Academic literature on the topic 'Irregular resonant structures'
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Journal articles on the topic "Irregular resonant structures"
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Bondarenko, I. N., I. Yu Bliznyuk, and Е. А. Gorbenko. "MICROWAVE IRREGULAR RESONANT STRUCTURES." Telecommunications and Radio Engineering 78, no. 5 (2019): 385–92. http://dx.doi.org/10.1615/telecomradeng.v78.i5.20.
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Houfek, Karel, Martin Čížek, and Jiří Horáček. "On irregular oscillatory structures in resonant vibrational excitation cross-sections in diatomic molecules." Chemical Physics 347, no. 1-3 (May 2008): 250–56. http://dx.doi.org/10.1016/j.chemphys.2007.11.017.
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Ni, Wenjun, Chunyong Yang, Yiyang Luo, Ran Xia, Ping Lu, Dora Juan Juan Hu, Sylvain Danto, Perry Ping Shum, and Lei Wei. "Recent Advancement of Anti-Resonant Hollow-Core Fibers for Sensing Applications." Photonics 8, no. 4 (April 19, 2021): 128. http://dx.doi.org/10.3390/photonics8040128.
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Specialty fibers have enabled a wide range of sensing applications. Particularly, with the recent advancement of anti-resonant effects, specialty fibers with hollow structures offer a unique sensing platform to achieve highly accurate and ultra-compact fiber optic sensors with large measurement ranges. This review presents an overview of recent progress in anti-resonant hollow-core fibers for sensing applications. Both regular and irregular-shaped fibers and their performance in various sensing scenarios are summarized. Finally, the challenges and possible solutions are briefly presented with some perspectives toward the future development of anti-resonant hollow-core fibers for advanced sensing.
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D’Acunto, Mario, Francesco Fuso, Ruggero Micheletto, Makoto Naruse, Francesco Tantussi, and Maria Allegrini. "Near-field surface plasmon field enhancement induced by rippled surfaces." Beilstein Journal of Nanotechnology 8 (April 28, 2017): 956–67. http://dx.doi.org/10.3762/bjnano.8.97.
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The occurrence of plasmon resonances on metallic nanometer-scale structures is an intrinsically nanoscale phenomenon, given that the two resonance conditions (i.e., negative dielectric permittivity and large free-space wavelength in comparison with system dimensions) are realized at the same time on the nanoscale. Resonances on surface metallic nanostructures are often experimentally found by probing the structures under investigation with radiation of various frequencies following a trial-and-error method. A general technique for the tuning of these resonances is highly desirable. In this paper we address the issue of the role of local surface patterns in the tuning of these resonances as a function of wavelength and electric field polarization. The effect of nanoscale roughness on the surface plasmon polaritons of randomly patterned gold films is numerically investigated. The field enhancement and relation to specific roughness patterns is analyzed, producing many different realizations of rippled surfaces. We demonstrate that irregular patterns act as metal–dielectric–metal local nanogaps (cavities) for the resonant plasmonic field. In turn, the numerical results are compared to experimental data obtained via aperture scanning near-field optical microscopy.
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Cotti, Giordano, and Davide Guzzetti. "Results on the extension of isomonodromy deformations to the case of a resonant irregular singularity." Random Matrices: Theory and Applications 07, no. 04 (October 2018): 1840003. http://dx.doi.org/10.1142/s2010326318400038.
