Tower Shell Research Articles

Influence of flange dimensions and geometrical imperfections on stress concentrations at welded flange necks

AbstractRing flange connections for tubular towers, like those for wind turbines or chimneys, are subjected to significant fatigue loading. Next to the bolts, the weld connecting the flange to the tower shell also needs to be checked against fatigue failure. The flange causes local bending moments in the shell, which increase the meridional stress, i. e. stress concentrations occur. In this paper, the influence of geometrical imperfections on such stress concentrations is quantified and the influence of flange geometry on resulting stress is investigated. Recommendations are given for flange dimensions and the design procedure.

Anomaly detection and prediction of high‐tension bolts by using strain of tower shell

AbstractIn this study, an anomaly detection and prediction method for high‐tension bolts is proposed by using the measured strain of tower shell. The finite element models (FEMs) for the high‐tension bolts and tower‐top are built and validated with measurement data. An algorithm of anomaly detection and prediction is then developed by applying Mahalanobis‑Taguchi system. The threshold of abnormal condition for high‐tension bolts is proposed, and the formula for the prediction of remaining axial bolt force is derived by using the strain of tower shell obtained from the FEM model. Finally, onsite measurements are performed at Taikoyama wind farm to investigate the relationship between the strain of tower shell and the remaining axial bolt force. It is found that the proposed threshold based on the FEM model succeeds in detecting abnormal bolt by the Mahalanobis‑Taguchi system, and the proposed formula accurately predicts the remaining axial bolt force.

Research on survivability of mesh hyperboloid structures

The object of study is a mesh hyperboloid tower, which has a base diameter of 34 meters and a height of 128 meters, constructed by an engineer V.G. Shukhov. The survivability property of the mesh hyperboloid tower was accepted as a subject of research. The aim of the work is to perform a numerical calculation of the mesh hyperboloid tower for survivability in a static setting, under conditions of failure of individual load-bearing elements of the system as a result of an accident. This calculation evaluates the survivability of the structure. The research methodology involves consideration of several options for the collapse of the bearing elements: 1. Collapse of the intermediate rings of the 1st and 2nd tiers and 16 racks of the mesh tower, excluding power transmission cables; 2. Collapse of the intermediate rings of the 1st and 2nd tiers and 16 racks of the mesh tower, taking into account the influence of the load from the power transmission cables during operation. As a result, the most dangerous destruction zones are identified, from the point of view of the survivability of the structure, the survivability coefficient of the mesh tower, as a whole is determined. As a result of the calculations, it was revealed that when the intermediate rings and 16 racks in the tower elements are removed, the efforts in the elements adjacent to the collapse zone increase by 2.6 times. The asymmetry of the load on the removed elements plays a significant role in changing the efforts. With the removal of the intermediate rings of the 1st and 2nd tiers and 16 racks, the zone of the 1st lower tier becomes the most loaded. Compression efforts in the remaining racks of this tier increase by 150%. In addition, the number of compressed-bendable elements of the tower shell increase. The results of this work can be used by designers to calculate structures’ survivability.

INDUSTRIAL TOWER LIFE CYCLE EXTENSION ACCORDING TO SIKA TECHNOLOGIES

Some aspects of the life cycle extension of RC tower which is a chemical enterprise was described. This technological tower of ammonium seliters granulation has a height of +71,30 m. From this height to the Mark +46,10 mthe tower is made in a metal frame with diameter at the axes of the column22,56 m. The facade of this part is made of mounted keramzytoconcrete panels and in line constructional glazing. Between the marks 0,00 ÷ +46,10 mthe building has a monolithic RC trunk, which has a cylindrical outline in the form of a shell with an outer diameter of12,88 mand a thickness of0,3 mwalls. During 46 years of operation in chemical influences, the surface layers of the tower’s concrete trunk significantly lost its design strength. According to the results of almost regular surveys, the category of RC trunk technical condition was consistently classified as unsuitable for normal maintenance. A significant deterioration of the technical condition came in 2017, after which the building was withdrawn from the technological process, which gave impulse to the searching process of technical solution for the strengthening and chemical protection of the tower to prolong the life cycle of the entire facility. As a result of the survey the construction of the tower shall strengthening by a system of radial and vertical stiffening ribs was developed. It required a substantial unloading of the entire tower. Swiss concern Sika, one of the world leaders in the field of development and implementation of innovative technologies and materials for construction and industry, successfully implements its developments in Ukraine. For the above-described construction the firm Sika offered repair and chemical protection systems against aggressive influences for the internal and external surfaces of the tower shell, which will allow to significantly protect it and prolong the life cycle of structure.

