The Sardinia Radio Telescope: A comparison between close-range photogrammetry and finite element models

2015 ◽  
Vol 22 (5) ◽  
pp. 1005-1026 ◽  
Author(s):  
Franco Buffa ◽  
Andrea Causin ◽  
Antonio Cazzani ◽  
Sergio Poppi ◽  
Giannina Sanna ◽  
...  
Keyword(s):  
Finite Element ◽  
Radio Telescope ◽  
Active Surface ◽  
Element Model ◽  
Wind Pressure ◽  
Primary Mirror ◽  
Actual Surface ◽  
Close Range Photogrammetry ◽  
Close Range ◽  
The Difference

The Sardinia Radio Telescope (SRT), located near Cagliari (Italy), is the world’s second largest fully steerable radio telescope endowed with an active-surface system. Its primary mirror has a quasi-parabolic shape with a diameter of 64 m. The configuration of the primary mirror surface can be modified by means of electro-mechanical actuators. This capability ensures, within a fixed range, the balancing of the deformation caused, for example, by loads such as self-weight, thermal effects and wind pressure. In this way, the difference between the ideal shape of the mirror (which maximizes its performances) and the actual surface can be reduced. In this paper the authors describe the characteristics of the SRT, the close-range photogrammetry (CRP) survey developed in order to set up the actuator displacements, and a finite element model capable of accurately estimating the structural deformations. Numerical results are compared with CRP measurements in order to test the accuracy of the model.

Sardinia radio telescope finite element model updating by means of photogrammetric measurements

2015 ◽  
Vol 22 (4) ◽  
pp. 885-901 ◽  
Author(s):  
Flavio Stochino ◽  
Antonio Cazzani ◽  
Sergio Poppi ◽  
Emilio Turco
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Radio Telescope ◽  
Model Updating ◽  
Active Surface ◽  
Element Model ◽  
Actual Surface ◽  
The Difference ◽  
The Finite Element Model ◽  
The Ideal

The 64 m diameter Sardinia Radio Telescope (SRT), located near Cagliari (Italy), is the world’s second largest fully steerable radio telescope with an active surface. Among its peculiarities is the capability of modifying the configuration of the primary mirror surface by means of electromechanical actuators. This capability enables, within a fixed range, balancing of the deformation caused by external loads. In this way, the difference between the ideal shape of the mirror (which maximizes its performance) and the actual surface can be reduced. The control loop of the radio telescope needs a procedure that is able to predict SRT deformation, with the required accuracy, in order to reduce deviation from the ideal shape. To achieve this aim, a finite element model that can accurately predict the displacements of the structure is required. Unfortunately, the finite element model of the SRT, although very refined, does not give completely satisfactory results, since it does not take into account essential pieces of information, for instance, thermal strains and assembly defects. This paper explores a possible update of the finite element model using only the benchmark data available, i.e. the photogrammetric survey developed during the setup of the reflecting surface. This updating leads to a significant reduction in the differences between photogrammetric data and results of the numerical model. The effectiveness of this tuning procedure is then assessed.

scholarly journals A SIMULATION TOOL ASSISTING THE DESIGN OF A CLOSE RANGE PHOTOGRAMMETRY SYSTEM FOR THE SARDINIA RADIO TELESCOPE

2016 ◽  
Vol III-5 ◽  
pp. 113-120 ◽  
Author(s):  
F. Buffa ◽  
A. Pinna ◽  
G. Sanna
Keyword(s):  
Radio Telescope ◽  
Active Surface ◽  
Optimal Shape ◽  
Bundle Adjustment ◽  
Simulation Tool ◽  
Simulation Environment ◽  
Close Range Photogrammetry ◽  
Large Structures ◽  
Close Range ◽  
Realistic Images

The Sardinia Radio Telescope (SRT) is a 64 m diameter antenna, whose primary mirror is equipped with an active surface capable to correct its deformations by means of a thick network of actuators. Close range photogrammetry (CRP) was used to measure the self-load deformations of the SRT primary reflector from its optimal shape, which are requested to be minimized for the radio telescope to operate at full efficiency. In the attempt to achieve such performance, we conceived a near real-time CRP system which requires the cameras to be installed in fixed positions and at the same time to avoid any interference with the antenna operativeness. The design of such system is not a trivial task, and to assist our decision we therefore developed a simulation pipeline to realistically reproduce and evaluate photogrammetric surveys of large structures. The described simulation environment consists of (i) a detailed description of the SRT model, included the measurement points and the camera parameters, (ii) a tool capable of generating realistic images accordingly to the above model, and (iii) a self-calibrating bundle adjustment to evaluate the performance in terms of RMSE of the camera configurations.

