Tower Wall Research Articles

Structural health monitoring of an onshore steel wind turbine

The study presents the development of a structural monitoring system installed in a 45-m-high steel wind tower located in Italy. The installed monitoring system was composed by 16 strain gauges placed in the tower wall, in a pattern of four Wheatstone bridges at 45°, together with thermal couples, at 21 m from the ground (half-height of the tower). Moreover, several accelerometers were placed along the tower height (with one of them located next to the strain gauges). The wind velocity and directions were obtained directly from the turbine own monitoring system. Such a monitoring system was designed because, due to the decrement of the total height from the original design, the tower suffers from resonance problems. In fact, the investigated tower was originally designed with 65 m of height but then, to comply with local regulations, the height was decreased to the actual size. Therefore, to allow safe operation and avoid excessive fatigue due to the increased displacements, the velocity of the rotor has been manually limited causing an important reduction in the energy production. The results of the study show the importance of monitoring the resonance issue. The differences between the damage indexes obtained with two different working conditions are discussed: tower working with limited operational capacity and tower working at its maximum capacity (in resonance).

Deformation of High Rise Cooling Tower through Projection of Coordinates Resulted from Terrestrial Laser Scanner Observations onto a Vertical Plane

The appearance and development of new construction materials, technology and accurate geodetic instruments have led to the necessity of their inevitable use in the health monitoring, maintenance, and restoration of civil structures and special structures such as high-rise cooling towers. This paper presents an accurate practical and analytical method for determining the structural deformation and axis inclination of high rise cooling towers using terrestrial laser scanner (TLS) observations through the projection of tower surface points coordinates on a vertical plane. Four cooling towers in El-Mahla El-Kubra city, Egypt are observed and studied. Two of them with height 56 m, and the others were 36 m height. The studied four towers have different cross-section diameters along the tower height. Each tower has a cone shape with a curved wall. The equation of the tower wall is determined using TLS observations and least squares adjustment techniques. The equations of cone projection with a curved wall are derived and presented in this paper. From TLS observations, the radii and accuracy of each 2 m tower height are determined with center coordinates, and then the inclination of the tower axis is calculated and drawn. From the results of TLS observations, data processing, and analysis using the suggested techniques, it is deduced that there is a deformation in tower walls with small values. The specified technique for observations collection and TLS data analysis through projection on a vertical plane is significant and valuable for determining the structural deformation of circular high rise buildings and towers. From the results, there are obvious deformation values in some cooling towers, so maintenance work must be included. The towers also must be checked and monitored several times at brief intervals.

The analysis of the destabilizing motion of a hyperbolic cooling tower during demolition blasting

The destabilizing motion characteristics of the hyperbolic cooling tower in demolition blasting are thoroughly investigated through the establishment of a numerical simulation calculation model, leading to the following conclusions regarding its destabilizing motion. The tensile-compression elastic-plastic model, which possesses the characteristics of parameter modification function and independence from unit size, can more effectively capture the mechanical properties of concrete materials and find better application in the simulation and calculation research of reinforced concrete structures. The self-oscillation frequency check and collapse morphological analysis are employed to validate the accuracy of the simulation calculation model for hyperbolic cooling towers, as well as to assess the rationality of parameters in the tensile-compression elastic-plastic model. The collapse of a cooling tower induces flexural deformation in the lateral wall, tensile disturbance in the upper and middle sections of the cylinder, and compressive disturbance in the vertical cross-section. The cylinder body has incurred damage as a result of the tower wall’s front end striking the ground at the directional window position on the front side of the throat, leading to a significant extrusion deformation issue. The buckling deformation in the central and lower sections of the rear wall propagated towards the back side of the tower wall upon reaching the ground, ultimately resulting in an “inverted V-shaped” damage along the buckling deformation line. The research findings hold significant relevance for future endeavors.

