Shear Dissipation Research Articles

Seismic retrofitting optimization model using fiber-reinforced polymer jacketing and NSGA-III

Fiber-reinforced polymer (FRP) is widely used for retrofitting structural elements due to its easy application. However, establishing a retrofit strategy is challenging due to conflicting objectives, such as cost and performance level, requiring optimization for effective decision-making. This study proposes a many-objective optimization model for seismic retrofitting using FRP and the Non-dominated Sorting Genetic Algorithm (NSGA)-III. The model's efficacy was demonstrated through two numerical examples: a reinforced concrete building retrofitted with FRP jackets and a masonry-infilled reinforced concrete building retrofitted with FRP bracings. Each example included three objective functions and multiple constraints. Nonlinear static pushover analysis provided optimal strategies to enhance base shear and energy dissipation while minimizing costs and retrofitting locations. Among the Pareto-optimal solutions, the optimal solution with the minimum Euclidean distance was selected. NSGA-III offered a wider distribution and more Pareto-optimal solutions compared to NSGA-II, demonstrating its potential in addressing many-objective problems related to retrofit decision-making.

Effect of sepiolite on the rheological properties of shear thickening fluid and improvement mechanism analysis

To improve the performance of shear thickening fluids (STFs), we propose the addition of fibrous sepiolite. Through macroscopic rheological tests and microscopic characterization, the effects of different sepiolite mass fractions (0 wt%, 1 wt%, 2 wt% and 3 wt%) on the shear thickening of a SiO2-STF system (with a PEG200 dispersion medium) at different ambient temperatures (20 °C, 30 °C, 40 °C and 50 °C) were investigated. Rheological experiments revealed a significant improvement in the shear thickening of SiO2-STF with the addition of sepiolite (Sep/SiO2-STF), with 7.11- and 1.94-fold increases in absolute and relative shear thickening, respectively. As the sepiolite mass fraction increased from 0 wt% to 3 wt%, the temperature sensitivity coefficient decreased from 13.493 to 4.839, indicating that the Sep/SiO2-STF system still exhibited favourable shear thickening at 50 °C. Dynamic oscillatory shear testing revealed that with an increase in sepiolite mass fraction from 0 wt% to 3 wt%, the maximum energy storage modulus, maximum energy dissipation modulus and shear stress increased by 5196.25 %, 1676.16 % and 377.54 %, respectively. Microscopic characterization revealed that sepiolite induced the formation of more clusters in the STF system primarily through the physical adsorption of silica particles and Si–OH on its surface, leading to a significant increase in the shear thickening effect.

The mechanical performance of reinforced bituminous interfaces with paving fabric under freeze-thaw conditioning

The application of paving fabric at the interface of bituminous layers as a rehabilitation strategy has proved its effectiveness in extending the pavement service life by delaying the manifestation of reflective cracking on the surface. However, this enhanced performance relies on the adhesion bond supplied at the interface, which in the case of debonding, the structural benefits provided by the interlayer can be compromised. Gaining authentic knowledge about the bonding condition at a reinforced interface exposed to different conditioning impacts helps to improve the reliability of the input data, which has not been adequately considered in the mechanistic-based design methods proposed for reinforced bituminous structures. This research was dedicated to understanding the mechanical behavior of double-layer bituminous layers composed of two different hot mixtures and reinforced with paving fabric when subjected to freeze-thaw cycling. To attain this objective, the initial step involved determining the optimal dosage of bitumen for use as a tack coat at the interface of the paving fabric, which was established as 0.0014 m3/m2 through asphalt retention tests. Subsequently, the results from the shear test, conducted using the slant shear device, were utilized to establish three comparative criteria at the interface, aimed at elucidating distinctions when compared to unreinforced cases. These criteria include the energy absorbed by the interface during shearing, shear stiffness, and the coefficient of interface bonding (CIB). This study revealed that by increasing the number of freeze-thaw cycling, the reinforced interface keeps the shear stiffness and the CIB values unchanged. However, in terms of energy absorption capabilities, the unreinforced interfaces showed better performance. This study showed that using the CIB value to quantify the bonding strength at the interface and energy dissipation and initial shear stiffness to quantify the evolution of interface bonding over number of F-T cycles are all proper representatives to include into mechanistic-empirical design methods for reinforced structures in order to present realistic models.

