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In the conventional sand casting process, the size of the riser is made larger than that of the cavity (product part) in order for the molten metal in the riser to solidify at a later stage than the molten metal in the cavity. In this study, a continuous heating method is developed and applied to the riser, using a cylindrical heater, to minimize the size of the riser. A mold having four cavities is designed for casting turbine housings. The height and diameter of the riser are chosen to be 80 mm and 20 mm, respectively. Solidification analysis results, using the analysis program MAGMA soft for casting simulation, showed that when the heater is implemented, the riser is the last to solidify. However, without the heater, the riser solidifies before the cavity, thus causing the riser to function improperly. Moreover, misruns are generated in the casted product if the heater is not implemented, as opposed to the case of a solid product without any defects, with the heater attached in the riser. [ABSTRACT FROM AUTHOR]

Tubular strings in oil and gas wells are the backbone and central nervous system of oil and gas drilling and production operations. Tubular mechanics in oil and gas wells is the most important applied fundamental science in petroleum and gas engineering. This paper first introduces monographs on tubular mechanics in oil and gas wells, as well as scholars engaged in investigating this field. Then the methods used in this research are explored, and basic concepts are clarified. The paper then focuses on research progress and debates about the fundamental principles of tubular mechanics in oil and gas wells, the motion states of tubular strings in oil and gas wells, the fundamental equations for dynamic analysis of the rod and pipe string in oil and gas wells, the stability of the rod and pipe string in oil and gas wells, the steady-state tension and torque in the rod and pipe strings in oil and gas wells, three-dimensional mechanical analysis of the bottom hole assembly, the drill string dynamics, casing string mechanical analysis, testing string mechanical analysis, fracturing/water injection/steam injection tubing string mechanical analysis, diagnosis and parameter optimization of the sucker rod pump system as well as energy savings, vibration of the gas production tubing string, impact vibration of the string, expansion screen pipe/casing mechanical analysis, riser string and deepwater pipeline mechanical analysis, vibration wave signal transmission in the string, wear and corrosion as well as erosion of the string, and residual strength and fatigue strength forecasts, connections mechanical analysis, strength design and verification of the string. In the end, the paper discusses key future research directions. [ABSTRACT FROM AUTHOR]

In this paper, a coupled dynamic analysis method on the drive-off of deepwater platform/riser system is proposed. The dynamic analysis model of deepwater riser is established in ABAQUS software, and the drive-off dynamic solver of deepwater platform is developed in FORTRAN language. The parameter transfer and iterative calculation between riser analysis model and platform drive-off solver are carried out by ABAQUS subroutine DISP. In an application case, the drive-off dynamics and the coupling effect of deepwater platform and riser system are discussed comprehensively. The results show that the coupling effect between the deepwater platform and riser is obvious. And the response hysteresis effect in bottom of riser during the platform drive-off is found. [ABSTRACT FROM AUTHOR]

Effects of temperature on pressure drop across a riser due to solids holdup in the riser of a circulating fluidized bed (CFB) were investigated at the atmospheric pressure condition. The bed material was a group of sorbent particles and the experimental variables included temperature, gas velocity, and solids flux in the riser. With gas velocity and solids flux held constant, the riser pressure drop decreased as temperature increased. However, temperature effects decreased with increase in gas velocity. The effects of temperature on riser pressure drop were confirmed qualitatively by the same effects on the average ratio of gravity to drag force on a single spherical particle while the particle was accelerated. The pressure drop across the riser increased almost linearly with the ratio of solids flux to gas flux at the given gas velocity. Because gas momentum per unit mass of gas transferred to solids increased, the slope of the linear relationship decreased as temperature increased. This result confirmed the validity of the concept of momentum transfer from gas to particles at high temperature, proposed at ambient temperature in the prior study. The amount of gas momentum per unit mass of gas available to carry over the solid particles was finite; thus as the solids flux increased at the given gas velocity, the gas momentum shared to the unit mass of solids decreased and the mean residence time of solids in the riser, i.e., the pressure drop across the riser increased linearly. The slope of the linear relationship was proportional to the ratio of momentum flux by gravity and buoyancy forces on solids to gas momentum per unit mass of gas by drag force transferred to solids. Correlations were proposed to predict effects of temperature on the pressure drop across the riser and the solids flux in the riser within the range of experimental conditions. [ABSTRACT FROM AUTHOR]

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Vortex-induced vibrations (VIVs) of a top tensioned riser (TTR) subjected to flows with spanwise varying directions have been simulated and studied in this paper. The riser is simplified as an Euler–Bernoulli beam and its dynamics is described using the finite element method with the Absolute Nodal Coordinate Formulation (ANCF). The hydrodynamic forces due to vortex shedding are modelled with wake oscillators attached to nodes along the riser. The model has been firstly used to simulate an experiment and acceptable model results have been obtained in comparison with the measurements. Then, the VIVs of the TTR under two flow conditions, one with uniform and the other with linearly sheared velocity, have been simulated. In both cases, the direction of the flow varies linearly along the riser. Simulation results have shown different response characteristics at small and high flow velocities with respect to the frequency, amplitude and vibrating direction of the riser. In general, at a small flow velocity where the response of the riser is dominated by the standing wave, the variation in the flow direction has a major influence on the VIV of the riser. However, when the travelling wave is predominant at a high flow velocity, the effect of the spanwise varying flow direction is insignificant. The energy transfer between the structure and flow has been studied to reveal the possible mechanism that leads to these differences in the responses of the riser at small and high flow velocities. The results of the present paper suggest that the engineering simplification of ignoring the influence of flow direction variation on VIV may only be applicable at high flow velocities when the response of the riser is dominated by the travelling wave. [Display omitted] • VIVs of a top tensioned riser subjected to flows with spanwise varying directions are studied. • Preliminary validation of the numerical model is made against the only publicly available experiment. • The influence of the spanwise varying flow direction is only significant for the standing wave dominant VIV. • The energy transfer exhibits different patterns between cells separated by nodes of the standing wave. [ABSTRACT FROM AUTHOR]

