Unsteady Linearisation of Bed Shear Stress for Idealised Storm Surge Modelling

The modelling of time-varying shallow flows, such as tides and storm surges, is complicated by the nonlinear dependency of bed shear stress on flow speed. For tidal flows, Lorentz’s linearisation circumvents nonlinearity by specifying a (steady) friction coefficient r based on a tide-averaged criterion of energy equivalence. However, this approach is not suitable for phenomena with episodic and irregular forcings such as storm surges. Here, we studied the implications of applying Lorentz’s energy criterion in an instantaneous sense, so that an unsteady friction coefficient r(t) adjusts to the temporal development of natural wind-driven flows. This new bed-stress parametrisation was implemented in an idealised model of a single channel, forced by time-varying signals of wind stress (acting over the entire domain) and surface elevation (at the channel mouth). The solution method combines analytical solutions of the cross-sectionally averaged linearised shallow-water equations, obtained in the frequency domain, with an iterative procedure to determine r(t). Model results, compared with a reference finite-difference solution retaining the quadratic bed shear stress, show that this new approach accurately captures the qualitative and quantitative aspects of the surge dynamics (height and timing of surge peaks, sloshing, friction-induced tide-surge interaction) for both synthetic and realistic wind forcings.

Download Full-text

INFLUENCE OF NON-LINEAR WAVES AND UNDERTOW IN SANDBAR DEVELOPMENT

Coastal Engineering Proceedings ◽

10.9753/icce.v33.sediment.55 ◽

2012 ◽

Vol 1 (33) ◽

pp. 55 ◽

Cited By ~ 3

Author(s):

Tiago Abreu ◽

Francisco Sancho ◽

Paulo A. Silva

Keyword(s):

Shear Stress ◽

Sediment Transport ◽

Transport Model ◽

Relative Strength ◽

Correct Prediction ◽

Data Sets ◽

Time Varying ◽

Bed Shear Stress ◽

Linear Waves ◽

Non Linear

As waves propagate from deep into shallow waters, they begin to interact with the sea floor and undergo through several changes due to non-linear effects. These interactions cause the waves to transform and become non-linear as they decelerate and finally break. These local nonlinearities are reflected on the near-bed oscillatory flow and are inextricably linked to sediment transport, causing erosion-accretion patterns and bar migration. In this work the ability of a practical transport model that includes the effects of velocity and acceleration skewness in the time-varying bed shear stress (Abreu et al., 2011) is assessed to predict sediment transport rates under oscillatory flows and currents. The results are compared with two different data sets obtained under sheet flow conditions, showing a good agreement with the measurements. Moreover, its performance to the undertow and to non-linear characteristics is further assessed. The practical sediment transport model is coupled to a simple bed-evolution model, enabling to evidence the relative strength of mechanisms associated with the wave and current induced sand transports. The results show that the formation of the bar and its migration is affected by a new term introduced in the bed shear stress predictor. This time-varying term accounts for the shape of the wave and is described through two non-linear parameters recently proposed in Abreu et al. (2010).This work provides further insights in the correct prediction of sediment transport modeling and sandbar developments, due to the combined influence of non-linear waves with undertow currents.

Download Full-text

Efficiency prediction for storage chambers using computational fluid dynamics

Water Science & Technology ◽

10.2166/wst.1996.0202 ◽

1996 ◽

Vol 33 (9) ◽

pp. 163-170 ◽

Cited By ~ 4

Author(s):

Virginia R. Stovin ◽

Adrian J. Saul

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Shear Stress ◽

Particle Tracking ◽

Critical Value ◽

Complex Geometries ◽

Bed Shear Stress ◽

Breadth Ratio ◽

Computational Fluid Dynamics Cfd ◽

Simulated Flow

Research was undertaken in order to identify possible methodologies for the prediction of sedimentation in storage chambers based on computational fluid dynamics (CFD). The Fluent CFD software was used to establish a numerical model of the flow field, on which further analysis was undertaken. Sedimentation was estimated from the simulated flow fields by two different methods. The first approach used the simulation to predict the bed shear stress distribution, with deposition being assumed for areas where the bed shear stress fell below a critical value (τcd). The value of τcd had previously been determined in the laboratory. Efficiency was then calculated as a function of the proportion of the chamber bed for which deposition had been predicted. The second method used the particle tracking facility in Fluent and efficiency was calculated from the proportion of particles that remained within the chamber. The results from the two techniques for efficiency are compared to data collected in a laboratory chamber. Three further simulations were then undertaken in order to investigate the influence of length to breadth ratio on chamber performance. The methodology presented here could be applied to complex geometries and full scale installations.

