Rod Modes Research Articles

Microstructure of Rod-Based Capillary Suspensions with Different Rod Aspect Ratios under Quiescent and Shear Flow

A particle-assembled microstructure in ternary capillary suspensions consisting of polyisobutylene (PIB) as the matrix phase, poly(ethylene oxide) (PEO) as the minor fluid phase, and silica (SiO2) particles with different aspect ratios (ARs) is probed by an in situ optical-shear technique, scanning electronic microscopy, and confocal laser scanning microscopy as well as rheometry. It is found that the capillary bridging force brought by the presence of the PEO wetting layer between particles can be influenced by the AR of particles and shear rate, which all play decisive roles in determining the microstructure and rheological properties of suspensions. Moreover, two novel aggregation modes of rods and an interesting spatiotemporal organization phenomenon of particle aggregates (vorticity-aligned particle bands) are found under shear flow.

Robust design of fuel rods against potential structural damage by flow-induced vibration

We studied the flow-induced vibration (FIV) and fretting wear of fuel rod with grid relaxation. According to the flow distribution around a type of pressurized water reactor (PWR) fuel rod, the power spectral density (PSD) is obtained to characterize the turbulence excitation. By combining the correlation of PSD test parameters, the mean square value of the vibration displacement of each rod mode is found, and then the wear depth of dimple position is calculated based on the ARCHARD wear formula. The grids may relax due to inaccurate manufacturing, fuel transportation and in-core irradiation. The absence of grid clamping force would significantly influence the rod mode and thereby changes its FIV responses. Simulation results show that the failure of the leaf spring has negligible effect on the rod natural frequency whereas the dimple failure near the location with larger FIV amplitude has a much significant effect. The lateral flow velocities at the inlet and outlet of the core are larger. For the fully clamped fuel rod, the responses amplitude of turbulent excitation at the bottom and top of the fuel rod are larger. This is even more obvious with a failed dimple at these locations. Comparatively, the effect of dimple support failure in the middle is less influential. The influence of dimple support failure on the rod wear depth depicts basically the same trend as on the maximum FIV amplitude.

The lowest vibration spectra of multi-component structures with contrast material properties

The paper is concerned with the lowest vibration modes of multi-component rods and cylinders with alternating high contrast material properties of the components. It is demonstrated that these modes correspond to almost rigid body motions of the “stiffer” components. A general perturbation scheme is developed. At leading order polynomial frequency equations are derived, along with linear algebraic equations for the associated eigenforms. In addition, for multi-component rods, higher order corrections are also obtained. Examples of three- and five-component structures are presented, illustrating the efficiency of the proposed approach.

Tunable mode-selective characteristics of a mode-filter petal-fiber with liquid rods

In this paper, a novel tunable mode-filter optical fiber consisting of a high-index core and petal-shaped cladding surrounded by a high-index outer ring is proposed. The cladding of the fiber is formed with periodically arranged liquid rods that support cladding modes with effective indexes. These cladding modes form a two-super-mode group. The mode-selection is realized by the coupling between the core mode and the super-mode group. With the petal-shaped cladding, cladding mode can be transmitted at high loss. With the liquid rods, the index-band of super-mode group can be adjusted by external temperature field, thereby achieving the purpose of tunable mode-selective. The super-mode group formed by the LP<sub>11</sub> mode of the liquid rods effectively increases its operating bandwidth and temperature tuning range. The numerical simulation results show that the mode-filter fiber with a length of only 71.4 mm can achieve a particular mode loss more than 20 dB, while other modes’ losses are below 1 dB. This special fiber can be used as a mode-filter in the few-mode fiber transmission system to reduce mode crosstalk of converters, multiplexer/demultiplexer, optical switch and optical routing.

