EJPAU, 2008, Volume 11, Issue 1
Agricultural Engineering

Relaxation spectrum is a very useful tool in the characterization of viscoelactic materials as the knowledge on them enables the calculation of any linear material functions such as the creep compliance, the Poisson's ratio or shear and bulk modulus. The paper deals with the problem of recovery of continuous relaxation spectrum from discrete-time noise corrupted measurements of relaxation modulus obtained in stress relaxation test. An optimal orthogonal scheme of the least-squares approximation of the spectrum of relaxation frequencies by the finite series of Laguerre functions is presented. The approach proposed allows us to reduce the primary infinite dimensional dynamic optimization problem to a static linear-quadratic programming task. The problem of relaxation spectrum identification is the practical ill-posed problem of reconstructing solution of Fredholm integral equation of the first kind from the measured data. Thus, Tikhonov regularization is used to guarantee the stability of the scheme. Generalized cross validation (GCV) is adopted for the optimal choice of the regularization parameter. The numerical realization of the scheme by using the singular value decomposition (SVD) is discussed and the resulting computer algorithm is outlined. An analysis of the model accuracy is conducted for noise measurements and the linear convergence of the approximations generated by the scheme is proved. It is also indicated that the accuracy of the spectrum approximation depends both on measurement noises and regularization parameter as well as on the proper selection of the basic orthogonal functions. The method combines effectiveness and accuracy and is general enough to cover both viscoelastic solids and liquids. Applying the scheme proposed, the relaxation spectrum of an unconfined cylindrical specimen of the beet sugar root is determined.

Utilization of multi-cutting grass is connected with multiple passes of equipment what involve deleterious effect on the growth of plants and results in decrease the productivity. A three year study was conducted on silty loam Mollic Fluvisol covered by Dactylis glomerata. The multiple passes (2, 4 and 6) were applied in comparison with untreated object. Height of plants was measured once a week and dry matter yields were established three times a year. The obtained results indicated that the regrowth of Dactylis glomerata consisted of three phases differ in their growth dynamic. The tractor traffic affected the speed of growth in adversely proportion to number of passes. However, this effect was significantly determined only during the first phase of growth. The growth moderation of Dactylis glomerata according to tractor traffic results in decrease in DM yields. DM production decreased according to an increase in number of tractor passes.

The purpose of the paper was to study the effect of the conditions of freezing and defrosting of spice vegetables on selected determinants of their quality considering the freezer storage. The studies were conducted on carrot, parsley and chive. The studied raw materials were frozen (sample weight 0.5 kg): using the method of impingement (air temperature -20°C), in a freezer (temperature -30°C) and in an ultrakryostat (temperature -70°C). Freezing in a freezer and an ultrakryostat was continued until the temperature of -20°C was reached in the thermal centre of samples. After freezing, the raw materials were stored at the temperature of -20°C for the period of three months. Defrosting was continued until the temperature of 10°C was reached in the thermal centre of the sample: in the conditions of free convention in the air, by the method of revered fluidization, and in a water bath, keeping constant temperature of the environment of 15°C. The analysis was made of the kinetics of the processes, losses of the weight of samples, and an organoleptic evaluation was made of the samples after freezer storage and defrosting. During the storage, on average every 18 days the weight and the general state of the samples were examined comparing them with the samples of fresh raw materials. The lowest weight losses of carrot in freezing (2.35%) were caused by the air chilling method, while in case of parsley it was reversed fluidization. In case of chive no change of the weight after freezing and after defrosting was observed. Carrot weight losses after defrosting were the lowest (1.59%) among the samples frozen and defrosted by impingement method. The lowest losses of the weight of parsley samples (0.04%) were caused by freezing with air chilling method and defrosting in a water bath. Vegetables frozen by the method of reversed fluidization, stored and defrosted in the air in the conditions of free convention received the highest scores in the organoleptic test and hence their quality was only slightly changed in comparison with that of the fresh state. The condition of obtaining such quality of the examined vegetables is the period of the frozen storage which should not exceed 2.5 months at the temperature of -20°C.