Buffeting Effect Research Articles

Numerical simulation analysis of wind load on an integral bridge with steel-concrete composite girder based on cloud platform

The integral bridge with steel-concrete composite girder will be affected by wind load in the natural environment, so the buffeting effect of wind on the integral bridge with steel-concrete composite girder cannot be ignored. In order to solve the above problems, the numerical simulation analysis on the wind load on integral bridge with steel-concrete composite girder based on cloud platform is carried out. Before the buffeting analysis of the bridge, the wind environment condition should be calculated. Taking the integral bridge with steel-concrete composite girder as an example, based on empirical formula, the influence of girder size change on static wind load and static wind load under different wind speeds are calculated and analyzed. With the help of Davenport fluctuating wind’s power spectrum, the fluctuating wind field of integral bridge with steel-concrete composite girder under certain wind speed is simulated by harmonic synthesis method, the wind load value of integral bridge with steel-concrete composite girder is simulated, and the structural design of bridge is carried out, in order to ensure the scientificity and safety of bridge design. The numerical simulation can correctly react the test law, and can predict the wind resistance of the structure with the existing model.

ROV Sliding Mode Controller Design and Simulation

Underwater robots play a vital role in the exploration and development of marine resources and the inspection and maintenance of offshore platforms. In this paper, the motion control technology of ROV is studied, the kinematics and dynamics of ROV are analyzed, the kinematics and dynamics models of ROV are established, and the degrees of freedom of the models are decouple according to the control requirements. The fluid damping coefficient of ROV was obtained using Fluent software, and an ROV control system based on sliding mode variable structure was designed. The saturation function was introduced into the sliding mode controller to reduce the adverse effects of buffeting. The classical PID controller, fuzzy PID controller, and sliding mode controller designed in this paper were simulated and analyzed by Simulink. A semi-physical simulation platform based on Unity3D was established. It can be seen from the simulation results and the pool experiment results that the performance of the sliding mode controller designed in this paper is better than the classical PID controller and the fuzzy PID controller. The sliding mode control method is used to control the ROV motion, which has better control effect and precision.

Frequency domain identification of modal characteristics and loads from output‐only measurements

AbstractThis paper proposes a frequency domain framework for concurrently estimating the modal structural parameters and modal loads from the measured output response. A mathematical load model is theoretically developed and compared to the load determined by force identification. Unlike conventional modal identification schemes, the proposed approach can effectively accommodate the spectral shape of the external load in the frequency domain, enabling the determination of the modal parameters without explicit white noise assumption. The proposed approach is verified by applying it to a single‐degree‐of‐freedom system system representing a modal response, an aeroelastic model in an atmospheric boundary layer wind tunnel, a multi‐degree‐of‐freedom system, and the measured acceleration response of a 40‐story building. The simulation results demonstrate that the proposed technique can reliably estimate the modal parameters and load model and is robust against the noise present in the response and the order of the load model. Additionally, the proposed technique can be applied to various loading conditions such as vortex‐induced and buffeting effects since the modal parameters and the load model can be identified for any shape of the loading spectrum.

Buffeting Chaotification Model for Enhancing Chaos and Its Hardware Implementation

Many shortcomings of chaos-based applications stem from the weak dynamic properties of the chaotic maps they use. To alleviate this problem, inspired by the buffeting effect in aeroelasticity, this article proposes the buffeting chaotification model (BCM). Using the especially designed buffeting and modulo operators, the BCM can generate numerous new chaotic maps with strong dynamic properties from existing one-dimensional chaotic maps. The effectiveness of the BCM is mathematically proven according to the Lyapunov exponent, and further numerical experiments confirm the superiority of the chaotic maps generated by the BCM in terms of the dynamic properties. The field-programmable gate array implementation also shows that the BCM owns simplicity in hardware devices. To investigate the practical application, a scheme for constructing the pseudorandom number generator is designed. Performance analyses indicate that our generators have a strong ability to produce high-quality pseudorandom sequences rapidly.