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We explain some results of [G. Cotti, B. A. Dubrovin and D. Guzzetti, Isomonodromy deformations at an irregular singularity with coalescing eigenvalues, preprint (2017); arXiv:1706.04808 .], discussed in our talk [G. Cotti, Monodromy of semisimple Frobenius coalescent structures, in Int. Workshop Asymptotic and Computational Aspects of Complex Differential Equations, CRM, Pisa, February 13–17, (2017).] in Pisa, February 2017. Consider an [Formula: see text] linear system of ODEs with an irregular singularity of Poincaré rank 1 at [Formula: see text] and Fuchsian singularity at [Formula: see text], holomorphically depending on parameter [Formula: see text] within a polydisk in [Formula: see text] centered at [Formula: see text]. The eigenvalues of the leading matrix at [Formula: see text], which is diagonal, coalesce along a coalescence locus [Formula: see text] contained in the polydisk. Under minimal vanishing conditions on the residue matrix at [Formula: see text], we show in [G. Cotti, B. A. Dubrovin and D. Guzzetti, Isomonodromy deformations at an irregular singularity with coalescing eigenvalues, preprint (2017); arXiv:1706.04808 .] that isomonodromic deformations can be extended to the whole polydisk, including [Formula: see text], in such a way that the fundamental matrix solutions and the constant monodromy data are well defined in the whole polydisk. These data can be computed just by considering the system at point of [Formula: see text], where it simplifies. Conversely, if the [Formula: see text]-dependent system is isomonodromic in a small domain contained in the polydisk not intersecting [Formula: see text], and if suitable entries of the Stokes matrices vanish, then [Formula: see text] is not a branching locus for the fundamental matrix solutions. The results have applications to Frobenius manifolds and Painlevé equations.
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Tsutsumanova, Gitchka G., Neno D. Todorov, Stoyan C. Russev, Miroslav V. Abrashev, Victor G. Ivanov, and Alexey V. Lukoyanov. "Silver Flowerlike Structures for Surface-Enhanced Raman Spectroscopy." Nanomaterials 11, no. 12 (November 24, 2021): 3184. http://dx.doi.org/10.3390/nano11123184.
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Micro- and nanoflowers are a class of materials composed of particles with high surface-to-volume ratio. They have been extensively studied in the last decade due to simple preparation protocols and promising applications in biosensing, as drug delivery agents, for water purification, and so on. Flowerlike objects, due to their highly irregular surface, may act also as plasmonic materials, providing resonant coupling between optical waves and surface plasmon excitations. This fact allows us to infer the possibility to use micro- and nanoflowers as effective surface-enhanced Raman scattering (SERS) substrate materials. Here, we report on the design and Raman enhancement properties of silver flowerlike structures, deposited on aluminum surface. A simple and cost-effective fabrication method is described, which leads to SERS substrates of high developed surface area. The morphology of the silver flowers on a nanoscale is characterized by self-organized quasiperiodic stacks of nanosheets, which act as plasmonic cavity resonators. The substrates were tested against rhodamine-6G (R6G) water solutions of concentration varying between 10−3 M and 10−7 M. Optimal SERS enhancement factors of up to 105 were established at R6G concentrations in the 10−6–10−7 M range.
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Firdaus, Nurman, Eko Budi Djatmiko, Rudi Walujo Prastianto, and Muryadin. "Experimental Study on Coupled Motion of Floating Crane Barge and Lifted Module in Irregular Waves." IOP Conference Series: Earth and Environmental Science 972, no. 1 (January 1, 2022): 012070. http://dx.doi.org/10.1088/1755-1315/972/1/012070.
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Abstract Installation and decommissioning activities of offshore structures often applied a floating crane barge for a lifting operation. The excessive movement response of lifted module affected by the motion of floating crane barge in waves can increase a large amplitude. However, the coupled motions of a floating crane barge and lifted module are not easy to predict accurately due to the dynamic movement of a lifted module and the complex coupling system. The coupled motion responses of a floating crane barge and a lifted module during lifting operation were investigated based on time domain by experimental method in this study. The model tests are carried out at Manoeuvring and Ocean Basin of Indonesian Hydrodynamic Laboratory, BRIN. The experimental conditions include the load cases of without and with a load of lifted module in crane tip, and the lifting operation was evaluated under irregular wave conditions. The experimental results show in that the phenomena of shift resonant frequency for the dynamic responses are clearly observed on the coupled motion of multibody system. The dynamic oscillations of the lifted module have a significant effect on the motion response of the floating crane barge. And the hoisting of lifted module has an obstructed effect on the rolling motion of crane barge.