3D Point Cloud Analysis for Damage Detection on Hyperboloid Cooling Tower Shells

The safe operation and maintenance of the appropriate strength of hyperboloid cooling towers require special supervision and a maintenance plan that takes into consideration the condition of the structure. With three series of terrestrial laser scanning data, the paper presents an automatic inspection system for reinforced concrete cooling tower shells that ensures detection and measurement of damage together with the verification of the quality and durability of surface repairs as required by industry standards. The proposed solution provides an automatic sequence of algorithm steps with low computational requirements. The novel method is based on the analysis of values of the local surface curvature determined for each point in the cloud using principal component analysis and transformed using the square root function. Data segmentation into cloud points representing a uniform shell and identified defects was carried out using the region growing algorithm. The extent of extracted defects was defined through vectorisation with a convex hull. The proposed diagnostics strategy of reinforced concrete hyperboloid cooling towers was drafted and validated using an object currently under repair but in continuous service for fifty years. The results of detection and measurement of defects and verification of surface continuity at repaired sites were compared with traditional diagnostics results. It was shown that the sequence of algorithm steps successfully identified all cavities, scaling, and blisters in the shell recorded in the expert report (recognition rate—100%). Cartometric vectorisation of defects determined the scope of necessary shell repairs offering higher performance and detail level than direct contact measurement from suspended platforms. Analysis of local geometric features of repaired surfaces provided a reliable baseline for the evaluation of the repairs aimed at restoring the protective properties of the concrete surround, desirable especially in the warranty period.

Resonance Investigation and its Effects on Weight Optimization of Tubular Steel Wind Turbine Towers

The dynamic behavior of tubular steel wind turbine towers is investigated, with emphasis on discussing how the effort to avoid resonance of the soil-foundation-tower system, by keeping its eigenfrequencies outside specific ranges around the rotor (1P) and blade-passing (3P) frequencies, influences tower optimization. For modern, tall towers avoidance of resonance becomes critical compared to other structural design checks, such as buckling and fatigue. Considering that the rotor and blades have predefined mass and rotation frequencies, the tower’s fundamental frequencies should be controlled considering the cross-sectional properties of the tower as well as the flexibility of its foundation. The objective of the optimization problem formulated in this work is to reduce tower weight, while satisfying the resonance and buckling criteria and considering restrictions pertaining to fabrication, transportation and erection. The vibration modes and frequencies of a 120m tall tower are determined via detailed as well as simplified finite element models, with the latter proving to be sufficiently accurate. The dependence of the tower’s vibration frequencies on the soil and foundation is also investigated. The numerical models are introduced into the high performance optimization computing platform (HP-OCP), to obtain an optimum distribution of tower shell thickness over the height.

Internal flow reconstruction strategies to improve both thermo-flow performance and flue gas diffusion characteristic of the integrated dry-cooling tower and stack system

The interaction between thermo-flow performance and flue gas injection in an integrated dry-cooling tower and stack system was revealed. Flue gas injection slightly increases the ventilation and heat rejection of the tower, and rear radiators are protected due to the blocking effect of the desulfurizer and stack. Both the swirl and downwind deflection of internal rising airflows contribute to the chaotic diffusion of flue gas. Two internal flow reconstruction strategies were proposed. One works in the stage of inflow air mixing, and the other works in the following stage of airflow rising. Numerical results show that the former strategy performs better on tower performance improvement, since the latter one causes a decline of tower ventilation at low wind speed. Both the two strategies have evident superiority in controlling gas diffusion inside the tower, especially at the medium wind speed of 10 m/s, the chaos of internal rising airflows reduces remarkably, and the contact area between flue gas and inner tower shell reduces over 85%. Thanks to the mitigation of plume downwash after flow reconstruction, diffusion passage of flue gas in the atmosphere is uplifted, and the reduction of contact area between flue gas and outer tower shell reaches 40%.

Coupled wind turbine design and layout optimization with nonhomogeneous wind turbines

Abstract. In this study, wind farms were optimized to show the benefit of coupling complete turbine design and layout optimization as well as including two different turbine designs in a fixed 1-to-1 ratio in a single wind farm. For our purposes, the variables in each turbine optimization include hub height, rotor diameter, rated power, tower diameter, tower shell thickness, and implicit blade chord-and-twist distributions. A 32-turbine wind farm and a 60-turbine wind farm were both considered, as well as a variety of turbine spacings and wind shear exponents. Structural constraints as well as turbine costs were considered in the optimization. Results indicate that coupled turbine design and layout optimization is superior to sequentially optimizing turbine design, then turbine layout. Coupled optimization results in an additional 2 %–5 % reduction in the cost of energy compared to optimizing sequentially for wind farms with turbine spacings of 8.5–11 rotor diameters. Smaller wind farms benefit even more from coupled optimization. Furthermore, wind farms with closely spaced wind turbines can greatly benefit from nonuniform turbine design throughout the farm. Some of these wind farms with heterogeneous turbine design have an additional 10 % cost-of-energy reduction compared to wind farms with identical turbines throughout the farm.

