Force Envelope Research Articles

Non-linear behaviour of soil–pile interaction phenomena and its effect on the seismic response of OWT pile foundations. Validity range of a linear approach through non-degraded soil properties

The effect of non-linear and inelastic behaviour of the soil–pile interaction on the seismic response of offshore wind turbine pile foundations embedded in sandy soils is analysed. For this purpose, the responses obtained assuming three different Beam on Dynamic Winkler Foundation (BDWF) models are compared: a Plastic Non-Linear Model (PNLM), an Elastic Non-Linear Model (ENLM) and a simple elastic linear model with non-degraded properties of soil (NDLM). The influence of non-linearity and plasticity assumption is studied by evaluating the effects of the kinematic and inertial interaction within soil–pile interaction. Two soil stiffness levels are analysed: very loose and medium dense sand. The seismic response under ten earthquakes is computed in terms of mean envelopes of internal forces along the pile length. The non-linearity and inelastic influence of soil–pile interaction is quantified by means of relative differences with respect to the linear elastic model. Results show that the non-linear and inelastic models acquire relevance when the contribution of the inertial interaction dominates, leading to lower maximum responses than the linear elastic model. If the inertial interaction is not significantly activated, similar results between the three models are obtained, being the linear elastic model enough to reproduce the soil–pile dynamic interaction.

Influence of Axial Load and Transverse Impact Velocity on the Behavior of Concrete Shear Walls Reinforced with GFRP Bars

A three-dimensional numerical model was established to investigate the impact resistance of concrete shear walls reinforced with fiber-reinforced polymer (FRP) bars, considering the strain rate effect of FRP reinforcement and concrete materials. After validating the numerical model, the failure mechanism of concrete shear walls reinforced with glass fiber–reinforced polymer (GFRP) bars under impact load was studied. The influence of impact velocity and axial load ratio on the impact resistance of GFRP-reinforced concrete shear walls was discussed. The results showed that GFRP-reinforced concrete walls have similar behavior to conventional reinforced concrete walls under impact loadings. The former experienced more considerable deformation due to the lower elastic modulus of GFRP bars. The peak and residual displacement at the center of the wall increased linearly with the impact energy. In addition, the peak value, plateau value, impulse, and duration of impact force grew linearly with respect to impact velocity. The proportion of energy absorbed by concrete increased in the cases of larger impact velocity. From the perspective of the internal force envelope along the wall height, the dangerous sections under impact were located at both ends of the wall under axial load. The peak value of the internal force improved with an increase of the axial load ratio. When the axial load ratio was between 0.3 and 0.4, the impact force of the wall reached the largest, and the minimum deformation occurs, indicating the best impact resistance of the shear walls. As the axial load ratio increased from 0.1 to 0.5, the total energy consumption increased from 68% to 89%, among which the external force work is 57 times that of the 0.1 axial load ratio, aggravating the failure of walls.

Control of Electromagnetic Formation Flight of Two Satellites in Low Earth Orbits

Electromagnetic formation flight uses the electromagnetic interaction between satellites to provide maneuver control for formation satellites, with the advantages of no propellant consumption, long life, and high flexibility. However, high-precision control for electromagnetic formation flight is challenging because of the nonlinear and coupling characteristics of the dynamics, optimal assignment of magnetic dipoles, model uncertainties, and the angular momentum management issues caused by the geomagnetic field. This paper studies the 6-DOF control problem of two-satellite electromagnetic formation flight in low-Earth orbit. A new electromagnetic frame is introduced to promote the decoupling of the translation dynamics model and the electromagnetic model. The electromagnetic model can be expressed as a simple two-dimensional model in this electromagnetic frame. The proposed electromagnetic force envelope diagram can intuitively show the relationship between electromagnetic force and magnetic dipoles, providing practical guidance for dipole assignment. The frequency division multiplexing method is designed for angular momentum management considering the effect of the earth’s magnetic field on the electromagnetic satellites, and the active disturbance rejection control method is used to solve the 6-DOF stability problem with external disturbance and model uncertainties. Numerical simulation verifies the effectiveness of the proposed control method and angular momentum management strategy.