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Thejaswini, R. M., L. Govindaraju, and V. Devaraj. "Experimental and Numerical Studies on Setback Buildings Considering the SSI Effect under Seismic Response." Civil Engineering Journal 7, no. 3 (March 3, 2021): 431–48. http://dx.doi.org/10.28991/cej-2021-03091664.
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From the previous studies it is observed that due to the effect of the earthquake, several irregular buildings failed vulnerably. Further the effect of sub soil conditions where these buildings have been founded also play an important role on the seismic response of these buildings. In the past, experimental studies on the seismic response of different setback building configurations have not been carried out. Therefore, in the present study the seismic behaviour of setback buildings considering Soil Structure Interaction (SSI) has been evaluated by conducting experimental and numerical investigations. Buildings with various setback configurations were considered and are designed as pile foundation supported structures. The irregularity index of these building configurations have been determined as per the existing codal provisions. These piles supported buildings representing the prototype structure have been scaled down according to geometric, kinematic and dynamic scaling laws. The scaled building models are subjected to vibrations beyond resonant frequencies using shake table facility. A comparison of the results has been made between experimental and numerical investigations. Based on the study it has been observed that storey displacements of building with regular configurations are higher in comparison with the setback buildings. It is also found that asymmetrical and symmetrical setback buildings having different irregularity indices as per IS:1893-2016 indicate nearly the same displacements at resonant frequencies. Doi: 10.28991/cej-2021-03091664 Full Text: PDF
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Georgiou, I. T., I. Schwartz, E. Emaci, and A. Vakakis. "Interaction Between Slow and Fast Oscillations in an Infinite Degree-of-Freedom Linear System Coupled to a Nonlinear Subsystem: Theory and Experiment." Journal of Applied Mechanics 66, no. 2 (June 1, 1999): 448–59. http://dx.doi.org/10.1115/1.2791069.
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The interaction dynamics of a cantilever linear beam coupled to a nonlinear pendulum, a prototype for linear/nonlinear coupled structures of infinite degrees-of-freedom, has been studied analytically and experimentally. The spatio-temporal characteristics of the dynamics is analyzed by using tools from geometric singular perturbation theory and proper orthogonal decompositions. Over a wide range of coupling between the linear beam and the nonlinear pendulum, the coupled dynamics is dominated by three proper orthogonal (PO) modes. The first two dominant PO modes stem from those characterizing the reduced slow free dynamics of the stiff/soft (weakly coupled) system. The third mode appears in all interactions and stems from the reduced fast free dynamics. The interaction creates periodic and quasi-periodic motions that reduce dramatically the forced resonant dynamics in the linear substructure. These regular motions are characterized by four PO modes. The irregular interaction dynamics consists of low-dimensional and high-dimensional chaotic motions characterized by three PO modes and six to seven PO modes, respectively. Experimental tests are also carried out and there is satisfactory agreement with theoretical predictions.
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Tarucha, Seigo. "Transport in Quantum Dots: Observation of Atomlike Properties." MRS Bulletin 23, no. 2 (February 1998): 49–53. http://dx.doi.org/10.1557/s0883769400031274.