Analysis of the Temperature Field Effect on the Thermal Stress of the Main Tower of Long-Span Suspension Bridges

To investigate the temperature field variation of the main tower of large-span suspension bridges, the Nanjing Xinshengwei Yangtze River Bridge was selected as the objective of the present study. The finite element model of the main tower was developed, and the analysis of the effect of the temperature field on the structure of the main tower was carried out. The calculation parameters of the temperature field of the main tower were determined, and the influence of the solar radiation temperature of the main tower within 24 h was investigated. Differences in the temperatures inside and outside the wall of the tower column were analyzed, and the thermal stress of the tower wall under the most unfavorable temperature difference was calculated. Results show that under the positive temperature difference, the area of tensile stress is mainly concentrated on the inner wall, the maximum value is located at the corner of the intersection of the tower wall, and the range of tensile stress is mainly diffused along the vertical wall. Under the action of negative temperature difference, the area of tensile stress is mainly concentrated in the outer tower wall, the maximum value is located in the upper part of the western outer tower wall, and the range of tensile stress is mainly diffused along the center of the tower wall to both sides. The maximum tensile stresses in the inner and outer tower wall are 2.8 MPa and 1.3 MPa, respectively, which meets the standard value of 2.85 MPa for the tensile strength of C60 concrete specified in the Chinese national standard.

CFD analysis of the spray droplet parameters effect on gas-droplet flow and evaporation characteristics in circulating fluidized bed desulfurization tower

The circulating fluidized bed flue gas desulfurization (CFB-FGD) process is a promising semi-dry flue gas desulfurization technology. The gas-droplet flow characteristics and droplets evaporation characteristics are critical to improving the desulfurization efficiency of the FGD tower. The effects of droplet parameters, including spray droplet diameter, spray droplet velocity, spray droplet mass flow rate and spray angle are investigated. Two evaluation indices, the coefficient of variation of droplet concentration (CV) and droplet mass-weighted life, are adopted to evaluate mixing degree of gas-droplet and droplet evaporation time, respectively. Results show that as the spray droplet diameter increases from 40 µm to 80 µm, the amount of water droplets trapped by tower wall increases from 3% to 21%. Increasing the spray droplet velocity and spray droplet mass flow rate could effectively increase the turbulent kinetic energy, which could improve the turbulent mixing ability. Moreover, droplet with smaller diameter and high velocity are beneficial to improving the temperature distribution uniformity. When the spray droplet mass flow rate exceeds 2.7 kg/s, the temperature in the tower would be lower than the dew point temperature, resulting in corrosion of the tower wall. Furthermore, the evaporation rate of droplets decreases with the increase of droplet diameter, spray droplet velocity and spray mass flow rate, while increases with the increase in the spray angle. This study would provide a better reference for the optimum operating scheme in practical applications.

Youths as recipients and providers of agriculture information – the vertical vegetable gardening case in Busia County, Kenya

The intent of this study was to assess the feasibility of engaging youths in secondary schools in disseminating agricultural information among smallholder farmers using a five-month vertical vegetable gardening technology case in Busia County, Kenya. The research employed mixed research design targeting smallholder farmers and youths in secondary schools. A sample of 132 smallholder farmers and 132 youths in their first, second, and third years of study were selected to participate in the study at the baseline survey, during the intervention, and at the closure survey. The baseline survey was used to identify gaps, followed by participatory training intervention on the mound bed, primary tower, and second wall, to create awareness about vertical vegetable gardening through young farmers' clubs, and a closure survey to assess the change caused by the intervention and the feasibility of the approach. The study used kales, black nightshade, swiss chard, capsicum and carrots as examples of vegetables suitable for vertical gardens. Data was analyzed using the Wilcoxon sign-rank test at p0.05 level of significance, thematic and descriptive analysis. The results showed that there was a significant change in access and use of vertical gardening information by smallholder farmers. At P = 0.000, 22% of the smallholder farmers appreciated the use of vertical vegetable gardening at the closure survey, compared to 1% at the baseline survey. The dissemination of information through secondary school youths allowed for multiple delivery channels, was a good technology result demonstration approach for technology replication, and had sufficient agricultural extension activity learning scope. Significant change in the level of technology acceptance offer practical implications for policy makers to support the role of youths in agricultural extension. Future studies are needed to examine suitable agricultural extension policies and strategies to increase the successful implementation of agricultural extension through secondary schools.

