• Tribology and Lubricants
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• v.38 no.2
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• pp.63-69
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• 2022

In this research, the rotordynamic characteristics of the labyrinth seal with and without swirl brake were predicted using the computational fluid dynamic (CFD) model. Based on previous studies, a simple swirl brake consisting of square vanes without stagger angle is designed and placed in front of the seal inlet. The rotating frame of reference is utilized to consider the whirling motion of the rotor in the steady-state analysis since the whirling motion is transient behavior in nature. CFD analysis was performed in the range of -1 to 1 pre-swirl ratio for a given seal and swirl brake design and operating conditions. The CFD analysis result shows that the swirl brake effectively reduces the pre-swirl since the circumferential fluid velocity of labyrinth seal with swirl brake was lower than that without swirl brake. The cross-coupled stiffness coefficient, which is greatly affected by the circumferential fluid velocity, increased with an increasing pre-swirl ratio in a seal without a swirl brake but showed a low value in a seal with a swirl brake. The change in the damping coefficient was relatively small. The effective damping coefficient of the labyrinth seal with swirl brake was generally constant and showed a higher value than the labyrinth seal without swirl brake.

• Journal of Power System Engineering
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• v.1 no.1
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• pp.98-105
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• 1997

In general, crankshafts which are used in internal combustion reciprocating engines are subjects to high torsional vibration. Therefore, a damper is often used to minimize the torsional vibration in reciprocating engines. In this paper, in order to investigate damping performance of viscous damper, the real effective viscosity and complex damping coefficient of silicone oil, and the effective inertia moment of inertia ring are calculated considering the relative motion between damper casing and inertia ring. Based on these results multi-cylinder shaft is modeled into equivalent 2-degree of freedom system and optimum condition is estimated by calculating the amplification factor of viscous damper. Also the test damper was manufactured according to the result of theoretical investigation, the performance and durability was ascertained through experimental examination.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.10a
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• pp.399-406
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• 2000

Viscous dampers have been utilized as bearings and STU`s (Shock Transmission Unit) in earthquake resistant designs for bridges. Some viscous dampers are used as energy dissipators on one hand, but some dampers such as STU`s are used as fixing devices during an earthquake on the other hand. This paper discusses the effect of viscous dampers on the response of bridge with respect to the magnitude of damping coefficients. For this purpose, a typical bridge was taken as an example, and time-history dynamic analysis have been carried out. The input seismic data used in the analyses are relevant to the response spectra in the Koreans design code. The results show that there is an optimum value of coefficient considered most effective in the design. A STU with a large value of coefficient seems to make its support fixed. The response of the bridge is not much sensitive to the variation of the damping coefficients.

• Smart Structures and Systems
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• v.23 no.6
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• pp.521-536
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• 2019

Using magnetorheological (MR) dampers in multiswitch open-loop control mode has been shown to be cost-effective for cable vibration mitigation. In this paper, a method for analyzing the damping performance of taut cables incorporating MR dampers in open-loop control mode is developed considering the effects of damping coefficient, damper stiffness, damper mass, and stiffness of the damper support. Making use of a three-element model of MR dampers and complex modal analysis, both numerical and asymptotic solutions are obtained. An analytical expression is obtained from the asymptotic solution to evaluate the equivalent damping ratio of the cable-damper system in the open-loop control mode. The individual and combined effects of the damping coefficient, damper stiffness, damper mass and stiffness of damper support on vibration control effectiveness are investigated in detail. The main thrust of the present study is to derive a general formula explicitly relating the normalized system damping ratio and the normalized damper parameters in consideration of all concerned effects, which can be easily used for the design of MR dampers to achieve optimal open-loop vibration control of taut cables.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5A
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• pp.467-475
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• 2009

Existing studies have suggested Universal Curve only for supplemental damping by damper. Therefore net damping has been determined by means of arithmetic summation between intrinsic, aero-damping of cable and supplemental damping of damper. However linear combination approach by means of the arithmetic summation is not enough theoretical background. So validity of this approach should be verified in order to design adequate cable-damper system by engineers. This study establishes governing differential equation which can consider intrinsic, aero-damping and supplemental damping as well. And also analysis method is solved by combination of muller method and successive iteration method. Consequently, this study succeeds in verification for validity of linear combination approach. As a result of this study, linear combination approach is limitedly effective in case of low stiffness and optimum damping coefficient of damper, short distance from support to damper, lower vibration mode, low aero-damping, and normal windy environment. Whereas this study will be effective in case of opposite conditions, and existing studies or linear combination approach occur to further error. Meaning of this study presents exact solution for net damping of cable-damper system, and verifies linear combination approach by means of the analysis method. In the future, if monitoring of optimum damping coefficient of a damper against aero-damping is feasible on time, algorithm of this study will be available for control of cable and semi-active damper system such as magneto-rheological damper.

