Search

This paper aims at investigating the synchronization of unbalanced rotors and rigid frames in a vibration system, consisting of three elastically connected rigid frames and two counter-rotating unbalanced rotors, which are mounted on different inner rigid frames. Using the Lagrange approach, the governing equations of motions are derived. Using the method of averaging, the existence condition of synchronization for two unbalanced rotors is determined. Applying Lyapunov stability theory, the condition of the system to get stable synchronous states is obtained. In order to analyze the selected motion characteristic of unbalanced rotors and rigid frames, numerical simulations are performed. Specifically, the phase difference between two unbalanced rotors and motion lag phases of rigid frames is studied by considering different synchronous frequencies and ratios of masses of unbalanced rotors. Furthermore, a series of experiments for different frequency regions of vibrations is carried out to validate the obtained theoretical results. The coupling motion characteristics of unbalanced rotors are studied by comparing the cases of excitation of a single and two unbalanced rotors. The present work and obtained results can serve as theoretical and experimental basis for the design of vibration jaw crushers in engineering. [ABSTRACT FROM AUTHOR]

Copyright of Ingenius, Revista Ciencia y Tecnología is the property of Universidad Politecnica Salesiana and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract Structural engineers should appropriately design concrete structures to resist lateral loads. Determining the adequate system for resisting the expected lateral loads is important to control the building drift. Choosing the appropriate system is usually conducted assuming the predicted forces are applied to completed concrete buildings at one step which is commonly known as ordinary analysis (OA). Nevertheless, these structures are constructed sequentially which requires using staged analysis (SA) instead of OA. In this paper, a comprehensive numerical model for SA of concrete buildings, which accounts for time dependent effects, is utilized using a well-validated commercial software. Six reinforced concrete buildings with 10 and 20 storeys are analyzed using the developed model. Three various structural systems are considered (Rigid Frame (RF), Shear Wall (SW), and Wall Frame (WF). A comparison is conducted between the displacements and internal forces in beams and slabs obtained from the SA and OA. For a 10-storeys RF building, maximum bending moment from SA is 29.9% higher than that from OA. The same conclusion was observed for the maximum shearing force with a percentage of 19.6%. Moreover, maximum bending moments and shearing forces from SA for the 20-storeys RF building are, respectively, 35.0% and 23.5% larger than those from OA. The RF and WF systems provided the minimum difference in differential displacement between the OA and SA analyses. The RF system produced the least differences in internal forces from OA and SA for all studied buildings.

The marine fishery will be the main form of the marine economy in the future. Simulating a hydrodynamic response under normal and extreme working conditions is the main means of structural analysis and design of a mariculture ship. In this paper, a simulation methodology is proposed based on potential flow theory, focusing on a semi-submersible large-scale mariculture ship with a rigid frame. Abaqus/Aqua 2020 software is used to establish a full-scale dynamic analysis model of the fishery. In the simulation, a nonlinear implicit integration method is applied, and the non-deterministic boundary conditions of the floating body are optimized using dynamic equilibrium principles. By varying the wave and flow conditions, the variations in mooring forces, vibration amplitudes, and average vibration values are analyzed. Furthermore, the dynamic changes in the overall spatial displacements of the fishery, characteristics of longitudinal and vertical oscillations, and mid-span deflections are analyzed. It is concluded that the mooring force is linearly correlated with the flow velocity, that a higher wave increases the longitudinal oscillation amplitude, and that a longer wave period leads to higher mooring forces and longitudinal heaving amplitude. These dynamic response and displacement results of the mariculture ship are expected to provide a basis for its design and safety assessment. [ABSTRACT FROM AUTHOR]

Structural engineers should appropriately design concrete structures to resist lateral loads. Determining the adequate system for resisting the expected lateral loads is important to control the building drift. Choosing the appropriate system is usually conducted assuming the predicted forces are applied to completed concrete buildings at one step which is commonly known as ordinary analysis (OA). Nevertheless, these structures are constructed sequentially which requires using staged analysis (SA) instead of OA. In this paper, a comprehensive numerical model for SA of concrete buildings, which accounts for time dependent effects, is utilized using a well-validated commercial software. Six reinforced concrete buildings with 10 and 20 storeys are analyzed using the developed model. Three various structural systems are considered (Rigid Frame (RF), Shear Wall (SW), and Wall Frame (WF). A comparison is conducted between the displacements and internal forces in beams and slabs obtained from the SA and OA. For a 10-storeys RF building, maximum bending moment from SA is 29.9% higher than that from OA. The same conclusion was observed for the maximum shearing force with a percentage of 19.6%. Moreover, maximum bending moments and shearing forces from SA for the 20-storeys RF building are, respectively, 35.0% and 23.5% larger than those from OA. The RF and WF systems provided the minimum difference in differential displacement between the OA and SA analyses. The RF system produced the least differences in internal forces from OA and SA for all studied buildings. [ABSTRACT FROM AUTHOR]

