Field Component In Direction Research Articles

Corrected Statistical Energy Analysis Model in a Non-Reverberant Acoustic Space

Statistical Energy Analysis (SEA) is a well-known method to analyze the flow of acoustic and vibration energy in a complex structure. This study investigates the application of the corrected SEA model in a non-reverberant acoustic space where the direct field component from the sound source dominates the total sound field rather than a diffuse field in a reverberant space which the classical SEA model assumption is based on. A corrected SEA model is proposed where the direct field component in the energy is removed and the power injected in the subsystem considers only the remaining power after the loss at first reflection. Measurement was conducted in a box divided into two rooms separated by a partition with an opening where the condition of reverberant and non-reverberant can conveniently be controlled. In the case of a non-reverberant space where acoustic material was installed inside the wall of the experimental box, the signals are corrected by eliminating the direct field component in the measured impulse response. Using the corrected SEA model, comparison of the coupling loss factor (CLF) and damping loss factor (DLF) with the theory shows good agreement.

Pengukuran Sound Pressure Level (SPL) dalam kabin mobil dengan menggunakan SEA Model

Statistical energy analysis (SEA) is a well-known method to analyze the flow of acoustic and vibration energy in a complex structure. For an acoustic space where significant absorptive materials are present, direct field component from the sound source dominates the total sound field rather than a reverberant field, where the latter becomes the basis in constructing the conventional SEA model. Such environment can be found in a car interior and thus a corrected SEA model is proposed here to counter this situation. The model is developed by eliminating the direct field component from the total sound field and only the power after the first reflection is considered. A test car cabin was divided into two subsystems and by using a loudspeaker as a sound source, the power injection method in SEA was employed to obtain the corrected coupling loss factor and the damping loss factor from the corrected SEA model. These parameters were then used to predict the sound pressure level in the interior cabin using the injected input power from the engine. The results show satisfactory agreement with the directly measured SPL.Keywords : Statictical Energy Analysis (SEA), Sound Pressure level (SPL), DLF and CLF

Pengaruh dari Direct Field Component pada Ruang Akustik dengan menggunakan SEA Model

Statistical Energy Analysis (SEA) is a well-known method to analyze the flow of acoustic and vibration energy in a complex structure. This study investigates the application of the corrected SEA model in a non-reverberant acoustic space where the direct field component from the sound source dominates the total sound field rather than a diffuse field in a reverberant space which the classical SEA model assumption is based on. A corrected SEA model is proposed where the direct field component in the energy is removed and the power injected in the subsystem considers only the remaining power after the loss at first reflection. Measurement is conducted a box divided into two rooms separated by a partition with an opening where the condition of reverberant and non-reverberant can conveniently be controlled. In the case of a non-reverberant space where acoustic material was installed inside the wall of the experimental box, the signals are corrected by eliminating the direct field component in the measured impulse response. Using the corrected SEA model, comparison of the coupling loss factor (CLF) with the theory shows good agreement.

Corrected Statistical Energy Analysis Model for Car Interior Noise

Statistical energy analysis (SEA) is a well-known method to analyze the flow of acoustic and vibration energy in a complex structure. For an acoustic space where significant absorptive materials are present, direct field component from the sound source dominates the total sound field rather than a reverberant field, where the latter becomes the basis in constructing the conventional SEA model. Such environment can be found in a car interior and thus a corrected SEA model is proposed here to counter this situation. The model is developed by eliminating the direct field component from the total sound field and only the power after the first reflection is considered. A test car cabin was divided into two subsystems and by using a loudspeaker as a sound source, the power injection method in SEA was employed to obtain the corrected coupling loss factor and the damping loss factor from the corrected SEA model. These parameters were then used to predict the sound pressure level in the interior cabin using the injected input power from the engine. The results show satisfactory agreement with the directly measured SPL.

Magnetic pileup boundary and field draping at Comet Halley

The approach of the Rosetta S/C to Comet Churyumov–Gerasimenko in 2014 reactivates the interest in the plasma interaction of the solar wind with the cometary coma. In preparation for the upcoming S/C observations and the start of outgassing of the cometary nucleus, we reinvestigate the magnetic field data from the Vega-1 S/C at the flyby of Comet Halley (1986), in search of the magnetic pileup boundary and increase of field line draping. The magnetic pileup boundary has been identified as a common feature for unmagnetized bodies with an induced magnetosphere. This boundary marks the outer edge of the magnetic pileup region, also known as the magnetic barrier region, in which the magnetic field is strong and highly draped. Initially, the magnetic field draping around Comet Halley was clearly identified from the Vega-1 magnetometer data through reversal of the field component in direction to the Sun at closest approach.Here, a detailed analysis is performed in regions further upstream in the magnetosheath. The Vega-1 high resolution magnetometer data on the in- and outbound leg but inside the bow wave are reinvestigated in search for the magnetic pileup boundary as an indicator for the outer edge of the magnetic barrier. The magnetic field pileup region is studied using the correlation between the field component towards the Sun and the radial component in an aberrated cometocentric frame; this technique proved very successful for Mars and also for comets Giacobini–Zinner and Halley in the case of Giotto observations. We can clearly identify the different regimes in the magnetic field data, on the in- and outbound leg of the orbit. Waves just within the newly determined magnetic pileup region have properties different from mirror mode waves, whereas waves observed out of the magnetic pileup boundary are confirmed as mirror mode. The boundaries found at Comet Halley prove that also the detailed structure of the interaction of unmagnetized bodies with an atmosphere with the solar wind is valid for active comets, but with larger space scale.

