Displacement Reconstruction Research Articles

Robust actuator dynamics compensation method for real-time hybrid simulation

Abstract Real-time hybrid simulation (RTHS) is a practical, cost-effective, and versatile experimental technique to evaluate structural performance under dynamic excitation. The simulated structure is commonly split into a physically tested rate-dependent substructure (PS) and a numerically simulated substructure (NS). A transfer system such as a servo-hydraulic actuator is used to impose boundary conditions on the PS. Consequently, efficient actuator control is necessary to guarantee reliable simulation results. However, time delay and uncertainties exist due to the dynamics of the actuator, which adversely influence the accuracy and stability of RTHS. Therefore, an innovative robust actuator dynamics compensation method is proposed in this study comprising three components, namely a mixed sensitivity-based robust H∞ controller to stabilize the actuator–specimen dynamics, a polynomial extrapolation module to further cancel the actuator delay, and an adaptive filter for displacement reconstruction of the actuator–specimen system. A detailed design procedure of the proposed strategy is presented. The efficacy of the proposed strategy is validated through a series of virtual tests on the benchmark problem for RTHS. Results show that the proposed method exhibits excellent tracking performance and robustness. In particular, the maximum values of the calculated time delay (TD), root mean square of the tracking error (RMSE), and peak tracking error (PE) are 0 ms, 2.56%, and 2.12%, respectively, whereas the maximum values of the standard deviation of TD, RMSE, and PE are 0 ms, 0.25%, and 0.33%, respectively.

Displacement Response Reconstruction of Slender Flexible Structures Based on Cubic Spline Fitting Method

How to reconstruct a dynamic displacement of slender flexible structures is the key technology to develop smart structures and structural health monitoring (SHM), which are beneficial for controlling the structural vibration and protecting the structural safety. In this paper, the displacement reconstruction method based on cubic spline fitting is put forward to reconstruct the dynamic displacement of slender flexible structures without the knowledge of mode-shapes and applied loading. The obtained strains and displacements are compared with the results calculated by ABAQUS to check the method’s validity. It can be found that the proposed method can accurately identify the strains and displacement of slender flexible structures undergoing linear vibrations, nonlinear vibrations, and parametric vibrations. Under the concentrated force, the strains of slender flexible structures will change suddenly along the axial direction. With locally densified measurement points, the present reconstruction method still works well for the strain concentration problem.

Shoreline Displacement, Coastal Environments and Human Subsistence in the Hanö Bay Region during The Mesolithic

Southern Scandinavia experienced significant environmental changes during the early Holocene. Shoreline displacement reconstructions and results from several zooarchaeological studies were used to describe the environmental changes and the associated human subsistence and settlement development in the Hanö Bay region of southern Sweden during the Mesolithic. GIS-based palaeogeographic reconstructions building on shoreline displacement records from eastern Skåne and western Blekinge together with a sediment sequence from an infilled coastal lake were used to describe the environmental changes during five key periods. The results show a rapid transformation of the coastal landscape during the Mesolithic. During this time, the investigated coastal settlements indicate a shift towards a more sedentary lifestyle and a subsistence focused on large-scale freshwater fishing. The development of permanent settlements coincided with an extended period of coastline stability and the development of rich coastal environments in a more closed forest vegetation. This study provides a regional synthesis of the shoreline displacement, coastal landscape dynamics and settlement development during the Mesolithic. It also demonstrates a new way of combining zooarchaeological and palaeoecological approaches, which can produce multi-faceted and highly resolved palaeoenvironmental reconstructions in a wide range of settings.

Displacement Reconstruction Using Acceleration Time History Measured by Seismic Acceleration Sensor Installed on the Center of Main Girder of Cable-stayed Bridge: Case Study on Pohang Earthquake

Displacement Reconstruction Using Acceleration Time History Measured by Seismic Acceleration Sensor Installed on the Center of Main Girder of Cable-stayed Bridge: Case Study on Pohang Earthquake

Effect of Linewidth Enhancement Factor on Fringe in a Self-Mixing Signal and Improved Estimation of Feedback Factor in Laser Diode

The optical output power of a laser diode is modulated by the self-mixing effect when the optical beam is back-reflected or back-scattered into the laser cavity by a target. The optical feedback factor C is the most important one that defines the feature of the self-mixing signals (SMSs). And the estimation of C is indispensable for the displacement reconstruction by the phase unwrapping method because it is impossible to reconstruct the displacement with sub-wavelength resolution, provided the exact value of C is unknown. Unfortunately, C is subject to constant change during the measurement and, what is worse; its estimation is usually very time-consuming. This paper studies the feature of a high and low fringe of SMSs in moderate and strong feedback regime and the effect of the feedback factor and the linewidth enhancement factor on the fringes and presents a simple approach to the estimation of C when C > 1.5 based on the behavioral model proposed by Plantier et al. In particular, the novel approach enables fast direct estimation of C because it is based on analytic relations between C and the amplitudes of the high and low peak in SMSs.

