphical and computer-aided approaches to plan experiments

Design of experiments is a quality technology to achieve product excellence, that is to achieve high quality at low cost. It is a tool to optimize product and process designs, to accelerate the development cycle, to reduce development costs, to improve the transition of products from R & D to manufacturing and to troubleshoot manufacturing problems effectively. It has been successfully, but sporadically, used in the United States. More recently, it has been identified as a major technological reason for the success of Japan in producing high-quality products at low cost. In the United States, the need for increased competitiveness and the emphasis on quality improvement demands a widespread use of design of experiments by engineers, scientists and quality professionals. In the past, such widespread use has been hampered by a lack of proper training and a lack of availability of tools to easily implement design of experiments in industry. Three steps are essential, and are being taken, to change this situation dramatically. First, simple graphical methods, to design and analyse experiments, need to be developed, particularly when the necessary microcomputer resources are not available. Secondly, engineers, scientists and quality professionals must have access to microcomputer-based software for design and analysis of experiments.¹ Availability of such software would allow users to concentrate on the important scientific and engineering aspects of the problem by computerizing the necessary statistical expertise. Finally, since a majority of the current workforce is expected to be working in the year 2000, a massive training effort, based upon simple graphical methods and appropriate computer software, is necessary.² The purpose of this paper is to describe a methodology based upon a new graphical method called interaction graphs and other previously known techniques, to simplify the correct design of practically important fractional factorial experiments. The essential problem in designing a fractional factorial experiment is first stated. The interaction graph for a 16-trial fractional factorial design is given to illustrate how the graphical procedure can be easily used to design a two-level fractional factorial experiment. Other previously known techniques are described to easily modify the two-level fractional factorial designs to create mixed multi-level designs. Interaction graphs for other practically useful fractional factorial designs are provided. A computer package called CADE (computer aided design of experiments), which automatically generates the appropriate fractional factorial designs based upon user specifications of factors, levels and interactions and conducts complete analyses of the designed experiments is briefly described.¹ Finally, the graphical method is compared with other available methods for designing fractional factorial experiments.     

Concurrent manual-order-picking warehouse design: a simulation-based design of experiments approach

The design of manual-order-picking warehouses is a combination of interdependent decisions with enormous possible varieties in design components. The strong interrelationship between these components, in addition to the dynamic and interconnected stochastic nature of the problem; necessitate the utilisation of a simultaneous simulation-based approach. This study proposes a concurrent simulation-based design of experiments approach for the design of manual-order-picking warehouses. The proposed approach can investigate all possible warehousing design combinations with their stochastic nature and interactions; hence, widening the search for performance improvement. The examined design components include warehouse throughput, size, layout, operational policies and manpower/carts. Furthermore, the presented approach captures the probabilistic nature of all the key warehouse functions of receiving, unloading, put away, storage, preparation and picking and shipping; and evaluates the performance of the studied designs using the cycle time for a stock keeping unit in the warehouse. Statistical analysis of the simulation results showed several interesting findings; horizontal layout was preferable over all other types of layouts and small size warehouses perform better than other large sizes. The study has also recommended using high throughput for traditional layout-small size warehouses.     

Statistically constrained economic design of the multivariate exponentially weighted moving average control chart

This paper shows that economic statistical design can provide for better statistical properties without significantly increasing optimal total costs. Cost comparisons between optimal economic statistical designs and optimal economic designs show no significant cost increases. The average run length (ARL) constraints added by economic statistical design significantly improve the statistical properties of the control chart scheme. False alarm frequency is limited while keeping good shift detection characteristics. In addition, the Multivariate Exponentially Weighted Moving Average (MEWMA) control schemes performed better from the cost standpoint than the benchmark pure statistical design—the Hotelling T² control chart. This improvement held for unconstrained and constrained designs. Finally, cost comparisons at small values of n showed significant advantage for the MEWMA schemes. Copyright © 2001 John Wiley & Sons, Ltd.     