Finite element analysis of a crossing panel under dynamic moving load – effect of support conditions and implications on foot fatigue

The dynamic behaviour of a complete crossing panel under a transient moving load is considered using finite element method (FEM). A 3D model is developed in ANSYS software and validated using recent field measurements data from the UK. Four assumptions of trackbed stiffness distribution are tested. The best matching assumption to the field measurements is suggested and taken forward in the current study. Vibration modes are classified by comparing the modal and transient analysis results in frequency domain based on physical interpretation of the modes. A comparison is made between the so-called ‘P2’ dynamic force value in the current study and that calculated by Jenkin’s formula as specified in the UK Network Rail standard NR/L2/TRK/012 relating to crossing fatigue calculation. It is shown that this standard over-estimates the P2 dynamic force. The crossing stress results are presented and the most critical point on the foot, where the stress is considered to be in the elastic domain is introduced, in relation to the various support conditions. It is concluded that approximating the dynamics load with an equivalent P2 force envelope is sufficient to capture peak stresses for foot fatigue analyses. Finally, two scenarios for modelling hanging bearer effects are analysed in terms of foot stresses. Considering 5 mm initial gap at three consecutive bearers leads to a significant 40% increase in stress value.

A numerical model for geometrically nonlinear analysis of a pipe-lay on a rough seafloor

Despite a detailed assessment of a potential route for offshore oil and gas transport pipelines, the pipelines are still often being subjected to a pipe-lay on a rough seafloor, which can substantially increase the internal forces within the pipeline.To ensure pipeline integrity during the installation, it is essential to obtain internal force envelope diagrams, which provide the historical maximum and minimum force bounds at every location along the pipeline throughout the entire pipe-lay proceeding.This paper provides a simple numerical technique for calculating the internal force envelope diagrams. The entire pipeline is modeled as a single continuous segment considering geometrical nonlinearity induced by large deformations. The solution technique is based on consistent minimization of the total potential energy of the system discretized as a Riemann sum and the solution of the subsequent algebraic system of nonlinear finite difference equations with a Newton-Raphson technique.The feasibility of the proposed technique is demonstrated through several scenarios of a pipe-lay across the basic types of seafloor irregularity. The results have revealed that, in general, any seafloor irregularity leads to an increase in maximum internal force values at certain locations.The proposed technique provides a time-saving alternative to commercial special-purpose finite element software.

Anisotropic Deformation Model for Hawkesbury Sandstone Incorporating Inherent Mobilised Shear Strength

An extensive study on modelling progressive Hawkesbury Sandstone degradation by anisotropic deformation subjected to monotonic loadings is presented and discussed in this study. Hawkesbury Sandstone was used due to its unique behaviour, which was initially assumed to be a uniform testing lithology with respect to grain size, compressive strength and stiffness. This study identified a theoretical approach to the anisotropic model of rock deformation. The model utilizes the stress-strain curve to derive the development of mobilised shear strength and applies it to the rock to simulate how it compresses in anisotropic. Monotonic loading tests were performed in triaxial conditions at variations of confining pressure, 4MPa and 8MPa. An increment of confining pressure was used to obtain elevation in the stress-strain curve. Progressive monotonic loading changed the mechanical characteristics of the rock; the level of the applied stress is compressed axially and then expanded laterally. During applied loading, the rock may experience damage or rock failure; the correlation between the magnitude of the mobilised shear strength and the axial stress associated with it is regarded as an intrinsic property in the rock mass. The stress-strain behaviour of rocks under anisotropic stress conditions can be predicted using this method. The mobilised minimum friction angle is used to determine the location of the mobilised shear strength envelope. The results reveal that the mobilised intrinsic shear strength is developed if the rock is forced to compaction. This is evidenced by the envelope rotating upward to the shear force envelopes during failing. Consequently, it can be deduced that the cementation (c') of the rock increases.

Flux-Decay Test: A Viable Solution to Evaluate the Induction Motor Rotor Time-Constant

This article deals with the determination of the rotor time-constant of an induction machine by performing a flux-decay test in generic load conditions. The flux-decay transient occurs when the supply stator voltage is turned off suddenly. In this way, from the decay envelope of stator back-electromotive forces and, in the case of the wound rotor machine, from that of the rotor currents, the rotor time-constant can be extrapolated with a high level of accuracy. In this article, an in-depth analysis of this methodology is reported, whose validation has been carried out on both the squirrel cage and wound rotor motors. The estimated value of rotor time-constant can be used for the machine torque regulation, using the well-known control schemes presented in the literature and whose performance in the low-speed operation is affected by the detuning of this parameter. Since the inverter-fed motors nowadays characterize most of the share in the market of adjustable speed drives, experimental results concerning the flux decay test performed under the pulsewidth modulation supply are also presented.