A downward pointed feed injection scheme in which the feed jets contact with the catalysts countercurrently is put forward to improve the nonuniform distribution of solids in the feed injection zone of FCC riser. The radial nonuniformity index ( RNI ) is used to quantify the nonuniformity in radial distributions of catalyst particles in the new and traditional feed injection scheme. Comparison between the two types of schemes is made. Experimental results show that the particles distribute more uniformly in the initial contact region of oil with catalysts in the downward pointed feed injection scheme. The influence region of feed spray above the nozzles shortens considerably. Based on the axial profile of RNI , the proposed scheme is divided into three subzones. The proper operating conditions and setting angle of nozzles are also given. In addition, the correlations for calculating the distributions of solids holdup and particle velocity are established through which an industrial example are predicted. [ABSTRACT FROM AUTHOR]

Two different approaches for modelling the particle-wall collisions, the frequently employed Johnson & Jackson model and the recently proposed Schneiderbauer model, were evaluated in a fluidized bed riser by comparing simulation results to experimental data over a range of fluidization velocities and solids fluxes. For the Johnson & Jackson model, it was shown that partial slip settings recommended for denser fluidization conditions (a specularity coefficient in the order of 0.1) failed to predict cluster formation at the walls at higher gas flow rates due to unrealistically large granular temperature generation in the near-wall regions. By reducing wall friction to settings approaching a free-slip condition (specularity coefficient in the order of 0.001), this problem is overcome by eliminating excessive granular temperature generation from over-predicted strain rates at the walls. However, this approach results in an overestimation of the downward velocity of the clusters at the wall in dense cases. Despite this shortcoming, predictions are remarkably accurate for most of the cases. The Schneiderbauer model, with model parameters close to recommended settings, performs similarly well for most of the cases, slightly under-predicting cluster formation at the walls in the dilute cases. Generally, it also predicts more realistic flow behaviour since it prevents dense clusters from falling rapidly at the walls. The Schneiderbauer wall friction model is therefore recommended for use in future studies of risers, since it is able to deliver reasonable results over a wider range of flow conditions than the Johnson and Jackson model, using a single set of friction parameters. Furthermore, it has the benefit of using experimentally measurable quantities as input. [ABSTRACT FROM AUTHOR]

A three-dimensional reactive gas-particle CFD model was built to study the hydrodynamics, heat transfer and cracking reaction behaviors within an industrial Fluid Catalytic Cracking (FCC) riser reactor designed to maximize propylene production. The two-fluid methodology (TFM) was used to simulate the riser hydrodynamics with solid phase properties derived from the kinetic theory of granular flows (KTGF). An 11-lump kinetic model was selected to represent the cracking reaction network in the CFD model. The selection of the kinetic model is dictated by the properties of the feedstock processed and the aim of the process which is maximizing propylene. A novel treatment of the coke component was conducted by incorporating coke into the secondary granular phase which is more realistic since carbon deposition occurs on catalyst phase. Momentum transfer, heat transfer and reaction behavior inside the riser were discussed in detail and inhomogeneity in these aspects were observed especially above the high speed injection nozzles. The numerical results of this investigation show a good agreement with the process real data on the yield distribution despite the use of a coarse grid to mesh such an industrial scale FCC riser. The methodology employed used and the results obtained should serve as guidelines for possible process redesign and optimization. [ABSTRACT FROM AUTHOR]

The effect of a hollow riser on the upper heat dissipation of 76 tons and 8 corners ingots is studied by numerical simulation in this paper. Through the simulation of the heat transfer of the traditional riser, the 1 gap riser and the 2 gaps riser ingot, this paper draws a conclusion that the solidification time of the riser part of the riser is the longest in the 2 gaps scheme, and the solidification time of the central molten steel is 31417s, which is far higher than the other two schemes. The heat flux in the riser of the 2 gaps scheme is obviously larger than the other two schemes, which slows down the advance of the solidification front. The 2 gaps scheme is stronger than the other two schemes for reducing the cooling speed of the riser line center and the shoulder joint. It is particularly significant to reduce the cooling rate of the shoulder joints, which is more conducive to expanding the angle of the solidification front and fully filling. [ABSTRACT FROM AUTHOR]