STABILITY ASSESSMENT OF ROOT-REINFORCED SLOPES USING FINITE ELEMENT LIMIT ANALYSIS

Slope instability poses serious threats to infrastructure and environmental sustainability. As a result, numerous reinforcement techniques have been used as disaster mitigation attempts to prevent slope failure. Among various traditional slope reinforcement methods, the use of vegetion root is more cost-effective and environmentally friendly. This paper presents stability assessment of root-reinforced slopes. Firstly, slope models were built for case of bare and root-reinforced slopes. The slope angles were varied in the range of 15º ~ 55 º. The root cohesion and depth of root zone were adjusted within the ranges of 0 ~ 20 kPa and 0 ~1.5 m, respectively. The strength reduction finite element limit analysis method was applied to evaluate the stability of the slopes in this study. The results indicate that factor of safety increases with the increasing of root cohesion and depth of root zone. The best factor of safety was obtained for the case with root cohesion and depth of root zone of 20 kPa and 1.5 m, respectively. Shear dissipation contours of the slope models also show that root reinforcement reduces shear dissipation energy along the failure surface, consequently lowering the possibility of slope failure.

Failure prediction of butterfly-shaped steel plate shear keys under cyclic loadings

A novel energy dissipation shear key (BSP shear key) is proposed using multiple butterfly-shaped steel plates arranged in parallel for small-to-medium-span highway bridges. Two series of quasi-static experiments have been conducted to investigate the influence of loading protocols on the energy dissipation behavior of the BSP shear keys. Based on the test results, a simplified bilinear model is developed to represent the force-displacement skeleton curves of the BSP shear keys subjected to different loading protocols. And the force-displacement hysteretic curve of the BSP shear keys is decomposed into the skeleton part and the Bauschinger one. The energy dissipation capacity of the BSP shear keys can then be approximately calculated by adding the energies dissipated by the two parts respectively. The energy dissipation of the skeleton part can be determined using the simplified bilinear model and the one of the Bauschinger part is derived according to the loading protocols. The calculated energy dissipation capacity of the BSP shear key specimens can be validated by the test results with the maximum error of 13.9%. Finally, a flowchart is proposed to predict the failure of the BSP shear keys based on their energy dissipation capacity under cyclic loadings. The prediction results indicate that the proposed flowchart can capture with a satisfactory accuracy the failure of the BSP shear keys due to their energy dissipation capacity being exhausted. This study demonstrates that the failure prediction is feasible based on the energy dissipation capacity of the BSP shear keys.

Energy dissipation evaluation of butterfly-shaped steel plate shear keys under different loading protocols

This paper proposes a novel energy dissipation shear key (ED shear key) for small-to-medium-span highway bridges using butterfly-shaped steel plates for enhanced energy dissipation capacity. Reversed cyclic loading tests were conducted on two series of specimens which had different designs of structural dimensions. Four distinctive loading protocols were adopted to allow an in-depth examination of the seismic hysteretic behavior and energy dissipation capacity of the ED shear keys. The test results reveal that the ED shear keys exhibited distinctive characteristics before and after buckling of steel plates. The recorded force-displacement curves of the ED shear keys were plump before buckling and typically became pinched after buckling. The loading protocol had a significant effect on the energy dissipation of the ED shear key specimens, with an over 90% increase in energy dissipation observed under the constant-amplitude loading protocol compared to the incremental-amplitude ones. It was found from the test results that the profile of the force-displacement skeleton curves was hardly affected by the loading protocols, as a result a trilinear skeleton model is developed to characterize the force-displacement relationship of the ED shear keys. Furthermore, by decomposing the force-displacement hysteresis curve into a skeleton part and a Bauschinger part, an evaluation model is established for predicting the energy dissipation capacity of the ED shear keys. Validation against the test results indicates that the evaluation model can provide a satisfactory accuracy for predicting the energy dissipation of the ED shear keys subjected to various loading protocols.