Component Combination Rules of Wind Load Effects of Building Structures

Under the action of the same wind azimuth, the extreme values of the wind load effect components of building structures are generated in the along-wind, cross-wind, vertical, and torsional directions. In designing the wind-resistant structure, the extreme values of effect components need to be combined to determine the internal force envelope values of members. Complete quadratic combination (CQC) and Turkstra combination rules are often used to determine the combination value of extreme values of wind effect components. The extreme probability distribution expressions of the CQC, and the Turkstra and approximate rules, are derived. The simplified combination Equations and combination coefficients of the CQC and Turkstra approximate rules are proposed in this paper. We use the combination Equations and Monte Carlo simulation method to analyze the accuracy of Turkstra and its approximate rules. The results show that the combination extreme is associated with the correlation coefficients, mean values, ratios of standard deviations, and fluctuating extremes of effect components. The errors between Turkstra and its approximate rules are small when load effect components show a positive correlation. The errors are largest when the standard deviations of components are equal. Our research results provide a theoretical basis for the combination method of wind load effect components of building structures.

Forced Motion CFD Simulation and Load Refinement Evaluation of Floating Vertical-Axis Tidal Current Turbines

Abstract Simulation of the hydrodynamic performance of a floating current turbine in a combined wave and flow environment is important. In this paper, ANSYS-CFX software is used to analyse the hydrodynamic performance of a vertical-axis turbine with various influence factors such as tip speed ratio, pitching frequency and amplitude. Time-varying curves for thrust and lateral forces are fitted with the least squares method; the added mass and damping coefficients are refined to analyse the influence of the former factors. The simulation results demonstrate that, compared with non-pitching and rotating turbines under constant inflow, the time-varying load of rotating turbines with pitching exhibits an additional fluctuation. The pitching motion of the turbine has a positive effect on the power output. The fluctuation amplitudes of thrust and lateral force envelope curves have a positive correlation with the frequency and amplitude of the pitching motion and tip speed ratio, which is harmful to the turbine’s structural strength. The mean values of the forces are slightly affected by pitching frequencies and amplitudes, but positively proportional to the tip speed ratio of the turbine. Based upon the least squares method, the thrust and lateral force coefficients can be divided into three components, uniform load coefficient, added mass and damping coefficients, the middle one being significantly smaller than the other two. Damping force plays a more important role in the fluctuation of loads induced by pitching motion. These results can facilitate study of the motion response of floating vertical-axis tidal current turbine systems in waves.

Prediction of design loads for deep water subsea lifting operations based on non-stationary time response

Two methodologies for the prediction of the design loads of deep water subsea lifting operations crossing resonance zones are presented. These methodologies are applicable to models that consider the influence of the payout speed on the dynamics of the operation, leading to a non-stationary time series for the dynamic forces on the system. The first model is based on running several random simulations of the same scenario and using these simulations as a sample in which statistical parameters are inferred. The second model uses a weighted least squares approach to predict a normalizing function that is used to evaluate the statistical parameters of the response. Both models are tested by considering the installation of a typical manifold in the Pre-Salt fields, in Brazil, and are able to predict the general form of the envelope of forces on the cable for various sea states and payout speeds. The models also provided similar results for the availability of the vessel after evaluating the weather window for this operation. Finally, the advantages of using the weighted least squares approach in comparison to the direct method are discussed, since it may considerably reduce the total number of simulations required to perform a real operation assessment, especially during preliminary design phases.

Parametric Method Applicable in Assessing Breakout Force and Time for Lifting Slender Bodies from Seabed

Abstract The article presents a parametric method applicable in assessing the suction force of a slender body to the seabed, and prognosing the body extrication time. Along with the body weight in water, the information on the suction force is essential for assessing the force needed to lift the object from the seabed. Based on the Foda theory and the resulting integral equation, which relates the maximum suction force with basic parameters of the issue of concern, the parametric method has been developed which can be widely applied in engineering practice of lifting objects. A set of discrete values of parameters selected from the range of typical values for engineering practice was the basis for developing algebraic formulas approximating the integral Foda equation for slender bodies. The included results of tests present the variability of suction force characteristics and the envelopes of maximum forces needed to extricate the body from the seabed.

Modeling, simulation, and validation of a TB41 crash test of the H2/W5/B concrete vehicle restraint system

The paper addresses numerical simulations of a concrete vehicle restraint system. The model is described in detail. The advanced material law of the continuous surface cap model was used to analyze the damage locations in concrete barrier segments. The results were validated against the TB41 full-scale crash test. The test was conducted in compliance with European standard EN 1317, and the validation was performed in accordance with the PD CEN/TR 16303 technical report. The force and moment envelopes of the road safety barrier during a vehicle crash are provided. The detailed concrete segment model successfully reproduced the characteristic splitting failure cracks that were found near the connection of the adjacent barrier segments in the actual structure after the full-scale crash test.

