CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
Not a member yet
4735 research outputs found
Sort by
Comparison of behaviour of burnt beams models with effective and actual residual cross-sections in three point bending test
Get PDFGlued laminated timber beams exposed to fire of a variable duration were tested in three point bending. Three types of model geometries taking into account the effect of burning were created. Each model was examined for five material data sets. The maximum deflection obtained from FEM simulations was compared with the corresponding deflection wel derived from a three point bending test of burnt beams. The analysis was performed with the help of Ansys® software limiting attention to a liner elasticity with the maximum applied force Fel selected at the proportionality limit observed experimentally. Majority of FEM models provided smaller deflections compared to measurements except for the material set adopting Young’s moduli from the compression test. The best fit was observed for the material data set obtained from homogenization. No predominant preference among individual geometries was found promoting the computational model based on reduced cross-section as sufficiently accurate
STRESS AND DEFORMATION ANALYSIS OF A U-SHAPED THIN AQUEDUCT BASED ON SHELL ELEMENT
Get PDFIn order to study the stress and deformation characteristics of Jigongzui U-shaped thin shell aqueduct structure, shell element in ANSYS is proposed to establish the three-dimensional finite element model of the aqueduct for numerical calculation, and the relevant mechanical parameters are obtained by detecting the depth of concrete carbonization. The simulated results show that: (1) The concrete carbonization depth of Jigongzui aqueduct reached 20mm, accounting for about 20% of the total thickness of the channel wall; (2) With the increase of aqueduct water level, the deformation and stress of the aqueduct body gradually increase. The maximum deflection in the middle of the span is 6.98mm, which is less than the limit value of the specification, but the tension in some areas at the bottom of the middle of the span is obvious, exceeding the allowable tensile strength. It is suggested to strengthen the aqueduct body by pasting high-performance fiber materials to improve the stress distribution of the aqueduct body; (3) Shell element has fast calculation speed and high efficiency when simulating similar U-shaped thin shell aqueduct, which can be popularized in simulating similar thin shell structures
STUDY ON THE DRIVING GAZE SHIFT CHARACTERISTICS OF VISION INTERESTING AREA ON MOUNTAINOUS ROAD
Get PDFMountainous road landscape is the main source of driving information. The characteristics of two-lane mountainous road result in real-time dynamic changes in the driver\u27s vision interesting areas. In order to explore the dynamic gaze characteristics, a driving experiment is conducted, and the gaze data of 10 drivers are collected. Markov chain is used to analyze the change process of gaze. The results show that: (1) when the current gaze point is in the straight front area, different road landscape has no significant impact on the gaze shift probability; (2) when the current gaze point is in the near left area, next gaze will expand the search scope to obtain much more driving information; (3) when the current gaze point is in the near right area, there is a high probability that the driver\u27s next gaze will return to the front area; (4) when the current gaze point is in the far right area, the gaze will move back and forth between the near right and the far right areas; (5) when the current gaze point is in the far left area, there is a high probability that the gaze will remain in current area; (6) the main source of traffic information obtained by the driver in mountainous road landscape is the straight front area in the vision field, and the gaze point constantly shifts between the far ahead and the near ahead. The research results can provide technical reference for the construction of landscape in mountainous two-lane road
Experimental study on real bridge before and after simple-supporting to continuous reinforced concrete hollow slab
Get PDFThis article studies a concrete hollow slab simply supported-continuous actual engineering project in a certain city. Before the reinforcement of the bridge, there were cracks and exposed rebars, etc. In order to ensure the safe operation of the bridge, a reinforcement method of simply supported-continuous was adopted, prestressed steel strands are used to convert the simple-supported structure into a continuous structure, thereby improving the structural load-bearing capacity and overall integrity. Through conducting comparative analysis of load tests on a bridge before and after reinforcement, this article studies the improvement effect of the simply-supported-to-continuous reinforcement method on the bearing capacity of the bridge. A finite element model of the bridge was established, and comparative analysis was carried out before and after the reinforcement of the bridge. The bearing capacity and work performance of the bridge structure were evaluated. The research shows that the simply supported-continuous reinforcement method has a good improvement effect on the load-bearing capacity of the concrete hollow slab and can be used to improve the insufficient load-bearing capacity of the concrete hollow slab bridge in the city
Computer-aided Optical Plasma Postprocessing Applied on Model Spark Gaps
Get PDFSpark gaps are used as surge protective devices (SPD class 1) for low voltage grids protection against surge currents and overvoltages. For practical research of the narrow gap plasma of spark gaps, high-speed camera recordings are used in modified transparent test models. In this test setup, current densities of 1010 A/m2 are generated.
