Geometric Measurements Research Articles

Structural behaviour and design of press-braked S690 high strength steel angle section long columns

A testing and numerical modelling programme has been conducted to investigate the flexural buckling behaviour and resistance of press-braked S690 high strength steel angle section long columns. The testing programme adopted two press-braked S690 high strength steel equal-leg angle sections and included initial geometric imperfection measurements as well as twelve pin-ended column tests. The testing programme was accompanied by a numerical modelling programme, including a validation study, where finite element models were developed and validated against the test results, and a parametric study, where the validated finite element models were used to generate further numerical data over a wide range of cross-section dimensions and member effective lengths. The obtained test and numerical data were used to evaluate the existing design rules for press-braked S690 high strength steel angle section long columns, as specified in the North American specification, Australian/New Zealand standard and European code. The evaluation results revealed that the North American specification and Australian/New Zealand standard result in a high level of design accuracy and consistency, while the Eurocode leads to excessively conservative and scattered failure load predictions. Finally, a new design approach was proposed and shown to offer more accurate and consistent failure load predictions, with less calculation works, than the design codes.

Wide-viewing-zone Light-field Capturing Using Turtleback Convex Reflector

Light field cameras have been used for 3-dimensional geometrical measurement or refocusing of captured photo. In this paper, we propose the light field acquiring method using a spherical mirror array. By employing a mirror array and two cameras, a virtual camera array that captures an object from around it can be generated. Since large number of virtual cameras can be constructed from two real cameras, an affordable high-density camera array can be achieved using this method. Furthermore, the spherical mirrors enable the capturing of large objects as compared to the previous methods. We conducted simulations to capture the light field, and synthesized arbitrary viewpoint images of the object with observation from 360 degrees around it. The ability of this system to refocus assuming a large aperture is also confirmed. We have also built a prototype which approximates the proposal to conduct a capturing experiment in order to ensure the system’s feasibility.

WLTOG: An optimization approach for wild large‐range target omnidirectional geolocation based on monocular PTZ camera

AbstractThe pan‐tilt‐zoom (PTZ) cameras are increasingly popular in urban management and resource protection due to their omnidirectional coverage and reasonable cost. Traditionally, the research of monocular camera geolocation focuses on small‐range ones with a central projection camera under ideal conditions, making it challenging to meet the requirements of omnidirectional coverage and large‐range geolocation for PTZ cameras. In this article, a wild large‐range target omnidirectional geolocation (WLTOG) algorithm was proposed. Firstly, the WLTOG algorithm is used to transform the target in a single image to the camera's optical axis, thereby obtaining the camera posture value. After that, by using a high‐order overdetermined equation, it fits the nonlinear mapping relationship between multiple pairs of PTZ camera postures and the geospatial coordinates. At last, it realizes the bidirectional calculation between pixel coordinates and geospatial coordinates. The experimental PTZ camera is mounted on a communication tower in a wild environment. Therefore, this method can be utilized to construct an omnidirectional geolocation relationship that meets the requirements of omnidirectional geolocation within 945 m based on unknown accurate internal and external orientation elements. The WLTOG algorithm is conducive to the geometric measurement of video and GIS‐augmented video surveillance.

Hybrid welded T-section stub columns with Q690 flange and Q355 web: Testing, modelling and design

Comprehensive experimental and numerical investigations on hybrid T-section stub columns under compressive load were performed and are presented in this paper. The hybrid welded T-section stub columns comprise high strength steel Q690 flange and normal strength steel Q355 web. Material property studies were implemented through tensile coupon tests. Residual stress in membrane type was measured and recorded and its impact on structural performance was also assessed. Initial local geometric imperfection measurements were conducted for all the specimens. In conjunction with experimental studies, numerical investigation was performed to generate more test specimens extending the range of cross-section dimensions by which test data pool can be supplemented. The Eurocode of EN 1993-1-1, EN 1993-1-5 and EN 1993-1-12, the North American code of ANSI/AISC 360-16 and the Australian code of AS 4100 together with design approaches of Direct Strength Method and Continuous Strength Method were examined for its applicability for cross-section classification and compression resistance predictions of hybrid T-sections. Overall, the current specified limits were applicable for hybrid welded T-section and strength predictions from design codes were comparatively consistent and reliable. Strength predictions from Direct Strength Method and Continuous Strength Method were relatively appropriate though overly conservative predictions were provided for cross-section with large slenderness. In this study, modifications on the Direct Strength Method and Continuous Strength Method are proposed, which is shown to provide accurate predictions at cross-sectional level in a reliable manner.