A Modal‐Based Kalman Filter Approach and OSP Method for Structural Response Reconstruction

The objective of the work is experimental validation and optimal experimental design for structural response reconstruction. A modal‐based Kalman filter approach based on excitation identification Kalman filter is proposed for response reconstruction and excitation estimation of structures by using noisy acceleration and strain measurements. Firstly, different filters are introduced and discussed. Secondly, to avoid single type sensors, a displacement reconstruction based on modal method is introduced into the proposed approach. Thirdly, the backward sequential algorithm is given to obtain the optimal sensor locations. It is shown that the proposed method can avoid the divergency in the estimated process of excitation and displacements as a result of incomplete measurements. Reasonable estimates of strains, displacements, velocities, accelerations, and excitations of structures can be accomplished with few acceleration sensors and strain gauges.

Vibration Information Acquisition and Representation Control Strategy for Construction Vehicle Driver Seat

Vibration information acquisition and representation control strategy in the experiment of construction of vehicle driver seat are investigated in this study. An improved adaptive algorithm of multisensor attitude data fusion is proposed. The nonlinear equations of vehicle attitude quaternions are constructed by using the test information of accelerometers and magnetometers. Then, a complementary filter is used to fuse the obtained attitude with gyroscope information to obtain attitude information during vehicle travel. Weight matrix and filter coefficients in the algorithm are adjusted with vehicle motions to ensure accuracy of attitude measurement under static, low‐, and high‐acceleration conditions. The vehicle vibration displacement information is reconstructed by the low‐frequency attenuation integration method on the basis of attitude measurement to inhibit integral trend items and reduce vibration displacement reconstruction errors. The three‐state controller is designed to control a six‐degree‐of‐freedom hydraulic simulated vibration test bed, and the obtained vibration signal is used as an excitation signal to perform a vibration representation control test. Finally, results verify that the proposed method demonstrates favourable data fusion and representation accuracy.

A Modal Expansion Method for Displacement and Strain Field Reconstruction of a Thin-Wall Component During Machining

Machining complex thin-wall components (such as compressor disks and casings in aircraft engines) has been a challenging task, because workpiece deformations and vibrations not only compromise the surface integrity, but also induce residual stresses in the final products. This paper offers a physics-based method that accounts for the damping effects and external loads for reconstructing the dynamic displacement and strain fields of a thin-wall workpiece in real time with noncontact displacement measurements during machining. Given that part dynamic behaviors can be characterized by superposition of mode shapes, the time-varying displacement and strain fields are reconstructed with modal coefficients that are updated in real time using in situ measurements. The reconstruction method has been numerically verified with finite-element analyses with the sensor locations optimized using a genetic algorithm; both static and dynamic field reconstructions are analyzed. Tradeoffs between the number of sensors and the reconstruction efficiency in terms of computation time and error are discussed. The method has been evaluated experimentally on a lathe machine testbed, where the dynamics of the distributed physical fields have been successfully captured and analyzed, demonstrating its practicality as a real-time tool for continuously monitoring the displacement and strain distributions across a disk workpiece during machining.

Simultaneous Self-Sensing of Displacement and Force for Soft Dielectric Elastomer Actuators

This paper presents a novel self-sensing method for soft actuators based on dielectric elastomer (DE) membranes. The proposed self-sensing scheme permits the reconstruction of both membrane force and displacement during actuation, based on voltage and current measurements only. The simultaneous self-sensing of displacement and force allows one to implement interaction control strategies without the need for additional electro-mechanical transducers. To achieve this goal, an online estimation algorithm based on recursive least squares is implemented to reconstruct the membrane capacitance from voltage and current measurements. Subsequently, mathematical models are developed to relate the capacitance to membrane displacement and force. Several modeling approaches are compared, ranging from physics-based to black box ones (i.e., Hammerstein–Wiener models and neural networks), in order to evaluate which strategy maximizes the estimation accuracy. After discussing the complete self-sensing algorithm, experimental validation is performed on a prototype consisting of a cone DE membrane.