Application of artificial neural networks for predicting lateral and uplift capacity of buried rectangular box carrying pipelines

Urban and offshore subterranean comprehensive pipelines are currently utilized frequently as infrastructure for fitting different engineering pipelines used for electricity, signal transmission, natural gas, petroleum, heating, water supply, and drainage systems. This study utilizes the finite element limit analysis (FELA) and artificial neural network (ANN) to evaluate the pull-out capacity factor of the buried rectangular box carrying the pipelines with internal inclined force in cohesive soil. In FELA, rigorous upper bound and lower bound solutions are performed to achieve the exact result. In this study, a dimensionless parametric analysis is carried out by considering the effect of five parameters viz. buried depth ratio, width-depth ratio, overburden factor, internal inclination angles, and interface factor on the pull-out capacity factor of a buried rectangular box, which can be called as a rectangular pipeline. Two significant samples of the investigated parameters are selected to evaluate the soil failure pattern (failure envelope) using the shear dissipation of soil failure for the buried rectangular pipeline subjected to inclined loading. Using the FELA results, the predictive equations are proposed using ANN, and then sensitivity analysis is performed to examine the sensitivity of each investigated essential parameter on the stability of the underground rectangular pipeline. The predictive ANN model for the buried rectangular pipe subjected to inclined loading is presented as design charts for practice and further investigation.

On local isotropy and scale dependence of pair dispersion in turbulent canopy flows

Canopy flows in the atmospheric surface layer play important economic and ecological roles, governing the dispersion of passive scalars in the environment. The interaction of high-velocity fluid and large-scale surface-mounted obstacles in canopy flows produces drag and causes intense, inhomogeneous and anisotropic turbulence. In this work, we focus on the turbulent dispersion of passive scalars by studying the ‘pair dispersion’ – a statistical measure of relative motion between particles. We analyse the results of a three-dimensional particle tracking velocimetry experiment in a wind-tunnel canopy flow, focusing on small scales. We confirm the existence of local isotropy of pair dispersion at scales smaller than a characteristic shear length scale $L_\varGamma =(\epsilon /\varGamma ^3)^{1/2}$ , where $\epsilon$ and $\varGamma$ are the mean dissipation rate and shear rate, respectively. Furthermore, we show that pair dispersion in this locally isotropic regime is a scale-dependent super-diffusive process, similar to what occurs in homogeneous isotropic turbulent flows. In addition, we measure the pair relative velocity correlation function, showing that its de-correlation occurs in the locally isotropic regime, and discuss the implications of this observation for modelling pair dispersion. Thus, our study extends the fundamental understanding of turbulent pair dispersion to the anisotropic inhomogeneous turbulent canopy flow, bringing valuable information for modelling scalar dispersion in the atmospheric surface layer.

Geometry of stratified turbulent mixing: local alignment of the density gradient with rotation, shear and viscous dissipation

We introduce a geometric analysis of turbulent mixing in density-stratified flows based on the alignment of the density gradient in two orthogonal bases that are locally constructed from the velocity gradient tensor. The first basis connects diapycnal mixing to rotation and shearing motions, building on the recent ‘rortex–shear decomposition’ in stratified shear layers (Jiang et al., J. Fluid Mech., vol. 947, 2022, A30), while the second basis connects mixing to the principal axes of the viscous dissipation tensor. Applying this framework to datasets taken in the stratified inclined duct laboratory experiment reveals that density gradients in locations of high shear tend to align preferentially (i) along the direction of minimum dissipation and (ii) normal to the plane spanned by the rortex and shear vectors. The analysis of the local alignment across increasingly turbulent flows offers new insights into the intricate relationship between the density gradient and dissipation, and thus diapycnal mixing.

