Reduce Wind Loads Research Articles

Numerical analysis of wind microclimatic effects on a plastic greenhouse protected by a windbreak in different seasonal periods

Windbreaks are frequently used to protect greenhouses. Agricultural plastic nets are widely used for the construction of such windbreaks replacing the traditional natural windbreaks formed by trees. When installed against the dominant wind direction at an optimized distance from the greenhouse side walls, windbreaks may reduce wind loads. An additional effect of the provided protection against strong cold winds is the reduction of heat losses during the winter period. However, the effect of windbreaks in situations when cooling is necessary, particularly in cases of low wind speeds during summer period, has not been investigated so far. The present work aims to analyse the energy efficiency and the wind flow around and through an arched-roof greenhouse with two side and one roof opening (windows) in two extreme cases, namely a) a high velocity cold wind causing important heat losses on the greenhouse (closed windows), and b) a low velocity wind speed resulting to buoyancy-driven ventilation in the greenhouse (open windows). In the first case the reduction of heat losses due to the windbreak are explored. In the second case, the possible dissipation of the ventilation airflow and the corresponding temperature variations by the windbreak is investigated. Computational Fluid Dynamics (CFD) numerical simulations are used in the present work.

Protection of Greenhouses against Wind Damage

The paper presents a case study of a greenhouse building affected by wind loads. The building is a lightweight steel structure with a height of 7.1meters, 12.8 meters wide and 171m long. The roof of the building is a lattice cupola. The main purpose of the authors was to find solutions in order to reduce wind loads on the building envelope, using some wind protection barriers. In order to identify the optimal solution, different types of wind barriers were analyzed. Using Ansys CFX, the authors carried out numerical simulation for each type of wind barrier, in order to find out which reduces the most the wind pressures on the walls and on the roof of the analyzed building. The results provided by numerical simulation of wind action on the building were used to make a comparative study between different patterns of wind fences. The comparison between pressures developed on the walls and roof for each type of fence, has allowed the choice of an optimal solution that can be applied also to other similar buildings.

Development of a Building Structural System Using An IsoTruss® Grid

Conventional frame building methods use orthogonal placement of beams and columns at the exterior of the building. Modern buildings with unconventional structural systems, such as diagrid systems, are becoming popular. In this study, the IsoTruss® grid is applied to a building structural system and its behavior is compared with that of a diagrid system. Exterior columns, placed vertically and obliquely, are connected in a zigzag pattern over the height of the building, making a unique façade, and are instrumental in reducing wind loads. The results of our analysis show that the structural performance of the proposed system is comparable to that of the diagrid system.

Suction-based active aerodynamic control of wind loads on super high-rise buildings

This article introduces a new method, active flow field control through steady suction, to reduce wind loads on buildings. To test its effect, suction equipment was developed and installed on a Commonwealth Advisory Aeronautical Research Council super high-rise model. A series of experiments were then conducted in a wind tunnel. The effectiveness of this method for reducing wind loads is discussed through comparison of the suction bottom moment ratio under different wind incidence angles and different positions of steady suction. The results of the experiment demonstrate that steady suction reduces wind loads effectively.

Aerodynamic mitigation of wind-induced uplift forces on low-rise buildings: A comparative study

Negative pressures on roofs of low-rise buildings are a major source of losses and community disruption during windstorms. The main driver for negative pressures is the fact that buildings are bluff bodies that cause flow separtion, compared to streamline objects such as an airplane wing. Consequently, the separated flow may create conical vortices that can significantly increase wind-induced uplift loads on roofs. Although vortex suppression technologies play a role in reducing wind loads on buildings, the challenge is related to exploring techniques that can reduce loads on roofs and the mitigation features themselves. In this paper, several aerodynamic mitigation techniques/features are proposed and tested by computational fluid dynamics (CFD) simulations, in a comparative study to permit selection among different potential solutions. Modifications to eliminate the sharp corners that cause flow separation and uplift forces are carried out. Different aerodynamic mitigation features including barriers, circular edges, inclined edges and airfoil edges are investigated. The study explores mitigation devices that not only can reduce wind-induced uplift loads on roofs, but also have minimum drag and lift forces. The results show that the slope-in features, representatives of solar panels for green energy production, are effective in reducing wind-induced uplift forces. In fact, having solar panels on buildings can be a feasible solution, especially when there is a potential for power outage due to windstorms. Such features, among other devices, can potentially protect roofs under windstorms, creating economic and green buildings. In addition, compared to all mitigation features presented in the current study, the airfoil produced the minimum uplift loads, with promises to proceeding research in this area.

