Distortion Generation Research Articles

Modified second-order nonlinear infinite impulse response (IIR) filter for equalizing frequency response and compensating nonlinear distortions of electrodynamic loudspeaker

In this paper, we propose a modified second-order nonlinear infinite impulse response (IIR) filter for equalizing the frequency response and compensating nonlinear distortions of an electrodynamic loudspeaker. A problem of electrodynamic loudspeakers is the generation of nonlinear distortions, which degrade the sound quality. One of the approaches to reducing nonlinear distortions is to use a second-order nonlinear IIR filter. This filter is based on an equivalent circuit model of an electrodynamic loudspeaker and its coefficients are determined by physical parameters. However, it is difficult to compensate nonlinear distortions when a loudspeaker has a high Q factor at the lowest resonance frequency, at which the displacement of the diaphragm and nonlinear distortions become large. The Q factor determines the linear frequency response of the electrodynamic loudspeaker. Although it is necessary to compensate the Q factor of the loudspeaker, a nonlinear IIR filter cannot compensate the Q factor because it does not have a linear filtering feature. In this paper, we propose a modified second-order nonlinear IIR filter that can not only compensate the nonlinear distortions caused by the nonlinearities of the force factor and stiffness but also equalize the frequency response by employing the linear characteristics of the loudspeaker with the desired Q factor. Experimental results show that the proposed filter can compensate the linear and nonlinear distortions more effectively than a conventional filter.

StreamVane Turbofan Inlet Swirl Distortion Generator: Mean Flow and Turbulence Structure

Engine/airframe integration in advanced aircraft concepts must account for nonuniform flows ingested by turbofan engines. In this work, flow details from a vane-based distortion generator were analyzed for turbulence structure and aerodynamic scaling of the mean flow. Experimental results were obtained using particle image velocimetry in a small-scale facility and a full-scale research turbofan engine for the same vane geometry. Tests were performed at nearly the same Mach number to isolate Reynolds number effects, but analysis and prior work indicate that the flow development downstream of the vanes is Mach number independent in the subsonic regime. As hypothesized from inviscid vortex dynamics, the secondary mean flow angles were consistent across scales, indicating Reynolds number independence of the large-scale secondary flow profile generated. Vane wakes produced a complex structure in the streamwise velocity component not seen in the streamwise vorticity, which resembles the distribution from the desired secondary flow profile. The most intense turbulence is concentrated in the outer radial regions of the duct and, as shown by contrast to vane wake-dominated regions, is dominated by shear flow turbulence and unsteadiness due to the distortion profile itself rather than vane wakes. Taken together, these results provide fundamental understanding of the aerodynamics of swirling flows needed for implementing complex turning vanes in the design of distortion generators.

Assessment methods for unsteady flow distortion in aero-engine intakes

Peak events of unsteady total pressure and swirl distortion generated within S-duct intakes can affect the engine stability, even when within acceptable mean distortion levels. Even though the swirl distortion descriptors have been evaluated in S-duct intakes, the associated flow field pattern has not been reported in detail. This is of importance since engine tolerance to distortion is usually tested with representative patterns from intake tests replicated with steady distortion generators. Despite its importance in intake/engine compatibility assessments, the spectral characteristics of the distortion descriptors and the relationship between peak unsteady swirl and both radial and circumferential total pressure distortion has not been assessed previously. The peak distortion data is typically low-pass filtered at a frequency associated with the minimum response time of the engine. However the engine design is not always known a priori in intakes investigations and a standard approach to reporting peak distortion data is needed. In addition, expensive and time-consuming tests are usually required to capture representative extreme distortion levels. This work presents a range of analyses based on Delayed Detached-Eddy Simulation and Stereo Particle Image Velocimetry data at the outlet of a representative S-duct intake to assess these aspects of the unsteady flow distortion. The distorted pattern associated with different swirl distortion metrics is identified based on a conditional averaging technique, which indicates that the most intense swirl events are associated with a single rotating structure. The main frequencies of the flow distortion descriptors are found to lie within the range in which the engine stability may be compromised. The peak total pressure and swirl distortion events are found to be not synchronous, which highlights the need to assess both types of distortion. Peak swirl and total-pressure distortion data is reported as a function of its associated time scale in a more general way that can be used in the assessment of intake unsteady flow distortion. Extreme Value Theory has been applied to predict peak distortion values beyond those measured in the available dataset, and whose measurement would otherwise require testing times two orders of magnitude longer than those typically considered.

