Geometry Deviations Research Articles

Fully automated generation of parametric BIM for MEP scenes based on terrestrial laser scanning data

As-built building information modeling (BIM) has gained much attention in mechanical, electrical and plumbing (MEP) systems for better facility management. To create as-built BIMs, laser scanning technology is widely used to collect raw data due to its high measurement speed and accuracy. Currently, as-built models are mostly drawn by experienced personnel in BIM modeling software with point cloud data as reference, which is labor intensive and time consuming. This study presents a fully automated approach to converting terrestrial laser scanning data to well-connected as-built BIMs for MEP scenes. According to the geometry complexity, MEP components are divided into regular shaped components and irregular shaped components. A 2D to 3D analysis framework is developed to detect objects and extract accurate geometry information for the two categories of MEP components. Firstly, the MEP scene is divided into slices on which rough geometry information of components' cross sections is extracted. Then, the extracted information on different slices is integrated and analyzed in 3D space to verify the existence of MEP components and obtain refined geometry information used for modeling. Following the detection stage, an MEP network construction approach is developed for MEP components connection and position fine-tuning. Finally, the extracted geometry information and connection relationships are imported into Dynamo to automatically generate the parametric BIM model. To validate the feasibility of the proposed technique, experiments were conducted with point clouds acquired from three scenes in Hong Kong. A comprehensive assessment is presented to evaluate the as-built model quality with three indices: retrieval rate, geometry parameter accuracy and deviation from point clouds to as-built model. The experiment results show that the proposed technique could successfully transform laser scanning data of MEP scenes to as-built BIMs with sufficient accuracy for facility management purpose.

Lightweight nodal parts for large space truss structures enabled by SLM: modelling, manufacturing, and testing

Selective laser melting (SLM), as a method of metal additive manufacturing, has developed rapidly over the last years to become a breakthrough technology capable of upending the way that products from aerospace and other various industrial sectors are not only fabricated but also designed. The purpose of this paper is to investigate the potential benefits and drawbacks of SLM implementation in the frame of design and development of components for large space lightweight structures. The three types of the most common structural engineering solutions are compared, based on the different manufacturing techniques and materials. The paper describes the results of the measurement of the shape of fittings after fabrication and cryogenic temperature-cycle tests. An extra option for the weight reduction of structures is given via the implementation of the topology optimization method. Three challenges have been identified, including quality of surfaces, deviation of geometry, residual internal stresses. This work shows the possibility to solve this topical issue by using a waterjet inspection technique and represents one of the first attempts for its implementation to perform a fast evaluation of mechanical properties of structural materials manufactured using SLM.

Application of the geometrical models, graphs and elements of robots kinematics as the basic elements of the unified methodology for assurance of accuracy calculating stage in precision axisymmetric products assembling

The accuracy standards of engineering products, namely geometric parameters, such as tolerances, geometry deviations and surfaces form deviations, are indicative of parts and assembly units quality. The article discusses the integrated approach to the study of accuracy parameters using geometrical models, graphs and elements of robots kinematics as the basic elements of the unified methodology for assurance of accuracy calculating stage in precision axisymmetric products assembling. The integrated approach is to combine the developed techniques into a unified methodology for assurance of accuracy calculating stage in precision axisymmetric products assembling. The implementation of this approach is carried out by a phased study of the construction for all accuracy parameters in in a common reporting format based on key provisions Obtained results suggest quickly make changes to the studied design based on the phased analysis according with the developed integrated approach.