철도용 터널형 방음벽 개발연구: 설계 방향

본 연구에서는 철도 교량 위를 주행하는 철도 소음에 의한 고층 공동주택 거주민들의 철도 소음 피해를 최소화할 뿐 아니라, 방음시설에 미치는 풍하중 및 자중을 동시에 감소시키는 방안으로 터널형 방음벽의 벽면부 개방을 검토하였다. 광음향기법, 전산 유체 역학 및 구조 역학을 이용하여 방음 효과, 유동 효과 및 구조 경량화가 고려된 터널형 방음벽 설계 및 효과를 예측하였다. 해석결과, 벽면부를 부분 개방하여 경량화 및 풍하중 감소 효과를 얻을 수 있었으며, 방음시설의 풍하중은 최대 30% 감소되었다. 부분 개방으로 인해 철도소음의 피해가 특정 높이에서 증가하기 때문에 이를 보완하기 위하여 개방된 부분에 소음기 형태의 음향 루우버 설치를 검토하였다. 음향 루우버의 경우 기존 방음재료의 차음성능과 유사한 성능이 존재하도록 개공율에 따른 유동 해석과 차음성능 해석을 수행하였다. 개공율 30~40% 개방 시, 차음성능 10dB를 만족하며 풍하중이 약 25% 저감되는 것으로 분석되었다. 결과적으로 터널형 방음벽의 벽면부 개방과 음향 루우버 설치는 경량화 및 풍하중에는 긍정적인 효과를 보여주며, 부분 개방과 함께 적절한 방음 재료와 방음설계가 동시에 적용될 경우, 거주민들이 요구하는 5-10dB 수준의 소음저감 효과가 나타나는 것으로 분석되었다. In the present study, a tunnel type soundproof wall with partial opening is proposed to reduce the environmental noise caused by railway vehicles traveling on bridges, which affects residents of high-rise apartment buildings; the study also attempts to minimize load due to wind and the weight of the wall. Applying the principles of computational fluid dynamics and structural mechanics, and the ray tracing method, a reduction in noise as well as of the overall weight of the soundproof walls is estimated. Analysis results show that the proposed soundproof wall with a partial opening weighs less, while reducing the wind loading by up to 30%. To prevent direct propagation of sound through openings in the wall, an acoustic louver, which is a type of silencer, could be considered for the opening. In order to achieve a similar noise effect with existing insulation material, the fluid flow and the insulation effect of the acoustic louver are analyzed. As the considered opening is in the range of 30~40% of the total length of the soundproof wall, the noise effect and wind load are reduced by 10dB and 25% respectively. Consequently, opening some part of tunnel type soundproof walls and installing louvers on the wall openings can have the effects of weight-reduction and reduced wind load. If a partial opening is applied with proper sound material application, a gain of an additional 5~10dB of noise reduction can be achieved.

Semi-passive Solar Tracking Concentrator

A solar tracking concentrator (STC) has to adapt to the changes in the sun's position throughout the day and even more so, throughout the year. The function of sun tracking is to keep the sun's rays perpendicular to the absorber's cross-sectional area through a constant orientation, which requires an accurate electro-mechanical system that increases the cost of the whole concentrator. Sun tracking enables solar radiation to be concentrated in a limited and well-defined area of a receiver where the thermal energy collected is stored and then transformed into other kinds of energy. This heightens the prospects for the STC to use as little energy and movement as possible for solar tracking so as to achieve such a concentration. For this reason, a semi-passive solar tracking concentrator (SPSTC) whose configuration requires a minimal mechanical effort and reduced movement for sun tracking is proposed. It mainly consists of a micro-heliostat array, a Fresnel lens and a receiver. The array tracks the position of the sun to reflect the sun's rays toward the Fresnel lens, which remains horizontal, reducing wind loads over the whole system. The receiver, located on the lens focus, remains stationary, releasing its weight on the sun tracking system and thus reducing the energy required for movement. The SPSTC's kinematics for both altitude and azimuth tracking on a 25°39’15”N latitude is analyzed. An optimum fixed array's tilt of 49.054° was found to maximize the effective Fresnel lens area by reducing blocking and shading, both caused by the position of the array above the lens.

