Single Loading Conditions Research Articles

Weighted Transmissibility-Based Operational Modal Analysis for Identification of Structures Using Seismic Responses

Transmissibility-based operational modal analysis is an effective approach to identify the modal parameters using the output-only data from the ambient vibrations. This approach, based on the SVD technique, has a good ability to determine the vibrational modes with high certainty. However, the results of the present research indicate that the transmissibility approach has not an appropriate performance in identifying the vibrational modes using the short random records such as seismic records. These records have a high spectral leakage and dispersion due to the non-periodic harmonic components caused by the vibrational characteristics of the system and the strong ambient excitations (e.g., earthquake). In this paper, an efficient approach called weighted transmissibility-based operational modal analysis is proposed to properly identify the natural frequencies and mode shapes using the short seismic records. The proposed approach combines the single-reference weighted transmissibility functions associated with different transferring outputs obtained from single loading condition in a unique matrix formulation. It extracts the vibrational modes using the efficient $${\text{PIS}}\left( \omega \right)$$ function calculated by the singular values of the weighted transmissibility matrices. In this research, several theoretical examples, including 2-DOF, 3-DOF, 5-DOF and 10-DOF systems, have been provided to indicate the capabilities of the proposed approach in identifying the modal parameters of structural systems.

Performance and design of oval-ended elliptical CFT columns under combined axial compression-torsion

Previously, a series of studies focusing on the response of the oval-ended elliptical concrete-filled steel tubular (OECFT) columns under various single load conditions were performed due to its novel superiorities in flow smoothness, architectural aesthetics and structural efficiency. Nonetheless, the properties of the OECFT column imposed with combined forces have never been addressed. In attempt to fill this gap, this paper aims to present a numerical analysis via ABAQUS solver to explore the torsional behaviour of the axially-loaded OECFT column. Following that, the finite element (FE) modelling was verified by the existing experimental data, and then the comprehensive parametric research on the type of column was conducted. Detailed responses of the OECFT column subjected to combined axial compression-torsion, in aspect of the typical torque ratio (T/Tu) – angle (θ) curve, failure patterns, contact action and characteristic relationship of relative ultimate torque value (Tu/Tu0) versus axial compression ratio (N/Nu0), were respectively investigated. The numerical simulation revealed that the torsional resistance of the type of column increased with the increase of the steel strength, concrete strength and steel ratio, while a decrease was obtained with the increase of the aspect ratio. Accompanied by the changes in axial compression ratio, material strength and steel ratio, obvious influences on the Tu/Tuo-N/Nuo curve were obtained. Finally, a design provision to assess the torsional strength of the OECFT column under combined axial compression-torsion was proposed and was validated in compliance with the aforementioned analyses.

Nonlinear stress-dependent recovery behavior of the intervertebral disc

The intervertebral disc exhibits complex mechanics due to its heterogeneous structure, inherent viscoelasticity, and interstitial fluid-matrix interactions. Sufficient fluid flow into the disc during low loading periods is important for maintaining mechanics and nutrient transport. However, there is a lack of knowledge on the effect of loading magnitude on time-dependent recovery behavior and the relative contribution of multiple recovery mechanisms during recovery. In most studies that have evaluated disc recovery behavior, a single load condition has been considered, making it difficult to compare findings across studies. Hence, the objective of this study was to quantify unloaded disc recovery behavior after compressive creep loading under a wide range of physiologically relevant stresses (0.2–2 MPa). First, the repeatability of disc recovery behavior was assessed. Once repeatable recovery behavior was confirmed, each motion segment was subject to three cycles of creep-recovery loading, where each cycle consisted of a 24-h creep at a pre-assigned load (100, 200, 300, 600, 900, or 1200 N), followed by an 18-h recovery period at a nominal load (10 N). Results showed that disc recovery behavior was strongly influenced by the magnitude of loading. The magnitude of instantaneous and time-dependent recovery deformations increased nonlinearly with an increase in compressive stress during creep. In conclusion, this study highlights that elastic deformation, intrinsic viscoelasticity, and poroelasticity all have substantial contributions to disc height recovery during low loading periods. However, their relative contributions to disc height recovery largely depend on the magnitude of loading. While loading history does not influence the contribution of the short-term recovery, the contribution of long-term recovery is highly sensitive to loading magnitude.

Mechanical Assessment of Fatigue Characteristics between Single- and Multi-Directional Cyclic Loading Modes on a Dental Implant System.

