Design Phase Of Structures Research Articles

A Multivariate Machine Learning Approach for the Prediction of Wind Turbine Blade Structural Dynamics

Wind turbine blade structural dynamics are crucial in the turbine structural design phase. Blade deflections and loads can affect the weight of the rotor as well as the power performance of a wind turbine if the deflections are extremely high. Predictions of the turbine’s blade deflections and loads can lead to informative decisions on optimizing the design of the blade. In this work, a multivariate machine learning (ML) approach is used to predict the blade’s dynamics based on the wind flow conditions and control actions of the turbine. Three different datasets were generated using the OpenFAST software tool for three different wind turbulence classes. Various ML algorithms were trained to predict the blade deflections at the tip and blade loads at the root in the edgewise and flapwise directions. The ML models were tested for generalization of the model to different flow conditions. A model is trained for one dataset with one of the turbulence classes and then used to predict the outputs of the other two datasets. The random forest ML algorithm gave the best accuracy for predicting the outputs for the dataset it was trained for, as well as the other two datasets. The accuracy of predictions was found to be higher in the edgewise direction for both load and deflection outputs. In the flapwise direction, the model could predict the outputs of the data it was trained for with an accuracy of around 99% and for the other two datasets with an accuracy of over 75%. While in the edgewise direction, the model trained on only one dataset gave a prediction accuracy above 95% for all three datasets.

Finite element modelling of interacting indentation, flexural, and delamination damage in lap joints of composites

Composite lap joints are essential for various applications, such as aircraft wings, piping networks, sporting equipment, and civil engineering works. Low-velocity impact on such joints is a common occurrence in real-life situations. The response of these joints under such impacts is quite complex. This involves multiple interacting damage modes that include delamination failure, ply failure (in-plane damage), and bond interface (joint) failure. These damages may lead to significant degradation of joint strength without apparent complete failure. Thus, it is very important to predict the response and behavior of lap joints under such impacts. The objective of this study is to demonstrate the methodology for the evaluation of damage parameters for built-in damage progressive models in ABAQUS. By introducing the concept of characteristic length to address mesh dependency, the method ensures accurate and reliable computation of damage parameters. Further, the proposed progressive damage model was improved to include the laminate (in-plane) damage, in addition to delamination and bond failure. Finally, the proposed methodology was validated by applying it to a real-world lap joint impact problem. The present study can be helpful in the initial design phase of composite structures, as it provides a consistent and easy-to-use methodology to evaluate damage parameters for practical impact simulation problems.

Design method for the structure of a gravitational wave detection telescope with low TTL noise

As a critical payload of the gravitational wave detection interferometry system, the tilt-to-length (TTL) noise has a significant influence on the detection accuracy of the interferometry system. The non-geometric TTL (NG-TTL) noise, which is the main component of the TTL noise within the telescope, is closely related to the sensitive aberrations of the system’s small pupil. Due to the different environments of the earth and space, structural deformations of the telescope can cause significantly unfavorable changes in the sensitive aberrations at the small pupil. And its negative influence must be considered carefully during the whole structural design phase of the gravitational wave telescope. In this paper, the theoretical model of the NG-TTL noise within the telescope based on the Fringe Zernike polynomials has been summarized. An evaluation function of the NG-TTL noise within the telescope was proposed. A desensitization design method for the high-stability structure of the gravitational wave telescope was developed. The results show that under the same disturbances, the NG-TTL noise within the telescope was reduced to 0.1 pm·Hz− 1/2 from 2 pm·Hz− 1/2, taking the primary mirror (PM) as an example.

A machine learning assisted preliminary design methodology for bolted composite joints in large structures

Abstract Damage initiation hotspots around features, such as bolts and ply drops, must be investigated during the preliminary design phase of large composite structures, such as composite airframes. A global-local modelling approach is commonly employed to perform this investigation, whereby a global low-fidelity model is used to drive high-fidelity local models around the features of interest. However, this methodology is slow, repetitive and expert-dependent. In this investigation, we address these issues by applying machine learning techniques to this global-local modelling framework and demonstrate the time-saving benefit when predicting damage initiation of bolted composite joints. Feature engineering of model inputs and outputs, and appropriate customisation of machine learning methods enables damage initiation prediction. Special consideration is given to the boundary conditions that must be varied to simulate the response of the bolted composite joints. Results show over three orders of magnitude time-saving benefit and satisfactory accuracy of the proposed methodology. This indicates its potential to be developed further into a rapid design and optimisation tool.

