Frequency Response Method Research Articles

Nanopore Diffusion Rates for Adsorption Determined by Pressure-Swing and Concentration-Swing Frequency Response and Comparison with Darken's Equation

Two flow-through frequency response methods of concentration-swing frequency response (CSFR) and pressure-swing frequency response (PSFR) are applied to study the adsorption of chloroethane on BPL activated carbon over a wide range of concentrations. Chloroethane at low concentrations in helium, 500 ppmv and 10 mol %, are studied using CSFR. Two models which treat an adsorption bed with axial dispersion or a simplified well-mixed concentration have been developed for both isothermal and nonisothermal conditions. The results show that heat effects can be negligible for the CSFR method. Pure chloroethane at relatively high concentrations is studied using PSFR. The experimental data are described well by a nonisothermal nanopore diffusion model. The diffusivities obtained from these two distinct methods are identical for the same concentration. The modeling of the concentration behavior depends quite sensitively on the isotherm model and obeys Darken's equation for the D−R isotherm. The results show that the frequency response method can distinguish the importance of heat effects and the relative importance of the mass-transfer mechanisms.

Control design for an irrigation channel from physical data

In this paper a tool for initial design of decentralized controllers for an irrigation channel is developed, and field tests are carried out which demonstrate that it delivers controllers with good performance. A physical model of the channel is obtained using the Saint-Venant equations, and a data set is generated by simulating this model. A first order nonlinear model useful for control design is then estimated from the simulated data using system identification techniques, and a controller is designed based on the estimated model and given design specifications. The decentralized controller is a PI controller augmented with a first order low pass filter. The developed routine for controller design is based on frequency response methods, and configurations with and without feedforward from the downstream gate are considered. The designed controllers showed good performance in field experiments; the water levels recovered quickly from disturbances with small deviations from setpoints.

Investigation of ethene adsorption on Hmordenite and modified Hmordenite by frequency response method

The frequency response (FR) technique has been applied to study adsorption mechanism of ethene in parent Hmordenite (HMor) and the HMor (CuO/HMor, Cs +/HMor) which were modified by CuO and Cs +. The FR spectra of ethene in HMor, CuO/HMor and Cs +/HMor were recorded at temperatures between 252 and 273 K under the pressure of 0.2–30.0 Torr, and then those FR spectra were investigated. The results showed that two parallel adsorption processes exist in ethene/HMor system. Those two processes were attributed to adsorption process of ethene on proton acid sites (low frequency adsorption) and on hydrogen cation sites (high frequency adsorption); meanwhile the number of sites available for adsorption of ethene is 0.692 and 0.828 mmol g −1, respectively. The number of adsorption sites in low frequency is increased by the introduction of CuO which is located among the proton acid sites but covered the hydrogen ion sites in high frequency. Chemical adsorption of ethene is the main sorption process in CuO/HMor. The number of adsorption sites in low frequency is decreased by the introduction of Cs + which counteracted proton acid sites in low frequency. Physical adsorption is the main sorption process in Cs +/HMor channels. The optimum content of CuO for modification is 5% (weight/weight). Combining the FR spectra and other methods such as isotherms and Langmuir model, a thorough understanding of the ethene adsorption processes on zeolites can be achieved.

Frequency response method for terrain classification in autonomous ground vehicles

Many autonomous ground vehicle (AGV) missions, such as those related to agricultural applications, search and rescue, or reconnaissance and surveillance, require the vehicle to operate in difficult outdoor terrains such as sand, mud, or snow. To ensure the safety and performance of AGVs on these terrains, a terrain-dependent driving and control system can be implemented. A key first step in implementing this system is autonomous terrain classification. It has recently been shown that the magnitude of the spatial frequency response of the terrain is an effective terrain signature. Furthermore, since the spatial frequency response is mapped by an AGV's vibration transfer function to the frequency response of the vibration measurements, the magnitude of the latter frequency responses also serve as a terrain signature. Hence, this paper focuses on terrain classification using vibration measurements. Classification is performed using a probabilistic neural network, which can be implemented online at relatively high computational speeds. The algorithm is applied experimentally to both an ATRV-Jr and an eXperimental Unmanned Vehicle (XUV) at multiple speeds. The experimental results show the efficacy of the proposed approach.

