Wind-induced Stress Research Articles

Effect of Distributed Loading and Refined Modeling on Wind-Induced Stress Analysis of Long-Span Bridges

Wind-induced stress analysis is essential for evaluating the local failure and fatigue damage of long-span bridges in wind-prone regions. Nevertheless, the accuracy of stress-level analysis can be affected by the choice of wind loading and structure models. This study formulates three scenarios to calculate the wind-induced response of a long-span bridge, incorporating two types of wind load models (lumped force or distributed force) and two types of finite element (FE) models (spine-beam or substructure). Specifically, Case 1 employs the lumped force and beam model, Case 2 adopts the lumped force and substructure model, and Case 3 utilizes the distributed force and substructure model. The aerodynamic parameters for forces and POD pressure modes are obtained through wind tunnel tests. By comparing the wind-induced structural response in terms of global behavior (displacement, acceleration) and local behavior (stress), the influence of wind loading and structure models is discussed. The findings reveal that employing a simplified beam model underestimates local stress, and neglecting wind load distribution leads to further underestimation. Therefore, the refined FE model and distributed wind load models are recommended for the precise assessment of wind-induced stresses in long-span bridges.

Branching pattern of flexible trees for environmental load mitigation

Wind-induced stress is the primary mechanical cause of tree failures. Among different factors, the branching mechanism plays a central role in the stress distribution and stability of trees in windstorms. A recent study showed that Leonardo da Vinci’s original observation, stating that the total cross section of branches conserved across branching nodes is the optimal configuration for resisting wind-induced damage in rigid trees, is correct. However, the breaking risk and the optimal branching pattern of trees are also a function of their reconfiguration capabilities and the processes they employ to mitigate high wind-induced stress hotspots. In this study, using a numerical model of rigid and flexible branched trees, we explore the role of flexibility and branching patterns of trees in their reconfiguration and stress mitigation capabilities. We identify the robust optimal branching mechanism for an extensive range of tree flexibility. Our results show that the probability of a tree breaking at each branching level from the stem to terminal foliage strongly depends on the cross section changes in the branching nodes, the overall tree geometry, and the level of tree flexibility. Three response categories have been identified: the stress concentration in the main trunk, the uniform stress level through the tree’s height, and substantial stress localization in the terminal branches. The reconfigurability of the tree determines the dominant response mode. The results suggest a very similar optimal branching law for both flexible and rigid trees wherein uniform stress distribution occurs throughout the tree’s height. An exception is the very flexible branched plants in which the optimal branching pattern deviates from this prediction and is strongly affected by the reconfigurability of the tree.

Wind-Induced Response Analysis for a Fatigue-Prone Asymmetric Steel Arch Bridge with Inclined Arch Ribs

Steel arch bridges with inclined arch ribs under strong wind fields are prone to fatigue damage due to the stress concentration at the position of hanger connections. Therefore, it is essential to perform the wind-induced response analysis for specified shape hangers, such as inclined hangers, to determine the stress distribution and corresponding influencing factors. In this study, wind-induced response analysis for a fatigue-prone asymmetric steel arch bridge with inclined arch ribs is performed by the numerical simulation approach. The investigated bridge hangers’ models are established by using the COMSOL Multiphysics software. The wind-induced stress of the bridge hangers under different wind directions is obtained based on the finite element method. The influential factor of the stress distribution of the bridge hangers on both the windward side and the leeward side is discussed. In addition, the stress peaks of the long hanger and short hanger are achieved for further fatigue analysis. This paper provides a reference for determining the critical fatigue-prone position of an asymmetric steel arch bridge with inclined arch ribs.