The primary constitution of stairs is the arrangement of horizontal and vertical measures known as tread and riser. This is the simplest arrangement that essentially conveys people from one level to the other with required comfort and safety. Steps are a universal symbol with multiple interpretations. They are the most generally used similes in art, philosophy and psychology. Stairs occupy a unique status in the built environment because they not only convey people, but also symbolize the psychological, spiritual and artistic aspects of human nature. The mental significance and symbolic connotations of steps are deeply rooted. Understanding the role of stairs in different spheres of human need and expression is crucial in approaching its design. The pattern of stairs is dependent on the type of materials and other related design considerations. It is one of the unique architectural entities that reflect the various facets of social, psychological, artistic, metaphysical and religious dimensions. The importance of physical activity in the rising sedentary life styles is linked to the design of building elements, especially the staircases. The advancement in technology has displaced the role of stairs into an inconsequential means of emergency escape. But the importance of physical activity in the rising sedentary lifestyle has revitalized the concept of stairs as an active building component. The mono functional approach to staircases in high-rise buildings, especially as the means of escape in emergency situations, indicates that the design of staircases as multi functional element is still under the confines of design explorations. This paper is an attempt to understand the concept of stairs not only from the evolutionary point of view, but also the associated metaphoric meanings and its emerging multi facet identity. The concept of vertical accessibility in the form of tread and riser arrangement makes stairs a timeless phenomenon. The approach to multi utility architectural elements stretches beyond physical functions and should integrate the various dimensions of space making and society. In this regard stairs are a pioneering entity that has a potential to relate to many spheres of human thinking. It is clearly evident that stairs are not bound within the confines of architecture. Their origin, utility and design have far more influential qualities that travel beyond the realms of function and symbolism. It is further discussed that in the present age stairs have become as an inspiration for physical well being. The issues involved with age based capabilities demand a certain design approach that satisfies the sensitive relation between built environments and building elements. The primary constitution of stairs is the arrangement of horizontal and vertical measures known as tread and riser. This is the simplest arrangement that essentially conveys people from one level to the other with required comfort and safety. Steps are a universal symbol with multiple interpretations. They are the most generally used similes in art, philosophy and psychology. Stairs occupy a unique status in the built environment because they not only convey people, but also symbolize the psychological, spiritual and artistic aspects of human nature. The mental significance and symbolic connotations of steps are deeply rooted. Understanding the role of stairs in different spheres of human need and expression is crucial in approaching its design. The pattern of stairs is dependent on the type of materials and other related design considerations. It is one of the unique architectural entities that reflect the various facets of social, psychological, artistic, metaphysical and religious dimensions. The importance of physical activity in the rising sedentary life styles is linked to the design of building elements, especially the staircases. The advancement in technology has displaced the role of stairs into an inconsequential means of emergency escape. But the importance of physical activity in the rising sedentary lifestyle has revitalized the concept of stairs as an active building component. The mono functional approach to staircases in high-rise buildings, especially as the means of escape in emergency situations, indicates that the design of staircases as multi functional element is still under the confines of design explorations. This paper is an attempt to understand the concept of stairs not only from the evolutionary point of view, but also the associated metaphoric meanings and its emerging multi facet identity. The concept of vertical accessibility in the form of tread and riser arrangement makes stairs a timeless phenomenon. The approach to multi utility architectural elements stretches beyond physical functions and should integrate the various dimensions of space making and society. In this regard stairs are a pioneering entity that has a potential to relate to many spheres of human thinking. It is clearly evident that stairs are not bound within the confines of architecture. Their origin, utility and design have far more influential qualities that travel beyond the realms of function and symbolism. It is further discussed that in the present age stairs have become as an inspiration for physical well being. The issues involved with age based capabilities demand a certain design approach that satisfies the sensitive relation between built environments and building elements.

Fluid catalytic cracking (FCC) is an important petroleum process to convert heavy petroleum cuts into light cuts such as gasoline and LPG. In this work, a steady state one dimensional model of FCC riser using a 4-lump kinetic model was presented. Equations for mass, momentum and energy balance were written and coded by MATLAB. The model was written based on the upward movement of catalyst particles in the riser in a cluster formation. The modeling was based on the assumption that the clusters diameters were not constant, but varies all along the riser. Using the model, product yields, temperature profile in the riser, gas and solid velocity, catalyst decay rate and change in cluster diameter along the riser were investigated. The accuracy of the model was validated by 4 industrial cases that reported in the literature. The obtained results at the end of riser showed to be in good agreement with industrial data by average percentage error of 3.12% for gasoline yield, 5.35% for coke yield and 1.81% for riser temperature. The results showed a decrease in percentage error when they were compared with the assumption of the constant cluster diameter along the riser.

This paper deals with the observer-based dynamic optimal recoil controller design of a deepwater drilling riser system subject to friction force of fluid discharge and platform heave motion. First, by using exponential and polynomial functions conjunctively, a novel nonlinear computational model of the friction force is presented. Then, a linear system model is developed to describe dynamic characteristics of the friction force. Third, by using feedforward mechanisms and internal model principle jointly, a dynamic optimal recoil control scheme is proposed for the riser, where the feedforward mechanism is designed to compensate the friction force of fluid discharge, and the internal model principle is introduced to reject platform heave motion. The conditions of existence and uniqueness of a dynamic optimal recoil controller of the riser are developed. Fourth, a friction force observer is designed to solve the physically realizable problem of the recoil controller. Simulation results show that under the observer-based dynamic optimal recoil controller, the recoil of the riser can be attenuated significantly, and zero steady state errors of the riser can be guaranteed. In addition, from the perspective of achieving steady performance of the riser, the designed dynamic optimal recoil control scheme outperforms existing linear quadratic optimal control schemes. • An exponential-polynomial type friction force model of fluid discharge is developed.. • An augmented coupling riser-tensioner recoil control system is presented. • An observer-based dynamic optimal recoil controller with feedforward is designed. • The recoil controller can guarantee a zero steady–state error of the riser system. [ABSTRACT FROM AUTHOR]

