Passive vibration control of rotating nonlinear beams is crucial due to its potential to mitigate harmful vibrations in various engineering applications, including aerospace and industrial sectors. This study examines how different system parameters and inherent nonlinearities influence the vibrations of a nonlinear rotating beam subjected to periodic external forces. A nonlinear energy sink (NES) is attached to the beam's tip to attenuate vibrations. The system is modeled using the Euler-Bernoulli beam theory and von Kármán strain-displacement relations, with equations of motion derived via Hamilton’s principle. Complexification Averaging and Runge-Kutta methods are applied for analytical and numerical solutions, respectively. The findings reveal that increasing the stiffness reduces vibration amplitude, while a rise in the nonlinear coefficient induces hardening behavior. The system exhibits saddle-node and Hopf bifurcations under certain conditions, indicating complex dynamic transitions. These phenomena, driven by the beam's nonlinearity and the NES, effectively diminish the vibration amplitude, highlighting the system's complex dynamic responses and the NES's efficacy in vibration mitigation

Considering the stress cycles in the joints and members due to wave induced forces on offshore platforms, fatigue analysis is therefore one of the most important analyses in the offshore platforms design. Although most of the steel jacket type platforms are designed and located in areas with relatively high ratios of operational sea-states, for maximum environmental events, would have acceptable safety margin in an in-place and seismic analyses; but for fatigue analyses it faces critical condition. Therefore it seems utilizing control mechanisms with the aim of increasing fatigue life in such platforms will be more preferable, to merely deck displacement control. Investigation of tuned mass damper parameters optimality for vibration control of wave excited systems, implies that optimum tuning and damping ratios are strongly dependent on sea-state, in addition to system parameters. The efficiency of optimally designed tuned mass damper for fatigue damage mitigation in real steel jacket platforms has been evaluated using full stochastic spectral analysis method and the results have shown a great performance for TMDs in this application. Sea-state conditions are predictable through weather forecasting methods and this can be benefited also to increase the efficiency of TMDs with variable tuning parameters which have been optimally adjusted for each sea-state. In a case study, utilization of this auxiliary device resulted in 26.6 % reduction in maximum fatigue damage. This efficiency can be increased to 36.7 % using different tuning parameters for each sea-state.

In this paper the behavior of a sensitive box to vibration, which connected to the vehicle by means of four undamped passive vibration isolator mounts, is studied using a ten DOF model to the road excitation. First, the governing differential equations are obtained using the Lagrange method, and the power spectral density (PSD) of the road profile is determined based on the ISO. The natural frequencies and mode shapes are extracted using modal analysis, and the response to the random base excitation is calculated based on random vibration theory. The root of mean square (RMS) is calculated by integration of PSD curve. The RMS of vertical acceleration of the box is plotted vs. the RMS of its relative vertical displacement by varying the stiffness of isolators in a real interval and the optimal stiffness is selected as the minimum point on the curve. The results indicate that the optimum isolator can be selected gardless of wheels and suspension system and the natural frequencies of isolator are between the natural frequencies of wheels and of suspension system. The RMS of acceleration the box has low sensitivity to the variation of the isolator stiffness around the optimum point.

Performances of tuned mass dampers and friction dampers to mitigate the wave induced vibrations in jacket type offshore platforms have been compared in this study. Due to the random nature of ocean waves, a full stochastic analysis method has been used to evaluate the response of the structures equipped with these devices. A stochastic linearization technique has been used to take the nonlinear behavior of friction dampers into account. The developed mathematical formulation has been applied to evaluate the response of realistic models, and to find out the optimal values for the adjustable parameters of friction dampers. The results have been verified in comparison with time domain nonlinear analyses results. Also, a computer utility has been provided in FORTRAN to perform the spectral fatigue analysis of platforms and together with a Genetic Algorithm utility, it has been used to find out the optimal parameters of a tuned mass damper to dissipate the wave induced vibrations of the platforms. Although the efficiency of both dissipative systems increases for more exible platforms due to the dominancy of the dynamic response, the functionality of TMD devices is more dependent on the dynamic characteristics of the platform; friction dampers seem to be more efficient for fixed steel jacket platforms.

