Substructure Concept Research Articles

Quantifying the impact of modeling fidelity on different substructure concepts – Part 2: Code-to-code comparison in realistic environmental conditions

Abstract. Floating offshore wind is widely considered to be a promising technology to harvest renewable energy in deep ocean waters and increase clean energy generation offshore. While evolving quickly from a technological point of view, floating offshore wind turbines (FOWTs) are challenging, as their performance and loads are governed by complex dynamics that are a result of the coupled influence of wind, waves, and currents on the structures. Many open challenges therefore still exist, especially from a modeling perspective. This study contributes to the understanding of the impact of modeling differences on FOWT loads by comparing three FOWT simulation codes, QBlade-Ocean, OpenFAST, and DeepLines Wind®, and three substructure designs, a semi-submersible, a spar buoy, and the two-part concept Hexafloat, in realistic environmental conditions. This extensive comparison represents one of the main outcomes of the Horizon 2020 project FLOATECH. In accordance with international standards for FOWT certification, multiple design situations are compared, including operation in normal power production and parked conditions. Results show that the compared codes agree well in the prediction of the system dynamics, regardless of the fidelity of the underlying modeling theories. However, some differences between the codes emerged in the analysis of fatigue loads, where, contrary to extreme loads, specific trends can be noted. With respect to QBlade-Ocean, OpenFAST was found to overestimate lifetime damage equivalent loads by up to 14 %. DeepLines Wind®, on the other hand, underestimated lifetime fatigue loads by up to 13.5 %. However, regardless of the model and FOWT design, differences in fatigue loads are larger for tower base loads than for blade root loads due to the larger influence substructure dynamics have on these loads.

Quantifying the impact of modeling fidelity on different substructure concepts for floating offshore wind turbines – Part 1: Validation of the hydrodynamic module QBlade-Ocean

Abstract. To realize the projected increase in worldwide demand for floating offshore wind, numerical simulation tools must capture the relevant physics with a high level of detail while being numerically efficient. This allows engineers to have better designs based on more accurate predictions of the design driving loads, potentially enabling an economic breakthrough. The existing generation of offshore wind turbines is reaching a juncture, where traditional approaches, such as the blade element momentum theory, are becoming inadequate due to the increasing occurrence of substantial blade deflections. QBlade is a tool that includes a higher-fidelity aerodynamic model based on lifting-line theory, capable of accurately modeling such scenarios. In order to enable the simulation of offshore conditions in QBlade and to make use of this aerodynamic capability for novel offshore wind turbine designs, a hydrodynamic module called QBlade-Ocean was developed. In the present work, this module is validated and verified with two experimental campaigns and two state-of-the-art simulation frameworks on three distinct floating offshore wind turbine concepts. The results confirm the implementation work and fully verify QBlade as a tool to be applied in offshore wind turbine simulations. Moreover, a method aimed to improve the prediction of non-linear motions and loads under irregular wave excitation is analyzed in various conditions. This method results in a significant improvement in the surge and pitch degrees of freedom in irregular wave cases. Once wind loads are included, the method remains accurate in the pitch degree of freedom, while the improvements in the surge degree of freedom are reduced. A code-to-code comparison with the industry-designed Hexafloat concept highlights the coupled interactions on floating turbines that can lead to large differences in motion and load responses in otherwise identically behaving simulation frameworks.

Design and power calculation of HLFC suction system for a subsonic short-range aircraft

Hybrid laminar flow control (HLFC) can be a possible solution for future sustainable energy-efficient aviation. The current study proposes a MATLAB-based numerical tool for the design of the suction system for an airfoil optimized for a subsonic short-range HLFC application. Considerable energy losses may occur when the air passes through the perforated metallic outer surface and the inner structure of the suction system. A semi-empirical approach is used to design a layout that provides a target suction velocity based on measured pressure losses through porous medium and substructures. Flowbench measurements were performed on 3D-printed internal core test samples to quantify the pressure losses that can be used to create a lower pressure below the porous sheet matching the target suction velocity. The actual suction realized on the airfoil using this substructure concept has a discrete nature that increases with the distance between two adjacent walls. Finally, the suction system’s power requirement is calculated. The power requirement for distributed suction accounts for the pressure loss characteristics of the porous material, the internal core structure, and throttling holes. However, the study does not include the ducting losses from the substructure to the compressor. Approximately 80% of the total suction power is utilized to eject the sucked air back to the freestream conditions for a system with a compressor and propulsive system efficiency equal to one. The study analyses the performance of the designed internal core layout to different flight conditions and addresses the suction power requirement variation with lift coefficient and flight altitude.