This paper deals with the recoil suppression problem of a deepwater drilling riser system via active H ∞ control using both current and delayed states. First, based on the three degrees of freedom spring-mass-damping model of the riser system, an incremental dynamic equation of the system subject to the platform heave motion and the friction force induced by drilling discharge mud and seawater is established. Then, to reject recoil movements of the riser, a delayed state feedback H ∞ controller with delayed states as well as current states is designed. The existence conditions and the design method of the delayed H ∞ recoil controllers are presented. Third, the effects of the introduced time-delays on the recoil control of the riser are analyzed, and the design of optimal artificial time-delays is formulated as the minimum value problem of a series of quintic algebraic polynomials, which are related to the weights of average response amplitudes, steady-state errors, and the control force. Lastly, simulation results are provided to demonstrate the effectiveness of delay-free and delayed H ∞ recoil control schemes for the riser. It is shown that (i) under the delayed H ∞ controllers, the recoil responses of the riser can be controlled significantly; (ii) the decay rate of the recoil response under the delay-free H ∞ controller is slightly faster than the one under the delayed H ∞ controllers. However, the former requires more control cost than the latter; (iii) compared with the delayed H ∞ controller with the existing linear quadratic optimal controller, the control cost by the former is larger than that by the latter. However, the steady-state errors of the riser under the latter are slightly smaller than that under the former; (iv) the introduced time-delays with proper size play positive role of suppressing recoil response of the system, and the corresponding delayed H ∞ controller series provide more options for recoil control of the riser., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 ISA. Published by Elsevier Ltd. All rights reserved.)

Semi-empirical models are currently the state-of-the-art industry tool for flexible cylinder vortex induced vibrations (VIV) fatigue prediction. Accurate prediction of the structural response relies entirely on the accuracy of the acquired hydrodynamic coefficient database. The construction of systematic hydrodynamic coefficient databases from rigid cylinder forced vibration experiments can be time-consuming for simple cases and intractable for multi-parametric cases. An alternative approach has been implemented in this work to improve the flexible cylinder VIV prediction by machine-learning optimal parametric hydrodynamic databases using physical experimental measurements. The methodology is applied to a straight riser in uniform flow and extended to non-straight riser configurations and non-uniform incoming flow profiles. Moreover, database inference is extended to using direct sparse sensor measurements along the structure. Specifically, a 19-dimensional parametric hydrodynamic coefficient database is obtained for: (i) straight riser in uniform flow (using sparse strain measurements), (ii) straight riser in sheared flow, and (iii) catenary riser in uniform flow with a 60 deg incidence angle between the catenary plane and the incoming flow stream. The predicted amplitude and frequency responses, using the extracted databases, are compared with observed experimental results. • Modeling flexible body VIV. • Optimally predicting riser VIV. • Learning VIV hydrodynamic coefficient databases (lift and added mass coefficients) from experimental data. • Learning VIV hydrodynamic coefficient databases (lift and added mass coefficients) using raw data from sparse sensors. • Using hydrodynamic coefficient databases (lift and added mass coefficients) to explain VIV flow-structure interaction physics. [ABSTRACT FROM AUTHOR]

[Display omitted] • Solids flow rate in riser exit F s depended on riser solids amount M s. • F s depended on elutriation rate constant. • F s for circulating fluidized bed is similar with that for batch riser. • F s decreased with increasing riser diameter D. • M s increased with D. This study was conducted to provide improved relationships on the external solids circulation rate and solids inventory in the riser of the circulating fluidized bed (CFB) through increasing the basic understanding on how the solids flow rate in the riser exit establishes. The relation between the solids inventory in the riser and the solids flow rate in the riser exit was investigated in batch elutriation and CFBs, using air as fluidizing gas at atmospheric pressure and temperature. A batchwise riser (0.1 m-i.d., 2.75 m-height) and the riser of a CFB system (0.1 m-i.d., 2.5 m-height) were used to measure the relation for different gas velocities (1.5–2.4 m/s) and groups of solids (0.064–0.201 mm in diameter, 2045–4080 kg/m3 in apparent density). The batch elutriation indicated that the amount of solids inventory in the riser determined the solids flow rate in the riser exit, increasing with the amount of the solids inventory in the riser. The solids flow rate in the exit of the riser strongly depended on the elutriation rate constant combined with the amount of the solids inventory in the riser. When the riser was same in size, the relationship on the solids flow rate in the riser exit, derived in the batch elutriation, was valid in the CFB. Relationships on the external solids circulation rate and solids inventory in the riser of the CFB were proposed based on the data from this study and the literature. It was found that the external solids circulation rate per cross-sectional area of the riser decreased with increasing the riser diameter, however, the static bed height of solids in the riser (h st,c) increased with the riser diameter. The dependency of h st,c on riser diameter was greater in the fast bed than in the bed of pneumatic conveying. [ABSTRACT FROM AUTHOR]

In the context of challenging scenarios for offshore oil exploitation, robust numerical models are necessary to predict the risers’ mechanical behavior. This work presents a model to simulate offshore risers’ dynamics using the geometrically-exact approach for beams. Expressions are derived for the hydrodynamic loads due to riser-seawater flow interaction, adopting the Morison’s equation and considering large displacements and finite rotations, including the added mass and drag contributions. The consistent linearization of the weak form of such effects was obtained, permitting the use of Newton-Raphson method to solve risers’ dynamics using an implicit time-integration scheme. The riser-seabed interaction is also considered with a model that accounts for the possibility of rolling on the seabed. A catenary riser dynamics and a vertical riser experiencing parametric resonance due to heave-imposed motion were simulated. The model showed promising behavior to deal with large nonlinearities. [ABSTRACT FROM AUTHOR]