A constitutive model based on energy density for power-law variable thickness plates and its application

Variable thickness plates are relatively common structure in large-scale transportation equipment such as aerospace and ships. Due to their high running speed and large structural dimensions, such structures are usually induced high-frequency severe vibrations, which likely lead to structural damage. Therefore, it is crucial to accurately predict the high-frequency dynamic response characteristics during the structural design phase. The energy finite element method (EFEM) is a powerful tool for predicting high-frequency dynamic response. But, in recent EFEM for variable thickness plates, an approximate method (AEFEM) using a large number of constant thickness plate elements to approximate variable thickness plates is used. Due to that AEFEM is based on the constitutive equation for constant thickness plate, it will be imprecise and time-consuming. Aiming at power-law variable thickness plates, the constitutive equation based on energy density is derived and the finite element discrete scheme of the constitutive equation was studied. In this way, the precise new EFEM (NEFEM) for variable thickness plates was established. In addition, the dynamic response of a variable thickness plate was predicted by NEFEM presented and finite element method (FEM) respectively. The results are consistent. It is shown that the constitutive model presented is reliable and time-saving. Comparison of the results from AEFEM, the NEFEM can get more accurate results with fewer elements. The NEFEM based on the constitutive model presented can be used to predict precisely the high-frequency dynamic response for power-law variable thickness plates.

A macroscale damage model for the tensile and bending failure of C/C-SiC structural laminates

This work presents a Finite Element approach to model the in-plane mechanical behavior of C/C-SiC fabrics at the lamina level, including the non-linear response of diverse lay-ups and the bending-to-tensile strength ratio at failure. The material model employs a decomposition into two idealized phases, which can be exploited to capture matrix- and fiber-dominated responses at a high level of abstraction. The constitutive law of the matrix phase adopts a Continuum Damage approach driven by two Tsai-Wu surfaces, while a quasi-brittle behavior is attributed to the fibers phase. This decomposition effectively represents the influence of matrix degradation on the response and failure of the laminates. Moreover, simulations reveal that a statistical distribution of the strength is required to represent some of the experimental outcomes. The correlation with experimental data that was achieved points out that the technique is a promising tool for supporting the early design phase of CMC structures.

Identification of Wind Load Exerted on the Jacket Wind Turbines from Optimally Placed Strain Gauges Using C-Optimal Design and Mathematical Model Reduction

Wind turbine towers experience complex dynamic loads during actual operation, and these loads are difficult to accurately predict in advance, which may lead to inaccurate structural fatigue and strength assessment during the structural design phase, thereby posing safety risks to the wind turbine tower. However, online monitoring of wind loads has become possible with the development of load identification technology. Therefore, an identification method for wind load exerted on wind turbine towers was developed in this study to estimate the wind loads using structural strain, which can be used for online monitoring of wind loads. The wind loads exerted on the wind turbine tower were simplified into six equivalent concentrated forces on the topside of the tower, and the initial mathematical model for wind load identification was established based on dynamic load identification theory in the frequency domain, in which many candidate sensor locations and directions were considered. Then, the initial mathematical model was expressed as a linear system of equations. A numerical example was used to verify the accuracy and stability of the initial mathematical model for the wind load identification, and the identification results indicate that the initial mathematical model combined with the Moore–Penrose inverse algorithm can provide stable and accurate reconstruction results. However, the initial mathematical model uses too many sensors, which is not conducive to engineering applications. Therefore, D-optimal and C-optimal design methods were used to reduce the dimension of the initial mathematical model and determine the location and direction of strain gauges. The C-optimal design method adopts a direct optimisation search strategy, while the D-optimal design method adopts an indirect optimisation search strategy. Then, four numerical examples of wind load identification show that dimensionality reduction of the mathematical model leads to high accuracy, in which the C-optimal design algorithm provides more robust identification results. Moreover, the fatigue damage calculated based on the load identification wind loads closely approximates that derived from finite element simulation wind load, with a relative error within 6%. Therefore, the load identification method developed in this study offers a pragmatic solution for the accurate acquisition of the actual wind load of a wind turbine tower.

