Equivalent Frequency Response Research Articles

A new frequency domain based approach for a nonlinear aeroelasticity analysis

In this paper, a new frequency-domain based approach for the investigation of aeroelasticity problems is introduced that is capable of handling both linear and nonlinear problems. This approach is based on coupling a conceptual method used in a structural dynamic analysis and an optimum equivalent linear frequency response function (OELF). Additionally, a new criterion for determining the flutter speed and the instability of nonlinear systems is introduced that is based on the condition number of the aeroelastic matrices. Due to the global nature of the condition number, the new criterion proves to be efficient and simple to use. To examine the efficiency of the new technique, a two-dimensional nonlinear airfoil with an unsteady aerodynamic model is considered.

The Instrument Bandwidth Effect in Jitter and BER Test for High-Speed Serial Interconnection

Different from other electronics measurement, the bandwidth of the instrument can affect the test results more seriously in jitter and bit-error rate (BER) test. This paper analyzes the effect on the jitter and BER test results caused by instrument bandwidth in high-speed serial interconnection. An algorithm is presented to measure and estimate the equivalent frequency response of instruments. Computed data-dependent jitter (DDJ) results are produced based on the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -parameter of the serial interconnected channels and the equivalent frequency response of instruments, which are perfectly consistent with actual DDJ measure results. These methods can be used to measure and calibrate the instrument bandwidth effect precisely in jitter and BER test. At last, the paper gives the results of the instrument bandwidth effect for three channels and a set of instruments according to simulation, and presents a new concept “equivalent bandwidth” to roughly estimate the test error of DDJ caused by instrument bandwidth.

Identification of a nonlinear joint in an elastic structure using optimum equivalent linear frequency response function

As the main source of local nonlinearities, joints can lead to drastic changes in dynamic behavior of structures in a global scale. Finite element (FE) models often lack these nonlinearities and are incapable of representing nonlinear behavior. Therefore, the identification of nonlinear dynamic mechanical properties of the joint is necessary, in order to develop a faithful FE model of the structure. In the present work, dynamic parameters of a nonlinear joint are identified using an optimum equivalent linear frequency response function of the structure. A test rig, which includes a beam that can produce cubic stiffness spring characteristic as a nonlinear joint, is built, and nonlinear dynamic characteristics of the beam are identified. In addition to hardening behavior related to cubic stiffness, softening effects were also observed in some measured modes in which further investigation attributed that behavior to the presence of a bolt in the test rig.

The Research on Single-Disc Rotor Nonlinear Vibration Model and Mechanism

Based on mechanical properties of rotor nonlinear vibration and the assumption of large deformation, the rotor nonlinear vibration model in the form of Duffing equation is constructed from typical engineering problems. According to analytical solutions of Duffing equation, system’s equivalent frequency and frequency response equation are derived. Furthermore, the influences of stiffness, damping and nonlinear components are studied. The single-disc rotor nonlinear vibration experimental results verify the rationality and efficiency of nonlinear vibration model’s construction and Duffing equation’s analytical solution and frequency response equation. The mechanisms of resonance, amplitude jump and hysteresis are also revealed. It provides a new research method for rotor vibration characteristics analysis.

Identification of dynamic characteristics of nonlinear joint based on the optimum equivalent linear frequency response function

Abstract Identification of dynamic characteristics of local nonlinearities has been aimed in this paper. The spirit of the identification method is established on Optimum Equivalent Linear Frequency response function (OELF). Dynamic behavior of nonlinear elements in system is extracted from OELF using two different techniques. The first technique is “Direct Identification Method” (DIM) in which no pre-assumed model is considered for the nonlinearity's behavior and the second technique is “Model based Identification Method” (MIM). The second technique is introduced with two different formulations, in order to take into account the practical limits due to the inaccessibility of nonlinearity location and/or indeterminability of degree of freedom. Dynamic characteristics of common nonlinearity mechanisms like cubic stiffness, pure slip, and stick-slip have been identified using the proposed technique and it has been shown that, although the proposed identification technique is simple, it does not require any sophisticated measurement hardwares and techniques, as required by most of the identification methods proposed so far. Also, the relation of this technique to harmonic balance method is discussed.

