Structural and Acoustic Responses of a Submerged Stiffened Conical Shell

Shock and Vibration ◽

10.1155/2014/954253 ◽

2014 ◽

Vol 2014 ◽

pp. 1-14 ◽

Cited By ~ 4

Author(s):

Meixia Chen ◽

Cong Zhang ◽

Xiangfan Tao ◽

Naiqi Deng

Keyword(s):

Conical Shell ◽

Element Model ◽

Analytical Models ◽

Superposition Method ◽

Far Field ◽

Fluid Loading ◽

Low Frequencies ◽

Structural Responses ◽

The Individual ◽

Field Sound

This paper studies the vibrational behavior and far-field sound radiation of a submerged stiffened conical shell at low frequencies. The solution for the dynamic response of the conical shell is presented in the form of a power series. A smeared approach is used to model the ring stiffeners. Fluid loading is taken into account by dividing the conical shell into narrow strips which are considered to be local cylindrical shells. The far-field sound pressure is solved by the Element Radiation Superposition Method. Excitations in two directions are considered to simulate the loading on the surface of the conical shell. These excitations are applied along the generator and normal to the surface of the conical shell. The contributions from the individual circumferential modes on the structural responses of the conical shell are studied. The effects of the external fluid loading and stiffeners are discussed. The results from the analytical models are validated by numerical results from a fully coupled finite element/boundary element model.

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Experimental Characterization of a Flexible Two-Link Manipulator Arm

14th Biennial Conference on Mechanical Vibration and Noise: Vibration, Shock, Damage, and Identification of Mechanical Systems ◽

10.1115/detc1993-0282 ◽

1993 ◽

Author(s):

Randall L. Mayes ◽

G. Richard Eisler

Keyword(s):

Element Model ◽

Input Voltage ◽

Analytical Models ◽

Experimental Characterization ◽

Frequency Range ◽

Flexible Links ◽

Beam Elements ◽

Output Torque ◽

Manipulator Arm

Abstract Experiments were performed to verify the analytical models for a robotic manipulator with two flexible links. A finite element model (FEM) employing two-dimensional beam elements was used to model the structure. A proportional model relating input voltage to output torque was used for both hub and elbow joint motors. With some minor adjustments to the link stiffness, the FEM modal frequencies matched the experimentally extracted frequencies within 1.5%. However the voltage-torque relationship for the hub motor was found to exhibit dynamics in the frequency range of interest.

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Accurate Evaluation of Bolt and Clamped Members Stiffnesses Of Bolted Joints

10.1115/pvp2021-61621 ◽

2021 ◽

Author(s):

Rashique Iftekhar Rousseau ◽

Abdel-Hakim Bouzid ◽

Zijian Zhao

Keyword(s):

Finite Element ◽

Joint Stiffness ◽

Element Model ◽

Fe Analysis ◽

Bolted Joints ◽

Analytical Models ◽

Fe Modeling ◽

Bolted Joint ◽

A New Technique ◽

External Loads

Abstract The axial stiffnesses of the bolt and clamped members of bolted joints are of great importance when considering their integrity and capacity to withstand external loads and resist relaxation due to creep. There are many techniques to calculate the stiffnesses of the joint elements using finite element (FE) modeling, but most of them are based on the displacement of nodes that are selected arbitrarily; therefore, leading to inaccurate values of joint stiffness. This work suggests a new method to estimate the stiffnesses of the bolt and clamped members using FE analysis and compares the results with the FE methods developed earlier and also with the existing analytical models. A new methodology including an axisymmetric finite element model of the bolted joint is proposed in which the bolts of different sizes ranging from M6 to M36 are considered for the analysis to generalize the proposed approach. The equivalent bolt length that includes the contribution of the thickness of the bolt head and the bolt nominal diameter to the bolt stiffness is carefully investigated. An equivalent bolt length that accounts for the flexibility of the bolt head is proposed in the calculation of the bolt stiffness and a new technique to accurately determine the stiffness of clamped members are detailed.

