In recent years, robots have been widely used in assembly systems as called robotic assembly lines where a set of tasks have to be assigned to stations and each station needs to select one of the different robots to process the assigned tasks. Our focus is on u-type layouts because they are widely employed in many industries due to their efficiency and flexibility when compared to straight assembly lines. These lines offer more choices to group operations, a worker can be assigned to multiple stations located at entrance and exit sides. However, in many realistic situations, robots may be unavailable during the scheduling horizon for different reasons, such as breakdowns. This research deals with line balancing under uncertainty. The objective in this research is minimizing the cycle time for a given number of workstations and minimizing robot cost. This research deals with line balancing under uncertainty and presents one robust optimization model for balancing and sequencing of U-shaped robotic assembly line with considering set up times between task, failure robot times and preventive maintenance times for every robot. Since the NP-hard nature of the problem, multi-objective harmony search is developed to solve it. Numerical experiments demonstrated that by increasing uncertainty level, cost and cycle times increased.

This paper focuses on a novel model of the U-shaped assembly line balancing problem, in which the objective functions include cost, capacity, and quality. It is assumed that each task requires a set of equipment. In addition, the quality of tasks performed by each worker varies. Hence, the purpose of the model is that the total cost of the equipment is minimized and the quality of the work is maximized. Additionally, the number of workstations is minimized. At first, a multi-objective non-linear mixedinteger programming model is provided. Then, the model is linearized, and simulated annealing (SA) algorithm and two of its modified modes have been proposed to solve the problem. The proposed algorithm includes a new encoding/decoding scheme, as well as a local search for assigning the worker to each station. To determine the parameters in three algorithms, the experimental design has been used and various modes have been created by combining the parameters. Moreover, numerical examples were established based on the graphs found in the literature and the solution is compared with three algorithms, revealing the efficiency of each algorithm. Additionally, a case study on the nozzle assembly line in oil refineries was conducted to evaluate the efficiency of the proposed model and algorithm. Results from the case study show that the modified SA algorithms performed better.

In this study, to improve the efficiency of TLD, a Variably Baffled Tuned Liquid damper (VBTLD) was used. The baffles are so that they divide the tank into three equal parts when they are fully closed. Furthermore, when they are open or partially closed, they can serve as some obstacles and improve the energy dissipation parameters. When this damper meets an excitation with a specific frequency, the baffles can be tuned to make the frequency of sloshing equal to that frequency. VBTLD used in this paper could be set for frequency range from 1. 73 to 3 times of a specific frequency. Compared to a simple TLD, VBTLD can be tuned to a range of frequencies and improve the performance of structure against external excitation. At first, the benchmark building was modeled in OpenSees, then the performance of the device was verified by previous test results. To examine performance of VBTLD, Tuned Mass damper (TMD) with optimal parameters was used in this study. Results show that when the baffles are at the best angle, VBTLD with water depths of 42 mm has maximum response reduction for the numerical model subjected to the Kobe earthquake at intensities of 2, 4, 6 and 8% of the Initial maximum acceleration of the earthquake (PGA=0. 87g). The improvement of structural behavior compared to the optimal mass damper at maximum acceleration are respectively 23. 1, 22, 14. 6 and 10. 5% while for damper with water depths of 63 mm, they are respectively 8. 2, 9. 5, 6. 7 and 6. 8%.

Many existing buildings are irregular in plan or elevation because of asymmetric placement of masonry infills. The stiffness of masonry infill is a considerable value relating to that of the structure. Produced torsion from eccentricity because of infill stiffness leads to extra forces and deformations in structural members and diaphragms. An appropriate alternative to solve this problem especially in existing buildings is using dampers. dampers can enhance structural performance by reducing seismically induced lateral displacements and by reducing inelastic behavior of beams and columns. In this paper some simple models are used to show structural modeling and a conceptual discussion is presented on the numerical results. An accurate model for masonry infill has been used in structural model. Numerical results show the efficiency and high performance of added dampers to reduce the torsion effects in the structural elements.

