Non-uniform Gap Research Articles

Online parameterized dictionary matching with one gap

We study the online Parameterized Dictionary Matching with One Gap problem (PDMOG) which is the following. Preprocess a dictionary D of d patterns, where each pattern contains a special gap symbol that can match any string, so that given a text T arriving online, a character at a time, we can report all the patterns from D that parameterized match to suffixes of the text that has arrived so far, before the next character arrives. Two equal-length strings are a parameterized match if there exists a bijection on the alphabets, such that one string matches the other under the bijection. The gap symbols are associated with bounds determining the possible lengths of matching strings. Online Dictionary Matching with One Gap (DMOG) captures the difficulty in a bottleneck procedure for cyber-security, as many digital signatures of viruses manifest themselves as patterns with a single gap. Parameterized match captures possible encryption of the patterns. We also define the strict PDMOG problem, in which subpatterns of the same dictionary pattern should be parameterized matched via the same bijection. This captures situations where subpatterns of a dictionary pattern are encoded simultaneously. We study this problem for special case called alphabet-saturated dictionairy, where every subpattern contains all characters of the dictionary alphabet Σ. We use the following parameters to describe our results: D is the total size of the dictionary (not including the gaps), plsc is the longest parameterized suffix chain of subpatterns in D, op is the number of parameterized patterns occurrences in T, α⁎ and β⁎ are the minimum left and maximum right gap borders in the non-uniformly bounded dictionary case, δ(GD) is the degeneracy of the graph GD representing dictionary D. This graph is classified as sparse or dense according the value of the δ(GD) and plsc parameters. We obtain:–O˜(D) preprocessing time/space and O˜(δ(GD)⋅plsc+plsc⋅max⁡{|Σ|,M}+op) query time per text character algorithm for online PDMOG with sparse graph dictionaries.–O˜(D+d(β⁎−α⁎)) preprocessing time/space and O˜(plsc⋅d⋅(β⁎−α⁎)+plsc⋅max⁡{|Σ|,M}+op) query time per text character algorithm for online PDMOG with dense graph dictionaries.–O˜(D) preprocessing time/space and O˜(δ(GD)⋅plsc+op) query time per text character algorithm for strict PDMOG with alphabet-saturated dictionaries.These results are parallel to the ones obtained for the Dictionary with One Gap (DMOG) problem almost matching the lower bounds achieved for this problem [7]. While the parameter δ(GD) can be as large as d and much lager if the dictionary has non-uniform gap boundaries, and the parameter plsc could theoretically be as large as d, in many practical situations these parameters are actually small. The strength of our work is in achieving results that explore and exploit small values for these parameters, thus supplying algorithms that are suitable for some practical cyber security needs.

Effect of Surface Roughness on Adhesive Instabilities for the Elastic Layer

If an incompressible elastic layer bonded to a rigid plane is placed close to a second rigid plane, adhesive interactions between the surfaces can cause elastic instabilities. These lead to spatially non-uniform traction and gap distributions which exhibit a regular pattern with a characteristic wavenumber. However, real surfaces are never completely plane. In this paper, we consider the influence of surface roughness on the instability, with particular reference to the force-displacement relation. With random roughness profiles, the traction distributions are always spatially irregular, so the onset of instability is more difficult to define. One approach is to monitor the amplitude of the power spectrum of the distribution near the characteristic wavenumber. Since surface roughness generally reduces the mean adhesive traction, we might expect it to exert a stabilizing effect. Numerical results confirm this for moderate to large RMS amplitudes, but show that low RMS roughness can actually trigger the instability in ranges where the uniform layer would be stable. The resulting traction-displacement relation is then found to be approximately linear with a slope close to that at the point where the uniform solution loses stability.

Оценка влияния неравномерности газового зазора на характеристики объемного барьерного разряда

The results from simulating the operation of ozone generators based on the volume barrier dischargeprinciple with taking into account the nonuniformity of their geometrical parameters are presented. Theeffect the gas gap nonuniformity has on the barrier discharge power performance characteristics isevaluated. The results from calculating the power density distribution along an ozone generator with amonotonically varying gas gap size are presented. The power density distribution curves versus the gap width for different degrees to which the voltage exceeds its initial value are given for four types of ozone generators. New data on modeling the discharge processes in ozone generators with a nonuniform gap and on the influence of this nonuniformity on the discharge utilization efficiency are presented. The obtained results can be used in designing real ozonators, including large-capacity ones. Recommendations on selecting the optimal average gap size depending on the electrode manufacturing quality and on the gas gap setting up and adjustment accuracy are given.