Sternocleidomastoid-Clavicle Myoosseus Flap in Patient with Plate Displacement Post Resection and Reconstruction of Ameloblastoma

Background: ameloblastoma is a common tumor found in head and neck disorder. The definitive treatment include resection of tumor and reconstruction for filling the large defect which left after tumor resection. The reconstruction option which can be done is flap method. In this case, we used sternocleidomastoid-clavicle myoosseus flap in our patient with post traumatic plate displacement post resection and reconstruction of ameloblastoma. Case: a 22-year-old woman presented with unstability of jaw after hitting her chin to the table since 3 days prior to admission. On 2011, she had history of ameloblastoma which got resected and reconstructed with fibular graft and plate in the same year. While the plate seemed to be broken, she was managed with plate removal and reconstruct with sternocleidomastoid-clavicle myoosseus flap. Post operation, patient managed with gradual diet from liquid to solid. Observation Post Operation Day (POD) 3, flap is vital. Patient is discharged on POD 7 and visit as outpatient every 3-5 days until POD 14. Finally, we remove the suture, operation scar is good, and the flap is vital during one year follow up. Conclusion: sternocleidomastoid-clavicle myoosseus flap is practical and safe procedure, which can be used as alternative option in mandible reconstruction.

Interactive Correction of the Long-Period Trend in the Deconvolution Algorithm of Seismic Records

Ground displacement reconstruction is an ill-posed problem. Therefore, additional assumptions that ensure the stability of the resulting solution have been used to solve it. Interactive correction of the trend in the time domain, which makes it possible to remove a group of long-period trends from the seismic record without repeating the procedure, can be used as an alternative to the regularization of the solution in the deconvolution algorithm. Interactive trend correction is used within the proposed criterion. In the paper, the algorithm for calculating accelerograms from velocigrams with an integrated procedure for the interactive correction of the long-period trend has been given. The efficiency of the algorithm, which is based on the relationship of the differential equation of motion of the velocimeter pendulum to the true acceleration of the foundation bed, has been shown experimentally.

Silicone phantom validation of breast cancer tumor detection using nominal stiffness identification in digital imaging elasto-tomography (DIET)

Abstract Background and objective Cancerous tumors exhibit considerably higher stiffness than healthy breast tissues. This research develops a hysteresis loop analysis detection method for breast cancer diagnosis, which is validated using silicone phantom tests to provide an initial proof of concept of the overall DIET diagnostic approach. Methods Steady state sinusoidal displacements induced by mechanical actuation are captured using the DIET system for 4 silicone breast phantoms (1 homogeneous “healthy”; 3 with 10–20 mm stiffer inclusion “tumors” at different locations). Hysteresis loops for each measured reference point on the breast surface (N≈14,500/phantom) are constructed from the measured displacements and a calculated mass normalized restoring force. The distribution of nominal elastic stiffness over breast surface is estimated using a hypothesis test and regression analysis. A small motion threshold, Δ d , is used to reduce errors in identified elastance and its values determined from sensitivity analysis. Results Sensitivity analysis shows displacement reconstruction errors from very small motions can be eliminated using a threshold Δ d = 6 μ m to clearly reduce errors in identified nominal elastance. Results for all 4 phantoms indicate stiffer inclusions induce a greater number of reference points with stiffness ≥2 × higher in the segment with the inclusion than the nominal stiffness in the “healthy” segments in the x , y and total net 2D displacement directions. Therefore, the presence of a stiffer “tumor” inclusion is automatically detected and located by comparing the nominal stiffness to a calculated threshold, k t . Inclusion segments are finally localized algorithmically using an inclusion indicator, K index . Conclusions The overall results validate the capability of the proposed method to accurately detect and locate a stiff inclusion in typical, representative silicone breast phantoms without misidentifying other regions or a healthy no-inclusion phantom in the non-invasive DIET system. The methods are entirely generalizable to human clinical data from a DIET system, and the results justify such clinical trials.

