Top Of Tower Research Articles

Nonlinear 3D finite element analysis of suction caisson-tower-soil system subjected to horizontal earthquake excitation

Suction caissons are widely used as a promising alternative foundation for offshore structures under variable offshore environments. In this paper, a three-dimensional finite-element model which takes into account soil inelasticity was used to study the seismic behavior of a suction caisson in clay taken from an offshore wind farm in the Hebei province of China. The results showed that the maximum acceleration of the soil increases with increasing depth. There is a distinct amplification for relatively low frequencies when seismic waves propagate to the mudline. It was assumed that the rotation center of suction caisson under seismic conditions was virtually existent. The rotation center was obtained by the proposed formula to explore the movement positions of the suction caisson. The time of the peak of lateral displacement of the lid did not synchronize with that of the changing direction of displacement of the rotation center, indicating that the displacement of the lid can not be a comprehensive assessment of the position state of suction caissons. The point mass at the top of the wind turbine tower was responsible for the increase of vibration amplitude of displacement. • In this paper, a three-dimensional finite-element model taking account of soil inelasticity was carried out to study the seismic behavior of suction caisson in soft clay. A 3D equivalent viscous-spring artificial boundary element is applied to eliminate the unnatural reflection wave generated on the boundary. • It is assumed that the rotation center of suction caisson under seismic conditions is virtually existent and it was obtained by the proposed formula to explore the movement positions of the suction caisson. • The time histories of lateral and vertical displacement were extracted for studying seismic behavior of the wind turbine tower under seismic loading.

Wind load investigation of self-supported lattice transmission tower based on wind tunnel tests

Through a series of wind tunnel tests on a self-supported lattice transmission tower model, the wind loads on the tower were investigated in this paper. According to similarity laws, the scaled tower model was designed and fabricated, and the atmospheric boundary layer wind field of Category-B specified in Chinese load code was simulated in the wind tunnel laboratory. Based on the aeroelastic wind tunnel tests and the high frequency force balance tests, the dynamic vibrations, the nondimensional wind force coefficients and the generalized power spectral densities (PSDs) of dynamic wind forces were analyzed and discussed. For the convenient application, the empirical formulas of the generalized PSDs of dynamic wind forces were established and the nonlinear mode shape correction was introduced, which were verified via comparison between the aeroelastic tests and the calculated dynamic responses of tower top. It is indicated that the unfavorable wind attack angles may happen around θ = [15° 30°] and θ = [60° 75°] for this type of tower; the generalized PSDs of wind forces are unimodal in shape, and the corresponding effective bandwidths and the nondimensional frequencies of peaks vary with the wind attack angle θ, especially those of the cross-wind forces are larger than those of the along-wind forces obviously; the established empirical formulas of the generalized PSDs of dynamic wind forces and the derived nonlinear mode shape correction factor are applicable.

Study on Double-Deck and Four-Cable Stayed Bridge with Univalent Hyperboloid Column Tower

Aiming for the citywide deck cable-stayed bridge, a double separated deck and four-cable stayed bridge with univalent hyperboloid single column bridge tower was proposed. The bridge deck with double separated steel box girders replace the bridge deck wide steel box girder, the univalent hyperboloid single column bridge tower replaces the double column bridge tower, and the four-cable stayed bridge replaces the double-cable stayed bridge. The univalent hyperboloid single column tower bridge has a thick bottom, which can ensure the bearing capacity of the single column tower structure; the waist of the bridge tower is small and the driver’s vision is wide; the wider top of the bridge tower can facilitate the scattered anchoring of stay cables. Combined with the 200 m+420 m+200 m double separated deck and four-cable stayed bridge with the univalent hyperboloid single column tower, the engineering parameters are designed, the Midas finite-element analysis model is established, the static analysis and dynamic modal analysis are carried out, and the structural rationality of double separated deck and four-cable stayed bridge with the univalent hyperboloid single column tower is verified.

