Windless Environment Research Articles

Dynamic Deflection Measurement on Stiff Bridges with High Piers by Preloaded Spring Method

The deflection dynamic load allowance (DLA) of stiff bridges with high piers requires sub-millimeter accuracy. New technologies such as the vision-based optical method and GNSS are not yet recognized for use in DLA measurements due to their smaller SNR. Presently, the scaffolding method is widely utilized for dynamic deflection measurements in dynamic load tests owing to the reliability of employing rigid contact. When scaffolding is not available, engineers have to resort to a suspension hammer system. However, the mass eccentricity of the hammer, stretched-wire length, and wind will decrease the measurement accuracy. To overcome these drawbacks of the suspension hammer method (SHM), a preloaded spring method (PSM) and the related stretched-wire-spring system (SWSS) are proposed in this paper. The dynamic deflection of the coupled vehicle-bridge-SWSS was obtained by vehicle-bridge interaction (VBI) analysis. The sensitivity parameters of the PSM were analyzed and optimized to minimize the measurement error. Indoor experiments and field dynamic load tests were conducted to validate the feasibility and accuracy of the PSM. Additionally, the differences in dynamic deflection measurements between the PSM and SHM in windy environments were compared. The results show that, in a windless environment, the DLAs of the PSM are affected by the spring stiffness, stretched-wire length, and stretched-wire section stiffness, independently of the preload force. When the wind speed is less than or equal to 8 m/s and the pier height is less than 30 m, the maximum deflection measurement error of the PSM is −2.53%, while that of the SHM is −15.87%. Due to its low cost and high accuracy, the proposed method has broad application prospects in the dynamic deflection measurement of stiff bridges with high piers.

Laser cleaning assisted wire arc additive manufacturing of aluminum alloy thin-wall through synchronous wire-powder deposition

Due to the interference of ambient wind on arc burning and droplet transfer, wire arc additive manufacturing (WAAM) of aluminum alloy in field environment is hindered. The gas-slag joint protection by synchronous feeding of AlSi5 wire and mixed powder of 90Mg-5TiO2-5NaF (wt.%) was introduced. It was found the wind resistance for the stable deposition of thin-wall could be improved from 1.5 to 3.5 m/s. The added Mg benefited to refine the grain size by 21 % and promote the formation of Mg2Si, which improved the mechanical properties by induced solid solution-precipitation strengthening effects. Furthermore, with the assistance of laser cleaning, the porosity of thin-wall deposited at ambient wind speed of 3.5 m/s was reduced from 54.9 % to 28 %. These improvements increased the ultimate tensile strength and elongation to 166 MPa and 3.7 %, reaching 98.2 % and 31 % of the WAAM at indoor windless environment respectively.

Effect of near-surface winds on the measurement of forest soil CO2 fluxes using closed air chambers

Forest soil CO2 flux measurements are important for studying global climate change. Current monitoring methods are based on closed gas chambers, which block the wind pumping effect of near-surface winds in the measurements, resulting in biased values. Therefore, in this study, the effects of near-surface winds on chamber-monitored fluxes were investigated. The CO2 flux was quantified using a designed flux reference system with different CO2 concentrations, and the monitoring performance of the closed chamber was studied. Wavelet coherence was used to analyze the response relationship between near-surface winds and soil gas, and was combined with a flux calculation model to explore the relevant factors influencing gas chamber measurement-produced bias. The data indicate that at near-surface wind speeds greater than 0.8 m·s−1, gas transport enhancement was significant and further increased the deviation of the gas chamber-monitored CO2 fluxes. The monitoring error of the flow chamber (NSF) increased from 7% to 30% in soils with low carbon content, but did not vary significantly (3–7%) in soils with high CO2 concentrations. The flux measurement bias of the non-flow chamber (NSNF) was positively correlated with the soil carbon content, with the measurement error expanding by 16–24% with increasing soil CO2 concentrations. The measurement errors of the exponential and linear models in a windless environment were 9.8% (Exp) and 18.7% (Lin), respectively. The estimation errors of both models were positively correlated with both the time of a single monitoring event and the wind-induced coefficient Dw. Therefore, flux calculation models should be improved by considering environments with wind disturbances to reduce the effect of wind on measured values, which will help improve the accuracy of ecosystem carbon budgets.