Effect of non-deformable and deformable bubbles on static yield stress of cement mortar

While extensive research has delved into the impact of single size distribution and volume fraction of bubbles on the static yield stress of cement mortar, this investigation pertains to previously underexplored variables. These encompass the ramifications of multi-size bubble distributions, variations in bubble geometries, disparities in air-liquid interfacial characteristics, and surfactant concentrations. In order to scrutinize these factors, bubbles exhibiting distinct volume fractions and size distributions were deliberately induced through the admixture of varying concentrations of nonionic surfactants, while maintaining a water-to-cement ratio (w/c) of 0.42 under controlled conditions at a temperature of 20 °C. Experimental testing involved the analysis of bubble deformation during the yield process of cement mortar, including a surface tension tester, micro-CT, and numerical simulations. Furthermore, the study investigated the influence of nonionic surfactants on the interaction forces between cement particles, employing comprehensive analysis methods such as a total organic carbon analyzer, Zeta potential measurements, and contact angle tests. The consolidated outcomes from experimental trials and numerical simulations substantiate that augmenting the concentration of nonionic surfactants does not amplify the interparticle interaction forces within cement particles. Rather, it solely leads to an escalation in the volume fraction of bubbles. During the cement mortar yielding process, bubbles exhibit two distinct states: deformable and non-deformable, characterized by the Bingham capillary number. Notably, the research reveals that the effect of increasing the volume fraction of non-deformable bubbles on the static yield stress is more significant than the impact of these bubbles on reducing maximum packing density. This effect is attributed to the increased number of contacts between particles. Additionally, the larger and flatter surface area of deformable bubbles promotes the orderly arrangement of cement particles, thereby reducing local shear dissipation. Consequently, an increase in the volume fraction of deformable bubbles and the Bingham capillary number contributes to a reduction in the static yield stress. In consideration of these discoveries, this study introduces a qualitative approach for characterizing the static yield stress of aerated cement mortar, leveraging the volume fractions of deformable and non-deformable bubbles, in conjunction with the maximum packing density and Bingham capillary number.

Seismic behavior of the brick masonry rural building strengthened with polypropylene grid cement mortar coating: Shaking table tests

Brick masonry structures are widely applied around the world, especially in Chinese rural areas, but their seismic performance is not satisfactory due to high brittleness of material and poor integrity of structure. Accordingly, a low-cost and highly efficient strengthening method for brick masonry structure is needed. This paper presents the shaking table tests for a 1/2-scale single-story brick masonry rural building strengthened with polypropylene grid cement mortar coating. The damage states of the test model under earthquake motions with different intensity were observed. The dynamic characteristics including natural frequency and damping ratio were discussed. The seismic response, such as acceleration, displacement, torsion angle, base shear and hysteretic energy dissipation, were analyzed. The results show that the weak areas of the test model were the corners of windows and door, the intersections between longitudinal wall and transverse wall and the top of longitudinal walls. With the input PGA of 1.0 g, the natural frequencies of the test model in the X and Y directions decreased to 93.1 % and 88.2 % of the initial values, respectively, the damping ratio in the X and Y directions increased to 2.56 and 1.61 times the initial values, respectively, and the maximum story drift and horizontal torsion angle were 1/122 and 0.0037 rad, respectively. The comparison between actual earthquake damage and test results showed that the use of polypropylene grid cement mortar coating to strengthen brick masonry rural building could result in good seismic behaviors.

Energy loss analysis of transition simulation for a prototype reversible pump turbine during load rejection process

The dynamic behavior of a reversible pump turbine (RPT) during the load rejection process was investigated through numerical simulation and experimental testing. The study focused on various parameters, such as the operation of guide vanes, torque, flow, head, and runner forces. The pressure fluctuations at different monitoring points were analyzed using the time-frequency method, specifically the continuous wavelet transforms (CWT). The results revealed significant pressure pulsation amplitudes in the vaneless region. Additionally, the entropy production rate was employed to quantify energy loss in different domains, including direct dissipation, turbulent dissipation, and wall shear stress. Moreover, the study utilized the vorticity transport equation to examine vortex characteristics and transport in the stay vanes, guide vanes, and runner flow channels. The vortex characteristics were classified into relative vortex stretching (RVS), Coriolis force (CORF), and viscous diffusion (VISD). The findings highlight significant energy loss in flow patterns associated with high RVS and CORF regions. This study provides valuable insights into the transition process and energy loss of RPTs during load rejection, serving as a basis for future research aiming to enhance the safety and reliability of RPTs under load rejection conditions.

