Design Wind Velocity Research Articles

Study the Influence of Cable Breakage on Wind-Induced Vibration Characteristics of the Curved Beam Unilateral Stayed Bridge

Existing studies have found that curved beam unilateral stayed bridges (CBUSB) have a risk of cable breakage under the design wind velocity. To ensure structural wind-induced vibration security, it is necessary to study the wind-induced vibration characteristics of CBUSBs considering the influence of the impact load due to the cable breakage. Based on the aerodynamic coefficients determined by a wind tunnel test and the established impact load model, parametric analyses of important CBUSBs’ characteristics (beam curvature and cable arrangement scheme) and the location of the cable breakage are carried out to assess the influence of cable breakage on the time-domain statistical values and frequency-domain distribution characteristics of wind-induced vibration response. The DAF, considering the influence of cable breakages on the wind-induced vibration peak value of CBUSBs, is proposed through dynamic analysis. Study results show that, with increasing curvature, under the two-modes action of wind loads and impact loads, the fluctuation component of the CBUSB is changed, resulting in a smaller proportion of resonant response. For CBUSBs with unilateral or bilateral cable arrangements, their wind-induced vibration behavior is significantly different. The former have dynamic characteristics and the latter have quasi-static characteristics. The breakage of the shortest cable at 7/33 to 7/22 of the curved beam length and its symmetry part significantly increases the wind-induced peak response of CBUSBs. The DAF recommended values can consider the amplification effect of wind-induced vibration due to the cable breakage.

Effects of damping and helical fillets on galloping vibration of stay cable installed with a rectangular lamp

Lamps attached on the stay cable can change the stable circular cross-section of the stay cable, which is easy to cause galloping vibration. Stay cables of the Kuipu bridge in the Fuzhou City of China were equipped with damper and helical fillets. After the installation of rectangular lamps on this bridge, no obvious vibration of the stay cables was observed. This is totally different from another bridge, the Kuimen bridge in the Chongqing City of China, which has been recently reported by the authors. The purpose of this study is to clarify the effects of the helical fillets and the structural damping on galloping vibration. The features of galloping vibration of the stay cable attached to a rectangular lamp were carefully studied, and the effectiveness of damping and helical fillets in reducing the galloping vibration was evaluated. First, the force measurement wind tunnel tests on the segmental test model were carried out, and the lift and drag coefficients of the stay cable attached to the rectangular lamp were measured. The dangerous wind attack angle of galloping vibration was predicted by the galloping force coefficient. Second, 3-dimensional vibration measurement wind tunnel tests were carried out to measure the wind-induced response of the cable-lamp test models. The variation of wind-induced response of stay cable with yaw angle and wind velocity was measured for test models with and without helical fillets. In the test, the features of wind-induced vibration were studied at the damping level of 0.1%, 0.6%, 0.7%, 0.8%, and 1.0%. According to Den Hartog’s theory, the minimum coefficient of galloping force is about −9.8. The experimental results of 3-dimensional vibration measurement wind tunnel tests show that the helical fillets wrapped on the cable surface can enhance the critical wind velocity to a certain extent, but the critical wind velocity is still far lower than the design wind velocity. When the damping ratio of the stay cable is up to 1.0% ( SC = 35.1), the galloping vibration of the stay cable attached to a rectangular lamp on the Kuipu Bridge can be effectively mitigated.

A study on the influence of climatic conditions on the heating of an outer wall of a liquified hydrocarbon gas tank

Introduction. The article contains a theoretical study on the influence of climatic conditions in various regions of the Russian Federation on the heating of a side wall of a liquified hydrocarbon gas (LHG) tank if the firе runs through the whole vehicle, located at a gas station. Objectives of the study:analysis of the fire safety legislative framework applicable to gas station design;analysis of sources of domestic and foreign experimental studies on the fire impact of flames on an LHG tank;numerical simulation of the vehicle combustion in cold and warm seasons, taking into account the highest wind velocity in the Russian Federation;numerical simulations, conducted for a warm season to identify the critical surface temperature of a side wall of an LHG tank, and the design wind velocity corresponding to the air temperature in a Russian region.Materials and methods. The method of mathematical statistics is used to process maximum values of the air temperature and wind velocity for each Russian region and obtain the empirical values of the wind velocity and air temperature in the Russian regions. Calculations were made using the method of mathematical modelling of fire in warm periods to identify the critical surface temperature of a side wall of an LHG tank and the design wind velocity corresponding to the air temperature in the regions of Russia.Results. A dependence between the wind velocity and the air temperature in the Russian regions, as well as a dependence between the critical surface temperature of a side wall of an LHG tank and climatic conditions of the Russian regions was identified.Conclusions. The results, obtained by the researches, can be used to design the fire separation distance between the site designated for a fuel tanker truck (the parking lot for a vehicle before its fueling), an LHG tank and a gas station.

