The effect of the filling degree of the tumbling mill chamber on the bifurcation value of the froude number

The influence of the filling degree of the drum chamber on the bifurcation value of the Froude number in the case of self-excitation of self-oscillations of a two-fraction granular charge with a minimum swing is considered. Such a pulsating mode of the charge movement is used in the self-oscillating grinding process in a tumbling mill. The coarse fraction that simulated the milling bodies consisted of spherical particles of an incoherent granular material with a relative size in the chamber ψb=0.00733. The fine fraction, simulating the material to be ground, was cement with a relative particle size ψm≈0.092∙10-3. The value of the adopted analogue of the kinematic viscosity of the two-fraction granular loading approached the value of 10-3 m2/s. The main variable factor in experimental studies was the filling degree of the drum chamber with loading at rest κb=0.25, 0.35, and 0.45. An additional factor was the degree of filling the gaps between the spherical particles of the coarse fraction with particles of the fine fraction κb=0, 0.25, 0.5, and 1. The method of visual analysis through the transparent end wall of the chamber of transient processes of the loading behavior with a smooth change and fixation of the velocity was applied. The bifurcation minimum value of the rotation speed was recorded, at which the steady-state circulation mode of the load movement turns into a transient pulsation one with a minimum swing. A decrease in the bifurcation values of the Froude number Frb on the cylindrical surface of the chamber with an increase in κb has been established. An increase in the intensity of the decrease in Frb with an increase in κm was revealed. The recorded effect is due to an increase in the connected properties of a two-fraction loading during self-excitation of self-excited oscillations with an increase in κb and κm. The numerical values of the boundaries of the range of bifurcation values of the Froude number for a tumbling mill Frb=0.0484–1.17 have been determined. The obtained Frb range corresponds to the Reynolds value in the range Re=40–197. The maximum Frb value is obtained with coarse grinding. An increase in the likelihood of self-excitation of self-oscillations of the intra-chamber loading with a decrease in the fineness of grinding was revealed

Study Reduction of Resistance on The Flat Hull Ship of The Semi-Trimaran Model: Hull Vane Vs Stern Foil

Flat hull ships is appraised for its superiority due to the manufacturing simplicity and lower investment costs, yet the ship has its own weakness for it requires a greater resistance. As a matter of fact, a significant reduction on the resistance can be done with foil installation but it is necessary to study the optimal position of the foil installation. This study is aimed at revealing the effectiveness of the Hull Vane and Stern Foil installation in reducing the resistance experienced by the flat hull ship of the semi-trimaran model. The research was conducted by comparing the resistance experienced by the flat hull ship of the semi-trimaran model without foil, Hull vane and Stern foil installations. In addition, the disclosure of resistance experienced by each ship model was carried out by using CFD simulation. The simulation results revealed that the installation of the Hull vane and Stern foil was able to reduce the resistance experienced by the flat hull ship of the semi-trimaran model. The largest reduction occurred in Froude number 1.1, where the Hull vane installation was able to reduce resistance by 12.44% and on the ship model with Stern foil installation the resistance reduction was 5.25%. Based on the results of this CFD simulation, it can be concluded that the Hull Vane installation is more optimal in reducing resistance on the flat hull ship of the semi-trimaran model.

Interfacial Friction Prediction in a Vertical Annular Two-Phase Flow Based on Support Vector Regression Machine

Accurate prediction of interfacial friction factor is critical for calculation of pressure drop and investigation of flow mechanism of vertical annular two-phase flows. Theoretical models of interfacial friction factor based on physical insight have been developed; however, these are inconvenient in engineering practice as too many parameters need to be measured. Although many researchers have proposed various empirical correlations to improve computation efficiency, there is no generally accepted simple formula. In this study, an efficient prediction model based on support vector regression machine (SVR) is proposed. Through sensitivity analysis, five factors are determined as the input parameters to train the SVR model, relative liquid film thickness, liquid Reynolds number, gas Reynolds number, liquid Froude number and gas Froude number. The interfacial friction factor is chosen as the output parameter to check the overall performance of the model. With the help of particle swarm algorithm, the optimization process is accelerated considerably, and the optimal model is obtained through iterations. Compared with other correlations, the optimal model shows the lowest average absolute error (AAE of 0.0004), lowest maximum absolute error (MAE of 0.006), lowest root mean square error (RMSE of 0.00076) and highest correlation factor (r of 0.995). The analysis using various data in the literature demonstrates its accuracy and stability in interfacial friction prediction. In summary, the proposed machine learning model is effective and can be applied to a wider range of conditions for vertical annular two-phase flows.

A SIMPLE APPROACH TO THE STUDY OF WAVE PATTERNS

The paper revisits some pioneering work of Sir Thomas Havelock on wave patterns with particular attention focussed on his graphical method of analysis. Motivated by a desire to explore this method further using numerical methods, it is extended in a simple manner to give three-dimensional illustrations of the wave patterns of a point disturbance in deep and shallow water. All results are confined to the sub- and trans-critical regimes with some obtained very close to the critical Depth Froude Number. Some conclusions are drawn on the wave types produced when operating close to the critical speed and their decay with distance off.