Optimization of turbine design in wind farms with multiple hub heights, using exact analytic gradients and structural constraints

AbstractWind farms are generally designed with turbines of all the same hub height. If wind farms were designed with turbines of different hub heights, wake interference between turbines could be reduced, lowering the cost of energy (COE). This paper demonstrates a method to optimize onshore wind farms with two different hub heights using exact, analytic gradients. Gradient‐based optimization with exact gradients scales well with large problems and is preferable in this application over gradient‐free methods. Our model consisted of the following: a version of the FLOw Redirection and Induction in Steady‐State wake model that accommodated three‐dimensional wakes and calculated annual energy production, a wind farm cost model, and a tower structural model, which provided constraints during optimization. Structural constraints were important to keep tower heights realistic and account for additional mass required from taller towers and higher wind speeds. We optimized several wind farms with tower height, diameter, and shell thickness as coupled design variables. Our results indicate that wind farms with small rotors, low wind shear, and closely spaced turbines can benefit from having two different hub heights. A nine‐by‐nine grid wind farm with 70‐meter rotor diameters and a wind shear exponent of 0.08 realized a 4.9% reduction in COE by using two different tower sizes. If the turbine spacing was reduced to 3 diameters, the reduction in COE decreased further to 11.2%. Allowing for more than two different turbine heights is only slightly more beneficial than two heights and is likely not worth the added complexity.

Studies on the influence factors of wind dynamic responses on hyperbolic cooling tower shells

Wind induced dynamic responses on hyperbolic cooling tower (HCT) shells are complicated functions of structure and wind properties, such as the fundamental frequency fmin, damping ratio zeta wind velocity V, correlationship in meridian direction and so on, but comprehensions on the sensitivities of the dynamic responses to these four factors are still limited and disagree from each other. Following the dynamic calculation in time domain, features of dynamic effects were elaborated, focusing on the background and resonant components SigmaB and SigmaR, and their contributions to the total rms value SigmaT. The SigmaR is always less than SigmaB when only the maximum SigmaT along latitude is concerned and the contribution of SigmaR to SigmaT varies with responses and locations, but the SigmaR couldn\'t be neglected for structural design. Then, parameters of the above four factors were artificially adjusted respectively and their influences on the gust responses were illustrated. The relationships of SigmaR and the former three factors were expressed by fitted equations which shows certain differences from the existing equations. Moreover, a new strategy for wind tunnel tests aiming at surface pressures and the following dynamic calculations, which demands less experiment equipment, was proposed according to the influence from meridian correlationship.

Utilization of partial through-flow tower shell to cope with the excess cooling capacity of dry cooling tower in extremely cold days with crosswind

During low ambient temperature periods, the huge heat transfer temperature difference would result in an excess cooling capacity of the natural draft dry cooling tower. So low cooling water temperature and back pressure can be easily achieved in cold days due to the unavoidable air leakage in practical operation, and the excess cooling capacity is a great threat to the safe operation of the indirect dry cooling system. To cope with that problem, a novel partial through-flow tower shell is proposed. By numerical simulation of the tower, aerodynamic fields in and around the tower were presented, and cooling water temperature drop was exported as well. It was found that thermal performance of the tower would get enhanced by crosswind under the air leakage condition, but that can be counteracted by the proposed partial through-flow tower shell. The through-flow tower shell is effective to reduce air inflow rate and cooling capacity of the tower, and increase back pressure and cooling water temperature after the coupling of the tower and condenser. Compared with the sideward or leeward through-flow tower shell, the windward through-flow tower shell would provide a much larger feasible region for safe operation of the system, and achieve the maximum anti-freezing result at the moderate wind speed. At the fairly high wind speed, the sideward through-flow tower shell would bring the adverse effect, while the other two forms are still active, although their anti-freezing effects degrade a bit in this condition.