Three-Dimensional Temperature Field Simulation and Analysis of a Concrete Bridge Tower Considering the Influence of Sunshine Shadow

This paper forms a set of three-dimensional temperature field simulation methods considering the influence of sunshine shadow based on the DFLUX subroutine and FILM subroutine interface provided by the Abaqus platform to simulate the three-dimensional temperature field of concrete bridge towers and study its distribution law. The results show that the method has high accuracy for shadow recognition and temperature field calculation. The maximum difference between the shadow recognition results and the theoretical calculation value was only 19.1 mm, and the maximum difference between the simulated temperature and the measured temperature was 3.3 °C. The results of analyzing the temperature field of the concrete bridge tower using this algorithm show that the temperature difference between the opposite external surface of the tower column can reach 11.6 °C, which is significantly greater than the recommended temperature difference value of 5 °C in the specifications. For the concrete bridge tower, in the thickness direction of the tower wall, the temperature change was obvious only at a range of 0.3 m from the external surface of the tower wall, and the temperature change in the remaining range was small. In addition, the temperature gradient distribution of the sunshine temperature field in the direction of wall thickness conformed to the exponential function T(x) = T0e−αx + C. Additionally, the data fitting results indicate that using the temperature data at a distance of 0.8 m from the external surface as the calculation parameter in the function can achieve the ideal fitting result.

Numerical simulation on gas-droplet flow characteristics and spray evaporation process in CFB-FGD tower

Nozzle arrangement in the nozzle spray system has a significant impact on the gas-droplet flow characteristics and the temperature distribution within the circulating fluidized bed flue gas desulphurization (CFB-FGD) tower, which is critical to the SO2 removal efficiency. The effects of spray direction, nozzle number and nozzle spray angle on gas-droplet distribution and temperature distribution inside the FGD tower are investigated with numerical simulation based on a Eulerian-Lagrangian mathematical model. An optimal nozzle arrangement scheme is proposed to improve the contact between gas and water droplets and the flue gas temperature distribution. Results show that upward spray direction is beneficial to the interaction between water droplets, improving gas-droplet flow characteristics and spray evaporation process, and water droplets number trapped by tower wall could be reduced in the water droplets evaporation. With the increase in nozzle number, it is conducive to the contact between flue gas and water droplets to increase the evaporation efficiency of water droplets, as well as the uniformity of temperature distribution inside the tower. With nozzle spray angle increases from 30° to 120°, flue gas velocity decreases, water droplets number trapped by the tower wall increases. The temperature distribution at different cross-section is the most uniform when the nozzle spray angle is 60°.

Investigation of the strut‐and‐tie model of a single‐plane cable‐stayed bridge tower under vertical component of the cable force

AbstractThe design of reinforcement of concrete pylons in cable‐stayed bridges is a challenging task. Usually, only the influence of the strong horizontal component of the cable force is considered during the reinforcement design of the concrete tower, while the bursting forces caused by the vertical components of the cable forces are ignored. However, the latter is also an important factor for concrete cracking in bridge towers. In this paper, the concrete tower of a single cable plane cable‐stayed bridge is considered. The strut‐and‐tie model (STM) of the pylon wall subject to the vertical components of one single cable force was derived. Based on the minimum strain energy principle, an equation for predicting the bursting force was given. Then, the STMs of a concrete pylon with two cable forces with different vertical distances between cables were proposed. A series of equations for predicting the bursting force in different STMs were presented. The STMs of a concrete pylon with multiple cables were subsequently obtained from the STM for two cable forces. The analysis results show that the vertical distance between cables has a great influence on the STM configuration of the tower. When the cable distance is less than 0.7 times the width of the tower wall, the bursting force is larger than that when the cable distance is larger than 0.7 times the width of the tower wall. This study was expected to provide a reference in the design and applications of pylons of concrete cable‐stayed bridges.