Textile-reinforced concrete is becoming more and more popular. The material enables the realization of very thin structures and shells, often with organic shapes. However, a problem with this reinforcement occurs when the structure is bent (contains a corner), and the flexural stiffness around this bent area is required. This article presents the design, solution, and load-bearing capacity of an L-shaped rigid frame made of textile-reinforced concrete. Basic material parameters of concrete matrix and carbon textile reinforcement were supplemented by a four-point bending test to calibrate fracture energy Gf, critical compressive displacement Wd, solver type, and other parameters of a numerical model created by Atena Engineering in specialized non-linear structural analysis software for reinforced concrete structures. The calibrated numerical model was used to evaluate different variants of carbon textile reinforcement of the L-shaped frame. The carbon textile reinforcement was homogenized using epoxy resin to ensure the interaction of all fibers, and its surface was modified with fine-grained silica sand to increase the cohesion with the concrete matrix. Specimens were produced based on the most effective variant of the L-shaped frame reinforcement to be experimentally tested. Thanks to the original shaping and anchoring of the reinforcement in the corner area, the frame with composite textile reinforcement is rigid and can transmit the bending stresses in both positive and negative directions. The results of the mechanical loading test on small experimental specimens correspond well to the results of numerical modeling using Atena Engineering software. [ABSTRACT FROM AUTHOR]

The marine fishery will be the main form of the marine economy in the future. Simulating a hydrodynamic response under normal and extreme working conditions is the main means of structural analysis and design of a mariculture ship. In this paper, a simulation methodology is proposed based on potential flow theory, focusing on a semi-submersible large-scale mariculture ship with a rigid frame. Abaqus/Aqua 2020 software is used to establish a full-scale dynamic analysis model of the fishery. In the simulation, a nonlinear implicit integration method is applied, and the non-deterministic boundary conditions of the floating body are optimized using dynamic equilibrium principles. By varying the wave and flow conditions, the variations in mooring forces, vibration amplitudes, and average vibration values are analyzed. Furthermore, the dynamic changes in the overall spatial displacements of the fishery, characteristics of longitudinal and vertical oscillations, and mid-span deflections are analyzed. It is concluded that the mooring force is linearly correlated with the flow velocity, that a higher wave increases the longitudinal oscillation amplitude, and that a longer wave period leads to higher mooring forces and longitudinal heaving amplitude. These dynamic response and displacement results of the mariculture ship are expected to provide a basis for its design and safety assessment.

The paper deals with the verification of the stability of a new design concept of a hybrid harvester intended for thinning and with the determination of deviation between two methods of measuring the machine's center of gravity, i.e., between the methods of determining the center of gravity using the SolidWorks software made by Dassault Systems and using portable vehicle scales with the function of gravity center calculation. The machine was measured in five different positions from going up or down the slope or driving along the contour line. The new prototype of a harvester with a non-conventional rigid frame and both axles steered was found to be unstable at the maximum reach of hydraulic boom if it is situated at a right angle (±90°) to the machine longitudinal axis. A comparison of the two methods of determining the center of gravity resulted in a total deviation of 8.41%, with the deviation for x being on average 14.36% and for y only 3.08%. [ABSTRACT FROM AUTHOR]

