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Copyright of Study on Optical Communications / Guangtongxin Yanjiu is the property of Study on Optical Communications Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

【Objective】In order to study the temperature distribution and airflow requirements of high-speed optical modules, aiming to optimize the heat dissipation design and ensure the stable operation of optical modules.【Methods】The article adopts Flotherm simulation analysis to establish the numerical wind tunnel model of the optical module. The temperature distribution of each component during normal operation is obtained. The working air flow of the fan is also obtained when the system is stabilized, which are in line with the heat dissipation requirements in the specification of Multi-Source Agreement (MSA). In order to facilitate the testing and installation, the ”L” type wind tunnel fixture is designed. The actual surface temperature of each chip and the actual working wind flow rate of the wind tunnel are tested experimentally to verify the accuracy of the simulation results.【Results】The results show that in the case of the maximum temperature of 70 ℃, for the surface temperature of each chip, the difference between the simulation and the measured temperature is less than 2 ℃, with an error of less than 5%. For the airflow rate required for the heat dissipation of the entire optical module, the difference between the simulation and measured results is 0.2 Cubic Feet per Minute (CFM), with an error within 7%.【Conclusion】It can be shown that the simulation and measurement methods are feasible and the error is small, which provides an important reference value in the design and testing of heat dissipation of high-speed optical modules.

Flexible photovoltaic (PV) support structures are limited by the structural system, their tilt angle is generally small, and the effect of various factors on the wind load of flexibly supported PV panels remains unclear. In order to investigate the shape coefficients of the flexibly supported PV panel arrays, the grid-independent validation is carried out first, and then the case study validation is carried out to ensure the accuracy of the method in this paper. The CFD numerical simulation method is used to obtain the wind load variation of the PV panel array with different tilt angles, different spacing ratios, different wind angles, different heights above ground, different regions, and mountainous conditions. The distribution of wind pressure coefficients on the surface of PV panels with different inclination angles at different spacing ratios was investigated. The results show that the wind load shape coefficients with the increase in tilt angle and height above ground are basically a linear growth; the maximum value of PV shape coefficients appears in the wind angle at 30°, and 150° near the different tilt angles of the flexible PV array group shape coefficients distribution law is inconsistent. Different tilt angles of PV modules with the change rule of the spacing ratio of the wind load are inconsistent and have a greater impact on the wind load, so the PV panel array in all wind direction angles under the regional shape coefficients has a recommended value. The proposed value of the regional shape coefficients at all wind angles and the wind load calculation formula introducing height coefficients and spacing ratio coefficients are given. [ABSTRACT FROM AUTHOR]

Highlights: What are the main findings? Model of strong wind flow around sharp edges; Analysis of the impact of strong wind on structures. What is the implication of the main findings? Theoretical and numerical analysis; Observations and measurements of impacts on existing facilities; Comparison of results depending on the solutions used. The aim of this research is to analyze the pressure distribution caused by wind pressure on the structure of a single-family house. The research object is a model reflecting a real structure, which was damaged in 2018 because of heavy winds. The main idea is to create numerical models using various complex structural analysis software and compare the results. The obtained results will be compared with each other to analyze the impact of various factors, hereinafter referred to as boundary conditions, on the pressure values in characteristic places of the facility. The values closest to the normal distribution will be compared to the actual damage to the house structure. The essence of the research will be the identification of phenomena occurring during the action of heavy winds in global conditions (European and American), considering modifications and different ways of creating seemingly similar numerical models and the way they work. Everything will be compared with each other to find the most optimal design method in the given programs and to obtain wind pressure results that are closest to the real ones. [ABSTRACT FROM AUTHOR]