Seismic Damage Assessment for Isolated Buildings with a Substructure Method

A seismic damage detection method for isolated buildings is proposed based on substructure identification with incomplete contaminated measurements. A concept of a pseudo substructure with virtual conditions is constructed for the proof of the proposed substructure identification method. This identification method is implemented in a two-stage procedure. The interface forces of the target substructure are identified in the first stage and the parameter of the target substructure is updated in the second stage, which can enable the parameter identification of substructures with unknown input. Two computational methods are also proposed to improve the two-stage identification algorithm. A sub-time zone identification method is utilized to reduce the computation effort and the simultaneous identification of the unknown force and initial structural responses is presented in the first-stage identification for a general case in practical engineering. Numerical studies of a shear frame with nonlinear base isolation subject to earthquake ground motion are investigated to validate the proposed seismic damage detection method. A fourteen-storey concrete shear wall building with a two-storey steel frame on top connected by isolation is studied experimentally with shaking table tests to further validate the proposed method. The shear wall structure is taken as the target substructure for damage assessment. The interface force and parameter of the concrete shear wall building are estimated with the proposed method. Results from both the numerical simulations and laboratory tests indicate that the proposed method can estimate seismic isolated structures and detect damage effectively based on only a few accelerometers. It is also demonstrated that the parameter identification results based on the structure response measurement during the earthquake are more accurate than the identification with post-earthquake structural response measurement.

OrthoSpar, a novel substructure concept for floating offshore wind turbines: Physical model tests under towing conditions

An important condition of any port-assembled floating offshore wind turbine concept is the de-ballasted transport stage. As the hydrostatic and dynamic stability may vary greatly from the operational condition, it needs to be carefully investigated in early stages of the design-phase. In this work, physical modelling of the transport of the de-ballasted OrthoSpar device was carried out to determine roll and pitch RAOs, as well as load characteristics of the towing line. Towing was simulated with a stationary model being subjected to currents. To examine the influence of wave direction, a range of model orientations towards the incident waves were tested in still water and together with the simulated towing state. Roll and pitch motions were found to be highly dependent on the wave frequency and a result of a low damping ratio. The towing load amplitude was found to be influenced by the towing direction regarding the wave direction.

Frequency domain analysis method of tuned liquid damper controlled multi-degree of freedoms system subject to earthquake excitation

Tuned liquid damper (TLD) is a typical passive device to control structural response under wind and earthquake excitation. At present, TLD is often used to control single-mode of structure. Hence, the design theory of TLD is often based on single-degree of freedom (SDOF) system in frequency domain, which is hard to accurately evaluate seismic performance of TLD-installed multi-degree of freedoms (MDOFs) with consideration of higher mode. In this work, a frequency domain transfer function for TLD controlled MDOFs system is established through the concept of substructure to evaluate overall seismic performance of TLD-installed MDOFs. The accuracy of the transfer function is verified by real-time hybrid testing. Using this transfer function, the effect of TLD on the seismic performance of MDOFs was discussed in frequency domain by parametric analysis. The analytical results indicated that, based on the design theory for single-mode, the TLD with large mass ratio cannot enhance the seismic performance effectively comparing with small mass ratio. In order to improve the control efficiency of relatively large mass TLD, a design method for multi-mode control is established based on the developed frequency domain transfer function. The simulation results showed that, with same TLD mass, the multi-mode method performed smaller structural acceleration response and similar displacement response relative to the single mode method.

Vibro-acoustics of Central Africa harps

Central Africa harps are string instruments, often anthropomorphic, whose soundbox is built from a hollowed out tree trunk. There strings, usually 8 in number using nowadays fishing line, are wrapped to wooden tuning pegs on the neck and attached to a tailpiece placed under animal skin used as soundboard. Each instrument-making element can vary according to ethnic groups and material availability. This study aims at understanding the vibro-acoustic behavior of these instruments in order to determine relevant acoustic descriptors linked to there building process. Hence, a numerical model is developed based on the Udwadia-Kalaba modal formulation, relying on substructuring concepts. Each subsystem's dynamics is described by its modal parameters in terms of unconstrained modes and the coupling is enforced by boundary conditions. Strings displacement is described in two polarizations including geometrical nonlinear effects. Modal parameters are experimentally identified, on severa harps collected from different ethnic groups, and turn out to be discriminating descriptors. The reliability of the model is validated against laboratory measurements. Finally, sound syntheses based on the proposed approach are compared to experimental data, showing good agreement. [This work, part of the project NGombi, was funded by the Agence Nationale de la Recherche (French National research agency), Grant No. ANR-19-CE27-0013-01.]