Wind-induced equivalent static interference criteria and its effects on cooling towers with complex arrangements

Wind-induced interference is a controlling factor in the design of grouped cooling towers. To meet structural safety requirements, interference factor (IF) is commonly used to envelope the multiple complex static wind pressure distributions caused by it. However, the parameter turns out to be quite scattered for different evaluation criteria. To compare those criteria and study tower-group interference effects among complex arrangements, cooling tower groups with typical six-tower double-column arrangements were selected to perform wind tunnel tests and FEM calculation. Interference effects among classical rectangular and rhombic combinations were investigated, considering several typical center-to-center distances between towers. Wind pressure under 15 × 16 incoming flow conditions for 1:200 reduced-scale models was measured and corresponding 3-D quasi-static and static calculations were carried out to analyze the IFs. Totally, twenty-five kinds of IFs were compared based on criteria at three aspects: aerodynamic loading, structure response and reinforcement ratio. Some principal conclusions are synthesized as follows: the values of IFs for twenty-five criteria are quite different even for a same tower and their fluctuation under different cases is not the same as well, but those criteria are in accordance with each other in reflecting adverse interference conditions; the unified IF widely applied by loading codes cannot economically cover complex spatial wind pressure distributions caused by interference effects; multiple factors changing along the tower shell are recommended as a possible alternative, taking into account convenience, economy and rationality.

Analysis of cooling tower’s geometry by means of geodetic and thermovision method

Safe operation of thin-walled objects requires a regular monitoring of their technical condition. Geodetic measurements performed with a terrestrial laser scanning allow to determine the geometrical shape of the tested object with very high detail. Thermovision, as an auxiliary method, allows identification of places particularly exposed to changes in geometry caused by thermal influences. This paper presents a combination of both methods to analyse the geometry of reinforced cooling tower with a height of about 170 m. Laser scanning was performed from 11 stations arranged around the cooling tower, and the acquired point clouds were combined and unified in terms of density. Comparing the actual shape of the shell with the theoretical model, the values of geometrical imperfections were calculated. Thermograms were made by means of the thermovision camera, with particular emphasis on the lower part of the shell. The analysis of the imperfections’ distribution and the location of the largest temperature differences allowed to identify the most threatened places on the cooling tower shell.

Measurement point density and measurement methods in determining the geometric imperfections of shell surfaces

Abstract In geodetic measurements of deformations in shell cooling towers, an important factor is to optimize the number of points representing the exterior surface of the shell. The conducted analyses of damage to such structures proved that cooling towers exhibited shell deformation consisting of irregular vertical waves (three concavities and two convexities), as well as seven horizontal waves. On this basis, it is claimed that, in accordance with the Shannon theorem, the correct representation of the generated waves requires the measurement of the cooling tower shell in a minimum of 12 vertical and 14 horizontal sections. Such density of the points may not be sufficient to represent local imperfections of the shell. The article presents the results of test measurements and their analysis, which were conducted to verify the assumptions as to the optimal number of measurement points for the shell of a cooling tower. The evaluation was based on a comparative analysis of the data obtained by the Terrestrial Laser Scanning (TLS) method, creating a very detailed model of geometric imperfections in an actual cooling tower with a height of 100 m. Based on the data obtained by the TLS method, point grids of various density were generated. An additional measurement of the cooling tower shell deformation was performed using a precise electronic total station with reflectorless measurement option. Therefore, it was possible to assess the accuracy of measurements by laser scanning in relation to measurements obtained by reflectorless total stations.

Wind induced dynamic responses on hyperbolic cooling tower shells and the equivalent static wind load

Wind induced dynamic responses on hyperbolic cooling tower (HCT) shells and the equivalent static wind load (ESWL) are prime concerns for structural designers and researchers. Followed the dynamic calculation in time domain, using the wind pressure got from wind tunnel tests, the dynamic effects of internal forces and displacement of HCT shell were illustrated through the peak factor g and gust response factor G. The original 2-D distribution of G along latitude and meridian directions was degenerated reasonably to 1-D distribution just along meridian direction and the 2-D distribution of g to a single value, according to the structure behaviors, characteristics of dynamic responses and structural design principles of HCT shell. Based on these features of HCT shell and degenerations of g and G, a new approach pursuing ESWL was proposed whose objective is the reinforcement amount but not the internal forces. The ESWL is got by simple amplification of the mean wind load with a single parameter γ, but the γ used for the latitude and meridian directions are independent and the former is much larger. This is the actual reflection of the independent structural design and different dynamic effects of internal forces in latitude and meridian directions.