The twisted wind flow (TWF), referring to the phenomenon of wind direction varying with height, is a common feature of atmospheric boundary layer (ABL) winds, noticeably affecting the wind-resistant structural design and the wind environment assessment. The TWF can be effectively simulated by a guide vane system in wind tunnel tests, but the proper design and configuration of the guide vanes pose a major challenge as practical experience in using such devices is still limited in the literature. To address this issue, this study aims to propose an approach to determining the optimal wind tunnel setup for TWF simulations using a numerical wind tunnel, which is a replica of its physical counterpart, using computational fluid dynamics (CFD) techniques. By analyzing the mechanisms behind guide vanes for generating TWF based on CFD results, it was found that the design must take into account three key parameters, namely, (1) the distance from the vane system to the side wall, (2) the distance from the vane system to the model test region, and (3) the separation between the vanes. Following the optimal setup obtained from the numerical wind tunnel, TWF profiles matching both the power-law and Ekman spiral models, which, respectively, reflect the ABL and wind twist characteristics, were successfully generated in the actual wind tunnel. The findings of this study provide useful information for wind tunnel tests as well as for wind-resistant structural designs and wind environment assessment. [ABSTRACT FROM AUTHOR]

Large silo shell grids are used in a large number of coal storage sheds in power plants and other industries, where holes are cut in the ends as required by the process. Numerical wind tunnel analysis for the static wind effects of these semi-open structures are carried out by using the wind engineering calculation function of FLUENT. Based on the secondary development of the STADS and FLUENT interface program, the model conversion and the automatic reading and loading of wind pressure are completed through menu operation and parameter control, and the running speed of the program is optimized. With a dry coal shed in Bangladesh with an open upper section and a steel mill in India with an open lower section as research subjects, the wind pressure coefficients and wind speed vectors for different wind angles are given considering the combined effect of internal and external wind pressure. According to the wind pressure distribution law and the wind pressure similar partitioning criterion, the internal and external wind pressure partitioning body type coefficients of the upper and lower semi-open silo shell grids are provided, and the calculation results can be provided as reference for the structural design of similar structural projects. [ABSTRACT FROM AUTHOR]

Copyright of Builder (1896-0642) is the property of PWB MEDIA Zdzieblowski sp.j. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Flexible photovoltaic (PV) support structures are limited by the structural system, their tilt angle is generally small, and the effect of various factors on the wind load of flexibly supported PV panels remains unclear. In order to investigate the shape coefficients of the flexibly supported PV panel arrays, the grid-independent validation is carried out first, and then the case study validation is carried out to ensure the accuracy of the method in this paper. The CFD numerical simulation method is used to obtain the wind load variation of the PV panel array with different tilt angles, different spacing ratios, different wind angles, different heights above ground, different regions, and mountainous conditions. The distribution of wind pressure coefficients on the surface of PV panels with different inclination angles at different spacing ratios was investigated. The results show that the wind load shape coefficients with the increase in tilt angle and height above ground are basically a linear growth; the maximum value of PV shape coefficients appears in the wind angle at 30°, and 150° near the different tilt angles of the flexible PV array group shape coefficients distribution law is inconsistent. Different tilt angles of PV modules with the change rule of the spacing ratio of the wind load are inconsistent and have a greater impact on the wind load, so the PV panel array in all wind direction angles under the regional shape coefficients has a recommended value. The proposed value of the regional shape coefficients at all wind angles and the wind load calculation formula introducing height coefficients and spacing ratio coefficients are given.

In order to clarify the wind-induced vibration response law of variable cross-section cylindrical shell steel tower, a finite element calculation model based on fluid-structure coupling theory was established. The fluctuating wind speed corresponding to the basic wind pressure in different return periods was simulated by autoregressive model(AR) method. The numerical wind tunnel method was successfully used to calculate the dynamic response of variable cross-section cylindrical shell steel tower under the fluctuating wind. At the same time, the reliability of the numerical results was verified by field wind vibration monitoring. The results show that the displacement response amplitude gradually increases along the height direction under the action of fluctuating wind. The greater the wind speed, the greater the displacement response of the structure. However, the difference between the structural response under the wind speed of 50-year and 100-year return period is not very large, but it does not exceed the displacement limit of the structure. The stress decreases gradually along the height direction, and there is a sudden change of stress at the position of the variable section. The greater the wind speed is, the greater the stress is, and the difference of stress along the height direction is smaller and smaller. Under the action of wind speed in 50-year and 100-year return period, the allowable material stress value of desulfurization tower under working temperature exceeds 113 MPa. Therefore, for the evaluation of wind resistance performance of this kind of steel tower, stress control is mainly used at the bottom and variable section, and displacement control is mainly used at the top. [ABSTRACT FROM AUTHOR]