Coincident (simultaneous) three-component particle velocity measurements performed using two laser Doppler anemometry probes at the outlet section of a 9 m high cylindrical riser are for the first time presented for dilute flow conditions. Near the blinded extension of the T-outlet a solids vortex is formed. Particle downflow along the riser wall opposite the outlet tube is observed, which is restricted to higher riser heights at higher gas flow rates. Increased velocity fluctuations are observed in the solids vortex and downflow region as well as at heights corresponding to the outlet tube. Contrary to the rest of the riser, in the downflow region time and ensemble velocity averages are not equal. Given the local bending of the streamlines, axial momentum transforms to radial and azimuthal momentum giving rise to the corresponding shear stresses. Turbulence intensity values indicate the edges of the downflow region. © 2016 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 62: 3575-3584, 2016 [ABSTRACT FROM AUTHOR]

Theoretical modelling, design and operation of circulating and interconnected fluidized beds require an accurate prediction of solids holdup in the fully developed pneumatic conveying flow regime of the riser (i.e. the upper section of the riser). Existing empirical and semi-empirical solids holdup correlations have exhibited limited accuracy and application range. In this study, an empirical correlation was developed to predict the solids holdup at the upper section of the riser in circulating and interconnected fluidized beds with an improved level of accuracy for a broad range of operating conditions and riser dimensions. The correlation is based on a group of dimensionless quantities, which are typically used to describe the hydrodynamics of gas-solids fluidized beds, taking into account gas and particle properties, riser dimensions, and solid circulation rate. The reduced solids flux phenomenon also has been considered directly by introducing a system dependent exponent in the correlation. The correlation predicted 90% of the experimental data with an average deviation of 15%. The correlation is applicable for particle Reynolds numbers between 3.7 and 366. [ABSTRACT FROM AUTHOR]

Sediment-laden runoff is the primary pollutant in many watersheds, so sediment basins are commonly used to remove sediment before it leaves the site. In fact, for construction sites such basins are often required by statute. Sediment basins are usually drained by perforated vertical risers and more recently by floating skimmers. Whereas a traditional riser discharges primarily from its lower orifices because of the higher heads that exist at greater depths, skimmers drain the cleaner water at the top of the water column, thereby increasing sediment retention. The authors have developed an alternative solid state skimmer (given the moniker "solid state" because it has no moving parts) that provides a similar skimming function, but also provides the additional benefits of varying flow rate with head and serving as its own principal spillway. The solid state skimmer is comprised of two concentric vertical risers. Columns of orifices cut into each riser act in series such that the flow into the outer riser is always dominated by flow through the uppermost wetted orifices, enabling skimming of water from a basin for the purpose of increasing sediment retention. [ABSTRACT FROM AUTHOR]

Abstract The drift-off dynamic model of deepwater drilling platform and riser coupling system was established. An analysis method on drift-off warning limits of deepwater drilling platform and riser coupling system was proposed, and a deepwater drilling platform/riser system was taken for case study. The analysis model of deepwater riser, wellhead and conductor coupling system and the drift-off dynamic model of platform were established respectively. The drift-off dynamic solver of deepwater platform was developed. The coupling dynamic characteristics and coupling effect of the deepwater drilling platform and riser system were analyzed in combination with example, and the analysis method for drift-off warning limits was described. The results show that: the riser load acting on platform plays a driving role in the platform drift-off in the initial drift-off stage, and begins to inhibit the platform drift-off gradually as the drift-off displacement increases; During the platform drift-off, the transient response speed of upper riser parameters is high, while the transient response of lower riser parameters presents an obvious hysteresis effect; As the current speed increases or water depth decreases, the drift-off warning limits of deepwater drilling platform/riser coupling system decrease and the deepwater drilling riser should be disconnected earlier. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study on vortex-induced vibration (VIV) of a vertical riser subject to uniform and linearly sheared currents. The model vertical riser tested at the MARINTEK by ExxonMobil is considered. The predicted numerical results are in good agreement with the experimental data. It is found that the dominant mode numbers, the maximum root mean square amplitudes, the dominant frequencies and the fatigue damage indices increase with the flow velocity. A standing wave response is observed for the single-mode in-line (IL) and cross-flow (CF) vibrations. Dual resonance is found to occur at most of the locations along the riser. At some locations along the riser, a third harmonic frequency component is observed in the CF response and a frequency component at the CF response frequency is found in the IL response apart from the frequency component at twice the CF response frequency. The majority of the vortex shedding shows a clear 2S pattern, whereas a 2P mode is observed near the position where the maximum vibration amplitude appears. The higher IL fatigue damage in the present study emphasises the importance of the IL fatigue damage especially in the design of low flow velocity or low mode number applications. [ABSTRACT FROM AUTHOR]