EFFECTS OF MARINE CONDITION ON THE SPEED AND FUEL CONSUMPTION OF A FULLY – LOADED VLCC

Minimizing fuel consumption is a priority for ship-owners seeking to reduce their vessel costs due to sea conditions. One of the most reliable methods used to estimate fuel consumption is to identify field investigations for future voyages. The VLCC Salina was used based on daily field data collected over a proper period and year of 2014 was identified as a period of optimal performance after its periodic dry dock repair. According to verified results for Beaufort scales of 2, 3 and 4, the vessel exhibited an average speed loss of 2.2% due to wind and wave effects for a Froude number of 0.15 while its greatest speed loss was observed at angles of 30‒60° relative to its longitudinal axis. The results were finally used to develop a methodology for estimating fuel consumption of Salina and 3 other sister-ships, during future voyages, in the fleet of the National Iranian tanker company.

The influence of the layout features of the trimaran hull on its hydrodynamic resistance

В статье отражена история, состояние развития и сложившаяся тенденция применения аутригеров. Показано как сформировалась терминология по судам данного типа. В статье затронута тема влияния расположения аутригеров на гидродинамическое сопротивление тримарана. Целью работы является получение методики для нахождения гидродинамического сопротивления тримарана. Состояние данного вопроса на сегодня недостаточно изучено т.к. нет четкого ответа при какой схеме по длине и ширине судна необходимо располагать аутригеры для того, чтобы судно могло включить в себя все возможные положительные качества. На основании анализа полученных данных модельных испытаний были построены графики зависимости гидродинамического сопротивления от числа Фруда которые показывают влияние расположения аутригеров по длине и ширине относительно центрального корпуса на гидродинамическое сопротивление тримарана. Сделаны выводы о влиянии размеров аутригеров и их расположения относительно центрального корпуса тримарана на его гидродинамическое сопротивление. The article reflects the history, state of development and current trends in the use of outriggers. It is shown how the terminology for vessels of this type was formed. The article touches on the topic of the influence of the location of outriggers on the hydrodynamic resistance of the trimaran. The aim of the work is to obtain a methodology for determining the hydrodynamic resistance of a trimaran. The state of this issue has not been sufficiently studied to date, since there is no clear answer according to which scheme for the length and width of the vessel it is necessary to place outriggers so that the vessel includes all possible positive qualities. Based on the analysis of the obtained model test data, graphs of the dependence of hydrodynamic resistance on the Froude number were constructed, which show the influence of the location of outriggers along the length and width relative to the central body on the hydrodynamic resistance of the trimaran. Conclusions are drawn about the influence of the size of outriggers and their location relative to the central body of the trimaran on its hydrodynamic resistance.

Experimental study of the resistance to the movement of trimaran vessels

The aim of the work is to develop a method for finding the resistance of a trimaran ship at the initial stages of design, depending on the geometric characteristics of the central hull, outriggers and their mutual position. The program of model tests in the experimental tank is characterized. Based on the analysis of the experimentally obtained data, the graphs of the resistance dependence on the Froude number for the trimaran ship model with the fore, central and stern arrangement of outriggers are presented. A graph of the outriggers’ location influence along the vessel length on its hydrodynamic resistance is also shown. A method for calculating the hydrodynamic resistance for a trimaran vessel at the stages of research design is proposed, which is an adjustment of a single-hull vessel model tests’ recalculation classical principle. One of the developed graphs of the residual drag coefficient dependence on the relative speed according to the Froude number for various central hull geometric characteristics of the vessel, outriggers and their relative position is presented. The analysis of serial model tests made it possible to establish the dependence of the trimaran ship resistance on the geometric characteristics of the central hull and outriggers, and their relative position relative to each other in this study. The method proposed in this work will make it possible to substantiate the best layout of outriggers when solving the problem of optimizing the design elements and characteristics of a trimaran at the research design stage.

Fundamentals and Knowledge Relevant to the Drag Reduction Through Air Cavitation of Ship's Hulls

Numerous experiments with ship drag reduction by air bottom cavitation in diverse countries have exhibited very different achievements. Therefore, a paper clarifying mechanics of this drag reduction and describing the proven design algorithms is appropriate. Solutions of an ideal fluid problem existing in diverse ranges of Froude number are compared and the solutions suitable for ship drag reduction are considered in more detail. It is emphasized in this paper that a cavity locker at the trailing edge of the bottom niche (recess) assigned for the cavity is necessary to reduce the necessary air supply to the cavity and to mitigate the cavity tail pulsation resulting in a drag penalty. It is also pointed out that the bottom niche depth must allow for cavity withstanding under impact of waves in seaways. Bottom cavitation may even reduce wave-induced loads on the hull. With taking into account the above-mentioned design aspects, the energy spent on the air supply can be minimized. An algorithm of bottom design based on ideal fluid theory is also explained in the paper. Comparisons with several model test results are provided to illustrate the algorithm employment.

Effect of Cross-section Geometry on Air-Demand Ratio in High-head Conduits With Sluice Gate

When the researches on the gated conduits were examined, it was determined that the air-demand ratio changed according to the hydraulic and geometric parameters. However, no study investigated the effect of the cross-section geometry of gated conduits on the air-demand ratio. In this study, the effect of conduit cross-section geometry on the air-demand ratio was examined. Results showed that conduit cross-section geometry was an important effect on the air-demand ratio especially at 10% and 15% gate opening rates. It was seen that the effect of the conduit geometry on the air-demand ratio decreased at 20%, and greater gate opening rates. In addition, a design formula related to the gate opening rate, Froude number, hydraulic radius, and conduit length was presented for estimating the air-demand ratio.