A novel reduced column section approach for the seismic protection of wind turbines

The rapid increase in global energy demand over the coming decades must be sustained by a more consistent increment of energy production from renewable sources of which wind energy is currently one of the fast-growing resources. New onshore and offshore wind farms will be rapidly constructed in challenging environments, especially in earthquake-prone areas. As a result, the mitigation of the dynamic vibrations of the wind turbines becomes a fundamental aspect of the seismic design to guarantee their normal operativity and structural safety. Different from past proposals based on traditional passive control devices such as tuned mass dampers or tuned liquid column dampers, this study aims to propose a novel approach, the Reduced Column Section (RCS), to derive an innovative mitigation device which replaces the traditional transition piece of the wind turbine. Analytical formulas to design the proposed RCS will be established. The benefits of the proposed device will be assessed on a real onshore wind turbine located in Italy. Modal properties obtained from the continuous dynamic monitoring of the wind turbine will be used to characterize the numerical finite element model. Therefore, a direct integration analysis with spectrum-compatible real earthquakes and an incremental dynamic analysis will be conducted to evaluate the dynamic mitigation induced by the proposed RCS. Soil-structure interaction effects will be also considered. This study shows that RCS can efficiently mitigate the effective stresses on the wind tower wall by up to 70% compared to the stresses computed on the existing structure.

Digging Up Jericho: Past, Present and Future

Digging Up Jericho: Past, Present and Future

Dynamic analysis on monopile supported offshore wind turbine under wave and wind load

Monopile offshore wind turbine (OWT) accounts for more than 65% of all OWT types. Monopile OWT is a soil-pile-tower system and can be divided into three stages: the stage embedded in the soil, the stage submerged in the seawater and the stage exposed to the air. Based on the improved Tajimi formulation and dynamic principle, this paper establishes a three-stage monopile OWT model to predict the dynamic response of the structure. The displacement of the tower under different wind velocities is obtained. The solution is compared with the Finite Element Method (FEM) result to verify its correctness. The influences of different parameters on the structure are discussed. The results indicate that the structure natural frequency is sensitive to the tower length and nacelle-rotor mass. The increasing seawater depth due to scour effect can significantly decrease the foundation stiffness. The influence of axial force and wave load on the foundation stiffness is also investigated. The tower diameter and tower wall thickness are found of vital importance to the tower displacement.

Study on the mass transfer of SO2 in ammonia-based desulfurization process

The coal hydrogen production process requires high-temperature steam as a reactant. Coal-fired boilers are usually used to provide high-temperature steam. The ammonia-based desulphurization process is an effective technology to remove SO2 in the coal-fired flue gas. However, the mass transfer coefficient of SO2 in such an engineered process is not readily available in the literature. In this paper, experiments were carried out to investigate the mass transfer process of SO2 absorption. Combing calculating the air and liquid contact area of the droplet and liquid membrane on the tower wall, the mass transfer coefficient contain parameters pH, gas flue rate and liquid to gas ratio was proposed. The comparison results show that the calculated SO2 mass transfer rate agrees well with the measured data. The relative error of the calculated and experimental values was less than ±20%. This proposed mass transfer coefficient appears to be beneficial for the design and operation of ammonia-based desulfurization FGD system.

Research on atomization evaporation characteristics and parameter optimization of a novel spray evaporation desalting system

Rotary spray evaporation technology has received particular attention due to its superiority in high-salinity wastewater's zero liquid discharge (ZLD). This research develops a new type of high-efficiency and low-energy-consumption rotary spray evaporation tower. The effects of atomization speed, feed flow, feed liquid concentration, hot air temperature, and hot air velocity on high-salinity wastewater's atomization and evaporation characteristics were studied. The numerical results show that the atomization speed can reduce the droplet spraying to the tower wall to reduce the sticky wall phenomenon and prolong the droplet residence time to increase the evaporation rate. By controlling the atomization speed, feed flow, and feed concentration, the droplet SMD can be reduced by 6.0 % to 37.3 % so that the droplets are evenly dispersed. With reasonable hot air temperature and speed, the outlet temperature drops by 19.1 % to 29.0 %, and the evaporation rate increases by 8.7 % to 11.8 %. The optimal working conditions are 16,000 r/min atomization disk speed, 10 kg/h feed flow, 433 K hot air temperature, 10 m/s hot air flow rate, and 93.2 % evaporation rate at this time. The results show that the rotary spray evaporation technology can be a powerful means of ZLD of high-salinity wastewater.