Structural failure performance of the confined liner with a non-uniformly annular gap subjected to a point load under a thermal rise field

The present investigation focuses on the failure performance of the confined liner with a non-uniform annular gap. The liner is subjected to a radial point load under a temperature rise field. An admissible displacement function is assumed to establish the nonlinear equilibrium equations. The principle of minimum potential energy is employed to obtain the analytical expressions of the critical buckling load (failure load) for the elastic liner encased in the rigid medium. It is found that the temperature rise field has a substantial increase in the critical buckling load. Subsequently, the buckling and post-buckling load-displacement equilibrium paths are plotted by the analytical solutions, and such equilibrium paths can also be traced by developing a two-dimensional (2D) finite element model (FEM). The maximum load (buckling load) obtained from the numerical results show excellent agreement with that from the proposed analytical solutions, and other closed-form expressions. Furthermore, the liners with inelastic material properties and geometric nonlinearities are considered numerically, and the critical buckling load shows its sensitivity to the initial gap, the initial out-of-roundness imperfection, and Young's modulus of the medium. Finally, the effect of friction is examined and plays a small role in the critical buckling load.

Bending-torsional coupled vibration of a rotor-bearing-system due to blade-casing rub in presence of non-uniform initial gap

In most of investigations on rub, the initial gap between blades and casing is considered to be in uniform distribution around the circumstance. Actually, due to several factors, such as flight loads, thermal loads and coating inhomogeneity, the initial gap may be non-uniform. The aim of this paper is to gain insight into bending-torsional coupled vibration of a dynamic model of an aero engine subjected to blade-casing rub in presence of non-uniform initial gap. At first, a rotor-bearing-system is modelled, in which a non-uniform gap exists in on location or multiple locations. Utilizing the impact experiment performed at a rotor test rig, the Lankarani–Nikravesh model is proved to be able to reveal the impact mechanism between blades and casing under a non-uniform initial gap. In the tangential direction, the Coulomb model is applied to describe the friction characteristics at the contact points. After that the bending-torsional coupled vibration of the system is solved numerically and the response in the presence of a non-uniform gap is determined. Additionally, the effects of the features of the non-uniform initial gap are examined.

Elastic and inelastic buckling of thin-walled steel liners encased in circular host pipes under external pressure and thermal effects

This study aims to develop an analytical solution for the elastic buckling pressure and its corresponding equilibrium path of confined, thin-walled liners subjected to temperature variations. The admissible radial displacement function and the minimum potential energy of liners are employed to establish the equations of equilibrium. The steel liners are modelled with two-dimensional finite elements for both elastic and inelastic behaviors. The elastic buckling pressure and the equilibrium path from the computational model are in excellent agreement with the analytical predictions. The analytical solutions for elastic liners and the numerical results for inelastic liners with material and geometric nonlinearities compare well with their respective test results available in the literature. Parametric studies are performed in terms of temperature variation, out-of-roundness imperfection, non-uniform liner-pipe gap, pipe supporting medium flexibility, and steel liner yield strength.

Research on continuous roll forming for manufacturing 3D curved surface parts with variable transverse curvatures

A flexible and precise forming technology for die-less, small-lot manufacture of 3D curved surface sheet metal parts is urgently required. Continuous roll forming (CRF) is a novel technique for generation of 3D curved surface rolls bending by two flexible rolls. In CRF process, the two flexible rolls are positioned vertically to form curved configurations and non-uniform roll gap. Then 3D curved surface parts with different transverse and longitudinal curvatures can be obtained by adjusting the configurations of the flexible rolls and the distribution of the roll gap. In this study, the CRF process was used to manufacture 3D curved surface part with variable transverse curvature instead of constant transverse curvature. The forming mechanism of CRF was proposed, the method to design configurations of the upper and lower flexible rolls was presented, and its validity was verified by simulation and experiment.

Experimental and numerical analyses of the shimming effect on bolted joints with nonuniform gaps

In order to investigate the effect of shim compensation for nonuniform gaps in aircraft assembly, the influence of the shims with different material and parameters on bolted joints is studied in this paper. According to the real material and assembly conditions of the aircraft joint structures, the specimen and experiment are designed to obtain the tensile performance of the joint structures with different shims. A three-dimensional finite element model, which incorporates the Johnson–Cook material property of the alloys, traction-separation law of liquid shims, contact relationships between the joint elements, and boundary conditions of the tensile process, is established with the specimen configurations. After validating through comparing with the experimental results, the modeling method is adopted to simulate the tensile response of the bolted joints with shims. Furthermore, both the influence of the shim material and thickness on the mechanical behaviors of bolted joints is investigated in detail. Shims can considerably reduce the assembly stress of joint structures and improve the joint stiffness and load capacity, and this effect is more remarkable with the increase of gap values. Liquid shims improve the joint stiffness due to its cohesive ability, while solid shims improve the joint load capacity. Hybrid shims possess a composite shimming effect of liquid and solid shims. Whatever the shim material is applied, the joint stiffness and strength drop with the growth of shim thickness, so strict deviation control method should be taken to ensure the assembly gaps as small as possible. The research results enhance the knowledge of shimming effect on joint structures, and thus offer positive guidance for practical application in aircraft assembly.