Design and scale-up of fluid catalytic cracking (FCC) riser is still largely empirical, owing to limited understanding of inherent multiphase flow in this equipment. The multiphase flow of FCC riser has therefore been extensively investigated both experimentally and computationally. The experiments have provided significant insight into gas–solid flow patterns inside cold-flow risers, but simultaneous observations on flow and performance parameters (conversion and yields) in FCC riser are rarely found in literature. Consequently, computational fluid dynamic (CFD) models of FCC riser that can simultaneously account for flow, interphase interactions, droplet vaporization and cracking kinetics have been developed. The CFD modelling of FCC riser, despite several efforts, has still remained a challenge as it requires careful consideration of governing equations and closure models. This review presents state-of-the-art in CFD modelling and experimental analysis of gas–solid hydrodynamics and reactive flow of FCC riser. The CFD models are explained in greater detail with governing equations, constitutive relations, and physical significance of all the terms. A brief review of DNS studies on cluster formation, gas–solid drag, and turbulent interactions is also presented. Impact of important closure models such as drag models, viscous stress models, boundary conditions, droplet vaporization models, and kinetic models on predictions is critically examined. The review identifies major shortcomings of current CFD models and makes detailed recommendations for future work. [ABSTRACT FROM AUTHOR]

The influence of abrupt exit (T-shaped) configuration on the riser axial pressure profile in a large-scale circulating fluidized bed (CFB) is examined. A new analysis was developed to predict the axial voidage along the length of influence in the exit region with T-shape geometry. The exit region was characterized using non-dimensional analysis of the continuum equations (balances of masses and momenta) that described multiphase flows. In addition to deceleration length due to abrupt exit, the boundary condition for the solid fraction at the top of the riser and the fully developed regions, were measured using an industrial scale circulating fluidized bed (CFB) of 0.3 m diameter and 15 m tall. The operating factors affecting the flow development in the exit region were determined for three materials of various sizes and densities in core annular and dilute regimes of the riser. Performance data were taken from statistically designed experiments over a wide range of Fr (0.5–39), Re (8–600), Ar (29–3600), load ratio (0.2–28), riser to particle diameter ratio (375–5000), and gas to solid density ratio (138–1381). A series of correlations were developed to predict the voidage at the exit of the riser and length of influence due to the exit geometry. The correlations are based on gas and solid properties, operating conditions, and riser geometry. [ABSTRACT FROM AUTHOR]

A unidirectional three-mode reduced-order model (ROM) for the lateral motion of a slender and immersed rod subjected to harmonic and axial top motion was derived from the continuum equation of motion. Simple trigonometric functions were employed as approximations for the vibration modes and projection functions in Galerkin׳s method. The non-linear character of the ROM comes from the extensibility of the rod axis and the quadratic hydrodynamic damping. The focus of this investigation is the principal Mathieu׳s instability with respect to the first vibration mode, i.e., the condition in which the top-motion frequency is twice the structural first natural frequency. Time histories of modal amplitude, as well as maps of post-critical steady-state vibration amplitudes were obtained and discussed. It is seen that, within the principal parametric instability region of the first mode, the time history corresponding to the second classic (sinusoidal) mode oscillates with dominant frequency of the first classic (sinusoidal) mode. Another finding is that, besides the principal Mathieu׳s instability region, there are also other regions of instability, but with considerably smaller amplitudes. This aspect is due to the non-linear character of the coupled system of equations that defines the ROM. [ABSTRACT FROM AUTHOR]

In this paper, simulation of jet fire in the splash zone due to 30" riser leakage are performed by 3D CFD fire modelling software KFX to study the impacts of the jet fire on people safety and platform structure. The radiation flux of jet fire caused by 20 mm and 50 mm orifices leakage and rupture are analyzed as well as the influence to escape route， living quarter， life boat， helideck，platform structure and other risers. The simulation results show that the jet fire impacting area due to 20 mm and 50 mm orifice leakage is limited because of the obstruction of platform decks and blockage. The jet fire would not impair the escape route on platform significantly, but the escalation potential of other risers should be taken into consideration. The jet fire due to riser rupture would cause impairment of the platform structure. Ignition source isolation and shut down of the riser are the effective measures to mitigate the riser rupture accident. [ABSTRACT FROM AUTHOR]

The vortex-induced vibration of two identical rigidly mounted risers in a parallel arrangement was studied using Ansys- CFX and model tests. The vortex shedding and force were recorded to determine the effect of spacing on the two-degree-of-freedom oscillation of the risers. CFX was used to study the single riser and two parallel risers in 2-8 D spacing considering the coupling effect. Because of the limited width of water channel, only three different riser spacings, 2 D, 3 D, and 4 D, were tested to validate the characteristics of the two parallel risers by comparing to the numerical simulation. The results indicate that the lift force changes significantly with the increase in spacing, and in the case of 3 D spacing, the lift force of the two parallel risers reaches the maximum. The vortex shedding of the risers in 3 D spacing shows that a variable velocity field with the same frequency as the vortex shedding is generated in the overlapped area, thus equalizing the period of drag force to that of lift force. It can be concluded that the interaction between the two parallel risers is significant when the risers are brought to a small distance between them because the trajectory of riser changes from oval to curve 8 as the spacing is increased. The phase difference of lift force between the two risers is also different as the spacing changes. [ABSTRACT FROM AUTHOR]

An experiment was performed in a deep-water basin to investigate VIV mechanisms under shear flow. Lift force, drag force, and tension response were obtained. Results show that multiple frequencies are appeared for nonuniform vortex shedding frequency and interaction between the IL and CF vibrations. Beat phenomenon is observed in time history of lift force, and decreased with the increasing riser pretension. Dominant frequencies of riser tension are consistent with the IL and CF dominant frequency, and amplitudes of the tension are not uniform. VIV is inhibited with increasing riser pretension and the dominant frequencies also increase with increasing riser tension. [ABSTRACT FROM AUTHOR]