On the Efficient Reconstruction of Displacements in FETI Methods for Contact Problems

The final step in the solution of contact problems of elasticity by FETI-based domain decomposition methods is the reconstruction of displacements corresponding to the Lagrange multipliers for ''gluing'' of subdomains and non-penetration conditions. The rigid body component of the displacements is usually obtained by means of a well known but quite complex formula, the application of which requires reassembling and factorization of some large matrices. Here we propose a simple formula which is applicable to many variants of the FETI based algorithms for contact problems. The method takes a negligible time and avoids reassembling or factorization of any matrices.

Sensitivity Analysis for Stiffness Identification Using a DIET Breast Cancer Screening System

Cancerous tumors exhibit significantly higher stiffness than healthy breast tissues. a hysteresis loop analysis method is used to identify the nominal elastic stiffness in different horizontal directions for breast cancer diagnosis in a Digital Imaging Elasto-tomography (DIET) screening system. The sensitivity of the method to measurement errors from the DIET system is first evaluated using a homogeneous healthy phantom with different camera angles. The identification method is then validated against 4 phantoms with stiffer inclusions of 10-20mm diameter over a range of actuation frequencies. Results show displacement reconstruction errors from very small motion can be eliminated by using a threshold ∆d to significantly reduce errors in identified nominal elastane. The stiffer inclusion induced a greater number of reference points with higher stiffness in the inclusion segment than other segments in x and y directions. The presence of a stiffer “tumor” inclusion is detected by comparing the nominal stiffness to an automatically defined threshold, kt. Inclusion segments can then be localized using an inclusion indicator, Kindex. The overall results validate the method is capable of providing robust estimations of nominal stiffness over a realistic range of actuation frequencies, and inclusion sizes and angle for the DIET concept.

Measurement of absolute displacement based on dual-path submicron-aperture fiber point-diffraction interferometer

The measurement of three-dimensional absolute displacement within large range can be achieved with submicron-aperture fiber point-diffraction interferometer (SFPDI), in which the numerical iterative algorithm for displacement reconstruction and point-diffraction wavefront determine the achievable measurement accuracy, reliability and efficiency of the system. To avoid the poor measurement accuracy in the lateral direction parallel to the fringe direction in the SFPDI with only one fiber pair, a dual-path SFPDI (DP-SFPDI) based on modified fast searching particle swarm optimization (PSO) algorithm is proposed to realize the rapid and accurate measurement of three-dimensional absolute displacement. Based on the DP-SFPDI with two submicron-aperture fiber pairs and modified PSO method, the measurement reliability, efficiency and accuracy in all the three dimensions of the system are significantly improved, making it more feasible for practical application. The effect of point-diffraction wavefront error on the measurement is analyzed. Both the numerical simulation and comparison experiments have been carried out to demonstrate the accuracy and feasibility of the proposed DP-SFPDI system, high measurement accuracy, convergence rate and efficiency have been realized with the proposed method.

Structural health monitoring of cylindrical bodies under impulsive hydrodynamic loading by distributed FBG strain measurements

Various mechanical, ocean, aerospace and civil engineering problems involve solid bodies impacting the water surface and often result in complex coupled dynamics, characterized by impulsive loading conditions, high amplitude vibrations and large local deformations. Monitoring in such problems for purposes such as remaining fatigue life estimation and real time damage detection is a technical and scientific challenge of primary concern in this context. Open issues include the need for developing distributed sensing systems able to operate at very high acquisition frequencies, to be utilized to study rapidly varying strain fields, with high resolution and very low noise, while scientific challenges mostly relate to the definition of appropriate signal processing and modeling tools enabling the extraction of useful information from distributed sensing signals.Building on previous work by some of the authors, we propose an enhanced method for real time deformed shape reconstruction using distributed FBG strain measurements in curved bodies subjected to impulsive loading and we establish a new framework for applying this method for structural health monitoring purposes, as the main focus of the work. Experiments are carried out on a cylinder impacting the water at various speeds, proving improved performance in displacement reconstruction of the enhanced method compared to its previous version. A numerical study is then carried out considering the same physical problem with different delamination damages affecting the body. The potential for detecting, localizing and quantifying this damage using the reconstruction algorithm is thoroughly investigated. Overall, the results presented in the paper show the potential of distributed FBG strain measurements for real time structural health monitoring of curved bodies under impulsive hydrodynamic loading, defining damage sensitive features in terms of strain or displacement reconstruction errors at selected locations along the structure.

