Multiple Loading Scenarios Research Articles

Simulation-based Optimal Sensor Placement in Tunnel Structures considering Uncertain in-situ Conditions and Multiple Loading Scenarios

The expansion of the underground infrastructure and the necessity to maintain the full functionality of the existing tunnels highlights the role of structural health monitoring in keeping track of the behaviour of the structure over time. In the study, the focus is on segmental tunnel lining for deep and long tunnels. The aim of this research is to investigate the best position for sensor placement based on the potential loading scenarios that might insist on the tunnel structure. Since for the evaluation of the lining safety we are interested in the maximum stresses reached in the structure, which might lead to durability critical cracking or crushing of concrete, a method is presented to suggest optimal positions for strain gauges. Due to uncertain geological conditions, multiple loading configurations acting on the tunnel structure are simulated using a finite element model. The results are employed to better identify the sensor locations, on the basis of where damage is prone to occur and where maximum information about the stress state in the structure can be inferred. The results obtained by the framework are discussed in light of a practical engineering perspective and the advantages as well as the limitations of the proposed approach are expounded.

The value of real-time adjustable remedial action schemes

Remedial action schemes (RAS) are often seen as an inexpensive way to relieve contingency-related grid congestion without building new transmission infrastructure. However, RAS settings often remain fixed during real-time operation and do not adapt to variation in operating conditions due to renewable and distributed generation. This lack of adaptability may cause suboptimal settings and possibly insecure operations. To assess the value of allowing RAS settings to vary real time and the benefit of considering multiple load and generation scenarios, we propose a mixed integer optimization framework which identifies optimal RAS actions while incorporating multiple load and renewable energy scenarios. We also propose an iterative algorithm that efficiently solves the optimization problem, leveraging the fact that only a few scenarios and contingencies are binding at optimality. We demonstrate the benefits of (i) updating RAS more frequently and (ii) considering multiple load scenarios by performing case studies on the RTS-GMLC system.

DRAGen in Application-An Approach for Microstructural Fatigue Predictions of Non-Oriented Electrical Steel Sheets.

This study investigates multiple cyclic loading scenarios of non-oriented electrical steel sheets through both experimental and numerical approaches. The numerical simulations were conducted using Representative Volume Elements generated with DRAGen. DRAGen allowed for the generation of Representative Volume Elements with a non-cubic shape to cover the complete sheet thickness and enough grains to represent the material's texture. The experimental results, on the other hand, are utilized to calibrate and validate a prediction model, highlighting the significance of accumulated plastic slip as a suitable parameter correlated with fatigue life. Using the accumulated plastic slip from the simulations, a fatigue fracture locus is introduced, which describes a 3D surface dependent on the maximum stress, fatigue life, and the fatigue stress ratio. The study shows reliable results for the fatigue life prediction using the calibrated fatigue fracture locus. While substantial progress has been made in predicting the fatigue life at multiple fatigue stress ratios, notable disparities between experimental and simulation results suggest the need for further investigations regarding the influence of the surface quality. This observation motivates ongoing research efforts aimed at refining simulation methodologies to better incorporate surface roughness effects. In summary, this study presents a validated model for predicting fatigue life in non-oriented electrical steel sheets, offering valuable insights into material behavior at different loading scenarios and informing future research directions for enhanced structural performance and durability.

HFFB Test and Wind-Induced Vibration Analysis on 1 000 kV Transformer Frame

In order to propose a complete, wind-resistant design method for ultra-high voltage (UHV) transformer frames, the wind-induced vibration characteristics of a 1 000 kV transformer frame (TF1000) were studied using a high-frequency force balance (HFFB) test. Five section models and one whole model of the TF1000 were designed and constructed using 3D printing, and these were evaluated in a wind tunnel by means of HFFB tests for multiple loading scenarios. The finite element method (FEM) was used on the test data to analyze the wind-induced vibration on the TF1000. The results demonstrate that the shape factor of the TF1000 is significantly affected by the flow field type and solidity ratio; the minimum value occurs when the wind direction is between 30 and 45°. Moreover, all the shape factor values obtained by the test are larger than those established by the Chinese code. The wind-induced vibration analysis indicates that the most unfavorable wind direction for the TF1000 is approximately 60°, with a wind-induced vibration coefficient between 1,7 and 3,9.

