Unsteady Environment Research Articles

Review on Mathematical Modelling of Boomerang for Novel Outfield Applications

A boomerang is an aerodynamically built object that, when thrown precisely, makes a quasi-circular flight and returns closely to its starting position. Numerous academics have analysed the boomerangs' motion and aerodynamics. None of the researchers in the field investigated the possibility of using the boomerangs for novel field applications rather than hunting and playing. Using boomerangs for field applications is beneficial in several ways because, unlike general drones, these boomerangs do not consume power continuously and low manufacturing cost. Using a boomerang in outfield applications is challenging because the external field is always unsteady and turbulent; therefore, a boomerang should be mathematically modelled for unsteady environment for precisely predict the trajectory. Few steady mathematical models were developed and validated in the reported literature and an unsteady mathematical model of boomerang was developed recently though it was not experimentally validated. The article reviews the mathematical modelling of boomerangs for certain novel outfield applications like agricultural inspection and weather monitoring. The depth of study in the mathematical modelling of boomerang is insufficient for developing novel applications. The article will aid the industrialists and researchers to advance in the field, and they can see the possibility of replacing the drones in novel outfield applications.

Investigation on the differences in unsteady film cooling behaviors of gas turbine blades between mainstream and cooling air pulsations for a cylindrical hole

In practice, film cooling on gas turbine blade inevitably works in an unsteady environment, which is introduced by periodical rotor/stator interaction and unsteady combustion. Previous studies have introduced two methods to simulate the realistic unsteady condition: 1) the pulsation of mainstream velocity; and 2) the pulsation of coolant injection. However, up to this point, the differences in instantaneous film cooling behaviors between these two methods remain unclear. This work presents a series of large eddy simulations to exhibit the unsteady flow and film cooling behaviors under steady and the two unsteady flow conditions. The numerical strategy is validated against our time-resolved experimental data. Time-averaged results show that the difference between the two pulsations is not significant if the averaged blowing ratio remains the same. However, the pulsation type plays a dominant role on the transient mode of film coverage. Under the steady condition, film coverage instability is induced by the unsteady trajectory of near-wall vortex structure; but with pulsed environments, the unsteadiness magnitude increases, and the area with high unsteadiness level enlarges. The pulsation of the mainstream velocity induces a more severe film coverage instability compared to the pulsation of the cooling air injection, because of the higher fluctuation energy of the mainstream bulk. Under mainstream pulsation, the probability distribution of instantaneous cooling effectiveness is the most scattered, and the corresponding fluctuation range is the largest.

A Study of Using VRTECH Virtual Reality Technology in Physical Education Teaching to Improve Students’ Learning Interests

Abstract Based on the combination of literature related to virtual reality technology, physical education learning interest, and the impact of virtual reality technology on physical education learning interest, a blended teaching mode design with VRTECH technology as the dominant technology and virtual reality technology as the supplementary technology is carried out. Then, the accuracy of the influence of the blended physical education teaching mode designed based on VRTECH technology on students’ interest in physical education learning is examined, and table tennis class is taken as an example for instance analysis. The results show that the COSELM algorithm has the highest accuracy, and COSELM in able to adapt quickly in an unsteady environment. The T-test results of physical education learning interest in each dimension before and after the teaching experiment showed that the physical education learning interest in the experimental group would be significantly increased under the assisted teaching of VRTECH technology (T=2.15, P=0.032). The T-test results of the five dimensions of students in the -experimental group under the blended teaching mode were -4.25, −3.07, −2.11, −4.45, and −4.99, and the significance of the dimensions was <0.01 except for independent and inquiry learning. The blended teaching mode based on the VRTECH technology can give the students a novel teaching environment, and it can effectively enhance the student’s interest in physical education learning, thus improving the new perspective of students’ interest in physical education learning and providing certain theoretical basis and practical experience for the integration of virtual reality technology into physical education teaching.

