An effective method for comparing the turbulence intensity from LDA measurements and CFD predictions within a ship propeller jet

The mean velocity and turbulence intensity are the two main inputs to investigate the ship propeller induced seabed scouring resulting from a vessel is manoeuvring within a port where the underkeel clearances are low. More accurate data including the turbulence intensity is now available by using the laser doppler anemometry (LDA) measurement system and computational fluid dynamics (CFD) approach. Turbulence intensity has a loose definition, which is the velocity fluctuation as the root mean square (RMS) referenced to a mean flow velocity. However, the velocity fluctuation and mean velocity can be the overall value includingx, y and z directions or the value of a single component. LDA and CFD results were obtained from two different acquisition systems (Dantec LDA system and Fluent CFD package) and therefore the outputs cannot be compared directly. An effective method is proposed for comparing the turbulence intensity between the experimental measurements and the computational predictions within a ship propeller jet. The flow patterns of turbulence intensity within a ship propeller jet are presented by using the LDA measurements and CFD results from turbulence models of standard k-e, RNG k-e, realizable k–e, standard k–?, SST k–?and Reynolds stresses.

Time-averaged velocity and turbulence intensity at the initial downstream flow from a six-bladed propeller

The current study investigated the time-averaged velocity and turbulence intensity at the initial downstream flow from a six-bladed ship propeller. The six-bladed propeller provided the rapid periodical pulses of thrust in one revolution due to the blades leading to a complex downstream jet. The six-bladed propeller is popular as a boat racing propeller, but the presentation of its flow structure was rarely found in the previous studies. In this study, the experiments were carried out in a water tank to measure the time-averaged velocity and turbulence intensity by using a Laser Doppler Anemometry (LDA) system. The jet was produced by rotating the propeller at a constant speed powered by an electric motor. The maximum tangential and radial velocities of the six-bladed propeller were of 76% and 17% of the maximum axial velocity respectively. The study found that the six-bladed propeller has a lower tangential velocity, but a higher radial velocity with its own diffusing mechanism when comparing to the three-bladed propeller.

The analysis of large-scale turbulence characteristics in the Indonesian seas derived from a regional model based on the Princeton Ocean Model

Turbulence characteristics in the Indonesian seas on the horizontal scale of order of 100 km were calculated with a regional model of the Indonesian seas circulation in the area based on the Princeton Ocean Model (POM). As is well known, the POM incorporates the Mellor–Yamada turbulence closure scheme. The calculated characteristics are: twice the turbulence kinetic energy per unit mass, <i>q</i>²; the turbulence master scale, &ell;; mixing coefficients of momentum, <i>K</i>_M; and temperature and salinity, <i>K</i>_H; etc. The analyzed turbulence has been generated essentially by the shear of large-scale ocean currents and by the large-scale wind turbulence. We focused on the analysis of turbulence around important topographic features, such as the Lifamatola Sill, the North Sangihe Ridge, the Dewakang Sill, and the North and South Halmahera Sea Sills. In general, the structure of turbulence characteristics in these regions turned out to be similar. For this reason, we have carried out a detailed analysis of the Lifamatola Sill region because dynamically this region is very important and some estimates of mixing coefficients in this area are available. <br><br> Briefly, the main results are as follows. The distribution of <i>q</i>² is quite adequately reproduced by the model. To the north of the Lifamatola Sill (in the Maluku Sea) and to the south of the Sill (in the Seram Sea), large values of <i>q</i>² occur in the deep layer extending several hundred meters above the bottom. The observed increase of <i>q</i>² near the very bottom is probably due to the increase of velocity shear and the corresponding shear production of <i>q</i>² very close to the bottom. The turbulence master scale, &ell;, was found to be constant in the main depth of the ocean, while &ell; rapidly decreases close to the bottom, as one would expect. However, in deep profiles away from the sill, the effect of topography results in the &ell; structure being unreasonably complicated as one moves towards the bottom. Values of 15 to 20 × 10^&minus;4 m² s^-1 were obtained for <i>K</i>_M and <i>K</i>_H in deep water in the vicinity of the Lifamatola Sill. These estimates agree well with basin-scale averaged values of 13.3 × 10^&minus;4 m² s^-1 found diagnostically for <i>K</i>_H in the deep Banda and Seram Seas (Gordon et al., 2003) and a value of 9.0 × 10^&minus;4 m² s^-1 found diagnostically for <i>K</i>_H for the deep Banda Sea system (van Aken et al., 1988). The somewhat higher simulated values can be explained by the presence of steep topography around the sill.

Pharmaceutical applications of dynamic mechanical thermal analysis

The successful development of polymeric drug delivery and biomedical devices requires a comprehensive understanding of the viscoleastic properties of polymers as these have been shown to directly affect clinical efficacy. Dynamic mechanical thermal analysis (DMTA) is an accessible and versatile analytical technique in which an oscillating stress or strain is applied to a sample as a function of oscillatory frequency and temperature. Through cyclic application of a non-destructive stress or strain, a comprehensive understanding of the viscoelastic properties of polymers may be obtained. In this review, we provide a concise overview of the theory of DMTA and the basic instrumental/operating principles. Moreover, the application of DMTA for the characterization of solid pharmaceutical and biomedical systems has been discussed in detail. In particular we have described the potential of DMTA to measure and understand relaxation transitions and miscibility in binary and higher-order systems and describe the more recent applications of the technique for this purpose. © 2011 Elsevier B.V.

Water-compatible imprinted polymers for selective depletion of riboflavine from beverages

Artificial riboflavin receptors adapted to aqueous environments were studied for their ability to selectively extract riboflavine (Rf) from three types of beverages i.e. milk, beer and a multivitamin mixture. The basic receptor was first prepared by molecular imprinting in nonaqueous medium using a hydrogen-bond donor-acceptor-donor functional monomer (2,6-bis(acrylamido)pyridine), complementary to the imide motif of the template, riboflavin tetra-acetate as template and pentaerythritol triacrylate (PETA) as a hydrophilic cross-linking monomer. The polymer was then packed in columns and used for extraction of riboflavine from beverages. Riboflavine (Rf) was selectively removed from milk and an artificial vitamin mixture but the nonspecific binding was still significant, as judged from the binding of Rf to a control nonimprinted polymer. In order to suppress this nonspecific binding, attempts to hydrolytically hydrophilize the polymer matrix were performed. The preferred approach consisted in a controlled base hydrolysis of pendent unreacted acrylate groups, using hydroxides with differently sized counterions as reagents. This resulted in a decreased binding of Rf to both polymers, but to an equal extent implying a preferential suppression of the nonspecific contribution to the binding. The hydrophilized polymers, when subjected to beer, showed larger imprinting factors at lower phase ratios compared to the nontreated polymers and a maximum removal of 86% compared to 47% for the nonimprinted control polymer.