The sustainability of the ecological system in Alpine regions is being increasingly threatened by grassland desertification under climate change conditions. In order to address this global issue, this study took the typical desertified grassland in the northeastern edge of the Tibetan Plateau, as a case, proposing a low-coverage meadow paving layout forms for mitigating wind and sand erosion. Six paving layout forms ("spacing strips" (SS-1, SS-1.5), "lattice-shaped" (LS-1, LS-2), checkerboard intervals" (CI), "square intervals" (SI)) were designed and comprehensive analysis of their windproof effects were explored by numerical wind tunnel experiments. The patchy meadow is generalized as a porous medium and the porosity source terms were added to the RNG k-ε turbulence model to simulate the disturbance of the meadow on the airflow characteristics. The improved mathematical model was verified by the field experiments of Hesp et al. (2019). Following that, a series of numerical wind tunnel experiments were conducted on the 6 arrays, with the single meadow coverage of 40.00 %, at incoming wind speeds of 7 m/s (low), 11 m/s (medium) and 15 m/s (high) (wind speed is 2 m from the surface). In addition, this study uses flow field, windproof efficiency (E), downwind speed percentage (DSP), integrated cumulative distribution function of wind speeds below the threshold of 4.19 m/s in Maqu (P < 4.19 m/s) and economy to comprehensively evaluate the windproof effects based on the results of numerical wind tunnel experiments. Evaluation results based on individual index indicated that: (1) The meadow array significantly reduces the wind speed, and the meadow array pattern changes the airflow field around the meadow. (2) The E value in windproof areas for different meadow layouts ranking from largest to smallest is as follows: LS-1 > SS-1 > CI > SS-1.5 > LS-2 > SI. (3) Within the windproof area, the DSP of various meadow arrays revealed significant distribution differences, with significant reduction occurring especially for SS-1, SS-1.5, and LS. (4) As for the value of P <4.19 m/s , the order from largest to smallest for the 6 layouts reveals a law of LS-1 > SS-1 > SS-1.5 > CI > LS-2 > SI. (5) The paving decrement compared to the full pavement ranking from largest to smallest is SS-1.5 > CI > SS-1 > SI > LS-2 > LS-1. Based on the comprehensive evaluation results, which consider ecological economic benefits, it can be concluded that SS-1 demonstrates superior effectiveness as a low-coverage wind and sand control mode for a single wind direction. On the other hand, LS is found to be more suitable for scenarios involving multiple wind directions or variable wind directions. The anticipated outcomes of this study are poised to offer a novel approach for managing wind and sand, as well as facilitating ecological restoration in the alpine desertified grassland in the future. • Porosity source is added for RNG k-ε air flow modeling on flexible meadow medium. • 6 layout forms are designed representing the randomness of natural patchy meadows. • Near surface wind speed (40 cm below) decreased significantly on 6 meadow arrays. • SS-1 & LS-1 are proven the best for single and multi wind directions, respectively. • A low coverage paving mode is proposed for Alpine desertified meadow restoration. [ABSTRACT FROM AUTHOR]

The aim of this research is to analyze the pressure distribution caused by wind pressure on the structure of a single-family house. The research object is a model reflecting a real structure, which was damaged in 2018 because of heavy winds. The main idea is to create numerical models using various complex structural analysis software and compare the results. The obtained results will be compared with each other to analyze the impact of various factors, hereinafter referred to as boundary conditions, on the pressure values in characteristic places of the facility. The values closest to the normal distribution will be compared to the actual damage to the house structure. The essence of the research will be the identification of phenomena occurring during the action of heavy winds in global conditions (European and American), considering modifications and different ways of creating seemingly similar numerical models and the way they work. Everything will be compared with each other to find the most optimal design method in the given programs and to obtain wind pressure results that are closest to the real ones.