In gas-solids risers of fast fluidization regime, the gross particle flux determined by integrating the product of the measured average particle concentration and velocity is always found several times or even larger than that measured by direct experimental methods. Based on analysis of the measurement mechanisms and a simple model for two-phase flow structure in gas-solids risers, this big unidirectional deviation is first explained in depth in this study. It is concluded that the unique two-phase flow structure (i.e. the low-velocity dense phase and high-velocity dilute phase in a gas-solids riser) and the bad coupling quality of the measured transient particle concentration and velocity during data processing lead to this big unidirectional deviation. Finally, this explanation is extended to wider multiphase flow systems and advices are proposed in measuring phase fluxes. [ABSTRACT FROM AUTHOR]

BACKGROUND The riser pattern, an abnormal blood pressure (BP) rhythm in which sleep BP exceeds awake BP, is a predictor of future stroke events. Although the riser pattern is caused by autonomic dysfunction, its significance in heart failure (HF) patients is not established. HF patients often suffered from cognitive impairment (CI), but the relationship between riser pattern and CI is not clearly understood. We tested the hypothesis that the riser pattern is associated with mild CI, a form of brain damage that could develop to dementia. METHODS We performed Mini-Mental State Examination (MMSE), ambulatory BP monitoring (ABPM), echocardiography, and blood tests in 444 HF patients just before leaving hospitals. Mild CI, a measure of cognitive function, was defined as the score <26. RESULTS The mean age of the patients was 68 ± 13 years; 61.5% were male; 22.5% were riser pattern. The MMSE score was significantly lower in the Riser group than in the Non-dipper and Dipper group (23 ± 4 vs. 25 ± 5, 26 ± 4, respectively, P < 0.01). In multivariable logistic regression analysis, a riser pattern was significantly associated with mild CI (odds ratio 2.38, 95% confidence intervals 1.29-4.42, P < 0.01) after adjusting for significant covariates. CONCLUSIONS The riser pattern was associated with mild CI in HF patients. An abnormal circadian BP rhythm in HF patients is clinically significant as a potential indicator of subclinical brain damage. [ABSTRACT FROM AUTHOR]

To describe the impact of clusters as the meso-scale structure, a cluster-structure-dependent (CSD) drag model is proposed based on stability criterion of the minimum energy dissipation consumed by drag, where the heterogeneous flow structure is characterized by the gas-rich dilute phase and the particle-rich dense phase. Under the framework of the two-fluid model, the CSD drag model is employed for the investigation of the hydrodynamics in risers with Geldart B particles. By comparisons with experimental results, the CSD drag model shows reasonable predictions. Local structural parameters including dense phase fraction, local velocities in dense and dilute phases are obtained. Meanwhile, the profiles of energy consumption by drag with local gas volume fraction are analyzed, which reveals that the direction of particles will significantly alter the distribution of energy consumption by the heterogeneous drag. [ABSTRACT FROM AUTHOR]

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Gasification in dual fluidized bed gasifiers (DFBGs) has proven itself as one of the promising technologies. In DFBGs, the bubbling fluidized bed (BFB) acting as a gasifier and a riser applied as combustor are coupled with the provision of solid transfer between them. The hydrodynamic characteristics of these reactors are very important in improving their performance and achieving better operational control. In the present study, a cold model of dual fluidized bed gasifier of configuration – riser as combustor and BFB as gasifier with loop-seal as the upper connection and L-valve as the lower connection – has been constructed. The influence of operating parameters such as fluidization velocity in the riser, aeration velocity in the L-valve as well as the inventory on the pressure drops and solid circulation rate was inspected. Results show that the pressure drop in the riser decreased with the increase of the riser velocity whereas it increased with the increase of L-valve aeration velocity. Besides, the solid circulation rate was found increasing with the increase of both riser velocity and L-valve aeration velocity. However, the increase of the riser pressure drop and solid circulation rate with the increase of L-valve aeration velocity was limited due to the excessive fluidization in L-valve which disrupted the solid flow. This was termed as the maximum L-valve aeration velocity for the stable operation. The results show that the maximum L-valve aeration velocity increased with the increase of solid circulation rate and riser velocity. Furthermore, a correlation was proposed to relate solid circulation rate to riser velocity and L-valve aeration velocity. [ABSTRACT FROM AUTHOR]

In chemical looping combustion systems, accurate measurement of the solid circulation rate (SCR) is crucial for optimising the system performance. Conventionally, the SCR is predicted using the riser total pressure drop leading to an overestimation of up to 70%. In this work, a model has been proposed for the SCR prediction using the pressure drop at the top section of the riser. The height of this top section was determined by the riser gas–solid flow characteristics, namely, the axial solid holdup profile and lateral solid flux profile. A kinematic model was developed to predict the axial solid holdup profile and the reduced solid flux model developed by Rhodes et al. (1992) was employed to predict the mass fraction of upwards flowing solids. The prediction results of the proposed model were validated against the experimental data obtained in this work and those reported in the literature, where the prediction accuracy of SCR was significantly improved (by up to 60%) with a deviation of around 15%. [ABSTRACT FROM AUTHOR]