In situ measuring and evaluating the thermal resistance of building construction

This paper introduces an in situ measuring method for the thermal resistance of buildings, including the test chamber, measuring points’ arrangement, and measurement results, in Nanjing during 2000 and 2001. Three methods for the analysis of in situ data are also presented to determine the thermal resistance of buildings although the R-values evaluated by these methods have smaller values than those of design due to the limitation of field conditions. The synthetic temperature method only requires measuring the heat flow rate on the inside surface of the building construction and both the synthetic indoor and outdoor temperatures. And the surface temperature method just requires testing the heat flow rate on the inside surface of building envelopes and both the inside and outside surface temperatures of building construction. However, the frequency response method introduced in this paper only relates to the mean synthetic indoor and outdoor temperatures and the average inside surface temperatures of the building envelopes. In other words, it is not involved with the heat flow rate, which is difficult to measure. Thus, on this point, the frequency response method is better than the other two methods to evaluate the in situ R-value of buildings.

Partial Blockage Detection in Pipelines by Frequency Response Method

A new technique is presented utilizing the frequency response for the detection of partial blockages in a pipeline. In the system frequency response, a partial blockage increases the amplitude of the pressure oscillations at even harmonics. Such an increase in amplitude has an oscillatory pattern, the frequency and amplitude of which may be used to predict the location and size of a partial blockage. In this technique, the pressure transient history at only one location is sufficient, and the history of the transient in the pipe prior to blockage is not needed, which is an advantage over a number of other available techniques, in addition to being simpler to use. It is shown that the technique successfully detects the location of a blockage in a number of simple systems with blockage size as small as 10%. The technique is verified by comparing the computed results with those computed by the method of characteristics and with measurements from simple laboratory setups. A number of practical issues and limitations for field implementations are discussed.

Estimation of Electrical Cell–Capillary Admittance During Injection with Frequency Response Method

This paper describes electrical equivalent circuit models of cell–capillary admittance during injection of a living cell and presents a measurement system to estimate corresponding frequency responses during microinjection tests. Since the admittance estimate is calculated from data collected during injection, the amount of data is limited. To overcome this constraint, the approach proposed in this paper takes advantage of properties of periodic pseudo random binary sequence (PRBS) excitation signal and avoids end effect anomalies of correlation calculation. The fast and accurate estimation is used to detect the degree of contact during cell injection and to detect breakage and clogging of capillary during a sequence of multiple operations.

3158 動圧型空気フォイル軸受の安定性に対する組立予圧の影響(S35-3 機械要素の設計・製造・応用技術(3) 軸受及びしゅう動要素の特性,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

Bump foil journal bearings are prospective applicants that can support a small-sized rotor of high-speed rotary machinery. In the previous report two models were presented to the bearing, one of which corresponds to the bearing with an excessive static friction between the top and bump foils and the other to the bearing without the friction, and the assembly preload was shown to have a large influence on the maximum load-carrying capacity of the bearings. In this report the stability threshold speed of a horizontal rigid rotor supported in the bearings are predicted, by applying the frequency response method. It is shown that the assembly preload has an effect on the stability and the larger assembly preload results in the larger modified stability threshold speed, where the mean radial clearance in the assembled bearing is chosen as the representative clearance, of the bearing with no friction.

H35 振動数応答法を適用した動圧型空気フォイル軸受の安定性解析(H3 機素潤滑設計1)

H35 振動数応答法を適用した動圧型空気フォイル軸受の安定性解析(H3 機素潤滑設計1)

Dynamic Behavior of Plate Heat Exchanger

The mathematical modeling of plate heat exchanger was studied by introducing rectangular pulse change in inlet cold water flow rate and measuring the temperature of outlet cold water. A theoretical model for the plate heat exchanger was developed based on the heat balance and used the frequency response analysis techniques to determine the best model parameters. The results show that the dynamic behavior of plate heat exchanger can be approximated by a time delay with first order system and a closed fit between the theoretical coefficients of the system and these data by using frequency response method.

Stability analysis of the simplest Takagi-Sugeno fuzzy control system using circle criterion

A frequency-domain-based sufficient condition is derived to guarantee the globally asymptotic stability of the simplest Takagi-Sugeno (T-S) fuzzy control system by using the circle criterion. The analysis is performed in the frequency domain, and hence the condition is of great significance when the frequency-response method, which is widely used in the linear control theory and practice, is employed to synthesize the simplest T-S fuzzy controller. Besides, this sufficient condition is featured by a graphical interpretation, which makes the condition straightforward to be used. Comparisons are drawn between the performance of the simplest T-S fuzzy controller and that of the linear compensator. Two numerical examples are presented to demonstrate how this sufficient condition can be applied to both stable and unstable plants.