Failure analysis and prediction based on corrosion thinning behaviour of atmospheric tower top and volatilization line connection area

Dew point corrosion is one of the most common corrosion forms in an atmospheric tower. In this paper, process analysis and numerical simulation were performed to reveal the corrosion phenomenon at the top of atmospheric tower and the volatilization lines in a petrochemical enterprise. Through the analysis of corrosion morphology and corrosion products, it shows that the corrosive area is caused by the dew point corrosion under the H2O-HCl-H2S environment, and the dew point temperature is 97.8 °C. Moreover, the Eulerian Wall Films (EWF) model is established to simulate the formation process of liquid film at the initial stage of dew point condensation. The high-risk area of dew point corrosion is the aggregation position of the liquid phase which is located at the interface at the top of the tower, the inner elbow of the volatilization line, and the lower wall of the horizontal tube of the volatilization line. It is found that low-temperature and low-velocity are two main reasons that cause dew point condensation. The predicted corrosion areas are in line with the actual failure location, which verifies that the CFD simulation can be used to predict the thinning area of the atmospheric tower.

Design strategies of vibration mitigation systems for an existing suspended footbridge

The paper investigates an existing suspended footbridge located in Seriate (Bergamo, Italy) which suffered structural problems due to human-induced vibrations and then was equipped with vibration mitigation systems, i.e. the Tuned Mass Dampers (TMD). Despite the adopted solution, in the paper different mitigation strategies are critically compared, showing their advantages and weakness, in order to identify the most effective solution at avoiding the resonant effect, shifting the frequencies of the principal modes out of the critical ranges interested by walking and running and mitigating the acceleration values. Starting from the available results of dynamic tests performed on the footbridge, the 3D finite element models of the footbridge before and after the TMDs installation are validated in terms of frequencies and modal shapes. Furthermore, two mitigation systems alternative to the TMDs are considered: the former involves four inclined stays linking the top of the footbridge tower to the deck, the latter proposes a combined mitigation system consisting of two TMDs and four inclined stays. The effects of the proposed mitigation strategies are evaluated by comparing the frequency values with the critical ones and the peak acceleration values with the most restrictive limit values suggested by the requirements of the technical guidelines taken as a reference in this study (EC0, HiVoSS and Sétra). Finally, it can be stated that the proposed combined solution is the most convenient also from an economic standpoint.

Comparison of 3-D and 2-D Cylindrical Symmetry FDTD Simulation Results of a Lightning Strike to Gaisberg With ALDIS Sensor Measurements

In this article, numerical computations applying the finite-difference time-domain (FDTD) method are performed. Lightning electromagnetic fields radiated by a lightning strike to the Gaisberg Tower in Salzburg, Austria, and propagating over irregular terrain are calculated. The field propagation is computed with a three-dimensional (3-D) FDTD and, for comparison, a 2-D cylindrical symmetry FDTD. With topographic height maps, seven different propagation paths for a selected lightning strike to the Gaisberg tower are simulated and the resulting magnetic field (H-field) is compared with the received signal strength at seven sensors of the ALDIS sensor network for that event. The return stroke is represented by a transmission line model and the current waveform recorded at the top of the Gaisberg tower was used. The results of the 3D-FDTD simulation correlate well with H-fields registered at sensor sites in mountainous environments. Hence, 3D-FDTD can represent complex local reflection phenomena correctly, which the 2D-FDTD cannot. The results of recent studies, which show that a lightning strike to a mountain gives rise to a field enhancement at the sensor site for a relatively flat propagation path, could be verified by comparing the FDTD results with a set of existing sensor measurements. For the, otherwise, very hilly terrain conditions in Austria, the field enhancement caused by the mountain is attenuated along the paths to the respective sensors.

An Extension of the Guided Wave M‐Component Model Taking Into Account the Presence of a Tall Strike Object

AbstractWe present in this paper an extension of the guided‐wave M‐component model of Rakov et al. considering the presence of a vertically elevated strike object. The tall object is represented as a lossless, uniform transmission line. Expressions for the current distribution along the channel and along the strike object are derived. Simulation results for the electric field at close (100 m), intermediate (15 km), and far (100 km) distance ranges are presented, considering fast and slow M‐component currents. The results show that, for very tall structures and fast M‐component waves, the presence of a tall strike object can result in a sharp peak superimposed on the M‐component electric field at intermediate and far distance ranges (e.g., 15 and 100 km). At close distances, the electric field of a fast M‐component is characterized by an initial negative excursion followed by a polarity change. It is shown that the presence of the tower results in a decrease of the negative initial excursion of the field. For slow M‐component waveforms or for moderately tall structures, the presence of the tall strike object can be disregarded in the M‐component field calculations. A discussion on the influence of the M‐wave channel height and velocity on the electric fields for fast M‐component currents is also presented. The study suggests a noticeable effect of the M‐wave velocity on the electric fields at all distance ranges. The variations of the wave velocity and channel length affect the time of appearance of the superimposed sharp peak on the electric fields. However, the sharp peak magnitude, which is due to the presence of the tower, is independent of the channel length and wave velocity. It is determined by the injected current and the reflection coefficients from the ground and tower top.