A Surface Vibration-based Method for Tumor Detection of Women Breast in a DIET System

This paper presents a hysteresis loop analysis (HLA) method based on dynamic force-displacement relationship to detect and localize cancerous tumors that exhibit significantly higher stiffness than soft healthy tissues in women breast. Steady state sinusoid displacements induced by mechanical actuation for 2 silicone phantoms (1 homogeneous “healthy”; 1 with 20mm stiffer inclusion “tumor”) are captured using a non-invasive Digital Image Elasto Tomography (DIET) system. Hysteresis loops for each measured reference point across the phantom surface are reconstructed using the measured displacement and a calculated mass normalized restoring force. The distribution of the elastic nominal stiffness over the breast surface is estimated using an F-type hypothesis test and regression analysis. The sensitivity of the method to measurement errors from the DIET system is evaluated using a homogeneous healthy phantom with different camera angles. Results show displacement reconstruction errors from very small motion can be eliminated by using a threshold ∆d to significantly reduce errors in identified nominal elastance. The stiffer inclusion induced a greater number of reference points with higher stiffness in the inclusion segment than other segments in the x and y directions, while a consistent distribution of stiffness for the homogeneous control phantom was identified. The overall results show the capability of the method to accurately detect and locate the inclusion in typical, representative silicone breast phantoms without misidentifying other regions or a healthy no-inclusion phantom.

Multiple self-mixing interferometry for displacement measurement based on quadrature demodulation technique

To improve the accuracy of displacement measurements in self-mixing interferometry (SMI), a multiple self-mixing interferometry (MSMI) process that involves phase modulation is proposed. The phase is modulated using an electro-optic modulator that is placed in the external cavity. Phase demodulation is performed using the quadrature demodulation algorithm. In theory, the displacement reconstruction accuracy of MSMI is better than that of SMI, and this is demonstrated using simulations. A series of experiments are also conducted to confirm the effectiveness of the proposed method. The method is shown to meet the requirements for real-time high-precision measurements. In addition, the quadrature demodulation technique used does not involve complex computations.

A comparative study of techniques of distant reconstruction of displacement and strain fields using the DISTRESS simulator

Reconstruction and monitoring of displacement and strain fields is an important problem in engineering. We analyze the remote and non-obtrusive method of Digital Image Correlation (DIC) in 2D based on photogrammetry. The method involves covering the photographed surface with a pattern of speckles and comparing the images taken before and after the deformation. The analysis is based on a specially developed Digital Image Synthesizer To Reconstruct Strain in Solids (DISTRESS) Simulator to generate synthetic images of displacement and stress fields in two dimensions in order to investigate the intrinsic accuracy of the existing variants of DIC. We investigated the Basic DIC and a commercial software VIC 2d, both based on displacement field reconstruction with post processing strain determination based on numerical differentiation. We also investigated what we call the Extended DIC where the strain field is determined independently of the displacement field. While the Basic DIC is faster, the Extended DIC delivers the best accuracy. The speckle pattern is found to be playing a critical role in achieving high accuracy for DIC. Increase in the subset size for DIC does not significantly improves the accuracy, while the smallest subset size depends on the speckle pattern and speckle size. Increase in the overall image size provides more details but does not play significant role in improving the accuracy, while significantly increasing the computation cost. We observed that it is not reliable to measure very small strains using grayscale images in DIC. Thus, we propose Color DIC using color images and found that it improves the accuracy in measuring small strains.

Significados del espacio público en contextos de transformación por desastres socionaturales

Socio-natural disasters and reconstruction raise awareness of the built environment and generate narratives among the dwellers of affected communities. This is a process that combines different spatial meanings which, as in the case of major discourses on public space, is based on the signification given to the urban space and the conditioning of appropriation practices. This research analyzes the narrations provided by the victims of three socio-natural disasters that have affected Chile in recent years: the 2007 Tocopilla earthquake, the eruption of Chaiten in 2008 and the 2010 Maule earthquake and tsunami. In order to compile the meanings given to the public space by those who have experienced urban transformation processes as the consequence of displacement or post-disaster reconstruction, this research conducted 17 focus groups with 117 inhabitants from Chaiten, Constitucion, Dichato and Tocopilla. From a qualitative perspective, this contribution analyzes the narrations that establish a relationship among the different approaches to the public space: the public space as a lost place, the public space as an agent of civility and as the place to attain social justice.