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Recent advances in nanofabrication technologies have enabled us to fabricate semiconductor quantum dots in which electrons are three-dimensionally confined. These quantum dots are often referred to as artificial atoms since their electronic properties—for example the ionization energy and discrete excitation spectrum—resemble those of real atoms. Electrons bound to a nucleus potential encounter sufficiently strong effects of quantum-mechanical confinement and mutual Coulomb interactions that they are well arranged in ordered states, and this leads to the arrangement of atoms in the periodic table. It is well known in atom physics that the threedimensional spherically symmetric potential around atoms gives rise to the shell structure 1s, 2s, 2p, 3s, 3p,…. The ionization energy has a large maximum for atomic numbers 2, 10, 18,…. Up to atomic number 23, these shells are filled sequentially. Hund's rule determines whether a spin-down or a spin-up electron is added. This article describes how closely we can approach the electronic properties of real atoms through the use of semiconductor quantum dots.Both the effects of quantum confinement and Coulomb interaction become strong in quantum dots when the dot size is comparable to the electron wavelength and contains just a few electrons. The consequence of these factors on transport have only recently been studied in vertical-dot devices, which contain a dot located between source and drain contacts by means of heterostructure tunnel barriers because the few-electron regime is only accessible in the vertical-dot device. Studies include transport measurements through submicron resonant tunneling devices and submicron gated resonant-tunneling devices, and capacitance measurements on submicron double-barrier structures. However quantum-dot devices usually contain some disorder—for instance because of impurities or when the shape of the dot is irregular—which readily causes sample specific inhomogeneity in the electronic properties. Clean quantum dots, in the form of regular disks, have only recently been fabricated in a semiconductor heterostructure (Figure 1), and have been used to study the atomlike properties of artificial atoms.
Dissertations / Theses on the topic "Irregular resonant structures"
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Бондаренко, И. Н., and А. В. Галич. "Безэлектродная лампа на основе резонансной нерегулярной СВЧ структуры." Thesis, Вебер, 2013. http://openarchive.nure.ua/handle/document/6852.
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Проведены исследования нерегулярных резонансных структур, возбуждаемых на высших высокодобротных типах колебаний. Показана возможность достижения величин напряженности электрических полей, достаточных для формирования светоизлучающей плазмы в серосодержащей среде, при мощности микроволновой накачки не более 10 Вт. Особенностью рассматриваемых структур является возможность одновременной адаптации их конфигурации под обеспечение направленного светового излучения. Investigations of irregular resonant structures at the highest of high-Q oscillation modes are conducted. The possibility of achieving the electric fields is sufficient for the formation of sulfur-containing light-emitting plasma in the environment with power microwave pumping not exceeding 10 watts is shown. The feature of these structures is the ability to adapt their configuration simultaneously by providing directional light emission.
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Бондаренко, И. Н., and А. В. Галич. "Resonant irregular hybrid structures." Thesis, 2016. http://openarchive.nure.ua/handle/document/6781.
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Numerical model simulation and experimental device examination defines the conditions of excitation and types of high-Q oscillations in irregular hybrid structures and the conditions for communication of high-Q oscillations with an aperture of a coaxial probe parts are also identified. Irregular hybrid structure in configurations discussed can be effectively used to create high-Q resonator transducers for contactless microwave diagnostics of different objects. The possibilities of the use of irregular resonator structures for the formation of ionizing microwave fields in the electrodeless sulfur lamps, and as a guide elements of light are also investigated. The analysis of resonator structures of different geometry, configuration of the field strength, which are formed, and magnitude of the field strength, amplitude-frequency characteristics are carried out.
Conference papers on the topic "Irregular resonant structures"
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Bondarenko, Igor, and Aleksandr Galich. "Resonant irregular hybrid structures." In 2016 13th International Conference on Modern Problems of Radio Engineering. Telecommunications and Computer Science (TCSET). IEEE, 2016. http://dx.doi.org/10.1109/tcset.2016.7452007.
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Johannessen, Thomas B. "High Frequency Loading and Response of Offshore Structures in Steep Waves." In ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2011. http://dx.doi.org/10.1115/omae2011-50110.