Applied Statistics: Analysis of Variance and Regression

A new robust criterion for experimental designs is proposed. For a given design, the criterion is to minimize, over all possible run orders, the absolute value of the change of the variance function due to possible correlation between the observations. The resulting design is robust against possible auto-correlation among the observations in the sense that confidence-interval coverage levels are maintained accurately. Applications are given for 2^k factorial designs and one mixed-level fractional experiment, and robust runs are obtained. Computational strategies are also discussed, and a simulated annealing algorithm is developed to search for robust designs.     

基于STAMP的民航进餐推车人因设计

目的 为解决空乘人员因工作负荷大、工作环境颠簸易发生碰撞事故等导致患肌肉骨骼病概率逐年上涨的问题,对民航进餐推车造型设计过程进行研究。方法 确定民航进餐推车系统中的安全约束,构建基于层级模式的民航进餐推车事故风险控制—人因模型;识别控制模型中潜在的不安全控制行为,采用层次分析法对这些行为的综合权重值进行计算并排序;运用虚拟仿真软件进行人因分析与设计优化,得到最优方案。结果 通过民航进餐推车设计实践,验证该方法的可行性与有效性。结论 在民航进餐推车设计过程的前期,引入STAMP模型和人因工程理论,可提升空乘人员在进餐推车服务过程中的安全性与舒适性,为研制符合空乘人员行为方式的新型民航进餐推车提供新的思路。     

Construction of mixed-level supersaturated designs and comparison of their performance: Application to a gas chromatographic method

A supersaturated design is a design for which there are fewer runs than effects to be estimated. Although two-level supersaturated designs are becoming increasingly popular, mixed-level designs are scarcely used. Mixed-level designs are needed when the response is based on a polynomial response surface model or in situations where factors are nominal variables (with more than two modalities). The aim of this study is to explore the construction of mixed-level supersaturated designs and to evaluate their performance from the analysis of peppermint oil using a gas chromatographic method as application. This experimental setup requires the study of seven factors at two levels and five factors at three levels. Different building methods are tested from asymmetric or symmetric supersaturated designs. The mixed-level supersaturated designs obtained are compared from the point of view of a priori criteria with the aim of evaluating which criteria are better suited to judge the quality and fitness for purpose of these experimental designs. Finally, the results of the supersaturated designs are compared to the complete classical design.     

A comparison of two-level designs to estimate all main effects and two-factor interactions

We compare cost-efficient alternatives for the full factorial 2⁴ design, the regular 2^5-1 fractional factorial design, and the regular 2^6-1 fractional factorial design that can fit the model consisting of all the main effects as well as all the two-factor interactions. For 4 and 5 factors we examine orthogonal arrays with 12 and 20 runs, respectively. For 6 factors we consider orthogonal arrays with 24 as well as 28 runs. We consult complete catalogs of two-level orthogonal arrays to find the ones that provide the most efficient estimation of all the effects in the model. We compare these arrays with D-optimal designs found using a coordinate exchange algorithm. The D-optimal designs are always preferable to the most efficient orthogonal arrays for fitting the full model in all the factors.     

Design optimization using multiple dominance relations

A challenge in engineering design is to choose suitable objectives and constraints from many quantities of interest, while ensuring an optimization is both meaningful and computationally tractable. We propose an optimization formulation that can take account of more quantities of interest than existing formulations, without reducing the tractability of the problem. This formulation searches for designs that are optimal with respect to a binary relation within the set of designs that are optimal with respect to another binary relation. We then propose a method of finding such designs in a single optimization by defining an overall ranking function to use in optimizers, reducing the cost required to solve this formulation. In a design under uncertainty problem, our method obtains the most robust design that is not stochastically dominated faster than a multiobjective optimization. In a car suspension design problem, our method obtains superior designs according to a k-optimality condition than previously suggested multiobjective approaches to this problem. In an airfoil design problem, our method obtains designs closer to the true lift/drag Pareto front using the same computational budget as a multiobjective optimization.     