Mechanical testing based on ISO 14801 standard is generally used to evaluate the performance of the dental implant system according to material and design changes. However, the test method is difficult to reflect on the clinical environment because the ISO 14801 standard does not take into account the various loads from different directions during chewing motion. In addition, the fracture pattern of the implant system can occur both in the horizontal and the vertical directions. Therefore, the purpose of this study was to compare fatigue characteristics and fracture patterns between single directional loading conditions based on the ISO 14801 standard and multi-directional loading condition. Firstly, the static test was performed on five specimens to derive the fatigue load, and the fatigue load was chosen as 40% of the maximum load measured in the static test. Subsequently, the fatigue test was performed considering the single axial/occlusal (AO), AO with facial/lingual (AOFL) and AO with mesial/distal (AOMD) directions, and five specimens were used for each fatigue loading modes. In order to analyze the fatigue characteristics, the fatigue cycle at the time of specimen fracture and displacement change of the specimen every 500 cycles were measured. Field emission scanning electron microscopy (FE-SEM) was used to analyze the fracture patterns and the fracture surface. Compared to the AO group, the fatigue cycle of the AOFL and AOMD groups showed lower about five times, while the displacement gradually increased with every 500 cycles. From FE-SEM results, there were no different surface morphology characteristics among three groups. However, the AOMD group showed a vertical slip band. Therefore, our results suggest that the multi-directional loading mode under the worst-case environment can reproduce the vertical fracture pattern in the clinical situation and may be essential to reflect on the dental implant design including connection types and surface treatments.

Fatigue life prediction of the wire rope based on grey theory under small sample condition

The fatigue life prediction of wire rope has the characteristics of large sample size required and many uncertain factors. In this paper, the 40 6 × 31SW FC type wire rope is taken as the research object. Under the condition of fatigue life data of small sample size, the fatigue life prediction of wire rope under different load conditions is realized based on gray theory. As a first step, for the problems existing in the current fatigue life prediction of wire rope, this paper constructs an improved GM (1,1) model and predicts the reliability life data of wire rope under small sample size condition. Subsequently, based on this, combined with the equivalent alternating stress of the critical locations of wire rope during the fatigue test, the reliability stress-life curve of the critical locations of wire rope is determined; Finally, the fatigue life prediction model of wire rope is obtained by combining with the cumulative damage theory of fatigue. The fatigue life of wire rope under different loads is predicted and compared with the experimental value. The results show that the proposed method has high accuracy in predicting the small sample fatigue life of wire rope under single and combined loading conditions, which proves the effectiveness of this method.

Effects of freeze and cyclic flexural load on mechanical evolution of filling layer self-compacting concrete

As one of the core components, high quality self-compacting concrete filling layer is of great importance to the long-term safe service of CRTS III type slab ballastless track. The present paper designed a freeze and flexural-loading coupling action testing system to investigate the mechanical characteristics of self-compacting concrete applied in filling layer (FLSCC), aiming at understanding the service behavior of filling layer under severe environment condition. The effects of temperature, cycle number and stress level on mechanical properties including flexural strength, dynamic elastic modulus and damping ratio of FLSCC were discussed. Results show that the freeze and cyclic load coupling action aggravates the deterioration of concrete compared to single cyclic load condition. FLSCC exhibits better resistance to freeze and cyclic load action than other three investigated concretes in term of flexural strength, dynamic elastic modulus and damping ratio. The flexural strength of FLSCC decreases with increasing cycle number stress level at low temperature (−20 °C) and the damage variable of FLSCC increases exponentially with cycle number. The outstanding resistance of FLSCC to freeze and cyclic load coupling action results from the excellent microstructure which can maintain its good deformation capacity and delay the damage propagation.

Geometrically projected discrete dislocation dynamics

Three-dimensional discrete dislocation dynamics methods (3D-DDD) have been developed to explicitly track the motion of individual dislocations under applied stress. At present, these methods are limited to plastic strains of about one percent or less due to high computational cost associated with the interactions between large numbers of dislocations. This limitation motivates the construction of minimalistic approaches to efficiently simulate the motion of dislocations for higher strains and longer time scales. In the present study, we propose geometrically projected discrete dislocation dynamics (GP-DDD), a method in which dislocation loops are modeled as geometrical objects that maintain their shape with a constant number of degrees of freedom as they expand. We present an example where rectangles composed of two screw and two edge dislocation segments are used for modeling gliding dislocation loops. We use this model to simulate single slip loading of copper and compare the results with detailed 3D-DDD simulations. We discuss the regimes in which GP-DDD is able to adequately capture the variation of the flow stress with strain rate in the single slip loading condition. A simulation using GP-DDD requires ∼40 times fewer degrees of freedom for a copper single slip loading case, thus reducing computational time and complexity.

