• 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.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.2 s.95
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• pp.23-30
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• 1999

This paper investigates the radial performance of self-acting spiral-grooved air bearing, used to support small high-speed rotating bodies. Repeatable runout, nonrepeatable runout, stiffness and supporting load are selected as the performance. The clearance between rotor and stator, the stator groove depth, and the rotating speed are chosen as three main parameters affecting the performances. Force application and displacement measurement are done in a noncontact manner, in order not to disturb operation: electromagnetic force is applied to the rotor and gap sensors are used to measure the displacement of the rotor. Experimental results show that repeatable runout decreases as speed, groove depth and clearance decrease. Nonrepeatable runout decreases as clearance decreases, and it has a minimum value at $5.5{\mu}m$ of grove depth and a maximum value at speed of 18.000rpm. Stiffness increases as speed increases and clearance decreases, and has a maximum value around $5.5{\mu}m$ of groove depth. The relationship between force and displacement is linear for small displacement, but becomes nonlinear for large displacement. Supporting load is linearly proportional to the stiffness, and it is a maximum value around $4.75{\mu}m$ of clearance.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.2
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• pp.103-109
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• 2012

Fish generates large thrust through an oscillating motion with a compliant joint of caudal fin. The compliance of caudal fin affects the thrust generated by the fish. Due to the flexibility of the fish, the fish can generate a travelling wave motion which is known to increase the efficiency of the fish. However, a detailed research on the relationship between the flexible joint and the thrust generation is needed. In this paper, the compliant joint of a caudal fin is implemented in the driving mechanism of a robotic fish. By varying the driving frequency and stiffness of the compliant joint, the relationship between the thrust generation and the stiffness of the flexible joint is investigated. In general, as the frequency increases, the thrust increases. When higher driving frequency is applied, higher stiffness of the flexible joint is needed to maximize the thrust. The bending angles between the compliant joint and the caudal fin are compared with the changes of the thrust in one cycle. This result can be used to design the robotic fish which can be operated at the maximum thrust condition using the appropriate stiffness of the compliant joint.

• Journal of the Korean Geotechnical Society
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• v.34 no.2
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• pp.55-63
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• 2018

In order to support the load of the train with enough stiffness, a study on an effective method for the characterization of the stiffness of the compacted subgrade is required. In this study, the crosshole-type dynamic cone penetrometer (CDCP) is used for the stiffness characterization of the subgrade along the depth. For the application of the CDCP test, three points of compacted subgrades are selected as the study sites. For the study sites, CDCP test, in-situ density test, and light falling weight deflectometer (LFWD) test are conducted. As the results of CDCP tests, shear wave velocity profiles are obtained by using the travel times and the travel distances of the shear waves along the depth. In addition, maximum shear modulus ($G_{max}$) profiles are estimated by using the density of the subgrades and the shear wave velocity profiles. The averaged maximum shear moduli at each testing point are highly correlated with the dynamic deflection moduli ($E_{vd}$) determined by LFWD tests. Therefore, a reliable stiffness characterization of the subgrade can be conducted by using CDCP tests. In addition, because CDCP characterizes the stiffness of the subgrade along the depth rather than a representative value, CDCP test may be effectively used for the stiffness characterization of the subgrade.

• Structural Engineering and Mechanics
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• v.73 no.6
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• pp.641-649
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• 2020

The determination of midtower longitudinal stiffness has become an essential component in the preliminary design of multi-tower suspension bridges. For a specific multi-tower suspension bridge, the midtower longitudinal stiffness must be controlled within a certain range to meet the requirements of sliding resistance coefficient and deflection-to-span ratio. This study presents a numerical method to divide different types of midtower and determine rational range of longitudinal stiffness for rigid midtower. In this method, influence curves of midtower longitudinal stiffness on sliding resistance coefficient and maximum vertical deflection-to-span ratio are first obtained from the finite element analysis. Then, different types of midtower are divided based on the regression analysis of influence curves. Finally, rational range for longitudinal stiffness of rigid midtower is derived. The Oujiang River North Estuary Bridge which is a three-tower four-span suspension bridge with two main spans of 800m under construction in China is selected as the subject of this study. This will be the first three-tower four-span suspension bridge with steel truss girders and concrete midtower in the world. The proposed method provides an effective and feasible tool for engineers to design midtower of multi-tower suspension bridges.

• Transactions of the Society of Information Storage Systems
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• v.9 no.2
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• pp.62-66
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• 2013

For the production method, stamp base is increasing the market share. But also, by the manufacturing method, stiffness of the stamp base is small. Many studies have been carried out in order to increase the stiffness of the stamp base. In this study, we optimally designed according to the position of bolting using a screening method in order to increase the stiffness base. After establishing a simulation model, the maximum deformation and frequency of the first mode based having relevance with stiffness of the base, were optimized. There for, it was possible to expect of increasing the stiffness of the stamp base.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.4
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• pp.125-131
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• 2014

In order to develop stretchable substrates for wearable packaging applications, the variation behavior of elastic modulus was evaluated for transparent PDMS Sylgard 184 and black PDMS Sylgard 170 as a function of the base/curing agent mixing ratio. Both for Sylgard 184 and Sylgard 170, the true elastic modulus evaluated on a true stress-true strain curve was higher more than two times compared to the engineering elastic modulus obtained from an engineering stres-sengineering strain curve, and their difference became larger with increasing the stiffness of the PDMS. Sylgard 184 exhibited a maximum engineering elastic modulus of 1.74 MPa and a maximum true elastic modulus of 3.57 MPa at the base/curing agent mixing ratio of 10. A maximum engineering elastic modulus of 1.51 MPa and a maximum true elastic modulus of 3.64 MPa were obtained for Sylgard 170 at the base/curing agent mixing ratio of 2.