Innovative pier comprised of CFST-columns and steel-shear-links: Conception, design principle, experimental investigation

An innovative fabricated energy dissipation pier comprised of concrete filled steel tubular (CFST) columns and steel shear links was proposed and its mechanical performance was experimentally investigated. Firstly, based on basic mechanical behavior analysis of such pier, the design principles of its components, including the CFST column, energy dissipation shear links and joints, were suggested. Furthermore, two test specimens with different shear link configurations were designed and experimentally investigated. The bearing and deformation capacity of the specimens were obtained, and experimental phenomenon and failure mode were analyzed. In addition, load-displacement curve, strain distribution characteristics, bearing capacity, ductility and energy dissipation capacity of the specimens were also comparatively analyzed and discussed. The results showed that the suggested design principles could achieve reasonable failure mode. During the loading process, the energy dissipation shear links firstly occurred shear yielding, and the stiffness of piers decreased correspondingly due to yielding of links. Then, with continuous increase of the lateral loading displacement at top of the pier, the shear displacement of energy dissipation links gradually increased, and the piers exhibited significant secondary stiffness due to plastic over strength of shear links. In addition, the feet of columns gradually yielded due to the moment in column feet and tension or compression in columns induced by the shearing force in the links. Finally, the piers failed in column feet due to cyclic tension-flexure and compression-flexure at large lateral drift ratio. Before column feet failure occurred, the pier exhibited stable bearing capacity and excellent energy dissipation capacity.

Combined SCD-SPSW system subjected to ground excitation

PurposeIn this study, the application of a novel combined steel curved damper (SCD) and steel plate shear wall (SPSW) system in the 5-, 10- and 15-storey steel moment-resisting frames (SMR) subjected to earthquake excitation has been investigated. The proposed system is called here as the SMR-WD (steel moment resisting–wall damper).Design/methodology/approachAt the beginning of this research, an SMR-W and an SMR-D are separately modeled in ABAQUS software and verified against the available experimental data. After that, three different heights SMR-WD systems (5-, 10- and 15-storey) are designed and simulated. Then, their performances are examined and compared to the corresponding SMR-W under the effects of six actual earthquake records.FindingsThe obtained results show that the proposed system increases the mean values of the base shear for 5-, 10- and 15-storey SMR-WD equal to 27, 20.15 and 16.51%, respectively compared to the corresponding SMR-W. Moreover, this system reduces the drift of the floors so that the reduction in the average values of maximum drift for 5-, 10- and 15-storey SMR-WD is equal to 10, 7 and 29%, respectively with respect to the corresponding SMR-W. The results also reveal that the considered system dissipates more energy than SMR-W so that the increase in the mean values of the energy absorption for 5-, 10- and 15-storey SMR-WD is 30.8, 25.6 and 41.3%, respectively when compared to the SMR-W. Furthermore, it is observed that SMR-WD has a positive effect on the seismic performance of the link beams and panel zones of the frames. By increasing the height of the structure in the SMR-WD, the energy dissipation and base shear force increases and the drift of floors decreases. Hereupon, the proposed SMR-WD system is more useful for tall buildings than SMR-W frames.Originality/valueFor the first time, the application of a novel combined steel curved damper (SCD) and steel plate shear wall (SPSW) system in the 5-, 10- and 15-storey steel moment-resisting frames (SMR) subjected to earthquake excitation has been investigated.