Joint Entropy Based Multi-Objective Evolutionary Optimization of Water Distribution Networks

It is essential to consider resilience when designing any water distribution network and surrogate measures of resilience are used frequently as accurate measures often impose prohibitive computational demands in optimization algorithms. Previous design optimization algorithms based on flow entropy have essentially employed a single loading condition because the flow entropy concept formally has not been extended to multiple loading conditions in water distribution networks. However, in practice, water distribution networks must satisfy multiple loading conditions. The aim of the research was to close the gap between the prevailing entropy-based design optimization approaches based on one loading condition essentially and water distribution practice that must address multiple loading conditions. A methodology was developed and applied to a real-world water distribution network in the literature, based on the concept of the joint entropy of independent probability schemes. The results demonstrated that the critical loading conditions were design specific. In other words, the critical loading and operating conditions cannot readily be determined beforehand. Consequently, maximizing the joint entropy provided the most consistently competitive solutions in terms of the balance between cost and resilience. The results were derived using a penalty-free genetic algorithm with three objectives. Compared to previous research using flow entropy based on a single loading condition and two objectives, there was a substantial increase of 274% in the number of nondominated solutions achieved.

Biomechanical effects of USS fixation with different screw insertion depths on the vertebrae stiffness and screw stress for the treatment of the L1 fracture.

To evaluate the biomechanical effects of internal fixation with different screw insertion depths on vertebrae stiffness and screw stress for L1 fracture. The established L1 fracture was fixed with 10 different depths of screw insertion: 10-100% screw-path length (SPL). Loading on the T12 endplate was simulated. Screws inserted to 60-100% depths has a higher axial displacement of screw against injured vertebrae and maximum stress of screws compared to those of screws inserted to 30-50% depths and 10-20% (P< 0.05). No significant difference was noted among 60-100% SPL groups. Under single loading condition, the incidence rate of maximum stress of each screw ranged from 16.7-50.0%. Chi-square test showed superior screw has a higher incidence rate of maximum stress than inferior screw (P< 0.05). Screws inserted to 60% depth or more can achieve effective strength to withstand the postoperative height correction loss of the L1 vertebrae fracture. However, continuous prolonged depth of screw insertion did not significantly increase the effective strength of the screw against injured vertebrae and maximum equivalent stress of screws. The incidence rate of the maximum stress of each screw in correlated with position of screw insertion but not associated with the screw insertion depth.

Aerostructural Optimization of Drooped Wings

Through aerostructural optimization, this paper presents progress toward characterizing the potential efficiency gains of drooped wings for commercial aircraft in transonic flight. The drooped wing is a nonplanar configuration with downward spanwise camber from the wing root to the tip. The aerostructural optimization cases include two load conditions: cruise and . The single maneuver load condition is used for structural sizing of the wing. In all cases, the projected span of the wing remains unchanged. The results show that such a wing has the potential to improve aircraft range by 2.6% relative to an optimized planar wing of the same projected span. The reason is that the drooped wing pushes the tip vortex further away than the planar wing and increases the projected span at the deflected state. Furthermore, if the drooped wing is permitted to have curved leading and trailing edges, a 4.9% range improvement in comparison to an optimized planar wing with straight leading and trailing edges is possible by further reducing wing weight and wave drag.

Finite element wear prediction using adaptive meshing at the modular taper interface of hip implants.

The use of modular components in total hip arthroplasty introduced an additional interface with the potential for fretting and corrosion to occur. Fretting and corrosion at this interface have been reported as a potential cause of early failure of the implant system. Using finite element (FE) analyses the mechanics at the taper junction can be studied. However, most FE studies are based on a single load condition and do not take geometry changes over time into account. Therefore, in this study an FE routine was developed, in which adaptations to the implant geometry are made to account for material removal during the fretting process. Material removal was simulated based on Archard's Law, incorporating contact pressure, micromotions and a wear factor which used input from in vitro fretting tests. A wear factor of 2.7*10-5mm3/Nmm was used to match the FE predicted volumetric wear to the measured experimental volumetric wear of 0.79mm3 after 10 million cycles. The maximum experimental wear depth found was 30.5 ± 17µm, while the FE predicted a maximum wear depth of 27µm. The adaptive meshing method has delivered results that are more similar to the experimental test data in comparison to the results from modelling a single cycle without adaptive meshing.