Experimental characterization of the turbulent intake jet in an engine flow bench

The turbulent intake flow of an optically accessible internal combustion engine is modeled using an air flow bench to reduce the complexity in the number of variables inherent within engine flows. By removing the piston and introducing a new optically accessible housing and outlet channel, the flow bench design simulates engine flows in the region just downstream of the intake valves and offers the possibility to measure and calculate quantities that would be difficult or impossible to obtain in the unsteady environment of a dynamic engine. Velocity data obtained via high-speed particle image velocimetry of the flow bench in the symmetry and valve planes are compared with data from a base operating condition of the motored engine at an intake pressure of 0.95 bar and a speed of 800 rpm at - 270°CA (270 crank-angle-degrees before compression top dead center), beginning with stationary valves at the corresponding valve lift of - 270°CA, then with moving valves. Analysis of the intake jet turbulence for increasing mass flow rates reveals a coherent flapping of the jet at a frequency of 752.5 Hz for only the 100% mass flow rate case. The vortex shedding frequency of the valve stem is estimated to being in the range of 634–799 Hz, indicating a possible link between the coherent jet flapping and the vortex shedding surviving the acceleration through the valve gap. Through comprehensive analysis, this study provides valuable validation data and insight into the intake flows of internal combustion engines.

Value-based modeling of economic decision making in conditions of unsteady environment

Value-based modeling of economic decision making in conditions of unsteady environment

Fast-growing Arctic Fe–Mn deposits from the Kara Sea as the refuges for cosmopolitan marine microorganisms

The impact of biomineralization and redox processes on the formation and growth of ferromanganese deposits in the World Ocean remains understudied. This problem is particularly relevant for the Arctic marine environment where sharp seasonal variations of temperature, redox conditions, and organic matter inflow significantly impact the biogenic and abiotic pathways of ferromanganese deposits formation. The microbial communities of the fast-growing Arctic Fe–Mn deposits have not been reported so far. Here, we describe the microbial diversity, structure and chemical composition of nodules, crust and their underlying sediments collected from three different sites of the Kara Sea. Scanning electron microscopy revealed a high abundance of microfossils and biofilm-like structures within the nodules. Phylogenetic profiling together with redundancy and correlation analyses revealed a positive selection for putative metal-reducers (Thermodesulfobacteriota), iron oxidizers (Hyphomicrobiaceae and Scalinduaceae), and Fe-scavenging Nitrosopumilaceae or Magnetospiraceae in the microenvironments of the Fe–Mn deposits from their surrounding benthic microbial populations. We hypothesize that in the Kara Sea, the nodules provide unique redox-stable microniches for cosmopolitan benthic marine metal-cycling microorganisms in an unsteady environment, thus focusing the overall geochemical activity of nodule-associated microbial communities and accelerating processes of ferromanganese deposits formation to uniquely high rates.

Nonidealities in Rotating Detonation Engines

A rotating detonation engine (RDE) is a realization of pressure-gain combustion, wherein a traveling detonation wave confined in a chamber provides shock-based compression along with chemical heat release. Due to the high wave speeds, such devices can process high mass flow rates in small volumes, leading to compact and unconventional designs. RDEs involve unsteady and multiscale physics, and their operational characteristics are determined by an equilibrium between large- and small-scale processes. While RDEs can provide a significant theoretical gain in efficiency, achieving this improvement requires an understanding of the multiscale coupling. Specifically, unavoidable nonidealities, such as unsteady mixing, secondary combustion, and multiple competing waves associated with practical designs, need to be understood and managed. The secondary combustion processes arise from fuel/air injection and unsteady and incomplete mixing, and can create spurious losses. In addition, a combination of multiple detonation and secondary waves compete and define the dynamical behavior of mixing, heat release distribution, and the overall mode of operation of the device. This review discusses the current understanding of such nonidealities and describes the tools and techniques used to gain insight into the extreme unsteady environment in such combustors.