Contact acoustic nonlinearity (CAN)-based continuous monitoring of bolt loosening: Hybrid use of high-order harmonics and spectral sidebands

Abstract The significance of evaluating bolt tightness in engineering structures, preferably in a continuous manner, cannot be overemphasized. With hybrid use of high-order harmonics (HOH) and spectral sidebands, a contact acoustic nonlinearity (CAN)-based monitoring framework is developed for detecting bolt loosening and subsequently evaluating the residual torque on a loose bolt. Low-frequency pumping vibration is introduced into the bolted joint to produce a “breathing” effect at the joining interface that modulates the propagation characteristics of a high-frequency probing wave when it traverses the bolt, leading to the generation of HOH and vibro-acoustic nonlinear distortions (manifested as sidebands in the signal spectrum). To gain insight into the mechanism of CAN generation and to correlate the acquired nonlinear responses of a loose joint with the residual torque remaining on the bolt, an analytical model based on micro-contact theory is established. Two types of nonlinear index, respectively exploiting the induced HOH and spectral sidebands, are defined without dependence on excitation intensity and are experimentally demonstrated to be effective in continuously monitoring bolt loosening in both aluminum-aluminum and composite-composite bolted joints. Taking a step further, variation of the index pair is quantitatively associated with the residual torque on a loose bolt. The approach developed provides a reliable method of continuous evaluation of bolt tightness in both composite and metallic joints, regardless of their working conditions, from early awareness of bolt loosening at an embryonic stage to quantitative estimation of residual torque.

An assessment model for RFID impacts on prevention and visibility of inventory inaccuracy presence

Bullwhip effect has been considered as one of major research topics in supply chain management. Most of the studies disregarded the mismatch between the recorded inventory and the reality. However, it is shown that the inventory inaccuracy under uncertainty is a widespread phenomenon in both retail and distribution centers. Due to the propagation of information distortion along the supply chain, the financial impacts of inventory inaccuracy include not only the cost of direct inventory loss but also the increasing holding and shortage cost at each stage. The emergence of RFID technology offers a possible solution to alleviate the growing cost of inventory inaccuracy. By making full use of RFID technology, this paper attempts to compare the inventory inaccuracy impact on bullwhip effect in terms of order variance amplification and supply chain performance under two scenarios: (1) all members are aware of the inaccuracy and optimize their operations; (2) all members deploy RFID technology to reduce inventory inaccuracy. Informed order policy is used as benchmark to capture the true RFID value and differentiate two types of RFID impacts, prevention and visibility, to provide more manageable insight. In particular, the incentive of sharing information in supply chain is also provided by comparing the cost of two supply chain settings.

Attenuation compensation in anisotropic least-squares reverse time migration

Anisotropic and attenuating properties of subsurface media cause amplitude loss and waveform distortion in seismic wave propagation, resulting in negative influence on seismic imaging. To correct the anisotropy effect and compensate amplitude attenuation, a compensated-amplitude vertical transverse isotropic (VTI) least-squares reverse time migration (LSRTM) method is adopted. In this method, the attenuation term of an attenuated acoustic wave equation is extended to a VTI quasi-differential wave equation, which takes care of effects from anisotropy and attenuation. The finite-difference method is used to solve the equation, in which attenuation terms are solved in the wavenumber domain, and other terms are solved in the space or wavenumber domain. Stable regularization operators are derived and introduced to the equations to eliminate severe numerical noise in high-frequency components during backward propagation. Meanwhile, a demigration operator, migration operator, and gradient formula for attenuated VTI media are derived to implement the amplitude-compensated VTI LSRTM. Test of a homogeneous model proves the accuracy of the attenuated VTI quasi-differential equations and the effectiveness of the regularization operators. A numerical example for a modified Marmousi model verifies the accuracy and superiority to the amplitude-compensated VTI LSRTM. Our results show that the sensitivity to anisotropic parameters is much higher than that to the [Formula: see text] parameters.