Estimating Forces Along Continuum Robots

Continuum robots can be slender and flexible to navigate through complex environments, such as passageways in the human body. In order to control the forces that continuum robots apply during navigation and manipulation, we would like to detect the location, direction, and magnitude of contact forces distributions as they arise. In this paper, we present a model-based framework for sensing distributed loads along continuum robots. Using sensed positions along the robot, we use a nonlinear optimization algorithm to estimate the loading which fits the model-predicted robot shape to the data. We propose that Gaussian load distributions provide a seamless way to account for a wide range of loadings, including approximate point loads and uniform distributed loads, while avoiding the ill-conditioning associated with highly resolved force distributions. In addition, we gain computational efficiency by re-framing the problem as unconstrained weighted least-squares minimization and by solving this problem with an Extended Kalman-filter framework. We validate the approach on two prototype tendon-driven continuum robots in multiple 3D loading scenarios, displaying a mean error of 0.58 N in load magnitude and 7% mean error in load location with respect to the length of the respective robot.

Hydrostatic high strain rate loading response of closed-cell polymeric foams as a function of mass density

Closed cell polymeric foams are widely used in naval structures as sandwich core material owing to their lightweight and high energy absorption capabilities. There has been a great push towards understanding their material response under multiple loading scenarios, however, the loading scenarios have been limited to uniaxial or multiaxial in air loadings at different strain rates. Here, the hydrostatic elastic response and yield behavior of PVC foams with varying mass densities under a high strain rate hydrostatic loading state have been investigated. A novel underwater high strain rate loading facility is utilized to subject these foams to near blast strain rate hydrostatic loading. Using the 3-D Digital Image Correlation (DIC) technique in conjunction with ultra-high-speed photography, full-field volumetric deformation data is obtained. The dynamic loading data is obtained using a piezoelectric pressure sensor. This enables the measurement of material yield strength and bulk modulus for these materials under high strain rate hydrostatic loading conditions. The foams demonstrate increment in bulk modulus and yield strength under high strain rate loading. Further, the increment observed is highly sensitive to the material bulk mass density.

Size optimization design of members for shear wall high-rise buildings

Structural optimization can lead to efficient designs for high-rise concrete buildings. However, the high computational cost of the structural analysis step hinders its application in practical cases. With regards to this problem, a novel hybrid optimization framework is developed in this study. Discrete variables, code-stipulated constraints and other construction requirements under multiple loading scenarios are considered. The hybrid optimization framework contains two steps: in the first step, a computationally efficient approximation of the optimization formulation is constructed using a combined response surface methodology (RSM). Combining all the design constraints, three sub-optimization problems are proposed based on the relaxation model of the original problem to update the response surface model in the near-optimum region. When the response surface model has sufficient accuracy in the near-optimum region, in the second step, a discrete Particle Swarm Optimization (PSO) technique is applied to search for the optimal solution utilizing the response surface model. By integrating the commercially available ETABS, a dedicated optimization software with an independent interface is developed and details for practical software development are included in this paper. Three examples of high-rise concrete building design are presented to demonstrate the effectiveness of the proposed optimization framework, and the results are compared to those of a general PSO algorithm. It is shown that, compared to the conventional design approach, a 14.3% reduction in material usage is achieved by the hybrid optimization framework. Additionally, the proposed framework significantly improves the computational efficiency compared to PSO. This methodology can therefore be used by engineers to optimize member sizes for high-rise buildings so that stable and sustainable designs can be achieved.