Multiple Spacecraft Formation Flying Control around Artificial Equilibrium Point Using Propellantless Approach

This paper demonstrates a detailed analysis of the feasibility for compact formation system around an L2-type artificial equilibrium point by means of continuous low-thrust propulsion in the hybrid form of solar sail and Coulomb force propulsion. Firstly, in view of non-ideal solar sail, the position of L2-type artificial equilibrium point and numerical periodic orbits around L2 utilized as leader’s nominal trajectory are given. Secondly, considering the external disturbances in the deep space environment, the nonlinear dynamic model of the spacecraft formation system based on the circular restricted three-body problem (CRTBP) is derived, under the assumption that the leader covers the nominal trajectory and each follower adjusts its propulsive acceleration vector (that is, both its sail attitude and electrostatic charge) in order to track a desired relative trajectory. Thirdly, based on a new double power combination function reaching law, a fast integral terminal sliding mode control methodology (MFITSM) is ameliorated to achieve orbital tracking rapidly, which has better robustness against external disturbances and the buffeting effect during spacecraft propulsion simultaneously. To properly allocate control inputs, a novel optimal allocation scheme is designed to calculate the charge product of the spacecrafts and sail attitude angles, which can make the magnitude of the acceleration required from the Coulomb propulsion system minimum and avoid formation geometry instabilities by balancing electrostatic interaction between adjacent spacecraft. Finally, several numerical examples are conducted to validate the superiority of the proposed control algorithm.

Vibration serviceability of all-GFRP cable-stayed footbridge under various service excitations

The paper presents a study on a vibration serviceability assessment of the cable-stayed Fiberline Bridge made entirely of Glass Fiber Reinforced Polymer (GFRP) based on ambient vibration tests. In situ monitoring in the vertical direction included modal identification and vibration tests under various specific dynamic excitations (21 events) such as human-induced activities, scooter-induced excitations and aerodynamic buffeting effects induced by trains passing under the footbridge. A total of 7 natural frequencies ranging up to 21 Hz, corresponding mode shapes and damping ratios of the footbridge were identified. It was found that the footbridge meets the minimum comfort level in accordance with the Sétra rules for most of the considered events. More restrictive acceleration limits suggested by Eurocode 0 were not met for these events. The obtained results provided relevant data for structural health monitoring of other all-GFRP footbridges with a similar structural system exposed to similar excitation conditions.

On the Importance of Transition Control at Transonic Compressor Blades

AbstractThe flow through a transonic compressor cascade is characterized by high unsteadiness and a high loss level. This results from the shock waves in the blade cascade and their interaction with the blade suction side boundary layer. In the case of a laminar shock wave boundary layer interaction, the loss level is higher due to the occurrence of a laminar separation bubble below the shock wave compared to the shock wave interaction with a turbulent boundary layer. In addition, the oscillation of the shock position in both cases influences the working range concerning the point of stall onset as well as leading to an unsteady interaction with the blade called buffeting. The reduction of losses and of unsteadiness in the shock wave oscillation, connected to a decrease of the blade buffeting effect, is the aim of the current investigation. Therefore, experimental investigations using a roughness patch as well as air jet vortex generators in order to control the transition in a transonic compressor cascade have been conducted at the transonic cascade wind tunnel of the German Aerospace Center (DLR) at Cologne. At an inflow Mach number of 1.21, a loss reduction for both transition control cases is achieved. In spite of a nearly uninfluenced fluctuation range of the passage shock wave compared to the reference cascade, the oscillation spectra of the transition control cases show a reduction of the shock movement amplitude at a frequency below 500 Hz and above 1 kHz. In the closing section of the paper, a detailed discussion on the reasons for the resulting flow behavior based on particle image velocimetry and high-speed shadowgraphy data is given. The resulting conclusion of the study is that the consideration of transition control at transonic compressor blades is very important in order to reduce losses and flow unsteadiness that directly influences blade buffeting and the numerical prediction quality of the stall onset.