Temporally Dependent Rate-Distortion Optimization for Low-Delay Hierarchical Video Coding.

Low-delay hierarchical coding structure (LD-HCS), as one of the most important components in the latest High Efficiency Video Coding (HEVC) standard, greatly improves coding performance. It groups consecutive P/B frames into different layers and encodes them with different quantization parameters (QPs) and reference mechanisms in such a way that temporal dependency among frames can be exploited. However, due to varying characteristics of video contents, temporal dependency among coding units differs significantly from each other in the same or different layers, while a fixed LD-HCS scheme cannot take full advantage of the dependency, leading to a substantial loss in coding performance. This paper addresses the temporally dependent rate distortion optimization (RDO) problem by attempting to exploit varying temporal dependency of different units. First, the temporal relationship of different frames under the LD-HCS is examined, and hierarchical temporal propagation chains are constructed to represent the temporal dependency among coding units in different frames. Then, a hierarchical temporally dependent RDO scheme is developed specifically for the LD-HCS based on a source distortion propagation model. Experimental results show that our proposed scheme can achieve 2.5% and 2.3% BD-rate gain in average compared with the HEVC codec under the same configuration of P and B frames, respectively, with a negligible increase in encoding time. Furthermore, coupled with QP adaption, our proposed method can achieve higher coding gains, e.g., with multi-QP optimization, about 5.4% and 5.0% BD-rate saving in average over the HEVC codec under the same setting of P and B frames, respectively.

Monitoring the gelation and effective chemical shrinkage of composite curing process with a novel FBG approach

Chemical shrinkage and gelation are critical issues in curing process of composite structures since they have significant influence on generation of distortion or residual stress. In this paper, a new in-situ method to capture the gel point and to measure the effective transverse chemical shrinkage was presented. A tailed FBG (Fiber Bragg Grate) set consists of several FBG sensors with various tail lengths was embedded perpendicular to the fiber direction to monitor the curing process. Gel point was determined with the aid of profile turning point of the FBG set and the results matched well with DMA test. The effective transverse chemical shrinkage which occurs between gelation and vitrification was obtained and compared with the one determined by TMA or bi-material strip test. Both results were used to predict the spring-in of C-specimen manufactured on CFRP tube. It turns out that accurate prediction of spring-in can be obtained with the effective transverse chemical shrinkage determined by tailed FBG set. The in-situ monitoring method with tailed FBG set is an alternative and promising technology to capture the gel point and to reveal the mechanism of curing distortion.

Design of pump beam delivering optical system and doped YAG length to minimize the wavefront distortion in a high-power Nd:YAG zigzag slab laser

An end-pumped high-power Nd:YAG zigzag slab continuous wave laser amplifier was designed through a computational simulation to minimize the wavefront distortion of the output laser beam. The pump beam delivering optical system was optimized with an acylindrical slow-axis lens to lower the distortion of nonzigzag propagation for the beam height axis. In addition, the wavefront distortion of the zigzag propagation for the beam width axis was studied and minimized by slightly changing the doped YAG length. The simulation results of the final design showed a peak-to-valley optical phase difference (OPDP−V) of 0.83 μm and a very low beam quality of 1.19× diffraction limit, even with a total pump power of 10 kW.

Strip distortion generator for simulating inlet flow distortion in gas turbine engine ground test facilities

A methodology has been developed to generate a non-uniform/distorted inlet flow field to test a gas turbine engine in ground test facilities. The distorted flow field is generated by positioning radial and circumferential strips of varying widths upstream of the Aerodynamic Interface Plane. The interacting wakes from these strips are used to generate a given target flow field. The approximate superposition of these wakes is investigated and used to construct the strip arrangement which is subsequently validated by computing the flow field by solving the Navier–Stokes equations. The strip geometry designed using the present methodology is able to produce the target Mach number distribution with a root-mean-square error of 5.06%.