Optimization and Improvement of Output Performance in G-Band Extended Interaction Klystron

To improve the output performance of G-band extended interaction klystron (EIK), several practicable methods have been discussed. Firstly, the synchronization characteristics of the electron beam with the operating mode are analyzed in order to obtain large output power for optimized period. The influence of input gap voltage on the beam-wave interaction is studied, and the well-matched condition is established by optimizing the structure of input cavity. The gap length of output cavity is optimized to improve the electric field distribution. By adopting the optimized gap length and non-uniform gap lengths, the output power significantly increases from 360 to 570 W and 660 W, respectively; the corresponding bandwidth reaches to 650 MHz and 470 MHz. Moreover, AJDISK calculation is adopted to compare the results with CST simulation, and the similar gains and tendencies validate the relative reliability of our designed beam-wave interaction circuit. Therefore, our proposed methods for improving the output performance of G-band EIK are feasible and utilizable.

Numerical modeling of preloaded filling spiral case structure

Abstract A spiral case with its steel spiral case (SSC) being embedded in reinforced concrete under a pressurized condition is called a preloaded filling spiral case structure (PFSCS) in a hydropower plant. As a steel-concrete composite structure, a PFSCS is designed to work reliably. The non-uniform gap and contact nonlinearity between the SSC and the surrounding mass concrete have a great effect on the bearing mechanism of the composite structure. However, the description of the gap and contact nonlinearity in a PFSCS is a tough work. With the aim of efficiently describing the evolution process of the non-uniform gap and contact nonlinearity, we performed an experimental investigation and proposed a novel numerical simulation technique for structural finite element analyses (FEA) of PFSCSs. In the technique, the gap and contact nonlinearity as well as the construction process and operation process of a PFSCS are taken into account. A friction-contact model is used to simulate the sliding of the SSC against the concrete. A plasticity damage model is employed to describe the concrete. The development of the gap, contact status between the steel liner and the surrounding concrete, stresses of the steel liner and the steel bars, as well as the concrete cracking time and crack pattern, are presented in this work. The FEA results agree well with the experimental results. The agreement provides evidence that the applicability and competence of the proposed technique are valid and satisfactory.

Design Space Exploration of Microring Resonators in Silicon Photonic Interconnects: Impact of the Ring Curvature

A detailed analysis of fundamental tradeoffs between ring radius and coupling gap size is presented to draw realistic borders of the possible design space for microring resonators (MRRs). The coupling coefficient for the ring-waveguide structure is estimated based on an integration of the nonuniform gap between the ring and the waveguide. Combined with the supermode analysis of two coupled waveguides, this approach is further expanded into a closed-form equation that describes the coupling strength. This equation permits to evaluate how the distance separating a waveguide from a ring resonator, and the ring radius, affect coupling. The effect of ring radius on the bending loss of the ring is furthermore modeled based on the measurements for silicon MRRs with different radii. These compact models for coupling and loss are subsequently used to derive the main optical properties of MRRs, such as 3-dB optical bandwidth, extinction ratio of resonance, and insertion loss, hence identifying the design space. Our results indicate that the design space for add-drop filters in a wavelength division multiplexed link is currently limited to 5–10 $\mu$ m in radius and gap sizes ranging from 120 to 210 nm. The good agreement between the results from the proposed compact model for coupling and the numerical FDTD and experimental measurements indicate the application of our approach in realizing fast and efficient design space exploration of MRRs in silicon photonic interconnects.