Atherosclerotic Plaque Segmentation Based on Strain Gradients: A Theoretical Framework

Background: Atherosclerotic plaque detection is a clinical and technological problem that has been approached by different studies. Nowadays, intravascular ultrasound (IVUS) is the standard used to capture images of the coronary walls and to detect plaques. However, IVUS images are difficult to segment, which complicates obtaining geometric measurements of the plaque. Objective: IVUS, in combination with new techniques, allows estimation of strains in the coronary section. In this study, we have proposed the use of estimated strains to develop a methodology for plaque segmentation. Methods: The process is based on the representation of strain gradients and the combination of the Watershed and Gradient Vector Flow algorithms. Since it is a theoretical framework, the methodology was tested with idealized and real IVUS geometries. Results: We achieved measurements of the lipid area and fibrous cap thickness, which are essential clinical information, with promising results. The success of the segmentation depends on the plaque geometry and the strain gradient variable (SGV) that was selected. However, there are some SGV combinations that yield good results regardless of plaque geometry such as ▽εvMises+▽εrθ, ▽εyy+▽εrr or ▽εmin+▽εTresca. These combinations of SGVs achieve good segmentations, with an accuracy between 97.10% and 94.39% in the best pairs. Conclusions: The new methodology provides fast segmentation from different strain variables, without an optimization step.

Calibration of 3D scan trajectories for an industrial computed tomography setup with 6-DOF object manipulator system using a single sphere

In industrial x-ray computed tomography (CT), the application of more complex scan paths in comparison to the typical circular trajectory ( rotation of the measurement object) can extend the potential of CT. One way to enable such 3D scan trajectories is to use a 6-degrees-of-freedom (DOF) object manipulator system. In our case, a hexapod is mounted on top of the rotary table of a commercial CT scanner. This allows for adaptive tilting of the measurement object during the scan. For high accuracy, the geometry calibration of such setups is typically done using the x-ray projections of a calibrated multi-sphere object. Contrary to this, here, we demonstrate a procedure that is based on only a single sphere and can therefore experimentally be implemented with low effort. Using the intrinsic geometry parameters of the CT device as prior information, the hexapod coordinate system with respect to the CT machine coordinate system is determined by means of a one-step optimization approach. The resulting parameters are used to calculate projection matrices that enable the volume reconstruction for 3D scan trajectories. The method is validated using simulated x-ray images and experimental investigations including dimensional measurements. For the used setup, geometric measurement results for 3D scan trajectories that are calibrated with the presented method show in sum increased errors compared to the circular scans. A limited pose accuracy of the manipulator system is discussed as a potential cause. The results nevertheless indicate that the presented method is generally feasible for dimensional CT measurements provided that the pose accuracy is sufficient. The calibration procedure can therefore be a low-cost and easier to implement alternative compared to trajectory calibration methods based on multi-sphere objects, but with a tendency towards lower measurement accuracy. The methodology can in principle be transferred to different setups with 6-DOF manipulator systems, e.g. C-arm CT devices with a robot arm.

Revisiting digital twins: Origins, fundamentals, and practices

The digital twins (DT) has quickly become a hot topic since it was proposed. It appears in all kinds of commercial propaganda and is widely quoted by academic circles. However, the term DT has misstatements and is misused in business and academics. This study revisits DT and defines it to be a more advanced system/product/service modeling and simulation environment that combines most modern information communication technologies (ICTs) and engineering mechanism digitization and characterized by system/product/service life cycle management, physically geometric visualization, real-time sensing and measurement of system operating conditions, predictability of system performance/safety/lifespan, and complete engineering mechanisms-based simulations. The idea of DT originates from modeling and simulation practices of engineering informatization, including virtual manufacturing (VM), model predictive control, and building information modeling (BIM). On the basis of the two-element VM model, we propose a three-element model to represent DT. DT does not have its unique technical characteristics. The existing practices of DT are extensions of the engineering informatization embracing modern ICTs. These insights clarify the origin of DT and its technical essentials.