Maximum common property: a new approach for molecular similarity

The maximum common property similarity (MCPhd) method is presented using descriptors as a new approach to determine the similarity between two chemical compounds or molecular graphs. This method uses the concept of maximum common property arising from the concept of maximum common substructure and is based on the electrotopographic state index for atoms. A new algorithm to quantify the similarity values of chemical structures based on the presented maximum common property concept is also developed in this paper. To verify the validity of this approach, the similarity of a sample of compounds with antimalarial activity is calculated and compared with the results obtained by four different similarity methods: the small molecule subgraph detector (SMSD), molecular fingerprint based (OBabel_FP2), ISIDA descriptors and shape-feature similarity (SHAFTS). The results obtained by the MCPhd method differ significantly from those obtained by the compared methods, improving the quantification of the similarity. A major advantage of the proposed method is that it helps to understand the analogy or proximity between physicochemical properties of the molecular fragments or subgraphs compared with the biological response or biological activity. In this new approach, more than one property can be potentially used. The method can be considered a hybrid procedure because it combines descriptor and the fragment approaches.

Physical synthesis of six-string guitar plucks using the Udwadia-Kalaba modal formulation.

Extending the previous work done by the authors, this paper develops a time domain synthesis method for the classical guitar based on substructuring concepts and using the Udwadia-Kalaba modeling strategy. Adopting a modal description of the dynamics of the separate flexible subsystems in terms of their unconstrained modes and enforcing coupling constraint conditions for the assembly, the result is an explicit dynamical modal formulation for the coupled system that directly lends itself to time-stepping methods for simulation. The guitar model couples six strings through an experimentally based body model of an actual instrument, includes two string polarizations, and the string geometrical nonlinear effects, as well as the string/fret interaction as the instrument is played. Details are given for putting all the vibrating components together in a satisfying manner, and a specific strategy is explored to allow for a nonrigid fret using flexible-dissipative-inertial constraints. The reliability of the approach is demonstrated with simulation examples that confirm the features one would expect regarding the dynamical behavior of classical guitars. Finally, a pragmatic approach is made to calculate the radiated sound by convolution, combining the computed bridge force with a measured vibro-acoustic impulse response of the instrument, which proved to give satisfactory sounding results.

Structure-preserving low-order modeling approach of laminated composite plates integrated with macro-fiber composite transducers for dynamic applications

An Equivalent Substructure Modeling (ESM) approach of laminated composite plates with integrated macro-fiber composite (MFC) transducers is described. The proposed approach generates structure-preserving low-order system models for dynamic applications such as vibration suppression and energy harvesting. The direct piezoelectric effect of MFC transducers is derived from the electrical boundary conditions and it has the same coupling patterns as equivalent forces which describe the inverse piezoelectric effect. Hence, the reversibility of the piezoelectric effect is ensured and the electrical dynamics of the system can be simulated. The dual electromechanical couplings are assigned to a low-order structural model generated by an equivalent substructure concept. A laminated composite plate with integrated MFC transducers is used for validations and the simulated results agree well with experimental data. Two given study cases demonstrated that the ESM approach not only can generate accurate low-order system models but also provides a flexible fashion to design piezoelectric composite systems.

Fabrication and installation constraints for floating wind and implications on current infrastructure and design

Industrialization of floating wind technology is key for future cost reductions to become competitive. Within the scope of the LIFES50+ H2020 research project, the floating-specific constraints with respect to fabrication, assembly and installation for different floating substructure concepts are investigated for large future 10MW floating wind turbines and 500MW wind farms. The presented study focusses on three selected LIFES50+ sites in the Scottish North Sea, French Mediterranean and Gulf of Maine. General constraints are identified, which are not specific for a certain proprietary concept, but depending on the material, concept type, fabrication, assembly and installation procedures and site location.