Erratum to Gaussian process regression for active sensing probabilistic structural health monitoring: experimental assessment across multiple damage and loading scenarios

Erratum to Gaussian process regression for active sensing probabilistic structural health monitoring: experimental assessment across multiple damage and loading scenarios

Gaussian process regression for active sensing probabilistic structural health monitoring: experimental assessment across multiple damage and loading scenarios

In the near future, Structural Health Monitoring (SHM) technologies will be capable of overcoming the drawbacks in the current maintenance and life-cycle management paradigms, namely, cost, increased downtime, less-than-optimal safety management paradigm and the limited applicability of fully-autonomous operations. One of the most challenging tasks is structural damage quantification. Existing quantification techniques face accuracy and/or robustness issues when it comes to varying operating and environmental conditions. In addition, the damage/no-damage paradigm of current industrial frameworks does not offer much information to maintainers on the ground for proper decision-making. In this study, a novel structural damage quantification framework is proposed based on the widely-used Damage Indices (DIs) and Gaussian Process Regression Models (GPRMs) in order to overcome the aforementioned shortcomings. The proposed framework takes a simple approach to the damage quantification problem by using DI values for training, and provides confidence bounds on the estimated states. In addition, the proposed method is shown to quantify multiple structural states simultaneously from incoming DI test points. This framework is applied to three test cases: a Carbon Fibre-Reinforced Plastic (CFRP) coupon with attached weights as simulated damage, an aluminum coupon with a notch and an aluminum coupon with attached weights as simulated damage under varying loading states. The novel state prediction method presented herein is applied to single-state quantification in the first two test cases, as well as the third one assuming the loading state is known. Finally, the proposed method is applied to the third test case assuming neither the damage size nor the load is known in order to predict both simultaneously from incoming DI test points. In applying this framework, two forms of GPRMs (standard and variational heteroscedastic) are used in order to critically assess their performance with respect to the three test cases.

A practical discrete sizing optimization methodology for the design of high-rise concrete buildings

PurposeIn this article, a practical design methodology is proposed for discrete sizing optimization of high-rise concrete buildings with a focus on large-scale and real-life structures.Design/methodology/approachThis framework relies on a computationally efficient approximation of the constraint and objective functions using a radial basis function model with a linear tail, also called the combined response surface methodology (RSM) in this article. Considering both the code-stipulated constraints and other construction requirements, three sub-optimization problems were constructed based on the relaxation model of the original problem, and then the structural weight could be automatically minimized under multiple constraints and loading scenarios. After modulization, the obtained results could meet the discretization requirements. By integrating the commercially available ETABS, a dedicated optimization software program with an independent interface was developed and details for practical software development were also presented in this paper.FindingsThe proposed framework was used to optimize different high-rise concrete buildings, and case studies showed that material usage could be saved by up to 12.8% compared to the conventional design, and the over-limit constraints could be adjusted, which proved the feasibility and effectiveness.Originality/valueThis methodology can therefore be applied by engineers to explore the optimal distribution of dimensions for high-rise buildings and to reduce material usage for a more sustainable design.

METHODOLOGIES TO PREDICT HYDRODYNAMIC CHARACTERISTICS OF PUSHER AND PULLER PODDED PROPULSORS IN OBLIQUE FLOWS

This paper presents the outcome of a numerical simulation based research program to evaluate the propulsive characteristics of puller and pusher podded propulsors in a straight course and at static azimuthing conditions while operating in open water. Methodologies to predict the propeller thrust and torque, and pod forces and moments in three dimensions using a Reynolds-Averaged Navier Stokes (RANS) solver at multiple azimuthing conditions and pod configurations are presented. To obtain insight into the reliability and accuracy of the results, grid and time step dependency studies are conducted for a podded propulsor in straight-ahead condition. The simulation techniques and results are first validated against measurements of a bare propeller and a podded propulsor in straight ahead condition for multiple loading scenarios and in both puller and pusher configurations. Next, simulations were carried out to model the podded propulsors in the two configurations at multiple loading conditions and at various azimuthing angles from +30° to –30° in 15° increments. The majority of the simulations are carried out using both steady state and unsteady state conditions, primarily to evaluate the effect of setup conditions on the computation time and prediction accuracy. The predicted performance characteristics of the pod unit using the unsteady RANS method were within 1% to 5% of the corresponding experimental measurements for all the loading conditions, azimuthing angles and pod configurations studied. The non-linear behaviour of the performance coefficients of the pod unit are well captured at various loading and azimuthing conditions in the predicted results. This study demonstrates that the RANS solver, with proper meshing arrangement, boundary conditions and setup techniques can predict the performance characteristics of the podded propulsor in multiple azimuthing angles, pod configurations and in the various loading conditions with a same level of accuracy as experimental results. Additionally, the velocity and pressure distributions on and around the pod-strut- propeller bodies are discussed as derived from the RANS predictions.