New retrofit method to cooling capacity improvement of mechanical draft wet cooling tower group

The airflow distribution of the mechanical draft wet cooling tower group will become very uneven under crosswind conditions, and the cooling capacity of leeward towers can be seriously reduced. To strengthen the heat and mass transfer of the leeward tower and improve the cooling capacity of the tower group, a new retrofit method is proposed that removes the tower wall between the rain zone of the tower group. The airflow can enter the leeward tower from the windward tower, even flow out from the air inlet of the leeward tower under crosswind conditions, and the airflow distribution becomes more uniform in the tower group. A 3D numerical model of the mechanical cooling tower group is established and validated. The cooling capacity of the tower group is studied under variation crosswind velocities (0 m/s–12 m/s) and crosswind angles (0°–90°) by numerical calculation. The results show that the distribution of outlet water temperature in the retrofit tower group is more uniform. The retrofit tower group can increase the circulating water temperature drop of the leeward tower under the crosswind angle of 0° and 45°. Under the crosswind angle of 0°, the temperature drop of the circulating water increases 0.52 ℃ maximum and 0.31 ℃ on average. Under the crosswind angle of 45°, it increases 0.92 ℃ maximum and 0.59 ℃ on average. Under the crosswind angle of 90°, it increases 0.19 ℃ maximum and 0.09 ℃ on average.

An Accurate Estimation of the Eigenfrequency of an Offshore Wind Turbine Considered as the Stepped Euler-Bernoulli Beam in Three-Spring Flexible Foundation Using the Power Series Method

The present study employs the power series method (PSM) to accurately predict the natural frequencies of eleven offshore wind turbines (OWT). This prediction is very important as it helps in the quick verification of experimental or finite element results. This study idealizes the OWT as a stepped Euler-Bernoulli beam carrying a top mass and connected at its bottom to a flexible foundation. The first part of the beam represents a monopile and the transition piece while its second part is a tower. The foundation is modeled using three springs (lateral, rotational, and cross-coupling springs). This work’s aim is at improving therefore the previous researches, in which the whole wind turbine was taken as a single beam, with a tower being tapered and its wall thickness being negligible compared to its diameter. In order to be closer to real-life OWT, three profiles of the tapered tower are explored: case 1 considers a tower with constant thickness along its height. Case 2 assumes a tower’s thickness being negligible compared to its mean diameter, while case 3 describes the tower as a tapered beam with varying thickness along its height. Next, the calculated natural frequencies are compared to those obtained from measurements. Results reveal that case 2, used by previous researches, was only accurate for OWT with tower wall thickness lower than 15 mm. Frequencies produced in case 3 are the most accurate as the relative error is up to 0.01%, especially for the OWT with thicknesses higher or equal to 15 mm. This case appears to be more realistic as, practically, wall thickness of a wind tower varies with its height. The tower-to-pile thickness ratio is an important design parameter as it highly has impact on the natural frequency of OWT, and must therefore be taken into account during the design as well as lateral and rotational coupling springs.