Morphing Blades

Tidal turbines experience large load fluctuations due to the unsteady environment and the shear in the tidal flow. Mitigating these fluctuations without affecting the mean load would result in lower capital and operational costs. In this paper we discuss how this could be achieved through blades that passively and elastically adapt their camber and angle of attack to counteract unsteady flow conditions. Firstly, we discuss the underlying principles of unsteady thrust mitigation. We show that complete cancellation of the thrust fluctuations would be possible if every blade section could pitch passively and independently of neighbouring sections. Secondly, we provide proof of principle for two practical implementations through physical experiments and computational fluid dynamics simulations. We consider a blade that is rigid near the leading edge and flexible near the trailing edge. We show that the unsteady load mitigation is proportional to the ratio between the length of the flexible and rigid parts of the blade. For example, for a blade section where the flexibility is concentrated in a hinge at 3/4 of the chord, the amplitude of the fluctuations is 3/4 of the original amplitude. Secondly, we consider a solid, rigid blade with a passive pitch mechanism. We show that, for a 1 MW turbine operating in shear flow, more than 80% of the unsteady loading is mitigated. These results demonstrate the potential effectiveness of morphing blades for mitigating thrust fluctuations on tidal turbines.

A Transfer Learning‐Based Method for Facilitating the Prediction of Unsteady Crystal Growth

AbstractReal‐time prediction and dynamic control systems that can adapt to an unsteady environment are necessary for material fabrication processes, especially crystal growth. Recent studies have demonstrated the effectiveness of machine learning in predicting an unsteady crystal growth process, but its wider application is hindered by the large amount of training data required for sufficient accuracy. To address this problem, this study investigates the capability of transfer learning to predict geometric evolution in an unsteady silicon carbide (SiC) solution growth system based on a small amount of data. The performance of transferred models is discussed regarding the effect of the transfer learning method, training data amount, and time step length. The transfer learning strategy yields the same accuracy as that of training from scratch but requires only 20% of the training data. The accuracy is stably inherited through successive time steps, which demonstrates the effectiveness of transfer learning in reducing the required amount of training data for predicting evolution in an unsteady crystal growth process. Moreover, the transferred models trained with relatively more data (no more than 100%) further improve the accuracy inherited from the source model through multiple time steps, which broadens the application scope of transfer learning.

Structural optimization to reduce the environmental crosswind negative influence on the performance of a solar chimney power plant system

The solar chimney power plant system (SCPPS) is a clean and pollution-free facility for generating electric power. To further improve the heat collection efficiency of SCPPS, reduce the influence of external unsteady environment crosswind, a bank of transparent baffles was proposed to be installed at the entrance of transparent cover in SCPPS. Combined with the discrete ordinates (DO) radiation model and solar load model in Fluent, the latitude and longitude of Hohhot and actual weather parameters were taken as boundary conditions. Numerical simulation of SCPPS model with external air domain and different number of baffles were carried out. The accuracy of numerical simulation was verified by experimental results. There are three different types of models discussed here: the SCPPS with no baffle, the SCPPS with one baffle, the SCPPS with two baffles. Under the condition of different baffle number, the distribution of temperature, velocity, pressure, turbulence and heat collecting efficiency were given to determine the optimal baffle number. The results show that the average temperature of chimney inlet with one baffle and two baffles are 0.92% and 3.92% higher than that with no baffle, respectively; the average velocity of chimney inlet with one baffle and two baffles are 11.83% and 18.70% higher than that with no baffle, respectively; the average collector efficiency of one baffle and two baffles are 28.45% and 58.52% higher than that of without baffle, respectively. Compared with without baffle and one baffle, adding two baffles can more effectively reduce the heat loss of SCPPS in Hohhot under different environmental crosswind speeds, and alleviate the negative effects of environmental crosswind.