Structural damage prognosis of three-dimensional large structural systems

A novel procedure for the health assessment of large three-dimensional (3D) structures with several significant attractive features and improved implementation potential is proposed. Structures are represented by 3D finite elements and a substructure concept is used so that acceleration time histories can be measured only at small part(s) of the structure. Just by measuring relatively few noise-contaminated responses in the substructure, the health of the whole structure can be assessed by the system identification (SI) concept by tracking the stiffness parameter of all the elements using a significantly improved unscented Kalman filter (UKF) algorithm. Since measuring excitation time histories can be very problematic and expensive, the UKF algorithm is integrated with 3D iterative least-squares with unknown input algorithm. UKF fails to identify large structures due to convergence-related issues. The authors used short duration responses and multiple global iterations with weight factor and objective function instead of one long duration response generally used in UKF. For the preselected excitation, short duration eliminates multiple sources of excitation beyond the control of inspector. The weight factor helps accurately locate the defect spot. With informative examples, it is documented that the proposed method is superior to various other forms of Kalman filter-based algorithms.

Charting Biologically Relevant Spirocyclic Compound Space.

Spirocycles frequently occur in natural products and experience increasing interest in drug discovery, given their richness in sp3 centers and distinct three-dimensionality. We have systematically explored chemical space populated with currently available bioactive spirocycles. Compounds containing spiro systems were classified and their scaffolds and spirocyclic ring combinations analyzed. Nearly 47 000 compounds were identified that contained spirocycles in different structural contexts and were active against roughly 200 targets, among which several pharmaceutically relevant members of the G protein-coupled receptor (GPCR) family were identified. Spirocycles and corresponding compounds displayed notable scaffold diversity but contained only limited numbers of combinations of differently sized rings. These observations indicate that there should be significant potential to further expand spirocyclic chemical space for drug discovery, exploiting the privileged substructure concept. Inspired by those findings, we embarked on the design and chemical synthesis of three distinct novel spirocyclic scaffolds that qualify for downstream library synthesis, thus exploring principally new chemical space with high potential for pharmaceutical research.

Vibrations inside buildings due to subway railway traffic. Experimental validation of a comprehensive prediction model

The present paper focuses on the experimental validation of a numerical approach previously proposed by the authors for the prediction of vibrations inside buildings due to railway traffic in tunnels. The numerical model is based on the concept of dynamic substructuring and is composed by three autonomous models to simulate the following main parts of the problem: i) generation of vibrations (train–track interaction); ii) propagation of vibrations (track–tunnel–ground system); iii) reception of vibrations (building coupled to the ground). The experimental validation consists in the comparison between the results predicted by the proposed numerical model and the measurements performed inside a building due to the railway traffic in a shallow tunnel located in Madrid. Apart from the brief description of the numerical model and of the case study, the main options and simplifications adopted on the numerical modeling strategy are discussed. The balance adopted between accuracy and simplicity of the numerical approach proved to be a path to follow in order to transfer knowledge to engineering practice. Finally, the comparison between numerical and experimental results allowed finding a good agreement between both, fact that ensures the ability of the proposed modeling strategy to deal with real engineering practical problems.

Unscented Kalman filter with unknown input and weighted global iteration for health assessment of large structural systems

A novel concept denoted as unscented Kalman filter with unknown input and weighted global iterations (UKF-UI-WGI) to assess health of large structural systems is proposed. It incorporates the basic features of UKF to identify systems in the presence of severe nonlinearity but then added a few desirable features to increase its implementation potential. Because the information on excitation and unknown initial state vector is necessary to implement any UKF-based approach, a substructure concept is introduced to generate them. The traditional UKF concept attempts to identify small structural systems using large duration of response histories in one global iteration. Because it fails to assess the defective states of large structures in most cases, a weighted multiple global iterations procedure with objective functions using short duration responses is introduced. The superiority of UKF-UI-WGI over the traditional UKF is demonstrated with the help of several illustrative examples using single and multiple substructures in identifying both defect-free and defective states. With the help of the same examples, the superiority of the proposed method over the extended Kalman filter-based method developed by the team earlier is conclusively documented. With the help of parametric studies, it is documented that the proposed method is robust, accurate, and stable. The study confirms that UKF-UI-WGI can identify large structural system using only limited response information measured at a small part of a structure without using any excitation information. The concept significantly advances the state-of-the-art in UKF-based nonlinear system identification and considerably improves its implementation potential. Copyright © 2015 John Wiley & Sons, Ltd.

Novel Unscented Kalman Filter for Health Assessment of Structural Systems with Unknown Input

AbstractA novel procedure for structural health assessment, denoted as unscented Kalman filter with unknown input (UKF-UI), is proposed using the nonlinear system identification concept. To increase its implementation potential, a substructure concept is introduced, producing a two-stage approach. It integrates the unscented Kalman filter concept and an iterative least-squares technique. The two most important features of the method are that it does not need the information on the time history of the excitation to identify structural systems represented by finite elements, and that it can identify defects in them using only a limited amount of noise-contaminated nonlinear response information. The proposed method is robust enough to detect the locations and severity of defects at different locations in the structure. The defect detection capability increases significantly if the defective member is in the substructure or close to it. The method is conclusively verified with the help of two examples using ...