Correction of historical records to improve the reliability of design wind speeds

It is not uncommon that design wind speeds are derived from measured data for which the sampling period is longer than the averaging time, e.g. 10-min averages measured once every hour; we call these downsampled data. Using downsampled data has the effect of shifting the calibrated distribution of the yearly maxima to the left, thus reducing the predicted return wind speed. The origin of this has probably to be found in the fact that a large amount of research on the assessment of design wind speeds was developed in the UK, where hourly wind speed averages were available, measured twenty-four times a day, i.e. contiguously. Procedures were then applied also in the case in which downsampled data were available, apparently disregarding the bias this brings. Indeed, even contiguous measurement of mean wind speeds is insufficient, as for the proper evaluation of the return wind speed continuous measurements would be needed. In this paper, the difference between continuous, contiguous disjunct and downsampled disjunct data measurements is pointed out, and the effects of downsampling on the statistics of the extreme wind speed are quantified. A technique for correction of disjunct measurements is proposed and validated in order to remove the bias deriving from downsampling and to improve the reliability of design wind speeds and velocity pressures. Finally, the procedure is applied to datasets from four Italian meteorological stations showing an increase of the return velocity pressure after correction of about 10% to 30%.

A Comparative Study of Wind Tunnel Tests and Design Codes in Evaluation of Along-Wind Effects on Towers

This study aims to estimate the wind loads acting on a tower structure by comparing and reviewing design codes and the results of wind tunnel tests. To this end, the modal properties of the tower were identified through short-term on-site measurements of the Busan Tower in Korea. The wind load acting on the tower was calculated using four design codes: KBC2009 (Korea), ASCE7-10 (USA), EUROCODE (Europe), and AIJ2004 (Japan). Additionally, force measurement tests and aeroelastic model tests were conducted for comparison. The results obtained indicated that the design wind velocity of each design code differed slightly, reflecting the individual characteristics of each country. The base shear force, base moment, and maximum displacement obtained from each design code were similar to those obtained in the wind tunnel tests. The magnitudes of the base moments and maximum displacements calculated by each design code were in the order of KBC > AIJ ≈ EUROCODE > ASCE7. The overall results indicate that each design code reasonably estimates the wind forces and the responses of the tower and also has an appropriate safety margin. The scatter in the predicted wind loads occurs primarily from the variations in the design wind velocity in the respective design codes.

Interference effects on aeroelastic responses and design wind loads of twin high-rise reinforced concrete chimneys

Twin chimney arrangement is a typical layout for power stations. The most unfavorable wind-induced responses of twin chimneys usually overwhelm those of the corresponding isolated chimney due to interference effects. The present paper investigates the aeroelastic responses and design wind loads of twin high-rise reinforced concrete chimneys through wind tunnel tests with L/D varying from 2 to 6 (L being the center-to-center spacing and D being the mean diameter). The results from rigid and aeroelastic model tests are analyzed and compared with the codes. It is revealed that the most unfavorable response interfered by the upstream chimney is inferred to be induced by the vortex impingement resonance at critical wind velocity when L/D = 3. It is also found that the interference factor nominally specified in ACI 307-08 is feasible with a modest conservation in the lock-in regime (Ud/UCr = 0.8–1.6). When the design wind velocity is far beyond the critical wind velocity (Ud/UCr ≥ 2), the interference factor can be reduced, which is not covered by the codes. An empirical formula is proposed for this situation which leads to an economic practical design considering the aeroelastic interference effects.