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Offshore structures such as the TLP or the GBS have natural frequencies which are much higher than the frequencies of the incident waves in the survival conditions. Nevertheless, many offshore structures experience significant resonant response of modes with periods in the range of 2s to 5s, particularly in steep waves. In particular the ringing response of offshore structures characterised by sudden, large and isolated resonant response packets, has been a concern for many years. The loads which give rise to these events are difficult to describe both because they are small in magnitude relative to the load level close to the wave spectral peak and also because they are nonlinear in nature. In the present paper, available theoretical methods for high frequency loading is employed for irregular waves and compared with model tests. The methods which are used in the present are first and second order diffraction methods as well as a third order loading model for slender cylinders applied to irregular waves with continuous wave spectra. The results are compared with measurements of tether response and overturning moments on a TLP and a GBS respectively. Provided that the incident waves are treated carefully and care is taken in treating the high frequency tail of the incident wave, it is found that methods which are presently available give a good representation of the resonant response for the GBS structure. The GBS structure has a relatively low natural frequency and a mode shape which is excited easily by horizontal loading in the surface zone. In contrast, weakly nonlinear theory does not capture the high frequency loading on a TLP which has resonant frequencies at more than five times the spectral peak in the survival seastates. For this case it is found that wave impact with both the columns and the deck gives significant contributions to the resonant tether response. This is the case even if no significant horizontal deck impact is observed and highlights the need for a reliable deck impact load model.
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Crimaldi, D., and R. Singh. "Vibro-Acoustic Studies of Transmission Casing Structures." In ASME 1998 Design Engineering Technical Conferences. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/detc98/ptg-5788.
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Abstract Automotive transmission casing plates of irregular shape, with complex boundary conditions and non-uniform material properties, are experimentally and computationally studied to acquire a fundamental understanding of their dynamic and acoustic radiation characteristics. A modified flat cover is designed which simplifies the geometry while providing uniform thickness and material properties. Both covers (“real-life” and “laboratory”) are studied with free and bolted boundary conditions. In particular, the free boundary conditions are useful because they eliminate the cover-housing interaction allowing for a more detailed analysis of the cover plate. Finite element models for both covers under the free boundary conditions are developed and refined. Predicted natural frequencies and mode shapes are in excellent agreement with measured modal data. Then the finite element models are coupled with boundary element models to predict acoustic radiation properties. Predictions match well with measured acoustic directivity at resonant frequencies.
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Iwanowski, Bogdan, So̸ren Astrup, Marc Lefranc, and Rolf Hansson. "Identification of Ringing Events for a Slender Tubular Marine Structure." In ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2011. http://dx.doi.org/10.1115/omae2011-49511.
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Marine structures can experience loads coming from steep, non-linear waves. A transient response of the structure can be amplified in some circumstances due to phenomenon known as “ringing”. Exact conditions of the ringing response excitation are not well known and various definitions of what constitutes a ringing event appear in bibliography. This article aims at identification of ringing events for a slender marine structure subjected to the second order nonlinear irregular waves. Loads on the structure are calculated from Morison equation with extensions known as Rainey’s slender body theory. Consistent second order formulation for the flow kinematics above mean water level is employed. The excitation load is non-linear due to wave non-linearity, Morison equation’s drag term and non-linear inertia terms which can be found in Rainey’s formulation. The structure’s dynamic response is obtained by Finite Element calculations in time domain. Overall randomly-excited vibrations are analysed by statistical and spectral methods, and application of Continuous Wavelet Transform (CWT) is presented. The simulations show a number of sudden, high amplitude resonant events which can be classified as ringing.
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Liu, Yuming, Hongmei Yan, and Tin-Woo Yung. "Nonlinear Resonant Response of Deep Draft Platforms in Surface Waves." In ASME 2010 29th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2010. http://dx.doi.org/10.1115/omae2010-20823.