A reconstruction method for structural stress distribution of wind turbine tower using optimised mathematical model

Wind turbine towers experience complex dynamic loads during actual operation, and these loads are difficult to accurately predict in advance, which may lead to inaccurate structural strength assessment during the structural design phase, thereby posing safety risks to the wind turbine tower. Therefore, a reconstruction method for structural stress distribution of wind turbine tower was developed based on modal expansion and linear superposition theory to estimate the full-field stress distribution of a tower, which can be used for online monitoring of structural strength. The dynamic stress distribution of the tower is assumed to be the superposition of several structural modal stress distributions, in the reconstruction method for structural stress distribution developed in this study. The modes with the greatest contribution to the wind turbine structural response were selected based on the modal effective mass, and used for the base functions of an initial mathematical model for the reconstruction of structural stress distribution of the tower, in which many candidate strain gauge locations and directions were considered. Then, the initial mathematical model was expressed as a linear system of equations. Two numerical examples were used to verify the accuracy and stability of the initial mathematical model for the reconstruction of structural stress distribution of the tower, and the reconstruction results indicate that the initial mathematical model combined with the Moore–Penrose inverse algorithm can provide stable and accurate reconstruction results. However, the initial mathematical model uses too many sensors, which is not conducive to engineering applications. Therefore, D-optimal and C-optimal design methods were used to reduce the dimensions of the initial mathematical model, optimise the system of equations, and determine the location, direction and number of strain gauges. Finally, the numerical examples of stress distribution reconstruction show that dimensionality reduction of the mathematical model leads to higher accuracy, in which the C-optimal design algorithm providing a more robust reconstruction outcome.

Thermal network model for anisotropic heat transfer in 3D printed complex geometry structures

The sustainability of 3D printed buildings has drawn increasing attention in research. As a foundation for assessing energy efficiency and sustainability, it is crucial to consider the thermal performance of 3D printed walls during the structural design phase. 3D printed walls exhibit anisotropic thermophysical properties and complex heat transfer processes. However, there is a lack of studies accounting for these aspects. This work proposes a thermal network model suitable for objects with changing directions of principal thermal conductivities. The key is to store information on sizes, directions and properties. Analytical solution verification and experimental verification under two-dimensional conditions agree well with the actual results. The numerical simulation of the anisotropic 3D printed wall with complex geometry shows that the reinforced structures and the cavities cause alternating surface temperature distributions, with an average temperature difference of about 0.75 °C. Due to the barrier effect of the inclined printed structure, the triangular cavities show higher temperatures than the square cavities. The proposed model is significant for characterizing the relationship between structure and thermal performance and can be used to optimise the thermal design of 3D printed walls.

Performance-based plastic design and seismic fragility assessment for chevron braced steel frames considering aftershock effects

Observations from past earthquakes demonstrated that buildings in high seismic regions might be exposed to several aftershocks following the mainshock which can significantly increase the damage level. Since aftershocks have the potential to increase the vulnerability of buildings damaged under mainshocks, it is crucial to consider aftershock effects in the structural design phase. Performance-based Plastic Design (PBPD) method is an innovative seismic design method in which the building designed by this method shows a desirable performance under severe ground motions. PBPD allows the designer to avoid time-consuming trial and error process of analyses that are usually done in Performance-based Design method to reach a desirable performance. However, this efficient method is only valid for mainshocks only and does not consider aftershock effects in the structural design process. In this study, initially, the seismic performance (interstory drift and plastic hinges distribution) of the three 3-, 6-, and 9- story PBPD designed Chevron-braced Steel frames (CBSF) are compared under mainshocks (MS) and mainshock-aftershock (MS-AS) sequences. Subsequently, a PBPD method is developed for CBSFs considering the aftershock effects in the structural design process. Incremental dynamic analysis (IDA) has been performed using a suite of mainshocks and aftershock ground motions to develop a design base shear modification factor. Using the developed method, the performance of CBSFs under MS and MS-AS sequences is evaluated and compared with the existing PBPD method. Fragility curves are developed to compare the seismic vulnerability of the frames designed based on PBPD and proposed PBPD methods under MS-AS sequences. The outcomes of this study provide a practical design approach for CBSFs under MS-AS sequences and shows that the structures designed using developed PBPD method show more desirable behavior under MS-AS sequences compared with the structures designed using the conventional PBPD method.