Cooling/Lubrication Performance of Dry and Supercritical CO2-Based Minimum Quantity Lubrication in Peripheral Milling Ti-6Al-4V

Cryogenic environments are often adopted in machining difficult-to-cut materials such as Ti-6Al-4V alloy to control its cutting heat and improve machinability. This paper aims to study the machinability of Ti-6Al-4V in finish milling process under four green cutting environments (CEs), i.e. dry, supercritical carbon dioxide (scCO2), supercritical CO2-based minimum quantity lubrication with water-based cutting fluid (scCO2-WMQL), supercritical CO2-based minimum quantity lubrication with oil-on-water droplets cutting fluid (scCO2-OoWMQL). Peripheral finish-milling of Ti-6Al-4V was conducted under various cutting speeds, feed rates, radial depth of cut and CEs. The cutting force, cutting temperature, surface morphology and surface roughness were analysed. The experiment results show that the minimum cutting force and its coefficients, cutting temperature and surface roughness are obtained in scCO2-OoWMQL environment because of its excellent cooling/lubrication and chip evacuation performance, whereas the worst friction in the tool-workpiece interface leads to the worst performance under scCO2 CE. Additionally, the machined surface profile, cutting force and their spectrums under four CEs were studied. The fundamental frequency of machined surface profile is equal to that of cutting force envelope under dry and scCO2 CEs, which is also called beat frequency, therefore scCO2-WMQL and scCO2-OoWMQL CEs can improve the milling stability. The results indicate that scCO2-OoWMQL provides the best performance with regard to cutting force, cutting temperature, surface finish and clean production.

Electron tomography of mouse LINC complexes at meiotic telomere attachment sites with and without microtubules

Telomere movements during meiotic prophase I facilitate synapsis and recombination of homologous chromosomes. Hereby, chromosome movements depend on the dynamic attachment of meiotic telomeres to the nuclear envelope and generation of forces that actively move the telomeres. In most eukaryotes, forces that move telomeres are generated in the cytoplasm by microtubule-associated motor proteins and transduced into the nucleus through the LINC complexes of the nuclear envelope. Meiotic LINC complexes, in mouse comprised of SUN1/2 and KASH5, selectively localize to the attachment sites of meiotic telomeres. For a better understanding of meiotic telomere dynamics, here we provide quantitative information of telomere attachment sites that we have generated with the aid of electron microscope tomography (EM tomography). Our data on the number, length, width, distribution and relation with microtubules of the reconstructed structures indicate that an average number of 76 LINC complexes would be required to move a telomere attachment site.

Parametrical Study of the Shear Resistance of the Approach Slabs

The transition zone of the road bridges is located right behind the abutment. Function of this structure is to ease the vehicle transition from the bridge on the rigid support to the embankment with much smaller stiffness. The main function of the approach slab is, as a part of the transition zone, helping the backfill to overcome different stiffness of the bridge foundations and embankment. The paper deals with shear resistance of the slabs for different lengths and widths. Parametrical study was performed according to Eurocode loading model 1 (Uniformed distributed load and Tandem system). Each of the analysed slabs was loaded with sets of different TS positions and location of the loading lanes. Envelopes of the shear forces of the approach slabs were analysed for each type of the slab. After that shear resistance of the slab with or without the shear reinforcement was calculated. The slab was divided into areas with same shear reinforcement distribution. The analysis is the part of the engineering tool for the bridge designers. According to length and width of the slab, the engineer can easily choose the shear reinforcement diameter and its distribution. The tool also provides the construction details of the shear reinforcement. There will be also the option for the reinforcement design of the slab, with hints for the structural scheme and calculation method.

Relevance of soil-pile tangential tractions for the estimation of kinematic seismic forces: Formulation and setting of a Winkler approach

• A BDWF model including the distributed moments produced by the pile rotation and the action of the seismic field is presented. • The performance of the proposed model for computing the pile seismic internal forces is tested against a BE formulation. • The influence of the contact condition between pile and soil on the pile seismic forces is also analysed. • Depending on the contact condition, pile shear forces can be duplicated, while bending moments remain practically unaltered. The effects of considering the tangential tractions that act on the soil-pile interface in the estimation of the pile seismic response are studied through a Beam on Dynamic Winkler Foundation model, which includes the distributed moments produced by the rotation of the pile cross-section and the action of the incident field. The performance of the developed Winkler formulation is evaluated by using a rigorous continuum model based on boundary elements that allows the use of both smooth and welded contact conditions at the soil-pile interface. In order to do the analyses, the seismic response of a fixed-head single pile embedded in different soils subjected to planar shear waves is computed in terms of envelopes of maximum bending moments and shear forces. Two soil profiles are assumed: homogeneous and two-strata halfspaces. The tangential tractions are found to significantly increase the pile maximum shear forces, but to have a minor impact on the pile maximum bending moments. The proposed Winkler model accurately reproduces the results of the continuum formulation for both contact conditions. However, some differences are found in the evaluation of the inter-layer envelopes, for which the simplified model underestimates their values.