Experimental Study on Bearing Capacity of Reinforced Steel Tubular Scaffold under Uniform Loads

Five groups of tests were designed to analyze the influence of node types (fastener connection and mortise‐and‐tenon joint) and reinforcement modes of top horizontal cross rods (weak truss and stiffening truss) on the bearing capacity of the steel tubular scaffold under vertical uniform loads. Loading phenomenon, bearing capacity, failure mode, displacement at key positions, and strain development characteristics during tests were analyzed. The following conclusions were drawn: (1) The fastener scaffold reinforced by a top truss showed the highest bearing capacity and high material utilization. (2) The fastener scaffold reinforced by a top weak truss increased the bearing capacity and caused coordinated deformation of the top horizontal force rods. (3) The node displacement of the mortise‐and‐tenon scaffold was smaller than that of the fastener joint, whereas its bearing capacity was higher. (4) Vertical diagonal bracing can slightly increase the bearing capacity of the mortise‐and‐tenon scaffold but can also constrain the deformation of the vertical rods and change the failure mode.

Effects of Hydrostatic Pressure on the Surface Plasmon Resonance of Gold Nanocrystals.

The surface plasmon resonances of gold nanospheres and nanorods have been measured as a function of hydrostatic pressure up to 17 GPa in methanol-ethanol 4:1 solvent and up to 10 GPa in paraffin. Both the sphere resonance and the longitudinal rod resonance exhibit redshifts, whereas the transverse rod mode shows an extremely weak redshift or blueshift depending on the nanorod aspect ratio. Solidification of the solvent around 11 GPa causes some aggregation of the particles, readily identified through broadening of the surface plasmon band and further redshifting. Spectra collected during loading and unloading cycles exhibit only minimal hysteresis if the pressure remains below 11 GPa. The surface plasmon shifts are the result of two competing effects. Compression of the conduction electrons in the metals increases the bulk plasma frequency, which causes a blueshift. However, the increase in the solvent density under hydrostatic load leads to an increase in the solvent refractive index, which in turn leads to a redshift. We find that after accounting for the solvent contribution, we can spectroscopically determine the bulk modulus of the gold nanoparticles with a precision of 10%. The value obtained of K0 = 190 GPa is significantly higher than the value for bulk gold (167 GPa). Furthermore, we show that pressure-induced solidification causes a significant broadening and anomalous shift of the surface plasmon band that we attribute to aggregation and nanorod deformation.

Optical Characterization of Gold Nanoblock Dimers: From Capacitive Coupling to Charge Transfer Plasmons and Rod Modes

The optical properties of plasmonic dimers consisting of two adjacent metal nanoparticles can be tuned over a broad spectral range by changing only slightly the dimer geometry. Most drastic are the changes in the smallest interparticles distances, and often only optical spectroscopy together with electromagnetic simulations yields insights into the geometry of the junction. Here, we study the coupling of gold nanoblock dimers, two square nanoantennas with different nanogaps between their closest corners. We identify three different coupling regimes—capacitively coupled, conductively bridged, and fused dimers—and optically characterize the transitions between them. By combining sample array fabrication, single-particle hyperspectral measurements, and electromagnetic simulations, we were able to examine in detail the effects of junction geometry on the resonance energy and intensity of the plasmon modes supported by gold nanoblock dimers.

Continuous micro-feeding of fine cohesive powders actuated by pulse inertia force and acoustic radiation force in ultrasonic standing wave field

Stable continuous micro-feeding of fine cohesive powders has recently gained importance in many fields. However, it remains a great challenge in practice because of the powder aggregate caused by interparticle cohesive forces in small capillaries. This paper describes a novel method of feeding fine cohesive powder actuated by a pulse inertia force and acoustic radiation force simultaneously in an ultrasonic standing wave field using a tapered glass nozzle. Nozzles with different outlet diameters are fabricated using glass via a heating process. A pulse inertia force is excited to drive powder movement to the outlet section of the nozzle in a consolidated columnar rod mode. An acoustic radiation force is generated to suspend the particles and make the rod break into large quantities of small agglomerates which impact each other randomly. So the aggregation phenomenon in the fluidization of cohesive powders can be eliminated. The suspended powder is discharged continuously from the nozzle orifice owing to the self-gravities and collisions between the inner particles. The micro-feeding rates can be controlled accurately and the minimum values for RespitoseSV003 and Granulac230 are 0.4 mg/s and 0.5 mg/s respectively. The relative standard deviations of all data points are below 0.12, which is considerably smaller than those of existing vibration feeders with small capillaries.