Ecosystem models indicate zooplankton biomass response to nutrient input and climate warming is related to lake size

Zooplankton is an essential part of the simulation in ecological process-based models and rigorous calibration of the zooplankton module lacks relevant modeling research that can predict the response of zooplankton biomass to varied environmental factors. The paper therefore builds a one-dimensional lake ecology model PCLake, which quantifies the dynamic effects on zooplankton in small water bodies distinguished by lake size and eutrophication status in warming climates. Based on the main geometric characteristics among a series of shallow water bodies, we constructed three lake models, namely, a northern lake with a larger area (> 0.1 ha) in Poland (Lake NL), a northern lake with a smaller (< 0.1 ha) area in Poland (Lake NS), and a southern lake with the smallest area in Croatia (Lake SS). Data from 2017 to 2018, including water temperature, dissolved oxygen (DO), total nitrogen (TN), total phosphorus (TP), chlorophyll a (Chl a), and zooplankton, were used to calibrate and verify models for three shallow water body categories and uncertainty analyses were carried out to support the credibility of our models. Further, to discuss the potential driving forces of environmental factors on zooplankton, we set up a series of scenarios in which atmospheric temperature and nutrient input were changed. Zooplankton are only considered as a common pool and therefore only how biomass varied can be obtained. Warming resulted in a decline of zooplankton in the lakes located in Northern Europe, with peak decreases in zooplankton biomass more than four times higher in Lake NS than in Lake NL. In addition, due to multiple nutrient loading scenarios, incoming nitrogen and phosphorus concentrations were found to have a huge impact on zooplankton biomass in Lake NL. Specifically, relative to the original eutrophic level, the average annual biomass of zooplankton increased by 90% with a 75% increase in organic nitrogen over the original eutrophic level and decreased by more than 50% with a 75% decrease in inorganic phosphorus. Hence, lake size characteristics should be taken into account in management and restoration as they may be synergistic with in-lake biological and abiotic processes under complex environmental forces.

Parallelized optimization design of bumper systems under multiple low-speed impact loads

Majority of existing design optimization of bumper systems has focused on one single impact loading case in literature, which may not offer proper performance under other loading cases. This study aims to address this issue by developing a multiobjective optimization approach, in which multiple impact loading scenarios are considered to optimize the intrusion and energy absorption of the bumper system. Modeling of real-life impact scenarios is first validated by comparing the numerical results with the experimental data. Based upon the Latin hypercube design (LHD) and Kriging surrogate approaches, energy absorption (EA) and maximum intrusion (MI) are formulated in terms of design variables to consider the structural crashworthiness and repair/maintenance cost, respectively. In order to generate Pareto solution in the multiobjective optimization effectively, the recently developed Kriging Believer based parallelized efficient global optimization (EGO) algorithm is adopted to optimize the bumper system subject to three impact loads, namely the low-speed sled crash, dynamic three-point bending and 40% offset impact, respectively. These different load cases are considered through a weighted average scheme. The optimization results indicate that the Pareto solutions largely depend on the assignment of weight factors to different load cases. In order to generate more reasonable results, the National Automotive Sampling System-Crashworthiness Data System (NASS-CDS) database is also used to determine the weighting factors for each loading case. It is found that for the intrusion objective, the design under the multiple impact loads offers an intrusion reduction of 20.27% in the sled crash, 5.84% in the 40% offset impact, in comparison with the baseline design. The intrusion of three-point bending is the same as that of baseline design to compromise other more frequently occurring load cases. For the energy absorption objective, although the design leads to increase in EA by 3.01% in the sled crash and 1.79% in 40%-offset impact, the performance in the three-point bending is actually sacrificed to compromise the other more frequently occurring load cases. The study help gain insights into the design optimization of a bumper system for real-life automotive engineering.

