Non-linear buffeting response analysis of long-span suspension bridges with central buckle

The rigid central buckle employed in the Runyang Suspension Bridge (RSB) was the first time it was used in a suspension bridge in China. By using a spectral representation method and FFT technique combined with measured data,a 3D fluctuating wind field considering the tower wind effect is simulated. A novel FE model for buffeting analysis is then presented,in which a specific user-defined Matrix27 element in ANSYS is employed to simulate the aeroelastic forces and its stiffness or damping matrices are parameterized by wind velocity and vibration frequency. A nonlinear time history analysis is carried out to study the influence of the rigid central buckle on the wind-induced buffeting response of a long-span suspension bridge. The results can be used as a reference for wind resistance design of long-span suspension bridges with a rigid central buckle in the future.

Analysis of the Quasi-Static Buffeting Responses of Transmission Lines to Moving Downburst

Downburst event is identified as a major cause to failure of transmission lines in non-coastal regions.In this paper,a novel nonlinear analytical frame for quasi-static buffeting responses of hinged and multi-span insulator-line systems are derived based on the theory of cable structure.The closed-form solutions are presented and applied to predict nonlinear response including displacements and other reactions of the system subjected to a moving downburst wind in a case study.Accuracy and efficiency of the derived analytical frame are validated via comparisons with results from finite element method.

A Review of Buffeting Loading on Bridge Decks

The strip assumption is the basis of current buffeting analysis. However, the strip assumption has limitation in describing the buffeting load on a line-like structure. The validity of strip assumption was presented and an empirical 3-D aerodynamic admittance was proposed to describe the lift on streamlined decks. The relations between the 3-D admittance and Sears function are depicted.

Field measurement on wind characteristic and buffeting response of the Runyang Suspension Bridge during typhoon Matsa

Field measurement on wind characteristic and buffeting response of existing bridge is of great value to the development of bridge wind engineering,and the structural health monitoring system(SHMS) em-ployed in many long-span bridges provide a research basis for the field measurement.In order to pro-vide reliable basis for wind resistant evaluation of Runyang Suspension Bridge(RSB),two anemome-ters and 85 accelerometers were installed in the SHMS of RSB.In August 2005,Typhoon Matsa crossed over Jiangsu,the SHMS timely recorded the typhoon and structural vibration responses.In this paper by using the time-frequency technique and statistical theory,the recorded data were analyzed to obtain the strong wind characteristics,the buffeting response characteristics of the cable and deck,and the variation of buffeting response RMS versus wind speed.Results obtained in this study can be em-ployed to validate the credibility of current buffeting response analysis theory techniques,and provide reference values for wind resistant evaluation of other long-span bridges.

Application of Omega vortex identification method in cavity buffeting noise

The cavity buffeting noise is related to the free shear layer oscillation and the periodic vortex shedding,where weak vortices coexist with strong vortices and the strong shear phenomenon also exists at the opening of the cavity.Therefore,it is of great significance to accurately capture vortices at the opening for the control of the cavity buffeting noise.This paper first compares the Omega vortex identification method with the Q andλ2criteria based on the large eddy simulation(LES)of the backward-facing step flow,and it is found that the Omega method enjoys the following advantages:it is not sensitive to a moderate threshold change andΩ=0.52 can be used as a fixed threshold,it can capture both the strong and weak vortices at the same time;and it will not be contaminated by the shear.Then the Omega(Ω)method is applied to the LES of the cavity buffeting noise:the mechanism of the cavity buffeting noise is studied based on a simple cavity model firstly,and then the effects of the incoming boundary layer thicknesses and the incoming boundary layer shapes on the cavity buffeting noise are analyzed.The results show that:theΩmethod clearly captures the processes of the vortex generation,development,collision and fragmentation,verifying that the generation of the cavity buffeting noise is related to the free shear layer oscillation and the periodic vortex shedding;as the thickness of the incoming boundary layer increases,the free shear layer becomes more stable and the Helmholtz resonance is avoided effectively,thereby the cavity buffeting noise is reduced effectively,adding a convexity upstream of the cavity opening to interfere the shape of the incoming boundary layer to reduce the acoustic feedback effect can reduce the cavity buffeting noise effectively.