СТАТИСТИЧНИЙ АНАЛІЗ РЕЗУЛЬТАТІВ ГЕОДЕЗИЧНИХ ЗЙОМОК КОЛІЙ МОСТОВИХ КРАНІВ У ВИРОБНИЧИХ БУДІВЛЯХ

Abstract. The studies were carried out in order to develop effective methodology for the statistical analysis of the results of geodetic surveys of the rails of overhead cranes. The findings will provide generalization of the measurement results, demonstration of their changes over time, as well as comparison with the permissible values of deviations from the design position. The analysis includes the results of geodetic surveys of the position of the rails of overhead cranes in machine-building shops during four years. The position of the heads of the crane rails was determined using a level, a transit theodolite, and a laser sight. In accordance with the requirements of regulatory documents for the operation of overhead cranes, three parameters of the position of the crane rail heads were controlled: the height difference on adjacent pillars of the same row; height difference on pillars of different rows in one transverse frame; deviation of the distance between the rails from the design value. The controlled parameters are random variables that should be analyzed by statistical methods. Deviations of the distance between the axes of the crane rails from the design value are presented in the form of a random variable with the normal distribution law. The differences in the elevation marks of the heads of the crane rails, which are monitored without taking into account the sign, are described by the distribution law of the modulus of a random variable. As a generalized characteristic of the state of crane rails, it is proposed to use the probabilities of horizontal and vertical deviations of the crane rails beyond maximum permissible values established by the norms. Based on the results of the research, conclusions were drawn about the need for systematic control of the position of overhead crane rails by geodetic methods, the applicability of the above distributions for the probabilistic description of deviations of crane rails from the design position, as well as the feasibility of using the probability of deviations of the crane rails geometry beyond the permissible values established by the norms.

Modelling imperfections in unreinforced masonry structures: Discrete element simulations and scale model experiments of a pavilion vault

The structural assessment of doubly-curved vaulted masonry structures, such as pavilion vaults, poses challenges specific to their high degree of indeterminacy. Two-dimensional equilibrium analysis methods may provide a lower bound of load or displacement capacity, but they do not accurately describe the three-dimensional (3D) behaviour of these structures, particularly when shear deformation (e.g. sliding) is important. Therefore, discrete element modelling (DEM) methods, which can effectively simulate 3D load re-distribution, have been used to investigate support displacement capacity and corresponding 3D collapse mechanisms. DEM analyses are usually conducted on perfect digital geometries. Meanwhile, both real structures and small-scale physical models have implicit assembly and fabrication imperfections, which may significantly alter their response. The present paper aims to investigate the influence of geometrical and mechanical imperfections by comparing DEM analyses with the results obtained from tests on a scale model. In particular, a new method to simulate imperfections within the DEM framework is proposed, and a DEM parametric analysis is compared to the measured behaviour of a 3D-printed scale model of a pavilion (or cloister) vault on spreading supports. The influence of both mechanical imperfections andgeometrical imperfections, due to element geometry deviations or imprecision of the assembly process, have been investigated. Based on these analyses, the three-dimensional behaviour of a pavilion vault subjected to horizontal displacement of the supports is described, and the variability of results due to imperfections is demonstrated. A good agreement between DEM analyses and 3D-printed scale model tests is achieved, in terms of crack patterns and mechanisms. Geometrical imperfections did change the load paths within the vault, as expected, and also influenced the displacement capacity.

Estimating umbilical cord flow resistance from measurements of the whole cord

Measuring umbilical blood pressure in utero is challenging and for this reason non-invasive methods are required. However, the total vessel blood pressure drop can be estimated using numerical and empirical results by studying the mechanics of fluids in coiled and straight tubes. Two key findings emerge from such an analysis. Firstly, the total pressure drop along a vessel at a given blood flow-rate depends on both the tightness of the coils and the total cord length. Relatively short and straight cords exhibit low pressure, while long, tightly coiled cords with large width exhibit high pressure. It follows that an estimate of the pressure requires three measurements: the full cord length, its average width and number of coils. Using this result we propose two prototype indices for clinical testing that estimate umbilical cord flow resistance. The umbilical pressure index (PX) and flow index (QX) quantify the deviation of a cord geometry from defined typical conditions by considering the steady pressure drop and flow-rate, respectively. These indices can be quickly calculated, and require only a single additional measurement to the conventional umbilical coiling index (UCI); namely the cord coiling width. Unlike the UCI, these indices are derived from blood-flow properties and provide a measure of the relative flow-resistance inherent to a cord geometry. Furthermore, the pressure index can be applied to irregularities, including loose true knots, which we show must be accounted for.

Measurement and Evaluation of the Ellipsoid Deviation in Cartesian Coordinates

Ellipsoid part is now increasingly applied to the product manufacturing, while the high-quality ellipsoid part depends not only on the manufacturing and machining techniques, but also on the adopted measurement and evaluation approaches. Based on the typical quadratic surface, an evaluation method of the least squares ellipsoid deviation is proposed in this paper to quantify the form deviation of measured ellipsoid. The method can overcome the weakness of the low measurement adaptability compared with other evaluation methods. With obtaining the coefficients of surface equation to replace the linear superposing of the coordinates of measured points, the measurement error existing in the coordinates of measured points is homogenized and reduced effectively, which prompts to obtain the accurate measurement result. Finally, the results from experimental verifications show that the proposed method is effective for the measurement and evaluation of the ellipsoid deviation in Cartesian coordinates, and the adaptability is also a significant advantage in the measurement and evaluation of geometry deviation.

