In the Part 1 paper, a constitutive law for the extrusion process of aqueous-based ceramic pastes was created. In the study described herein, a capillary rheometer was used to calibrate the viscosity of an alumina paste, and a single extruder system was used to conduct extrusion experiments to validate the constitutive model. It is shown that the extrusion response time and its change both depend on the amount of air in the extruder and the magnitude of the extrusion force. When the extrusion force is small, the rapid change of extrusion response time gives the extrusion dynamic an apparent quadratic response. When the extrusion force is large, the extrusion response time changes slowly, and is dominated by a first-order response. Air bubble release was observed in some of the experiments. A series of simulation and experimental studies were conducted to validate the predictive capabilities of the constitutive model for both steady-state and transient extrusion force behaviors. Good agreements between the simulation and experimental results were obtained. The experimental results demonstrate that the constitutive model is capable of capturing the characteristics of the highly nonlinear response at low extrusion forces and the air bubble release phenomenon. The numerical studies show that the decrease in the extrusion force during an air bubble release depends on the volume of the air bubble.
The elimination of hazards caused by cavitation phenomena is an important issue to be considered in the design of process equipment including flow machinery. These hazards are: cavitation erosion, efficiency decrease as well as vibration and noise. One of the most intensive and dangerous forms of cavitation is vortex cavitation that accompanies the operation of hydraulic machines in which components comprised of rotating blades are applied.
Velocity fields around cavitation vortices generated by the model of a propeller blade were experimentally studied in a cavitation tunnel. Flow images were recorded using a high-speed camera and processed using particle image velocimetry (PIV) complemented with computer-aided techniques that had been developed for the purpose of this research. These techniques included the removal of image distortions on the basis of a calibration mask, determination of instantaneous velocity distributions and removal of air-bubble traces from flow images.
Experimental studies result examples were presented in the form of velocity fields determined in the longitudinal plane as well as in three transverse planes remote from the blade. Instabilities of the cavitating vortex stream and of the local liquid-flow velocity in its surrounding were detected. The effect of the angle of attack of propeller blade on the instability of the vortex stream and the effect of the presence of the cavitating vortex kernel on the local velocities of the surrounding liquid, were determined.
Articulated towers consist of surface piercing columns pinned to sea floor and have increased applications in deep water oil exploration. Vital component is the buoyant shaft connected to sea bed through a universal joint. Design methodologies of these towers ensure reduced motion characteristics with less deck acceleration while loads at the articulated joint are kept to minimum; this is required to establish sufficient stability under working conditions. A Scaled model of a multi-legged articulated tower is experimentally investigated under regular and random waves. Influence of different parameters on the tower response, namely, deck load and wave approach angle are examined in detail. Apart from having increased deck area, multi-legged articulated towers showed controlled dynamic response behavior under environmental loads. Conclusions drawn from the study bring a detailed insight to the design of such platforms. Though few observations inferred from the study are not new, important dynamic response characteristics like bending stress variations are quantified through experimental investigations.
The paper substantiates scientific background for development of lubricant compositions used in moulds for concrete products with high-quality surface. It has been shown that consideration of interaction between air bubbles, lubricant and liquid phase of modified concrete is of great importance. A release agent must allow air to migrate to a certain extent and leave “formwork – concrete mix” interface. In this regard the lubricant must have low viscosity. In addition, the lubricant should give maximum hydrophobization to a mould and have minimal adhesion in respect of the concrete mix. Additives of hydrophobic substances in liquid lubricants significantly reduce surface porosity of products. Chemical plasticizing additives and, in particular, additives of polycarboxylate type substantially reduce surface tension of liquid sгж, thereby they significantly reduce work for fixing an air bubble on concrete surface and contribute to its ejection. In addition, adsorbed molecules of the chemical additives interfere with interaction of cement paste particles and mould surface. Polycarboxylate additive molecules diffuse from a diffuse layer of the concrete mix, fill capillaries in the lubricant film, reduce its viscosity, act as additives that regulate spreading of lubricant and facilitate removal of air bubbles in a surface layer. Experimental studies of the combined effect while using low viscosity grease based on vegetable oils and modifying additives have confirmed the above provisions. The polycarboxylate-based additive has made the greatest impact on reduction of concrete surface porosity and content of all types of pores in the concrete has been approximately at the same level.
The main objective of this research is to collect statistical information concerning momentum phase coupling between the continuous phase and a single air bubble in turbulent flow in a horizontal pipe, and to develop data that can be used for the verification of numerical modeling efforts. In comparison with vertical pipe bubble flow, horizontal bubble flow has received less attention, especially from the experimental side. Thus, an experimental investigation of bubble behaviour in a horizontal square pipe was performed. Tracking of a single bubble released in water flow in a 56.8 mm × 56.8 mm square pipe was performed to provide a basis for characterizing the behaviour of the single bubble in turbulent pipe flow. A Shack Hartman Wavefront Sensor and a High Speed Video Camera were used to collect images at various points downstream from the bubble injection point, providing information on bubble size, velocity, and spatial location as a function of Reynolds number. Velocity profile information of the continuous phase was collected using Particle Image Velocimetry (PIV) in order to perform a complete characterization of the flow. The data collected using PIV coupled with the analysis of the three-dimensional trajectory of a single bubble provides information about parameters such as a gas slippage velocity with the fluid phase and bubble distribution as a function of both Reynolds number and mean velocity profile.
In recent years, some small and midsize gas fields are being developed all over the world, and FLNG systems which include LNG FPSO and shuttle LNG tank are going to be used. In rough sea, when produced LNG is offloaded from the FPSO to the shuttle tanker, two ships will be moored. In this study, we are focusing on characteristics of FLNG systems in waves and wind. Experimental studies were performedto observe motion of two floating bodies in tandem condition in regular waves. In the tank test, we observed drastic yawing and drift motions of a shuttle LNG tanker. These phenomena might be a threatto the safety of a FLNG system. In this paper, we will reveal a cause of these phenomena and evaluate a FLNG system by using a simple method.