• Journal of Drive and Control
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• v.14 no.3
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• pp.40-49
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• 2017

This study presents an online estimation of an excavator's rotational inertia by using recursive least square with forgetting. It is difficult to measure rotational inertia in real systems. Against this background, online estimation of rotational inertia is essential for improving safety and automation of construction equipment such as excavators because changes in inertial parameter impact dynamic characteristics. Regarding an excavator, rotational inertia for swing motion may change significantly according to working posture and digging conditions. Hence, rotational inertia estimation by predicting swing motion is critical for enhancing working safety and automation. Swing velocity and damping coefficient were used for rotational inertia estimation in this study. Updating rules are proposed for enhancing convergence performance by using the damping coefficient and forgetting factors. The proposed estimation algorithm uses three forgetting factors to estimate time-varying rotational inertia, damping coefficient, and torque with different variation rates. Rotational inertia in a typical working scenario was considered for reasonable performance evaluation. Three simulations were conducted by considering several digging conditions. Presented estimation results reveal the proposed estimation scheme is effective for estimating varying rotational inertia of the excavator.

• International Journal of High-Rise Buildings
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• v.10 no.3
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• pp.229-242
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• 2021

Dynamic characteristics of tall building structures with double negative stiffness damped outriggers (2NSDO) are parametrically studied using the theoretical formula. Compared with one negative stiffness damped outrigger (1NSDO), 2NSDO can achieve a similar maximal modal damping ratio with a smaller negative stiffness ratio. Besides, the 2NSDO can improve the maximum achievable damping ratio to about 30% with less consumption of an outrigger damping coefficient compared with the double conventional damped outriggers (2CDO). Besides, the responses of structures with 2NSDO under fluctuating wind load are investigated by time-history analysis. Numerical results show that the 2NSDO is effective in reducing structural acceleration under fluctuating wind load, being more efficient than 1NSDO.

• Structural Monitoring and Maintenance
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• v.5 no.4
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• pp.489-506
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• 2018

This paper reported test of full-scale cables attached with four types of dampers: viscous damper, passive Magneto-Rheological (MR) damper, friction damper and High Damping Rubber (HDR) damper. The logarithmic decrements of the cable with attached dampers were calculated from free vibration time history. The efficiency ratios of the mean damping ratios of the tested four dampers to theoretical maximum damping ratio were derived, which was very important for practical damper design and parameter optimization. Non-ideal factors affecting damper performance were discussed based on the test results. The effects of concentrated mass and negative stiffness were discussed in detail and compared theoretically. Approximate formulations were derived and verified using numerical solutions. The critical values for non-dimensional concentrated mass coefficient and negative stiffness were identified. Efficiency ratios were approximately 0.6, 0.6, and 0.3 for the viscous damper, passive MR damper and HDR damper, respectively. The efficiency ratio for the friction damper was between 0-1.0. The effects of concentrated mass and negative stiffness on cable damping were positive as both could increase damping ratio; the concentrated mass was more effective than negative stiffness for higher vibration modes.

• Journal of Biosystems Engineering
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• v.29 no.5 s.106
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• pp.385-394
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• 2004

The objectives of this study were to investigate the effectiveness of rubber as an engine mount of walking-type cultivators and to determine its optimal spring constant and damping coefficient using a dynamic simulation of the engine mount system. Four different types of rubber mounts were tested to determine their spring constants and damping coefficients, and the best type was selected for the isolation of the engine vibrations transmitted to the handle. The total vibration levels transmitted to the handle when the rubber mounts weren't installed were 17.52 $m/s^2$. The total vibration levels transmitted to the handle when the rubber mounts were installed were 10.69 $m/s^2$ for Stripe 1, 11.33$m/s^2$ for Stripe 2, 10.92$m/s^2$ for Stripe 3 and 14.19$m/s^2$ for Hive, respectively, resulting in an average of $30\%$ reduction when compared with that without the engine mount. A dynamic model of the cultivator's engine-mount system and its simulation program were developed and verified. A method was proposed to determine the optimal spring constant and damping coefficient of the engine-mount system. It was found from the simulation that a spring constant of 4,100 kN/m and the largest damping coefficient were the most effective for the vibration isolation.

• Structural Engineering and Mechanics
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• v.86 no.4
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• pp.573-587
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• 2023

A conventional tuned mass damper (TMD) provides a passive control option to suppress the structures' wind- or earthquake-induced vibrations. However, excessive displacements of the TMD raise concerns in the practical implementation. Therefore, this study proposes a novel TMD designed for and deployed on a high-rise sightseeing tower. The device consists of an integrated two-way slide rail mount and an eddy current damper (ECD) with a stroke control mechanism. This stroke control mechanism allows the damping coefficient to automatically increase when the stroke reaches a predetermined value, preventing excessive damper displacements during large earthquakes. The corresponding two-stage damping parameters are designed with a variable-thickness copper plate to enable the TMD stroke within a specified range. Thus, this study discusses the detailed design schemes of the device components in TMD. The designed two-stage damping parameters are also numerically verified, and the structural responses with/without the TMD are compared. As seen in the results, the proposed TMD yields effective control authority to limit the acceleration response within a comfort level. In addition, this TMD resolves the spatial availability for the damper movement in high-rise buildings by the controllable damping mechanism.