Quantization parameter cascading for video coding: leveraging a new temporal distortion propagation model

In video coder, inter-frame prediction causes distortion propagation among temporally adjacent frames. This distortion dependency is a crucial factor for rate control optimization. Quantization parameter cascading (QPC) is an efficient technique to achieve dependent rate distortion optimization (RDO). This paper proposes a general framework for temporal dependency analysis by leveraging a distortion propagation model, which is derived by employing window-based preanalysis on original frames. Then, a quantization parameter offset \(\delta \) model is proposed for achieving fine-granularity quantization control, according to the amount of distortion propagation measured by the relative propagation cost \(\rho \). This paper applies competitive decision in exploring \(\delta \)–\(\rho \) model as accurate as possible and then proposes an improved \(\delta \)–\(\rho \) model tailored for dependent RDO. The simulation results verify that the temporal QPC algorithm with the proposed model achieves up to 1.1–1.4 dB PSNR improvement, with smaller temporal distortion fluctuation contributed by efficient bit allocation.

Transient distortion behavior during TIG welding of thin steel plate

To examine the generation characteristics of excessive distortions involved with the welding-induced buckling of a thin steel plate, the temperature profiles and distortion behaviors of welded plates during tungsten inert gas (TIG) welding were experimentally measured. Large-deformation thermal elastic–plastic analysis based on arc physics-based heat source modeling was utilized to accurately simulate the thermomechanical behavior of the plate during welding. The calculated and measured temperature profiles and distortion behaviors were compared to validate the developed numerical analysis technique. On the basis of the developed analysis technique, the effect of geometric imperfections on the thermomechanical behavior of welded thin steel plates was further investigated. Both angular and longitudinal bending distortions were found to monotonically increase with increasing heat input because of excessive longitudinal bending distortion and the secondary generation of angular distortion during the cooling process when buckling occurred. The through-thickness gradient of the plastic strain that developed with the transient distortion behavior during welding resulted in excessive angular distortion in the welded thin steel plate. It was concluded that the transient distortion behavior during welding should be taken into consideration to accurately predict and control large welding-induced distortions in thin steel plates.

Ultra Broadband Predistortion Circuit for Radio-over-Fiber Transmission Systems

A dual Schottky diode-based ultrabroadband predistortion circuit (PDC) is designed and experimentally verified to linearize both directly and externally modulated radio-over-fiber (RoF) transmission systems. A monolithic dual Schottky diode is used in the PDC to reduce the footprint and improve the bandwidth. The measured S-parameters show that the circuit is able to work for up to 40 GHz. The theory of third order intermodulation distortion (IMD3) generation by the PDC is established, and calculated IMD3 agrees well with the measured. Two measures are used to verify the PDC: spurious-free dynamic range (SFDR) and error vector magnitude (EVM) for WiFi signal at 2.4 GHz. For a directly modulated RoF transmission linearized by the PDC, the SFDR is improved by ∼12 dB. For an externally Mach–Zehnder modulator (MZM) modulated RoF transmission linearized by the PDC, the SFDR is improved by higher than 5 dB from 2 to 30 GHz, and in particular higher than 12 dB from 2 to 5 GHz. For 2.4–GHz WiFi signal over the externally modulated RoF transmission linearized by the PDC, the EVM for WiFi signal is improved by up to 5.1 dB for back-to-back and 3.5 dB for 20-km SMF transmission.

The Influence of Preheat on Distortion and Fatigue Crack Propagation Rate of FCAW Weld in A 36 Steel Structure

Welding is one of the joining processes and it has been widely used, especially for steel welded structure in off-shore, pipeline or ship construction. Advantages of the welding joint are inexpensive, process joining can be done quickly and can produce light structure compared to other joining processes. One of welding techniques mostly used for joining steel construction is flux cored arc welding (FCAW). The commonly problems arise in this welding technique are distortion and low resistance of crack propagation. The aim of this study is to minimize distortion and to increase fatigue crack growth resistance of weld joint.In this research, FCAW welding was conducted without preheat and the other was preheated around welding area with temperature of 200 °C. Each of temperature welding process was measured using data acquisition. After completing the welding process, a sequence of experiment was conducted including chemical compositions, distortion and fatigue test. Result of this research shows that preheat temperature of 200 °C can decrease distortion and improve fatigue performance.