Effect of bend angle on plastic limit loads of pipe bends under different load conditions

The effect of bend angle on plastic limit loads of pipe bends under different load conditions is presented using three-dimensional non-linear finite element analyses. Based on finite element analysis, the characteristics of deformation, stress and strain were studied and effect of bend angle on the limit load was discussed. The results show that the effect of bend angle on limit load is great both at 0°∼120° range under internal pressure, torsion moment and in-plane bending moment and at 0°∼90° under out-of-plane moment. Then existing expressions of limit load and the finite element results were compared, and the solutions of limit load under single load condition were made. The proposed unified load solutions were obtained by fitting the finite element data under internal pressure, in-plane bending moment, out-of-plane bending moment and torsion moment. The results show that the proposed unified load solutions are consistent and in good agreement with the current finite element results.

A Bayesian Assessment of Real-World Behavior During Multitasking

Multitasking is common in everyday life, but its effect on activities of daily living is not well understood. Critical appraisal of performance for both healthy individuals and patients is required. Motor activities during meal preparation were monitored in healthy individuals with a wearable sensor network during single and multitask conditions. Motor performance was quantified by the median frequencies (fm) of hand trajectories and wrist accelerations. The probability that multitasking occurred based on the obtained motor information was estimated using a Naïve Bayes Model, with a specific focus on the single and triple loading conditions. The Bayesian probability estimator showed task distinction for the wrist accelerometer data at the high and low value ranges. The likelihood of encountering a certain motor performance during well-established everyday activities, such as preparing a simple meal, changed when additional (cognitive) tasks were performed. Within a healthy population, the probability of lower acceleration frequency patterns increases when people are asked to multitask. Cognitive decline due to aging or disease might yield even greater differences.

Force density method for simultaneous optimization of geometry and topology of trusses

A new method of simultaneous optimization of geometry and topology is presented for plane and spatial trusses. Compliance under single loading condition is minimized for specified structural volume. The difficulties due to existence of melting nodes are successfully avoided by considering force density, which is the ratio of axial force to the member length, as design variable. By using the fact that the optimal truss is statically determinate with the same absolute value of stress in existing members, the compliance and structural volume are expressed as explicit functions of force density only. After obtaining optimal cross-sectional area, nodal locations, and topology, the cross-sectional areas and nodal coordinates are further optimized using a conventional method of nonlinear programming. Accuracy of the optimal solution is verified through examples of plane trusses and a spatial truss. It is shown that various nearly optimal solutions can be found using the proposed method.

Dynamic modulus characteristics of saturated clays under variable confining pressure

Dynamic loadings, induced by earthquakes and other causes, will lead to the cyclic variation of both shear stress and normal stress components on the soil elements. A series of cyclic triaxial tests with and without variable confining pressure were carried out to investigate the coupling effects of cyclic shear stress and cyclic normal stress on the normalized shear modulus, G/Gmax, characteristics of saturated clays. Results indicated that both the phase differences and ratios between the cyclic deviatoric stress and cyclic confining pressure exerted a constant and pronounced influence on the G/Gmax, indicating that the G/Gmaxproperties under combined loadings will be more representative of actual field conditions than from single-loading conditions. A modified hyperbolic model considering the effects of cyclic confining pressure was further proposed.

Multi-Objective Neutrosophic Optimization Technique and its Application to Structural Design

In this paper, a multi-objective non-linear neutrosophic optimization (NSO) approach for optimizing the design of plane truss structure with multiple objectives subject to a specified set of constraints has been developed. In this optimum design formulation, the objective functions are the weight of the truss and the deflection of loaded joint; the design variables are the cross-sections of the truss members; the constraints are the stresses in members. A classical truss optimization example is presented here in to demonstrate the efficiency of the neutrosophic optimization approach. The test problem includes a three-bar planar truss subjected to a single load condition. This multi-objective structural optimization model is solved by neutrosophic optimization approach with linear and non-linear membership function. Numerical example is given to illustrate our NSO approach..