Lessons learned from the 2011 Great East Japan Earthquake: A case study of tsunami risk assessment in a Japanese chemical corporation

AbstractNatural hazard triggering technological disasters (Natech) pose a major risk to chemical industries. Natural disasters, such as earthquakes, floods, and tsunamis, may cause massive fires, explosions, and toxic chemical release into the environment. Thus, Natech risks have recently attracted considerable research attention. Although Natech‐related case studies are seldom reported in the literature, the results obtained thereof facilitate concrete risk assessments and countermeasure implementation against natural hazards. This article presents a case study on tsunami risk assessment performed by Asahi Kasei Corporation, Japan, based on four steps: (1) review of Natech events caused by the 2011 Great East Japan Earthquake, (2) hazard identification at the plant, (3) risk assessment considering human casualties, equipment loss, environment, and business continuity, and (4) evaluation and implementation of appropriate countermeasures. The risks posed by tsunamis were identified and analyzed. The inundation heights of Level‐1 and Level‐2 tsunamis were estimated to be 1 and 10 m, respectively. A tsunami evacuation tower and tidal wall were built as appropriate countermeasures to prevent or mitigate fatalities, loss of containment, and business interruption. The results obtained in this study facilitate adequate preparedness of chemical plants against future tsunami occurrences.

Lightning Overvoltage Protection of Step-Up Transformer Inside a Nacelle of Onshore New-Generation Wind Turbines

This paper presents an electromagnetic transient analysis of lightning-initiated overvoltage stresses of the step-up transformers installed inside a nacelle of onshore, multi-megawatt, new-generation wind turbines. The increase in the wind turbine (WT) nominal power output, necessitated introducing the step-up transformer into the nacelle. A transformer installed inside a nacelle is subjected to completely different overvoltage stresses from those present if it were installed at the base of the WT tower. This has serious repercussions on its overvoltage protection (i.e., selection and installation of surge arresters) and insulation coordination. Furthermore, the overvoltage protection of medium-voltage cables (inside the tower) is also problematic when considering their length, proximity to the tower wall, and their screen grounding practices, and needs to be tackled in conjunction with that of the step-up transformer. This paper presents detailed models for the various components of the latest-generation WTs, intended for fast-front transient analysis and assembled within the EMTP software package. We further present the comprehensive results of the lightning-transient numerical simulations, covering both upward and downward (first and subsequent) strikes, their analysis, and recommendations for the optimal selection of medium-voltage surge arresters for the step-up transformers installed inside a nacelle.

Juegos infantiles en los ciclos de las Edades de la vida. Una conquista de la pintura europea entre los siglos XIV y XVII

La representació dels jocs infantils va despuntar en l’art clàssic. No obstant això, cal esperar fins al segle XIV perquè sorgeixi un renovat interès per les escenes relacionades amb la infància. Aquest «despertar» iconogràfic va irrompre en el cicle de les edats de la vida a través de manuscrits i pintures murals. Exemple d’això són els frescos de Longthorpe Tower a Anglaterra (1330) i unes pintures murals de temàtica profana a Itàlia entre 1360 i 1524. Aquestes pintures van servir de model per a noves imatges en les enciclopèdies i els tractats morals. A partir del segle XV la iconografia va multiplicar el nombre i l’especificitat de les joguines, però també va conquerir nous suports —tapissos, objectes mobiliaris, pintures sobre taula i llenç, així com emblemes xilogràfics i estampes. Les edats es van convertir en el centre d’un complex debat sobre els beneficis i els perills del joc en l’educació moral de l’home, alhora que la seva presència en l’art i la literatura revelava una creixent consciència sobre la infància, una edat amb dret propi en la cultura dels adults.

Dynamic analysis of offshore steel wind turbine towers subjected to wind, wave and current loading during construction

In the present paper the dynamic response of tall offshore monopile steel wind turbine towers under wind, wave and current during the erection stage is studied. In particular, in the present paper the effect of current-wave-wind interaction as dynamic loading on the dynamic response of offshore wind turbine towers is for first time studied experimentally. Various loading states involving wind-wave, wind-current, wave-current, wind-wave-current to measure the displacement, velocity and acceleration of the tower model at three points on the tower wall respectively. A statistical analysis of the dynamic displacements of the model is conducted to study the effect of various loading states on the respective dynamic response. As outcome of the present study it was confirmed that the current field strongly affects the dynamic response of offshore monopoles and in particular, more significantly than the wave field. In the final part, an advanced finite element model is proposed for the efficient study of the structural response of the tower model during erection under current, wave and wind interaction.