Dynamic Inflow Research Articles

THE ROLE OF FLUID DYNAMIC FACTOR IN HOLOCENE SAPROPEL ACCUMULATION IN THE BLACK SEA

The accumulation of the Holocene sapropelic sediments may be closely associated with the processes of hydrocarbon degassing through the bottom of the Black Sea. It is an endogenous fluid dynamic carbon-hydrogen inflow, activation that occurs periodically and with varying intensity, which explains the breaks in the accumulation of organic matter, as well as changes lithotypes of sapropelic sediments in the Black Sea. Activation of the fluid-dynamic flow occurred periodically, which explains the breaks in the accumulation of organic matter in the Black Sea sediments.

The effect of stream shading on the inflow characteristics in a downstream reservoir

AbstractIn thermally stratified reservoirs, inflows form density currents according to the interplay between inflow temperature and reservoir stratification. The temperature of inflowing water is affected by catchment properties, including shading by riparian vegetation. We hypothesize that the degree of shading in the catchment can affect the inflow dynamics in downstream reservoirs by changing inflow temperature and consequently the nature of the density current. We test it for a subtropical drinking water reservoir by combining catchment‐scale hydrological and stream temperature modeling with observations of reservoir stratification. We analyze the formation of density currents, defined as under, inter and overflow, for scenarios with contrasting shading conditions in the catchment. Inflow temperatures were simulated with the distributed water‐balance model LARSIM‐WT, which integrates heat‐balance and water temperature. River temperature measurements and simulations are in good agreement with a RMSE of 0.58°C. In simulations using the present state of shading, underflows are the most frequent flow path, 63% of the annual period. During the remaining time, river intrusion form interflows. In a scenario without stream shading, average inflow temperature increased by 2.2°C. Thus, interflows were the most frequent flow path (51%), followed by underflows (34%) and overflows (15%). With this change, we would expect a degradation of reservoir water quality, as overflows promote longer periods of anoxia and nutrient loads would be delivered to the photic zone, a potential trigger for algae blooms. This study revealed a potentially important, yet unexplored aspect of catchment management for controlling reservoir water quality.

Rapid changes in river plume dynamics caused by advected wind‐driven coastal upwelling as observed in Lake Geneva

AbstractBased on field investigations carried out in Lake Geneva during summer stratification in 2019, this study documents, for the first time, the rapid change of negatively buoyant river inflow dynamics caused by the passing of a coastal upwelling. Under calm conditions, the negatively buoyant Rhône River, entering at the eastern end of the lake, interacts with the lake density profile such that the river intrusion moves as an interflow in the thermocline layer straight out into the lake. A strong, large‐scale spatially homogeneous wind that lasts for several days causes a downward thermocline tilt at the western end of the lake, coastal downwelling on the northern shore, and coastal upwelling on the southern shore. This cold‐water upwelling progresses like a Kelvin wave around the lake after wind forcing ceases. When it arrives at the river inflow area, it homogenizes the lake water temperatures, and the river inflow transforms into an intrusion that spreads over the whole water column. Trapped by strong alongshore currents generated by the progressing coastal upwelling, the river plume is sharply deviated and flows along the shore in the nearshore zone, potentially bringing nutrients directly into the phototrophic near‐surface layer. Following the passage of the coastal upwelling, the river inflow transforms back into an interflow. This change in inflow dynamics, which is documented for five strong wind events between June and September by combining in situ measurements, remote sensing, and numerical simulation, can be expected to occur in other large lakes with comparable wind‐induced large‐scale thermocline displacement.