Study of the stability of the geometric dimensions of wax models of GTE blades using rapid prototyping technology

The work presents the results of a study of the stability of geometric dimensions of wax models of compressor stator blades of the 15th stage, manufactured using rapid prototyping technology. In the process of performing the work, the algorithm for assigning the total shrinkage was studied. It is established that the deviation of geometric dimensions, both in the greater and in the lesser direction relative to the nominal size of the blade is caused by the amount of volumetric shrinkage of the material used. Measuring the linear dimensions of wax models of blades allowed us to determine the nature of the geometry deviation for further accounting and compensation.

18‐3: Impact Study of Windshield Geometry on the Subjective Customer Perception for Augmented Reality Head‐up Displays (AR HUD)

New Generations of Head‐up Displays (HUD) are expected to grow in size and projection distance. For these reasons, even smallest deviations in the windshield geometry may cause new optical image defects. These image defects need to be specified, measured, and correlated with subjective customer perceptions. Based on a customer study (n=54), this paper gives first indications that heterogeneous image quality disturb customers.

Ultra-compact and high-performance polarization beam splitter assisted by slotted waveguide subwavelength gratings

We propose an ultra-short polarization beam splitter (PBS) consisting of two slot waveguides assisted by slotted waveguide subwavelength gratings (SWSWGs), located between the two slotted waveguides. By controlling the optical momentum of evanescent waves with the anisotropic characteristics of the SWSWGs, we considerably suppress and enhance the couplings of transverse-electric (TE) and transverse-magnetic (TM) modes, respectively, concurrently improving performances and reducing length of the proposed PBS, compared with conventional slotted waveguide couplers (CSWCs). Exceptionally, a transition point is found to show almost zero crosstalk between waveguides for the TE mode, i.e., infinite coupling length. Differing from conventional single-material SWGs, the SWSWGs not only simplify the fabrication process but improve polarization extinction ratio (PER). Numerical results demonstrate the improvement in PERTM (PERTE) from approximately 13 (23) dB for the CSWCs to 26 (24) dB for the present structure, with a > 70% reduction in device length, operating at the wavelength of λ = 1,550 nm. Our design achieves performance of PERTM > 25 dB and PERTE > 20 dB, and insertion loss (IL) < 0.05 dB for TE and < 0.3 dB for TM modes within a bandwidth width (BW) of ~ 50 nm from λ = 1,530 to 1,580 nm. Additionally, geometry deviation is also investigated to assess experimental tolerance. The present idea provides an approach for improving PER, device length, and operating BW of PBSs composed of various waveguide couplers.

Precise imprecision: flexible construction with robotics

This research demonstrates a new methodology—stack casting, which combines fabric formwork and robotic assembly. In the following research, a robot placed a textile mold on top of a precast environment to erect a significant architectural object. Through this method the robotic casting process obtained further contextual information to create highly customized assemblies. The natural form-fit boundary of the fabric strengthened the identification between global and local systems. As the digital method met the natural form-finding process, an interactive tectonic was generated—calibrating itself for any composition and accommodating deviations in geometry. Driven by the correspondence between digital and physical, the technique extended the building method of a dry-fitted cast in situ wall. To build a full-scale prototype, robotic stack casting collaborated with other versatile methods to invent new set-up strategies, which link to both on-and off-site construction. This research is part of a bigger picture rising in soft robotics. By interpreting unique forming into the computational design, precise and imprecise fabrication were redefined in a playful phenomenon. In traditional robotic stacking, the robot bridges the digital and physical world but its lack of adaptivity causes problem when placing imprecise objects. In this research’s process, the use of inexact fabric molds fixed the tolerance and found centers of gravity through relative reactions. They adjusted to the unique personal properties of their surroundings and compensated for discrepancies in material. As an alternative to the application of sensor feedback for accommodating tolerance in material, the use of stack casting digital formwork instead adjusts and reshapes the non-ideal masonry from the real-time architectural context. This playful process opens the door to further imaginations from design to build.

