Multi-load Method Research Articles

An Advanced Inductively Coupled Wireless Charging System For Electric Vehicle Applications

Any day today, the globe transitions to electrified transportation, reducing non-renewable fossil fuel pollutant emissions. Electromagnetic energy is transferred from the power source to the electrical charge without interconnection wires and the operation is carried out in every device. Electric cars are seen in the potential mobility area to be substitutions for the vehicles propelled by oil fueled internal combustion engine. In this project wireless charging technologies are examined using the inductive coupling approach. Numerous factors, including magnetic flow, inductance of the resonant bob, determine the performance of wireless power transfer and mutual inductance. The paper focuses in particular on static (stationary) charge, while dynamic loading (loading during driving) involves a dramatically different method. The Multi-Load method is modelled and the efficiency expression for each charge is determined with a different resonant frequency.

Engine characterization using experimental method and prediction of insertion loss of the exhaust system

The evaluation of the acoustic performance of an exhaust system at the design stage requires a correlated engine model and reasonably approximate input boundary conditions to simulate the end results, both of which are not easily available. It is known that the input boundary conditions for insertion loss analysis require two engine parameters, namely, source impedance and source strength spectra. This study describes experimental measurements for these parameters using in-duct measurement via the multi-load method for a six-cylinder diesel engine and calculation for insertion loss using GT-Power. The research discusses the approach taken to select the acoustic load cases considered for the multi-load method and then the execution of the test plan for different engine operating conditions The time domain data sets were processed to obtain the frequency spectra and was used to get the impedance of the acoustic load cases and finally the source impedance and source strength spectra for different engine operating conditions. The results obtained using all the acoustic load cases were optimized by filtering out unacceptable load cases and then re-evaluating the source characteristics to use them as input boundary conditions for insertion loss analysis. The analysis results were then compared to the experimental insertion loss.

Using the Moebius Transformation to Predict the Effect of Source Impedance on Insertion Loss

Knowledge of the strength and internal impedance of the sound source is essential to predict the overall acoustic performance of an exhaust or intake system. Source impedance is sometimes measured directly using a strong external source. At other times, a suitable external source is difficult to identify and an indirect multi-load method is used to determine source impedance and strength. Data can be processed using the commonly used circuit analogy or via a similar wave decomposition model. In this work, the two processing schemes are used to determine the source impedance and strength of a diesel engine. Results are compared to one another and to assumed source impedances and equations in the literature for source strength. The sound pressure in the exhaust is predicted from the measured source strength and impedance and compared with measurement. There is good agreement especially at the first few harmonics of the firing frequency. It is then observed that the equation relating the source impedance to the acoustic response is in the form of the Moebius transformation, which maps straight lines or circles in one complex domain into straight lines or circles in another complex domain. It is demonstrated that the range of source impedance, defined as an outline in the complex plane, can be transformed to a corresponding outline of the mufi¬,er insertion loss complex amplitude, and the minimum and maximum insertion loss can be computed at a given frequency. This permits the expected insertion loss range to be plotted as a function of frequency.

IC-engine acoustic source characterization in-situ with capsule tube method

Typically, a component level approach is used in control of internal combustion engine (IC-engine) exhaust noise. This has enabled the development of new, cost-efficient silencers, for example. However, prediction of sound emission from a tailpipe or insertion loss of a silencer requires a more extensive, system level approach. Therefore, valid IC-engine source characteristics and a valid model of the whole transmission path are needed. When characterizing an IC-engine as a source with the commonly used in-duct multi-load method, the requirements for load impedance variation must be fulfilled. It is fairly easy to vary the load in automotive cases, whereas new methods must be developed for large IC-engines, used e.g. in power plants. In this study, the source data determination process is investigated in detail, a novel “capsule tube method” is developed further and used for experimental acoustic source data determination of medium speed IC-engine exhaust system in harsh environment. With suitable filtration and statistical outlier rejection methods presented in this paper, the source data of a test IC-engine exhaust system was derived with success.