Ionic Wind Driven Fog Collection in Windless Environment

Fog collection is a promising technique to harvest water from the atmosphere. However, the fog collection in the windless environment is still a challenge. An ionic wind-driven fog collector was numerically designed. Numerical results demonstrated that the discharge electrode location significantly influenced the ionic wind flow pattern and fog collection rate. The fog collection rate corresponding to a nearly unidirectional flow pattern was several times of that corresponding to the vortices dominant flow pattern. An enhancement of 6.7 times in the fog collection rate was realized by increasing the input power. The fog collection rate increased linearly with the liquid water content under a fixed power consumption. A fog collector prototype was fabricated. The measured ionic wind velocity and fog collection rate supported the numerical design. In a windless foggy environment with a liquid water content of 0.62 g m–3, a collection rate of 0.46 L h–1 was achieved.

Pull-Force Generated by the Revolving High-speed Drill Shaft Results in Unexpected Tissue Wrapping Around the Shaft

Despite holding soft tissue away from high-speed drills during surgery, tissue can unexpectedly wrap around the drill shaft. We performed experiments to examine what precipitates such mishaps. In a windless environment, a Signature Drill System (Stryker) featuring a 4-mm diameter coarse diamond or cutting bit was placed parallel to a suspended strip of polypropylene. The distance between the end of the strip and the drill shaft or bits was 4 or 8mm. In another experiment, we placed the drill horizontally 10mm above the top of dry-ice fog. The maximum drill speed was 75,000rpm, and the horizontal motion of the polypropylene strip and the vertical motion of the dry-ice fog were recorded by a video camera. In the experiments, the strip parallel to the vertical shaft and the dry-ice fog were pulled toward the shaft; the higher the revolving drill speed, the faster its motion. On the other hand, in experiments where the end of the strip was next to either bit, no such motion was observed. The pulling force generated by revolving high-speed drill shafts may result in tissue wraparound even when soft tissue is held away from the shaft.

The effect of opening window position on aerosol transmission in an enclosed bus under windless environment.

The potential risk of spreading a virus during bus transportation motivates us to understand the aerosol transmission of SARS-CoV-2 and seek effective ways to protect passengers in a bus. In this paper, a typical scenario in which the virus spreads in a bus under a windless environment is numerically studied for further understanding of the spreading characteristics of aerosol transmission in an enclosed space. The air flow in the bus and the spreading processes of droplets with different open windows configurations are obtained and analyzed. The variations of droplet concentration in the air with time are examined and analyzed. In addition, the transient droplet concentration deposited on the passengers is also counted to analyze the potential contact transmission. The results indicate that opening a window next to an infected person shows an unsatisfactory performance in limiting droplet spreading range and reducing droplet concentration, eventually leading to a high risk of infection by aerosol transmission following contact transmission. In addition, opening multiple windows also shows an unsatisfactory result for removing droplets in a bus since the turbulence flow accelerates the spreading speed and expands the spreading range. In contrast, the droplets are removed from the indoor space of the bus quickly if a window is opened in the row in front of the infected person, which is beneficial for reducing aerosol and contact transmission in the bus. Furthermore, it is strongly recommended to avoid sitting in the row in front of the infected person where the highest droplet concentration can be observed.