scholarly journals A SIMULATION TOOL ASSISTING THE DESIGN OF A CLOSE RANGE PHOTOGRAMMETRY SYSTEM FOR THE SARDINIA RADIO TELESCOPE

2016 ◽  
Vol III-5 ◽  
pp. 113-120 ◽  
Author(s):  
F. Buffa ◽  
A. Pinna ◽  
G. Sanna
Keyword(s):  
Radio Telescope ◽  
Active Surface ◽  
Optimal Shape ◽  
Bundle Adjustment ◽  
Simulation Tool ◽  
Simulation Environment ◽  
Close Range Photogrammetry ◽  
Large Structures ◽  
Close Range ◽  
Realistic Images

The Sardinia Radio Telescope (SRT) is a 64 m diameter antenna, whose primary mirror is equipped with an active surface capable to correct its deformations by means of a thick network of actuators. Close range photogrammetry (CRP) was used to measure the self-load deformations of the SRT primary reflector from its optimal shape, which are requested to be minimized for the radio telescope to operate at full efficiency. In the attempt to achieve such performance, we conceived a near real-time CRP system which requires the cameras to be installed in fixed positions and at the same time to avoid any interference with the antenna operativeness. The design of such system is not a trivial task, and to assist our decision we therefore developed a simulation pipeline to realistically reproduce and evaluate photogrammetric surveys of large structures. The described simulation environment consists of (i) a detailed description of the SRT model, included the measurement points and the camera parameters, (ii) a tool capable of generating realistic images accordingly to the above model, and (iii) a self-calibrating bundle adjustment to evaluate the performance in terms of RMSE of the camera configurations.

Growth Behavior of Two Interacting Surface Cracks of Dissimilar Size (Comparison for Tensile and Bending Load)

2010 ◽  
Author(s):  
Masayuki Kamaya ◽  
Masanori Kikuchi ◽  
Eiichi Miyokawa
Keyword(s):  
Finite Element ◽  
Element Model ◽  
Growth Behavior ◽  
Multiple Cracks ◽  
Surface Cracks ◽  
Element Mesh ◽  
Loading Direction ◽  
Parallel Surface ◽  
Bending Load ◽  
The Difference

When multiple cracks approach one another, the stress intensity factor is likely to change due to the interaction of the stress field. This causes change in growth rate and shape of cracks. In particular, when cracks are in parallel position to the loading direction, the shape of cracks becomes non-planar. In this study, the complex growth of interacting cracks is evaluated by using the S-Version finite element method, in which local detailed finite element mesh (local mesh) is superposed on cores finite element model (global mesh) representing the global structure. In this study, two parallel surface cracks are subjected to two types of loading; tensile and bending load. Comparisons are made on the growth behavior under two types of loading. It is shown that the smaller crack stop growing due to the interaction when the difference in size of two cracks is large. This tendency is more significant for the bending load. The procedure for evaluating crack growth for Fitness-for-Service assessment is discussed.

scholarly journals Effect of Torsional Element towards High-Speed Rotating Shaft’s Critical Speed at Different Boundary Conditions

2019 ◽  
Vol 8 (4) ◽  
pp. 6787-6792
Keyword(s):  
Finite Element ◽  
Boundary Conditions ◽  
High Speed ◽  
Critical Speed ◽  
Element Model ◽  
Accurate Estimation ◽  
Fe Model ◽  
Rotating Shaft ◽  
Different Boundary Conditions ◽  
The Difference

Efficiency improvement that can be provided by the high-speed rotating equipment becomes a concern for designers nowadays. Since the high-speed rotating machinery was capable of rotating at very near to critical speed, the accurate estimation of critical speed needs to be considered. This paper investigated the effect of torsional element towards critical speed of high-speed rotating shaft system for pinned-pinned (P-P), clamped-free (C-F) and clamped-free (C-F) boundaries condition. The Nelson’s finite element model that considers the torsional effect was developed for formulating the finite element (FE) model. This FE model was used to derive Mathieu-Hill’s equation and then solved by applying the Bolotin’s theory. From the solution, the Campbell’s diagram of the high-speed shaft was plotted. It was found that torsional motion has significant effect on the critical speed for different boundary conditions. The difference between critical speed of 4DOF and 5DOF models can be as high as 6.91 %.

