Torsional Structure Research Articles

Effects of soil–structure interaction on inelastic response of torsionally-coupled structures

In this paper, effect of torsion on the inelastic responses of structures resting on a nonlinear flexible medium is studied. Similar studies have shown that soil–structure interaction can result in augmentation of nonlinear responses of lower stories. The focus here is on the plan-wise distribution of inelastic responses of a torsional structure considering soil–structure interaction (SSI). For this purpose, 4, 8, and 12-story steel structures consisting of special moment frames are considered on a relatively soft soil. A nonlinear set of non-uniform springs is used for modeling of SSI. For each building, different structural responses are calculated under 11 suitably scaled earthquake ground motions at the design basis and maximum considered earthquake hazard levels. The mass eccentricity ratio is varied from zero to 30%. The inelastic responses include the story drift ratios and distribution of plastic hinge rotations and performance levels of each story and frame. The results clearly show that SSI increases the drift ratio of the first story up to 30% regardless of the eccentricity value. On the other hand, SSI amplified the cumulative plastic hinge rotation of the upper stories, especially in the taller buildings. The maximum value of amplification exceeded 3 and it was very sensitive to the extent of eccentricity. The local amplification effect of combination of torsion and SSI was much more severe where it reached values over 8 in the outer frames of the buildings, with SSI having the larger share in amplification.

Photothermal and Moisture Actuator Made with Graphene Oxide and Sodium Alginate for Remotely Controllable and Programmable Intelligent Devices.

Functional materials with energy storage and conversion properties have been useful for actuating devices. Here, a new kind of torsional fiber-based actuator including graphene oxide (GO) and natural sodium alginate was prepared by traditional wet spinning and twisting methods, during which the fiber structure was reconstructed, and the mechanical energy was prestored. When the twisted GO/SA (graphene oxide/sodium alginate) fiber was stimulated by infrared light or moisture, the torsional structure of the fiber was activated instantaneously to generate rapid and reversible rotational motion, thus realizing the automatic release and re-storage process of rotational kinetic energy. In addition, the full revolutions of the twisted GO/SA fiber have no attenuation after 100 reversible rotations when stimulated by moisture, which proves the excellent rotational stability. Due to its excellent flexibility and wettability, the twisted GO/SA fiber can be woven into a network or prepared into a series of programmable intelligent devices, which is of great significance for future flexible intelligent electronic devices.

CFD modelling of pressure and shear rate in torsionally vibrating structures using ANSYS CFX and COMSOL Multiphysics

This paper discusses numerical methodologies to simulate micro vibrations on a nontrivial torsionally oscillating structure. The torsional structure is the tip of a viscosity-density sensor using micro vibrations to measure the fluid properties. A 2D transient simulation of the fluid domain surrounding the tip of the sensor has been conducted in ANSYS CFX and COMSOL Multiphysics software. ANSYS CFX uses a frame of reference to induce the micro vibration whereas a moving wall approach is used in COMSOL Multiphysics for the full Navier-Stokes equation as well as their linearized form. The shear rate and pressure amplitude have been compared between the different numerical approaches. The obtained results show good agreement for both pressure and shear rate amplitudes in all models.

A Miniature Resonant and Torsional Magnetometer Based on Lorentz Force.

A microelectromechanical system (MEMS) torsional resonant magnetometer based on Lorentz force was investigated, consisting of torsional structures, torsional beams, metal plates, a coil, and a glass substrate. The Lorentz force, introduced by the interaction between the current in the MEMS coil and an external horizontal magnetic field, leads to displacement of the torsional structure. The strength of the magnetic field is proportional to this displacement, and can be detected with two sensing capacitors fabricated on the torsion structure and the substrate. To improve sensor sensitivity, a folded torsional beam and a double-layer excitation coil were introduced. The fabrication processes included lift-off, anodic bonding, chemical mechanical planarization, silicon nitride (SiNx) deposition, plasma-enhanced chemical vapor deposition, and inductively coupled plasma release. The prototype of the magnetometer was finished and packaged. The sensor performance, including its sensitivity and repeatability, was tested in a low-pressure environment. Additionally, the influences of structural parameters were analyzed, including the resistance of the excitation coil, the initial value of the capacitors, the elastic coefficient of the torsional beam, and the number of layers in the excitation coil. The test results demonstrated that this sensor could meet the requirements for attitude determination systems in low earth orbit satellites.