Elasto-capillary circumferential buckling of soft tubes under axial loading: existence and competition with localised beading and periodic axial modes

We provide an extension to previous analysis of the localised beading instability of soft slender tubes under surface tension and axial stretching. The primary questions pondered here are as follows: under what loading conditions, if any, can bifurcation into circumferential buckling modes occur, and do such solutions dominate localisation and periodic axial modes? Three distinct boundary conditions are considered: in case 1 the tube’s curved surfaces are traction-free and under surface tension, whilst in cases 2 and 3 the inner and outer surfaces (respectively) are fixed to prevent radial displacement and surface tension. A linear bifurcation analysis is conducted to determine numerically the existence of circumferential mode solutions. In case 1 we focus on the tensile stress regime given the preference of slender compressed tubes towards Euler buckling over axisymmetric periodic wrinkling. We show that tubes under several loading paths are highly sensitive to circumferential modes; in contrast, localised and periodic axial modes are absent, suggesting that the circumferential buckling is dominant by default. In case 2, circumferential mode solutions are associated with negative surface tension values and thus are physically implausible. Circumferential buckling solutions are shown to exist in case 3 for tensile and compressive axial loads, and we demonstrate for multiple loading scenarios their dominance over localisation and periodic axial modes within specific parameter regimes.

Understanding Influence of Powerplant Component Connection Strategies on Aircraft Engine Structural Deformations

In conventional aircraft design, engine loads are transferred directly from the engine core and fan case to the pylon via engine mounts. Literature is available on the modeling of individual powerplant components, but limited work is available on the whole assembled system (engine, pylon, and nacelle). The influence of the structural connections between the components on overall system performance has not been investigated. Herein, a finite element model is described and can be used to assess connection strategies between powerplant components and if such arrangements can effectively enhance engine performance by reducing detrimental engine structural deformations (engine carcass bending, rotation, and ovalization). The method is demonstrated for a generic high bypass ratio engine design, focusing on connections between the engine and thrust reverser unit. The method identifies a modified attachment scheme between the engine rear turbine casing and the inner barrel of the thrust reverser unit, which reduces engine deformations across multiple loading scenarios. Maximum reductions of 97 and 96% have been observed in carcass bending and ovalization, respectively.

Effectiveness of Friction Dampers in Seismic and Wind Response Control of Connected Adjacent Steel Buildings

Effectiveness of friction dampers (FDs) is investigated for connected dynamically similar and dissimilar steel buildings under uncorrelated seismic ground motion and wind excitations. The steel buildings involving moment-resisting frame (MRF) and braced frame (BF) are varied from five storeys to twenty storeys, which are connected by different configurations of the FDs. The steel buildings without and with bracing systems are modeled as plane frame structures with inertial masses lumped at each joint node. The FDs are modeled an element having yield force equal to slip load, with force-deformation behavior as elastic-perfectly plastic material. The dynamic responses of the unconnected and connected steel buildings are obtained in terms of top floor displacement and acceleration under the considered ground motion and wind excitations. It is concluded that the FDs help minimizing the gap between two adjacent buildings having utilized the space to connect the buildings. Moreover, the effectiveness of the FDs in terms of response reduction in dynamically dissimilar buildings is more than that in the similar buildings under the considered excitation scenarios. However, the effectiveness of the installed devices varies significantly under the multiple loading scenarios. Finally, the separation gap may be reduced by ∼30%, which would eventually minimize structural pounding as well as utilize the space for effective construction. Hence, important essential guidelines are outlined for structures installed with such passive control devices against such multiple scenario loadings.

Optimal Meter Placement in Low Observability Distribution Networks with DER

This paper presents a mixed integer linear programming (MILP) approach to deal with the volatility associated with loads and distributed energy resources (DER) in low observability distribution networks. Distribution networks, characterized by having many buses and few meters, have recently faced massive integration of DER, whose injection increases net load volatility. To better understand how to act under such increased volatility, the accuracy of state estimation (SE) needs to be improved. Our approach improves SE accuracy by providing meter placement solutions that take into account uncertainty as expressed by multiple load and DER profile scenarios, this way mitigating the impact of net load volatility. Solution results are illustrated and discussed for different case studies carried out over a radial 9 bus test feeder.

