Innovative Energy-Saving Propulsion System for Low-Speed Biomimetic Underwater Vehicles

This article covers research on an innovative propulsion system design for a Biomimetic Unmanned Underwater Vehicle (BUUV) operating at low speeds. The experiment was conducted on a laboratory test water tunnel equipped with specialised sensor equipment to assess the Fluid-Structure Interaction (FSI) and energy consumption of two different types of propulsion systems. The experimental data contrast the undulating with the drag-based propulsion system. The additional joint in the drag-based propulsion system is intended to increase thrust and decrease energy input. The tests were conducted at a variety of fins oscillation frequencies and fluid velocities. The experiments demonstrate that, in the region of low-speed forward movement, the efficiency of the propulsion system with the additional joint is greater.

EXPERIMENTAL INVESTIGATION INTO THE EFFECTS OF REDUCED VERTICAL CENTRE OF GRAVITY OF AN ARTICULATED CONCRETE MATTRESS IN CURRENT FLOW

An articulated concrete mattress model has been utilised to investigate the effects of reduced vertical centre of gravity on the stability of a 400 series block. Experimental testing was conducted at the AMC CWC, Beauty Point. To determine the effects that a reduced centre of gravity has on stability, the 3 by 3 articulated concrete mattress model was subject to pure uniform current flow. The subsequent forces were analysed with a six degree of freedom underwater force sensor. In order to gain a range of real world scenarios, the experimental model was tested at six flow angles ranging from -15 degrees through to 60 degrees, at 15 degree increments. Additionally, five fluid velocities starting at 0.6 m/s through to 1.4 m/s, at 0.2 m/s increments were investigated. These results explain how the inversion of a 400 series block increases its hydrodynamic coefficients and subsequently decreases its stability performance in current flow. Ultimately, this study provides experimental information for the installation of 400 series articulated concrete mattresses in the inverted orientation.

Integrated Approach to Maximize Production and Improve HSE

Slugging is an ongoing flow assurance risk in some of the ADNOC Onshore production systems, leading to difficulty in operations, inefficiencies, integrity and HSE concerns. For example stagnant water increases the risk of pipeline corrosion, especially with increased levels of H2S and CO2, potentially leading to leaks, pressure rating downgrading and reduction in the overall system capacity. With more reservoirs being under different schemes of secondary and tertiary recovery (WI, WAG, EOR – CO2, etc.), slugging in wells and transfer lines is expected to continue to be a challenge for the efficient and safe production operations across the entire ADNOC Onshore. This paper summarizes an integrated approach to understand the underlying causes of slugging in an onshore production system, reviews the current slug mitigation philosophy and proposes a stepwise approach to improve performance of the system, leading to production acceleration, improved profitability, efficiency and HSE performance. The system under investigation is experiencing slugging in the Transfer Line (TL) leading to liquid surges in the first stage separator (SEP) located at the Central Facilities. The slugging in the Transfer Line is attributable to a combination of wells and terrain induced slugging, and not so much to the hydrodynamic effects of the multiphase flow. In the current slug management philosophy, the pressure (RP) recorded at the TL receiver location is used in an algebraic formula to calculate a level set-point (LSP) that, in relation to the actual oil level in the separator (SEP), is used to act on the Surge Control Valve (SCV) located at the separator inlet. When the LSP is below the actual oil level in the separator, the SCV is tripped to 30% opening. The RP signal acts as a tell-tale sign of the incoming slug. In an initial phase, the system performance is evaluated using real time data available in the Control Room and offices. The initial data driven approach is complemented by complex dynamic multiphase modeling efforts. The models are used for further insights into the system behavior under different operational conditions, with a focus on identifying a more stable operating envelope, where the effects of slugging are mitigated while the production levels are maintained or increased. The focus on this paper is on the interface between the Transfer Line (TL) and inlet separator (SEP), including the Slug Control Valve (SCV). Results indicate a more stable flow regime is achieved at higher fluid velocities in the TL, where the RM pressure is increased to 35 barg from the current 29 barg. (N.B. The 35 barg is the maximum TL operating pressure, as identified in a separate study, and limited by the current HIPPS setpoints. The corresponding increase in production capacity is up to 10,000 bopd, thus accelerating the cumulative oil by up to 3.5 MMBBl / year, and accelerating revenue by up to USD 180 MM / year). However, in the current control scheme, operation at 35 bar is limited by the SCV characteristic and control scheme. To mitigate the problem, a staggered approach is proposed. A reduction in SCV tripping frequency is expected to be achieved in the short term, by modifying the algebraic equation that govern the SCV actions. A slight increase in the B factor by 2.5% is expected to reduce the SCV tripping frequency by up to 10%. Reduction in SCV tripping frequency will further reduce the mechanical stress on the valve and associated piping, thus reducing the risk of structural damage of the system. Also, it will allow for starting to increase the fluid velocities and move towards a more stable flow regime and reduced water holdup in the pipeline (reduced corrosion risk). Additional increase in fluid velocities appears to be limited by the SCV characteristic. In the current control scheme the pressure drop across the valve becomes sizeable at higher flowrates, leading to frequent tripping. As a longer term measure, increasing the SCV capacity is expected to facilitate operation of the system at higher fluid velocities, thus reducing the slugging, mechanical stress and corrosion risk in the TL. As slugging will continue to be a challenge to safe and efficient operations across ADNOC Onshore, it is important to develop in house the ability to understand the underlying causes for such flow instabilities, identify mitigation and optimization workflows. This paper demonstrates that a combination of data driven analytics and integrated physics based modeling, carried out in an integrated approach by a mixed team of subsurface and surface engineers, can help understanding the system behavior under slugging conditions and identify opportunities to improve production system efficiency and profitability, while operating within a safer envelope.