In this research, the seismic performance of 5story buildings having dual systems of moment frame and chevron bracings, chevron panels along with zipper columns, inverted chevron panels, inverted chevron panels along with zipper columns is evaluated based on conducting nonlinear time history analyses under an ensemble of 3-component far and near-field records. Behavioral features of resistant skeletons having chevron braced panels are controlled through a near-buckling performance of diagonal limbs under pressure. It has been observed that when intensive earthquakes occur, this type of resistant skeleton reveals a gradual loss in resistant features. The appearance of the effects of the two phenomena of stiffness deterioration and strength degradation would be remarkable. A desirable solution in dealing with this weakness is adding a zipper column to the braced panel. The major criterion in selecting near-field records has been the existence of distinct or compound pulses with long period and large amplitude in the ground velocity time history. It has been noticed that this feature affects the seismic response parameters of the building to a great extent. All structures have been designed with a regular plan and according to seismic provisions in the code 2800 and also the 6th and 10th issues of the Iranian National Building Regulations. The specific outlook of this research lies in assessing the changes in maximum displacement responses, relative velocity, absolute acceleration of the floors, plastic hinge formation mechanism and the axial force of the columns. Results show a moderate superiority in the seismic performance of dual skeleton having zipper elements compared to the same resistant system with a lack of zippers.

Textile-reinforced concrete is becoming more and more popular. The material enables the realization of very thin structures and shells, often with organic shapes. However, a problem with this reinforcement occurs when the structure is bent (contains a corner), and the flexural stiffness around this bent area is required. This article presents the design, solution, and load-bearing capacity of an L-shaped rigid frame made of textile-reinforced concrete. Basic material parameters of concrete matrix and carbon textile reinforcement were supplemented by a four-point bending test to calibrate fracture energy Gf, critical compressive displacement Wd, solver type, and other parameters of a numerical model created by Atena Engineering in specialized non-linear structural analysis software for reinforced concrete structures. The calibrated numerical model was used to evaluate different variants of carbon textile reinforcement of the L-shaped frame. The carbon textile reinforcement was homogenized using epoxy resin to ensure the interaction of all fibers, and its surface was modified with fine-grained silica sand to increase the cohesion with the concrete matrix. Specimens were produced based on the most effective variant of the L-shaped frame reinforcement to be experimentally tested. Thanks to the original shaping and anchoring of the reinforcement in the corner area, the frame with composite textile reinforcement is rigid and can transmit the bending stresses in both positive and negative directions. The results of the mechanical loading test on small experimental specimens correspond well to the results of numerical modeling using Atena Engineering software.

In this paper, a dynamic model is adopted to investigate the stability and response characteristics of a vibrating system driven by four vibrators placed on two different rigid frames (RFs). Using the equations of motion of the system derived, the conditions for synchronization and stable operation of the system are studied by the average method and Hamilton's rules, respectively. Based on the theoretical results obtained, some factors are further studied concerning the stable phase differences (SPDs), the coefficients for ensuring stability, and the vibration amplitudes of the two RFs in different resonant regions. These serve to reveal the stability and response characteristics of the system that determine the ultimate function of the vibrating machine. Finally, numerical simulations are carried out to examine the validity of the theoretical methods and numerical qualitative results. Based on the results from the theory and simulation analyses, it is suggested that the working region of the system should be selected in the sub-resonant region corresponding to the natural frequency (NF) of the main vibrating system in the x - and y -directions. In this case, the ideal relative circular motion for two RFs with a well isolation effect can be achieved, and the energy is saved. [ABSTRACT FROM AUTHOR]

The paper deals with the verification of the stability of a new design concept of a hybrid harvester intended for thinning and with the determination of deviation between two methods of measuring the machine’s center of gravity, i.e., between the methods of determining the center of gravity using the SolidWorks software made by Dassault Systems and using portable vehicle scales with the function of gravity center calculation. The machine was measured in five different positions from going up or down the slope or driving along the contour line. The new prototype of a harvester with a non-conventional rigid frame and both axles steered was found to be unstable at the maximum reach of hydraulic boom if it is situated at a right angle (±90°) to the machine longitudinal axis. A comparison of the two methods of determining the center of gravity resulted in a total deviation of 8.41%, with the deviation for x being on average 14.36% and for y only 3.08%.

The article provides reasonable proposals for amending the current regulatory documents of the Russian Federation, regulating the quality control of dumping coarse grained soil into the dam body. In addition, the standards of Russia and the USA are also compared. [ABSTRACT FROM AUTHOR]

The requirements of regulatory documents imposed on the selection of control samples of coarse fragmental material often hamper the rate of erection of earth and rockfill dams and complicate operational assessment of work quality. Through the evaluation of the possibility of quality control of the stacking of coarse fragmental material in pits of reduced size by controlling the density of all the soil material relative to the density of fractions 200 mm, similar to the determination of the entire soil density relative to the density of fine material (5 mm), it becomes possible to optimize these types of operations without worsening their quality. [ABSTRACT FROM AUTHOR]