Anti-disturbance speed control of low-speed high-torque PMSM based on second-order non-singular terminal sliding mode load observer

This paper presents an anti-disturbance speed control of low-speed high-torque permanent magnet synchronous motor (PMSM) based on the second-order non-singular terminal sliding mode load observer. According to the coordinate transformation theory, the mathematical model of PMSM is established. Subsequently, the second-order non-singular terminal sliding mode observer (SNTSMO) is designed to observe the changes of load disturbance in the PMSM system. The SNTSMO combines the advantages of both high-order sliding mode and non-singular terminal sliding mode to achieve the fast convergence and no chattering. Next, the sliding mode controller (SMC) is designed to achieve speed loop control of PMSM. Then, the anti-disturbance compound speed controller is established on the basis of SMC and SNTSMO, wherein the feed-forward compensation is used to reduce the disturbance from the load. Finally, the numerical simulations and experiments are presented according to the schematic diagram of the designed compound speed controller of PMSM. The results demonstrate that the designed SNTSMO can precisely estimate the load disturbance and suppress the effects of buffeting in the traditional sliding mode observer (SMO). Additionally, the designed compound speed controller of PMSM can achieve smooth speed control in the presence of load disturbance, achieve the purpose of anti-disturbance speed control and further improve the robustness of the control system.

Passive Flow Control for Reduced Load Dynamics Aft of a Backward-Facing Step

Passive flow control devices for a fully turbulent backward-facing step flow were investigated experimentally with particle image velocimetry and dynamic pressure transducers in the Trisonic Wind Tunnel Munich at Mach numbers of 0.80 and 2.00, as well as at Reynolds numbers of and 210,000, respectively. The results showed that these flow control devices, which are comprised of circular and square convoluted trailing edges on the backward-facing step, were a far more effective alternative to active flow control. The mean reattachment length was reduced by over 80% for the most effective configuration: so-called square lobes with a protrusion height of 0.4 step heights. This geometry also reduced the root mean square of the pressure fluctuations experienced by the reattachment surface by nearly 50% in transonic conditions. It was shown that the harmful step mode was weakened by forcing streamwise vorticity onto the flow through the presence of the lobes. The square lobes were more effective in diffusing this mode when compared to the circular lobes. Similarly, with increasing lobe sizes, the effectiveness of the flow control devices increased. Thus, a simple passive solution was determined for reducing the buffeting effects experienced by space launchers in transonic flight, for instance.

Dynamic Response of an FRP Footbridge Due to Pedestrians and Train Buffeting

Fibre-Reinforced Polymers (FRPs) are an increasingly popular option for the construction of bridges as they possess high strength to weight properties and good durability qualities. In particular, they are well suited to pedestrian bridges over railway lines as they can be installed without much disruption and require little maintenance. However, as they are typically lighter and less stiff than traditional materials there is concern about their dynamic response in such locations both due to human induced actions and as a train buffeting. During such events, the aerodynamic loading from the movement of the train causes a buffeting effect on the bridge and may result in vibrations which exceed pedestrian comfort limits. There is currently a lack of experimental information on this subject, and further data is needed if such bridges are to be used on future lines, especially with higher speed limits.This paper presents an experimental investigation of the response of a 14.5m FRP truss bridge due to crowd loading and train buffeting. First the hammer impact tests were conducted to identify the vertical and lateral modes of interest, and their frequencies and damping. An array of accelerometers were used to measure the vertical and lateral vibrations during two crowd loading events with 15 and 8 people walking continuously, and multiple train passes. The results were then compared to serviceability guideline limits. These results add to the understanding of the vibration response of FRP bridges and can be used to help designers assess conditions in which such effects become critical.

Computational fluid dynamics modeling of rope-guided conveyances in two typical kinds of shaft layouts.

The behavior of rope-guided conveyances is so complicated that the rope-guided hoisting system hasn’t been understood thoroughly so far. In this paper, with user-defined functions loaded, ANSYS FLUENT 14.5 was employed to simulate lateral motion of rope-guided conveyances in two typical kinds of shaft layouts. With rope-guided mine elevator and mine cages taken into account, results show that the lateral aerodynamic buffeting force is much larger than the Coriolis force, and the side aerodynamic force have the same order of magnitude as the Coriolis force. The lateral aerodynamic buffeting forces should also be considered especially when the conveyance moves along the ventilation air direction. The simulation shows that the closer size of the conveyances can weaken the transverse aerodynamic buffeting effect.