Impact Loads Identification in Standoff Metallic Thermal Protection System Panels

This article describes two experimental approaches for the identification of transient impact loads applied to a metallic composite thermal protection system (TPS) panel. The critical nature of the TPS to the survival of the vehicle and crew warrants the development of a technique that can detect, quantify, and locate transient impact loads. This information will provide an opportunity to identify specific panels that are more or less prone to damage from transient impacts. Furthermore, a historical database of impact loads encountered can be retained for use in the development of statistical models that relate impact loading to panel life. The two techniques presented herein are a physics-based approach, where the panel is assumed to behave as a rigid body at low frequencies, and an inverse frequency response approach, where the system impedance matrix is measured, from which the loads acting on the panel can be estimated using the measured response. The validity of approaches is verified experimentally, and it is shown that the inverse frequency response method is capable of detecting, locating, and quantifying transient impact loads to a high degree of accuracy.

Nonlinear frequency response method for estimation of single solute adsorption isotherms. Part II

The aim of this paper is to investigate the possibility of applying a nonlinear frequency response (FR) method described by Ilić et al. [2007b. Nonlinear frequency response method for estimation of single solute adsorption isotherms. Part I. Theoretical basis and simulations, this volume, doi: 10.1016/j.ces.2007.05.004] to determine single solute adsorption isotherms. The method is based on the analysis of the nonlinear FR of a chromatographic column to a periodical change of the inlet concentration around several steady-state concentrations. The first, second and third local derivatives of single solute isotherms are estimated from the low-frequency asymptotic behaviour of the corresponding FR functions. The adsorption of 4- tert-butylphenol and ethyl benzoate as single solutes is studied on octadecyl silica ( C 18 ) from methanol–water mixture (60:40). Experiments are performed using a standard gradient HPLC unit capable to realize inlet concentration changes in a nearly sine waveform. Small injections of compounds into the not preloaded column, as well as conventional frontal analysis experiments are performed for rough estimation of the adsorption isotherm coefficients and comparison with the results obtained using the nonlinear FR method.

Sorption kinetics of atmospheric gases on Li,RE(rare earth)-LSX zeolite beads as sorbents for oxygen PVSA processes

Sorption kinetics of argon, oxygen and nitrogen on beads of a representative sample of the oxygen PVSA sorbent Li,RE(rare earth)-LSX zeolite was investigated by a frequency-response method. Characteristic time constants and their dependencies on temperature and sorption-phase concentration were determined, rate-determining mass-transfer steps were identified, and the results were compared for the three gases.

Nonlinear frequency response method for estimation of single solute adsorption isotherms. Part I. Theoretical basis and simulations

A method for determination of single solute adsorption isotherms based on the analysis of the nonlinear frequency response (FR) of a chromatographic column is developed theoretically. In order to demonstrate this method, the FR of a chromatographic column is simulated for the periodical inlet concentration changes (sine waveform) around several steady-state concentrations. The frequency response functions (FRFs) up to the third order are calculated from the inlet and outlet concentration changes, which are analysed using the fast Fourier transform. Afterwards the coefficients of an adsorption isotherm are estimated from the low-frequency asymptotes of the FRFs and their derivatives. The obtained coefficients compare well with those used for simulations. Also discussed are some aspects that might affect the accuracy of the suggested method when it is applied to the analysis of experimental data, e.g. influence of velocity fluctuations, noise and size of the analysed data set.

Mixture Diffusion in Nanoporous Adsorbents: Development of Fickian Flux Relationship and Concentration-Swing Frequency Response Method

A frequency response method using concentration variation is developed theoretically and experimentally and applied to investigate mixture diffusion in nanoporous adsorbents. The method is based on periodically time-varying species feed concentrations with a constant total molar inlet flow rate. It can be used without the need of a carrier gas. A mathematical model is formulated considering nanopore diffusion, surface barrier resistance, external film resistance, and axial dispersion. The related analytical solutions for frequency response are derived. For nanopore diffusion, a theory for nonconstant mixture Fickian diffusivity with cross-terms is developed from irreversible thermodynamics and shows that mixture Fickian diffusivities can be expressed as the product of corrected diffusivities and a thermodynamic factor that accounts for concentration dependence. The number of unknown variables for Fickian diffusivities is the same as the number for Onsager coefficients or Maxwell−Stefan diffusivities. Adso...

