Effort-saving product representations in design—results of a questionnaire survey

During the last years engineers of the Munich Technical University and psychologists of the Dresden Technical University have investigated requirements for improved computer tools for designers. Prior studies of the early stages of the design process have shown that generating solutions is largely associated with the use of external representations such as sketches and physical models. In a postal survey 106 designers were consulted regarding the extent and the effects of using such external representations in the early stages of the design process. The results show the dominance of sketches as an external aid and the increasing use of CAD. The designers confirmed that external representations do not only serve as external information storages but as important external aids for, for example, solution development, testing and communication.     

Machinery-related injuries:: Regional Rural Injury Study—I (RRIS—I)

Although it is known that farm machinery is a source of serious and catastrophic farm work-related injuries, little is known about the magnitude of, and potential risk factors for, this problem. The study population is from the five-state Regional Rural Injury Study—I (RRIS—I) that included 3 939 farm households and 13 144 persons who were interviewed about their injury experience and farming operation-related exposures during 1990. Rates were calculated for sociodemographic variables and various exposures pertinent to large farm machinery (excluding tractors). Multivariate analyses were conducted using logistic regression, based on a model developed a priori and further confirmed using backward stepwise logistic regression. Among the total farming-related injury events (n=764), 151 (20%) were related to large machinery use (1 127 injured persons per 100 000 persons per year). Through multivariate analyses, several variables were associated with elevated rate ratios that were important in both models: hours worked per week on the farm (40–59, 60–79, 80+); operation of an auger; field crops as the enterprise requiring the most time; and male gender. In addition, in the backward stepwise model, certain marital status categories (married; separated/widowed/divorced) were also associated with elevated rate ratios that were important. The majority of injury events occurred while persons were lifting, pushing, or pulling (21%), adjusting a machine (20%), or repairing a machine (17%). While only 5% of the cases were hospitalized, 79% required some type of health care. Among all injured persons, 34% were restricted from regular activities for 1 week or more and 19% were restricted for 1 month or more; 25% continued to have persistent problems. In summary, the RRIS—I permitted one of the most comprehensive studies of agricultural machinery-related injuries, to date. The findings indicate that these injuries represent a significant problem, based on the relevant rates, potential risk factors, and consequences from trauma.     

An enthalpy control-volume—unstructured-mesh (cv—um) algorithm for solidification by conduction only

Recently, control volume methods have been developed for fluid flow and heat transfer on unstructured meshes. This approach has been extended here to implement the enthalpy based solidification algorithm on an unstructured mesh. A range of two-dimensional test problems are solved using triangular and quadrilateral cells (or elements). The accuracy of the CV–UM algorithms compare favourably with the structured-mesh algorithm, though the former algorithms require 1.5–3 times as much CPU as the latter. This overhead is associated with the extra work caused by the unstructuredness of the mesh; the number of sweeps to achieve convergence is roughly comparable for all algorithms. The CV–UM algorithms should perform well on complex geometry problems and, therefore, show potential to be a productive technique in casting solidification analysis.     

The use of probability in engineering design—an historical survey

The development of the use of probabilistic and statistical concepts in engineering design is traced from nineteenth-century beginnings through the period in the 1950s and 1960s when reliability engineering became established as an important component of engineering practice and onward to the present day when safety as well as reliability goals can form part of the design specification.     

Mechanics and mechanisms of delamination in a poly(ether sulphone)—Fibre composite

The interlaminar fracture behaviour of AS4/PES (poly(ether sulphone)) composite has been investigated in Mode I, Mode II and for fixed Mode I to Mode II ratios of 0·84, 1·33 and 2·13. The data obtained from these tests have been analysed using several different analytical approaches. The results obtained show that in Mode I the interlaminar crack growth in double cantilever beam (DCB) specimens is accompanied by fibre bridging behind the crack tip and by splitting at the crack tip, and in Mode II by the formation of a damage zone at the crack tip. These failure mechanisms are shown to increase the value of the interlaminar fracture energy considerably as the crack propagates through the composite, i.e. a rising ‘R-curve’ is measured. It is shown also that the value of the interlaminar fracture energy at crack initiation in Mode I, G_CI (init), increases as the length of the initial precrack is increased. The lowest G_IC (init) value obtained for the poly(ether sulphone) (PES) composite in this study is 0·8 kJm⁻², and this value was ascertained from a specimen with the precrack being grown by about 2 mm ahead of the initial crack (a₀ = 23 mm, a_p = 25 mm). The typical Mode II steady-state propagation energy, G_IIC (s/s-prop), value obtained for the specimens was about 2·0 kJm⁻². The length of the initial precrack had no significant effect on the G_IIC (init) and G_I/IIC (init) values. The Mode II tests gave values of G_IIC (init) = 1·25 kJm⁻² and of G_IIC (s/s-prop) = 1·85 kJm⁻². Finally, the failure loci for the PES composite have been constructed and theoretical expressions to describe these data considered.     

Discrete differential operators on irregular nodes (DDIN)

A previous research made an integral mathematical contribution for obtaining local function interpolation using neighboring nodal values of the solution function. Subsequent researchers developed mesh‐free methods for Finite Element Method (FEM). This principle can also be used to obtain discrete differential operators on irregular nodes. They may be successfully applied to Finite Difference method, Moving Particle Semi‐implicit (MPS) method and Random Collocation Method (RCM). In this paper, we obtain discrete differential operators on irregular nodes and successfully apply them to solve differential equations using the RCM. We also discuss mathematical aspects of the MPS method. Copyright © 2011 John Wiley & Sons, Ltd.     

具有离散参数齐次随机场的线性预测（XV）

本文进一步研究了预测问题9（N，M）及17（N，M），在频域上及时域上都求得了齐次随机场{x（m，n）}在任意点上的预测值及预测误差，从而改进了徐业基已往的结果。     

具有离散参数齐次随机场的线性预测(IV)

本文提出和研究了4个具有离散参数齐次随机场的线性预测问题;预测问题12,13,14,15。并 求出了它们的预测值与预测误差。