On the Influence of Inflow Model Selection for Time-Domain Tiltrotor Aeroelastic Analysis

The methods of using the viscous vortex particle method, dynamic inflow, and uniform inflow to conduct whirl-flutter stability analysis are evaluated on a four-bladed, soft-inplane tiltrotor model using the Rotorcraft Comprehensive Analysis System. For the first time, coupled transient simulations between comprehensive analysis and a vortex particle method inflow model are used to predict whirl-flutter stability. Resolution studies are performed for both spatial and temporal resolution in the transient solution. Stability in transient analysis is noted to be influenced by both. As the particle resolution is refined, a reduction in simulation time-step size must also be performed. An azimuthal time step size of 0.3 deg is used to consider a range of particle resolutions to understand the influence on whirl-flutter stability predictions. Comparisons are made between uniform inflow, dynamic inflow, and the vortex particle method with respect to prediction capabilities when compared to wing beam-bending frequency and damping experimental data. Challenges in assessing the most accurate inflow model are noted due to uncertainty in experimental data; however, a consistent trend of increasing damping with additional levels of fidelity in the inflow model is observed. Excellent correlation is observed between the dynamic inflow predictions and the vortex particle method predictions in which the wing is not part of the inflow model, indicating that the dynamic inflow model is adequate for capturing damping due to the induced velocity on the rotor disk. Additional damping is noted in the full vortex particle method model, with the wing included, which is attributed to either an interactional aerodynamic effect between the rotor and the wing or a more accurate representation of the unsteady loading on the wing due to induced velocities.

Evaluation of Finite-State Dynamic Inflow for Rotors

In an effort to evaluate the accuracy of the finite-state dynamic inflow of Peters and He (“Finite State Induced Flow Models Part II: Three-Dimensional Rotor Disk,” Journal of Aircraft, Vol. 32, No. 2, 1995, pp. 323–333) for use in rotor design, comparisons between dynamic inflow-based calculations and measured test data are presented for a wide variety of single rotor configurations and operating conditions. The quantities compared include rotor performance parameters, blade flap bending moments, blade airloads, and blade pitch angles. The dynamic inflow calculations are performed using the U.S. Army’s Rotorcraft Comprehensive Analysis System. Rotor performance calculations are mostly accurate prior to stall, except for rotor torque calculations from an individual blade pitch control phase sweep. Blade airloads calculations do exhibit the correct dominant features, including those from blade tip vortices, but the calculated amplitudes of the wake-induced loading are significantly less than the test data; this leads to significantly lower amplitudes in the flap bending moment response and is problematic for calculating half peak-to-peak values in conditions with significant blade–wake interactions. Blade collective and cyclic pitch angles are reasonably accurate in edgewise flight.

An Approximate Finite State Dynamic Wake Model for Predictions of Inflow below the Rotor

The velocity potential based finite state dynamic inflow model can predict inflow anywhere in the flow field once velocity potential states and costates are known. However, solution to costate equations requires backward time marching, making it incompatible for integration into real-time flight simulation. This paper explores two types of quasi-steady approximations to the costate equations, both of which eliminate the need for backward time marching. The fidelities of the resulting inflow models are assessed through comparisons of off-disk inflow predictions for an isolated rotor. Further, the implication of the inflow model approximations on the flight simulation fidelity is assessed using the coupled body/rotor/inflow dynamics model of a generic helicopter model. It is shown that, in both cases, the quasi-steady approximations to the inflow model retain simulation model fidelity at low frequencies, a typical frequency range of pilot control inputs. Notable fidelity loss is seen at high-frequency control inputs, specifically for cases where horizontal tail is operating at a higher dynamic pressure within the rotor wake.

Dynamic LVAD Inflow Cannula Obstruction Due to Mobile Thrombi

<h3>Introduction</h3> While LVAD outflow cannula obstructions are commonly described, we present a rare case of fulminant heart failure secondary to dynamic inflow cannula obstruction due to mobile thrombi within the left ventricular cavity. <h3>Case Report</h3> A 65 year old man with a history of ischemic cardiomyopathy and chronic kidney disease (CKD) underwent implantation of a continuous flow left ventricular assist device (LVAD; HeartWare™ HVAD™, Medtronic plc) as a bridge to transplantation. Three years following implantation, he presented with progressive fulminant right heart failure (RHF) followed by a sudden decrease in LVAD flow from 3.5 to 1.5 liters/min (Figure 1A). INR was 2.6, lactate dehydrogenase (LDH) level was normal and transthoracic echocardiogram showed a midline septum and the aortic valve opening with every beat. On admission, flows did not improve despite inotropic support. Outflow graft obstruction was suspected, however imaging was not pursued due to the risk of further renal injury with intravenous contrast, and that ultimately definitive treatment strategy remained heart transplantation. His UNOS listing status was upgraded from 4 to 2E. Anticoagulation was not escalated beyond aspirin and warfarin due to recurrent gastrointestinal bleeding. He continued to experience recurrent abrupt changes in LVAD flows (Figure 1B) without additional evidence to support pump thrombosis. Five weeks later, at the time of heart-kidney transplant, a partially obstructive thrombus within the inflow cannula as well as a mobile thrombus attached to the endocardium, prolapsing intermittently into the inflow cannula were visualized (Figure 1C-1D). <h3>Summary</h3> Dynamic inflow cannula obstruction should be suspected in the setting of heart failure and sudden changes in LVAD pump power consumption even when a lack corroborating imaging and laboratory evidence exists.