Far-red light interacts with wind-induced stress in cucumber seedlings

Strong wind inhibits plant growth by creating mechanical stress and increasing water loss by increased transpiration. In the present study, we focused on far-red (FR) light as a factor that interacts with the effects of strong wind. We investigated the effect of wind speed (0.5 or 6.5 m s–1) on growth, photosynthate allocation, and stomatal conductance (gs) of cucumber (Cucumis sativus) seedlings under illumination with FR light (FR+) or without it (FR–). Interactions between wind speed and FR light influenced plant growth; strong wind decreased plant growth under FR+, but not under FR–. The growth decrease caused by strong wind resulted from decreases in the net assimilation rate (NAR) and leaf area ratio (LAR). The decreased LAR caused by strong wind was probably caused by decreased photosynthate allocation to the leaves as a result of the increased photosynthate allocation to the stem to resist the wind-created mechanical stress. The strong wind did not influence the photosynthate allocation under FR–, probably because the mechanical stress caused by the strong wind was smaller when stem elongation was decreased by FR–. The decrease in gs due to strong wind was smaller under FR– than under FR+. This may be a result of increased tolerance to water stress, which is associated with the increased proportion of active phytochrome under FR–, and may explain why the decrease in NAR due to the strong wind was smaller under FR–.

POD-based modelling of distributed aerodynamic and aeroelastic pressures on bridge decks

To extend the knowledge of aerodynamic and aeroelastic behaviour of long-span bridges and to acquire an accurate wind-induced stress distribution of the bridge deck for fatigue analysis, the modelling of distributed aerodynamic and aeroelastic pressures on the bridge deck is imperative. A modelling method based on proper orthogonal decomposition (POD) is therefore proposed in this paper. The characteristic parameters of POD pressure modes, such as covariance modes, principal coordinates, pressure modal coefficients, pressure modal admittance functions and pressure modal derivatives are introduced. Indicial function-based parameter identification method is developed to identify pressure modal derivatives and admittances. Wind tunnel pressure tests were conducted on a spring-suspended sectional twin-box deck model of the Stonecutters cable-stayed bridge. With the pressure modal coefficients, covariance modes, and principal coordinates calculated from the measured distributed pressures, the pressure modal derivatives were identified. Thereupon, the aerodynamic and aeroelastic components of the pressure modes were separated, and the pressure modal admittance functions were then identified with the isolated aerodynamic components. The results show that the aerodynamic and aeroelastic components of wind-induced pressures can be separated successfully and the distributed pressures on the deck can be well reconstructed with a limited number of POD pressure modes.

Investigation of persistent coherent structures along the Southern Brazilian Shelf

Abstract The freshwater-influenced region of the Patos Lagoon discharge to the Southern Brazilian Shelf (SBS) is a region of complex fluid dynamics. Seasoning and synoptic variable winds and coastal current conditions create an alternating flow pattern. The aim of this paper was to investigate the occurrence of persistent coherent structures in this environment. A numerical approach was chosen to describe the main hydrodynamic features of the region during a climatological year. The open-source finite-element code Telemac-Mascaret was applied to the three-dimensional domain. In addition the two-equation k-epsilon model described the turbulence mechanisms. The presence of persistent high-turbulent structures was identified within the study area. These occur as a strong curvilinear disturbance characterized by higher turbulent production and dissipation rates, which increase local mixture. As a result, upward circulation flow was observed, which may be due to irregularities in bottom topography associated with wind-induced stress forces. These results increase the information about the circulation structures of the study area by means of numerical modelling analysis.

New Screening tool for Obtaining Concentration Statistics of Pollution Generated by Rivers in Estuaries

Rivers represent an essential pathway for waterborne transport, and therefore estuaries are critical coastal areas for a pollution hazard that might lead to eutrophication and general water quality deterioration. When addressing these problems, the decision makers and coastal managers often need additional skills and specialists, so they engage consultants in developing models and providing potential solutions. Different stakeholders’ interests present a challenge in the implementation process of proposed solutions. Nevertheless, if the relevant institutions were presented with a screening tool, enabling them with a certain level of solution ownership, potentially more involvement would occur. There are numerous intertwined physical processes present in the estuary ecosystem, including river discharge, tidal forces, wind-induced stress and water density variations. This research utilizes an analytical model based on ensemble averaging and near-field approximation of the advective-diffusion equation for the case of continuous, steady, conservative solute transport in a stratified, river-dominated estuary. Such an approach significantly reduces the costs and time needed to obtain enough measured data required for common statistical analysis or the need for a more complex numerical model. The developed methodology is implemented into a simple software named CPoRT (Coastal Pollution Risk Tool) within a recently conducted research project funded by European Social Fund.