Analysis of pipeline networks using two-ports

Majority of vibration problems arise in pipeline networks are attributed to the high-pressure pulsations. Pulsations are generated by fluid machines such as compressors and pumps. These pulsations turn into shaking forces at elements such as pipe bends and pipe reducers, which in turn excite vibrations in the connected piping network. High vibrations beyond the endurance limit of the pipe material may cause damage to pipes, supports, and equipment. In addition, if the source pulsation frequency coincides with one of the natural frequencies of the piping network, resonance will take place and the vibrations will be magnified to a large scale. Obviously, if these vibrations are not well controlled, they might cause damage to the whole system and foundation, and might lead to substantial financial losses. Thus, prediction of pulsations is important for safe and proper operation. In this paper, a pilot plant equipped with a reciprocating compressor, pipes, bends, and terminated by a vessel is built. The network is modeled using the two-port theory that splits the network into several cascaded elements, and predicts the response of the network. The prediction model uses the measured compressor source data as an input, which is determined by the indirect multi-load method that is usually used to characterize internal combustion engines. A pulsation suppression device is designed, modeled, manufactured and inserted into the pilot network. The pressure pulsations are measured with and without the pulsation suppression device, and compared to the predictions using the two-port theory.

Analysis of the load selection on the error of source characteristics identification for an engine exhaust system

Linear time-invariant assumption for the determination of acoustic source characteristics, the source strength and the source impedance in the frequency domain has been proved reasonable in the design of an exhaust system. Different methods have been proposed to its identification and the multi-load method is widely used for its convenience by varying the load number and impedance. Theoretical error analysis has rarely been referred to and previous results have shown an overdetermined set of open pipes can reduce the identification error. This paper contributes a theoretical error analysis for the load selection. The relationships between the error in the identification of source characteristics and the load selection were analysed. A general linear time-invariant model was built based on the four-load method. To analyse the error of the source impedance, an error estimation function was proposed. The dispersion of the source pressure was obtained by an inverse calculation as an indicator to detect the accuracy of the results. It was found that for a certain load length, the load resistance at the frequency points of one-quarter wavelength of odd multiples results in peaks and in the maximum error for source impedance identification. Therefore, the load impedance of frequency range within the one-quarter wavelength of odd multiples should not be used for source impedance identification. If the selected loads have more similar resistance values (i.e., the same order of magnitude), the identification error of the source impedance could be effectively reduced.

Acoustic Source Characterization for Prediction of Medium Speed Diesel Engine Exhaust Noise

To achieve reliable results when simulating the acoustics of the internal combustion engine (IC-engine) exhaust system and its components, the source characteristics of the engine must be known. In the low frequency range only plane waves propagate and then one-port source data can be determined using, for example, the acoustic multiload method. For the medium speed IC-engines used in power plants and ships, the exhaust duct noise often needs to be analyzed up to 10 kHz, i.e., far beyond the plane wave range, and it is then more appropriate to use acoustic power to characterize the source. This power should ideally be measured under reflection-free conditions in the exhaust duct. The results from an earlier study showed that a suitable way to characterize the source for any frequency is to determine the in-duct sound power by extending the plane wave formulation with frequency band power weighting factors. The aim of this study is to apply this high frequency range method in situ to a real test engine. Another aim is to define, theoretically, how to combine the source data in the low frequency plane wave range with those in the high frequency nonplane wave range using a source sound power formulation.

On the characterization of acoustic two-port sources using multi-load method

A multi-load method for determining the source data of acoustic two-port sources is presented. By eliminating the term of source strength, the scattering matrix can then be obtained by solving a set of nonlinear algebraic equations, and the source strength is determined by the scattering matrix and the directly measured spectrum matrix corresponding to one of the acoustic loads. Numerical simulations indicate that the proposed method is effective. The method has been tested on a loudspeaker and an axial flow fan in a duct. The source data obtained by this method show reasonable agreement with that measured by the direct method. The multi-load method avoids using external sources, and it can be used as an alternative method when the external source is not easy to realize in practice.