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To minimize body motions, floating marine structures are often designed with natural frequencies far away from the spectrum of ocean waves. Such design considerations led to a class of deep draft caisson vessels (DDCV or spars). Even so, large resonant responses may still be generated by excitation from nonlinear interactions of waves with body motions. Past experiments indicated that a DDCV experiences large-amplitude heave and pitch resonant motions when the incident wave frequency is much larger than the heave and pitch natural frequencies. Such resonant motions are not predicted by classical theories without considering nonlinear effects. This nonlinear mechanism has received little attention because of the complex nonlinear wave-body dynamics involved. In this work, we investigate nonlinear wave-wave and wave-body interaction effects on dynamic instability of such marine structures. We first perform a linear stability analysis of the wave-frequency body motion. From the analysis, we find that at certain incident wave frequencies the body motion is unstable with natural heave and pitch motions growing exponentially with time by taking energy from the incident wave through nonlinear wave-body interactions. The condition for the occurrence of instability and the key characteristic features of unstable natural heave and pitch motions, predicted by the analysis, agree well with the experimental measurement and our full-nonlinear numerical simulations. As time-domain fully nonlinear numerical simulations are computationally expensive, we further develop an approximate time-domain analytic model, by including the second-order body nonlinearity only, for predicting the onset of instability and ultimate response of DDCVs in both regular and irregular waves. We use this model to systematically investigate the dependence of unstable motions on frequency detuning, damping, body geometry, and wave parameters.
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Yan, Hongmei, Yuming Liu, and Yile Li. "Unstable Motion of a Floating Structure in Surface Waves." In ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2011. http://dx.doi.org/10.1115/omae2011-49621.
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Unstable resonant heave and pitch motions of a floating deep draft platform, under the action of a regular wave with the frequency equal to the sum of the heave and pitch natural frequencies, can be developed by nonlinear instability (Liu, Yan & Yung 2010). The instability is associated with difference-frequency interactions between the body motion and the ambient wave. In this work, we study the effect of the nonlinear instability upon floating platforms with relatively shallow drafts whose wave damping at heave/pitch natural frequencies may not be small. Direct time-domain numerical simulations of wave-structure interactions, which can take into account different levels of nonlinearity effects, are applied to understand the characteristics of the unstable coupled heave/pitch (or heave/roll) resonant motion and its dependence on the key physical factors. In particular, it is found that such a nonlinear instability at other wave conditions involving sum-frequency interactions between the body motion and the ambient wave can also occur. For practical applications, long-time nonlinear simulations with irregular waves are also performed. The results show that depending on the sea conditions and damping in the system, the unstable resonant motion associated with the nonlinear instability can be significant for platforms with shallow drafts.
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Wong, Brian Stephen, and Cheng Guan Tui. "Evaluation of Delaminations in Aluminium Honeycomb Structures Using the Mechanical Impedance Technique." In ASME 1997 Turbo Asia Conference. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/97-aa-069.
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This paper describes an evaluation of the capability of a mechanical impedance instrument, for detecting delamination defects in aluminium honeycomb structures. The resonant frequency was found to decrease as the centre of a defect was approached. The defects have been found to be accurately represented by a model for a vibrating plate, which is rigidly clamped at its edges. It was also possible to use resonant frequency to determine the size of the defects in the specimens used in this paper. An irregularly shaped defect showed that the rate of drop in resonant frequency across an extremity of the defect was affected by the radius at the extremity and the proximity to the main central area of the defect. An important result was that an ellipsoidal shaped defect would be sized as a circular defect of diameter equal to the minor diameter of the ellipse. Also a boron skinned honeycomb was found to behave similarly to a glass fibre skinned honeycomb.
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Nestega˚rd, Arne, Arve Johan Kalleklev, Kjell Hagatun, Yu Lin Wu, Sverre Haver, and Erik Lehn. "Resonant Vibrations of Riser Guide Tubes Due to Wave Impact." In ASME 2004 23rd International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2004. http://dx.doi.org/10.1115/omae2004-51545.