Experimental investigation of combined vibrations for a hydrofoil-rod system at low Reynold numbers

A hydrodynamic tunnel experimental investigation and analysis of vibration characteristics for a hydrofoil in a transient regime is considered. Tests are performed for NACA 0017 models with a non-uniform section at an angle of attack AOA = 5o and Reynolds numbers up to Re = 7.0 × 106. This study is related to a project design of experiments in a complex facility that involves several parameters. The analysis focuses on the vibrations of a hydrofoil for different values of the bracing stiffness kh, the torsional stiffness ka, and the locations of the elastic axis ā and of the center of gravity xa. The structural bracing response is investigated via measurements of the displacement of the free tip section of the hydrofoil using a three-axis acceleration sensor, and the torsional response of the structure is analyzed via measurements of displacements with single-axis acceleration sensors. The hydrofoil is made of reinforced plastics without flexibility, and elastic functions are provided by a spring support mechanism combined with a torsional structure. The study shows that an increase of the velocity V∞ results in different behaviors of the bracing and torsional amplitudes. Another notable result of the study is that the emergence of transition occurs simultaneously with additional peaks and changes of vibration amplitudes.

Twisted angle effects in the absorption spectra of carbon nanotube

The spectral characteristics of carbon nanotubes is essential for the development of optoelectronic components and sensors with application in many fields. The linear polarizability absorption spectra of the carbon nanotube with a twisted angle have been calculated by using the tight-binding model and sum-over-state method. First, a structural model of carbon nanotubes based on PPP(Pariser-Parr_Pople) was established, then a certain carbon atom was moved to a position where the carbon nanotubes are angled, and the torsional carbon nanotube structure model was calculated based on the change in bond length. Finally, the absorption spectrum at different twisted angles based on SOS(Sum-over-State) was calculated, and then the detailed analysis was made. It is found that the twisted angle has real impact on the absorption spectra of different types carbon nanotubes. The torsional angle leads to changes in the position and number of absorption peaks of the carbon nanotubes. Its influence on absorption spectra of different types of carbon nanotubes is different, but mainly concentrated in the low frequency region. Exactly, altering the twisted angle has an important effect on the absorption spectra of the carbon nanotube. This work offers a guidance of fabricating carbon nanotubes in the applications of photonic device in many fields.

Torsional Appearance of the Anterior Cruciate Ligament Explaining “Ribbon” and Double-Bundle Concepts: A Cadaver-based Study

To investigate the effect of the anterior cruciate ligament (ACL) torsion in 90° knee flexion on the morphological appearance of the ACL. Sixty knees from fresh frozen anatomical specimens were dissected. Eighteen knees were excluded according to selection criteria (torn ACL, mucoid degeneration of the ACL, arthritic lesions of thenotch, or knees harboring synovial inflammatory pathologies). After the removal of the synovial membrane, themorphology of the ligamentous fibers of the ACL and the twist were analyzed. Twisting of the ACL was measured using a goniometer in 90° knee flexion and defined by the angle of external rotation of the femur on the axis of the tibia required to visualize a flat ACL. The orientation of tibial and femoral footprint was described in a coronal plane for the tibia and a sagittal plane for the femur. In the 42 knees that were finally included, the ACL was always displayed as a single ribbon-like structure. The torsion of the fibers was on average 83.6° (± 9.4°) in 90° knee flexion. Thetwistingcouldbe explained by the different orientations of the femoral (vertical in a sagittal plane) and tibial (horizontal in a coronal plane) footprints. An intraligamentous proximal cleavage area was encountered in 11 cases (i.e.,26%). The ACL is a twisted structure with 83.6° of external torsion of fibers in 90° knee flexion. It is the torsion in the fibers, due to the relative position of bone insertions, which gives the ACL the appearance of being double bundle. The concept of the torsional flat structure of the native ACL may be of importance during ACL reconstruction, both in terms of graft choice (flat rather than cylindrical) and of technical positioning (torsion).