In order to optimize and automate the evaluation process of camera recordings, an image analysis tool is developed further in this contribution. After basic image improvement and segmentation, this research optimizes a detection algorithm for plasma location and distribution. As a result, the known plasma distribution gives access to significantly more information about the plasma behaviour and the spatial distribution of radiation
Surface Average Temperature Measurement of Cu-W Contact Material Burning in CO2: Preliminary Study
Get PDFThe surface average temperature and the electrode temperature distribution are key parameters to predict the electrode erosion. Experimental research on the arc erosion has been carried out in a model circuit breaker, in which CO2 is filled in the chamber and Cu-W is used as the contact material. The surface average temperatures of plug contact exposed to electric arc with sinusoidal currents of 5kA were determined by a high-speed pyroscope. In order to establish a relationship between the average temperature of the contact surface and current squared, the data statistics and fitting curves in the current-rising and current-falling stages were given. It has been found that there are two different types of arc erosion processes by comparing the temperature-current squared curves. In other words, the structure of contact surface and the electrode material change significantly after repeated arc erosions
Neural network based patient recovery estimation of a PAM-based rehabilitation robot
Get PDFRehabilitation robots have shown a promise in aiding patient recovery by supporting them in repetitive, systematic training sessions. A critical factor in the success of such training is the patient’s recovery progress, which can guide suitable treatment plans and reduce recovery time. In this study, a neural network-based approach is proposed to estimate the patient’s recovery, which can aid in the development of an assist-as-needed training strategy for the gait training system. Experimental results show that the proposed method can accurately estimate the external torques generated by the patient to determine their recovery. The estimated patient recovery is used for an impedance control of a 2-DOF robotic orthosis powered by pneumatic artificial muscles, which improves the robot joint compliance coefficients and makes the patient more comfortable and confident during rehabilitation exercises
Mechanical characteristics of large-section tunnel in soft rock based on various rock conditions and excavation footages
Get PDFTaking the V-class surrounding rock section at the entrance and exit about Qianqi Tunnel as an example, the deformation rules as well as mechanics about the tunnel in different rock conditions and excavation footages are compared by numerical calculation, and the suitable excavation footage of the relied engineering is also proposed. The results show that the displacements about surrounding rock are greatly influenced by the excavation footage, namely, the arch settlements, horizontal convergences as well as surface settlement of the tunnel increase significantly with the excavation footage. For the preferred rock condition, the maximum bending moments about the preliminary linings at middle step after excavation occurs in the vault, and its increase amplitude has little correlation with the excavation footage. For the poor surrounding rock, the maximum bending moment is transferred from the vault to the arch waist with the increase of excavation footage, and it is basically manifested as the inner tension of the lining. The relationship between excavation footage and maximum deformation as well as mechanical index of vault is also revealed, respectively. The excavation footage of shallow-buried tunnel sections in V-grade surrounding rock is suggested, that is, 1.8m for the preferred surrounding rock condition and 1.2m for the poor surrounding rock condition
Thermomechanical calculation within the HERA programme
Get PDFHERA (High Burnup Experiments in Reactivity Initiated Accident) is one of the programmes which should replace closed Halden reactor. As the name implies HERA is focused on the tests simulated RIA (Reactivity Initiated Accident) and the aim of the programme is to investigate the performance and behaviour of high burnup fuel in RIA transients. The first phase of HERA programme consists of two steps which are the blind calculation of different RIA scenarios (different pulse width, enthalpy increase, hydrogen content and gap size) and in-reactor test with fresh fuel.The set of thermomechanical calculation was performed with the FRAPTRAN computer code as part of the first phase of HERA. The influence of several parameters on the fuel behaviour was observed, the varying parameters were the pulse width, peak radial average enthalpy increase, hydrogen content and the hydrogen rim size and gap size. In addition, the effect of type and setting of boundary condition was investigated
Providing stability to a highway cut in a landslide area with the use of diaphragm wall panels
Get PDFThe route of the D1 highway in the Lietavská Lúčka - Dubná Skala section near Žilina is taken forward by a 17 m deep cut in a section about 300 m long. The first proposed solution of the highway route was based on the assumption that it is a stable area. However, during the construction of the highway cut an old landslide area with a depth of shear surfaces of up to 25 m was identified right in the area of the cut. Therefore, massive measures had to be designated to assure that the area above the highway and the access to the tunnel portal were not threatened by landslides. When addressing the security of the cut, an unusual solution was used - anchored diaphragm wall panels of underground concrete walling oriented towards the slope. Currently, this given solution is under construction and is controlled by inclinometers incorporated into selected diaphragm wall panels