Dynamic modes of inflow jet in brain aneurysms

The transition of the inflow jet to turbulence is crucial in understanding the pathology of brain aneurysms. Previous works Le et al. (2010, 2013) have shown evidence for a highly dynamic inflow jet in the ostium of brain aneurysms. While it is highly desired to investigate this inflow jet dynamics in clinical practice, the constraints on spatial and temporal resolutions of in vivo data do not allow a detailed analysis of this transition. In this work, Dynamic Mode Decomposition (DMD) is used to identify the most energetic modes of the inflow jet in patient-specific models of internal carotid aneurysms via the utilization of high-resolution simulation data. It is hypothesized that dynamic modes are not solely controlled by the blood flow waveform at the parent artery. They are also dependent on jet-wall interaction phenomena. DMD analysis shows that the spatial extent of low- frequency modes corresponds well to the most energetic areas of the inflow jet. The high-frequency modes are short-lived and correspond to the flow separation at the proximal neck and the jet’s impingement onto the aneurysmal wall. Low-frequency modes can be reconstructed at relatively low spatial and temporal resolutions comparable to ones of in vivo data. The current results suggest that DMD can be practically useful in analyzing blood flow patterns of brain aneurysms with in vivo data.

Real-Time Flight Simulation for Multirotor UAV Integrated with the Dynamic Inflow Aerodynamics

A real-time flight simulation for multirotor unmanned aerial vehicles (UAV) is performed in combination with dynamic inflow aerodynamics. The present combination procedure includes rotor/fuselage aerodynamics and trim analysis. The rotor aerodynamics is based on dynamic inflow aerodynamics, which is appropriate for the analysis of multirotor UAVs. The present simulation uses an appropriate formulation for fuselage aerodynamics. Trim analysis was conducted for climb and forward flight to determine the physical constraints of the UAV. Based on this procedure, a simulation was performed and validated against the flight test. It was found that the accuracy of flight simulation increased if the simulation is performed in combination with dynamic inflow aerodynamics. Using this methodology, the dynamic characteristics that affect the performance of UAVs were investigated.

Dynamic Interception Effect of Internal and External Nitrogen and Phosphorus Migration of Ecological Ditches

The “ecological ditch” (eco-ditch) is an effective measure used to alleviate agricultural non-point-source pollution. However, information is lacking about the continuous transport characteristics of internal and external nitrogen and phosphorus in the interstitial water of the bottom mud of these ditches and overlying water under dynamic continuous inflow conditions. Understanding of the effect of matrix dams and microbial communities inside eco-ditches on the continuous transport characteristics of the N and P therein needs to be improved. To determine the interception effects of eco-ditches on the transfer of endogenous and exogenous N and P, an eco-ditch combining plants and a matrix dam was built to explore the transport distribution characteristics of N and P in the intermittent water and overlying water in the bottom of the eco-ditch and in the bottom of the soil ditch. We compared and analyzed the composition characteristics of the microbiological communities along the ecological and soil ditches. The research results showed that: (1) The concentration gradient between the interstitial water and the overlying water in the soil ditch is the main reason for the transport and diffusion of pollutants. However, in eco-ditches, the absorption function of plant roots and the differences between the structures of the microbial communities destroy the correlation of this concentration gradient diffusion, especially the effect on ammonium N; (2) a large number of mycelia adhere to the surface of the matrix dam in an eco-ditch, and are conducive to the adsorption and purification of pollutants in the water; (3) Proteobacteria, Chloroflexi, Actinomycetes, and Acidobacteria were the main bacterial groups in the ditches. The aquatic plants in the eco-ditch changed the microenvironment of the sediment, and both the microbial diversity and abundance along the eco-ditch were higher than in the soil ditch.