Enjoy our meal!——小学英语“自助餐”式作业设计实践与探讨

设计具有针对性、合理性和分层性的英语作业不仅是让学生提升英语综合能力的有效手段,更是帮助学生在现有基础上“踮踮脚尖摘苹果”的最佳途径。根据语言学习的特点,把作业设计贯穿于整个教学过程中,让教与学相辅相成的同时,也让学生真正成为学习的主人;让作业形式多样、丰富有趣的同时,也让学生拥有更多作业选择自主权,让“双减”的落实真正成为“双质”的提升。

Feature identification in complex fluid flows by convolutional neural networks

Recent advancements have established machine learning's utility in predicting nonlinear fluid dynamics,with predictive accuracy being a central motivation for employing neural networks.However,the pattern recognition central to the networks function is equally valuable for enhancing our dynamical insight into the complex fluid dynamics.In this paper,a single-layer convolutional neural network(CNN)was trained to recognize three qualitatively different subsonic buffet flows(periodic,quasi-periodic and chaotic)over a high-incidence airfoil,and a near-perfect accuracy was obtained with only a small training dataset.The convolutional kernels and corresponding feature maps,developed by the model with no temporal information provided,identified large-scale coherent structures in agreement with those known to be associated with buffet flows.Sensitivity to hyperparameters including network architecture and convolutional kernel size was also explored.The coherent structures identified by these models enhance our dynamical understanding of subsonic buffet over high-incidence airfoils over a wide range of Reynolds numbers.

Effects of non-stationary wind velocity models on buffeting performance of closed-box girder suspension bridges

Non-stationary characteristic in nature wind has a great effect on buffeting performance of long-span bridges.The influence of key parameters in non-stationary wind velocity models on nonlinear buffeting responses of a super long-span suspension bridge was investigated in this paper.Firstly,four non-stationary wind velocity models are established by combing the time-varying average wind velocity with an exponential function and the fluctuating wind velocity with four modulation functions,respectively.These non-stationary wind velocity models have obvious non-stationary characteristics and then are validated by the classical power spectrum densities.Finally,three displacement responses of the bridge deck under four different independent variables ofβin the exponential function and four modulation functions were compared,respectively.Results show that the turbulence intensities using two non-uniform modulation functions(NMF)are larger than those using uniform modulation functions(uMF).Moreover,the root mean square(RMS)values of three displacement responses increase with the decrease ofβ.Besides,the RMS values of three displacement under two NMFs are larger than those under two uMFs,and their RMS values under the second uMF are the smallest.

Wind-induced vibration control of bridges using liquid column damper

The potential application of tuned liquid column damper (TLCD) for suppressing wind-induced vibration of long span bridges is explored in this paper.By installing the TLCD in the bridge deck,a mathematical model for the bridge-TLCD system is established.The governing equations of the system are developed by considering all three displacement components of the deck in vertical,lateral,and torsional vibrations,in which the interactions between the bridge deck,the TLCD,the aeroelastic forces,and the aerodynamic forces are fully reflected.Both buffeting and flutter analyses are carried out.The buffeting analysis is performed through random vibration approach,and a critical flutter condition is identified from flutter analysis.A numerical example is presented to demonstrate the control effectiveness of the damper and it is shown that the TLCD can be an effective device for suppressing wind-induced vibration of long span bridges,either for reducing the buffeting response or increasing the critical flutter wind velocity of the bridge.

Nonlinear Control Method for Hypersonic Vehicle Based on Double Power Reaching Law of Sliding Mode

The intelligence nonlinear control scheme via double power reaching law based sliding mode control method is proposed to solve the problems of model uncertainties and unknown outside disturbances.Firstly,the aerodynamic parameters of the morphing vehicle are replaced with curve-fitted approximation to build the accurate model for control design in the hypersonic flight.Then the nonlinear vehicle model is transformed into the strict feedback multi-input/multi-output nonlinear system by using the input-output feedback linearization approach.At the same time,the disturbance observer is used to approximate the unknown disturbance,and the sliding mode method is used to solve the problem of non-matching and uncertainty.Finally,according to the buffeting problem in sliding mode control,the double power is improved.Simulation results show that the proposed method can ensure the global stability of the closed-loop system,and has good tracking and robust performance.

Effects of Tuned Mass Damper on Wind-Induced Vibration of Free Standing Pylon by Wind Tunnel Test

In order to assess the effects of tuned mass dampers （TMDs） on wind actions, an aeroelastic model with a scale of 1：60 was constructed. Tests were performed in an atmospheric boundary layer wind tunnel to investigate the buffeting response of the pylon with a TMD fixed by a wire rope instead of a spring. The model was tested under different levels of damping. The experimental and numerical results showed that with the TMD in the optimal condition, the buffeting response was reduced by 47%.

