Volume 29, Issue 1
February 2004, pages 1-141
pp 1-12 February 2004
In this work, a new candying procedure with partial re-use of sugar syrup is proposed. Physicochemical analysis, together with sensory evaluation, of candied celeriac samples was done. Candying was performed in a pilot unit at 65‡C, through three cycles of 5 hours duration each. Sugar syrups of 75‡ Brix were used. Effects of 1 % (m/v) citric and 1 % (m/v) ascorbic acid addition, as well as the drying of candied celeriac (60‡C for 8 h) were studied. Sugar syrup deterioration was estimated by the concentration of hydroxymethylfurfural. The results obtained showed that there were no significant(P < 0.01) differences in total dry matter and total sugar content between samples, while the increases after drying were significant(P > 0.01). Differences were observed in sugar compositions between samples. After three cycles, samples turned lighter, with decreasedL* values after drying. The celeriac from the first cycle of the ascorbic acid addition procedure was adjudged best with respect to all quality parameters. The decreased concentration of hydroxymethylfurfural confirmed that re-use of sugar syrup is possible.
pp 13-26 February 2004
Tribomechanics is a part of physics that is concerned with the study of phenomena that appear during milling under dynamic conditions. Tribomechanical micronization and activation (TMA) of whey protein concentrates (WPC) and zeolites (type clinoptilolite) were carried out. Samples of powdered WPC and zeolite were treated with the laboratory TMA equipment. The treatment was carried out at two various rotor speeds: 16,000 and 22,000 r.p.m. at ambient temperature. Analyses of the particle size and distribution as well as the specific area and scanning electron microscopy were carried out on the powdered WPC and zeolite, before and after the TMA treatment. Suspensions of the WPC and zeolite were treated with ultrasound, just before determining the particle size distribution, at 50 kHz. The results showed that tribomechanical treatment causes significant decrease in particle size, change in particle size distribution and increase in specific area of WPC and zeolite. These changes of the treated materials depend on the type of the material, the level of inserting particles, the planned angle of the impact, internal rubbing and the planned number of impacts. The effects found became stronger as the rotor speed of the TMA equipment increased (16,000 to 22,000 rpm). Ultrasonic treatment of suspension of tribomechanically treated WPC resulted infurther breakdown of partly damaged protein globules as proved with the statistic analyses. No further changes in their granulometric composition were caused by ultrasonic treatment of a suspension of tribomechanically treated zeolite.
pp 27-34 February 2004
The aim of this paper is to investigate plane waves in a thermally conducting viscous liquid half-space with thermal relaxation times. There exist three basic waves, namely; thermal wave, longitudinal wave and transverse wave in a thermally conducting viscous liquid half-space. Reflection of plane waves from the free surface of a thermally conducting viscous liquid half-space is studied. The results are obtained in terms of amplitude ratios and are compared with those without viscosity and thermal disturbances.
pp 35-56 February 2004
Experimental investigation of the 3D turbulent flow field around a 45‡ wing-wall abutment, resting on a rough rigid bed, is reported. The experiment was conducted in a laboratory flume using the Acoustic Doppler Velocimeter (ADV). Profiles of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy and Reynolds stresses at different azimuthal planes are presented. Vector plots of flow fields at azimuthal and horizontal planes show the presence of a primary vortex associated with the downflow in the upstream side of the abutment and a wake vortex on the downstream side. The shear stresses acting on the bed around the abutment are estimated from the Reynolds stresses and velocity gradients. The data presented in this study would be useful to researchers for future development and comparison of theoretical models of flow fields around bridge abutments.