Bell 412 System Identification and Model Fidelity Assessment for Hover and Forward Flight

Frequency domain system identification of higher order models for the Bell 412 helicopter was performed. First, a frequency response database was derived from flight-test data. For hover, a combination of sweep and 2311-multistep maneuvers had to be used to achieve good results. In addition to the classical six-DoF (degrees of freedom) rigid body states, the identified hover model includes dynamic inflow, rotor coning dynamics, and uses a Padé approximation for the influence of engine dynamics, to improve the response in the vertical axis. The forward flight (60 kn) model includes as extension first-order flapping dynamics, mainly to improve the roll and pitch response. Besides the simple Padé approach used in the hover model, two different engine model structures were investigated but they provided no significant improvement compared to the Padé solution when coupled to the rigid-body model. Finally, a method derived from feedforward principles of model following control is shown, to use the identified hover model to analytically derive an "input filter" correction that improves the fidelity of a linearized FLIGHTLAB simulation model.

Comparison of a radially resolved dynamic inflow pitch step experiment to mid-fidelity simulations and BEM

In this paper a detailed comparison of the experimental and numerical results of a scaled wind turbine model in a wind tunnel subjected to fast pitching steps leading to the so-called dynamic inflow effect is presented. We compare results of an Actuator Line LES tool, a vortex code and four engineering models, to the experiment. We perform one and two time constant model analysis of axial wake induction and investigate the overshooting of integral loads. Our results show, that the effect is captured better by the two time constant models than by the one time constant models. Also the experiment and mid-fidelity simulations are best described by a two time constant fit. We identify the best dynamic inflow model to be the 0ye model. Different possibilities for the improvement of dynamic inflow models are discussed.

Experimental test of variable loads on a vertical-axis wind turbine

The paper presents an experimental study of applying variable loads on a vertical-axis wind turbine (VAWT). The experiment is conducted in an open-jet wind tunnel on a two-bladed Darrieus VAWT equipped with active individual blade pitch control. Variable loads are achieved by dynamically changing the pitch angle of the individual blades and by keeping the wind speed of the tunnel constant. The blade loads are measured using strain gages and the flow velocity is measured upwind and downwind of the rotor using a hotwire. Dynamic inflow phenomena are clearly visible both in the turbine loads and in the velocity field. A time delay based upon the flow convection in the wake is identified. It results that the induction of the turbine can be controlled by changing the pitch of the blades. The experimental database allows to validate a new dynamic inflow model for VAWT and will be made publicly available for research purposes.

Performance evaluation of an integrated floating energy system based on coupled analysis

An integrated floating energy system consisting of different types of energy devices is an ideal option for reducing the levelized cost of energy by enhancing the power production capacity. This study proposes a concept of an integrated energy system by combining two tidal turbines with a floating wind turbine. In order to investigate the power performance and dynamic responses of the hybrid concept, a novel coupled aero-hydro-servo-elastic tool is developed based on a commercial hydrodynamic analysis software package. In addition, a torque-pitch controller and the AeroDyn module are integrated within the coupled tool for evaluating the power performance of the tidal turbines under dynamic inflow conditions. Experimental data and numerical results obtained by OpenFAST are used to verify the accuracy of the coupled tool in predicting dynamic responses of the integrated energy system. The dynamic responses and power production under different environmental conditions are obtained by conducting a series of simulations. The results indicate that the total power production is increased by 3.84% to 6.46%. The transient behavior of the platform is improved and the tension fluctuation in mooring lines are significantly reduced by the hydrodynamic damping provided by the tidal turbines. In addition, the tidal turbines have no negative influences on the aero-elastic responses and power performance of the wind energy system. The results have demonstrated the advantages of the integrated energy system in enhancing the power production and improving the dynamic performance.