In some aerospace vehicles, the tracking sensors which act in a tracking loop as stabilizer are mounted on a two degree of freedom gyro. The gyro must align its rotor axis with the line of sight in order to remove tracking errors. The tracking precision and sensitivity are functions of the gyros performance. One of the main factors in reducing the precision and producing instabilities is nutation vibration. This fluctuating motion, which is a dynamical inherent property of the system, is related to the gyro lateral moment of inertia, the length of gyro and its rotating speed. In order to investigate the capabilities of nutation damper and removing the wobble motion of a freely processing body, this paper analyzes a ring damper partially filled with viscous liquid with taking into account the behavior of the damper and its subsystems. The equations of motion for the dynamical motion of gyro, are obtained using Lagrangian approach, taking into account the friction of dampers and interaction of the liquid with the system equations of motion.

One of the most up-to-date seismic control devices are friction tuned mass damper (FTMD). This type of damper is a combination of a tuned mass damper (TMD) and a nonlinear frictional damper. In this paper, the governing equations for a single-degree-of-freedom (SDOF) structure equipped with a FTMD and effective parameters on these systems performance are expressed first. Then, SDOF structures with linear behavior equipped with a FTMD are modeled and validated in OpenSEES software. Finally, the sensitivity analysis of these models to their effective parameters is performed. The structures mass is assumed to be 10 tons, their period is 0. 5 second and their damping ratio is assumed to be 2%. Nonlinear time history analyses are done for these structures using 40 strong ground motions from the SAC project. These ground motions consist of 20 records (La01-La20) at design basis earthquake (DBE) level and 20 records (La21-La40) at maximum considered earthquake (MCE) level for the Los Angeles area. Effective parameters on the performance of FTMD assumed in this study are the friction coefficient of the damper, the mass ratio of the damper to the structure and the frequency ratio of the damper to the structure. Average of the structures' maximum displacement is determined for two ground motion records sets and effects of the mentioned parameters on the structural performance are discussed. Results show that the responses are more sensitive to frequency ratio rather than friction coefficient and mass ratio. The best value for the friction coefficient varies between 0. 1 and 0. 3 at DBE level, and varies between 0. 2 and 0. 4 for MCE level. Based on the results obtained for SDOF structures, application of FTMD on multi-degree-of-freedom (MDOF) is discussed in the next step. This is done for short period structures because this type of damper is more effective on these structures. Three MDOF structures with linear behavior and period of 0. 3, 0. 5 and 1 second are selected and the seismic performance of these structures equipped with FTMD is investigated and compared with the same structures equipped with tuned mass damper (TMD). The mass of stories is uniformly distributed among structure and the mass of each story is 10 ton. In addition, the damping ratio for the main structure in all models is assumed to be 2% and the stiffness of the stories is decreased linearly with the triangular pattern. Same ground motion records are used for the nonlinear time history analysis of MDOF structures and the results for the mean maximum relative displacement of the stories under DBE and MCE levels are compared for structures with FTMD and TMD. Results show that the structures equipped with FTMD have better performance than the structures equipped with TMD, but with increasing structures period, performance of two systems approach each other. In addition, 3 and 5 story structures equipped with FTMD have better performance at DBE level while a 10-story structure equipped with this damper has better performance at DBE level

In the Seismic design of Structures, in order to energy damping applied to Structure, when an earthquake occurs, various solutions have been proposed that dampers are also in this category. Due to the relatively simple design and also more economical than other methods of energy dissipations, dampers have been more attention of researchers, In this study, in order to performance improvement of rotational inertia damper, friction and viscous mechanisms added to this type of damper. The experimental sample of rotational friction damper was made in the Urmia university earthquake laboratory and studied in a simple frame. The 8-story structure under Kobe and Tabas will be analyzed to study the effects of made hybrid damper compared with the rotational inertia damper. These intended dampers can be used with different type of braces that embedded in the structure such as Chevron and diameter. At the first in the model studied the 8-story symmetrical structure are modeled in Sap2000. Subsequently the resulting section is modeled in Abaqus2016 to study the effects of different dampers. Experimental laboratory result, is significantly improved Rotational inertia friction damper compared to other friction damper and the loss of their sudden brakes.Also the dynamic responses of structure indicate the reduction of maximum roof displacement and also the base shear of structure. Analytical results indicate that Rotational inertia viscous damper act quickly compared with Rotational inertia friction damper and dissipate the energy applied to structure. But finally Rotational inertia friction damper will behavior better than similar viscous damper.