Sand-ejecting fire extinguisher parameter sensitivity analysis based on experiments and CFD-DEM coupling simulations

This study was conducted for parameter sensitivity analysis of an eco-friendly fire-fighting device, the sand-ejecting fire extinguisher, by means of experiments and CFD-DEM coupling simulations. The paper presents a total of nine impeller design schemes. Simulations were carried out to reproduce the sand ejection process with each scheme. The results show that the gas flow field has an effect on the ejection process under the windless environment, so the sand ejection characteristic analyses are based on DEM calculations. The phenomenon that a greater number of blades could provide longer ejection distance is also found in the simulation process. Radial and forward schemes may be more suitable for gas-station fires while backward schemes not because of the sand accumulation character. The CFD-DEM calculation shows that increasing the sand mass flow could extend the ejection distance but is more susceptible to ambient wind.

Thermal and electrical performance of a novel photovoltaic-thermal road

The solar road is a new type of technology for solar energy conversion. As the solar energy utilization efficiency of a solar road is too low, to solve this issue, a novel photovoltaic-thermal road is proposed in this paper. In addition, a mathematical model is developed to evaluate thermal and electrical performance of the photovoltaic-thermal road, and it is validated by experimental data. Moreover, the performance of a simple water system of the photovoltaic-thermal road is investigated and compared with that of a photovoltaic road. The results show that overall energy efficiency of the photovoltaic-thermal road system is 3.95 times that of the photovoltaic road system. In addition, this study analyzed the effects of some meteorological and geometric parameters on the system performance. The pipe diameter was found to have little effect on the overall performance of photovoltaic-thermal road. Furthermore, the solar-radiation intensity, packing factor of photovoltaic cell, mass flow rate of circulating water, and transparent surface transmissivity have positive influences on the overall energy efficiency; in contrast, the wind speed and burial depth of the pipe have negative influences, implying that a windless environment is conducive to the energy output of the PVTR system. An optimum thermal conductivity of asphalt concrete can maximize the overall energy efficiency; for this study, the recommended range of this value is from 1.0 to 1.5 W/(m·K). The results of this study substantially contribute to the state of knowledge regarding photovoltaic-thermal road designs.

Actively and passively aspirated temperature sensors in a windless environment like greenhouses

Windless environments are prevalent in greenhouses, where precise temperature control is critical to the health of plants and errors in temperature measurement must be avoided. A mathematical model based on heat balance is used to estimate the error in temperature sensors under different conditions and sensor geometries. The model is then applied to two geometries and solved numerically. The sensors used are a T-type thermocouple and a Sensirion SHT 75. Experiments are carried out in a greenhouse prototype to replicate conditions in a greenhouse and validate the error model. Active ventilation of the sensors is provided by a fan and passive ventilation is provided using a model built on the concept of a ‘solar chimney’. It is shown that even small flow rates can decrease the error shown by unventilated sensors by as much as 10°C.

Development of a method for estimating oesophageal temperature by multi-locational temperature measurement inside the external auditory canal.

We aimed to develop a practical method to estimate oesophageal temperature by measuring multi-locational auditory canal temperatures. This method can be applied to prevent heatstroke by simultaneously and continuously monitoring the core temperatures of people working under hot environments. We asked 11 healthy male volunteers to exercise, generating 80W for 45min in a climatic chamber set at 24, 32 and 40°C, at 50% relative humidity. We also exposed the participants to radiation at 32°C. We continuously measured temperatures at the oesophagus, rectum and three different locations along the external auditory canal. We developed equations for estimating oesophageal temperatures from auditory canal temperatures and compared their fitness and errors. The rectal temperature increased or decreased faster than oesophageal temperature at the start or end of exercise in all conditions. Estimated temperature showed good similarity with oesophageal temperature, and the square of the correlation coefficient of the best fitting model reached 0.904. We observed intermediate values between rectal and oesophageal temperatures during the rest phase. Even under the condition with radiation, estimated oesophageal temperature demonstrated concordant movement with oesophageal temperature at around 0.1°C overestimation. Our method measured temperatures at three different locations along the external auditory canal. We confirmed that the approach can credibly estimate the oesophageal temperature from 24 to 40°C for people performing exercise in the same place in a windless environment.