Inflow Dynamics in Weakly Stratified Lakes Subject to Large Isopycnal Displacements

AbstractThe effect of large‐amplitude isopycnal displacements, frequently observed in deep medium‐size arctic lakes during the ice‐free period, on the near‐ and far‐field fate of negatively buoyant river inflows is explored in this work. A three‐dimensional transport and hydrodynamic model of sub‐arctic Lake Lagarfljót was used to simulate the fate of river inflows during the summer stratification period. The intrusion dynamics are strongly affected by the amplitude and direction (downwelling/upwelling) of the isopycnal displacements induced by the wind near the river inlet. These displacements control the distance of travel of the river plume until reaching the layers with maximum density gradients (pycnocline) and, thus, the mixing ratio between the river plume and the lake water. Specifically, strong upwelling near the inlet causes the river to flow to the bottom as an underflow. Under downwelling, river plumes tend to form metalimnetic intrusions. The influence of the isopycnal displacements on the initial river fate can be parameterized using a time‐varying density Richardson number, which needs to be smoothed to account for the effects of unsteadiness. Large amplitude internal motions, of up to 70 m in Lake Lagarfljót, move deep underflows upwards to shallower basins where they could be readily incorporated into the surface mixed layer and rapidly flushed out of the lake. Metalimnetic currents associated with the V2H1 internal circulation can also accelerate riverine transport out of the lake.

Multistation coordinated and dynamic passenger inflow control for a metro line

Passenger inflow control is an efficient way to relieve peak passenger flow and reduce security risks in metro networks. However, station operators develop passenger inflow control strategies independently, thus ignore the interactions among stations and lines in the actual operation. Subsequently, the single-fixed control intensity usually fails to satisfy dynamic temporal passenger demand, resulting in great stranded passengers. To address this problem, a coordinated and dynamic inflow control method is proposed to generate an optimal demand-driven control pattern in metro systems. First, a mixed integer programming model with the concept of the equivalent time interval is formulated to minimise the total number of stranded passengers on one line. Second, special consideration is paid to the transfer passengers with the aim of ensuring the safety of transfer stations. Finally, an actual passenger flow and train operation data in Beijing Batong line is conducted to test the performance of the approach. Compared with the non-coordinated and dynamic inflow control method, results show that the proposed model can balance the utilisation of transportation capacity and reduce the total number of stranded passengers by 20.6%. Sensitivity analysis results indicate that both transportation capacity and transfer capability are the main factors affecting the inflow control.

Effects of rotor inflow models on dynamic responses of variable-pitch quadrotors

In this paper, effects of rotor inflow models on dynamic responses of variable-pitch quadrotors is investigated. The rotor inflow include both the static and dynamic inflow model formulated in first order form and fit quite into the formulation and solution methodology of the developed mathematical model. The main advantage of these models referred to computationally inexpensive and their particular form required to be coupled to the developed quadrotor model representing in the state space. Accordingly, the linear Drees model and Pitt-Peters dynamic inflow model are proposed to modify the quadrotor dynamic model and to capture the effects of rotor trailed wake provided unsteady properties for rotor aerodynamic model. This dynamic inflow is a three state model consists of uniform, sine, and cosine inflow components formulated based on rotor thrust, pitching, and rolling moments and it represents a linear radial distribution with first harmonic azimuthal distribution over the rotor disc. The linear and non-linear controllers are also designed for the variable-pitch quadrotor to improve the quality of dynamic responses. Furthermore, the non-linear controller, feedback linearization, guarantees the stability of the quadrotor in different maneuvers using the Lyapunov functions. The obtained results against experimental data show that the suggested inflow models can support the quadrotor dynamic responses with a higher resolution.

Assessment of blade element momentum codes under varying turbulence levels by comparing with blade resolved computational fluid dynamics

Abstract Unsteady load calculations for a large wind turbine using two blade element momentum (BEM) codes (FAST, HAWC2) are compared with results from blade resolved computational fluid dynamics simulations (FLOWer). This is to assess the performance of BEM under varying turbulence levels. Instantaneous and mean of power, spectral data and sectional blade forces are analysed for the three codes. The AVATAR research turbine with a radius of 102.88 m is used in this study. Based on comparisons, FLOWer and HAWC2 show a very close trend in mean power variations with different turbulence intensities. In contrast, FAST does not show a similar trend. This is conjectured to be due to different implementation in the BEM codes of the unsteady turbulence inflows, such as azimuthal variation of induction and dynamic inflow. The maximum error of C P is 6 % for FAST and 1 % for HAWC2 compared to FLOWer.