Wearable strain gauge-based technology measures manual tactile forces during the activities of daily living.

IntroductionCurrent methods of determining applied forces in the hand rely on grip dynamometers or force-measurement gloves which are limited in their ability to isolate individual finger forces and interfere with the sense of touch. The objective of this study was to develop an improved force measurement system that could be used during various activities of daily living.MethodsCustom-made strain gauge sensors were secured to the fingernail of four fingers and two middle phalanges and calibrated to measure hand forces in eight healthy individuals during five activities of daily living.ResultsThese sensors were capable of measuring forces as small as 0.17 N and did not saturate at high force tasks around 15 N, which is within the envelope of forces experienced during daily life. Preliminary data demonstrate the ability of these tactile sensors to reliably distinguish which fingers/segments were used in various tasks.ConclusionsUntil now, there has been no method for real-time unobtrusive monitoring of force exposure during the tasks of daily life. The system used in this study provides a new type of low-cost wearable technology to monitor forces in the hands without interfering with the contact surface of the hand.

Conversion between solid and beam element solutions of finite element method based on meta-modeling theory: development and application to a ramp tunnel structure

In this study, a new method for conversion of solid finite element solution to beam finite element solution is developed based on the meta-modeling theory which constructs a model consistent with continuum mechanics. The proposed method is rigorous and efficient compared to a typical conversion method which merely computes surface integration of solid element nodal stresses to obtain cross-sectional forces. The meta-modeling theory ensures the rigorousness of proposed method by defining a proper distance between beam element and solid element solutions in a function space of continuum mechanics. Results of numerical verification test that is conducted with a simple cantilever beam are used to find the proper distance function for this conversion. Time history analysis of the main tunnel structure of a real ramp tunnel is considered as a numerical example for the proposed conversion method. It is shown that cross-sectional forces are readily computed for solid element solution of the main tunnel structure when it is converted to a beam element solution using the proposed method. Further, envelopes of resultant forces which are of primary importance for the purpose of design, are developed for a given ground motion at the end.

Design procedure for precast fibre‐reinforced concrete segments in tunnel lining construction

AbstractThis paper presents a procedure for designing precast tunnel segments for mechanically excavated tunnel linings in fibre‐ reinforced concrete, without any traditional steel reinforcement. Both ultimate and serviceability limit states are considered as well as structural checks at different construction stages of the segment, including demoulding, positioning on floor, storage, transportation, handling and the final stage concerning the loads due to the ground pressure.The structural checks are performed by means of bending moment‐axial force interaction envelopes for both the considered limit states, once the constitutive relationship of the material is defined for each stage. Traditional interaction envelopes are drawn for the ultimate limit state check, whereas for the serviceability limit state check, envelopes obtained by limiting the maximum crack opening and maximum concrete compressive stress are proposed. The shear action is also accounted for by reducing the bending moment‐axial force envelope. The possibility of having the assistance of a test procedure for particular loading situations is also proposed. Finally, a case study related to a precast steel fibre‐reinforced concrete segment is analysed in order to clarify the procedure and show, practically, how to define the actions and evaluate the interaction envelopes.

Kinematic internal forces in deep foundations with inclined piles

SummaryThis paper presents a parametric study that looks into the influence of pile rake angle on the kinematic internal forces of deep foundations with inclined piles. Envelopes of maximum kinematic bending moments, shear forces and axial loads are presented along single inclined piles and 2 × 2 symmetrical square pile groups with inclined elements subjected to an earthquake generated by vertically incident shear waves. Inclination angles from 0° to 30° are considered, and three different pile–soil stiffness ratios are studied. These results are obtained through a frequency–domain analysis using a boundary element–finite element code in which the soil is modelled by the boundary element method as a homogeneous, viscoelastic, unbounded region, and the piles are modelled by finite elements as Euler–Bernoulli beams. The rotational kinematic response of the pile foundations is shown to be a key factor on the evolution of the kinematic internal forces along the foundations. Copyright © 2015 John Wiley & Sons, Ltd.