Resonant SRS Filtering Fiber for High Power Fiber Laser Applications

We explore the properties of a novel stimulated Raman scattering (SRS) filtering fiber for high average or high peak optical power delivery applications. The fiber geometry is based on a series of circularly arranged high index rods embedded in a leaky silica cladding. The operation principle relies on the resonant coupling of the core and rod modes and the wavelength-dependent leaking of the structure. The fabricated fiber demonstrated wide transmission window and filtering of SRS with extinction in excess of 20 dB at the Raman Stokes wavelength, excellent robustness with bending, and high output beam quality. The fiber has been tested as a beam delivery fiber of a commercial pulsed fiber laser system in order to explore the filtering performance and its limitations.

Highly sensitive torsion sensor based on directional coupling in twisted photonic crystal fiber

We demonstrate a novel torsion sensor based on a twisted photonic crystal fiber with an embedded liquid rod waveguide. Only one resonant dip appears in the transmission spectrum in the range of 1,350–1,650 nm, which is associated with the directional coupling between the core and rod modes. The relative position of the fiber core with respect to the liquid rod waveguide is altered owing to the torsion stress, which changes the phase-matching condition and leads to a resonant-wavelength shift. The helical structure of the liquid rod waveguide can improve the torsion sensitivity of the device and provide an ability to distinguish the rotation direction. The measured torsion sensitivities were as high as ∼203 and ∼208 nm·mm·rad−1 in the clockwise and counterclockwise rotations, respectively.

Experimental Research on Destruction Mode and Anchoring Performance of Carbon Fiber Phyllostachys pubescens Anchor Rod with Different Forms

The anchoring technology is extensively applied in reinforcing protection of the earth relics. Now that no specification is available for different new anchor rods in earth relics protection due to diversified destruction modes of earth relics and complexity of engineering technology conditions, it is urgent to guide reinforcing design and construction with a complete detailed anchor rod research document. With the new carbon fiber Phyllostachys pubescens anchor rod as the research object, six lots of in situ tests are designed to, respectively, study the destruction mode and anchoring performance of the carbon fiber Phyllostachys pubescens anchor rod under different anchor length L, anchor rod diameter D, bore diameter H, grouting material S, rib spacing R, and inclination angle A in this paper. By studying load shift curve experiment in drawing of the anchor rod, the destruction mode and ultimate bearing capacity of the carbon fiber Phyllostachys pubescens anchor rod in different experiment lots are obtained, and the concept of permitted application value N in anchor rod design is proposed. By studying strain distribution characteristics of anchor rods in experimental lots along the length direction under action of the permitted application value N and combining the existing destruction mode and ultimate bearing capacity, this paper analyzes influences of L, D, H, S, R, and A on anchoring effect of the carbon fiber Phyllostachys pubescens anchor rod; gives the reasonable value range of L, D, H, and R when the carbon fiber Phyllostachys pubescens anchor rod is used for reinforcing design of the earth relics; and provides favorable experiment basis for reinforcing design of the earth relics based on the carbon fiber Phyllostachys pubescens anchor rod.