Wind pressures on tapered and set-back tall buildings

Recent tall buildings tend to have irregular and unconventional shapes as a prevailing but unavoidable trend, which is very effective for suppressing across-wind responses. Suppression of across-wind responses is a major factor in safety and habitability design of tall buildings, and the so-called aerodynamic modification method is comprehensively used. While the effectiveness of aerodynamic modification in reducing wind loads has been widely reported, there have been few detailed investigations of pressure fluctuations. The purpose of the present work is to investigate the spatio-temporal characteristics of pressure fluctuations applied to height-modified tall buildings comprehensively, including differences of vortex formation and shedding mechanism based on the previously reported mechanism of a conventional square tall building. The results show that taper and set-back affect on the bandwidth of power spectra and position of peak frequencies. And through taper and set-back, the height at which the vortex begins to form moves up, and due to the small building dimension, the vortex component formed at that height sheds from the building more frequently before an inverted conical vortex is formed over the whole height.

Behavior of a Nuclear Power Plant Ventilation Stack for Wind Loads

This paper describes behavior of self supporting tall reinforced concrete (RC) ventilation stack of a nuclear power plant (NPP) for wind loads. Since the static and equivalent dynamic wind loads are inter-dependant on overall size of the stack, proper sizing of the stack geometry is important for reducing wind loads. The present study investigated the influence of engineered backfill soil on lateral response of ventilation stack. Ignoring backfill soil stiffness up to ground height does not allow to predict actual critical wind velocity causing across wind oscillation. The results show that proposed modification in the stack geometry modeled using 2D beam-spring elements is economical than that of single tapered geometry. Shaft diameter reduced in the proposed geometry indicates that there is a scope for overall space savings in the NPP layout.

Wind and tall buildings: negatives and positives

AbstractWind is often regarded as the foe of tall buildings since it tends to be the governing lateral load. Careful aerodynamic design of tall buildings through wind tunnel testing can greatly reduce wind loads and their affect on building motions. Various shaping strategies are discussed, aimed particularly at suppression of vortex shedding since it is frequently the cause of crosswind excitation. The use of supplementary damping systems is another approach that takes the energy out of building motions and reduces loads. Different applications of damping systems are described on several buildings, and an example of material savings and reduced carbon emissions is given. Wind also has some potential beneficial effects particularly to tall buildings. One is that, since wind speeds are higher at the heights of tall buildings, the potential for extracting wind energy using wind turbines is significantly improved compared with ground level. This paper explores how much energy might be generated in this way relative to the building's energy usage. Other benefits are to be found in judicious use of natural ventilation, sometimes involving double‐layer wall systems, and, in hot climates, the combination of tailored wind and shade conditions to improve outdoor comfort near tall buildings and on balconies and terraces. Copyright © 2008 John Wiley & Sons, Ltd.

Interference effects on wind loading of a row of closely spaced tall buildings

Interference effects on a row of square-plan tall buildings arranged in close proximity are investigated with wind tunnel experiments. Wind forces and moments on each building in the row are measured with the base balance under different wind incidence angles and different separation distances between buildings. As a result of sheltering, inner buildings inside the row are found to experience much reduced wind load components acting along direction of the row ( x) at most wind angles, as compared to the isolated building situation. However, these load components may exhibit phenomena of upwind-acting force and even negative drag force. Increase in x-direction wind loads is observed on the upwind edge building when wind blows at an oblique angle to the row. Other interference effects on y-direction wind loads and torsion are described. Pressure measurements on building walls and numerical computation of wind flow are carried out at some flow cases to explore the interference mechanisms. At wind angle around 30° to the row, wind is visualized to flow through the narrow building gaps at high speeds, resulting in highly negative pressure on associated building walls. This negative pressure and the single-wake behavior of flow over the row of buildings provide explanations for the observed interference effects. Interference on fluctuating wind loads is also investigated. Across-wind load fluctuations are much smaller than the isolated building case with the disappearance of vortex shedding peak in the load spectra. Buildings in a row thus do not exhibit resonant across-wind response at reduced velocities around 10 as an isolated square-plan tall building.

The Effects Of Pruning Type On Wind Loading Of Acer Rubrum

The wind load, bending moment, height, and weight were determined for 81 red maples (Acer rubrum) before and after pruning. Trees were thinned, reduced, lion tailed, or stripped of foliage. All three pruning treatments reduced wind load significantly compared to unpruned trees at all tested velocities (11, 16, and 20 m/sec [25, 35, and 45 mph]). Reduction in wind load increased with increasing velocity. Differences in wind-load reduction between reduction pruning and thinning were not significant at any velocity. The reduction in wind load was linearly related to the amount of weight removed by pruning treatments. Compared to the same trees prior to pruning, the center of pressure height was significantly lowered on thinned and reduced trees, while the center of pressure height did not change on lion-tailed trees.