Shifts of radiocesium vertical profiles in sediments and their modelling in Japanese lakes

Vertical profiles of radiocesium concentrations were measured in sediment cores collected at various times after the 2011 Fukushima nuclear accident in five Japanese lakes (Hinuma, Kasumigaura, Kitaura, Onogawa and Sohara) with different morphological and trophic characteristics in order to investigate the sedimentation-diffusion processes. In lakes where sediments had high porosities and experienced considerable wave action due to shallowness, we observed rapid penetration of radiocesium to a certain depth just after the accident, followed by downward movement of the peak depths. In contrast, gradual downward transfers of distinct peaks were found in other types of lakes. A one-dimensional differential sediment model with water-sediments interaction processes was constructed to describe the vertical shift of radiocesium profiles. Our proposed submodels relating to the length scales of the mixing using wind-induced stress and porosity of sediments were constructed based on one measurement of the vertical distribution of radiocesium in three lakes (Hinuma, Kasumigaura and Sohara). This model was then validated using samples from those lakes in different years, as well as from two other lakes. Good agreement was obtained. We discuss our findings, the limits of model application, and future research targets.

Variation in susceptibility to wind along the trunk of an isolated Larix kaempferi (Pinaceae) tree.

• Premise of the study: The force of the wind is a significant hazard to the survival of trees and can affect tree morphology. However, the actual distribution of the stress that wind causes to a tree trunk is not well understood in spite of its expected importance to tree morphology. The uniform stress hypothesis (i.e., tree trunks take a form that equalizes the distribution of stress along the outer surface of the stem) has been tested indirectly as a model, placing high importance on the mechanical safety of a trunk, and rejected theoretically. But stress on a tree's trunk has not yet been measured directly.• Methods: Actual strains at the surface of the trunk of an isolated Larix kaempferi tree due to wind loads were measured at seven heights on the trunk for 1 yr.• Key results: During the measurement period, wind-induced stress was higher in the upper portions of the trunk than in the lower portions, regardless of wind speed, and the difference increased as wind speed increased. The deflection of the trunk recorded at each position was also larger in the upper portions than in the lower portions.• Conclusions: The results indicate that the upper portions of the trunk of an isolated Larix kaempferi tree are more susceptible to wind than are the lower portions. These results do not support the uniform stress hypothesis and suggest that another limitation (either mechanical or nonmechanical) acts on the morphology of the tree.

Effects of Tree Crown Structure on Dynamic Properties of Acer rubrum L. ‘Florida Flame’

Knowledge of tree dynamic properties is important to improve one’s ability to assess tree risk. Pull-and-release tests were performed on 16 Acer rubrum L. ‘Florida Flame’ trees in summer and winter over a two-year period, and natural frequency and damping ratios were calculated. One year prior to testing, trees were designated as either excurrent or decurrent and pruned to impose that form. During summer tests, trees were pruned to maintain designated form, and tests were performed before and after pruning. Trees were then systematically dissected to measure morphological and allometric characteristics. Excurrent trees had a higher natural frequency than decurrent trees in summer and winter, and pruning in summer increased the frequency of excurrent trees more than decurrent trees. Tree form and pruning had little effect on damping ratio. Decurrent trees had a larger percent of their branch mass in the top half of the crown than excurrent trees, which would subject them to larger wind-induced stress on their trunks and increase the risk of failure.

Field measurement of wind-induced stress on glass facade of a coastal high-rise building

The glass facade of high-rise building in coastal areas is vulnerable under typhoon. The research works in the literature on facade’s wind-resistance performance, however, have some limitations to apply to this issue. During typhoon landing, the whole facade will vibrate and deform due to the change of atmosphere, temperature and impacted torrential rain, to result in a quite different strain or stress distribution in the glass facade from those in model test and wind tunnel test. In this paper, the field measurement on glass facade of a coastal high-rise building in Xiamen was performed, the wind pressure on the glass facade was measured and a large number of wind-induced stress data were obtained during typhoon landing. The relationship between wind pressure and stress or strain of the glass panel was analyzed and the situation of stress distribution was summarized.