Finite element models can reproduce the effect of nucleotomy on the multi-axial compliance of human intervertebral discs

Finite element (FE) models can unravel the link between intervertebral disc (IVD) degeneration and its mechanical behaviour. Nucleotomy may provide the data required for model verification. Three human IVDs were scanned with MRI and tested in multiple loading scenarios, prior and post nucleotomy. The resulting data was used to generate, calibrate, and verify the FE models. Nucleotomy increased the experimental range of motion by 26%, a result reproduced by the FE simulation within a 5% error. This work demonstrates the ability of FE models to reproduce the mechanical compliance of human IVDs prior and post nucleotomy.

Damage evaluation of a full-scale RC frame exposed to multiple extreme loads

Purpose The occurrence of multiple hazards in extreme conditions is not unknown nowadays, but the sustainability of the reinforced concrete structures under such scenarios form competitive challenges in civil engineering profession. Among all, fire following earthquake (FFE) is categorized under multiple extreme load scenarios which causes sequential damages to the structures. This paper aims to experiment a full-scale RC frame sub-assemblage for the FFE scenario and assess each stage of damage through the nondestructive testing method. Design/methodology/approach Two levels of simulated earthquake damages, i.e. immediate occupancy (IO) level and life safety (LS) level of structural performance were induced to the test frame and then, followed by a realistic compartment fire of 1 h duration. Also, the evaluation of damage to the RC frame after the fire subsequent to the earthquake was carried out by obtaining the ultimate capacity of the frame. Ultrasonic pulse velocity and rebound hammer test were conducted to assess the structural endurance of the damaged frame. Cracks were also marked during mechanical damages to the test frame to study the nature of its propagation. Findings Careful visual inspection during and after the fire test to the test frame were done. To differentiate between concrete chemically affected by the fire or physically damaged is an important issue. In situ inspection and laboratory tests of concrete components have been performed. Concrete from the test frame was localized with thermo-gravimetric analysis. The UPV results exhibited a sharp decrease in the strength of the concrete material which was also confirmed via the DTA, TGA and TG results. It is important to evaluate the residual capacity of the entire structure under the FFE scenario and propose rehabilitation/retrofit schemes for the building structure. Research limitations/implications The heterogeneity in the distribution of the damage has been identified due to variation of fire exposure. The study only highlights the capabilities of the methods for finding the residual capacity of the RC frame sub-assemblage after an occurrence of an FFE. Originality/value It is of find kind of research work on full-scale reinforced concrete building. In this, an attempt has been made for the evaluation of concrete structures affected by an FFE through nondestructive and destructive methods.

Operations- and Uncertainty-Aware Installation of FACTS Devices in a Large Transmission System

Decentralized electricity markets and greater integration of renewables demand expansion of the existing transmission infrastructure to accommodate inflected variabilities in power flows. However, such expansion is severely limited in many countries because of political and environmental issues. Furthermore, high renewables integration requires additional reactive power support, which forces the transmission system operators to utilize the existing grid creatively, for example, take advantage of new technologies, such as flexible alternating current transmission system (FACTS) devices. We formulate, analyze, and solve the challenging investment planning problem of installation in existing large-scale transmission grid multiple FACTS devices of two types (series capacitors and static var compensators). We account for details of the ac character of power flows, probabilistic modeling of multiple load scenarios, FACTS devices flexibility in terms of their adjustments within the capacity constraints, and long-term practical tradeoffs between capital versus operational expenditures. It is demonstrated that proper installation of the devices allows to do both—extend or improve the feasibility domain for the system and decrease long-term power generation cost (make cheaper generation available). Nonlinear, nonconvex, and multiple-scenario-aware optimization is resolved through an efficient heuristic algorithm consisting of a sequence of quadratic programmings solved by CPLEX combined with exact ac power flow resolution for each scenario for maintaining feasible operational states during iterations. Efficiency and scalability of the approach are illustrated on the IEEE 30-bus model and the 2736-bus Polish model from Matpower.