Research on flexible asymmetric rolling process for three-dimensional surface parts

To realize rapid fabrication of three-dimensional surface parts, flexible asymmetric rolling process for continuously forming surface parts is developed. This process employs an auxiliary roll, a pair of upper and lowers bendable rolls as forming tools. By adjusting the height of the auxiliary roll, the sheet metal is inclined before non-uniform rolling, which is conducive to longitudinal bending deformation of the sheet metal after rolling. Meanwhile, the non-uniform thickness reduction of the sheet metal caused by the non-uniform roll gap between the upper and lower rolls makes itself bend in the transverse and longitudinal directions. Owing to small bending behavior of the bendable roll in the experiment, the forming precisions of formed parts are not ideal by the 3D rolling process without the auxiliary roll. In this paper, the flexible asymmetric rolling process is introduced to improve the 3D rolling process for surface parts with well forming precisions. An auxiliary roll is employed in the flexible asymmetric rolling process except a pair of upper and lower rolls. The formation mechanism of the curved surface is set forth, and the parametric equations of the formed surface in flexible asymmetric rolling process are derived. Typically simulations and experiments for forming spherical and saddle surfaces have been performed. The dimensional accuracies of the forming parts are measured, and the differences of the 3D rolling and flexible asymmetric rolling processes are investigated though numerical simulations. The forming results with good dimensional accuracies show that the flexible asymmetric rolling process is feasible for manufacturing three-dimensional surface parts with a broader range.

Transverse bending deformation analysis of 3D surface part in continuous roll forming process

This paper introduces a newly developed technique called continuous roll forming process which is applied to manufacture 3D surface part with various shapes, especially for doubly curved parts. In continuous roll forming process, the twin bendable rolls are placed to form a nonuniform roll gap. The bendable rolls rotate in opposite directions around the bend axis with equal angular velocity. The sheet metal is bitten into the roll gap by friction force and compressed nonuniformly across its width. At the present, how to precisely predict transverse bending deformation of 3D surface part has become a critical issue for guiding practical forming in the continuous roll forming process. This work focuses on analysis of the transverse bending deformation characteristics in continuous roll forming process.

Contribution of non-uniform EBG antenna arrays to the enhancement of MIMO channel capacity

The work proposes novel multiband and of low profile antenna arrays with hybrid type elements, for the realization of a MIMO (Multiple Input–Multiple Output) wireless communication system with great capacity. Each element is composed of a linear dipole integrated with a non-uniform Electromagnetic Band Gap (EBG) lattice. This EBG type, influences the system by two ways, the strong reduction of the Mutual Coupling (MC) among the closely positioned array's elements and the high radiation gain values of each element, inside wide space areas. Both of them make the antenna element capable of enhancing the MIMO channel capacity. It was ascertained by the results which were received taking into account globally, the MC and the radiation patterns of the antenna elements. The Spatial Channel Model (SCM) scenario for Urban Micro and Urban Macro environments was applied and the capacity calculation was made in one step which incorporates both the channel and the antenna characteristics. Results for the capacity at all three bands of operation are presented, for 10dB SNR level, along with respective ones received from dipole arrays in front of Perfect Electric Conductor (PEC). The comparison shows clearly the superiority of the proposed hybrid type array and its robust performance in wireless propagation scenarios.

Study of generating nitrogen plasma jet by using glow discharge in non-uniform gap

Experimental studies of a larger-scale atmospheric pressure glow discharge (APGD) nitrogen plasma jet are presented in this paper. A chamber with non-uniform gap formed in the electrode structure is designed by using non-uniform thickness of dielectrics. Through the electric field simulation, it is found that there is a non-uniform electric field distribution in the lateral and longitudinal directions of the chamber. The discharge starts from the larger electric field intensity of the submillimeter and then is followed by the development to the left and right sides of the smaller electric field intensity of the long gap. Moreover, the non-uniform electric field distribution in the lateral and longitudinal directions can help to suppress the generation of filament discharge. The experiments indicate that a uniform APGD in nitrogen is formed in the chamber and the inner electrode surface has a large luminous intensity. Through the fluid simulation, it is found that the velocity of the gas at the inner electrode surface is large. As a result, the nitrogen flow can effectively bring out the high-density plasmas on the inner electrode surface, which is beneficial to the formation of the plasma jet. The experimental results show that the electrode structure can generate APGD nitrogen plasma jets with the length of 10 mm and width of 15 mm, which is of relatively high application value.