Download Full-text

Particle Responses to Near-Bed Shear Stress in a Shallow, Wave- and Current-Driven Environment

10.1002/essoar.10507100.1 ◽

2021 ◽

Author(s):

Grace Chang ◽

Galen Egan ◽

Joseph D McNeil ◽

Samuel McWilliams ◽

Craig Jones ◽

...

Keyword(s):

Shear Stress ◽

Bed Shear Stress

Download Full-text

Study on bed shear stress around channel constriction.

Doboku Gakkai Ronbunshu ◽

10.2208/jscej.1985.357_115 ◽

1985 ◽

pp. 115-121

Author(s):

Susumu HASHIMOTO ◽

Yoshitaka FUKUI ◽

Hideo KIKKAWA

Keyword(s):

Shear Stress ◽

Bed Shear Stress ◽

Channel Constriction

Download Full-text

Slip-Clutch Torque Estimation via Real-Time Adaptive Lookup Table

ASME Letters in Dynamic Systems and Control ◽

10.1115/1.4052462 ◽

2021 ◽

Vol 2 (2) ◽

Author(s):

Wenpeng Wei ◽

Hussein Dourra ◽

Guoming Zhu

Keyword(s):

Friction Coefficient ◽

Real Time ◽

Mean Squared Error ◽

Surface Friction ◽

Lookup Table ◽

Recursive Least Squares ◽

Time Varying ◽

Squared Error ◽

Output Torque ◽

Clutch Torque

Abstract Transfer case clutch is crucial in determining traction torque distribution between front and rear tires for four-wheel-drive (4WD) vehicles. Estimating time-varying clutch surface friction coefficient is critical for traction torque control since it is proportional to the clutch output torque. As a result, this paper proposes a real-time adaptive lookup table strategy to provide the time-varying clutch surface friction coefficient. Specifically, the clutch-parameter-dependent (such as clutch output torque and clutch touchpoint distance) friction coefficient is first estimated with available low-cost vehicle sensors (such as wheel speed and vehicle acceleration); and then a clutch-parameter-independent approach is developed for clutch friction coefficient through a one-dimensional lookup table. The table nodes are adaptively updated based on a fast recursive least-squares (RLS) algorithm. Furthermore, the effectiveness of adaptive lookup table is demonstrated by comparing the estimated clutch torque from adaptive lookup table with that estimated from vehicle dynamics, which achieves 14.8 Nm absolute mean squared error (AMSE) and 2.66% relative mean squared error (RMSE).

Download Full-text

The influence of deposit body on the near-bed shear stress

Proceedings of the Institution of Civil Engineers - Water Management ◽

10.1680/jwama.20.00139 ◽

2021 ◽

pp. 1-29

Author(s):

Yan He ◽

Jing Zhang ◽

Huling Jiang ◽

Zhixue Guo ◽

Hongxi Zhao

Keyword(s):

Shear Stress ◽

Bed Shear Stress

Download Full-text

Accurate Measurements of Wall Shear Stress on a Plate with Elliptic Leading Edge

Sensors ◽

10.3390/s18082682 ◽

2018 ◽

Vol 18 (8) ◽

pp. 2682 ◽

Cited By ~ 2

Author(s):

Guang-Hui Ding ◽

Bing-He Ma ◽

Jin-Jun Deng ◽

Wei-Zheng Yuan ◽

Kang Liu

Keyword(s):

Shear Stress ◽

Wind Tunnel ◽

Wall Shear Stress ◽

Leading Edge ◽

Reynold Number ◽

Micro Electro Mechanical System ◽

Flow Speed ◽

Silicon On Insulator ◽

Micro Sensor ◽

Wall Shear

A micro-floating element wall shear stress sensor with backside connections has been developed for accurate measurements of wall shear stress under the turbulent boundary layer. The micro-sensor was designed and fabricated on a 10.16 cm SOI (Silicon on Insulator) wafer by MEMS (Micro-Electro-Mechanical System) processing technology. Then, it was calibrated by a wind tunnel setup over a range of 0 Pa to 65 Pa. The measurements of wall shear stress on a smooth plate were carried out in a 0.6 m × 0.6 m transonic wind tunnel. Flow speed ranges from 0.4 Ma to 0.8 Ma, with a corresponding Reynold number of 1.05 × 106~1.55 × 106 at the micro-sensor location. Wall shear stress measured by the micro-sensor has a range of about 34 Pa to 93 Pa, which is consistent with theoretical values. For comparisons, a Preston tube was also used to measure wall shear stress at the same time. The results show that wall shear stress obtained by three methods (the micro-sensor, a Preston tube, and theoretical results) are well agreed with each other.

Download Full-text