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Monitoring the dynamic behaviors of the Bosporus Bridge by GPS during Eurasia Marathon

Nonlinear Processes in Geophysics ◽

10.5194/npg-14-513-2007 ◽

2007 ◽

Vol 14 (4) ◽

pp. 513-523 ◽

Cited By ~ 5

Author(s):

H. Erdoğan ◽

B. Akpınar ◽

E. Gülal ◽

E. Ata

Keyword(s):

Frequency Domain ◽

Element Model ◽

Traffic Load ◽

Suspension Bridges ◽

Engineering Structures ◽

Low Frequencies ◽

Temperature Changes ◽

Bridge Responses ◽

Special Complex ◽

Short Time

Abstract. Engineering structures, like bridges, dams and towers are designed by considering temperature changes, earthquakes, wind, traffic and pedestrian loads. However, generally, it can not be estimated that these structures may be affected by special, complex and different loads. So it could not be known whether these loads are dangerous for the structure and what the response of the structures would be to these loads. Such a situation occurred on the Bosporus Bridge, which is one of the suspension bridges connecting the Asia and Europe continents, during the Eurasia Marathon on 2 October 2005, in which 75 000 pedestrians participated. Responses of the bridge to loads such as rhythmic running, pedestrian walking, vehicle passing during the marathon were observed by a real-time kinematic (RTK) Global Positioning System (GPS), with a 2.2-centimeter vertical accuracy. Observed responses were discussed in both time domain and frequency domain by using a time series analysis. High (0.1–1 Hz) and low frequencies (0.00036–0.01172 Hz) of observed bridge responses under 12 different loads which occur in different quantities, different types and different time intervals were calculated in the frequency domain. It was seen that the calculated high frequencies are similar, except for the frequencies of rhythmic running, which causes a continuously increasing vibration. Any negative response was not determined, because this rhythmic effect continued only for a short time. Also when the traffic load was effective, explicit changes in the bridge movements were determined. Finally, it was seen that bridge frequencies which were calculated from the observations and the finite element model were harmonious. But the 9th natural frequency value of the bridge under all loads, except rhythmic running could not be determined with observations.

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Numerical simulation of free shear flows and far-field sound pressure directivity

International Journal for Numerical Methods in Fluids ◽

10.1002/fld.1650180403 ◽

1994 ◽

Vol 18 (4) ◽

pp. 337-359 ◽

Cited By ~ 2

Author(s):

W. Y. Soh

Keyword(s):

Numerical Simulation ◽

Sound Pressure ◽

Shear Flows ◽

Far Field ◽

Field Sound

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Dynamic Response Evaluation of Long-Span Reinforced Arch Bridges Subjected to Near- and Far-Field Ground Motions

Applied Sciences ◽

10.3390/app8081243 ◽

2018 ◽

Vol 8 (8) ◽

pp. 1243 ◽

Cited By ~ 4

Author(s):

Iman Mohseni ◽

Hamidreza Lashkariani ◽

Junsuk Kang ◽

Thomas Kang

Keyword(s):

Ground Motion ◽

Dynamic Performance ◽

Time History ◽

Bending Moment ◽

Element Model ◽

Structural Performance ◽

Far Field ◽

Inelastic Behavior ◽

Earthquake Loads ◽

Arch Bridges

This study assessed the structural performance of reinforced concrete (RC) arch bridges under strong ground motion. A detailed three-dimensional finite element model of a 400 m RC arch bridge with composite superstructure and double RC piers was developed and its behavior when subjected to strong earthquakes examined. Two sets of ground motion records were applied to simulate pulse-type near- and far-field motions. The inelastic behavior of the concrete elements was then evaluated via a seismic time history analysis. The concept of Demand to Capacity Ratios (DCR) was utilized to produce an initial estimate of the dynamic performance of the structure, emphasizing the importance of capacity distribution of force and bending moment within the RC arch and the springings and piers of the bridge. The results showed that the earthquake loads, broadly categorized as near- and far-field earthquake loads, changed a number of the bridge’s characteristics and hence its structural performance.