This paper provides a comparison of the maximum inter-story drifts and tip acceleration of both a 16 and 30 stories building each with different structural systems; hybrid R.C moment frame with shear walls and hybrid steel frame with shear walls and X bracing which are equipped by passive dampers. Each of the building models were analyzed as fully non-linear structures for variety of dampers placements and subjected to a total of 4 different earthquake excitations. Three-dimensional (3D) finite-element models have been developed in the (FE) code LUSAS to predict the effects of passive damping on the vibrating structures. The manuscript tries to presents a rational comparison for determining dynamic response of seismic-excited high-rise buildings installed with friction and viscoelastic dampers in the cut outs of shear walls in order to capture their advantages in creating efficient damping systems. The results have shown that it is possible to achieve seismic mitigation, under all earthquake excitations, for all the structures considered in this study, by using appropriate damper types suitably located within the structure.

Nowadays one of the challenges that engineers and structural designers encounter is reduced vibrations of structures due to lateral forces such as earthquakes and winds. Taking into consideration that the design and construction of tall buildings is one of the most common methods of land-use in highly populated urban areas, the necessity and importance of identifying methods of controlling structural vibrations is felt more keenly than before. One of the methods of structural motion control is passive structural motion control with friction dampers. In this study, the main focus on the application and performance of friction dampers is new ideas for using the friction phenomenon to control structural vibrations and the design challenges of structures with friction dampers. For this purpose, first, we try to point out the important concepts in vibration control. Then, the goals, methods and results of various existing researches are examined to provide a clear view of friction dampers for structural engineers and as a start for future research to develop and improve the performance of friction dampers.

Objective: Active and passive smoking lead to the production of a number of oxidants and antioxidants with various adverse health effects compromising the immune system. Tobacco use increases the production of free radicals as well. The purpose of this study was to determine the effects of passive smoking on total antioxidant capacity (TAC) of serum and saliva in rats.Methods: This experimental study was conducted on 18 rats with an age range of 7-11 weeks weighing 160-200 g; 9 of them were exposed to cigarette smoke 3 times daily for 8 minutes. The 9 controls were not exposed to cigarette smoke. After injection of 0.2 mg/kg midazolam and 0.5 mg/kg pilocarpine, serum and saliva samples were taken from subjects in the exposure and control groups at 0, 15 and 30 days. Serum cotinine was measured using ELISA kit. TAC of saliva and serum was measured using ferric reducing antioxidant power (FRAP) assay. TAC values at different time points were statistically analyzed in each group using Repeated Measures ANOVA and compared between the two groups using t-test.Results: At baseline, no significant difference existed between the two groups in terms of serum cotinine concentration but at days 15 and 30, cotinine serum concentration significantly increased in the exposure group. At baseline and 30 days, no significant difference existed between the two groups of passive smoker and non-smoker in terms of serum TAC values but at day 15, serum TAC values were significantly higher in the exposure group. Also, TAC of salivawas significantly higher in the passive smoker group at baseline and at day 15 but at day 30, the difference in this respect between the two groups was not statistically significant.Conclusion: Based on the obtained results, changes in TAC of serum and saliva in rats due to exposure to cigarette smoke were compensated by their immune system activity. However, further investigations are still required in this respect.

With the increasing development of military weapons around the world and the variety of explosives, terrorist attacks are growing threats. The vibration control technology is well developed against natural loads. Although blast loads are different than natural loads, this technology can also be used to reduce explosive load responses. For this purpose, passive and semi-active methods, including tuned mass damper (TMD) and magnetorheological (MR) damper, have been used to reduce the vibrations caused by the blast load in the base-isolated structure. In this study, a type-2 fuzzy system has been used to determine the appropriate voltage of the MR damper so that the existing uncertainties do not adversely affect its performance. The numerical simulation of two explosives at 15m from 5 degrees of freedom system, has been performed through theoretical and empirical equations. The use of the proposed control tools along with the base isolation system showed that not only can these methods maintain the proper performance of the base isolated system but limit the displacement and possible damages at larger excitations. The comparative results show that the use of MR damper along with the base isolation system can have the best performance against blast and seismic loads. The use of this system, on average reduces the maximum drift of the stories to about 36% in blast loads, 68% in far-field earthquakes and 46% in near-field earthquakes. Furthermore, the drift of the isolation bearing is significantly limited compared to the base-isolated system with TMD.