Effectiveness of a tiny tuned liquid damper on mitigating wind-induced responses of cylindrical solar tower based on elastic wind tunnel tests

A tiny TLD was specially designed and manufactured to investigate its effectiveness on mitigating the wind-induced responses of a 243-meter-high solar tower by using wind tunnel tests based on an elastic test model. First, an elastic test model of the solar tower was made, and its structural parameters, including natural frequency, the first three mode shapes and structural damping ratio, were identified. Second, six types of tiny TLDs with different inner diameters (9, 10, 11, 12, 13 and 14 ​mm) were designed and manufactured, and the natural frequency and sloshing damping ratio of water in these tiny TLDs were identified to compare them with the theoretical values. The results show the measured and theoretical natural frequencies agree well with each other, while the measured sloshing damping of water is much larger than the theoretical value. Then, a series of wind tunnel tests were carried out to obtain the wind-induced responses of the solar tower. The effectiveness of TLD on mitigating the wind-induced responses of the solar tower was systematically investigated based on a series of parametric studies. The results show the wind-induced responses in the cross-wind and along-wind directions, including the acceleration at the top, the shear and moment at the bottom, can all be significantly reduced by the tiny TLDs with optimized parameters. It seems that the efficiency of the TLDs at the vortex-induced vibration critical wind velocity is significantly higher than that at the design wind velocity. In addition, the parametric studies indicate that the effectiveness of the TLDs is considerably sensitive to the frequency ratio, the height of the TLDs and the mass ratio.

Integrated transfer function for buffeting response evaluation of long-span bridges

An experimental approach to the prediction of the buffeting response of long-span bridges is presented, and the concept of the integrated transfer function, which directly relates the fluctuation characteristics of turbulent flow to the buffeting response of bridge structures, is introduced in this paper. The integrated transfer function is independent of the characteristics of turbulent flow, so once the integrated transfer function is identified in wind tunnel experiments, it can be directly used to calculate the buffeting response of the actual bridge in the atmospheric boundary layer. To verify the presented approach, a long-span suspension bridge is taken as an example and a series of experiments are carried out in a wind tunnel. Experiments in two different flow fields at the design wind velocity are performed to investigate the effects of turbulent flow characteristics on the integrated transfer functions, and the results measured at another wind velocity are given for comparison. The results show that the integrated transfer functions of the bridge measured in the two flow fields are almost identical, which confirms that it is independent of the flow field. An application example is also performed to evaluate the buffeting response with the use of the measured integrated transfer functions. Compared to the traditional approach, the presented experimental approach based on the integrated transfer function avoids errors caused by the inaccurate simulation of the turbulent flow (such as the integral scales, wind spectra and wind spatial correlations) and provides a more accurate prediction of the buffeting response of long-span bridges.

Dynamic response of structures to thunderstorm outflows: Response spectrum technique vs time-domain analysis

Thunderstorms are transient events. Design wind velocity and wind-induced damage are often related to them. Despite this, research on thunderstorm loading of structures is still fragmentary and uncertain due to their complexity, short duration and small size. These issues make it difficult to set physically realistic and simple models as well as to gather real data. This favoured the implementation of refined methods based on limited measurements. The European Projects “Wind and Ports” and “Wind, Ports and Sea” realised an extensive monitoring network from which many thunderstorm outflow records were extracted. They were analysed to inspect their characteristics and to formulate methods coherent with measurements. Firstly, the response spectrum technique conceived for earthquakes was extended to thunderstorms. Then, a hybrid simulation strategy was proposed and time-domain integrations of the structural response were applied. This paper provides a joint calibration and advancement of these two methods, leading to results that substantially agree, especially faced with their conceptual and operative diversities. This confirms the potential of the response spectrum technique to become a suitable tool for calculating the thunderstorm loading of structures and the efficiency of hybrid simulations and time-domain analyses to investigate, with a limited computational burden, advanced structural issues.