An Experimental Investigation of Sunroof Buffeting Characteristics of a Sedan

After a short introduction about vehicle wind buffeting noise generation mechanisms, sunroof buffeting characteristics of a production sedan under different wind speeds and operating modes are investigated through full-scale aeroacoustic wind tunnel tests. As sunroof fully open, the severest buffeting effect occurs at wind speed 50kph, with the peak SPL 122dB and the corresponding resonance frequency 18Hz for the test point at the front row. From ca. 60kph it seems that the buffeting effect disappeared. As sunroof tilt, the severest buffeting effect occurs at wind speed equal or less than 30kph, the resonance frequency equal or less than 15Hz. From ca. 40kph the buffeting effect almost disappeared. Whether sunroof fully open or tilt, the resonance frequency increases all along as wind speed goes up till the buffeting effect disappeared (less than 20Hz). Different test positions at the front row or back row show very similar buffeting characteristics.

Reproducibility of flow past two-dimensional rectangular cylinders in a homogeneous turbulent flow by LES

A large-eddy simulation technique has been applied for prediction of flow past rectangular cylinders influenced by free-stream turbulence. A stochastic method was used to generate homogeneous turbulence with specified power and cross spectra in the oncoming flow. It has been found that the buffeting effects due to the inflow turbulence on front surface of cylinders are predicted well. In case of a cylinder of small length-to-height ratio ( B/ D=1.0), just Strouhal number increases slightly and for large ( B/ D=2.5), enhanced turbulent mixing causes reattachment of separated shear flow on the cylinder side. These are in good agreement with the results of previous experimental studies, and the present method appears to be sufficient for practical applications.

Unbalanced wind buffeting effects on bridges during double cantilever erection stages

This paper is focused on the torsional effects that are induced on bridge piers by unbalanced windrnbuffeting on the deck during double cantilever erection stages. The case of decks with variable cross section isrnconsidered in particular as this characteristic is typical of most frame bridges that are built by the cantileverrnmethod. The procedure outlined in the paper is basically an application of the method that Dyrbye and Hansenrn(1996) have illustrated for decks with constant cross section. This format was chosen because it is suitable forrndesign purposes and may easily be implemented in structural codes. As a complement, the correspondence withrnthe format that is adopted in the Canadian code (NBCC 1990) for the gust factor is established, which might bernuseful to bridge designers used to the North-American approach to the gust effects on structures. Onlyrnalongwind turbulence and horizontal movements of the deck are considered. The combination of torsional andrnbending effects is also discussed and it is illustrated with an example of application.

LESによる一様乱流中における2次元角柱周りの流れの再現性

Abstract A large-eddy simulation technique has been applied for prediction of flow past rectangular cylinders influenced by free-stream turbulence. A stochastic method was used to generate homogeneous turbulence with specified power and cross spectra in the oncoming flow. It has been found that the buffeting effects due to the inflow turbulence on front surface of cylinders are predicted well. In case of a cylinder of small length-to-height ratio ( B / D =1.0), just Strouhal number increases slightly and for large ( B / D =2.5), enhanced turbulent mixing causes reattachment of separated shear flow on the cylinder side. These are in good agreement with the results of previous experimental studies, and the present method appears to be sufficient for practical applications.

TDMA based adaptive modulation with dynamic channelassignment (AMDCA) for large capacity voice transmission in microcellular systems

The authors propose an adaptive modulation with dynamic channel assignment (AMDCA) to achieve high capacity voice transmission in microcellular systems. The proposed system measures the received carrier-to-noise plus interference power ratio (C/(N+I)) of each time division multiple access (TDMA) slot to search for available slots and to discover the optimum modulation parameters for each slot, thereby effectively combining the buffeting effect of spatially distributed electric field strength by slow adaptive modulation, and that of spatially and temporally distributed traffic by dynamic channel assignment (DCA). Computer simulation confirms that the proposed AMDCA system can achieve ~7.5 times higher system capacity than the conventional QPSR with a fixed channel assignment (FCA).