Seismic fragility analysis of monopile offshore wind turbines considering ground motion directionality

The necessity of performing a detailed seismic fragility analysis of offshore wind turbines (OWTs) is well established in the wind power industry. This paper presents a seismic fragility analysis for large-scale monopile offshore wind turbines (MOWTs) considering ground motion directionality. Based on recommendations by the Eurocode EN 1993-1-6, DNVGL-ST-0126 and literature study, the critical displacement, rotation, local buckling strength for structural components were proposed. Fragility curves under different angles of ground motion incidence were obtained by using the truncated incremental dynamic analysis (TIDA) and compared between the first scenario of the wind turbine parked in a calm sea and the second scenario of the wind turbine in normal operation at the rated wind speed of the turbine. The results show that ground motion directionality has obvious influence on the seismic fragility of the MOWT. Wind and wave loads increase the probability of the MOWT exceeding limit states and amplify the ground motion directionality effects on the structural fragility. Neglecting aerodynamic damping leads to an overestimation of the structural fragility. The excessive displacement at the tower top, local buckling at the bottom of the tower and in the monopile at the mudline section, and tension fracture in the grouted connection are the critical failure modes of the MOWT being subjected to earthquakes.

Estimation of voltage waveform at top of transmission line tower struck by lightning of negative and positive polarity

The object of research is a circuit that simulates a lightning strike to a tower of 220 kV power transmission line, taking into consideration the reflection of a current wave from 10 nearest towers. Computation of the voltage arising at the top of the struck tower is necessary further to determine the lightning performance of transmission line by various methods. The lightning current has several maxima, in the case of a positive impulse polarity and, accordingly, several minima, in the case of a negative polarity, which are generally being called peaks. In addition, the lightning current impulse has a non-constant steepness in the entire area of current rise up to the first peak. The approximation of the real lightning current by simplified mathematical expressions cannot take into account all its real features. For a more detailed study of transient processes caused by thunderstorm activity, there is a need to use oscillograms of real lightning currents when modeling. The problem of determining the voltage at the top of the stricken transmission line tower was solved using circuit simulation. For an in-depth study of how the shape of the lightning current impulse affects the shape of the voltage at the top of the tower struck, digitized oscillograms of real lightning currents were used. The simulation was carried out for 7 negative lightning impulses with the first peak varying from –33.380 kA to –74.188 kA. In the case of positive lightning, 3 oscillograms were used with the first peak varying from +38.461 kA to +41.012 kA. The article shows that the shape of the front of the lightning current impulse and the amplitude of the first peak of the lightning current have a decisive effect on the maximum voltage value at the top of a power transmission line tower struck by lightning. The maximum voltage occurs precisely at the front of the current wave before the first peak of the lightning current. Therefore, the back flashover of the insulation from the tower to the phase conductor is most likely at a moment in time at the front of the current wave. By the time the maximum current is reached, the voltage at the top of the tower will be reduced by several tens of percent, compared to the maximum voltage at the tower, which occurs much earlier at the front of the current wave. The conducted research contributes to the development of methods for calculating the lightning performance of power lines and extends the scope of application of circuit simulation programs.