Aerodynamic Coefficients and Risk‐consistent Design

A simple procedure is presented for estimating the reliability of windsensitive structures whose orientation is not specified. The procedure is based on a second moment reliability approach and makes use of: (1) Aerodynamic coefficients obtained experimentally as functions of wind direction, and (2) climatological data consisting of sets of largest annual speeds associated with winds blowing from each of the 8 (or 16) compass directions. An illustration of the procedure, based on sets of actual data, is presented. It is then shown that the tools presented in the paper can be applied to develop, from directional, aerodynamic, and climatological data, nominal aerodynamic coefficients which in effect reduce wind loads with respect to those inherent in current U.S. practice, in a manner that reflects the directional dependence of both the aerodynamic behavior of structures and the extreme wind climate, while being consistent with respect to failure risk. These tools are first developed for the general case wh...

Description and Performance of the Saturn Launch Vehicle's Navigation, Guidance, and Control System

A review of the navigation, guidance, and control system of the Saturn launch vehicle includes the system analysis and design, signal flow diagrams, redundancy, and self-checking features used to obtain extreme reliability for crew safety.The iterative path adaptive guidance mode, featuring flight path optimization, is explained and presented in its computational form. Following the analytical considerations, the main guidance and control components are described. The navigation and control information is obtained inertinlly by a gyro-servo-stabilized, three-gimbal platform system with three mutually orthogonal pendulous-integrating gyro accelerometers; the single-degree-of-freedom gyros as well as the accelerometers use externally-pressurized gas bearings. Rate gyroscopes provide attitude staoilization; some vehicle configurations require additional accelerometer control to reduce wind loads. The digital computer system serves as the computation, central data, and onboard programing center, which ties in with the ground computer system during the prelaunch checkout of the overall system. The control signals are combined, shaped, attenuated, and amplified by an analog type control computer for engine actuator control.Results obtained in recent launchings of Saturn V vehicles are presented to confirm the adequacy of the navigation, guidance, and control system and its overall performance even under extreme flight perturbations.

The effect of dry and fluid lubrication on instrument, ball-bearing torques at high speed : H. H. Mabie, Lubrication Eng., 21 (6) (1965) 242–249; 21 figs., 1 table

A review of the navigation, guidance, and control system of the Saturn launch vehicle includes the system analysis and design, signal flow diagrams, redundancy, and self-checking features used to obtain extreme reliability for crew safety.The iterative path adaptive guidance mode, featuring flight path optimization, is explained and presented in its computational form. Following the analytical considerations, the main guidance and control components are described. The navigation and control information is obtained inertinlly by a gyro-servo-stabilized, three-gimbal platform system with three mutually orthogonal pendulous-integrating gyro accelerometers; the single-degree-of-freedom gyros as well as the accelerometers use externally-pressurized gas bearings. Rate gyroscopes provide attitude staoilization; some vehicle configurations require additional accelerometer control to reduce wind loads. The digital computer system serves as the computation, central data, and onboard programing center, which ties in with the ground computer system during the prelaunch checkout of the overall system. The control signals are combined, shaped, attenuated, and amplified by an analog type control computer for engine actuator control.Results obtained in recent launchings of Saturn V vehicles are presented to confirm the adequacy of the navigation, guidance, and control system and its overall performance even under extreme flight perturbations.

Gyroscope research at the Franklin Institute

A review of the navigation, guidance, and control system of the Saturn launch vehicle includes the system analysis and design, signal flow diagrams, redundancy, and self-checking features used to obtain extreme reliability for crew safety.The iterative path adaptive guidance mode, featuring flight path optimization, is explained and presented in its computational form. Following the analytical considerations, the main guidance and control components are described. The navigation and control information is obtained inertinlly by a gyro-servo-stabilized, three-gimbal platform system with three mutually orthogonal pendulous-integrating gyro accelerometers; the single-degree-of-freedom gyros as well as the accelerometers use externally-pressurized gas bearings. Rate gyroscopes provide attitude staoilization; some vehicle configurations require additional accelerometer control to reduce wind loads. The digital computer system serves as the computation, central data, and onboard programing center, which ties in with the ground computer system during the prelaunch checkout of the overall system. The control signals are combined, shaped, attenuated, and amplified by an analog type control computer for engine actuator control.Results obtained in recent launchings of Saturn V vehicles are presented to confirm the adequacy of the navigation, guidance, and control system and its overall performance even under extreme flight perturbations.