The twisted wind flow (TWF), referring to the phenomenon of wind direction varying with height, is a common feature of atmospheric boundary layer (ABL) winds, noticeably affecting the wind-resistant structural design and the wind environment assessment. The TWF can be effectively simulated by a guide vane system in wind tunnel tests, but the proper design and configuration of the guide vanes pose a major challenge as practical experience in using such devices is still limited in the literature. To address this issue, this study aims to propose an approach to determining the optimal wind tunnel setup for TWF simulations using a numerical wind tunnel, which is a replica of its physical counterpart, using computational fluid dynamics (CFD) techniques. By analyzing the mechanisms behind guide vanes for generating TWF based on CFD results, it was found that the design must take into account three key parameters, namely, (1) the distance from the vane system to the side wall, (2) the distance from the vane system to the model test region, and (3) the separation between the vanes. Following the optimal setup obtained from the numerical wind tunnel, TWF profiles matching both the power-law and Ekman spiral models, which, respectively, reflect the ABL and wind twist characteristics, were successfully generated in the actual wind tunnel. The findings of this study provide useful information for wind tunnel tests as well as for wind-resistant structural designs and wind environment assessment.

Local wind pressures on tiny rods of complex grid structures are difficult to obtain through wind tunnel tests due to their small sizes after scaling down, resulting in a lack of data support in wind load calculations for similar structures. However, local wind pressures on tiny rods can be obtained through numerical wind tunnel simulation using full-sized models. In order to investigate the wind pressure distribution of a grid structure and the influence of grid structures on the wind load of core tubes, three different television tower models are established based on an engineering example for large eddy simulations. A turbulence inlet generator (NSRFG) is adopted in the simulations while reproducing a portion of the wind tunnel test section including the mean and fluctuating pressures for validation. The results indicate that the mean wind pressures on the intersection of rods in the windward zone of the grid structure are higher than those on adjacent rods. Distinct reductions in the mean and fluctuating wind pressure of the grid structure are found in different zones. Moreover, resultant wind load forces and bending moments in the X and Y direction of the grid structure generally exceed 70% of the total wind loads. Based on simulation results, extreme net wind pressures of the grid structure and shape coefficients of enclosed regular octagonal cross-section buildings with the grid structure are provided for reference. [ABSTRACT FROM AUTHOR]

In order to study the two-dimensional vortex-induced vibration of streamlined box girder of Changshan Bridge, based on the method of numerical wind tunnel, Gambit was used to establish the flow field of bridge section and divide the grid. The vortex-induced vibration model of bridge section was simplified to a vertical single-degree-of-freedom spring system and solved. The results of study show that the vortex of streamlined box girder is generated at the wind inlet of the bridge section, and gradually moves to the tail of the section through the upper section of the bridge, and falls off in the tail flow of the section. The converted wind speed that is easy to cause vortex-induced vibration is 8~20. The research conclusions provide reference for the prevention of vortex-induced resonance and vortex-induced vibration emergency treatment of bridges. [ABSTRACT FROM AUTHOR]

For acquisition of accurate aerodynamic parameters of the pipeline suspension bridge, the numerical wind tunnel model for the typical girder section of the oil and gas pipeline suspension bridge was built, and SST k-ε model was used as the numerical wind tunnel turbulence model. The bypass flow pressure field distribution acquired from the numerical wind tunnel shows that the negative pressure area on the upper and lower surfaces of the pipeline is obvious, the largest positive pressure area appears on the windward side of the pipeline, and the pressure difference between the windward side and the leeward side of the truss girder in the inflow direction is particularly obvious. The bypass flow velocity field distribution shows that the pipeline and truss girder exert significant blocking effect on the wind speed, and the flow separation and vortex shedding phenomena occur apparently on the pipeline, windward railings and truss girder. According to the root mean square pressure of the flow field, vortex vibration is most likely to occur in the inflow side truss. Through the analysis of the three component coefficients of different pipeline diameters and different girder widths at the wind attack angles of －3°, 0° and 3°, it is concluded that the girder width has little influence on resistance coefficient and lift coefficient, and the torsion coefficient decreases with the increase of the girder width at －3° wind attack angle. The pipeline diameter definitively influences the three component coefficients, that is, with the increase of pipeline diameter, the resistance coefficient increases gradually, while the lift coefficient and torsion coefficient decrease gradually. The research results are expected to provide wind-resistant data support for the design of suspension bridge deck structure and the piping layout.