Wind induced buckling of large circular steel silos with various slenderness

Large steel silos are typical kinds of thin-walled structures that are widely used to store large quantities of granular solids in the industrial and agricultural sectors. In the present analyses, the buckling design of large steel silos subjected to wind pressure is demonstrated in accordance with Eurocode (EN1990, 1991, 1993) and proposed combinational Load Cases WE (wind and empty silo) and WF (wind and full silo). Six steel silos with capacities of 30,000–60,000 m3 with slenderness from 4.77 to 0.35 and thus representing very slender, slender, intermediate slender, squat and retaining silos are examined as examples. The finite element model is established using the commercial general purpose computer package ANSYS. Five types of buckling analyses are conducted on geometrically perfect and imperfect models with and without consideration of material plasticity. These models are designated as LBA, GNA, GMNA, GNIA, and GMNIA in EN 1993 Part 1–6. The concept of critical wind velocity vb,cr is put forward and defined for the first time in reference to our wind induced buckling analysis, according to which the silo structure obtains the equivalent buckling strength for Load Case WE and WF. The dominant loading conditions of Load Cases WE and WF can be determined by drawing comparisons between the critical wind velocity and designed wind velocity proposed by meteorological conditions. Nonlinear buckling deformations corresponding to the critical point in Load Case WE are governed by circumferential compression generated in the windward region of shells localized at the top of the silo wall. Nonlinear buckling modes of Load Case WF take the form of well-known elephant-foot deformations found at the base of the shell wall, which are induced by meridional compressive stress. Effects of geometrical and material nonlinearities and weld imperfection on the buckling behaviour of steel silos are very complex and are closely correlated with the slenderness of silo structures.

Extreme wind speed distribution in a mixed wind climate

The meteorological services of mid-latitude countries record wind speeds averaged over 10 min or 1 h periods and peak wind speeds for the same averaging period or a full day. Design wind speeds based on the statistical analysis of this data in a mixed wind climate may prove to be imprecise and unsafe due to the occurrence of intense, small and rapid extreme wind events such as thunderstorm outflows. Considering the 6 year continuous high-frequency records registered in two Port areas of the Upper Tyrrhenian Sea, a preliminary but representative analysis of the extreme wind speed distribution has been carried out in a mixed wind climate area frequently struck by thunderstorms. Results show that wind speeds with a high return period are always related to thunderstorm outflows. The mixed extreme distribution asymptotically overlaps with that for thunderstorms for high return periods and always provides the highest wind speeds. Gathering the ensemble of all extreme values into a single set leads to underestimating of the extreme wind speed. The Italian code provides conservative estimates of the extreme wind speed that protect designers from thunderstorms as well. However, refined analyses of the local wind climate that ignore thunderstorm events may lead to severe underestimations of the design wind velocity.

Effects of structural damping on wind-induced responses of a 243-meter-high solar tower based on a novel elastic test model

The effects of structural damping to the responses of the vortex-induced vibration of solar tower should be investigated carefully to provide a reference for the structural designers. A new type of elastic test model for a 243-meter-high solar tower is particularly designed and manufactured. A core beam is designed in the test model to simulate the stiffness of the concrete structure, and a coat with baseplate (like a cup) is designed to simulate the steel structure. A structural damping ratio as low as 0.3% is realized, and four level of structural damping ratio, including 0.7%, 1.0%, 1.5% and 2.0%, can be conveniently achieved. A series wind tunnel tests are carried out to investigate the features of the wind-induced responses of the solar tower at the structural damping level of 0.3%, 0.7%, 1.0%, 1.5% and 2.0%. The results show that obvious vortex-induced vibration could be found within wind velocity range of U10 = 21.5–28.4 m/s for the structural damping ratio of 0.7%. At this time, the highest vortex-induced responses (at the wind velocity of U10 = 23.2 m/s), including acceleration at the top, base shear and base moment, are far larger than those at the design wind velocity (U10 = 41.0 m/s). Moreover, it appears that the wind-induced responses in cross-wind direction are far higher than those in the along-wind direction. The most important point is that the base shear and moment in the cross-wind direction measured from wind tunnel tests are far higher than the values obtained from the Code ACI 307–08. The wind-induced responses of the solar tower are extremely sensitive to the structural damping of the test model. For example, the highest acceleration, base shear and moment in cross-wind direction are respectively reduced by about 67%, 74%, 71% when structural damping ratio slightly increases from 0.7% to 1.0%. It seems that the vortex-induced vibration of the solar tower could be effectively mitigated if the structural damping ratio could be enhanced over 1.0%.