Uncertainties in seismic response of a torsional irregular structure

Torsional effects may significantly modify the seismic response of asymmetric buildings. This is due to the influence of several complex and difficult parameters to apprehend. The present paper deals with the influence of the input parameters on the seismic response of an asymmetric structure. Thus, several nonlinear dynamic analyses are performed in order to evaluate the effects of torsion on the seismic response of an asymmetric structure and shown their preponderances. The importance of the uncertain characteristics of the input seismic motion on the structural damage and the sensitivity of the response to the input parameters are assessed by a probabilistic analysis. The influence of these parameters is quantified through the use of partial correlation coefficient (PCC). The response in terms of roof displacement is calculated and used to construct fragility curves in order to quantify the probability of different damage levels according to the input motion.

The high-resolution FTR spectrum of ethane between 3170 and 3430 cm−1

The high resolution FTIR spectrum of ethane has been reinvestigated in the region near 3μm, where three perpendicular and one parallel infrared active bands are found.The main perpendicular band is ν4+ν10. It is shown that the perpendicular partners of the combinations ν4+2ν8 and ν4+2ν11 are coupled with each other in such a way that only one resultant mode can interact effectively with ν4+ν10, becoming detectable by intensity stealing. The third perpendicular band is found to be the hot (2ν4+ν10)−ν4, lying at about 33cm−1 below the cold ν4+ν10, because of the strong anharmonicity of the torsional mode ν4, and then well separated cold and hot transitions occur in this region. It is suggested that they could be exploited in the temperature monitoring in atmospheric and planetary spectra.The complexity and the irregular rotation–torsion structure makes an analysis of this perpendicular system not practicable, but a considerable body of new line assignments, especially for the hot transitions, have been found.We have been able to analyze the parallel band, in spite of the anomalous torsional structure, and some peculiar torsional effects show that the vibrational upper state must be the infrared active ν2+ν9+ν12(A2u).A total of 304 transitions of this active parallel band were fitted with a rms deviation of 0.0097cm−1 to derive band parameters, and interacting parameters from the perturbers 3ν4+ν11∓1+ν12∓1 and ν11±1+ν9∓1+ν12±1/ν11±1+ν9±1+ν12∓1.

High-resolution Fourier transform synchrotron spectroscopy of the C–S stretching band of methyl mercaptan, CH332SH

The C–S stretching fundamental band of 12CH332SH, the principal isotopologue of methyl mercaptan, has been investigated by Fourier transform infrared spectroscopy on the Far-Infrared beamline at the Canadian Light Source synchrotron. The band is centered around 710cm−1 and shows well-resolved a-type parallel structure. Most of the A and E spectral sub-bands have been assigned up to K=12 for the vt=0 torsional state and K=9 for the vt=1 state, along with a smaller variety of sub-bands for vt=2. C–S stretching energy term values have been determined employing known ground-state energies, and have been fitted to series expansions in powers of J(J+1) to determine the substate origins. The origins have in turn been fitted to a Fourier model to characterize the oscillatory torsional energy structure of the C–S stretching state. The amplitude of oscillation of the vt=0 torsional curves is significantly larger for the C–S stretch state compared to the ground state. A strategy devised to relate this amplitude to an effective torsional barrier height indicates a decrease of about 7% in the effective V3 for the C–S stretch. The vibrational frequency determined for the stretching fundamental from the Fourier fit is 710.3cm−1. The C–S stretching manifold is crossed by excited vt=4 torsional levels of the ground state, and strong torsion–vibrational resonant coupling is observed via perturbations in the spectrum together with forbidden sub-bands induced by mixing and intensity borrowing.