Electromagnetohydrodynamic bioconvective flow of binary fluid containing nanoparticles and gyrotactic microorganisms through a stratified stretching sheet

Bioconvection has recently been the subject of dispute in a number of biotechnological fields that depend on fluids and their physical properties. When mixed nanofluids are subjected to heat and mass transmission, the process of bioconvection occurs. This attempt conveys the theoretical analysis of two-dimensional electrically conducting and magnetically susceptible binary fluid containing nanoparticles and gyrotactic microorganisms past a stratified stretching surface. Furthermore binary chemical reaction, thermal radiation, and activation energy are taken into assumptions. The analytical solution based on HAM has been performed. The convergence of HAM is presented with the help of figures. The present study is compared with previously published results and has established an excessive agreement which validate the present study. It is perceived that the presence and absence of an electric field influences the variations in fluid velocities due to presence of magnetic field. The micropolar constant heightens the velocity and microrotation of the fluid flow. The buoyancy parameter and bioconvection Rayleigh number diminish the velocity function while these parameters show dual impact on microrotation function. The skin friction and couple stress escalates with the increasing buoyancy ratio parameter and bioconvection Rayleigh number.

Turbulent Flow over Confined Backward-Facing Step: PIV vs. DNS

Particle Image Velocimetry measurements of the liquid velocity fields in the flow over the backward-facing step were performed in the same flow configuration as in the existing Direct Numerical Simulation (DNS). The experiment and the simulation were performed in an identical cross-section geometry with step expansion rate 2.25 and the square shape of the outlet duct at the Reynolds number in an inlet part of the section 7100. The experiment was performed in transparent test section, 1.2 m long, with 20 × 45 mm2 cross-section upstream and 45 × 45 mm2 downstream, while a domain that was three times shorter was used in the DNS. A 2D-2C PIV system with a single high-speed camera and a pulse laser was used for a series of two-dimensional measurements of the velocity field at several cross-sections from two different perspectives. Variables analyzed in the experiment are time-averaged fluid velocities, velocity RMS fluctuations and two components of the Reynolds stress tensor. The key novelty is the comparison of two very accurate approaches, PIV and DNS, in the same cross-section geometry. Comparison of the similarities, and especially the differences between the two approaches, elucidates uncertainties of both studies and answers the question on what kind of agreement is expected when two very accurate approaches are compared.

Determination of Boussinesq and Coriolis coefficients for pipelines operating with discharge connection along the path

Peculiarities of the diagrams of averaged fluid velocities in the cross-sections of pressure collecting perforated pipelines were determined on the basis of the experimental studies conducted by the authors. The most characteristic typical diagrams of averaged velocities in the pipelines cross-sections with their different design characteristics were given. A comparative analysis of the obtained diagrams with the diagrams of velocities that occur during uniform motion in pressure pipelines with solid walls was carried out. It is shown that the main difference between them occurs in the flow zones, which are located near the pipeline walls. It was explained by the connected liquid jets effect on the main flow. The degree of diagrams deformation was estimated by the value of the momentum coefficient α0 (Boussinesq coefficient) and the coefficient of kinetic energy α (Coriolis coefficient). It was determined that in the general case these coefficients will be variable in magnitude along the length of the studied pipes. Nevertheless, these coefficients are recommended to be constant in magnitude in engineering calculations. The limits of the structural characteristics of collecting perforated pipes for which this non-uniformity of the diagrams must be taken into account, and for which it can be neglected were determined on the basis of the analysis of the equation of fluid motion with a variable flow rate.