Aerodynamic design of horizontal axis wind turbine blades

Designing horizontal axis wind turbine (HAWT) blades to achieve satisfactory levels of performance starts with the knowledge of aerodynamic forces acting on the blades. In this paper, a design method based on blade element momentum (BEM) theory is explained for HAWT blades. The method is used to optimize the chord and twist distributions of the blades. Applying this method a 1000W HAWT rotor is designed. A user-interface computer program is written on VISUALBASIC to estimate the aerodynamic performance of the existing HAWT blades and used for the performance analysis of the designed 1000W HAWT rotor. The program gives blade geometry parameters (chord and twist distributions), coefficients of performance and aerodynamic forces (trust and torque) for the following inputs; power required from the turbine, number of blades, design wind velocity and blade profile type (airfoil). The program shows the results with figures. It also gives the three dimensional views of the designed blade elements for visualization after exported to AutoCAD.

Nonlinear aerostatic stability analysis of Hutong cable-stayed rail-cum-road bridge

To investigate the nonlinear aerostatic stability of the Hutong cable-stayed rail-cum-road bridge with ultra-kilometer main span, a FEM bridge model is established. The tri-component wind loads and geometric nonlinearity are taken into consideration and discussed for the influence of nonlinear parameters and factors on bridge resistant capacity of aerostatic instability. The results show that the effect of initial wind attack-angle is significant for the aerostatic stability analysis of the bridge. The geometric nonlinearities of the bridge are of considerable importance in the analysis, especially the effect of cable sag. The instable mechanism of the Hutong Bridge with a steel truss girder is the spatial combination of vertical bending and torsion with large lateral bending displacement. The design wind velocity is much lower than the static instability wind velocity, and the structural aerostatic resistance capacity can meet the requirement.

Aerodynamic stability of iced stay cables on cable-stayed bridge

Ice accretions on stay cables may result in the instable vibration of galloping, which would affect the safety of cable-stayed bridges. A large number of studies have investigated the galloping vibrations of transmission lines. However, the obtained aerodynamics in transmission lines cannot be directly applied to the stay cables on cable-stayed bridges. In this study, linear and nonlinear single degree-of-freedom models were introduced to obtain the critical galloping wind velocity of iced stay cables where the aerodynamic lift and drag coefficients were identified in the wind tunnel tests. Specifically, six ice shapes were discussed using section models with geometric scale 1:1. The results presented obvious sudden decrease regions of the aerodynamic lift coefficient for all six test models. Numerical analyses of iced stay cables associated to a medium-span cable-stayed bridge were carried out to evaluate the potential galloping instability. The obtained nonlinear critical wind velocity for a 243-meter-long stay cable is much lower than the design wind velocity. The calculated linear critical wind velocity is even lower. In addition, numerical analyses demonstrated that increasing structural damping could effectively mitigate the galloping vibrations of iced stay cables.

엔지니어링 PE방수.방근시트가 결합된 박스 유닛형 옥상 녹화 시스템 적용을 위한 성능평가

도심지 건물의 증가는 친환경 공간에 대한 요구를 발생시키고, 이에 따라 옥상 및 인공지반 녹화의 보급이 급속히 증가되고 있다. 본 연구는 녹화시스템의 보급 확대를 위해 공법의 단순화, 일체화, 프리훼브화 개념을 적용, 연속 토양층 형성 박스 유닛형 녹화시스템을 개발하고, 이 시스템의 주요 성능으로 부착성, 내풍성, 단열성을 평가하여 적용 가능성을 검토하였다. 부착성 및 내풍성 시험결과, 설계 풍압 및 풍속과 비교하면 100m 높이의 건물에 설치해도 안전한 것을 확인하였고, 단열성 평가를 위해 120일간 측정한 내부 온도의 변화를 분석한 결과, 개발 시스템이 연속된 토양층을 형성하여 기존 유닛박스 시스템보다 주간은 17%, 야간은 45% 우수한 단열성능을 보여 주었다. According to the increment of urban buildings, the demand of eco-environment space will be also increased. Therefore, the artificial ground green system on a roof will be supplied gradually. In this study, the concept of simplification, unification and prefabrication was widely applied to supply green system. Consequently, the box unit system with a continuous soil layer was developed, and adhesive property, wind resistance and insulation property of this system were evaluated for site application. As a results of adhesive property and wind resistance test, comparing with design wind pressure and wind velocity, this system was safe at the height of 100m building located in urban. In addition, results of temperature measurement for 120 days showed 17% higher insulation property at daytime and 45% higher insulation property at night than normal box unit system owing to continuous soil layer.