• Journal of The Korean Society of Integrative Medicine
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• v.8 no.3
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• pp.93-101
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• 2020

Purpose : Temporomandibular joint disorder (TMJD) is often accompanied by pain and limited range of motion of the jaw joint, which affect patients' quality of life and result in hypertrophy or hyperactivity of the muscles around the jaw joint. In this study, we compared the muscle thickness and tone of the masseter and sternocleidomastoid (SCM) muscles and the jaw range of motion in individuals with and without TMJD. Correlation comparison was performed on the results of the TMJD group. Methods : This study included 40 patients; 20 patients were assigned to an experimental group (TMJD group) and 20 to a control group (non-TMJD group). Ultrasonography, myotonometry, and measurements performed with digital Vernier calipers were used to determine the changes in muscle thickness, muscle tone, and maximum jaw opening, respectively. The independent t-test was used for intergroup comparison of data, and Pearson correlation coefficients were used to compare correlations in the TMJD group results. Results : We observed a significant intergroup difference in the masseter and SCM thickness during the relaxed and clenched phases (p<.05). A significant intergroup difference was also observed in maximum jaw opening (p<.05). With regard to muscle tone, we observed a significant intergroup difference in frequency (p=.011) and stiffness (p=.011) of the masseter, as well as in the frequency (p=.009) and stiffness (p=.026) of the SCM. We observed a moderate negative correlation (r=-.524) between maximum jaw opening and the frequency of the masseter. Additionally, we observed a moderately negative correlation between jaw opening and muscle stiffness (r=-.321). Conclusion : Planning exercise programs to treat patients with TMJD who present with pain should focus on efforts to reduce muscle thickness and achieve muscle relaxation (to reduce muscle tension) for improved jaw range of motion.

• Journal of the Korean GEO-environmental Society
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• v.2 no.4
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• pp.15-27
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• 2001

This paper proposes the force equations(thrust, moment) of corrugated steel culverts through the finite element method. The conditions for maximum thrust and maximum moment are determined from the analysis of soil-structure interaction during the three construction stages, such as backfill to the crown, backfill to the soil cover, and live loads. The proposed form of thrust and moment equations are deduced from the analysis of behaviour and the application of Castigliano's second theorem for the semi-arch structure. Finally, the coefficients used in the proposed equations are determined from a large number of analysis for the various geometries and the soil-structure relative stiffness under the conditions of maximum thrust and maximum moment.

• Steel and Composite Structures
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• v.1 no.4
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• pp.459-480
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• 2001

The damage suffered by steel structures during the Northridge (1994) and Kobe (1995) earthquakes indicates that the fully restrained (FR) connections in steel frames did not behave as expected. Consequently, researchers began studying other possibilities, including making the connections more flexible, to reduce the risk of damage from seismic loading. Recent experimental and analytical investigations pointed out that the seismic response of steel frames with partially restrained (PR) connections might be superior to that of similar frames with FR connections since the energy dissipation at PR connections could be significant. This beneficial effect has not yet been fully quantified analytically. Thus, the dissipation of energy at PR connections needs to be considered in analytical evaluations, in addition to the dissipation of energy due to viscous damping and at plastic hinges (if they form). An algorithm is developed and verified by the authors to estimate the nonlinear time-domain dynamic response of steel frames with PR connections. The verified algorithm is then used to quantify the major sources of energy dissipation and their effect on the overall structural response in terms of the maximum base shear and the maximum top displacement. The results indicate that the dissipation of energy at PR connections is comparable to that dissipated by viscous damping and at plastic hinges. In general, the maximum total base shear significantly increases with an increase in the connection stiffness. On the other hand, the maximum top lateral displacement $U_{max}$ does not always increase as the connection stiffness decreases. Energy dissipation is considerably influenced by the stiffness of a connection, defined in terms of the T ratio, i.e., the ratio of the moment the connection would have to carry according to beam line theory (Disque 1964) and the fixed end moment of the girder. A connection with a T ratio of at least 0.9 is considered to be fully restrained. The energy dissipation behavior may be quite different for a frame with FR connections with a T ratio of 1.0 compared to when the T ratio is 0.9. Thus, for nonlinear seismic analysis, a T ratio of at least 0.9 should not be considered to be an FR connection. The study quantitatively confirms the general observations made in experimental results for frames with PR connections. Proper consideration of the PR connection stiffness and other dynamic properties are essential to predict dynamic behavior, no matter how difficult the analysis procedure becomes. Any simplified approach may need to be calibrated using this type of detailed analytical study.