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Vibration Characteristics of Metamaterial Beams With Periodic Local Resonances

Journal of Vibration and Acoustics ◽

10.1115/1.4028453 ◽

2014 ◽

Vol 136 (6) ◽

Cited By ~ 53

Author(s):

M. Nouh ◽

O. Aldraihem ◽

A. Baz

Keyword(s):

Band Gap ◽

Low Frequency ◽

Element Model ◽

Small Mass ◽

Vibration Characteristics ◽

Structural Vibrations ◽

Low Frequencies ◽

Theoretical Predictions ◽

Gap Characteristics ◽

Unique Band

Vibration characteristics of metamaterial beams manufactured of assemblies of periodic cells with built-in local resonances are presented. Each cell consists of a base structure provided with cavities filled by a viscoelastic membrane that supports a small mass to form a source of local resonance. This class of metamaterial structures exhibits unique band gap behavior extending to very low-frequency ranges. A finite element model (FEM) is developed to predict the modal, frequency response, and band gap characteristics of different configurations of the metamaterial beams. The model is exercised to demonstrate the band gap and mechanical filtering capabilities of this class of metamaterial beams. The predictions of the FEM are validated experimentally when the beams are subjected to excitations ranging between 10 and 5000 Hz. It is observed that there is excellent agreement between the theoretical predictions and the experimental results for plain beams, beams with cavities, and beams with cavities provided with local resonant sources. The obtained results emphasize the potential of the metamaterial beams for providing significant vibration attenuation and exhibiting band gaps extending to low frequencies. Such characteristics indicate that metamaterial beams are more effective in attenuating and filtering low-frequency structural vibrations than plain periodic beams of similar size and weight.

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The effects of different frequencies of rhythmic acoustic stimulation on gait kinematics and trunk sway in healthy elderly population

10.1101/2020.11.20.390955 ◽

2020 ◽

Author(s):

Roberta Minino ◽

Emahnuel Troisi Lopez ◽

Pierpaolo Sorrentino ◽

Rosaria Rucco ◽

Anna Lardone ◽

...

Keyword(s):

Acoustic Stimulation ◽

Elderly Subjects ◽

Low Frequencies ◽

Healthy Elderly ◽

Gait Kinematics ◽

Trunk Sway ◽

Spatio Temporal ◽

The Individual ◽

Harmful Effects ◽

Healthy Elderly Subjects

ABSTRACTThe use of rhythmic acoustic stimulation (RAS) in improving gait and balance in healthy elderly subjects has been widely investigated. However, methodologies and results are often controversial. In this study, we hypothesize that both the kinematic features of gait and stability, depend on the frequency at which RAS is administered. Our aim was to observe, through 3D Gait Analysis, the effect of different types of RAS (at a fixed frequency or based on the average cadence of each subject) on both gait spatio-temporal parameters and stability. The latter was estimated through an innovative measure, the trunk displacement index (TDI) that we have recently implemented. We observed that the low frequencies RAS led to a general slowdown of gait, which did not provide any clear benefit and produced harmful effects on stability when the frequency became too low compared to the individual natural frequency. On the contrary, the high frequencies of RAS showed a slight acceleration of gait, accompanied by better stability (as documented by a lower TDI value), regardless of the type of RAS. Finally, the RAS equal to the individual natural cadence also produced an increase in stability.

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Hybrid multilevel plane wave based near-field far-field transformation utilising combined near- and far-field translations

Advances in Radio Science ◽

10.5194/ars-7-17-2009 ◽

2009 ◽

Vol 7 ◽

pp. 17-22 ◽

Cited By ~ 1

Author(s):

C. H. Schmidt ◽

T. F. Eibert

Keyword(s):

Near Field ◽

Measurement Techniques ◽

Plane Waves ◽

Low Complexity ◽

Far Field ◽

Computation Complexity ◽

Low Frequencies ◽

Field Transformation ◽

Translation Operators ◽

Equivalent Sources

Abstract. The radiation of large antennas and those operating at low frequencies can be determined efficiently by near-field measurement techniques and a subsequent near-field far-field transformation. Various approaches and algorithms have been researched but for electrically large antennas and irregular measurement contours advanced algorithms with low computation complexity are required. In this paper an algorithm employing plane waves as equivalent sources and utilising efficient diagonal translation operators is presented. The efficiency is further enhanced using simple far-field translations in combination with the expensive near-field translations. In this way a low complexity near-field transformation is achieved, which works for arbitrary sample point distributions and incorporates a full probe correction without increasing the complexity.

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