A robust one-dimensional approach for the performance evaluation of turbines driven by pulsed detonation combustion

Among the solutions to reduce emissions from stationary gas turbines, replacing conventional combustion through pressure gain combustion is one of the most promising options. Nevertheless, coupling pressure gain combustion with a turbine can result in increased losses within the cycle, mainly because of the resulting very unsteady turbine inflow conditions. A reliable simulation tool can help to overcome this challenge and optimize turbine geometries and designs for the specific application. The harsh unsteady flow downstream of pressure gain combustors makes three-dimensional CFD computationally expensive. Thus, the development of a fast computational method is crucial. This paper introduces and explores such an alternative methodology. A one-dimensional Euler gas dynamic approach is combined with blade source terms, computed out of a steady-state turbine meanline analysis. To evaluate the methodology, three-dimensional CFD simulations are performed in parallel and the results are compared with those of the 1D method. The energy extraction of a turbine expander is computed with both methods for three different configurations of pulsed detonation combustor arrays connected at the turbine inlet. The results show that the proposed approach is capable of simulating the turbine in such an unsteady environment accurately. Additionally, it is indicated that around 45% of the total unsteadiness is damped throughout the first blade row, which is almost irrespective of the inlet fluctuation amplitude. Due to its accuracy and very low computational cost, the developed methodology can be integrated into optimization loops in the early design and development stages of turbomachinery for pressure gain combustion applications.

Pulsed Flow Turbine Design Recommendations

A preliminary analysis of turbine design, fit for pulsed flow, is proposed in this paper. It focuses on an academic 2D configuration using inviscid flows, since pressure loads due to wave propagation are several orders of magnitude higher than friction and viscous effects do not significantly impinge on the inviscid part, as previously shown by Hermet, 2021. As such, a large parametric study was carried out using the design of experiments methodology. A performance indicator adapted to unsteady environment is carefully defined before detailing the factors chosen for the design of experiments. Since the number of factors is substantial, a screening design to identify the factors influence on the output is first established. The non-influential factors are then omitted in a more quantitative study of the output law. The surface response calculation allows determining the factor level favouring the best output. Consequently, the main trends in the turbine design driven by a pulsed flow can be stated.

Experimental investigation of supercritical carbon dioxide non-equilibrium condensation in a highly unsteady environment

The current work presents a study of qualitative relationships between the flow unsteadiness, induced by nozzle geometry variation, and non-equilibrium condensation behavior at high temporal scales for supercritical carbon dioxide (sCO2) flow. A closed sCO2 loop facility is used to drive a supercritical carbon dioxide flow through a rectangular converging–diverging channel. As the flow traverses through the channel, it experiences a local pressure reduction in a stalled region, eventually leading to non-equilibrium condensation of the working fluid. The flow is visualized using high-speed shadowgraphy and schlieren techniques to characterize the unsteady flow dynamics at the diverging section of the nozzle. Spectral information of the condensation behavior is retrieved from the optical diagnostics using power spectral density calculations, revealing multiple dominant frequencies in the diverging section of the nozzle. Three different nozzles are studied to understand how these dominant frequencies of condensation phenomenon change with respect to the nozzle geometry. Each nozzle design is distinguished with a unique dominant frequency, which is significantly impacted by the effect of flow throat velocity and the degree of adverse pressure gradient. Nozzles with divergence of 15° shows a dominant frequency in the range of 5 – 6.25 kHz in condensing behavior while nozzles with 6° divergence exhibited half the frequency of the phase change. These effects resulted from the extent of adverse pressure gradient imposed by the divergence angle of the nozzle. Additionally, these dominant frequencies are also compared to the wall-pressure signals acquired from high-frequency pressure transducers. Spectral analysis of wall-pressure signals, which are directly linked to nozzle designs, reveals a strong coupling between the condensation behavior and the wall-pressures.