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The Kristin platform is a catenary moored semi-submersible production vessel (SSPV) intended for production of gas at the Kristin field at Haltenbanken. Kristin has 24 riser guide tubes for tie in of flexible risers, umbilicals and electric cables to the riser balcony. The riser guide tubes (RGT) provide the necessary guiding, support and protection for risers and cables. The guide tubes run vertically from the deck and through the extended east pontoon. The guide tubes are welded to the pontoon and horizontally supported at the underside of the balcony deck. During model tests of the Kristin platform performed in the Ocean Basin laboratory at Marintek, high frequency in-line vibrations of the RGTs were observed during passage of steep waves. The resonance period for the individual RGTs is 0.3 sec. To mitigate the vibration problem, a vibration suppression arrangement of stiff rods was introduced between the guide tubes. Model tests were performed with respect to extreme- and fatigue loads in regular and irregular waves, with and without the suppression arrangement. The model included the floating framework representing the hull and the 24 RGTs with correct diameter and resonance period. The model was suspended in a horizontal mooring system, giving resonance periods in surge and sway close to the prototype platform. A load-response model for the interaction between large steep waves and vertical flexible cylinders has been developed. A slender body load model derived from Morison’s equation is shown to be able to excite the resonant vibrations. The dominant part of the loading comes from the rapid change of added mass momentum, giving rise to an additional slamming term in the load formulation. The structural response is calculated from a recognized non-linear slender body response program. Numerical simulations have been carried out and compared with model tests for both regular and irregular waves. The numerical predictions confirm the effect observed in the model tests; i.e. connecting the tubes generally leads to a reduction of the high frequency response amplitudes.
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van Essen, Sanne, Willemijn Pauw, and Joris van den Berg. "How to Deal With Basin Modes When Generating Irregular Waves on Shallow Water." In ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/omae2016-54134.
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Modeling shallow-water waves in a basin with a finite length and width introduces challenges related to low-frequency (LF) waves, especially for testing of moored vessels with long natural periods. Waves in this frequency range are also present in reality, as for instance bound set-down waves and unbound free waves formed by the geometry bathymetry. In model basins, additional unwanted LF wave components will be formed as a side-product of the wave generation and due to the basin geometry though. Standing waves over the basin length and width (basin modes) can generally be identified, which are difficult to dampen using beaches. This is the case for every wave basin, as they all have finite dimensions. Moored structures generally have natural frequencies in the LF range, which may be excited by basin modes with similar frequencies. It is therefore important to understand the natural modes of a basin before tests with moored structures in shallow water are done. The energy of these basin modes increases and their natural frequency decreases with decreasing water depth (waves travel slower in shallow water). Generally, it can be said that the issues with basin modes are present on very shallow water (typically ∼15–30 m water depth full-scale for structures with a length around 200 m at a scale around 1 to 40). The smaller the basin for the same water depth, the higher the basin mode frequencies and the higher the likelihood of resonance problems. The energy and frequencies of the basin modes and their relevance for specific tests depend on the effective length and width of the basin, the water depth, wave conditions and the (mooring stiffness of) the structure under consideration. The influence of these variables is evaluated in the current study. Tests were done in MARIN’s Offshore Basin (OB), but most of the results are also expected to be applicable to other basins. The observed basin mode frequencies during these tests were compared to the theoretical values, and an overview of the unwanted LF wave content as a function of water depth, wave height and period is presented. The energy and shape of individual basin modes is also discussed. Considering these results, a practical approach for future basin projects on shallow water is described.
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Huang, Z. J., B. J. O’Donnell, T. W. Yung, and S. T. Slocum. "Determination of Viscous Damping for Low Frequency Motions of Floating Structures." In ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2011. http://dx.doi.org/10.1115/omae2011-50351.
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ExxonMobil Upstream Research Company developed an advanced model test method to determine reliable damping values for predicting low frequency motions of an FLNG barge and an LNG carrier [1]. An inertial compensation system was introduced in the test to confidently isolate the relatively very small viscous damping force from the total measured forces in the forced oscillation tests. In the system, the spring stiffness in the restoring mechanism was tuned such that the test was done near resonance. This method has been successfully applied to ExxonMobil forced oscillation tests to measure damping of deeply submerged, double body models. Three types of motions were generated in the tests: sinusoidal motions, decay motions and motions with multiple frequencies. In this paper, the authors attempt to correlate the damping obtained from decay tests and from tests with motions of multiple frequency components. Findings from this work help determine damping for predictions of full scale motion in irregular waves.