Three-dimensional seismic face stability of shield tunnels in undrained clay

Tunnel face stability has received increasing research interest over the past few decades. However, computing time-efficient and safe three-dimensional solutions under seismic loading is still an unsolved problem, while case studies indicate that seismic loading can be one critical destabilizing factor affecting tunnel stability. The primary objective of this work is to fill this gap in knowledge by providing compromising and computationally efficient solutions, along with their respective lower and upper bounds, to compute face stability under seismic conditions. The analyses employ the finite element limit analysis method to evaluate the limit support pressure in undrained clay, considering horizontal pseudo-static seismic forces pointing outwards from the face. Moreover, the analyses employ both constant and linearly increasing shear strengths with depth. The results are summarized as dimensionless stability charts and tables to facilitate their interpretation and future use for tunnel design. A new design equation has been developed to evaluate the stability of the tunnel face considering the effect of seismic forces. Additionally, the effects of different parameters on the shape of the failure mechanism have been investigated by analysing the distribution of shear dissipation.

Modulation effect of linear shear flow, wind, and dissipation on freak wave generation in finite water depth

This paper studies the modulation effect of linear shear flow (LSF), comprising a uniform flow and a shear flow with constant vorticity, combined with wind and dissipation on freak wave generation in water of finite depth. A nonlinear Schrödinger equation (NLSE) modified by LSF, strong wind, and dissipation is derived. This can be reduced to consider the effects of LSF, light wind, and dissipation, and further reduced to include only LSF. The relation between modulational instability (MI) of the NLSE and freak waves represented as a modified Peregrine Breather solution is analyzed. When considering only LSF, the convergence (divergence) effect of uniform up-flow (down-flow) and positive (negative) vorticity increases (decreases) the MI growth rate and promotes (inhibits) freak wave generation. The combined effect of LSF and light wind shows that a light adverse (tail) wind can restrain (amplify) MI and bury (trigger) freak waves. Under the effect of a light tailwind, LSF has the same effect on the MI growth rate and freak wave generation as the case without any wind. The combination of LSF and strong wind enables both adverse and tail winds to amplify MI and trigger freak waves. In the presence of strong wind, LSF has the opposite effect to the case of a light tailwind.

Influence of proteins and phospholipids on strain softening behaviors of natural rubber

In natural rubber (NR), the non-rubber components such as protein and phospholipids strongly influence the Payne effect and Mullins effect while the mechanisms are not yet clarified so far. Herein deproteinized NR (DPNR) and transesterified DPNR (TEDPNR) are prepared and rheological behaviors are investigated. It is shown that the non-rubber components greatly retard the terminal flow behavior. In comparison with NR, DPNR and TEDPNR exhibit significant hysteresis and worse recoverability under large amplitude shear. During cyclic tensile deformation, the DPNR vulcanizate behaves similar to the NR one, while the TEDPNR one demonstrates higher deformation energy normalized with theoretical shear modulus and dissipation ratio. It is suggested that both the protein and phospholipids influence the Payne effect of NR gum by forming aggregates and creating intermolecular association. On the other hand, the phospholipids rather than protein strongly influence the Mullins effect by lowering their crosslinking density and associating the rubbery chains. This investigation would be enlightening for understanding the mechanisms of the Payne effect and Mullins effect of the NR materials.

Turbulence near a sandbar island in the lower Missouri River

AbstractRiver turbulence is spatially variable due to interactions between morphology of rivers and physical mechanics of flowing water. Understanding the variation of turbulence in rivers is important for characterizing transport processes of soluble and particulate materials in these systems. We present an exploratory effort to understand ecologically relevant flow patterns using measurements of mean flow and turbulence in a highly engineered river channel around an island in the lower Missouri River. Specifically, the profiles of mean river velocities were investigated to examine the logarithmic relation and associated parameters, including shear velocity and bed roughness. Turbulence intensity and Reynolds shear stress were compared with classic open‐channel profiles and previously reported river data in the hydraulics literature. With the capability of pulse‐to‐pulse coherent Doppler velocity profiling in high spatial resolution, we estimated the profiles of turbulence dissipation rate using resolved one‐dimensional velocity spectra. These measurement data allow us to examine the validity of turbulence production‐dissipation balance and the classic open‐channel profiles of turbulence statistics, including turbulence intensity, Reynolds shear stress, dissipation rate, and eddy viscosity. The field data show a strong variation of turbulence profiles in close vicinity of the river island. In shallow water depths close to the island, turbulence is substantially enhanced in comparison with classic open‐channel profiles. Such turbulence enhancement is likely attributed to non‐uniformity of the flow structures.