Numerical simulation of the spreading dynamic responses of the multibody system with a floating base

To simulate the dynamic responses of the multibody system with a floating base when the upper parts spread with a certain sequence and relative speed, the homogeneous matrix method is employed to model and simulate a four-body system with a floating base and the motions are analyzed when the upper parts are spread sequentially or synchronously. The rolling, swaying and heaving temporal variations are obtained when the multibody system is under the conditions of the static water along with the wave loads and the mean wind loads or the single pulse wind loads, respectively. The moment variations of each joint under the single pulse wind load are also gained. The numerical results showed that the swaying of the floating base is almost not influenced by the spreading time or form when the upper parts spread sequentially or synchronously, while the rolling and the heaving mainly depend on the spreading time and forms. The swaying and heaving motions are influenced significantly by the mean wind loads. The single pulse wind load also has influences on the dynamic responses. The torque of joint 3 and joint 4 in the single pulse wind environment may be twice that in the windless environment when the system spreads with 60 s duration.

The Influence of Atmospheric Circulation on Evacuation Safety in a Semi-Open Parking Garage

This study examines the influence of the atmospheric disturbance caused by a fire in a semi-open parking garage and the resulting rapid drop of toxic gases on evacuation safety. According to a FDS simulation, the air pressure in an atmosphere of 1 kgf/m2 or a windless environment is used, each factor for hazardous escape does not reach a significant level (SFPE Handbook of Fire Protection Engineers). This indicates that even if two sides of an exterior wall are closed, in order to escape, a semi-open space is safe. However, in the industry, there is a debate on whether the influence of a different spatial format and the air pressure in the atmosphere needs to be re-assessed.

Analytical solutions for outdoor sound propagation in the presence of wind

A theoretical analysis for the sound field due to a point monopole source in a fluid, layered atmospheric environment is described. The analysis has included explicitly the effect of fluid motion in the three-dimensional wave equation. The atmospheric environment is assumed to have sound-speed and vector wind-velocity profiles that either increase or decrease monotonically with height. In addition, the atmosphere is assumed to be vertically stratified. In such an environment, the solution can be expressed analytically in terms of Airy functions but the forms of solution are different for the situations of upward and downward refraction. Some sound-speed and wind-velocity profiles are amenable to exact analyses. Two notable examples are (i) a windless environment with a linear sound-speed profile; and (ii) a medium with a linear wind shear layer and a constant sound speed. These two profiles are studied analytically and compared numerically with other computational schemes. The validity of a heuristic approximation, which replaces the vector wind-velocity profile with an effective sound-speed profile, is also investigated numerically.

Three-Dimensional Orientation of Male Cadra cautella (Lepidoptera: Pyralidae) Flying to Calling Females in a Windless Enviromnent

A male Cadra cautella (Walker) flying in a windless environment first reacts behaviorally to the sex pheromone plume of a calling female from a distance of ≈40 cm. Its angular velocity (turning rate in degrees per second) increases and, if it approaches within ≈20 cm, its velocity decreases gradually until it lands near the female. The orientation pattern differs from orientation in wind primarily in the fraction of turns with net movement away from the female, initially ≈0.5.This fraction decreases to ≈0.2 if the male approaches within ≈10 cm. Previously developed computer models suggest that such behavior is less efficient for finding a pheromone source than pheromone–stimulated optomotor anemotaxis but more efficient than random searching. Thus, it can be expected that pheromone traps are less effective at sampling remote populations of insects in a warehouse than in a field, but are helpful in pinpointing nearby infestations.

Stimulation by Wind Motion of Collenchyma Formation in Celery Petioles

1. Comparisons were made of the size and number of collenchyma bundles differentiated in two series of celery seedlings grown in constant wind and in a windless environment. 2. Celery subjected to wind motion differentiates approximately the same number of collenchyma bundles per petiole as plants from a windless environment. 3. Wind motion stimulates the development of collenchyma within the bundles, resulting in (a) larger areas of collenchyma, (b) heavier thickenings of the cell wall, and (c) collenchyma cells of larger diameter.