Sliced Rotated Sphere Packing Designs

Space-filling designs are popular choices for computer experiments. A sliced design is a design that can be partitioned into several subdesigns. We propose a new type of sliced space-filling design called sliced rotated sphere packing designs. Their full designs and subdesigns are rotated sphere packing designs. They are constructed by rescaling, rotating, translating, and extracting the points from a sliced lattice. We provide two fast algorithms to generate such designs. Furthermore, we propose a strategy to use sliced rotated sphere packing designs adaptively. Under this strategy, initial runs are uniformly distributed in the design space, follow-up runs are added by incorporating information gained from initial runs, and the combined design is space-filling for any local region. Examples are given to illustrate its potential application.     

Model-Based Sampling Design for Multivariate Geostatistics

The quality of inferences made from geostatistical data is affected significantly by the spatial locations, or design, of the sites that are sampled. A large body of published work exists on sampling design for univariate geostatistics, but not for multivariate geostatistics. This article considers multivariate spatial sampling design based on criteria targeted at classical co-kriging (prediction with known covariance parameters), estimation of covariance (including cross-covariance) parameters, and empirical co-kriging (prediction with estimated covariance parameters). Through a combination of analytical results and examples, we investigate the characteristics of optimal designs with respect to each criterion, addressing in particular the design’s degree of collocation. We also consider the robustness of the optimal design to the strength of spatial correlation and cross-correlation; the effects of smoothness and/or separability of the sampled process on the optimal design; the relationship between optimal designs for the multivariate problems considered here and univariate problems considered previously; and the efficiency of optimal collocated designs. One key finding is that optimal collocated designs are highly efficient in many cases. Supplementary materials are available online.     

儿童摇摇车安全性与舒适性的改进设计

目的提升儿童摇摇车在使用过程中的安全性和舒适性。方法通过研究摇摇车曲柄连杆机构的杆长条件、极位夹角与急回运动等影响因素,进行基于减小急回运动的安全设计;通过研究外观结构,进行摇摇车外观设计。结论减小急回运动能有效地解决摇摇车的安全隐患,通过机械设计、外观设计、儿童摇摇车的附加音乐设计等进一步提升了安全性与舒适性。     

Screening Designs for Poly-Factor Experimentation

A survey is given of the following types of screening designs: Incomplete 2 ^k designs, srlpersaturated and grollp-screening designs. These designs are compared with each other. Some new results for group-screening are derived.     

Two-Level Multifactor Designs for Detecting the Presence of Interactions

A design optimality criterion, tr (L)-optimality, is applied to the problem of designing two-level multifactor experiments to detect the presence of interactions among the controlled variables. We give rules for constructing tr (L)-optimal foldover designs and tr (L)-optimal fractional factorial designs. Some results are given on the power of these designs for testing the hypothesis that there are no two-factor interactions. Augmentation of the tr (L)-optimal designs produces designs that achieve a compromise between the criteria of D-optimality (for parameter estimation in a first-order model) and tr (L)-optimality (for detecting lack of fit). We give an example to demonstrate an application to the sensitivity analysis of a computer model.     

Three‐level and mixed‐level orthogonal arrays for lean designs

Orthogonal arrays (OA's) are widely used in design of experiments. Each OA has a specific number of rows that is fixed by the number of factors in the OA and the number of levels in each factor. In a practical application of an industrial experiment, however, because of various operational constraints it could happen that the number of runs of the experiment cannot be set exactly equal to the number of rows of an OA. In this case, a lean design can be used. A lean design is obtained by removing some specific rows and columns from the extended design matrix formed from an OA, so that the resulting sub‐matrix still allows efficient estimation of the effects of some of the factors. Tables for 2‐level lean designs are already available in the literature. In this paper, the authors will investigate 3‐level lean designs and mixed‐level lean designs, and construct tables for such designs for convenient use. Copyright © 2009 John Wiley & Sons, Ltd.