Shimming design and optimal selection for non-uniform gaps in wing assembly

PurposeThis paper aims to provide a shimming method based on scanned data and finite element analysis (FEA) for a wing box assembly involving non-uniform gaps. The effort of the present work is to deal with gap compensation problem using hybrid shims composed of solid and liquid forms.Design/methodology/approachFirst, the assembly gaps of the mating components are calculated based on the scanned surfaces. The local gap region is extracted by the seed point and region growth algorithm from the scattered point cloud. Second, with the constraints of hole margin, gap space and shim specification, the optional shimming schemes are designed by the exhaustive searching method. Finally, the three-dimensional model of the real component is reconstructed based on the reverse engineering techniques, such as section lines and sweeping. Using FEA software ABAQUS, the stress distribution and damage status of the joints under tensile load are obtained for optimal scheme selection.FindingsWith the scanned mating surfaces, the non-uniform gaps are digitally evaluated with accurate measurement and good visualization. By filling the hybrid shims in the assembly gaps, the joint structures possess similar load capacity but stronger initial stiffness compared to the custom-shimmed structures.Practical implicationsThis method has been tested with the interface data of a wing tip, and the results have shown good efficiency and automation of the shimming process.Originality/valueThe proposed method can decrease the manufacturing cost of shims, shorten the shimming process cycle and improve the assembly efficiency.

Signature Analysis for Online Motor Diagnostics: Early Detection of Rotating Machine Problems Prior to Failure

The Stator-current signature analysis of induction motors is a proven method to diagnose rotor squirrel-cage winding defects and air-gap-eccentricity problems. With this technology, specific frequency-current components can be identified as an indication of cage-winding defects as well as a nonuniform gap between the stator and rotor. Since these data are generally collected periodically, it is important to identify the components as early as possible. The trendable parameters can then be monitored more often to avoid in-service failure. With the application of new processing technologies, the ability to identify these critical current-signature frequency components and trend the deterioration that they indicate has improved. This allows for maintenance activities to be scheduled earlier and performed prior to failure, avoiding costly motor component damage and unplanned downtime.

Analysis of continuous roll forming for manufacturing 3D surface part with lateral bending deformation

Continuous roll forming (CRF) is a novel technology for both single-piece and small-batch manufacturing of 3D surface sheet metal parts. In the CRF process, a pair of flexible rolls is placed to form a non-uniform roll gap. When the flexible rolls rotate in opposite directions with identical angular velocity, the sheet metal is bitten into the roll gap by frictional force, and the sheet metal is non-uniformly thinned in thickness direction and elongated in longitudinal direction. Thus, a 3D surface part with a desired shape is manufactured consecutively. In this paper, CRF is further developed and expanded into LB-CRF, which enables the CRF process to manufacture 3D surface parts not only with transverse and longitudinal bending deformation but also with lateral bending deformation (LB-CRF). The methods to design the curved profiles of flexible rolls and the distribution of the roll gap are provided. Through a series of numerical simulations on the LB-CRF processes, the proposed design methods are verified. The relationship between the distribution of the roll gap and radius of lateral bending curvature is discussed. The LB-CRF processes were presented through experiments, and the results validate the feasibility of adopting the LB-CRF process to manufacture 3D surface part with lateral bending.

NFC Antenna With Nonuniform Meandering Line and Partial Coverage Ferrite Sheet for Metal Cover Smartphone Applications

This paper proposes a near-field communication (NFC) antenna solution for metal-cover smartphone applications. In this NFC antenna solution, a narrow slot is initially loaded into the metal cover, and the position of this slot can be altered (with flexibility) according to the design of the smartphone’s external appearance. Next, an unconventional six-turn coil (with a six-sided irregular hexagonal shape) is designed that has a nonuniform linewidth and a nonuniform line gap between two lines, and it is partially loaded with a rectangular ferrite composite. In this design, an enhanced magnetic line of forces can be realized in certain specific locations, and an excellent inductively coupled near-field receiver is achieved. Notably, this proposed NFC antenna can pass the tests required by NFC forum certification, and its performances are comparable with the traditional NFC antenna that has nonmetallic cover.

Compact single/dual band BPF with harmonic suppression using open‐loop resonator and L‐shaped coupling arm

A new approach is presented to design a widestopband single and dual-band bandpass filter (BPF) using L-shaped coupling-arm and open-loop resonators (OLRs). Non-uniform gap between the L-shaped coupling-arm and OLR and the length of the coupling-arm lead to the selective and collective suppression of higher order harmonics. Using voltage wave analysis, it is shown that the coupling-coefficient reduces to zero for certain harmonics. To demonstrate the application of the proposed technique single and dual-band BPFs is designed and fabricated. Second- and fourth-order single-band BPFs are fabricated for the centre frequency of 2.24 GHz. Harmonic suppression up to 5.8 fo with the suppression level >30 dB is achieved in second-order BPF. One more second-order BPF is designed and fabricated using stub-loaded stepped impedance OLR. This BPF displays widestopband up to 8.4 fo with the suppression level of 30 dB. Further a compact dual-band BPF is also designed and fabricated. The response shows the harmonic suppression up to 5.3 fo. The measured results are in good agreement with the full-wave simulation performed by high-frequency structure simulator.