Interaction between BIM and FE models in structural health monitoring

Building Information Modeling (BIM) is already widely used in civil engineering projects. Digital building models that contain geometric as well as semantic information are usually generated and could be then managed throughout a structural service life. A BIM model could generally serve as a primary source of any required information on a building, including the finite element (FE) models or monitoring systems as well. The interaction between BIM and FE models is of great importance for structural engineering as it helps increase productivity and minimize mistakes due to human factors. Moreover, with the help of structural health monitoring (SHM), it should be possible to update BIM and FE models to the current state of the structure and to maintain the remaining service life. Obviously, FE models of different complexity and element dimensionality are required for the same structure in view of various structural or material limit states considered during the structural design phase and the service life as well. The present contribution describes the development of an approach that allows FE models of different complexity to be consistently extracted from the same BIM model. It focuses on the openBIM technology incorporating the Industry Foundation Classes (IFC) format. The corresponding IFC file is enriched with FEM and SHM relevant information, for example, FE size and dimensionality as well as positions and conditions of the sensors. Using such information in the BIM model, the FE model for ANSYS APDL can be consistently created. The simulation or monitoring results can be subsequently introduced back into the original BIM model, thus describing the actual structural state. The approach will be illustrated by an example of a laboratory structure.

Residual strength of corroded ring-stiffened cylinder structures under external hydrostatic pressure

Corrosion damage to submarine pressure hulls is a crucial consideration during the structural design phase because it diminishes the structural strength of a submarine, reducing its operational depth and posing a severe risk to the life of the crew. This necessitates using a validated analytical method to estimate the residual strength and assess the safety of corrosion-affected pressure hulls. This paper presents an experimental and numerical investigation of the residual strength of corroded ring-stiffened cylinders, which are typical components of submarine pressure hulls, the main legs of semi-submersibles, and Floating Offshore Wind Turbine (FOWT) foundations. Four steel ring-stiffened cylinder models were fabricated: two remained intact, whereas the other two were artificially corroded by machining. Hydrostatic collapse tests were conducted in a pressure chamber. To evaluate the effect of initial shape imperfections caused by welding fabrication on the strength of the structure, the initial shape imperfections were measured using a three-dimensional coordinate measuring machine. The experimental results illustrate a significant reduction in the residual strengths of the two damaged models compared with those of the intact models. The collapse processes simulated using the Abaqus software package are presented, demonstrating a close agreement between the experimental results and numerical predictions.

A case study on performance of structures during Turkey-Syria multiple earthquakes occurred on February 6, 2023

Buildings are an important components of both urban and rural infrastructure, and it is crucial that they perform well during a seismic event. The earthquakes occurred on February 6, 2023 in Kahramanmaras, Turkey, which also had an impact on eleven other locations surrounding it. Turkey has suffered significantly from fatalities as well as damage to structures and other facilities. The area was severely damaged by two earthquakes, Mw7.7 and Mw7.6, which occurred within a time window of roughly 9 hours on February 6, 2023 in Turkey. Seismic regulations only take into account the design of structures during a single earthquake; multiple earthquake occurrences are not taken into account. The performance of reinforced concrete buildings, masonry buildings, and precast buildings damaged during seismic sequences are discussed in this case study. From this study it is observed that, buildings that are subject to multiple earthquakes often collapse because of damage by previous earthquake, weak foundations, detailing errors at site, the use of poor materials, and inadequate craftsmanship. Multiple earthquakes should be considered during the analysis and design phase of structures, and seismic code regulations should be adjusted to allow for multiple earthquakes.