Distortion of surface plasmon polariton propagation on graphene due to chemical potential variation

The variation of graphene chemical potential owing to surface plasmon polariton excitation and its influence on the propagation properties of the latter is systematically examined in this paper. Although the chemical potential is controlled via a constant electric field bias, the excitation of the highly confined surface wave can considerably affect it, thus disrupting the wave natural propagation. To this aim, the propagation properties of the surface wave are extracted to reliably estimate the aforesaid distortion effect with regard to frequency. Numerical results, obtained in terms of an accurate finite-difference time-domain scheme, certify this interesting convention. Furthermore, the electrodynamic forces on the free electrons of the graphene layer are calculated to justify the electrostatic assumption.

A Virtual View PSNR Estimation Method for 3-D Videos

In three-dimensional videos (3-DVs) with ${n}$ -view texture videos plus ${n}$ -view depth maps, virtual views can be synthesized from neighboring texture videos and the associated depth maps. To evaluate the system performance or guide the rate-distortion-optimization process of 3-DV coding, the distortion/PSNR of the virtual view should be calculated by measuring the quality difference between the virtual view synthesized by compressed 3-DVs with one synthesized by uncompressed 3-DVs, which increases the complexity of a 3-DV system. In order to reduce the complexity of 3-DV system, it is better to estimate virtual view distortions/PSNR directly without rendering virtual views. In this paper, the virtual view synthesis procedure and the distortion propagation from existing views to virtual views are analyzed in detail, and then a virtual view distortion/PSNR estimation method is derived. Experimental results demonstrate that the proposed method could estimate PSNRs of virtual views accurately. The squared correlation coefficient and root of mean squared error between the estimated PSNRs by the proposed method and the actual PSNRs are 0.998 and 2.012 on average for all the tested sequences. Since the proposed method is implemented row-by-row independently, it is also friendly for parallel design. The execute time for each row of pictures with $1024 {\times }768$ resolution is only 0.079 s, while for pictures with $1920 {\times }1088$ resolution it is only 0.155 s.

鋼の連鋳鋳片の熱処理変形および応力発生挙動に及ぼす冷却条件の影響

鋼の連鋳鋳片の熱処理変形および応力発生挙動に及ぼす冷却条件の影響

Assessing the Potential Effects of the European Union Multilevel Approach to the Coexistence Policy

European Union (EU) coexistence policy is based on the principle of subsidiarity, which implies a multilevel governance framework. Different legislative approaches have been developed in EU Member States. These legal rules are oriented to both preventing on-farm adventitious admixture (ex-ante regulations) and reducing potential economic consequences (ex-post liability). So coexistence deals with a subject of negative externalities involving an issue of property-right allocation between farmers. Considering the impacts that coexistence policy has on GM (genetically modified) crop adoption rates and the generation of trade distortions, potential effects of the EU coexistence framework are reviewed from a theoretical property-right allocation view. Derived from the analysis, property-right allocation is focused on non-GM farmers according to EU regulation enforcement, which tends to rigid coexistence measures. Nonetheless, the multilevel EU framework has led Member States to pursue their aims: trade interests and social legitimation.

PROUD-based method for simple real-time in-line characterization of propagation-induced distortions in NRZ data signals

A simple, in-line method for real-time full characterization (amplitude and phase) of propagation distortions arising because of group velocity dispersion and self-phase modulation on 10-20 Gbps transmitted NRZ optical signals is reported. It is based on phase reconstruction using optical ultrafast differentiation (PROUD), a linear and self-referenced technique. The flexibility of the technique is demonstrated by characterizing different data stream scenarios. Experimental results were modeled using conventional propagation equations, showing good agreement with the measured data. It is envisaged that the proposed method could be used in combination with DSP techniques for the estimation and compensation of propagation distortions in fiber links, not only in conventional IM/DD systems, but also in coherent systems with advanced modulation formats.

Deposition of drops containing surfactants on liquid pools: Movement of the contact line, Marangoni ridge, capillary waves and interfacial particles

Abstract When a drop of aqueous surfactant solution is placed on a deep subphase of water, multiple phenomena occur. The contact line of the drop spreads until the drop merges with the subphase. A capillary wave train is initiated by the disturbance caused by the drop touching the subphase surface. Marangoni stresses cause the formation and propagation of a localized distortion of the subphase surface (subsequently called the Marangoni ridge). And particles pre-deposited on the subphase surface are propelled by the flow induced by Marangoni stresses. We examine all these phenomena simultaneously at early times (