Plasmonic modes of polygonal rods calculated using a quantum hydrodynamics method

Plasmonic resonances of nanoparticles have drawn lots of attentions due to their interesting and useful properties such as strong field enhancements. These systems are typically studied using either classical electrodynamics or fully quantum theory. Each approach can handle some aspects of plasmonic systems accurately and efficiently, while having its own limitation. The self-consistent hydrodynamics model has the advantage that it can incorporate the quantum effect of the electron gas into classical electrodynamics in a consistent way. We use the method to study the plasmonic response of polygonal particles under the influence of an external electromagnetic wave, and we pay particular attention to the size and shape of the particle and the effect of charging. We find that the particles support edge modes, face modes and hybrid modes. The charges induced by the external field in the edge (face) modes mainly localize at the edges (faces), while the induced charges in the hybrid modes are distributed nearly evenly in both the edges and faces. The edge modes are less sensitive to particle size than the face modes, but are sensitive to the corner angles of the edges. When the number of sides of regular polygons increases, the edge and face modes gradually change into the classical dipole plasmonic mode of a cylinder. The hybrid modes are found to be the precursor of the Bennett mode, which cannot be found in classical electrodynamics.

Generating elastic band gaps in square lattice grid by periodical cut-off operations

From periodically cutting off rods in square lattice grids, we give an easy and feasible way to generate elastic band gaps (BGs) in it. We define the model of the periodical cut-off (PCO) square lattice grid, and study the frequency dispersion relation and the motion modes of rods, as well as the frequency responses. On this basis, we confirm that the PCO operation is feasible to generate BGs in square lattice grids. Furthermore, the BGs generated in PCO square lattice grids are basically locally resonant BGs with low frequency ranges which attributes to the motions of exposed cantilevers.

Liquid modified photonic crystal fiber for simultaneous temperature and strain measurement

A liquid modified photonic crystal fiber (PCF) integrated with an embedded directional coupler and multi-mode interferometer is fabricated by infiltrating three adjacent air holes of the innermost layer with standard 1.48 refractive index liquids. The refractive index of the filled liquid is higher than that of background silica, which can not only support the transmitting rod modes but also the “liquid modified core” modes propagating between the PCF core and the liquid rods. Hence, the light propagating in the liquid modified core can be efficiently coupled into the satellite waveguides under the phase-matching conditions, resulting in a dramatic decrease of the resonant wavelength intensity. Furthermore, there is a multi-mode interference produced by modified core modes and rod modes. Such a compact (∼0.91 cm) device integrated with an embedded coupler and interferometer is demonstrated for high-sensitivity simultaneous temperature (∼14.72 nm/°C) and strain (∼13.01 pm/μϵ) measurement.

Crashworthiness of graded cellular materials: A design strategy based on a nonlinear plastic shock model

Dynamic behaviors and crashworthiness design of density graded cellular materials are investigated by using theoretical method and finite element simulation. A nonlinear plastic shock model is employed to guide the gradient design of cellular rod under mass impact and cell-based finite element models are used to verify the design strategy. Effects of impact-force parameter on the design of relative density distribution of graded cellular material and on the residual velocity of the striker for different lengths of graded cellular rods are explored. Three cases of design strategy with different impact-force parameters are analyzed and verified. The results reveal that the design strategy is reliable when the impact-force parameter is not less than zero. If the relative density distribution of graded cellular rod increases monotonically, the actual deformation mode of graded cellular rod is identical with the assumed one in the theoretical derivations. It is noticed that a portion of the graded cellular rods close to the distal end is not fully compacted. A scheme with restricting the shock strain not less than a specific value is proposed to shorten the graded cellular rods. Therefore, the desirable crashworthiness of graded cellular materials can be obtained by designing the density distribution of graded cellular materials.

Impact and blast mitigation using locally resonant woodpile metamaterials

We numerically and experimentally investigate impact/blast-induced shock mitigation using a quasi-1D woodpile mechanical metamaterial consisting of slender cylindrical rods. In this system, nonlinear stress waves generated by the impact or blast are coupled with local bending vibration modes of the constituent rods. This result in an order of magnitude reduction of transmitted shock without relying on material damping. Specifically, we identify that the arrangement of the local resonances from low to high frequencies enables efficient mitigation of impact/blast energy by splitting strong incident waves into weak ones. We also observe that optimized patterns of the woodpile configurations based on genetic algorithm help making the wave energy equipartition and radiate efficiently in both temporal and spatial domains. This wave attenuation mechanism based on local resonances shows a great potential for the development of nonlinear elastic metamaterials for efficient impact mitigation.