Probabilistic assessment of failure of infiltration structures under model and parametric uncertainty

We focus on the quantification of the probability of failure (PF) of an infiltration structure, of the kind that is typically employed for the implementation of low impact development strategies in urban settings. Our approach embeds various sources of uncertainty. These include (a) the mathematical models rendering key hydrological traits of the system and the ensuing model parametrization as well as (b) design variables related to the drainage structure. As such, we leverage on a rigorous multi-model Global Sensitivity Analysis framework. We consider a collection of commonly used alternative models to represent our knowledge about the conceptualization of the system functioning. Each model is characterized by a set of uncertain parameters. As an original aspect, the sensitivity metrics we consider are related to a single- and a multi-model context. The former provides information about the relative importance that model parameters conditional to the choice of a given model can have on PF. The latter yields the importance that the selection of a given model has on PF and enables one to consider at the same time all of the alternative models analyzed. We demonstrate our approach through an exemplary application focused on the preliminary design phase of infiltration structures serving a region in the northern part of Italy. Results stemming from a multi-model context suggest that the contribution arising from the adoption of a given model is key to the quantification of the degree of importance associated with each uncertain parameter.

Deep gated recurrent unit networks for time-domain long-term fatigue analysis of mooring lines considering wave directionality

Mooring lines are a crucial component of offshore mooring systems, and long-term fatigue damage assessment is a challenging task in mooring line design and structural health monitoring. Traditional methods require a large number of structural time-domain simulations. Because the sea state varies over time, the variations in wave parameters (e.g., wave heights, periods, and directions) must be considered in long-term fatigue damage assessment. Wave directions have usually been ignored in previous studies, while the wave direction sensitive analysis conducted in this study showed that the wave directions could not be neglected in the long-term fatigue damage assessment of mooring lines. Recent deep neural network (DNN) methods have shown great potential in mooring line/riser response prediction for offshore structures. However, the utilization of float responses as input data in these DNNs restricts their applicability during the structure design phase. To address this issue, a gated recurrent unit (GRU) network is proposed for mooring line tension modeling. The proposed GRU network surrogate models are capable of accurately predicting the mooring line tension using wave elevation components or float motion responses. The rain-flow counting algorithm, T-N approach, and Miner's rule were employed to estimate the structural fatigue damage. The results showed that the proposed method could replace the heavy cost numerical computation, assess the long-term fatigue damage with high accuracy and alleviate the data dependency of DNN methods.

Efficacies of suggested strength-based prediction models for estimation of compressive and tensile properties of normal concrete

One of the most crucial challenges faced by today’s construction industry for a speedy delivery is undeniably the ‘time-factor’ accompanied by promised quality within the framework of distinct budget. Strength based - Prediction models helps in estimating the early strengths as well as later-stage strength or strength at any age of concrete. Such models assist the structural and execution engineers in arriving at a fair judgement of compressive strength of concrete. A normal practice usually followed by the material testing laboratories and quality assurance cell at site is to assess the cube compressive strength of concrete which is an intrinsic engineering property governing the design and performance phase of structures. It is found from the literature that most of the prediction models that are formulated to estimate the compressive strength of concrete at any age are actually based on cylinder compressive strength of concrete. Therefore, this paper attempts to use some of the suggested prediction models with two sets of data, that is, one by considering experimental results of cube compressive strength found at the age of 7, 14 and 28-days and two by utilizing a conversion value, suitable cylinder compressive strength is obtained. These datasets are thoroughly used in the prediction models to accurately estimate the compressive strength of concrete. Similarly, appropriate prediction models are sought to determine the split tensile strength of normal concretes based on cubic compressive strength and cylinder compressive strength. Particularly, results of the present study showcase that although the prediction models are developed based on cylinder compressive strength, they can agreeably be used on cube strength data as the ratio of (Pi/Ai) obtained is the higher range of 0.85-1.00 and with only an early cube strength result, it is possible to predict an accurate value of split tensile strength of concrete at an age of 28-days. The effectiveness of suggested prediction models through statistical parameters are determined and their efficiencies are found to be in the higher range of 94% to 98%.

Design sensitivity analysis of structural systems with damping devices subjected to fully non-stationary stochastic seismic excitations

In the framework of dynamic excitations to be considered during the design phase of structures, the most crucial one is the ground motion acceleration. To increase the structural performances against seismic actions, one of the most effective design criteria is to introduce damping devices.An efficient approach to define the optimal parameters of the damping system is based on the design sensitivity analysis, which provides a quantitative estimate of desirable design change, by relating the available design variables.In this paper a method to evaluate the sensitivities of stochastic response characteristics of structural systems with damping devices subjected to seismic excitations, modelled as fully non-stationary Gaussian stochastic processes, is proposed. The main steps are: i) to define the time–frequency varying response (TFR) function for non-classically damped systems; ii) to evaluate closed form solutions for the first-order derivatives of the TFR function as well as of the one-sided evolutionary power spectral density function of the structural response, with respect to damping parameters of devices; iii) to perform a design sensitivity analysis selecting as performance measure function the non-geometric spectral moments of nodal displacements.A numerical application demonstrates how the proposed approach is suitable to cope with practical problems of engineering interest.