Observed Turbulent Dissipation Rate in a Landfalling Tropical Cyclone Boundary Layer

Abstract Based on turbulence measurements from sonic anemometers instrumented at multiple levels on a 356-m-tall meteorological tower located on the south coast of China, an observation study of the turbulent dissipation rate (ε) in a landfalling tropical cyclone boundary layer (TCBL) is conducted. Three indirect methods (i.e., the power spectra, the second- and the third-order structure functions) are compared for the calculation of ε. The third-order structure function computes the smallest ε among the three methods, but shows the largest uncertainty. The second-order structure function gives similar ε estimates as the power spectra, and is adopted for its reduced uncertainty. The measured ε in the landfalling TCBL is O(10−1) m2 s−3, much greater than typical atmospheric boundary layer values as well as oceanic TCBL values. The value of ε is found to scale with the local friction velocity rather than the surface friction velocity, implying a highly localized nature of turbulence. Conventional parameterizations of ε are evaluated against observations. Process-based ε models assuming a local balance between shear production and dissipation prove inadequate, as shear production merely accounts for half of the dissipation away from the surface. In comparison, scaling-based ε models used by planetary boundary layer (PBL) schemes are more advantageous. With both tuning of the model coefficients and adjustment of the dissipation length scale, the performance of an ε model in a widely used PBL scheme is shown to produce similar values to the observations. Significance Statement Dissipation in a turbulent flow refers to the conversion of kinetic energy to heat through molecular viscosity, and is of key dynamic and thermal–dynamic importance in the tropical cyclone boundary layer (TCBL). Past observations of ε in the TCBL have been rare. Few existing ones are based on surface and flight measurements that are either constrained in height or limited in time. This study utilizes turbulence measurements taken from a 356-m meteorological tower to study dissipation of a landfalling TC. The tall tower platform offers a valuable turbulence dataset that extends beyond the surface layer of the TCBL. The observations are used to improve the physical understanding of dissipation, and to evaluate diagnostic ε models for numerical weather prediction.

Turbulent mixing in a choked shallow lagoon and the impacts of remediation engineering

Turbulent mixing is an important mechanism that controls the transport of materials and energy in coastal transitional water bodies such as lagoons, thereby affecting their internal environments. In this study, a three-dimensional numerical model was employed to simulate the hydrodynamics and salinity distribution in a large, shallow, choked lagoon, yielding variables related to momentum and salinity mixing processes, such as shear stress, salinity mixing flux, and buoyancy flux. The results revealed the turbulent mixing pattern of the lagoon during tidal cycles. The characteristics of turbulent mixing are different between the downstream region with a complex topography and the flat upstream region. The frictional shear in the downstream channel and deep groove fully mixed the water column, resulting in a relatively unstratified state. In the upstream region, buoyancy effects dominate stratification in the middle-upper part of the water column, which supported turbulent mixing near the bottom therein and throughout the water column in the downstream region. The turbulent mixing in the lagoon was regulated by the spring-neap tidal cycle and was intensified during spring tides due to the increased tidal flow. Given the hydrodynamic and environmental issues in Xiaohai Lagoon (XHL), the government proposed a series of remediation schemes in connection with the inlet and channel of the lagoon. In this study, based on the characteristics of actual engineering, several typical scenarios were set up to analyze the impact of remediation projects on lagoon mixing processes. The openness parameter was selected to evaluate the extent of the lagoon regulations. As the openness parameter increased, the overall mixing of the lagoon was enhanced, whereas a larger increase in shear dissipation caused a drop in overall mixing efficiency. Excessive connectivity between lagoons and the ocean can lead to inefficiencies in turbulent mixing and intense marine effects, which are issues in lagoon management.