Validity of facial features’ geometric measurements for real-time assessment of mental fatigue in construction equipment operators

Operating construction equipment for extended periods of time may lead to mental fatigue and, as a result, an increased risk of human error-related accidents and jeopardized health problems for the operators. Therefore, to limit the risk of accidents and protect operators' wellbeing, their mental fatigue must be monitored reliably and in real time. Recently, many invasive technologies have been employed to alleviate this problem, but they entail the wearing of physical sensors, which may instigate irritation and discomfort. This study proposes a non-invasive mental fatigue monitoring method using geometric measurements of their facial features that does not require the operators to wear sensors on their body. The study further validates the proposed method by comparing it with wearable electroencephalography (EEG) technology to establish its ecological validity for construction equipment operators. To serve the purpose, a one-hour excavator operation by sixteen construction equipment operators was conducted on a construction site. Ground truth, brain activity using wearable EEG, and geometric measurements of facial features were extracted and analyzed at the baseline and every 20 min for one hour. A considerable temporal variation was found in the reported metrics (eye aspect ratio, eye distance, mouth aspect ratio, face area, and head motion) and were significantly correlated with ground truth and EEG metric. Furthermore, the brain visualization pattern obtained from EEG was also associated with the variations in the facial features. The findings of the study reveal that construction equipment operators’ mental fatigue can be monitored non-invasively using geometrical measurements of facial features.

Impact of the topology of urban streets on mobility optimization

Several natural and artificial structures and systems are somehow optimized for performing specific functionalities. The structure and topology of cities are no exception, as it is critically important to ensure effective access to the several resources as well as overall mobility. The present work addresses the important subject of improving the plan of a given city through the incorporation of avenues and other expressways such as bridges and tunnels. More specifically, we start with the topology of a real city and consider the incorporation of an expressway between any two locations in the city, keeping one location fixed and varying the angle of the other. The whole city area is covered in this manner, which allows us to derive a respective energy surface indicating the gain obtained regarding the average shortest path length for each of the possible situations. These surfaces therefore provide a complete picture of how much each city can be improved regarding minimal distances. Quite distinct surfaces have been obtained for 18 considered European cities. These surfaces are then characterized in terms of the number of local extrema and respective spatial complexity, expressed in terms of a raggedness measurement. Measurements are also obtained respectively to the geometry and topology of the considered cities. It is shown that the shortest path gain depends strongly on some of the considered measurements, especially lacunarity and transitivity. Interestingly, the intricacy of the energy surfaces resulted in relatively little correlation with the topological and geometrical measurements.

Evaluation of computed tomography dose profiler probe for computed tomography dose index and geometric efficiency measurements

The purpose of this study was to evaluate the performance of solid-state sensor based computed tomography dose profiler (CTDP) probe for measurement of standard computed tomography dose metric CTDI100 and free in air geometric efficiency for various beam widths available in a 128-slice CT scanner and also to estimate the efficiency of CTDI100 metric. The response accuracy of CTDP probe was verified using a standard 100 mm long ionization chamber. The geometric efficiency measurements performed by the CTDP probe were validated using XR-QA2 radiochromic film measurements. The efficiency of CTDI100 metric was assessed by calculating the ratio of CTDI100 measured in the center hole position to CTDI∞ measured in the same position of both head and body phantoms. The weighted CTDI values derived from CTDI100 measured by the CTDP probe showed an average difference of 8% from ionization chamber measured values. The efficiency of CTDI100 metric estimated using CTDP probe and 150 mm long phantoms was in the range of 82% to 86% and 76% to 80% for head and body phantom measurements respectively. The differences in the geometric efficiency values for various beam settings and tube voltages measured by the CTDP probe and films were within 7%. Taken together, the results of this study proved that unlike the 100 mm long ionization chamber, the CTDP probe can be efficiently used to determine CTDI for any length over which dose integration is desired and also measure geometric efficiency of MDCT scanners for various beam widths in helical mode of operation.