Scaled concrete beams containing maximum levels of coarse recycled aggregate: Structural verifications for precast‐concrete building applications

AbstractThe use of Recycled aggregate (RA) enhances concrete sustainability. If used on an industrial‐scale, structural verification, and testing will be required to confirm that RA concrete can meet relevant industrial standards and the requirements of manufacturers, especially in the precast‐concrete industry. In this paper, an experimental campaign with the participation of a precast‐concrete manufacturer is reported. The objective is to test a self‐compacting concrete (SCC) mix, designed for structural applications, that contains maximum amounts of 100% coarse RA, in order to establish its compliance with the habitual requirements of precast‐concrete manufacturers. Thus, scaled beams (12 × 24 × 180 and 24 × 24 × 130 cm) were subjected to bending, shear‐bending, shear, and long‐term‐deflection tests. In addition, the performance of that SCC mix in the bending and shear‐bending tests was compared with the performance of an SCC mix of similar compressive strength containing 0% coarse RA. In the failure tests, the experimental results were between 1.5 and 3 times higher than the required values. The elastic behavior of both SCC mixes was also very similar in those tests, regardless of the amount of coarse RA, due to the robust design of the water and superplasticizer content of the SCC, which balanced the decreased flowability and the lower compressive strength of SCC that resulted from the additions of coarse RA. The SCC mix with 100% RA showed a lower load‐bearing capacity after failure and narrow compliance margins with the deflection limits of the long‐term‐deflection test. Even though the SCC mix with 100% RA met all the standard technical specifications of the precast‐concrete manufacturer, reference should always be made to the serviceability limit states that are applicable at the time of the structural design phase.

Topology Optimization Framework for Simultaneously Determining the Optimal Structural Design and Current Phase Angle of the IPMSMs for the MTPA Control

Although it is crucial to design the magnetic flux path and the maximum torque per ampere (MTPA) current reference under the current limitation, it is challenging to simultaneously consider these features in developing an interior permanent magnet synchronous motors (IPMSM) due to complicated coupling effects. In this article, to overcome the above issue, the motor-design parameters are estimated by conducting electromagnetic finite element (FE) analysis two times at every iteration of topology optimization. Then, the MTPA current phase angle can be analytically expressed in terms of an elementwise relative density (i.e., design variable in topology optimization). In addition, the structural safety is assessed by conducting the structural FE analysis under design-dependent loads to reflect a high-speed rotation. The proposed two-stage topology optimization enables us to simultaneously optimize both a structural design and current phase angle to achieve the maximum electromagnetic performance. Structural safety and manufacturability are also considered to obtain a practically meaningful design. With two different types of permanent magnets, the optimized IPMSMs are obtained and manufactured to validate the proposed method. Simulation and experimental results demonstrate the validity and potential of this work.

Method and apparatus for dynamic testing of structural joints

The dynamic testing technique is used during the design phase of structures and series production. This test evaluates the structural capacity, especially of the assemblies, to withstand different forces and rates of impact encountered under realistic operational conditions. This study proposes a magnetic pulse exciter for high-speed impact loading in dynamic tests because of its capability to provide single and repeatable pulse loading over a wide range of force up to 20 kN and pulse durations from 10 up to 1000 ms. The method transforms accumulated electrical energy in a capacitor bank into mechanical energy. For experimental investigations, flat and cylindrical coil devices were used for a capacitor-type pulse current generator. The proposed method has been experimentally validated on timber beams in a specified volume of force loading. The technique demonstrated a potential for controlling force and energy parameters. The effects of operating voltage on coil and ‘metal plate - coil’ distance on the amplitude of dynamic loading have been investigated. Aluminium and steel plates fastened to the object at the point of impact were used to improve excitation efficiency. The developed technique can be used in experimental studies on model joints and real objects.