Ductility performance of lightweight concrete element containing massive palm shell clinker

Lightweight and high strength concrete are commonly needed for a variety of structural applications. Structure with lightweight concrete should assure adequate performance of member under heavy loading. In this study, experimental investigations have been conducted to study the displacement ductility and torsional ductility of lightweight concrete element containing high volume of waste materials. Crushed oil palm shell (OPS) is used as coarse aggregate in different mixes and palm oil clinker (POC) as fine aggregate for sand replacement. In this experiment using those waste materials palm shell clinker (PSC) concrete has been produced. Furthermore modulus of elasticity, modulus of resilience, modulus of toughness, stress–strain and torsional behavior of PSC concrete are obtained and compared with normal weight concrete (NWC) and POC lightweight concrete. The study reveals that PSC concrete, in contrast to various types of structural lightweight concrete (LWC) and NWC, is a ductile material in structural element. Though the modulus of elasticity of PSC concrete is 30% and 37% of NWC and POC lightweight concrete respectively, its modulus of resilience and modulus of toughness are significantly higher. The displacement ductility index of PSC concrete element is 2.8 times higher than NWC and POC lightweight concrete. In contrast the torsional ductility index of PSC lightweight concrete element is obtained 3.3 times higher than corresponding concretes. This study found that the torsional ductility of PSC concrete is higher than displacement ductility because of good interlocking properties yet for NWC, displacement ductility is higher than torsional ductility. Furthermore the modulus of toughness of PSC concrete is higher, more energy required to completely break this concrete containing high volume of waste materials. Thus PSC lightweight concrete may be more suitable than NWC and POC lightweight concrete in the earthquake-resistance of concrete structures subjected to compressive and torsional loading structure.

Jet-Cooled Fluorescence Spectroscopy of a Natural Product: Anethole

The jet-cooled fluorescence spectroscopy of the natural product molecule anethole ((E)-1-methoxy-4-(1-propenyl)benzene) has been studied. Single vibronic level fluorescence spectroscopy was used to verify the existence of two rotamers, syn and anti, with electronic origins at 32,889 and 32,958 cm(-1), respectively. The excitation and emission spectra show characteristics similar to those of styrene and styrene derivatives, including Cs symmetry and low amplitude motions of the propenyl (vinyl) group. As in styrene, the low amplitude modes show substantial Duschinsky mixing. Interestingly, the methoxy group shows very little activity in the spectroscopy of anethole but is found to influence the activity of the propenyl group. This activity is easily observed in the Franck-Condon activity of the propenyl-bending mode. Differences are explained using simple molecular orbital arguments. The observed torsional structure was modeled and compared to ab initio calculations, allowing us to determine a barrier to internal rotation of 623 cm(-1) for the propenyl group, in agreement with similar molecules. Calculated potential energy surfaces (using density functional theory) were used to construct a more complete representation of the torsion surface of anethole, incorporating the torsions of both substituents. Several anomalous features of the excitation spectra were assigned to van der Waals clusters of anethole with water. The assignments and analyses presented here are also consistent with density function calculations.

A zero torsional stiffness twist morphing blade as a wind turbine load alleviation device

This paper presents the design, analysis and realization of a zero stiffness twist morphing wind turbine blade. The morphing blade is designed to actively twist as a means of alleviating the gust loads which reduce the fatigue life of wind turbine blades. The morphing structure exploits an elastic strain energy balance within the blade to enable large twisting deformations with modest actuation requirements. While twist is introduced using the warping of the blade skin, internal pre-stressed members ensure that a constant strain energy balance is achieved throughout the deformation, resulting in a zero torsional stiffness structure. The torsional stability of the morphing blade is characterized by analysing the elastic strain energy in the device. Analytical models of the skin, the pre-stressed components and the complete blade are compared to their respective finite element models as well as experimental results. The load alleviation potential of the adaptive structure is quantified using a two-dimensional steady flow aerodynamic model which is experimentally validated with wind tunnel measurements.