Machine-Learning-Inspired Workflow for Camera Calibration.

The performance of modern digital cameras approaches physical limits and enables high-precision measurements in optical metrology and in computer vision. All camera-assisted geometrical measurements are fundamentally limited by the quality of camera calibration. Unfortunately, this procedure is often effectively considered a nuisance: calibration data are collected in a non-systematic way and lack quality specifications; imaging models are selected in an ad hoc fashion without proper justification; and calibration results are evaluated, interpreted, and reported inconsistently. We outline an (arguably more) systematic and metrologically sound approach to calibrating cameras and characterizing the calibration outcomes that is inspired by typical machine learning workflows and practical requirements of camera-based measurements. Combining standard calibration tools and the technique of active targets with phase-shifted cosine patterns, we demonstrate that the imaging geometry of a typical industrial camera can be characterized with sub-mm uncertainty up to distances of a few meters even with simple parametric models, while the quality of data and resulting parameters can be known and controlled at all stages.

Local–flexural interactive buckling behaviour and resistance of press-braked stainless steel slender channel section columns

The present paper reports experimental and numerical studies of the local–flexural interactive buckling behaviour and resistance of press-braked stainless steel slender channel section columns. A testing programme was firstly performed, including tensile coupon tests, initial geometric imperfection measurements and ten pin-ended column tests. The pin-ended column test setup, procedures and results were fully reported and analysed. The progression of local buckling and flexural buckling was discussed in detail. Following the testing programme, a numerical modelling programme was conducted, where finite element models were developed to replicate the test responses and then employed to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and member effective lengths. The obtained test and numerical data were employed to assess the accuracy of the relevant design rules for press-braked stainless steel slender channel section columns, as set out in the European code, American specification and Australian/New Zealand standard. The assessment results revealed that the European code leads to conservative and scattered interactive buckling resistance predictions, while the American specification and Australian/New Zealand standard result in many unsafe and scattered interactive buckling resistance predictions. A new design approach was then developed, based on the Eurocode column buckling curve and the continuous strength method, and shown to lead to accurate, consistent and safe interactive buckling resistance predictions for press-braked stainless steel slender channel section columns. The reliability of the new design approach was confirmed by means of statical analyses. Besides, the relevant design rules for press-braked carbon steel slender channel section columns, as given in the North American specification, were assessed, and shown to result in unsafe though consistent interactive buckling resistance predictions, when used for their stainless steel counterparts.

Microstructure, Mechanical Properties and Cross‐sectional Behaviour of Additively Manufactured Stainless Steel Cylindrical Shells

AbstractPowder bed fusion (PBF) is an additive manufacturing method that enables complex metallic components to be manufactured with high precision. The microstructure, mechanical properties and cross‐sectional behaviour of PBF additively manufactured stainless steel circular hollow sections are investigated through experiments in this paper, with a view to applications in construction. The experimental programme included tensile coupon tests, microstructural characterisation, initial geometric imperfection measurements and compression tests on PBF 316L stainless steel cylindrical shells with large diameter‐to‐thickness (D/t) ratios. Advanced measurement methods – 3D laser scanning and digital image correlation, were employed to measure the specimen geometries prior to testing and deformation fields during testing, respectively. The possible anisotropy in mechanical properties was examined through tensile coupon tests and correlated with the underlying microstructural and textural features. Compression tests were performed to investigate the resistance against local buckling of thin‐walled cylindrical shells produced by PBF. All cylindrical shells buckled below their yield loads with a chequerboard failure mode and revealed the anticipated trend of reducing capacity relative to the yield load with increasing local slenderness, reflecting the increasing susceptibility to local buckling.

Behaviour of S960 Ultra‐high Strength Steel Press‐braked Channel Sections

AbstractThis paper reports a comprehensive experimental and numerical study of the cross‐sectional behaviour and resistances of press‐braked S960 ultra‐high strength steel (UHSS) channel section structural members. The experimental study was conducted on eight different ultra‐high strength steel plain channel sections, and comprised material testing, initial local geometric imperfection measurements, as well as a total of 10 stub column tests and 20 four‐point bending tests performed about the minor principal axes in both the ‘u’ and ‘n’ orientations. The experimental study was then supplemented by a finite element (FE) simulation programme, in which FE models were firstly developed to replicate the test structural responses and subsequently used to generate further numerical data over a wide variety of cross‐section sizes. On the basis of the experimental and numerical results, the assessment of the applicability of the codified provisions and formulations, established in the European code, to the design of S960 UHSS channel section stub columns and beams was conducted.