Influence of MTP on Surface Roughness and Geometric Accuracy of Machined Surface at WEDM

Electrical discharge machining technology is one of the most precise machining methods. Therefore, even the smallest deviation of micro and macro geometry generally has a significant impact on the overall quality of products produced by this progressive technology. The quality of the machined surface after Wire Electrical Discharge Machining (WEDM) is influenced by a large number of factors, most of which are influenced by the Main Technological Parameters (MTP). The aim of the paper was to describe the results of experimental research aimed at assessing the impact of MTP for WEDM on the quality of machined surface in terms of geometric accuracy and roughness parameters Ra and Rz. The samples were made of high alloyed ledeburitic chromium-molybdenum-vanadium steel designated EN X155CrVMo12-1 on a Sodick AQ535 electroerosion machine. The tool used was a standard compact brass wire  0.25 mm with the designation Elecut Brass CuZn37.

Influence of MTP on Surface Roughness and Geometric Accuracy of Machined Surface at WEDM

Electrical discharge machining technology is one of the most precise machining methods. Therefore, even the smallest deviation of micro and macro geometry generally has a significant impact on the overall quality of products produced by this progressive technology. The quality of the machined surface after Wire Electrical Discharge Machining (WEDM) is influenced by a large number of factors, most of which are influenced by the Main Technological Parameters (MTP). The aim of the paper was to describe the results of experimental research aimed at assessing the impact of MTP for WEDM on the quality of machined surface in terms of geometric accuracy and roughness parameters Ra and Rz. The samples were made of high alloyed ledeburitic chromium-molybdenum-vanadium steel designated EN X155CrVMo12-1 on a Sodick AQ535 electroerosion machine. The tool used was a standard compact brass wire  0.25 mm with the designation Elecut Brass CuZn37.

Prediction of geometry deviations in additive manufactured parts: comparison of linear regression with machine learning algorithms

Dimensional accuracy in additive manufacturing (AM) is still an issue compared with the tolerances for injection molding. In order to make AM suitable for the medical, aerospace, and automotive industries, geometry variations should be controlled and managed with a tight tolerance range. In the previously published article, the authors used statistical analysis to develop linear models for the prediction of dimensional features of laser-sintered specimens. Two identical builds with the same material, process, and build parameters were produced, resulting in 434 samples for mechanical testing (ISO 527-2 1BA). The developed linear models had low accuracy, and therefore needed an application of more advanced data analysis techniques. In this work, machine learning techniques are applied for the same data, and results are compared with the previously reported linear models. The linear regression model is the best for width. Multilayer perceptron and gradient boost regressor models have outperformed other for thickness and length. The recommendations on how the developed models can be used in the future are proposed.

Additive Manufacturing Distortion Compensation Based on Scan Data of Built Geometry

Abstract Additive manufacturing (AM) processes such as direct metal laser sintering (DMLS) are highly attractive manufacturing processes due to the ability to create certain geometries which would be prohibitive or even impossible to manufacture by other means. However, with such high thermal gradients which are usually present in these processes, manufacturing distortions may result in the creation of unacceptable parts. This paper presents an approach to compensate input STL files based on registration of the point cloud from sacrificial part builds. A novel strain energy based non-rigid registration algorithm has been developed for robust registration of data points to the original computer-aided design (CAD) model. A neural network based approach is used to learn the deformation of the geometry based on the deviation of the scan geometry. This network is subsequently used to modify the STL file to generate a new compensated STL file. The compensated STL file was validated by building parts and comparing the change in the part distortion.

Preparing Track Geometry Data for Automated Maintenance Planning

Research on track quality behavior has been extensively published, and many different approaches have been presented to describe the process of track quality. The research goal of this paper is to form a basis for a data-driven tamping prediction based on track quality analyses over time. A research database containing asset information, executed maintenance tasks, and measuring data of some 4,400 km of track of the Austrian rail network in a time sequence of 16 years is available. The modified standard deviation of vertical track geometry is identified as an ideal track quality indicator for planning and predicting tamping tasks in Austria in the context of this research. Further analyses show that a linear regression function is best suited for describing track quality between two tamping tasks and shows the best accuracy for predicting track quality in the future. An algorithm was developed by means of the linear regression function that enables analyses of track quality behavior over time for long time series and the whole network. This includes track quality before and after tamping tasks as well as deterioration rates. In the future, these basics have to be combined with further technical evaluations to detect an optimal intervention limit. Furthermore, economical and operational considerations must be incorporated to find the optimal tamping strategy under the given conditions.