Local wind pressures on tiny rods of complex grid structures are difficult to obtain through wind tunnel tests due to their small sizes after scaling down, resulting in a lack of data support in wind load calculations for similar structures. However, local wind pressures on tiny rods can be obtained through numerical wind tunnel simulation using full-sized models. In order to investigate the wind pressure distribution of a grid structure and the influence of grid structures on the wind load of core tubes, three different television tower models are established based on an engineering example for large eddy simulations. A turbulence inlet generator (NSRFG) is adopted in the simulations while reproducing a portion of the wind tunnel test section including the mean and fluctuating pressures for validation. The results indicate that the mean wind pressures on the intersection of rods in the windward zone of the grid structure are higher than those on adjacent rods. Distinct reductions in the mean and fluctuating wind pressure of the grid structure are found in different zones. Moreover, resultant wind load forces and bending moments in the X and Y direction of the grid structure generally exceed 70% of the total wind loads. Based on simulation results, extreme net wind pressures of the grid structure and shape coefficients of enclosed regular octagonal cross-section buildings with the grid structure are provided for reference.

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Wind-induced interference effect commonly occurs among arched plastic greenhouse group. To describe such influence and finally determine the wind load shape coefficients considering the interference effects, we conducted a series of numerical simulations based on computational fluid dynamics (CFD). Combining the Reynolds-averaged N-S equations and the Realizable k-ε turbulence model, the surface wind pressure characteristics of the models for single greenhouse and greenhouse group under different wind direction angles and distances were studied separately. In combination with the actual production, 5 rows and 6 columns symmetrical layout was adopted as the greenhouse group’s model with different gap distances (2, 4, 6, 8, 10 and 12 m) and wind direction angles (0, 30, 45, 60 and 90 degrees). In order to achieve quantitative analysis of the wind-induced interference effects, the interference factor was introduced in this paper as an important contrast parameter. According to the characteristics of the greenhouse structure, the greenhouse partition was reasonably set to realize the key research of wind pressure characteristics in wind-sensitive areas. In the numerical wind tunnel simulation, unstructured grids suitable for greenhouse group’s model were used to divide the computational domain. The calculation parameters such as blocking ratio, inlet and outlet conditions, and near-wall treatments and so on were appropriately set. By comparing with wind tunnel test results of similar models, the present numerical simulations were verified. According to the simulation results, the arrangement of greenhouse group causes the wind-induced interference effects, which will change wind pressure characteristics of the greenhouses. The effects can result in amplification effects (the outer area of the greenhouse group) and the shielding effects (the middle area of the greenhouse group), among which the amplification effects threatens the safety of the structure and cannot be ignored. The interference effects is significantly affected by the wind direction angle and the gap distance, and specifically it decreases with the increase of distance, and tends to be stable when the distance between greenhouses is about 10 m. Based on the analysis of the variation law of the mean wind pressure coefficients and wind direction angles on the greenhouse group’s roofs, it is obvious that the interference effects weakens the wind pressure ventilation ability of the greenhouse group as a whole. From the point of view of advantageous to wind pressure ventilation, the suggestions on planning and layout of the greenhouse group are put forward, that is, the long axis direction of the greenhouses should be perpendicular to the dominant wind direction in summer of the area where the greenhouse group is located and the gap distance should be increased appropriately. Finally, according to the wind-induced interference effects, the wind load shape coefficients for arched plastic greenhouses (the rise-span ratio is 3:8) are given, which are convenient for design. The wind load shape coefficients of greenhouses which are located in the outer area of the greenhouse group: At 0 wind direction angle, +0.41 on the windward side, -0.78 on the middle roof, -0.26 on the leeward side and -0.48 on both sides of gables; at 90 degrees wind direction angle, +0.36 on the windward gable, -0.44 on the roof. The wind load shape coefficients of greenhouses which are located in the middle area of the greenhouse group: At 0 wind direction angle, +0.30 on the windward side, -0.71 on the middle roof, -0.26 on the leeward side and -0.48 on both sides of gables; at 90 degrees wind direction angle, +0.34 on the windward gable, -0.35 on the roof. Wind-induced interference effects exists in arched plastic greenhouses arranged in group, and wind pressure changes on the greenhouses caused by wind-induced interference effects should be considered in design. [ABSTRACT FROM AUTHOR]