Automated Posture Positioning for High Precision 3D Scanning of a Freeform Design using Bayesian Optimization

Three-dimensional scanning is widely used for the dimension measurements of physical objects with freeform designs. The output point cloud is flexible enough to provide a detailed geometric description for these objects. However, geometric accuracy and precision are still debatable for this scanning process. Uncertainties are ubiquitous in geometric measurement due to many physical factors. One potential factor is the object’s posture in the scanning region. The posture of target positioning on the scanning platform could influence the normal of the scanning points, which could further affect the measurement variances. This paper first investigates the geometric and spatial factors that could potentially influence scanning variance. This functional relationship is modeled as a Bayesian extreme learning model, which is later utilized to find the object’s optimal posture for variance reduction. A Bayesian optimization approach is proposed to solve this minimization problem. Case studies are presented to validate the proposed methodology.

An approach for monitoring prefabricated building construction based on feature extraction and point cloud segmentation

PurposeConstruction schedule delays and quality problems caused by construction errors are common in the field of prefabricated buildings. The effective monitoring of the construction project process is one of the key factors for the success of a project. How to effectively monitor the construction process of prefabricated building construction projects is an urgent problem to be solved. Aiming at the problems existing in the monitoring of the construction process of prefabricated buildings, this paper proposes a monitoring method based on the feature extraction of point cloud model.Design/methodology/approachThis paper uses Trimble X7 3D laser scanner to complete field data collection experiments. The point cloud data are preprocessed, and the prefabricated component segmentation and geometric feature measurement are completed based on the PCL platform. Aiming at the problem of noisy points and large amount of data in the original point cloud data, the preprocessing is completed through the steps of constructing topological relations, thinning, and denoising. According to the spatial position relationship and geometric characteristics of prefabricated frame structure, the segmentation algorithm flow is designed in this paper. By processing the point cloud data of single column and beam members, the quality of precast column and beam members is measured. The as-built model and as-designed model are compared to realize the visual monitoring of construction progress.FindingsThe experimental results show that the dimensional measurement accuracy of beam and column proposed in this paper is more than 95%. This method can effectively detect the quality of prefabricated components. In the aspect of progress monitoring, the visualization of real-time progress monitoring is realized.Originality/valueThis paper proposed a new monitoring method based on feature extraction of the point cloud model, combined with three-dimensional laser scanning technology. This method allows for accurate monitoring of the construction process, rapid detection of construction information, and timely detection of construction quality errors and progress delays. The treatment process based on point cloud data has strong applicability, and the real-time point cloud data transfer treatment can guarantee the timeliness of monitoring.

Determination of as-built properties of fiber reinforced polymers in a wind turbine blade using scanning electron and high-resolution X-ray microscopy

The fiber volume fraction (FVF) and porosity in fiber reinforced polymers (FRPs) depends strongly on the manufacturing process. These parameters influence the mechanical properties and thus the performance of an FRP. For this research, an epoxy-pre-impregnated glass FRP was investigated to determine the FVF and matrix mass fraction taking into consideration all material constituents, including sizing, stitching thread, as well as the porosity, the area density and the fiber orientations of each lamina, the filament fiber diameter, and the inter-laminar void size and shape. Therefore, samples from a commercially manufactured wind turbine rotor blade were experimentally investigated using scanning electron (SEM) and high-resolution X-ray microscopy (micro-CT), as well as a standardized calcination method and geometric measurements. Post-processing techniques such as thresholding and edge detection were used to analyze the images. There was good FVF agreement between SEM and the method of calcination. Micro-void cross-sectional shapes were well captured by SEM while meso- and macro-voids were volumetrically resolved with a reproducible void size distribution for two sample volumes by micro-CT.