Novel dual mode disk-shaped resonator filter with HTS thin film

We propose a novel dual mode disk-shaped resonator filter with high temperature superconductor (HTS) thin films. The 5 GHz-band YBa2Cu3O7-x (YBCO) microstrip dual mode disk resonator filter on an MgO (100) substrate keeps a perfect circle shape and a waveguide line of about a half-wavelength that is capacitively-coupled with the disk resonator to generate a dual mode. The fabricated filter had an equivalent frequency response of a two-pole filter with two attenuation poles. The coupled coefficient of two orthogonal modes can be controlled by the length of coupled waveguide line and the gap space between feeder and disk resonator. The fabricated filter showed very low third-order intermodulation distortion (IMD3) of -73 dBc with an output power of 10 W at a temperature of 65 K. In addition, the proposed structure can be fabricated using a side lithography and etching processes. This is an advantage for multi-stage filter applications. We believe this filter is a promising candidate structure for RF transmit system applications.

Equivalent Time-Invariant Modelling of Electrohydraulic Actuators with Application to Robust Control Synthesis

AbstractAn important aspect of robust control development around hydraulic actuators is establishing a set of equivalent linear time-invariant (LTI) models that describe the dynamics of the system over the desired envelope of operation. The nonlinearities inherent in the hydraulic functions must be recast into an equivalent linear form in order to make the robust control problem amenable to solution by linear techniques. This paper develops a simple model-based approach for evaluating equivalent LTI frequency response functions of an electrohydraulic actuator by Fourier transformation of acceptable actuator input-output data. The efficacy of the numerical procedure is compared with two other available methods, namely small-signal analysis and Golubev's least-squares approach. It is shown that the proposed approach can describe large signal effects and at the same time properly characterize the features of the hydraulic actuator frequency response that are important for robust control design, without the n...

An improvement to frequency-domain regression method for calculating conduction transfer functions of building walls

An improvement is proposed for the frequency-domain regression (FDR) method to calculate CTF (conduction transfer function) coefficients of multilayer constructions. This improvement aims at providing complete CTF coefficients with a unique set of d values. In the improvement, the external and internal polynomial s-transfer functions of heat conduction of a wall are identified based on equivalent frequency response characteristics by constraining their denominators equal to that of the cross polynomial s-transfer function while this cross polynomial s-transfer function of this wall is identified using FDR method in advance. The complete CTF coefficients of this wall (i.e., external CTF values a, cross CTF values b, internal CTF values c and a unique set of heat flow rate history coefficients d) can be easily calculated from these identified polynomial s-transfer functions. Examples and comparisons show that this improvement of the frequency-domain regression method works well.

Self-Similarity: Part I—Splines and Operators

The central theme of this pair of papers (Parts I and II in this issue) is self-similarity, which is used as a bridge for connecting splines and fractals. The first part of the investigation is deterministic, and the context is that of L-splines; these are defined in the following terms: s(t) is a cardinal L-spline iff L{s(t)}=Sigma kisinZa[k]delta(t-k), where L is a suitable pseudodifferential operator. Our starting point for the construction of self-similar splines is the identification of the class of differential operators L that are both translation and scale invariant. This results into a two-parameter family of generalized fractional derivatives, parttau gamma, where gamma is the order of the derivative and tau is an additional phase factor. We specify the corresponding L-splines, which yield an extended class of fractional splines. The operator parttau gamma is used to define a scale-invariant energy measure-the squared L2-norm of the gammath derivative of the signal-which provides a regularization functional for interpolating or fitting the noisy samples of a signal. We prove that the corresponding variational (or smoothing) spline estimator is a cardinal fractional spline of order 2gamma, which admits a stable representation in a B-spline basis. We characterize the equivalent frequency response of the estimator and show that it closely matches that of a classical Butterworth filter of order 2gamma. We also establish a formal link between the regularization parameter lambda and the cutoff frequency of the smoothing spline filter: omega0aplambda-2gamma. Finally, we present an efficient computational solution to the fractional smoothing spline problem: It uses the fast Fourier transform and takes advantage of the multiresolution properties of the underlying basis functions