A multiscale numerical framework coupled with control strategies for simulating a wind farm in complex terrain

Improving the accuracy of the evaluation on the performance of wind farms in complex terrain under the actual atmosphere is crucial to the sustainable development of wind power. To this end, a multiscale numerical framework (MNF) integrating the WRF model coupled with a wind farm parameterization and a LES model embedded with the wind turbine control strategies is developed. An interface for data exchange between the WRF and LES models is established. The simulated nacelle velocity and the generator power results agree well with the observations, proving that the MNF is capable of assessing the flow behavior and performance of a realistic onshore wind farm in complex terrain. Besides, the impacts of terrain on the operating process for wind turbines over the hill under the dynamic inflow condition are quantified. The results show that the wind turbine at the top of the hill can cut in the rated-state earlier and cut out later, which improves the power output by 5.5%, indicating that the total generation of wind farms can be enhanced by making full use of terrain acceleration. This high-fidelity multiscale numerical framework is expected to be an effective tool for the siting and optimization of wind farms.

ИДЕНТИФИКАЦИЯ ГИДРОДИНАМИЧЕСКОЙ МОДЕЛИ СКВАЖИНЫ С ЭЛЕКТРОЦЕНТРОБЕЖНЫМ НАСОСОМ ПО ДАННЫМ КОНТРОЛЯ ВОЗМУЩЁННЫХ РЕЖИМОВ ЭКСПЛУАТАЦИИ

Актуальность исследования связана с проблемами создания и сопровождения динамических моделей скважин с электроцентробежным насосом в контурах оперативного контроля и управления состоянием систем, в условиях дрейфа параметров подъёмника и притока. Оценка первопричин нарушения предписанного технологического режима работы скважины и прогноз ближайших негативных последствий имеют важное значение для принятия взвешенных (оптимальных) решений по коррекции режимных состояний и обеспечению стабильных условий эксплуатации. Цель: разработка алгоритма оценивания дрейфующих параметров подъёмника, включая электроцентробежный насос, по методу наименьших квадратов и притока динамической модели скважины и приёмов стабилизации оценок в условиях реальной эксплуатации по данным зашумлённых измерений. Методы: численное интегрирование нелинейных дифференциальных уравнений, методы регрессионного анализа по схеме наименьших квадратов, статистических вычислительных испытаний, пробных возмущений, приёмов регуляризации алгоритмов оценивания. Результаты. Разработан двухэтапный алгоритм оценивания дрейфующих параметров подъёмника (износы, засорения) и притока (параметры продуктивности и подпора пласта) для упрощенного представления комплексной динамической модели скважины класса: «приток–подъёмник– электроцентробежный насос–устье» по данным двухтемповой шкалы контроля режимных состояний системы с реализуемым наблюдателем динамики притока в условиях пробных частотных возмущений. Выводы. Предложенные правила стабилизации оценок параметров модели на основе генерации пробных возмущений, снижения размерности за счет декомпозиции комплексной модели на составные блоки, фильтрации зашумлённых сигналов измерений посредством аппроксимации целыми функциями, реализации динамического наблюдателя притока формируют основу конструкции алгоритма идентификации с надёжным оцениванием основной группы параметров деформации напорной характеристики насоса и притока. Несмотря на низкие показатели точности идентификации гидросопротивления подъёмника, ошибка воспроизведения динамики переменных состояний системы возмущённых режимов эксплуатации с выходов наблюдателя не превышает 2 %, что говорит о низкой чувствительности штатных режимов эксплуатации подъёмника в рамках используемых модельных решений к искомой настройке параметра. Требуемая точность идентификации гидросопротивления трубы должна соотноситься с условиями регламента периодической очистки подъёмника от сорбентов.