Estimating Method of Surface Roughness Using Geographic Information

Rapid urban expansion and densification of the various industrial facilities affect the changes of topography and building in urban areas. Even if buildings proceed with high rise, they get mixed with low-rise buildings such as houses and industrial parks that have existed in the area. This may confuse the designer in estimating a surface roughness, an important factor in calculating the design wind velocity of building. This study analyzed the surface roughness by using a geographic information. Referring to the criteria of each country's building code, this study proposed a method to distinguish the surface roughness depending on the height of the surrounding buildings where the design building is located and calculated the surface roughness using 1:5000 topographic map and GIS. It is expected to solve problems that an existing designer calculates the surface roughness in a subjective manner and to help to design more rational buildings resistant to wind.

Optimization of thermal performance of a smooth flat-plate solar air heater using teaching–learning-based optimization algorithm

AbstractThis paper presents the performance of teaching–learning-based optimization (TLBO) algorithm to obtain the optimum set of design and operating parameters for a smooth flat plate solar air heater (SFPSAH). The TLBO algorithm is a recently proposed population-based algorithm, which simulates the teaching–learning process of the classroom. Maximization of thermal efficiency is considered as an objective function for the thermal performance of SFPSAH. The number of glass plates, irradiance, and the Reynolds number are considered as the design parameters and wind velocity, tilt angle, ambient temperature, and emissivity of the plate are considered as the operating parameters to obtain the thermal performance of the SFPSAH using the TLBO algorithm. The computational results have shown that the TLBO algorithm is better or competitive to other optimization algorithms recently reported in the literature for the considered problem.

Numerical Research on the Change Regularity of S Series Airfoil Tip Vortex

This paper take the impeller of S series airfoil for instance, in view of the complex flow field which is in the condition for the optimum attack angle of design wind velocity with tip vortex, presents a new generating strategy of grid based on controlling gradient method which takes the non-uniform tetrahedral grid with gradient gradual change in the near blade wall flow field. The transition layer grid which is in the development from body-fitted field to the middle of the domain having relatively high density of grid contrast with the far flow field can well capture the size and location of tip vortex, and find that the decay rate of the vorticity magnitude of tip vortex of S series impeller is more quickly than the tip vortex of traditional airfoil impeller. As well as find a fraction of central vortex and tip vortex shaded into each other in the far field and Doppler effect in the downstream. Because the numerical experiment and analysis showed that through controlling gradient change of grid can get high precision of calculating results, can also get S series impeller had higher efficiency in conversion of wind energy contrast with NACA series impeller, so the generating strategy of grid is reasonable and effective.

A NEW DESIGN OF BLADE FOR SMALL HORIZONTAL-AXIS WIND TURBINE WITH LOW WIND SPEED OPERATION

In Thailand, the average wind speed throughout the country is comparatively low for normally-available wind turbine. Designing of a new blade suitable for applications in the average wind speed of 3-7 m sec-1 is, thus, a main objective of this study. High torque has to be obtained properly to generate electricity. In order to design and evaluate performance, our mechanical model has been developed based on Blade Element Momentum theory and, the model is consequently employed to determine the optimized blade shape under constrains that are rotor diameter of wind turbine is not higher than 3 m, design wind velocity is 6 m sec-1, 12 and 24 V battery chargers respectively. New wind turbine blade manually made from fiberglass (GRP) with safety factors of 4 (for 12 V battery) and 2.8 (for 24 V battery). Experimental study is conducted by testing both of commercial blades and our new blade with a specific wind turbine set. We found that, at designed wind velocity, the efficiency of our new wind turbine blade of 27% is obtained while that of the commercial wind turbine is only 16%.