Unique Temperature Dependence of Selectively Liquid-Crystal-Filled Photonic Crystal Fibers

We demonstrate a unique temperature-dependent characteristic of the selectively liquid-crystal-filled photonic crystal fiber, which is realized by a selectively infiltrating liquid crystal into a single air hole located at the second ring near the core of the PCF. Three-resonance dips are observed in the transmission spectrum. Theoretical and experimental investigations reveal that the three-resonance dips all result from the coupling between the LP01 core mode and the rod modes, i.e., LP03 and LP51. Then, we find that the dip shift induced by temperature shows good agreements with the thermo-optic performance of the LC employed. Furthermore, the dips shift greatly with changes in temperature, providing a method to achieve temperature measurement in such a compact structure.

Describing the dispersion of plasmonic nanorod arrays via coupling of elementary excitations

Metamaterials such as metal-dielectric multilayers and cylindrical nanowires are well known, for instance because of their hyperbolic dispersion. Here we examine in detail the mode characteristics in an array of square and rectangular metallic nanorods. In particular we propose a method to describe the dispersion via the coupling of specific elementary excitations. Apparently, these fundamental modes depend on the size and shape of the nanorods, and on the particular symmetry of the Bloch modes. Specifically, we show that arrays of relatively small square nanorods are associated with coupling of single rod modes. In contrast, large nanorod arrays correspond with a basic structure consisting of four metallic corners. In the medium size case, the nature of the elementary excitation depends on the frequency range and Bloch mode symmetry. Finally, we study rectangular nanorods, which turn out to derive from a basic geometry with two semi-infinite rods. The analysis method is thus useful for a better comprehension of many other types of metamaterials.

Investigation of wave propagation in double cylindrical rods considering the effect of prestress

This paper presents the investigation of guided wave propagation in prestressed double-cylinder structure. Based on Hertzian contact theory, the interaction between two rods is treated as a plane strain problem and the stress state in the waveguide under the static load is obtained. The stress state is considered as a prestressed configuration for elastic wave propagation analysis in double cylindrical rods. The elastodynamic equation of the prestressed structure is established with the updated Lagrangian formulation and the wave finite element (WFE) method. Firstly, the equation is verified by the application on an aluminum rod compared with the Euler–Bernoulli beam theory. Then, dispersion curves for single rod and double cylindrical rods without prestress are computed. Besides, at the dimensionless frequency 0.25 the propagating modes in double cylindrical rods are identified with mode shapes and displacement vectors. The guided waves in double rods consist of the modes different from single rod. Particularly, there exist two kinds of torsional-like modes, one of which has a twist center and the other has two. The latter changes obviously with the increase of prestress in the waveguide. At low frequencies, torsional-like modes are very sensitive to the variation of prestress; in addition, the prestress configuration has little influence on propagating modes at mid-frequencies but some at high frequencies.

Design of Single-Band Bandpass Filter Using Photonic Bandgap Fiber by Suppressing Core Modes in Higher Order Bandgaps

We present two designs of all-solid photonic bandgap fiber (PBGF) for higher order bandgap suppression to realize a unique transmission window for optical filtering purposes. These two approaches are based on either applying a low-refractive-index core or a high-refractive-index background. This paper describes direct calculations of different modes in high-index rods in the all-solid PBGF using the antiresonant reflecting optical waveguide model for a double-cladded step index fiber. The flat-top single-band bandpass filter was obtained with potential center wavelength over ultraviolet, visible, and infrared regions. We achieve the single-band bandpass filter with minimum passband-to-rejection-band ratio of 20 dB in core power. From the calculated performance, both analytical and simulation results are in good agreement with confinement loss calculation.