Summary: A cylindrical–conical steel cooling tower (SCT) is a new type of very large thin‐walled, flexible structure. This study focused on the wind loads on the internal and outer surfaces of this structure and its wind‐induced responses. First, using the computational fluid dynamics method, the numerical wind tunnel was conducted to simulate a 189‐m‐high cylindrical–conical SCT, Asia's highest cooling tower that is still under construction. This numerical method was validated by comparing the wind pressures across typical cross sections of the tower model's cylindrical and conical segments with known standard curves. Based on this, the features of the airflow around the typical cross sections and its wake were extracted, and the distribution of mean wind loads along the internal and outer surfaces of the cylindrical and conical sections was obtained. Then functions for estimating the internal and outer surfaces shape factors of the cylindrical and conical segments were obtained by fitting to the simulated data. Furthermore, finite element method was used to analyze the static wind‐induced response of the cylindrical–conical SCT under internal pressure, external pressure, or both internal and external pressure. The effect patterns of internal pressures on the wind‐induced responses of the main tube, stiffening trusses, and auxiliary trusses of the tower were derived from the analysis results. Main findings of the research can provide a reference for design of very large cylindrical–conical SCTs for wind resistance in the future. [ABSTRACT FROM AUTHOR]

The practice of reproducing wind tunnel tests by means of CFD numerical simulations, which is known as numerical wind tunnel (NWT), is becoming quite common in many research fields of wind engineering. Wind tunnel tests can provide the indispensable validation data needed for CFD numerical simulations; at the same time, CFD can be considered a complementary support for wind tunnel tests in order to obtain a more comprehensive description of the flow field. In the present paper, NWT technique is applied to study the flow around and inside a multi-stage vertical-axis wind turbine (VAWT) surrounded by stator vanes. At first, the flow field has been studied in the wind tunnel by means of experimental tests. Then the experimental results have been used to validate a CFD model. The numerical model has finally been used to study and describe how the results obtained by means of the physical model can be extended to more general conditions. [ABSTRACT FROM AUTHOR]

Abstract: Large Eddy Simulation of NREL Phase VI wind turbine was performed in a virtual wind tunnel (24.4m×36.6m) in order to achieve a better understanding of the turbine wake characteristics. For this purpose, ANSYS-Fluent package was used to run the simulation using the dynamic Smagorinsky-Lilly model. For the purpose of validation, the pressure distribution at different span-wise sections along the turbine blade and the power produced by the wind turbine were compared with the published experimental results for the NREL phase VI rotor tested in the NASA wind tunnel with the same dimensions as in the model and a good agreement was found between the two. The airflow immediately behind the wind turbine was observed to be a system of intense and stable rotating helical vortices, which determined the dynamics of the far-wake. The system of vortices in the near-wake became unstable and broke down due to wake instability at a distance of five rotor diameters downstream of the wind turbine. This was defined as the boundary between the near- and far-wake regions. The collapsed spiral wake was found to spread in all directions in the far-wake resulting in the formation of the two pairs of counter-rotating vortices which caused the gradual increase of turbulence in these regions. The turbulence intensity in the wake was observed to increase immediately behind the turbine with a maximum of 12.12% at a distance of three rotor diameters downstream of the turbine, after which a gradual decrease in the turbulence intensity was observed in the near-wake regions due to wake instability. However, in the far-wake regions, due to counter-rotating vortices formed by the wake instability, the turbulence intensity showed a tendency to increase intensity. Finally the time-averaged wake velocities from the LES, with and without the blockage corrections, were compared with WAsP and a comparatively good agreement for the axial velocity predictions was observed in the far-wake. [Copyright &y& Elsevier]