Comparative analysis of fatigue life of a wind turbine yaw bearing with different support foundations

The yaw bearing is a connection component which is located on the tower top of a wind turbine. The yaw bearing may be subjected to environmental dynamic loads and wave forces which contribute to the fatigue life of the yaw bearing. The fatigue life of a yaw bearing used in onshore wind turbines is well established, but less so for offshore wind turbines. In this work, fatigue life assessments of yaw bearings are compared in 5 MW wind turbines with six different support foundations: onshore, monopile, ITI barge, Tension Leg Platform (TLP), spar and semi-submersible. A time-domain method is applied to predict the wind and hydrodynamic loads on the yaw bearings using three wind velocities. A Gumbel distribution, rain flow counting algorithm, linear cumulative damage law and S–N curve theory are used to generate the life-time damage equivalent loads. The fatigue life of the yaw bearing is then calculated using a finite element method and a code-based approach. The results show the dynamics of the floating wind turbine concept are directly linked to the fatigue life of the yaw bearing and that the major components of the yaw bearing should be considered separately.

Full-wave black-box transmission line tower model for the assessment of lightning backflashover

In order to calculate the overvoltages across the insulator strings of overhead lines, electromagnetic transient (EMT)-type simulators require a model of the tower and its grounding system. In this paper, an electromagnetic field simulation model based on the solution of the full-wave frequency-domain Maxwell’s equations is established to obtain an EMT-compatible black-box representation of the transmission line tower for time-domain simulations. Details of the system, such as the grounding system consisting of counterpoise electrodes, shield wires, phase conductors, and tower cross arms and slant elements are considered in the simulation model. The frequency dependence of soil electrical parameters is included as well. The input data to the frequency-domain simulation model consists of the topology of the tower structure, grounding system, and the parameters of the surrounding medium. As a case study, the developed simulation model is applied to obtain the black-box representation (macromodel) of a 400kV double circuit tower, where the lightning current injected at the tower top is the input, and the output is the induced voltage across the insulator strings. The critical current leading to the flashover of the insulator strings is calculated according to various existing flashover models and two different first stroke lightning current waveforms. Finally, a probabilistic analysis is performed to obtain the percentage of downward negative first strokes leading to a backflashover.

Switching Control Strategy for Oscillating Water Columns Based on Response Amplitude Operators for Floating Offshore Wind Turbines Stabilization

In this article, a new strategy for switching control has been proposed with the aim of reducing oscillations in floating offshore wind turbines. Such oscillations lead to a shortage in the system’s efficiency, lifespan and harvesting capability of wind and wave energies. In order to study the decreasing of undesired oscillations in the system, particularly in pitch and top tower fore-aft movements, a square-shaped platform barge equipped with four symmetric oscillating water columns has been considered. The oscillating water columns’ air flux valves allow to operate the air columns so that to control the barge movements caused by oscillatory motion of the waves. In order to design the control scheme, response amplitude operators have been used to evaluate the performance of the system for a range of wave frequency profiles. These response amplitude operators analysis makes it possible to implement a switching control strategy to adequately regulate the valves opening/closing transition. The obtained results show that the proposed controlled oscillating water column-based barge present a better performance compared to the traditional barge one. In the case study with the period of 10 s, the results indicate the significant oscillation reduction for the controlled oscillating water column-based system compared to the standard barge system by 30.8% in pitch angle and 25% in fore-aft displacement.

Wind turbine tower failure analysis and wind-induced vibration control

Wind energy has great potential for development in clean energy. The economic loss caused by the destruction of the wind turbine tower in a wind turbine failure is very huge. Therefore, this paper analyzes the gray correlation between the tower damage type and the cause of the damage. The results show that storms, pitch system failure, and wind speed exceeding the design wind speed have a good correlation with the tower damage type. In a storm environment, the dynamic response of the tower top of the wind turbine tower is relatively large, even leading to the overall collapse of the tower. The tuned mass damper (TMD) has an obvious damping effect on the wind vibration response of the tower.

Alternative evaluation of voltage at top of transmission line tower stricken by lightning