Bridge vibration under complex wind field and corresponding measurements: A review

Due to increased demands in transportation development,bridge construction has been extended to areas with complex wind fields.In addition to common flow features such as high wind speeds and strong turbulence intensity,in coastal areas,bridges are likely to be exposed to non-stationary and non-Gaussian high-speed wind fields during hurricane events.Bridges built in mountainous regions will experience varying wind directions,incident angles of attack(AOA),and wind speed variation due to undulating terrain.The complex wind fields are challenging to the bridge engineering community to which accurate calculation methods and suppression measures for bridge vibration are urgently required.In this paper,state-of-the-art research results are introduced through three categories:(a)the distinctive characteristics of complex wind fields in offshore and mountainous areas,(b)the categories of wind-induced vibrations for bridges,and(c)the suppression measures employed in engineering practices.Until now,the studies regarding the coupled bridge vibration in complex wind fields have made considerable progress,but a richer database of actual wind measurement results and more efficient simulation methods still need to be further established.

Safety and serviceability assessment for high-rise tower crane to turbulent winds

Tower cranes are commonly used facilities for the construction of high-rise structures.To ensure their workability,it is very important to analyze their response and evaluate their condition under extreme conditions.This paper proposes a general scheme for safety and serviceability assessment of high-rise tower crane to turbulent winds based on time domain buffeting response analysis.Spatially correlated wind velocity field at the location of the tower crane was first simulated using an algorithm for generating the time domain samples of a stationary,multivariate stochastic process according to some prescribed spectral density matrix.The buffeting forces applied to the structure were computed according to the above-simulated wind velocity fluctuations and the lift,drag,and moment coefficients obtained from a CFD computation.Those spatially correlated loads were then fed into a well calibrated finite element model and the nonlinear time history analysis was conducted to compute structural buffeting response.Compared with structural onsite response measurement,the computed response using the proposed method has good precision.The proposed method is then adopted for analyzing the buffeting response of an in-use tower crane under the design wind speed and the maximum operational wind speed for safety and serviceability assessment.

Experimental investigation of shock-buffet criteria on a pitching airfoil

An experimental investigation of the shock-buffet phenomenon subject to unsteady pitching supercritical airfoil around its quarter chord has been conducted in a transonic wind tunnel.The model was equipped with pressure taps connected to the fast response pressuretransducers.Measurements were conducted at different free-stream Mach number from 0.61 to0.76.The principle goal of this investigation was to experimentally discuss the shock-buffet criterion over a SC(2)-0410 supercritical pitching related to the hysteresis loops of total drag and trailing edge pressure,the behaviour of the shock wave foot location,the pressure distribution over the upper surface,and by implementing the wavelet analysis of the normal force.To ensure capturing the buffet phenomenon by utilizing these criteria,a pressure port has been drilled exactly at the trailing edge of the airfoil where its output was used to detect the buffet phenomenon for different conditions.Visual representation of the flow using the shadow graph flow visualization technique for different test cases is further used to illustrate the unsteady shock wave motion.A comparative analysis of experimental measurements shows that the conducted criteria confirm each other when the buffet phenomenon occurs at the position of the oscillating cycle.

Impact Arresting Process Mechanical Modeling and Sliding Model Buffer Control Based on Magneto-Rheological Fluid

The research on the form and control method of impact load arresting buffer has been an active topic in the field of buffer arresting system(BAS).It becomes significant on reducing the weight of arresting system,improving the hindered efficiency,and guaranteeing the security of BAS.The hydraulic hindered device of impact load is currently used in BAS.There are some problems.For example,the system needs large power sources.However,once the power of active hydraulic control system is turned off,there arise unpredictable security risks.An arresting form of semi-active control based on magneto-rheological damper(MRD) is proposed,and the mechanical model of the BAS is established.Meanwhile,the state equation of impact load BAS is established according to the characteristics of impact load buffer arresting,and its sliding model buffer control is achieved.Due to the chattering characteristic of the output signal of sliding mode controller,the method to prevent chattering is designed based on short-term energy and zero-crossing rate detection.For the model and chattering suppression of sliding model buffer control algorithms,simulation results show that the proposed state equation and the arresting model are reasonable,and the design of semi-active control algorithm is effective.On the condition of the buffer control system requirement and the accuracy,the proposed algorithms effectively control the chattering of sliding mode control algorithms,and improve the security of the BAS.