Assessment of Degrees of Cumulative Fatigue Crack Initiation Damage at Guyed Mast Earplate Joint

This paper proposes a new method for assessing the degree of the cumulative fatigue crack initiation damage of the joint welds at the guyed mast earplate. Based on the multi-scale wind-induced stress analysis of the guyed mast earplate joint, and considering the welding residual stress in earplate joint, the critical plane approach is used for the calculation of cumulative strain fatigue damage due to the combined actions of the welding residual stress and the wind load.

Wind-Induced Response Analysis of Guyed Mast Earplate Considering Welding Residual Stresses

This paper proposes a new method to calculate the wind-induced dynamic stress response of guyed mast earplate node, which considering the welding residual stresses in earplate weld joint. Firstly, a numerical simulation of weld residual stress of key nodes based on finite element method is presented. Then, taking the welding residual stresses as initial stress, the dynamic stress analysis of the guyed mast earplate’s weld was completed. The results show that in the dual role of the welding residual stress and the wind load, the von Mises equivalent stress of some hot spots in welds have exceeded the material yield stress of steel.

Measuring thermal and mechanical stresses on optical fiber in a DC module using fiber Bragg gratings

Fiber Bragg gratings (FBGs) can be used as sensors to monitor stress and test temperature during the processing and handling of optical fiber. As the FBG experiences a combination of mechanical and thermal loading, the return Bragg wavelength will shift proportionately to the magnitude of the load. This paper discusses the use of these sensors in quantifying induced stress on fiber during the packaging of a dispersion-compensating module (DCM) and the ensuing environmental exposure. There are two potential fiber-failure modes for fiber wound in DCMs, namely microbend-induced attenuation and fiber failure from fatigue. The ability to quantify fiber stress provides a useful feedback tool in the design phase of these modules that can aid in reducing the risk of mechanical and optical failure modes. A practical characterization process was developed to decouple thermal and stress effects on FBGs based on results from current literature and from this study. Uncoated Bragg sensors were found to respond linearly between -40 to 80/spl deg/C. Gratings with a protective polymer recoat departed from the linear behavior of the uncoated gratings below -5/spl deg/C. It was determined that the recoat material places less than 25 MPa (3.6 klbf/in/sup 2/) of axial compression on the fiber at -40/spl deg/C. Four gratings with different Bragg wavelengths were spliced into 10 km of fiber and wound into a DCM. The wind-induced stress on all four gratings quickly relaxed. The module was then thermal cycled between -40 and +75/spl deg/C. The overall stress on each grating was acceptably low for reliability purposes. The maximum stress of 17 MPa (2.5 klbf/in/sup 2/) was observed at the lowest temperature.

Wind Tunnel Testing and the Sector-by-Sector Approach to Wind Directionality Effects

We examine the sector-by-sector approach used by some wind tunnel operators to specify extreme wind effects. According to this approach the design of a structural member subjected to wind loads is adequate if the stresses induced by the largest sectorial wind speed with a 50 year mean recurrence interval does not exceed the maximum allowable wind-induced stress for that member, sectorial wind speeds with a 50 year mean recurrence interval being estimated separately for each of the eight 45° (or the 16 22.5°) azimuthal sectors. We show that this approach leads to estimates of wind effects that are unconservative (i.e., on the unsafe side), owing to their failure to consider the overall effects of winds blowing from all sectors.

