On a finite element method for dynamic contact/impact problems

This paper addresses the formulation and discrete approximation of dynamic contact/impact initial-value problems. The continuous problem is presented in the context of non-linear kinematics. Standard semi-discrete time integrators are introduced and are shown to be unsuccessful in modelling the kinematic constraints imposed on the interacting bodies during persistent contact. A procedure that bypasses the aforementioned difficulty is proposed by means of a novel variational formulation. Numerical simulations are conducted and the results are reported and discussed.     

Approach to Separate Sand from Gravel for Bed-Load Transport Calculations in Streams with Bimodal Sediment

The bed material found in gravel-bed streams is nonuniform in terms of grain size and can typically be classified as unimodal or bimodal. The latter type of sediment distribution is usually represented by two modes, one of sand size and another of gravel. For this case, the movement of one mode becomes nonlinearly influenced by the other. As a result, the presence of the two modes in a bimodal material complicates the calculation of bed-load transport rates. The present study proposes an approach to separate the calculation of bed-load transport rates for bimodal materials into two independent fractions of sand and gravel, thereby rendering the bed sediment into two unimodal components. This approach is accomplished by decoupling the two fractions through scaling the reference Shields stresses of the sand and gravel modes to match the value of the mode of unimodal materials. Consequently, the contribution of each fraction to bed load can be estimated using a suitable relation derived for unimodal materials. Laboratory and field bed-load data available in the literature are used to examine the validity of the overall approach.     

Bedload Transport in Gravel-Bed Streams with Unimodal Sediment

Bedload transport in many gravel-bed streams becomes highly complicated because of the nonuniformity of the grain size and the vertical stratification of channel bed material. A new relation for computing bedload transport rates in gravel-bed streams is proposed here. In an effort to account for the variation of the makeup of the surface material within a wide range of Shields stresses, the relation employs a two-parameter approach, one related to the material in the pavement and the other to that in the subpavement layers. The mode is used to represent the grain sizes of each layer. Available bedload transport data from gravel-bed streams with unimodal sediment are used to test the accuracy of the relation. A comparison with other bedload transport relations is also considered.     

A yield‐limited Lagrange multiplier formulation for frictional contact

An analogy with rigid plasticity is used to develop a constitutive framework for quasi‐static frictional contact between finitely deforming solids. Within this setting, a Lagrange multiplier method is used to impose a sharp distinction between stick and slip. The scope of the multipliers is limited by a constitutively defined ‘yield’ function and a finite element‐based predictor–corrector scheme is employed to efficiently determine the regions of stick and slip and the associated tractions. Selected simulations of planar quasi‐static problems are presented to validate the method and illustrate its capabilities. Copyright © 2000 John Wiley & Sons, Ltd.     

A simple finite element‐based framework for the analysis of elastic pseudo‐rigid bodies

This article advocates a general procedure for the numerical investigation of pseudo‐rigid bodies. The equations of motion for pseudo‐rigid bodies are shown to be mathematically equivalent to those corresponding to certain constant‐strain finite element approximations for general deformable continua. A straightforward algorithmic implementation is achieved in a classical finite element framework. Also, a penalty formulation is suggested for modelling contact between pseudo‐rigid bodies. Representative planar simulations using a non‐linear elastic model demonstrate the predictive capacity of the pseudo‐rigid theory, as well as the robustness of the proposed computational procedure. Copyright © 1999 John Wiley & Sons, Ltd.     

Color Degradation of Beans During Storage

Kinetics of color changes of beans (Phaseolus vulgaris) were investigated using sensory evaluation and objective colorimetric measurements during storage at elevated temperatures (25°–45°C). Whiteness parameter appeared to be accurately correlated to sensory evaluation data. It was found that browning depended strongly on the storage temperature and on the initial moisture content. An Arrhenius relationship was used to describe the effect of the temperature on the loss of quality. Both parameters indicated that the shelf life of beans may be extended by decreasing the initial moisture content of beans and by controlling storage conditions.     

Performance of growing–fattening lambs fed whole cotton seed

Effects of diets containing increasing levels of whole cotton seed (WCS) on feed intake, liveweight gain, feed conversion, feeding margin and carcass characteristics were studied. Diets contained 0, 5, 10, 15, 20 and 30% WCS and were fed ad libitum to growing lambs for 54 days. All diets were approximately isonitrogenous (163–186 g crude protein kg⁻¹ dry matter) and isocaloric (19–20 MJ gross energy kg⁻¹ of dry matter). During the first 28 days, four groups of 10 Karagouniko male lambs with initial liveweights of approximately 17·6 kg were fed diets containing 0, 5, 10 and 15% WCS and then, for the next 26 days, diets containing 0, 10, 20 and 30% WCS, respectively. Lambs fed the 15–30% WCS diet ingested about 20 mg kg liveweight⁻¹ day⁻¹ of free gossypol. At 54 days and liveweights of approximately 34·7 kg, five lambs from each treatment were slaughtered and carcass data were collected. There were significant differences in feed intake, liveweight gain, cooler shrink, rumen contents, intestinal fat and liver weight among the lambs fed these diets. Cooler shrink and intestinal fat, and perirenal fat and the combined weight of intestinal and perirenal fat, were significantly (P < 0·05) correlated. Pelleting of the WCS diets reduced the concentration of free gossypol in these diets. It was concluded that WCS was satisfactory as a feed ingredient for growing sheep and can be incorporated into ruminant diets as a source of energy and protein. No indication of gossypol toxicity was detected. © 1998 Society of Chemical Industry     

A novel three‐dimensional contact finite element based on smooth pressure interpolations

This article proposes a new three‐dimensional contact finite element which employs continuous and weakly coupled pressure interpolations on each of the interacting boundaries. The resulting formulation circumvents the geometric bias of one‐pass methods, as well as the surface locking of traditional two‐pass node‐on‐surface methods. A Lagrange multiplier implementation of the proposed element is validated for frictionless quasi‐static contact by a series of numerical simulations. Published in 2001 by John Wiley & Sons, Ltd.