The construction of the Nelson Mandela Bridge at El Prat del Llobregat in Barcelona was finished in February 2015. The bridge is placed very close to the Llobregat river mouth and plays a key role in connecting Barcelona’s commercial port with both El Prat airport and an important industrial park in the metropolitan area. The bridge stands out as it has the longest arch in the Catalan region with its main span of 150 m. The total length of the bridge is 304 m and the deck width is 29 m. However, the singular point is the structural scheme, a combination of a frame and a half-through arch. During the construction process the structure was changed several times. This evolutionary process established the final forces and stresses in the bridge, tightly bonding the construction stage to the implementation. To verify all the construction phases, the structure was monitored in real time. The instrumentation, combined with the usual control, made it possible to evaluate the structure’s stress state and compare it with the models as well as verifying the correct ongoing of the construction and adjusting the next phases of the process where needed. [ABSTRACT FROM AUTHOR]

The propagation of a stationary acoustic wave through an infinite thin plate stiffened on two sides by a system of absolutely rigid, crossed ribs and located between two absolutely rigid barriers. It is assumed that the plate and the ribs evenly distributed along rectangular Cartesian axes are connected through elastic spacers (supports) without slip. The dynamic deformation of the plate is described by the linearized Kirchhoff-Love equations of the classical theory of plates, the dynamic deformation of the spacers is described by two-dimensional and one-dimensional relations based on linear approximations of displacements of points of the coating and spacers along the thickness and taking into account only transverse compression and transverse shear, and the motion of acoustic media by the well-known wave equations. The solution of the problem is obtained using the Ritz method. The constructed solution was used to investigate how the physico-mechanical and geometric parameters of the mechanical system and the frequency of acoustic waves incident on the plate influence the sound-insulating parameters and the stress-strain state of the plate. [ABSTRACT FROM AUTHOR]

In this paper, an acoustic method is presented for measuring the porosity and the viscous tortuosity of air-saturatedporous materials at low frequencies. The proposed method is based on a temporal model of the direct and inverse problem for the reflection of low-frequency waves by homogeneous isotropic slab of porous material having a rigid frame. Reflected coefficient for a slab of porous material is derived from the responses of the medium to an incident acoustic pulse where a simple relation between flow resistivity, porosity, viscous tortuosity and the reflected waves is obtained. A numerical method and efficient tool for the estimation of the porosity and the viscous tortuosity are presented and discussed. [ABSTRACT FROM AUTHOR]

Enhanced ultrasonic method for the evaluation of acoustic parameters of air-saturated porous material is presented. This method is based on the direct and inverse problem of the reflection of an oblique incident wave from the surface of the porous medium with rigid frame. The interaction of the sound pulse with the porous material is described by the equivalent fluid model using the Johnson-Champoux-Allard approach (JCA) to describe the visco-inertial dissipative effects and the thermal effects inside the porous media. Four parameters are involved in the calculation of the dynamic density and the bulk modulus at high frequencies, namely the porosity ϕ , the high frequency limit of tortuosity α ∞ , the viscous and thermal characteristic lengths Λ and Λ′. The sensitivity of each parameter on reflected waves from the surface of the porous medium is studied for different oblique angles of incidence. The advantage of the proposed method is that the inverted values of porosity, tortuosity, viscous and thermal characteristic lengths are simultaneously obtained by minimizing between the experimental and simulated reflected signals. Moreover, no relationship is assumed between the viscous and thermal characteristic lengths. The numerical and experimental validation of this method is presented and compared to the theoretical prediction. [ABSTRACT FROM AUTHOR]

Xiaodongshan Bridge of Mengzi-Wenshan-Yanshan Expressway is located in cross canyon between Zhili Village and Wenlan Town in Mengzi City, Honghe County, Yunnan Province, the project includes 13 more than 40 m hollow piers, the highest pier up to 92 m. It used the high-pier column hydraulic climbing construction technology, the I-shaped wood keel plywood template construction technology, the strong skeleton-assisted reinforcement banding technology, the ultra-high pier column vertical control technology, the ultra-high pillar concrete spray maintenance and section water recycling technology, and the banana-style safety ladder application and many other new technologies in the project implementation process. Through the use of these new technologies, we has achieved good results in quality, safety and progress management. [ABSTRACT FROM AUTHOR]