Transonic buffet control research with two types of shock control bump based on RAE2822 airfoil

Current research shows that the traditional shock control bump（SCB） can weaken the intensity of shock and better the transonic buffet performance. The author finds that when SCB is placed downstream of the shock, it can decrease the adverse pressure gradient. This may prevent the shock foot separation bubble to merge with the trailing edge separation and finally improve the buffet performance. Based on RAE2822 airfoil, two types of SCB are designed according to the two different mechanisms. By using Reynolds-averaged Navier-Stokes（RANS） and unsteady Reynolds-averaged Navier-Stokes（URANS） methods to analyze the properties of RAE2822 airfoil with and without SCB, the results show that the downstream SCB can better the buffet performance under a wide range of freestream Mach number and the steady aerodynamics characteristic is similar to that of RAE2822 airfoil. The traditional SCB can only weaken the intensity of the shock under the design condition. Under the off-design conditions, the SCB does not do much to or even worsen the buffet performance. Indeed, the use of backward bump can flatten the leeward side of the airfoil, and this is similar to the mechanism that supercritical airfoil can weaken the recompression of shock wave.

Flow characteristics around airfoils near transonic buffet onset conditions

In transonic flow,buffet is a phenomenon of flow instability caused by shock wave/boundary layer interaction and flow separation.The phenomenon is common in transonic flow,and it has serious impact on the structural strength and fatigue life of aircraft.In this paper,three typical airfoils:the supercritical OAT15A,the high-speed symmetrical NACA64A010,and the thin,transonic/supersonic NACA64A204 are selected as the research objects.The flow fields of these airfoils under pre-buffet and buffet onset conditions are simulated by Unsteady Reynolds Averaged Navier-Stokes (URANS) method,and the mode analysis of numerical results is carried out by Dynamic Mode Decomposition (DMD).Qualitative and quantitative analysis of the shock wave motion,shock wave intensity,shock foot bubble and trailing edge separation,and pressure coefficient fluctuation were performed to attain deep insight of transonic buffet flow features of different airfoils near buffet onset conditions.The results of DMD analysis show that the energy proportion of the steady mode of these airfoils decreases dramatically when approaching the buffet onset angle of attack,while the growth rate of the primary mode increases inversely.It was found that at the onset of buffet,there exist different degrees of merging behavior between shock foot bubble and trailing edge separation during one buffet cycle,and the instability of shock wave and separation induced shear layer are closely related to the merging behavior.

Estimating posterior inference quality of the relational infinite latent feature model for overlapping community detection

Overlapping community detection has become a very hot research topic in recent decades,and a plethora of methods have been proposed.But,a common challenge in many existing overlapping community detection approaches is that the number of communities K must be predefined manually.We propose a flexible nonparametric Bayesian generative model for count-value networks,which can allow K to increase as more and more data are encountered instead of to be fixed in advance.The Indian buffet process was used to model the community assignment matrix Z,and an uncol-lapsed Gibbs sampler has been derived.However,as the community assignment matrix Zis a structured multi-variable parameter,how to summarize the posterior inference results andestimate the inference quality about Z,is still a considerable challenge in the literature.In this paper,a graph convolutional neural network based graph classifier was utilized to help tosummarize the results and to estimate the inference qualityabout Z.We conduct extensive experiments on synthetic data and real data,and find that empirically,the traditional posterior summarization strategy is reliable.

Posterior contraction rate of sparse latent feature models with application to proteomics

The Indian buffet process(IBP)and phylogenetic Indian buffet process(pIBP)can be used as prior models to infer latent features in a data set.The theoretical properties of these models are under-explored,however,especially in high dimensional settings.In this paper,we show that under mild sparsity condition,the posterior distribution of the latent feature matrix,generated via IBP or pIBP priors,converges to the true latent feature matrix asymptotically.We derive the posterior convergence rate,referred to as the contraction rate.We show that the convergence results remain valid even when the dimensionality of the latent feature matrix increases with the sample size,therefore making the posterior inference valid in high dimensional settings.We demonstrate the theoretical results using computer simulation,in which the parallel-tempering Markov chain Monte Carlo method is applied to overcome computational hurdles.The practical utility of the derived properties is demonstrated by inferring the latent features in a reverse phase protein arrays(RPPA)dataset under the IBP prior model.

Buffet Moves Into China

Warren Buffett is financing BYD Co. Ltd.’s auto dream with a strategic investment of $230