Computational Fluid Dynamics Simulation of Suspended Solids Transport in a Secondary Facultative Lagoon Used for Wastewater Treatment

The facultative lagoon hydrodynamics has been evaluated using computational fluid dynamics tools, however, little progress has been made in describing the transport of suspended solids within these systems, and their effects on fluid hydrodynamics. Traditionally, CFD models have been built using pure water. In this sense, the novelty in this study was to evaluate the influence of suspended solids transport on the hydrodynamics of an facultative lagoon. Two three-dimensional CFD models were developed, a single-phase model (pure water) and a two-phase model (water and suspended solids), for a conventional FL in Ginebra, Valle del Cauca, Colombia. Model results were compared with experimental tracer studies, displaying different tracer dispersion characteristics. Differences in the fluid velocity field were identified when suspended solids were added to the simulation. The fluid velocities in the single-phase model were greater than the fluid velocities obtained in the two-phase model, (0.127 m·s−1 and 0.115 m·s−1, respectively). Additionally, the dispersion number of each model showed that the single-phase model (0.478) exhibited a better behavior of complete mixing reactor than the two-phase model (0.403). These results can be attributed to the effect of the drag and slip forces of the solids on the velocity of the fluid. In conclusion, the fluid of FL in these models is better represented as a two-phase fluid in which the particle–fluid interactions are represented by drag and slip forces.

Counter differential rigid-rotation equilibrium of electrically non-neutral two-fluid plasma with finite pressure

We derive the two-dimensional counter-differential rotation equilibria of two-component plasmas, composed of both ion and electron ( $e^-$ ) clouds with finite temperatures, for the first time. In the equilibrium found in this study, as the density of the $e^{-}$ cloud is always larger than that of the ion cloud, the entire system is a type of non-neutral plasma. Consequently, a bell-shaped negative potential well is formed in the two-component plasma. The self-electric field is also non-uniform along the $r$ -axis. Moreover, the radii of the ion and $e^{-}$ plasmas are different. Nonetheless, the pure ion as well as $e^{-}$ plasmas exhibit corresponding rigid rotations around the plasma axis with different fluid velocities, as in a two-fluid plasma. Furthermore, the $e^{-}$ plasma rotates in the same direction as that of $\boldsymbol {E \times B}$ , whereas the ion plasma counter-rotates overall. This counter-rotation is attributed to the contribution of the diamagnetic drift of the ion plasma because of its finite pressure.

Validity domains and parametrizations for white-noise and multiscale models in turbulence and wave-turbulence interactions

<p>Geophysical fluid dynamics systems generally involve a wide range of spatio-temporal scales. Numerical representation can only simulate some of the scales. The others, at the unresolved scales of motion, must be parameterized for each type of phenomenon (wave, eddy, current), in terms of expected effects on the resolved scales. Most developments then assume that the fluid transport velocity has a time-uncorrelated noisy component with zero mean and stationary statistics. These approximations generally simplify theoretical descriptions, numerical simulations, data comparisons or more recently model error quantifications for data assimilation.</p><p>In the present work, we will discuss the applicability of such approximations through two examples: a surface oceanic current dynamics and swell refractions by surface currents.</p><p>When the time-decorrelation assumption is valid, we propose simple and tuning-free parametric models to represent the spatial correlations of the white-in-time small-scale velocity to help simulate the geophysical system of interest. These parametric models relies on turbulence space self-similarity and their statistical properties (e.g. spectral slope) can be easily estimated from observations of larger scale fluid velocities.</p><p>When the white-in-time approximation is not valid, we extend the previous parametric models to follow self-similarity properties in both time and space.</p><p>Numerical simulations will illustrate these theoretical developments along the presentation.</p>

Three-Dimensional Stability Characteristics of Finite Electrified Conducting Fluids Streaming through a Porous Medium

A novel procedure is utilized to investigate the surface waves between two finite conducting fluids streaming through a porous medium in the presence of a horizontal electric field. Normal mode analysis is applied to study two- and three-dimension disturbances cases. The quadratic dispersion equation of complex coefficients representing the system is derived and discussed. It is noted that based on appropriate data selections, the stability criteria do not depend on the medium permeability. It is found that electrical conductivities, viscosities, medium porosity, and surface tension enhance the stability of the system while the dimension and the fluid velocities decrease the stability of the system. Finally, the fluid depths have a dual role (stabilizing as well as destabilizing effects) on the system.