Metric-torsional conformal gravity

When in general geometric backgrounds the metric is accompanied by torsion, the metric conformal properties should correspondingly be followed by analogous torsional conformal properties; however a combined metric torsional conformal structure has never been found which provides a curvature that is both containing metric-torsional degree of freedom and conformally invariant: in this Letter we construct such a metric-torsional conformal curvature. We proceed by building the most general action, then deriving the most general system of field equations; we check their consistency by showing that both conservation laws and trace condition are verified. Final considerations and comments are outlined.

High resolution difference bands of ethane C2H6 from torsionally excited lower states: rotation-torsion structure of the ν 2, ν 11 and ν 4 + ν 11 vibrational states

A high resolution Fourier transform infrared spectrum of C2H6, measured at a pressure of 173.3 Pa and an optical path of 153.2 m, was analysed between 1050 and 1295 cm−1. Extensive absorption due to the difference bands ν 11–ν 4, and several rotation–torsion lines of the difference band ν 2–ν 4, in the region of the x, y-Coriolis resonance of ν 2 and ν 11, were observed. This allowed a detailed rotation–torsion analysis of the upper states ν 11 and ν 2. The anomalous torsional structure, found in the non-degenerate vibrational state ν 2, can be explained as the effect of an Hamiltonian term accounting for a strong dependence of the torsional barrier height on the normal vibrational coordinate q 2. The value of the barrier height derivative is estimated to be 127 ± 10 cm−1. Also detected and assigned were ‘hot’ difference transitions belonging to the (ν 4 + ν 11)–2ν 4 band, yielding information on the upper state ν 4 + ν 11. It is believed that transitions from 3ν 4 to 2ν 4 + ν 11 are also detectable in the investigated region.

Torsional vibrational structure of the propene radical cation studied by high-resolution photoelectron spectroscopy

The pulsed-field-ionization zero-kinetic-energy photoelectron spectra of the X̃(+2)A(")←X̃(1)A' transition of CH(3)CHCH(2) (propene), CD(3)CDCD(2), and several partially deuterated isotopomers have been recorded in the region of their adiabatic ionization thresholds and up to 2000 cm(-1) of internal energy of the cations. The vibrational structure has been assigned on the basis of the frequency shifts resulting from deuteration of selected sites of the propene molecule. Two highly anharmonic progressions have been identified and assigned to the two torsional modes of the propene cation, the methyl and methylene torsions. The positions of the torsional levels could be approximately reproduced using one-dimensional models, allowing a semi-quantitative description of the potential energy surface along each torsional coordinate. The observation of forbidden vibrational bands and the analysis of their partially resolved rotational contours reveal the importance of the vibronic coupling between the X̃(+2)A(") and the Ã(+2)A(') states mediated by the methylene (ν(20)) and methyl (ν(21)) torsional modes.

ChemInform Abstract: Methyl Torsional Fine Structure in the High-Resolution S0 → T(n. pi.*) Excitation Spectrum of Acetophenone and Its Three Methyl- Deuterated Isotopomers.

ChemInform Abstract: Methyl Torsional Fine Structure in the High-Resolution S0 → T(n. pi.*) Excitation Spectrum of Acetophenone and Its Three Methyl- Deuterated Isotopomers.