Wind-induced stresses in cherry trees: evidence against the hypothesis of constant stress levels

We calculated the wind-induced bending moments and stresses generated in the stems of five Prunus serotina conspecifics differing in height and canopy shape and size (based on detailed measurements of stem projected area and location with respect to ground level) to test the hypothesis that wind-loads generate uniform and constant stress levels along the lengths of tree twigs, branches, and trunks. These calculations were performed using five different wind speed profiles to evaluate the relative importance of the shape of wind speed profiles versus the ’geometry’ of tree shape on stem stress distributions and magnitudes. Additionally, we evaluated the effect of absolute tree size and stem taper on wind- induced stresses by scaling the size of smaller conspecifics to the absolute height of the largest of the five trees yet retaining the original stem proportions (i.e., diameter relative to stem length) for each plant. Finally, we also determined how the factor of safety for wind-loading (i.e., the quotient of stem yield stress and wind-load stress) changed as a function of tree size (and, presumably, age). Our results indicate that wind-load stress levels (1) vary along stem length even for the same wind speed profile and the same maximum wind speed; (2) would increase to dangerous levels with increasing tree height if it were not for ontogenetic changes in stem taper and canopy shape that reduce stress intensities to manageable levels; (3) tend to be more dependent on stem taper and canopy shape and size than on the shape of the wind speed profile; and (4) the factor of safety against wind-induced mechanical failure decreases as trees get larger, but varies along the length of large trees such that preferential stem failure is likely and functionally adaptive. We thus (1) reject the hypothesis of constant wind-induced stress levels; (2) support the view that size-dependent changes in stem taper are required to maintain wind-load mechanical reliability; and (3) suggest that certain portions of mature trees are ’designed’ to fail under high winds speeds, thereby reducing drag and the bending moments and stresses experienced by trunks.

Effect of Wind-induced Mechanical Stress on Soluble Peroxidase Activity and Resistance to Pests in Cucumber

Wind-induced mechanical stress (MS) significantly increased the soluble peroxidase activity in leaves of cucumber over control levels after 9 days of treatment. In comparison, inoculation with the fungal pathogen Cladosporium cucumerinum induced significant increases in peroxidase after 4 days. Cucurbit anthracnose symptom development caused by Colletotrichum orbiculare was greater on leaves of seedlings exposed to 6 but not to 9 or 12 days of wind-induced MS than on leaves of control plants. In contrast, reproduction of melon aphids was significantly reduced on leaves exposed to 12 days of MS relative to controls. These results indicate that wind-induced MS can induce soluble peroxidase activity in cucumber and have divergent effects on the resistance to insects and pathogens. Zusammenfassung Wirkung von windinduziertem mechanischem Stres auf die Aktivitat loslicher Peroxidase und die Schadlingsresistenz bei Gurken Windinduzierter mechanischer Stres (MS) erhohte die Aktivitat loslicher Peroxidase in Gurkenblattern nach neuntagiger Behandlung im Vergleich zur Kontrolle signifikant. Eine Inokulation mit dem pathogenen Pilz Cladosporium cucumerinum induzierte dagegen nach vier Tagen einen signifikanten Anstieg der Peroxidasewerte. Die Blatter von Samlingen, die 6 Tage windinduziertem MS ausgesetzt waren, wiesen starker ausgepragte Symptome der von Colletotrichum orbiculare hervorgerufenen Brennfleckenkrankheit auf als die Blatter der Kontrollpflanzen. Nach 9- oder 12-tagiger Behandlung war das jedoch nicht der Fall. Die Vermehrung von Gurkenblattlausen auf Blattern war nach 12-tagigem MS im Vergleich zur Kontrolle signifikant verringert. Diese Ergebnisse zeigen, das windinduzierter MS die Aktivitat loslicher Peroxidase in Gurken induzieren und unterschiedliche Wirkungen auf die Resistenz gegen Insekten und Pathogene ausuben kann.