pp 57-81 February 2004
The work reported in this paper is motivated by the need to develop portable parallel processing algorithms and codes which can run on a variety of hardware platforms without any modifications. The prime aim of the research work reported here is to test the portability of the parallel algorithms and also to study and understand the comparative efficiencies of three parallel algorithms developed for implicit time integration technique. The standard message passing interface (MPI) is used to develop parallel algorithms for computing nonlinear dynamic response of large structures employing implicit time-marching scheme. The parallel algorithms presented in this paper are developed under the broad framework of non-overlapped domain decomposition technique. Numerical studies indicate that the parallel algorithm devised employing the conventional form of Newmark time integration algorithm is faster than the predictor-corrector form. It is also accurate and highly adaptive to fine grain computations. The group implicit algorithm is found to be extremely superior in performance when compared to the other two parallel algorithms. This algorithm is better suited for large size problems on coarse grain environment as the resulting submeshes will obviously be large and thus permit larger time steps without losing accuracy.
pp 83-92 February 2004
The present paper is concerned with the plane strain problem in homogeneous micropolar orthotropic elastic solids. The disturbance due to time harmonic concentrated source is investigated by employing eigen-value approach. The integral transforms have been inverted by using a numerical technique to obtain the component of displacement, force stress and couple stress in the physical domain. The results of these quantities are given and illustrated graphically.
pp 93-115 February 2004
This paper presents experimental studies on buckling of cylindrical shell models under axial and transverse shear loads. Tests are carried out using an experimental facility specially designed, fabricated and installed, with provision forin-situ measurement of the initial geometric imperfections. The shell models are made by rolling and seam welding process and hence are expected to have imperfections more or less of a kind similar to that of real shell structures. The present work thus differs from most of the earlier investigations. The measured maximum imperfections δmax are of the order of ±3t (t = thickness). The buckling loads obtained experimentally are compared with the numerical buckling values obtained through finite element method (FEM). In the case of axial buckling, the imperfect geometry is obtained in four ways and in the case of transverse shear buckling, the FE modelling of imperfect geometry is done in two ways. The initial geometric imperfections affect the load carrying capacity. The load reduction is considerable in the case of axial compression and is marginal in the case of transverse shear buckling. Comparisons between experimental buckling loads under axial compression, reveal that the extent of imperfection, rather than its maximum value, in a specimen influences the failure load. Buckling tests under transverse shear are conducted with and without axial constraints. While differences in experimental loads are seen to exist between the two conditions, the numerical values are almost equal. The buckling modes are different, and the experimentally observed and numerically predicted values are in complete disagreement.
pp 117-127 February 2004
Low frequency thermal cycling tests were carried out on four types of cast iron (viz., austempered ductile iron, pearlitic ductile iron, compacted/vermicular graphite iron and grey cast iron) at predetermined ranges of thermal cycling temperatures. The specimens were unconstrained.
Results show that austempered ductile iron has the highest thermal cycling resistance, followed by pearlitic ductile iron and compacted graphite iron, while grey cast iron exhibits the lowest resistance. Microstructural analysis of test specimens subjected to thermal cycling indicates that matrix decomposition and grain growth are responsible for the reduction in hardness while graphite oxidation, de-cohesion and grain boundary separation are responsible for the reduction in the modulus of elasticity upon thermal cycling.
pp 129-141 February 2004
Conventionally, the parameters of a sliding mode controller (SMC) are selected so as to reduce the time spent in the reaching mode. Although, an upper bound on the time to reach (reaching time) the sliding surface is easily derived, performance guarantee in the state/error space needs more consideration. This paper addresses the design of constant plus proportional rate reaching law-based SMC for second-order nonlinear systems. It is shown that this controller imposes a bounding second-order error-dynamics, and thus guarantees robust performance during the reaching phase. The choice of the controller parameters based on the time to reach a desirable level of output tracking error (OTE), rather than on the reaching time is proposed. Using the Lyapunov theory, it is shown that parameter selections, based on the reaching time criterion, may need substantially larger time to achieve the OTE. Simulation results are presented for a nonlinear spring-massdamper system. It is seen that parameter selections based on the proposed OTE criterion, result in substantially quicker tracking, while using similar levels of control effort.