Adverse Wind Loads on Low Buildings Due to Buffeting

The effect of large nearby buildings on the wind loading of low buildings has not been examined in the past. Wind loads for low buildings specified by current standards and Codes of Practice originate from wind tunnel studies on isolated buildings and give no guide for the assessment of loads under conditions of buffeting. The current paper presents the results of an experimental study carried out in a boundary layer wind tunnel in order to determine the wind loads on low buildings of different geometries (eave height and roof slope) in the presence of a tall nearby building at various relative locations. Results show significant adverse effects (wind load amplifications higher than 200%) for particular building proximity configurations. The complexity of the problem, however, indicates that it is very difficult to treat these buffeting effects with any degree of generality. Alternatively, it is suggested that local building officials should require the use of higher design loads after seeking a specialis...

Straked in-line steel stacks with low mass-damping parameter

In wind-tunnel tests on a single stack and a row of five slender stacks with a very low mass-damping parameter, M δ = 2 M δ s/ ϱ D 2 = 3.3, the locking-in and buffeting effects have been investigated. It has been shown that the influence of fitting a cone on the lower part of the stack is negligible for the vortex-exciting oscillation. The effectiveness of strakes on the upper part of the cylindrical stack depends on the mass-damping parameter, i.e. on the nondimensional oscillation amplitude. Below a specific limit of M δ the strakes lose their damping effect and the oscillation increases to a magnitude similar to that for the plain stack. For stacks in a row arrangement the dynamic response is distinctly increased by buffeting. For distance ratios of the stacks a/D ≌10, the enhancement is nearly 70%. Larger distance-ratios give lower enhancement, and for a/ D ⩾ 23 the buffeting effect may be neglected. The use of a dynamic damping-absorber of mass 2% of the total stack mass leads to very low amplitudes y 0 less than 0.02 D, due to a 30 times larger effective damping.

Central Nervous System Pathology Associated With Mask Ventilation in the Very Low Birthweight Infant: A New Etiology for Intracerebellar Hemorrhages

Mask-applied ventilatory support was noted to cause severe head molding in infants with birthweights under 1,501 gm. To determine if this molding was detrimental to the infant, the neonatal course and autopsy findings were reviewed for 106 infants. Twenty significant intracerebellar hemorrhages were found. An association between these hemorrhages and mask-applied positive pressure ventilation was demonstrated (P = .05). This relationship was maintained when all cases of generalized bleeding dyscrasia were removed (P = .021). It is proposed that the distortional forces produced by the mask attachment, together with the buffeting effect of intermittent positive-pressure ventilation, are causally related to the production of intracerebellar hemorrhages by direct contusion, by ischemic stasis, or by altered venous drainage. The authors urge strong caution when dealing with the small premature infant in using any attachment device that causes molding of the cranial vault, particularly in the occipital area.

Effects of transonic buffeting on a hammerhead-shaped payload.

An analytical and experimental program was conducted to improve the capability of determining the effects of transonic buffeting on pay loads of launch vehicles. An analytical method was developed to apply experimental data, using power spectral techniques, in the analytical prediction of vehicle structural loads. To solve the loads problem without unsupported assumptions, a wind-tunnel test was conducted on a hammerhead-shaped pay load to measure the needed power spectral and cross-power spectral density functions of the local buffeting forces or pressures. The reduced experimental data, circumferential correlations of unsteady pressures, longitudinal correlations of unsteady pressures and local normal force, power spectra and cross-power spectra of unsteady pressures, and local normal force for freestream Mach number 0.91, and angle of attack of 0° to 6° are illustrated. These data indicate large negative values of longitudinal correlation between fluctuating pressures and local normal force in the boattail region. Bending moment responses were computed on a launch vehicle using measured cross-correlation or cross-power spectra between the buffet disturbances. The responses were smaller than that computed using zero correlation between the disturbances, and larger than the calculated response caused by atmospheric turbulence.