A new finite element model of the SOFIA primary mirror cell to investigate dynamical behavior

2018 ◽  
Author(s):  
Benjamin Greiner ◽  
Bernhard Malicek ◽  
Michael Lachenmann ◽  
Jörg Wagner ◽  
Alfred Krabbe
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Dynamical Behavior ◽  
Element Model ◽  
Primary Mirror

The Local Stress Analysis for the Anchorage Zone of Tooth Plate in Steel Box Girder

2013 ◽  
Vol 477-478 ◽  
pp. 631-634
Author(s):  
Zuo Long Luo ◽  
Jiang Long Wang ◽  
Feng Hui Dong
Keyword(s):  
Finite Element ◽  
Comparative Analysis ◽  
Local Stress ◽  
Element Model ◽  
Maximum Difference ◽  
Box Girder ◽  
Steel Box Girder ◽  
Tooth Plate ◽  
The Difference ◽  
Different Parts

Calculating the local stress for the anchorage zone of each part in the tooth plate by establishing two kinds of finite element model: considering concrete effect and not considering concrete effect. The result of the comparative analysis of the two models shows that the local stress considering the concrete effect is smaller than that not considering the concrete effect and the maximum difference is about 170 MPa. The difference is not the same in different parts of the tooth plate. Although the design will be tend to be safe for not considering the concrete effect, the size of the tooth plate may increase. Therefore, in order to reduce the weight of the tooth plate , the concrete effect should be taken into consideration in the design.

Analysis of Torsion Stiffness of Flexible Pivot Bearing with Radial Array Rectangular Section

2013 ◽  
Vol 584 ◽  
pp. 214-219
Author(s):  
Chun Jie Liu ◽  
X.Q. Wu ◽  
W.M. Gan ◽  
Zhi Wei Chen
Keyword(s):  
Finite Element ◽  
Angular Displacement ◽  
Element Model ◽  
Simulation Method ◽  
Limited Range ◽  
Rectangular Section ◽  
Performance Specification ◽  
Pivot Bearing ◽  
The Difference ◽  
Torsion Stiffness

Flexible pivot bearing, a kind of precision elastic components, can provide necessary angular displacement within limited range. The torsion stiffness of the bearing, as the most important performance specification, is studied in the paper. The analytical expression (for array numberNand) of the torsion stiffness of the flexible pivot bearing with rectangular section is deduced by using static equilibrium theory. The constituent parts and physical meaning of the expression are discussed. The accuracy and applicability of the deduced expression are investigated in comparison with other equations in references. A finite element model is built accurately. Simulation of the flexible bearing (N=4) is carried out to compare the FEM solution with that obtained by the derived expression. The results show that the deduced equation is applicable to allNradial array flexible pivot bearing with rectangular section, and the difference of the stiffness value is about 7% comparing with that calculated by simulation method.

A Method for Determining the Springing Displacements of Arch Bridges without Technical Data

2011 ◽  
Vol 94-96 ◽  
pp. 375-380
Author(s):  
Xiao Dong Zhang ◽  
Yong Qiang Zhang
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Optimization Problem ◽  
Element Model ◽  
Technical Data ◽  
Numerical Examples ◽  
The Difference ◽  
Arch Bridges ◽  
The One ◽  
The Finite Element Model

A method for determining the springing displacements and arch axis of old arch bridges without technical data is presented. By minimizing the difference between the arch axis predicted by the finite element model and the one obtained by assumed arch equation, the optimization problem is formulated and solved. Two numerical examples are given and the results are discussed.

Prediction and Testing (ASTM E-837-89) of Residual Stresses in Structures (Operated in SOHIC Environment) Caused by Welding

2002 ◽  
Author(s):  
Sasan Armand ◽  
Stan Jones
Keyword(s):  
Finite Element ◽  
Residual Stresses ◽  
Finite Element Model ◽  
Element Model ◽  
Structural Testing ◽  
Finite Element Technique ◽  
Stress Cracking ◽  
Failure Investigation ◽  
The Difference ◽  
Element Technique

The study and testing of the structural behavior of a failed pipe with a spiral weld seam was conducted. Our study and testing was part of a larger failure investigation to determine the influence of residual stress for initiation of hydrogen stress cracking. Finite element and structural testing methods were used to guide the study for determination of residual stresses. All properties used in our study were measured per ASTM A-370. The validation of the finite element model of the pipe was conducted against the test results per ASTM E-837-89. The difference in predicted and measured residual stresses was 3% at the ID of the structure. Due to the small differences in the results from analysis and testing, no correlation was required, and the test-validated finite element model was used to predict the total stresses due to the manufacturing processes and operational loads. Based on the validation results, one can conclude that the finite element technique is accurate for predicting residual welding stresses. The finite element technique, however, is far less time -consuming and thus less expensive method than mechanical testing for determining the residual stresses.

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