A Frequency-Response Permittivity Sensor for Simultaneous Measurement of Multiple Soil Properties: Part I. The Frequency-Response Method

A microcontroller-based frequency-response permittivity sensor for simultaneously measuring multiple soil properties was developed and tested in the laboratory. The sensing system consists of a sensor probe designed based on a modified Wenner-array structure, hardware for measuring frequency-response data, and software for controlling the hardware. The frequency responses of the sensor were measured within the frequency range of 200 Hz to 100 MHz in soil samples at combinations of three soil textures (very fine sandy loam, silt loam, and silty clay loam), five gravimetric water contents (12% to 22%), five salinities (1.90 to 11.15 dS m-1), and five bulk densities (1.05 to 1.30 g cm-3). Frequency-response tests showed that both the magnitude and phase parts of the frequency-response data can be good indicators of multiple soil properties. A higher water content and a higher salinity yielded a lower magnitude ratio and a higher phase difference at all frequencies. The phase difference showed the potential to measure water content in saline soils and to measure salinity in wet soils. The R2 values achieved by the models for predicting water content under 7.89 dS m-1 salinity using the magnitude ratio and the phase difference obtained at 600 Hz were 0.982 with root mean square error (RMSE) of 0.005 m3 m-3 and 0.978 with RMSE of 0.005 m3 m-3, respectively. The R2 values achieved by the models for predicting salinity under 0.243 m3 m-3 water content using the magnitude ratio and the phase difference obtained at 20 MHz were 0.969 with RMSE of 0.328 dS m-1 and 0.982 with RMSE of 0.328 dS m-1, respectively. These results demonstrated that the sensor developed in this study is capable of measuring water content and salinity as accurately as commonly used soil moisture sensors, including TDR and capacitance sensors, and traditional four-electrode electrical conductivity sensors when only one variable (water content or salinity) of the soil is varied.

Stability and transient-behavioural assessment of power-electronics based dc-distribution systems. Part 2: The frequency response approach

Ideas and developments in electrical systems are being stimulated by progress in power electronics; nowhere is this more apparent than in the marine industry. Indeed, it may be that such advances may lead to dc-distribution systems appearing once again in vessels. Concomitant with these developments is the need for new methods, or adaptation of known methods, to be found to deal with design and analysis problems that will invariably arise.The problem considered in this paper is identical to that considered in Part 1, ie that of a dc-supply feeding a constant-power load. This arrangement is one that is susceptible to stability problems. Work on this problem, using the Nyquist criterion-based method has been reported1 and, more recently, using the root-locus technique.2 This paper is concerned with tackling this same problem using frequency-response methods, specifically Bode diagrams. A stability assessment of the system can be made and some notion of the robustness of this stability ascertained.Further, it is shown that if gain and phase margins can be determined and if the characteristic response of the system is dominated by the existence of a pair of complex-conjugate roots, means of extracting the damping-factor and natural-frequency of an approximating second-order system can be easily established. Once this is achieved, transient behaviour of the system to disturbances can be estimated.

Damping analysis of beams covered with multiple PCLD patches

An analytical approach for vibration damping analysis of beams with partial passive constrained layer damping (PCLD) treatments is extended to the case where the structure is covered by multiple patches. The energy-based approach and assumed-mode method are used to derive the equations governing the vibration displacement responses of the system, which is characterized in terms of the identical transverse displacement of all layers, and the longitudinal displacements of the base beam and the constraining layers. Furthermore, the longitudinal displacements of the base beam and constraining layer are independent of each other, which is in contrast to Kerwin's weak core assumption. The direct frequency response method is employed to determine the modal loss factors of the damped beam in a frequency range of interest. A convergence study is made on the damped beam to determine appropriate numbers of the mode functions for frequency response function (FRF) calculations. Parametric studies are performed with the established analytical approach and the determined numbers of mode functions to study the effects of dividing a PCLD patch into two pieces in different length ratios and also the spacing between the patches on the damping performance of a simply supported beam.

Experimental verification of the frequency response method for pipeline leak detection

This paper presents an experimental validation of the frequency response method for pipeline leak detection. The presence of a leak within the pipe imposes a periodic pattern on the resonant peaks of the frequency response diagram. This pattern can be used as an indicator of leaks without requiring the “no-leak” benchmark for comparison. In addition to the experimental verification of the technique, important issues, such as the procedure for frequency response extraction and methods for dealing with frequency-dependent friction are considered in this paper. In this study, transient signals are generated by a side-discharge solenoid valve. Non-linearity errors associated with large valve movements can be prevented by a change in the input parameter to the system. The optimum measuring and generating position for two different system boundary configurations—a symmetric and an antisymmetric system—are discussed in the paper and the analytical expression for the leak-induced pattern in these two cases is derived