Methodology for optimizing composite towers for use on floating wind turbines

A methodology for the design and optimization of a composite wind turbine tower for use on a floating offshore platform is presented. A composite turbine tower on a floating offshore platform not only has the potential to reduce maintenance and upkeep costs associated with the use of steel offshore but also has potential to reduce the tower mass and subsequently the support platform mass. The optimization problem is formulated to obtain a turbine tower that meets all strength and serviceability criteria and minimizes the tower mass. The optimization and design process link a number of dynamic analyses and finite element routines using a genetic algorithm. This work documents the optimization and design software and illustrates its use in various case studies for a 6 MW floating wind turbine system. Case studies include the optimization of a steel tower as a comparison to a composite material tower and the use of a cored, sandwich panel composite tower versus a solid composite tower. The results demonstrate that significant reductions in the tower mass are likely when comparing a steel tower with a composite tower. Also demonstrated for the platform and turbine configuration considered in this work is that the minimum mass tower design is driven towards a solid shell composite configuration, rather than a sandwich panel tower shell, in the face of reasonable design constraints.

Rebar section loss and carbon fiber reinforced plastic reinforcement effects on nonlinear behavior and ultimate load of cooling towers

The present paper quantifies the adverse effects that can generate rebar section loss, induced by corrosion, especially on the bearing capacity of nuclear power plant cooling towers under extreme wind conditions. Numerical simulations, taking into account, appearance of concrete cracks and their evolution via an appropriate material concrete law and rebar’s yielding, are conducted. Different levels of corrosion are considered which are approximated by rebar section loss. Finally, to restore the integrity of these structures, composite material such as a carbon fiber reinforced plastic (CFRP) layer is modelled. The enhancement of the bearing capacity of the damaged structure compared to the undamaged structure is evaluated in the pre- and post-cracking regime. The main conclusion drawn from the numerical results is that the CFRP reinforcement is very effective for improving the integrity of RC cooling tower shells even when the latter present an advanced corrosion rate.

Flue gas diffusion for integrated dry-cooling tower and stack system in power plants

For the integrated dry-cooling tower and stack, the flue gas diffusion characteristics are of great concerns for the pollutant control and tower anticorrosion. In this work, the computational models of flue gas diffusion for the integrated dry-cooling tower and stack system are developed and experimentally validated. By means of numerical simulations, the flue gas diffusions inside and outside the dry-cooling tower are investigated and the flue gas concentrations at different heights of the inner tower shell and on the ground level are obtained. The rising height of flue gas is studied and compared with the separate stack. The total mass flow rate of cooling air and heat rejection of air-cooled heat exchanger for both the dry cooling system with and without the stack inside the dry-cooling tower are also obtained. The results show that not only the thermo-flow performances of the natural draft dry cooling system with the integrated stack can be improved, but also the air pollution alleviation can be guaranteed. At high wind speeds, the inner tower shell faces corrosion risks due to the flue gas deposition, so the anticorrosion measures for the tower should be taken.

풍하중에 의한 손상해석을 이용한 기하형상에 따른 자연 습식 냉각탑의 구조성능 평가 - Part I : One-shell 기하형상

Determining of the shape in the process of design for natural draught cooling tower is very important, because the shape of hyperbolic shell is respond sensitively to dynamic behavior of the whole cooling tower against wind load. In engineering practice, the geometric parameters have been determining based on the natural frequency. This study analyses influence of the tower shell geometric parameters on the structural behavior. For three representative models were selected, they were analyzed based on evaluation of damage by means of nonlinear FE-method. As a result, a hyperbolic rotational shell with the small radius overall was the lowest damage index induced by sufficient capacity of the stress redistribution and thus a wind-insensitive structure.

Behavior of Reinforced Concrete Cooling Tower Shell under Lateral Load on Nonuniform Foundation

ABSTRACTThe stress distributions and the ultimate strength of a reinforced concrete (R/C) cooling tower shell under a self-weight and a lateral wind load were investigated under the conditions on nonuniform foundation. The construction site of the cooling tower is quite huge and the site may have different bearing capacities within location by location. Therefore, to design such structures, the effects of uneven settlements of supporting system due to the nonuniform foundation should be considered. In modeling the cooling tower, the height of the shell was about 150 m and the radius at the lintel was about 60 m. Two kinds of supporting column systems were considered. One was the V-Column systems. The other was the Vertical column supporting systems. Also, the effects of foundation beam were considered under uneven settlement. From the numerical analysis, the stress concentration was arisen near the connections between the unsettled column and the lintel and the ultimate strength was reduced by the uneven settlement depending on the wind direction. The foundation beam represented the improvement of the damage of R/C concrete shell under uneven foundation settlement and plays an important role to transfer the stresses.