Research of BJMOSFET frequency characteristics

The parasitic capacitance effect and its influence to the performance have been investigated in Bipolar Junction Metal-Oxide-Semiconductor Field-Effect Transistor (BJMOSFET). The frequency characteristic equivalent circuit and high frequency response model of BJMOSFET have been presented. The frequency characteristic of BJMOSFET is simulated using the multi-transient analytical method and PSPICE9 simulator. The conclusions that BJMOSFET owns less total capacitance, wider frequency band, better transient characteristic and better frequency responses are reached by comparing with the traditional MOSFET at the same structure parameters and bias conditions. BJMOSFET, as a novel promising high frequency device, would be desired to find application in future integrated circuit.

APPLICATION OF THE EQUIVALENT FREQUENCY RESPONSE METHOD TO NONLINEAR RUNOFF SYSTEM

This paper proposes a new approach using the Equivalent Frequency Response Method (EFRM) for analyzing St. Venant model for unsteady one-dimensional flow along with its related models such as kinematic wave, diffusion wave and gravity wave models with two different lower stream boundary conditions. It is possible to calculate the gain, time lag, and impulse response function by the proposed method. Moreover, a new criterion is presented for evaluating the validity of each model for a range of Froude and kinematic wave number based on the obtained impulse response function. Finally, this paper suggests the possibility of applications of EFRM to real runoff analysis.

Two approaches to the design of time-varying cascaded filters

Two approaches to the design of time-varying cascaded filters used in radar clutter rejection are presented. In the first approach, by fitting the cascaded filter to the noncascaded filter, the time-varying cascaded filter can be designed, which makes it possible that the time-varying cascaded filter behaves just like an optimum clutter filter The second approach can be used to design the second-stage filter in a time-varying cascaded one by setting zeros in its equivalent overall frequency response. It has been shown that it is difficult to express the frequency response of the second-stage filter in the time-varying cascaded one, however, it is convenient to be involved in the overall response.

Amplifier Fundamentals

The paper presents the fundamentals of a bipolar junction transistor amplifier and includes the following aspects: choice of Q point, classes of operation, incremental equivalent circuit, frequency response, cascading, broadbanding, and pulse testing. The emphasis is on understanding of the fundamentals, rather than rigorous analysis or elaborate design procedure.

Removal of Flatulence-Causing Sugars from Legumes and Oilseeds

The frequency response (FR) of the large-scale power system shows significant frequency spatial distribution characteristics (FSDC), still using uniform frequency models may cause large errors in the FR solution, and the FSDC should be preserved in the modeling. In this paper, a three-machine equivalent system frequency response (TM-SFR) model is proposed to preserve the FSDC by the parameter equivalent aggregation method, including load, network, and generator. The TM-SFR model is further simplified into a solvable forced vibration equation by loop-opening and approximation, and its closed-form solution (CFS) is obtained by the modal superposition method, to analytically solve the FR following a major disturbance. Case studies are introduced to verify the performance of the TM-SFR model and its CFS over the WSCC 9-bus system, the New England 39-bus system, and the IEEE 118-bus system. The results prove that the proposed model can preserve the intermachine frequency oscillation caused by the FSDC in various scenarios, and improve the FR solution accuracy at high solution speed, which can provide a more reliable basis for frequency stability emergency control.

An External System Equivalent for on-line Steady-State Generator Outage Simulation

This paper describes an external system equivalent for on-line generator outage simulation. The equivalent models the steady- state MW response of the external system after primary speed control actions. The proposed method is an extension to the Ward equivalent. Starting with the frequency response characteristics of the individual units and loads in the external system, equivalent frequency response characteristics for each boundary bus have been developed. These equivalent frequency response characteristics model not only the total in-rush, but also the distribution among the individual tie lines. In addition to the data required for branch outage simulations the incremental speed regulations and rated powers of all external units on the line are assumed to be known. No real-time measurement data from the external control areas are required. The suggested equivalent has been verified by off-line simulations of 10 severe generator outages in three European 380/220 kV networks.