LiteITD a MATLAB Graphical User Interface (GUI) program for topology design of continuum structures

Over the past few decades, topology optimization has emerged as a powerful and useful tool for the design of structures, also exploiting the ever growing computational speed and power. The design process has also been affected by computers which changed the concept of form into the concept of formation and the emergence of digital design. Topology optimization can modify existing designs, incorporate explicit features into a design and generate completely new designs. This paper will show how topology optimization can be used as a digital tool. The liteITD (lite version of Isolines Topology Design) software package will be described with the purpose of providing a tool for topology design. The liteITD program solves the topology optimization of two-dimensional continuum structures using von Mises stress isolines under single or multiple loading conditions, with different material properties in tension and compression, and multiple materials. The liteITD program is fully implemented in the MATrix LABoratory (MATLAB) software environment of MathWorks under Windows operating system. GUIDE (Graphical User Interface Development Environment) was used to create a friendly Graphical User Interface (GUI). The usage of this application is directed to students mainly (educational purposes), although also to designers and engineers with experience. The liteITD program can be downloaded and used for free from the website: http://www.upct.es/goe/software/liteITD.php.

Neural Network Fault Diagnosis of Voltage Source Inverter under variable load conditions at different frequencies

The major issue of open switch fault diagnosis in Voltage Source Inverters is false alarm generated as a result of load and frequency variations. The main objective of this paper is to solve such an issue by extracting minimum number of features from fault detection parameter. The fault diagnostic system (FDS) under variable load conditions requires more number of features to be extracted from detection parameter. Therefore stator currents are taken in the DQ coordinate that is Park’s Vector Transform (PVT). The PVT is used to normalize the currents without affecting nature of transients caused due to fault occurrence. The normalized currents are passed through Discrete Wavelet Transform (DWT) and features are extracted from detail coefficients of DWT under healthy and faulty conditions. As a result of normalized currents, the extracted features of three phase currents are same under different load conditions but have definite distinctive values under different faulty conditions. Hence, once features are extracted for single load conditions they remain same for all load conditions. An Artificial Neural Network is trained using these features. The results are presented for different fault configurations, single and multiple switch faults under variable load conditions at different frequencies. Additionally, the results are presented for the real-time diagnostic of faults, showing the instance of fault occurrence and the instance of fault isolation.

How accurately can subject-specific finite element models predict strains and strength of human femora? Investigation using full-field measurements

Subject-specific finite element models have been proposed as a tool to improve fracture risk assessment in individuals. A thorough laboratory validation against experimental data is required before introducing such models in clinical practice. Results from digital image correlation can provide full-field strain distribution over the specimen surface during in vitro test, instead of at a few pre-defined locations as with strain gauges. The aim of this study was to validate finite element models of human femora against experimental data from three cadaver femora, both in terms of femoral strength and of the full-field strain distribution collected with digital image correlation. The results showed a high accuracy between predicted and measured principal strains (R2=0.93, RMSE=10%, 1600 validated data points per specimen). Femoral strength was predicted using a rate dependent material model with specific strain limit values for yield and failure. This provided an accurate prediction (<2% error) for two out of three specimens. In the third specimen, an accidental change in the boundary conditions occurred during the experiment, which compromised the femoral strength validation. The achieved strain accuracy was comparable to that obtained in state-of-the-art studies which validated their prediction accuracy against 10–16 strain gauge measurements. Fracture force was accurately predicted, with the predicted failure location being very close to the experimental fracture rim. Despite the low sample size and the single loading condition tested, the present combined numerical–experimental method showed that finite element models can predict femoral strength by providing a thorough description of the local bone mechanical response.

Multi-objective structural design problem optimization using parameterized t-norm based fuzzy optimization programming technique

Real world engineering design problems are usually characterized by the presence of many conflicting objectives. In this paper, we will make an approach to solve multi-objective structural model using parameterized t-norms based on fuzzy optimization programming technique. Here, binary t-norms are expressed in extended n-ary t-norms and their basic properties and some special cases have been discussed. In this structural model formulation, the objective functions are the weight of the truss and the deflection of loaded joint; the design variables are the cross-sections of the truss members; the constraints are the stresses in members. A classical truss optimization example is presented here to demonstrate the efficiency of our proposed optimization approach. The test problem includes a three-bar planar truss subjected to a single load condition. This approximation approach is used to solve this multi-objective structural optimization model. The model is illustrated with numerical examples.