A view on the internal consistency of linear source identification for I.C. engine exhaust noise prediction

Considerable efforts have been devoted to the development of predictive models that, from a certain set of data related to an engine, and making use of an adequate representation of the effect of the silencing elements, provide an estimate of the exhaust noise emitted. Such models should allow for the consideration of the engine and its interaction with the exhaust system. This is properly achieved by gas-dynamic models, which are becoming the standard, but linear models solved in the frequency domain and representing the engine as a linear time-invariant source may still play a role in exhaust system design, as the engine is treated as a black box. Such a representation is very attractive for engine manufacturers, since it gives the possibility to provide data on the engine without any possibility to trace back to its real characteristics. In order to provide additional criteria for the suitability of the application of a linear time-invariant representation to an engine exhaust, in this paper a multi-load method has been used to extract source characteristics from gas-dynamic simulation results. The details of the method, in which the resulting over-determined system is solved by fitting the values of the source parameters in a least-squares sense, are described, and different approaches are used in order to check the internal consistency of the source representation: the identification of pressure and velocity sources, and the application of the least-squares criterion to the modulus or to the real and imaginary parts separately. In particular, eight different determinations of the source impedance are obtained and, considering the application of the formalism to an engine exhaust, the differences observed provide a suitable criterion for the evaluation of the suitability of the representation and of the particular set of loads chosen.

Approximate Empirical Expressions for the Aeroacoustic Source Strength Level of the Exhaust System of Compression Ignition Engines

Prediction of the un-muffled or muffled noise from internal combustion engines requires knowledge of the acoustic performance of the muffling system together with the engine source characteristics. The pressure time history downstream of the exhaust manifold or turbocharger is computed by means of a time-domain finite-volume numerical software. From this pressure time history, the electro-acoustic analogue source characteristics i.e. ps and Zs are determined indirectly using a multi-load method. This investigation has been conducted for both naturally aspirated and turbocharged diesel engines. Using this methodology and the resultant empirical relations one can analyze any compression-ignition IC-engine configuration for the prediction of the un-muffled noise without having to carry out the time-domain simulation of the exhaust source. The goal of this work is to parameterize the source characteristics of an engine in terms of basic engine parameters, so that a first assessment of the un-muffled noise can be made before a detailed design is taken up. Though this empirical approach may not be able to predict actual noise spectra precisely, yet this serves a useful purpose. One of the results has also been corroborated with the measured value in order to validate the methodology presented here.

Intake source characterization of a compression ignition engine: Empirical expressions

Unlike exhaust noise, the intake system noise off an automobile cannot be measured because of the proximity of the engine at the point-of measurement. Besides, the intake side is associated with turbocharger (booster),intercooler, cooling fan, etc., which will make the measurement of the intake noise erroneous. Therefore, in the present investigation, the source characteristics of the intake system have been expressed as functions of the engine's physical, operating and thermodynamic parameters. The pressure time history is first computed by means of the commercial software AVL-BOOST for different acoustic loads (induction pipe lengths), which are then used to determine source characteristics, Le.,p(s) and Z(S) (analogous to the open-circuit voltage and internal impedance of an electrical source), using an appropriate multi-load method. This investigation has been conducted for both naturally aspirated and turbocharged diesel engine. Using this methodology and the resultant empirical relations, one can analyze any compression-ignition (CI) engine configuration for the prediction of the un-muffled noise without having to carry out the rather cumbersome and time-consuming time-domain simulation of the intake side. The aim of the present study is to parameterize the source characteristics of an engine in terms of basic engine parameters, so that a first assessment of the un-muffled intake noise can be made by means of the frequency-domain transfer matrix method before a detailed design is taken up.

Modified multi-load method for nonlinear source characterisation

Linear frequency domain prediction codes are useful for calculation of low-frequency sound transmission in duct and pipe systems. To calculate insertion loss of mufflers or the level of radiated sound information about the acoustic source is needed. The source model used in the low-frequency plane wave range is the linear time invariant one-port model. The acoustic source data is usually obtained from experimental tests where multi-load methods and especially the two-load method are most commonly used. The exhaust pulsations of for example an IC-engine are of high level, and the engine is not a perfectly linear and time invariant source. It is therefore of interest to develop source models and experimental techniques that try to take this nonlinearity into account. In this paper a modified version of the two-load method to improve the characterisation of nonlinear acoustic one-port sources has been developed and tested. Simulation results as well as experimental data from various source configurations for a modified compressor and experimental data from 6-cylinder turbocharged truck diesel engine were used to validate the method. The influence of parameters controlling the linearity of the system was investigated. The time-variance of the source model was varied and the accuracy of source characterisation results using the two-load method and the modified two-load method was evaluated.