Synthesis of sampled feedback systems for prescribed time domain tolerance

This paper presents a design procedure for single-loop sampled feedback systems in which the plant transfer function has prescribed bounds on its parameters. The plant is imbedded in a ‘ two-degree-of-freedom system’, which is to be designed such that the system time response to a deterministic input lies within specified boundaries. The design procedure is based on frequency concepts. The time-domain tolerances are translated into equivalent frequency response tolerances. The latter lead to bounds on the loop-transmission L(jv) [v =tang (π/WS)[, in the form of continuous curves on the Nichols chart. However, due to inherent theoretical difficulties existing in sampled feedback systems, it might happen that no L(jv) can be found so that the design specifications of the problem are achieved. The design procedure is transparent enough to guide the designer in which direction to change the specifications of the problem so that the next trial design will be successful.

Feedback synthesis with plant ignorance, nonminimum-phase, and time-domain tolerances

This paper presents a design procedure for single-loop feedback systems in which the plant is nonminimum-phase, with ignorance in its parameters. The feedback system is to be designed such that the time response to a deterministic input lies within specified boundaries. Subject to the above, the design should be such as to minimize the effect of sensor noise at the input to the plant. The time domain tolerances are translated into equivalent frequency response tolerances. The latter lead to bounds on the loop-transmission L( jw), in the form of continuous curves on the Nichols chart. However due to the nonminimum-phase nature of the plant, it may happen that no L( jw) can be found so that the design specifications of the problem are achieved, unless they are changed accordingly.

Synthesis of Feedback Systems with Large Plant Ignorance for Prescribed Time Domain Tolerances

There is given a minimum-phase plant transfer function, with prescribed bounds on its parameter values. The plant is imbedded in a two-degree-of-freedom feedback system, which is to be designed such that the system time response to a deterministic input lies within specified boundaries. Subject to the above, the design should be such as to minimize the effect of sensor white noise at the input to the plant. This report presents a design procedure for this purpose, based on frequency response concepts. The time-domain tolerances are translated into equivalent frequency response tolerances. The latter lead to bounds on the loop transmission function L(jω), in the form of continuous curves on the Nichols chart. Properties of L(jω) which satisfy these bounds with minimum effect of sensor white noise, are derived. The design procedure is quite transparent, providing the designer with the insight to make necessary trade-offs, at every step in the design process. The same design philosophy may be used to attenuate the effect of disturbances on plants with parameter ignorance.

Synthesis of feedback systems with large plant ignorance for prescribed time-domain tolerances†

There is given a minimum-phase plant transfer function, with prescribed bounds on its parameter values. The plant is imbedded in a two-degree-of-freedom feedback system, which is to be designed such that the system time response to a deterministic input lies within specified boundaries. Subject to the above, the design should be such as to minimize the effect of sensor white noise at the input to the plant. This report presents a design procedure for this purpose, based on frequency response concepts. The time-domain tolerances are translated into equivalent frequency response tolerances. The latter lead to bounds on the loop-transmission function L(jω), in the form of continuous curves on the Nichols chart. Properties of L(jω) which satisfy these bounds with minimum effect of sensor white noise are derived. The design procedure is quite transparent, providing the designer with the insight to make necessary tradeoffs, at every step in the design process. The same design philosophy may be used to attenuate the effect of disturbances on plants with parameter ignorance.

Infrared 10.6-µm photodiode heterodyne detection

Expressions are given for heterodyne noise equivalent power, conversion gain, and frequency response in terms of diode parameters, local oscillator power, and IF amplifier noise factor. Experimental results are reported on heterodyne detection at 10.6 µm in a reverse-biased HgCdTe photodiode.