The effect of geometry on mechanical properties of Ti6Al4V ELI scaffolds manufactured using additive manufacturing technology

Owing to the possibility of direct processing of CAD models into three-dimensional objects, additive manufacturing (AM) is widely used in the production of individualized bone scaffolds that can lead to perfect restoration of anatomical structures of missing bone tissues. In this work, one of the AM technologies was applied, referred to as Electron Beam Melting (EBM), using Ti6Al4V ELI alloy to produce open-cell structures. Scaffold architecture influences its mechanical properties and is important from the point of view of biological considerations. To optimize mechanical properties, designed geometries were subjected to Finite Element Method analysis and experimental static compression tests. Also, geometric CT analysis of manufactured scaffolds was carried out (geometry deviations up to ± 300 µm). Obtained results have shown that AM can be used to produce Ti6Al4V ELI alloy scaffolds displaying mechanical parameters similar to those of bone tissue (E = 0.45–2.88 MPa). The EBM process affects the microstructure and macrostructural properties of manufactured parts, e.g., through internal porosities present in the material by to unmelted powder particles (internal porosity in range of 1.25–2.25%). To assess the quality and suitability of additively manufactured implants, a multidimensional verification of the impact of the manufacturing process on the properties of the final product was performed.

Analysis of the impact of the machining method and material environmental conditions on the strength of ZrO2

Over the years, zirconium dioxide has gained a very strong position in the medical and mechanical industries. Zirconia is very much used in dentistry, using CAD/CAM systems. The article presents the author's method of producing samples (grinding) with small geometry - proposed by the author and large - normative and by milling. The sintering process was carried out, and later the samples were subjected to metrological analysis to determine the deviations in geometry for nominal dimensions. The samples were divided into two groups, where they were placed in an aqueous and dry environment. Static tests of three-point bending strength according to the standard and fatigue durability tests were performed for each of the sample groups. It can be seen that the surface grinding process causes an increase in mechanical strength, which has been proven in static three-point bending tests. Initial fatigue tests were carried out and the spread of results was noticed, which may be caused by special properties of the material - strengthening transformation. Zirconium dioxide is a material that is sensitive to aging, this process causes a significant decrease in mechanical strength as shown in the above tests, the tests carried out are preliminary tests.

Uncertainty quantification of the effects of squealer tip geometry deviation on aerothermal performance

The first-stage rotor squealer tip is a key area in gas turbine for both aerodynamic performance and blade cooling tasks, which should be carefully designed. However, harsh operating conditions near the rotor squealer tip can cause the geometry of the squealer tip to degrade, and manufacturing inaccuracies can also cause the squealer tip geometry to deviate from the ideal design. These geometry deviations would change the flow field near the blade tip, which will influence the thermal and aerodynamic performance. Thus, it is important to quantitatively investigate the effects of squealer tip geometry deviation on the aerothermal performance. In this paper, a typical transonic first-stage turbine is employed, and three important geometric features of squealer tip, the tip clearance height (H), the squealer depth (D), and the squealer edge chamfer (R), are selected. An uncertainty quantification process is performed to study the effect of deviation of H, D, and R on the aerothermal performance. Many cases with different geometry features are checked in the current study using 3D Reynolds-averaged Navier–Stokes simulations. A parameter sensitivity analysis using Sobol Indice method is carried out to identify the key parameters to aerothermal performance of the squealer tip. The uncertainty quantification results show that the existence of the tip chamfer reduces the size of separation bubble and the dwelling range of the scraping vortex, thus, the blockage effect of the leakage flow is weakened, which results in larger amount of leakage flow and more mixing loss of squealer tips with edge chamfer than those without edge chamfer. The results of the parameter sensitivity analysis show that the height of tip clearance is the main factor that affects the aerodynamic performance of the squealer tip. This work provides a certain guiding direction for the optimization design of the turbine groove tip.

Design and Analysis of Fixture for Welding Casing Components of Cross-Flow Turbine

The purpose of this research is to improve the quality of the turbine casing product by using the welding fixture. The method used was to design and make welding fixture of turbine casing welding, test the straightness, alignment, straightness, and analyzes the deviation of measurement results. Based on the design result of welding fixture assembling of cross-flow turbine casing component, it had been obtained prototype welding fixture which can facilitate the assembling process of cross-flow turbine casing component. The conclusions of this research are the quality of cross-flow turbine casing products can be increased along with the small geometry deviations in the cross-flow turbine runners by using a fastening tool. The maximum deviation of the straightness of the turbine wall is 1.6 (wall A) and 0.85 (wall B). The process of assembling the components of the turbine runner is shorter by using a faster welding assembly tool with a better level of accuracy.