Jet-cooled vibronic spectroscopy of potential intermediates along the pathway to PAH: phenylcyclopenta-1,3-diene

The vibronic excitation spectrum of phenylcyclopenta-1,3-diene (PCP3D) has been recorded in a supersonic expansion using resonant-two-photon ionization (R2PI) and laser-induced fluorescence (LIF) techniques. The spectrum is dominated by the S(0)-S(1) origin transition (31,739 cm(-1)), with several low-frequency vibronic bands in the first 400 cm(-1), followed by a sharp cut-off in intensity due to turn-on of a non-radiative process. Single vibronic level fluorescence (SVLF) spectra were recorded for the S(1) origin and several vibronic bands of PCP3D. The excitation and emission spectra show that the molecule is planar with C(s) symmetry in both the ground and excited states. Torsional potentials were simulated from the observed torsional structure in the excitation and emission spectra. The S(0) potential (V(2) = 1237 cm(-1), V(4) = -256 cm(-1)) is associated with a flat-bottomed potential supporting large inter-ring angular changes with little cost in energy (+/-36 degrees at 200 cm(-1)), with a barrier of 1237 cm(-1) at the perpendicular geometry. The S(1) potential is much stiffer about the planar geometry, with a calculated barrier five times larger than in S(0) (V(2) = 6732 cm(-1), V(4) = -477 cm(-1)). Based on the torsional assignments, weak bands in the same frequency region assigned earlier to the structural isomer phenylcyclopenta-1,4-diene [J. J. Newby, J. A. Stearns, C. P. Liu and T. S. Zwier, J. Phys. Chem. A, 2007, 111, 10914-10927] have been re-assigned as hot bands arising from v'' = 1 in the inter-ring torsion, nu(57).

State-specific studies of internal mixing in a prototypical flexible bichromophore: Diphenylmethane

Laser-induced fluorescence, resonant two-photon ionization, UV-UV hole burning, UV depletion, and single vibronic level fluorescence (SVLF) spectra of jet-cooled diphenylmethane (DPM) have been recorded over the 37 300-38 400 cm(-1) region that encompasses the S(1)<--S(0) and S(2)<--S(0) transitions. All transitions in the laser-induced fluorescence excitation spectrum are due to a single conformational isomer of DPM with C(2) symmetry. The S(1)<--S(0) origin transition occurs at 37 322 cm(-1), supporting a short progression in the symmetric torsion T with spacing of 28 cm(-1). The S(2)<--S(0) origin transition occurs 123 cm(-1) above the S(1) origin and possesses very weak torsional structure, observable only under saturating laser power conditions. A combination of SVLF spectroscopy and hot band studies is used to assign the frequencies of the symmetric torsion (T), antisymmetric torsion (T), and butterfly (beta) vibrations in the S(0), S(1), and S(2) states. The emission from the S(2) origin is composed of two components, a set of sharp transitions ascribable to the S(2) state and a dense "clump" of transitions ending in ground-state levels 81, 88, and 93 cm(-1) above the S(0) zero-point level ascribable to S(1)(v) emission. Assignment of the transitions in the clump leads to the conclusion that the single vibronic level responsible for the emission has mixed S(2)/S(1) character. The mixing involves several torsional vibronic levels in the S(1) manifold close in energy to the S(2) origin, with the correct symmetry to couple the two states. These levels involve significant torsional excitation. The close energetic proximity of these levels leads to a breakdown of typical vibronic coupling selection rules.

Torsion−Vibration Coupling in Methanol: Diabatic Behavior in the CH Overtone Region

Through a fit to methanol CH overtone data, a previously developed 4-dimensional torsion-vibration Hamiltonian is extended to high CH stretch excitation as well as to high torsional excitation. The strength of the torsion-vibration coupling is found to increase with CH stretch excitation. Systematic patterns of near degeneracy (3-, 4-, and 6-fold) are found in different regions of quantum number space. In the region of the CH fundamentals, an approximate a diabatic separation of the torsion (slow degree of freedom) from the CH stretches (fast degrees of freedom) accounts for the pattern of the energy levels and for the signs of the torsional tunneling splittings. For the higher CH overtones (v(CH) > or = 4), a diabatic representation accounts for the torsional structure obtained from the fully coupled calculation and for certain trends found in the pattern of the energy levels.