Experimental and numerical investigations of S960 ultra-high strength steel slender welded I-section columns failing by local–flexural interactive buckling

The present paper reports experimental and numerical investigations into the local–flexural interactive buckling behaviour and resistance of S960 ultra-high strength steel slender welded I-section columns. A testing programme was firstly conducted and included initial geometric imperfection measurements and ten pin-ended column tests. The pin-ended column test setup, procedures and results were fully reported and analysed. The progression of local buckling and flexural buckling was discussed. Following the testing programme, a numerical modelling programme was conducted, where finite element models were developed to replicate the test structural responses and then employed to perform parametric studies to generate further numerical data. It is worth noting that the current European code and American specification are only applicable to steel structures with material yield strengths up to 700 MPa (or 690 MPa). Regarding the design of slender welded I-section columns failing by local–flexural interactive buckling, both codes adopt the same concept — combined use of effective width method to account for local buckling and buckling curve to account for flexural buckling. The obtained test and numerical data were employed to assess the applicability of the codified design rules to S960 ultra-high strength steel slender welded I-section columns. The assessment results revealed that the European code leads to conservative interactive buckling resistance predictions, mainly due to the use of conservative buckling curve, while the American specification yields a good level of design accuracy and consistency. Finally, a revised Eurocode design approach was proposed and shown to result in more accurate and consistent interactive buckling resistance predictions for S960 ultra-high strength steel slender welded I-section columns.

Method for extrinsic parameters calibration of Pan-Tilt camera using intersecting lines from two images

Pan-Tilt (PT) cameras are widely used in video surveillance because of larger field of view. The camera’s intrinsic parameters remain unchanged and the extrinsic parameters calibration of the PT camera should be addressed when it comes to visual geometric measurement. In this paper, the unknown parameters of the PT camera are only reduced to the rotation angles in horizontal and vertical directions, and a method for extrinsic parameters calibration using intersecting lines from two images is presented. An improved feature point matching algorithm is proposed to obtain the natural feature point pairs between images acquired before and after rotation, and direct linear transformation method is employed to obtain the rough rotation angles by using the natural feature point pairs. Based on rotation constraint, the optimization function established by the projections of the intersections of the straight lines in natural scene is then used to calculate the refined extrinsic parameters. Computer simulations and real experiments prove the effectiveness of the improved feature point matching algorithm and the proposed calibration method. Experimental data reflects the extrinsic parameters estimated by our method are close to reference values from high-precision stepper motors, and the average deviation of Euler angles representing rotation matrix and translations from our method relative to reference values does not exceed 0.03° and 0.27 mm, respectively.

Atmospheric gaseous aromatic hydrocarbons in eastern China based on mobile measurements: Spatial distribution, secondary formation potential and source apportionment

Monocyclic aromatic hydrocarbons (MAHs) and polycyclic aromatic hydrocarbons (PAHs) are both well known as hazardous air pollutants and also important anthropogenic precursors of tropospheric ozone (O3) and secondary organic aerosols (SOA). In recent years, there have been intensive studies covering MAHs emission from various sources and their behavior under stimulated photochemical conditions. Yet in-situ measurements of PAHs presence and variations in ambient air are sparse. Herein we conducted large geometrical scale mobile measurements for 16 aromatic hydrocarbons (AHs, including 7 MAHs and 9 PAHs) in eastern China between October 27 and November 8, 2019. This unique dataset has allowed for some insights in terms of AHs concentration variations, accompanying chemical composition, source contributions and spatial distributions in eastern China. In general, AHs showed a clear concentration variability between the south and the north of the Yangtze River Delta (YRD). The concentrations of PAHs were approximately 9% of AHs, but contributed 23% of SOA formation potential. Source apportionment via positive matrix factorization (PMF) model revealed that industrial processes as the largest source (44%) of observed AHs, followed by solvent usage (21%), vehicle exhaust (19%), coal combustion (11%) and coking processes (6%). In the perspective of PAHs sources, coal combustion emissions were identified as the dominating factor of a share of 41%–52% in eastern China. Our findings complemented the simultaneously monitoring information of PAHs and MAHs in eastern China, revealed the importance of PAHs to SOA formation and highlighted the necessity of formulating strategies to reduce emissions from anthropogenic sources and reduce risks to human health.