The object of the research is a circuit that simulates a lightning strike to a tower of 220 kV power transmission line, taking into consideration the reflection of a current wave from 10 nearest towers. Computation of the voltage arising at the top of the stricken tower is necessary further to determine the lightning performance of transmission line by various methods. For Indian conditions, the average number of lightning strikes to this power line per 100 kilometers per year is about 77, which is a fairly high figure. As a rule, for the tasks of lightning protection, the lightning current is approximated by some analytical expression. In most cases, such expressions are various combinations of exponential functions. However, the waveform of real lightning currents on oscillograms differs significantly from the waveform attributed to them and approximated by relatively simple exponential expressions. For a more detailed study of transient processes caused by thunderstorm activity, there is a need to use oscillograms of real lightning currents when modeling. The problem of determining the voltage at the top of the stricken transmission line tower was solved using circuit simulation. To simulate the lightning current, digitized oscillograms of real lightning currents with peak values of –5.256 kA and –133.586 kA were applied. The article shows that the proposed approach gives a more accurate and visual representation of the transient process at the top of the stricken tower than the approximation of the lightning current by simple exponential expressions. Applying a simplified exponential description of the lightning current leads not only to a simplification of the nature of the transient process at the tower top, but also to an underestimation of the results to 8.8%. The selection of the equivalent circuit for the power line towers also affects the result. Representation of towers in the equivalent circuit with lumped inductances leads to slightly higher values compared to application of surge impedances in the circuit. In this case, the smaller the current amplitude, the greater the difference (8.6 % in the domain of low currents and 1.9 % in the domain of high currents). Since this leads to some reserve during the computations of lightning performance, it is recommended to use an equivalent circuit with lumped inductance for a transmission line tower. The conducted research contributes to the development of methods for calculating the lightning performance of power lines and extends the scope of application of circuit simulation programs.

Ambient Seismic Noise and Microseismicity Monitoring of a Prone-To-Fall Quartzite Tower (Ormea, NW Italy)

Remote sensing techniques are leading methodologies for landslide characterization and monitoring. However, they may be limited in highly vegetated areas and do not allow for continuously tracking the evolution to failure in an early warning perspective. Alternative or complementary methods should be designed for potentially unstable sites in these environments. The results of a six-month passive seismic monitoring experiment on a prone-to-fall quartzite tower are here presented. Ambient seismic noise and microseismicity analyses were carried out on the continuously recorded seismic traces to characterize site stability and monitor its possible irreversible and reversible modifications driven by meteorological factors, in comparison with displacement measured on site. No irreversible modifications in the measured seismic parameters (i.e., natural resonance frequencies of the tower, seismic velocity changes, rupture-related microseismic signals) were detected in the monitored period, and no permanent displacement was observed at the tower top. Results highlighted, however, a strong temperature control on these parameters and unusual preferential vibration directions with respect to the literature case studies on nearly 2D rock columns, likely due the tower geometric constraints, as confirmed by 3D numerical modeling. A clear correlation with the tower displacement rate was found in the results, supporting the suitability of passive seismic monitoring systems for site characterization and early waning purposes.

Awe, daily stress, and elevated life satisfaction.

It is widely assumed that experiences of awe transform the meaning of daily stresses. Across six studies we tested whether and how the experience of awe is associated with reduced daily stress levels in the moment and, in so doing, leads to elevated life satisfaction. We first documented that individuals who tend to experience greater awe on a daily basis (Study 1) or who report higher levels of trait-like awe (Study 2) report lower levels of daily stress, even after controlling for other positive emotions. In follow-up experiments, after primed with awe (compared with amusement, joy, and pride), individuals reported lower levels of daily stress (Studies 3 and 5) and exhibited lower levels of sympathetic autonomic arousal when talking about their daily stresses (Study 4). Finally, in a naturalistic study, participants who took in an awe-inspiring view at the top of a 200-foot tower reported reduced levels of daily stress and central everyday concerns (Study 6). Mediation analyses revealed that (a) the association between awe and reduced daily stress can be explained by an appraisal of vastness vis-à-vis the self and (b) that the relationship between awe and decreased daily stress levels helps explain awe's positive influence upon life satisfaction. Overall, these findings suggest that experiencing awe can put daily stressors into perspective in the moment and, in so doing, increase well-being. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Reconstruction of operating loads in wind turbines with inertial measurement units

Wind turbines are a major source of renewable energy. Load monitoring is considered to improve reliability of the systems and to reduce the cost of operation. We propose a load monitoring system which consists of inertial measurement units. These track the movement of rotor blade, hub and tower top. In addition, wind turbine states, e.g. yaw angle, pitch angle and rotation speed, are recorded. By solving a navigation algorithm with a Kalman Filter approach, the raw sensor data is combined with an error model to reduce the tracking error. In total, five inertial measurement units are installed on the research wind energy converter AD 8–180 on the test site in Bremerhaven. Results show that tracking the blade movement in full operation is possible and that loads can be estimated with a model-based approach. In comparison to simulations, the blade deflections can be approximated by an aeroelastic model. The presented approach can be used as basis for comprehensive load monitoring and observer system with additional increase of system robustness by measurement redundancy.