On the selection of loads in the multiload method for measuring the acoustic source parameters of duct systems

The in-duct source can be characterized by two acoustical parameters such as the source strength and the source impedance, which permit the prediction of radiated sound pressure or insertion loss of the whole duct system. One-port acoustic characteristics of an in-duct source can be measured by the multiload method using an overdetermined set of open pipes or side-branch pipes with different lengths as applied loads. The input data, viz. load pressure and load impedance, are usually contaminated by measurement error in the actual measurements, which result in errors in the calculated source parameters. In this paper, the effects of the errors in the input data on the results have been studied numerically, varying the number of loads and their impedances in order to determine what combination of the loads will yield the best result. It is noted that, frequently, only a set of open pipes is used when applying the multiload method to the internal combustion engine sources. A set of pipe lengths, which cause the calculated results to be least sensitive to the input data error, can be found when using open pipe loads. The present work is intended to produce guidelines for preparing an appropriate load set in order to obtain accurate source properties of fluid machines.

Refined multiload method for measuring acoustical source characteristics of an intake or exhaust system

The one-port source characteristics in a duct system, viz., source impedance and strength, can be determined by using the four-load method. In this paper, to avoid the instability problem of the conventional four-load method, a new formulation for the multiload method has been proposed, which employs an error function based on the linear, time-invariant source model. It is shown that the method is less sensitive to input errors compared to the previous methods. For a 10% input error, the proposed method yields a relative error in the source resistance that is about 1/100 times smaller than for the conventional method. The effectiveness of the present method is demonstrated by two test examples, a loudspeaker and a blower, each operating in a duct. It is observed that the conventional and least-squares methods result in large errors, whereas the present method yields far better agreement with the actual source parameters, as measured by the direct method. The present method is then used to obtain the source parameters on the exhaust side of an operating internal combustion engine. The radiated sound spectrum from the exhaust opening is predicted by using the measured source parameters and the calculated result agrees very well with the measured one.

On the feasibility of determining discrete photoelastic parameters using the multi-load method

An alternative method for the determination of three-dimensional stresses in photoelastic models is discussed. The model is sectioned into discrete, imaginary slices and a relationship is derived between the retardation and isoclinic angle of each slice and characteristic photoelastic parameters measured using a transmission polariscope. An illustration of the multi-load method is given and the practical application of the technique is discussed.

Determination of source data for a thermoacoustic prime mover by the multiload method

A thermoacoustic prime mover can be used as a sound source to drive thermoacoustic refrigerators. The nitrogen-filled prime mover studied is a quarter-wavelength resonator that produces sound at nominally 86 Hz for a temperature difference of ΔT≥430 K. The pressure and specific impedance at the mouth of the prime mover were measured as a function of the load realized by different reservoirs. These measurements allow one to determine the characteristics of the prime mover at operation states and therefore to predict the maximum acoustic power at a perfect match. Nonlinear losses in the prime mover are analyzed by estimating the measured impedance.

A Least Squares Method For Evaluation Of Characteristics Of Acoustical Sources

A multi-load method to determine source characteristics is presented here. The method is simple: only one microphone is used and no second noise source is needed. It is shown that a larger amount of information gained from the system due to more loads avoids stability problems. The validity of the source parameters obtained by the method is compared with the prediction of insertion loss and of the noise production at the output of a known load. Both theoretical predictions and experimental results are compared: the agreement is good. Further explanations are given regarding stability problems occurring in the so-called four-load method. The method gives better results for relatively complex sources (non-constant impedance) than the four-load method, although consuming more time in measurement because of the extra loads.