Multisensor Aggregation Algorithms for Structural Damage Diagnosis Based on a Substructure Concept

One of the important goals of structural health monitoring is damage detection. Although many methods have been proposed to detect the existence of structural damage, relatively few studies are found on higher-level damage diagnosis such as identification of the location and extent of damage. In this paper, multiple substructural damage identification models based on regression between internal responses and boundary responses of individual beam elements in either plane or three-dimensional space are derived. Three damage indexes are defined from regression model characteristics, and two change-point analysis methods are adopted to capture changes in damage index sequences which are extracted from structural monitoring data sets from healthy and unknown states. Possible damage locations are identified as where the most significant changes in the damage indexes occur, and a voting scheme is used to synthesize the results from different algorithms. This damage detection approach is straightforward and efficient, with the regression coefficients directly related to the structural stiffness properties. The numerical and experimental application results show that the method successfully identifies and locates structural change in most of the cases.

InSARa: intuitive and interactive SAR interpretation by reduced graphs and hierarchical MCS-based network navigation.

The analysis of Structure-Activity-Relationships (SAR) of small molecules is a fundamental task in drug discovery. Although a large number of methods are already published, there is still a strong need for novel intuitive approaches. The inSARa (intuitive networks for Structure-Activity Relationships analysis) method introduced herein takes advantage of the synergistic combination of reduced graphs (RG) and the intuitive maximum common substructure (MCS) concept. The main feature of the inSARa concept is a hierarchical network structure of clearly defined substructure relationships based on common pharmacophoric features. Thus, straightforward SAR interpretation is possible by interactive network navigation. When focusing on a set of active molecules at one single target, the resulting inSARa networks are shown to be valuable for various essential tasks in SAR analysis, such as the identification of activity cliffs or "activity switches", bioisosteric exchanges, common pharmacophoric features, or "SAR hotspots".

InSARa: intuitive single-target (large-scale) SAR interpretation and multi-target cross-reactivity analysis

inSARa (intuitive networks for Structure-Activity-Relationships analysis) was primarily developed with the objective to support the medicinal chemist in tackling SAR analysis and visualization of large data sets in a more intuitive way than fingerprint-based approaches [1]. The method takes advantage of the synergic combination of the reduced graph (RG) and the maximum common substructure (MCS) concept [2]. The main feature of the inSARa concept is a hierarchical network structure of clearly-defined substructure relationships based on common pharmacophoric features. Thus, straightforward SAR interpretation is possible by interactive network navigation. When focusing on a set of active molecules at one single target, the resulting inSARa networks were shown to be valuable for various essential tasks in SAR analysis, such as the identification of activity cliffs or activity switches, bioisosteric replacements or SAR hotspots. Based on the identification of nearest neighbours in the networks, the prediction of bioactivities is also possible. Furthermore, inSARa can be used to investigate similarities between different targets. Targets are compared based on the overlap of common pharmacophoric pattern (RG MCSs) of the corresponding inSARa networks. According to the similar property principle, similar ligands are expected to bind to similar targets [3]. Therefore, this ligand-based analysis not only revealed meaningful similarity relationships between the analysed targets but is also beneficial for the detection of potential off-target relationships and cross-reactivities. Especially when investigating targets where no structural information is available but a set of active ligands is known (e.g. GPCRs), this complementary approach can provide important knowledge for drug design.

Nonparametric Stochastic Modeling of Structures with Uncertain Boundary Conditions/Coupling Between Substructures

The focus of this investigation is on the formulation and validation of a novel approach for the inclusion of uncertainty in the modeling of the boundary conditions of linear structures and of the coupling between linear substructures. This work is particularly relevant to complex structures assembled from simpler substructures as in aerospace applications. First, a mean structural dynamic model that includes boundary condition/coupling flexibility is obtained using classical substructuring concepts. The application of the nonparametric stochastic modeling approach to this mean model is next described and thus permits the consideration of both model and parameter uncertainty. Finally, the identification of the two parameters of this stochastic model, the mean boundary condition/coupling flexibility and the overall level of uncertainty, is shown and discussed. The methodology is demonstrated on three different structural dynamic models, of a rectangular plate and of two different wings.