The transport velocity (u) in an inclined fluidized-bed was investigated by varying the bed angle relative to the horizontal plane (0°-90°), the particle diameter (0.021-0.925mm), and density (1,272-4,503 kg/m). This study employed the emptying time method to determine the transport velocity. The transport velocity for the vertical fluidized- bed (u) was revealed to increase appreciably with the aspect ratio of the fluidized-bed. The transport velocity decreased as the bed angle increased. The ratio of the transport velocity to that for the vertical bed (u/u) decreased with an increase in either the bed angle or the ratio of the particle diameter (d) to the critical particle diameter (d*), i.e., the maximum particle diameter at which the sum of the interparticle adhesion forces had a dominant influence on particle entrainment. Correlations for the transport velocity according to the bed angle relative to the horizontal plane were proposed successfully, based on the experimental data. [ABSTRACT FROM AUTHOR]

Active control of axial dynamic stress response of deepwater risers with Linear Quadratic Gaussian controllers is presented in this paper. The risers are installed between the subsea wellhead and the Tension Leg Deck located in the middle of the moon-pool in the Floating Production, Drilling, Storage and Offloading unit. The inevitable heave motion of the floating hull causes a time-varying axial tension in the risers. As a result, the frequent occurrence of axial dynamic stress response of relatively large amplitude may cause fatigue damage to steel risers. This paper thus explores the possibility of using a winch to reduce axial dynamic stress response of deepwater risers. The equations of motion of actively controlled risers against waves are first established. Axial dynamic stress response of the system is then determined in terms of the complex dynamic characteristics and the pseudo-excitation method. Based on the derived formulae, the performance of the winch for reducing axial dynamic stress response of risers is numerically assessed. The investigations show that the winch not only provides great flexibility for selecting system parameters but also significantly reduces the axial dynamic stress response of risers under wave excitation. [ABSTRACT FROM AUTHOR]

The complex shape of helical impellers in centrifugal pumps increases the difficulty of investment casting. Determining means of predicting the form and location of defects in order to prevent the formation of defects is crucial to the casting process. This study employed AnyCasting to conduct flow analysis on the moulding of 17-4PH stainless steel impellers in centrifugal pumps. We identified the mechanisms underlying the formation of shrinkage defects that occur during pouring and solidification. To improve the casting process, the riser dimensions and gating system were optimised based on data obtained from mathematical modelling, which took into account the thermodynamic behaviour of the materials involved. [ABSTRACT FROM AUTHOR]

This paper presents a comparison of the results obtained from experiments and CFD studies of slug flow in a vertical riser. A series of two experimental investigations were carried out on a 6 m vertical pipe with a 0.067 m internal diameter charged with an air–silicone oil mixture. For the first set of experiments, the riser was initially full of air, and then liquid and gas flows set to liquid and gas superficial velocities = 0.05 and 0.344 m/s, respectively, electrical capacitance tomography (ECT) and wire mesh sensor (WMS) transducers were employed. In the second one, the riser was initially full of (static) liquid, and then liquid and gas flows set to liquid and gas superficial velocities = 0.05 and 0.344 m/s, respectively, only ECT was used. A characterisation of the observed slug flow regimes was carried out. This includes the evaluation of the instantaneous distribution of the phases over the pipe cross-section, the Probability Density Function (PDF) of void fraction, time series of cross-sectional void fraction, Power Spectral Density (PSD), structure velocity of the Taylor bubble, lengths of the liquid slug and Taylor bubble and void fractions in the liquid slug and Taylor bubble. The simulation results were validated both qualitatively and quantitatively against experimental data. A reasonably good agreement was observed between the results of the experiment and CFD. [ABSTRACT FROM AUTHOR]

This manuscript, based on the presentation given by one of the authors (M.P. Dudukovic) at the Technological and Engineering Forum in Pančevo, May 21 2002, summarizes the use of the computer automated radioactive particle tracking (CARPT) and gamma computed tomography (CT) in obtaining the data needed to validate the Euler-Euler based CFD simulations for solids distribution, flow pattern and mixing in a liquid-solid riser. The riser is one of the reactors considered for acid solid catalyst promoted alkylation. It is shown that CFD calculations, validated by CARPT-CT data, show promise for scale-up and design of this novel reactor type.

This paper deals with the problem of dynamic modeling and the optimal recoil control of a deepwater drilling riser system subject to the friction force of drilling fluid discharge. First, based on the whole fluid column model of the friction force and the curve fitting method, a linear exosystem model is established to describe the dynamic properties of the friction force, where the friction force of drilling fluid discharge is formulated as an output of the exosystem. Then a recoil dynamic model of the drilling riser in the event of emergency disconnection is proposed to describe the recoil response characteristics. Third, an optimal recoil control scheme with discharge feedforward compensation is developed to refrain the recoil response of the riser system. The existence and uniqueness conditions of the optimal recoil controller are derived, and the gain matrices of the controller can be obtained by solving an algebraic Riccati equation and a Sylvester equation. It is found through simulation results that the proposed optimal recoil controller with feedforward compensation can reduce recoil response of the riser system significantly. Moreover, the proposed controller outperforms the existing optimal recoil control scheme in the sense of the quadratic performance indices of the riser system. • An exosystem model of fluid discharge friction resistance on the riser is developed. • An optimal recoil control scheme with feedforward mechanisms is proposed. • The proposed scheme is effective to suppress recoil response of the riser system. [ABSTRACT FROM AUTHOR]