Inerter-enhanced tuned mass damper for vibration damping of floating offshore wind turbines

This paper investigates the use of an inerter-enhanced vibration absorber, the rotational inertia double tuned mass damper (RIDTMD), for damping in-plane vibrations of a floating offshore wind turbine (FOWT). First, a 17-degree-of-freedom (17-DOF) aero-hydro-servo-elastic model for the FOWT is developed and verified, based on which the damper performance can be evaluated in the time domain (TD) with realisitc load conditions. Next, a reduced-order 6-DOF model is established for the RIDTMD-controlled FOWT in-plane vibrations including rotor mass moment of inertia, hydrodynamic added mass, as well as stiffness contributions from mooring lines and buoyancy. This model enables revealing the dynamics of the coupled spar-tower-RIDTMD system, and provides an efficient yet robust procedure for optimal tuning of the FOWT-mounted RIDTMD in the frequency domain (FD). Comparison of the optimal RIDTMD and the optimal TMD is performed in both FD and TD. It is seen that both TMD and RIDTMD effectively suppress tower side-side vibrations when mounted at the tower top. RIDTMD consistently outperforms TMD due to the extra DOF (extra resonance) introduced into the device, at the cost of slightly larger damper stroke. Both dampers positively influence spar roll motion and blade edgewise vibration as well.

Separation and Rectification of Chloroacetyl Chloride from TiCl4

Titanium tetrachloride (TiCl4) is an important intermediate material for the preparation of titanium products. The organic impurities in TiCl4 are easily accumulated during the production of titanium sponges due to the problems of imperfect detection methods and the lack of effective control methods, resulting in a poor quality of sponge titanium. Among all impurities, chloroacetyl chloride (CAC) is the most important in TiCl4. Herein, the determination of the CAC content in TiCl4 solution, with a low detection limit of 0.633 ppm, was established by the standard addition method using Fourier transform infrared (FTIR) spectrometry. This test method presented good repeatability, excellent accuracy, and moderate precision. Furthermore, the influencing factors of CAC separation in the continuous rectification process, including the heating power (the ratio of total heating power to feed rate), reflux temperature, top tower pressure, and feed temperature were optimized based on an orthogonal experimental design. The experimental data demonstrated that the average CAC removal rate reached 78.94% ± 1.00% under the optimal distillation conditions, with 72.21% of the CAC removed via the off-gas system. Therefore, excellent control of the negative pressure of the tail gas is highly desirable for the removal of CAC impurities.

Passive control of jacket–type offshore wind turbine vibrations by single and multiple tuned mass dampers

Vibration control is gaining focuses in the field of offshore wind turbines (OWTs) in recent years as the turbine tower becomes taller and more slender. Although a number of research works have been carried out to control the OWT vibrations, using tuned mass damper (TMD) and multiple tuned mass dampers (MTMDs) to control the jacket–type OWT vibrations is rarely reported, especially for the MTMDs, of which the application in the field of OWTs is still in the initial stage. This study focuses on the performance of TMD and MTMDs in controlling the tower vibrations of the jacket–type OWT subjected to the combined wind, wave and current loads, which are the most common external vibration resources for OWTs. The control effectiveness is numerically investigated and evaluated by the reductions of the standard deviation displacement (σ(d)) and the standard deviation acceleration (σ(a)) of the tower top. After the installation of TMD, σ(d) and σ(a) are reduced by 32% and 29% respectively. Larger TMD mass ratios lead to better control effectiveness, but the improvement becomes less obvious as the mass ratios constantly increase. The control effectiveness of the MTMD system is slightly decreased compared with a single large TMD. However, the robustness of MTMDs is superior since the OWT vibrations can still be controlled effectively even if some TMDs do not function. The control effectiveness of the MTMD system can also be affected by the change in the positions of malfunctioned TMDs.