Age-Dependent Effects of Jasmonic Acid Treatment and Wind Exposure on Foliar Oxidase Activity and Insect Resistance in Tomato

Jasmonic acid (JA) treatment of tomato plants induces several defense-related oxidative enzymes and increases pest resistance in a manner thought to simulate natural insect wounding. In a full-factorial greenhouse experiment, we examined the independent and interactive effects of plant age and exposure to wind-induced mechanical stress (MS), on the ability of JA to induce defense in tomato. In general, treatment of 4-, 6-, and 8-week-old tomato plants with 1 mM JA resulted in the induction of peroxidase and polyphenol oxidase activity and reduced the relative growth rate of first-instar Manduca sexta larvae fed treated leaves, in accordance with other studies. Peroxidase activity increased with plant age and was induced by JA most strongly in older plants. In contrast, polyphenol oxidase activity did not change with plant age and was induced by JA most strongly in young plants. While relative growth rates of M. sexta were lower on older plants overall, JA reduced growth rates most strongly in young plants, in which JA treatment enhanced polyphenol oxidase activity by more than 70%. MS enhanced the activity of peroxidase, but substantially reduced the activity of polyphenol oxidase; the latter most intensely on older plants. M. sexta tended to grow more slowly on MS-treated plants, although this effect was not significant. Thus, reduced polyphenol oxidase activity in MS-treated plants did not lead to an increase in growth rate of M. sexta, possibly because peroxidase activity was still elevated in MS-treated plants. Significant interactions between JA and MS and three-way interactions were not detected for any variable, although the inductive effects of both JA and MS interacted in complex ways with plant age. Our results indicate that resistance traits in tomato are differentially affected by JA and wind exposure and differ in their relative contribution to defense as plants age.

Tide and surge dynamics along the Iberian Atlantic coast

The eastern Atlantic barotropic dynamics (in a region spanning from 20° N to 48° N and 34° W to 0°) are studied through numerical modelling and in situ measurements. The main source of data is the tidal gauge network REDMAR, managed by Clima Marítimo (Puertos del Estado). The numerical model employed is the HAMSOM, developed both by the Institut für Meereskunde (Hamburg University) and Clima Marítimo. In this paper, tidal and storm surge dynamics are studied for the region, focusing particularly on the nonlinear transfer of energy between the different forcings. The results of tidal simulations show good agreement between semidiurnal harmonic components and the values obtained from the tidal gauges (both coastal and pelagic) and current metres. The nonlinear transfers of energy from semidiurnal to higher order harmonics, such as M4 and M6, were mapped. Those transfers were found to be important in only two areas: The French continental shelf in the Bay of Biscay and the widest part of the African shelf, south of Cabo Bojador. The modelled diurnal constituents show larger relative differences with measurements than semidiurnal harmonics, especially in data concerning the phase. A method to isolate the nonlinear transfers of energy between tidal and atmospheric forcing during a storm surge was developed. These transfers were found to be significant in the same areas where tidal nonlinear activity was present. The effect of short period wind generated waves on sea surface elevation was also investigated. The magnitude of the spatial derivatives of radiation stress was compared with wind-induced stress. As a result of this comparison, we found the inclusion of a forcing term that depends on radiation stress in ocean model simulations at this scale and resolution to be not essential. The effect of computing wind-induced stresses, with a formulation that explicitly depends on sea state, was also explored by means of a coupled run of the HAMSOM and the spectral wave model WAM for a storm surge event in the Spanish coast. This formulation was not found to be an improvement over a classical parameterisation which only depends on wind fields.

Homogenization of potential vorticity in planetary gyres

The mean circulation of planetary fluids tends to develop uniform potential vorticity q in regions where closed time-mean streamlines or closed isolines of mean potential vorticity exist. This state is established in statistically steady flows by geostrophic turbulence or by wave-induced potential-vorticity flux. At the outer edge of the closed contours the expelled gradients of q are concentrated. Beyond this transition lies motionless fluid, or a different flow regime in which the planetary gradient of q may be dominant. The homogenized regions occur where direct forcing by external stress or heating within the closed isoline is negligible, upon the potential-density surface under consideration. In the stably stratified ocean such regions are found at depths greater than those of direct wind-induced stress or penetrative cooling. In ‘channel’ models of the atmosphere we again find constant q when mesoscale eddies cause the dominant potential-vorticity flux. In the real atmosphere the results here can apply only where internal heating is negligible. The derivations given here build upon the Prandtl–Batchelor theorem, which applies to non-rotating, steady two-dimensional flow. Supporting evidence is found in numerical circulation models and oceanic observations.