Investigation on the unsteadiness of centrifugal compressor exposed to pulsating backpressure

Centrifugal compressor is exposed to pulsating backpressure due to the movement of intake valves in internal combustion engine. The performance of compressor deviates from the steady performance map, which affects the matching between turbocharger and engine. The behavior of compressor system at pulsation conditions are investigated via an in-house developed 1D unsteady code validated by experimental results. The influence of pulse frequency, magnitude and compressor characteristic curve on the compressor transient responses, including filling-emptying effect and wave dynamics, are analyzed. Results show that the strength of wave dynamics grows stronger with the increasing of pulse frequency, while the strength of filling-emptying effect increases first then decreases. The rise of pulse magnitude results in an almost linearly increasing of filling-emptying effect, while it can hardly affect the wave dynamics. Furthermore, the influence of pulsation magnitude and frequency represents the influence of local pressure gradient, and a correlation as quadratic curve can be evaluated between the pressure gradient and compressor unsteadiness. On the other hand, the influence of operating point, including the average mass flow rate and the slope of characteristic curve, is confirmed to be evidently smaller, comparing to the influence of pulsation frequency and magnitude. This study is helpful to estimate the behavior of compressor and the discrepancy of performance when operating at unsteady environment or matched with engine.

Motor control of landing in an unsteady environment

BackgroundWhen landing from a jump or a drop, muscles contract before touchdown to anticipate imminent collision with the ground, soften ground contact and allow to return to a stable standing position without stepping or rebounding. Research questionThis study assesses the effect of the unsteadiness of the environment on the motor control of landing. The ‘unsteady environment’ was induced by asking participants to perform drop landings inside an aircraft that underwent trajectories parallel to Earth’s surface. The participants also performed the same task in a ‘steady environment’ in our laboratory. MethodsGround reaction forces, lower limb joints’ movements and the activity of lower limb muscles were recorded. The stability of the landing was assessed by the vertical and anterior-posterior stability indexes, center of pressure measures and by the coefficient of variation of kinetic and kinematic parameters. ResultsOn one hand, participants slowdown their joint movements and reduce the knee joint excursion during landing, probably to avoid excessive movements that may induce imbalance. On the other hand, the stability of the landing is reduced while the variability of the movement is increased, illustrating a less stable and less consistent landing. In addition, whatever the environment, landing parameters associated with increased stiffness (i.e., increased impact forces and decreased joint range of motion) are correlated with decreased landing stability. SignificanceOverall, landings in the‘unsteady environment’ appear to be more cautious but less stable and less finely tuned. Since the stability of the landing is not directly influenced by the steadiness of the environment, this more cautious behavior could be, at least in part, related to the fear/apprehension induced by sudden acceleration variations of the frame of the aircraft.

An error similarity-based error-compensation method for measurement in the nonuniform temperature field

Measurement error compensation is a key issue for the application of laser trackers in an unsteady environment, especially in the nonuniform temperature field. Aimed at reducing induced measurement uncertainty, a measurement error compensation method with error similarity analysis is proposed in this paper. The spatial similarity of measurement errors is qualitatively analyzed based on the mathematical model, and quantitative analysis is presented by means of simulation and semivariogram. We then model the error similarity, and an error-estimation model for target points is established with the radius basis function neural network and regularized extreme learning machine. The experiments are conducted to verify error similarity and the applicability and accuracy of the estimation model in practice. The results show that error similarity does exist in practical measurements, and the proposed method can reduce the absolute measurement error to less than 0.03 mm (). The method is applicable for measurements in different environments since the compensated point sets are almost coincident.

Numerical investigation of the unsteady coupling airflow impact of a full-scale warship with a helicopter during shipboard landing

In this paper, a comprehensive computational modeling study of the unsteady aerodynamic environment around a warship with a helicopter is performed. An experimental validation exercise is also conducted, comparing computational fluid dynamics (CFD) results of the airwake calculated for a reduced-scale model of the isolated Landing Helicopter Assault (LHA) model with high-quality particle image velocimetry experimental data provided by the NASA AMES Research Center. Comparisons of the results generally obtain agreement, indicating that the CFD numerical method is able to resolve the large-scale turbulent airflow. Building on this, a numerical simulation of a real Robin helicopter, immersed in the unsteady airwakes of a full-scale Amphibious Assault Ship (AAS), is performed. The aerodynamic simulation of the influence on the coupled airflow of warship–helicopter is explored and compared with that of the solitary ship airflow field and the superposition airwakes, where the vortex patterns and pressure on the ship surface, as well as the velocity distribution, are circumvented. As a further step, dynamic landing analysis of the airflow field for a shipborne helicopter is implemented at an important location through the landing path for headwind. The aerodynamic characteristics of a helicopter during a flight deck landing are also explored for the unsteady ship airwakes impacting on rotor force during shipboard landings. In addition, different shipboard landing paths of the helicopter are comparatively investigated for obtaining an optimal landing path decision. The present study demonstrates an effective aerodynamic analysis and robust numerical approach, which creates a solid foundation supporting further alternative evaluations of ship airflow fields.

