01.02: Bobtail^® bolt preload loss in wind turbine tower prototype: Hammerstein‐Wiener identification model

Abstract

Nowadays the wind turbines with the high power capacity are installed for the onshore wind parks. In order to achieve higher wind speeds and more stable wind, wind turbine towers are designed for higher altitude. Moreover, higher altitude reduces turbulence and wind shear induced vibrations. The convectional tubular towers are assembled using welded ring flanged joints. Moreover, preloaded bolts are used to connect the segments' flanges together. Therefore, the fatigue problem is predominant in the tall towers and fatigue failure due to welded connection and/or due to the bolts in tension may be the governing design situation. To tackle the fatigue problem in the bolted joints and discard the welded connections, a new friction connection is designed for tubular segment assembly. The tower segments are designed with long open slotted holes. The preloaded bolts are used to provide contact between the slotted holes and the intermediate auxiliary plate. Therefore, the connection will resist only by the friction in between the plates. In order to provide necessary friction between the plates, sufficient pre-load should be applied on the bolts. Moreover, it should be guaranteed that the load loss in the bolts is trivial. Therefore, Bobtail® bolt as free maintenance preloaded bolts are used in the friction connections. This paper deals with the identification of a function for bolts load loss behavior in the friction connections and provide an estimation for lifetime loss. A monitoring setup has been settle to measure the load in the bolts and the environmental temperature simultaneously for almost a year. Consequently, the Hammerstein-Weiner method, was applied to create the nonlinear dynamic model of the friction connection preloading behavior regarding the environmental temperature variation. Furthermore, the identified function output for the measured temperature was compared with the measured force and then the error was calculated. Based on the model, the load loss for constant temperature was calculated for the period of the measurement and was estimated for 20 years of life time span of the structure. The findings demonstrated acceptable amount of load loss in a year and estimation showed that bolts loads retain constant pre-load after a two years period. Moreover, it is obtained the initial fastening conditions were important to achieve free-maintenance bolts.

WH-EA: An Evolutionary Algorithm for Wiener-Hammerstein System Identification

“…As can be seen from (28) to (29), the search space for nonlinearity depends on the input signal, output signal, static gain of the BLA, and Ω which is a user-defined parameter. Since both linear subsystems will be estimated with unit gain, neither of these will amplify their input signals, therefore V min > min and V max < max .…”

“…Block-oriented models are attractive for their simplicity and great capabilities to model nonlinear dynamic systems [23][24][25][26][27][28]. Specifically, Wiener-Hammerstein models have proved to be able describe several systems like a paralyzed 2 Complexity skeletal muscle [29,30], a limb reflex control system [31], a DC-DC converter [32], a heat exchanger system and a superheater-desuperheater in a boiler system [33], and a thermal process [34], among others [35].…”

Experimental Investigations on load‐bearing Capacity and characteristic Preload of Lockstud Systems

“…Lockbolt systems according to Technical Bulletin DVS/EFB 3435-1 [8] and Technical Bulletin DVS/EFB 3435-2 [9] consist of a lockbolt made of carbon steel and an associated collar. Compared to classic bolted joints, these are characterised by a special suitability for maintaining the preload over the service life, [10][11][12] by a high level of assembly safety due to the frictionand torsion-free tightening process [13][14][15], a higher fatigue strength under concentric and eccentric load compared to structural steel bolts (system HV according to EN 14399-4 [16]) [17][18][19] and an effective securing effect for transverse loads above the theoretical threshold [20; 21]. Responding to the mentioned requirements, a studbolt is presented which combines the advantages of a bolt thread for making a tapped thread or through-bolt joint and the advantages of a lockbolt system.…”

Experimental and numerical study on mechanical behavior of high-strength lockbolted friction grip connections

“…The lockbolt fastener was already invented in the 1930s and mainly used for the aviation and space industry. Later on, the lockbolt fastener has been further developed and applied in many other fields such as railway transportation, agriculture, mining, military, and steel construction (Mariam et al, 2018; Mohammad et al, 2017; Smith and Potticary, 2000). As an illustration, Figure 1 shows the application of high-strength lockbolts in a typical high-strength lockbolted friction grip (HSLFG) joint of a continuous steel-concrete composite beam bridge of Chengdu Tianfu International Airport Expressway in China.…”