Graph-based change detection for condition monitoring of industrial machinery: an enhanced framework for non-stationary condition signals

The detection of change(s) in machine running state has become an important problem in the field of condition monitoring of industrial machinery. The graph model has been introduced very recently for this problem with an assumption of periodical stationarity of condition signals. In real-world engineering scenarios, however, machines often operate under unsteady environment and external loading conditions, thus resulting in non-stationary condition signals. This paper is a significant upgrade and expansion on the potential of the graph model to machine monitoring under unsteady operating conditions, where the collected signals are considered to be non-stationary. This paper proposes a new algorithm to achieve this end, which basically includes two steps: cycle segmentation and cycle normalization. Cycle segmentation is first performed to temporally divide the original data into individual cycles. The resulting cycles are subsequently normalized with a timing average procedure. With this, the obtained periodically normalized data can be appropriate for the graph model to process. Meanwhile, in order to avoid the over-segmentation problem, a control time-line is also designed, and simultaneously operates to report a potential change when performing cycle segmentation and normalization. The proposed algorithm is validated on both simulation data and real-world engineering signals. Experimental results reveal its great potential in real applications.

Unsteady hydrodynamics of a full-scale tidal turbine operating in large wave conditions

Tidal turbines operate in a highly unsteady environment, which causes large-amplitude load fluctuations to the rotor. This can result in dynamic and fatigue failures. Hence, it is critical that the unsteady loads are accurately predicted. A rotor's blade can experience stall delay, load hysteresis and dynamic stall. Yet, the significance of these effects for a full-scale axial-flow turbine are unclear. To investigate, we develop a simple model for the unsteady hydrodynamics of the rotor and consider field measurements of the onset flow. We find that when the rotor operates in large, yet realistic wave conditions, that the load cycle is governed by the waves, and the power and blade bending moments oscillate by half of their mean values. While the flow remains attached near the blade tip, dynamic stall occurs near the blade root, resulting in a twofold overshoot of the local lift coefficient compared to the static value. At the optimal tip-speed ratio, the difference between the unsteady loads computed with our model and a simple quasi-steady approximation is small. However, below the optimal tip-speed ratio, dynamic stall may occur over most of the blade, and the maximum peak loads can be twice those predicted with a quasi-steady approximation.

Wake impact on aerodynamic characteristics of horizontal axis wind turbine under yawed flow conditions

Wind turbines spend most of time in complex and unsteady environment, such as yawed flow, atmospheric wind turbulence, wind shear, and gust. Under yawed flow condition, velocity component parallel to the rotating plane causes a development of skewed wake structure, thus leading to an azimuthal variation in the aerodynamic loads on wind turbine blades. Moreover, the trailing and shed wake vortices unequally expand, and a strong wake interaction between the hub and tip vortices, and the asymmetrical velocity deficit around the rotor area occur. In the present study, the impacts of the skewed wake on the unsteady aerodynamic behavior around rotor blade were numerically investigated and a wake deflection mechanism was discussed in detail. For this purpose, the nonlinear vortex lattice method (NVLM) coupling with a time-accurate vortex particle method (VPM) was used. A numerical simulation on the NREL Phase VI wind turbine model, exposed to a low wind speed with different yaw angles, was carried out and predicted results were compared against measurements. Comparison results showed that the aerodynamic loads can be accurately calculated, even for highly yawed flow conditions and complex wake dynamics can be clearly observed.