The Effect of Direct Field Component on a Statistical Energy Analysis (SEA) Model

Statistical Energy Analysis (SEA) is a well-known method to analyze the flow of acoustic and vibration energy in a complex structure. The structure is divided into subsystems where the energy in each of the subsystem is assumed to be reverberant. This study investigates the application of SEA model in a 'damped' acoustic space where the direct field component from the sound source dominates the total sound field rather than a diffuse field in a reverberant space which the SEA model assumption is based on. A measurement was conducted in a scaled room divided into two acoustic spaces separated by a partition with an opening. Absorbent materials were installed on the room walls and the power injection technique was implemented to obtain the coupling loss factor (CLF) of the system. It is found that correction of the direct field component from the subsystem energy improves the prediction of the CLF of the system.

P 221. Subject specific finite element models predict cortical excitation volumes generated by transcranial magnetic stimulation

Introduction TMS is now widely used in research and holds therapeutic promise. Nevertheless there remains a high degree of variability in the effects reported across subjects, studies and treatment paradigms. Recently, computational approaches using realistic finite element models (FEM) ( Opitz et al., 2011 , Thielscher et al., 2011 , Windhoff et al., 2013 ) of the brain have enabled more accurate estimations of the electric fields generated during TMS protocols. These models help to differentiate between interindividual TMS variability due to gyral folding patterns and other confounds such as subject-specific conductivity anisotropy. Objectives Validation approaches of FEM-simulated electric fields induced by TMS by actual physiological responses, such as motor evoked potential (MEP) amplitudes are scarce. Here, we compared computational predictions with MR-guided TMS motor-mapping and fMRI. Furthermore, predictions of stimulated areas are compared between realistic finite element models and currently used projection approaches widely used in neuronavigation systems. Materials and methods Anatomical voxel based, diffusion weighted imaging (DTI) and functional MRI during voluntary finger movement was conducted on all subjects. An individual FEM model including conductivity anisotropy derived from DTI data was generated for each subject. We measured MRI-guided TMS-evoked MEP from four different muscles (FDI, ADM, ECR, FCR). The motor cortex was mapped at different locations with 1 cm spacing using 5 × 5 cm grids centered on the subject’s motor hot-spot for a given muscle. At each stimulus site, we evoked MEPs using two different TMS coil orientations (45° to midline and 90° to midline). For each coil position, FEM simulations of the TMS-induced electric field were generated and compared with TMS-evoked MEP amplitudes. In addition a theoretical comparison between different methods to determine stimulated cortical areas was conducted. Results FEM simulations reliably predicted motor areas as stimulation target independent of the given TMS orientations in a subject specific manner, although MEP amplitude maps differed significantly in spatial extent and amplitude across coil orientations. MEP amplitudes at different grid points were highly correlated with the perpendicular component of the electric field strength in regions with strong BOLD activations during voluntary finger movement. A similar relationship was found for the electric field component in direction of WM fiber bundles in M1. Realistic finite element simulations produce more robust results in indicating stimulated areas in comparison to projection approaches. Conclusion We conclude that taking subject-specific electric field distributions into account can improve our understanding of the variability of physiological measurements obtained during various TMS protocols. Furthermore, combining fMRI with FEM simulations may enhance the precision of targeting of brain circuits such as the dlPFC, which do not exhibit immediate behavioral responses to TMS.

Interpreting the Input Admittance of Violins and Guitars

The most widespread vibration measurement on musical instrument bodies is of the point mobility at the bridge. Analysis of such measurements is presented, with a view to assessing what range of information could feasibly be extracted from the corpus of data. Analysis approaches include (1) pole-residue extraction; (2) damping trend analysis based on time decay information; (3) statistical estimates based on SEA power-balance and variance theory. Comparative results are shown for some key quantities. Damping trends with frequency are shown to have unexpectedly different forms for violins and for guitars. Linear averaging to estimate the direct field component gives a simple and clear visualisation of any local resonance behaviour near the bridge, such as the bridge and reveals some violins that show a double hill, while viols show only weak hills, and guitars none at all. © S. Hirzel Verlag · EAA.

Ferrite cores as back yoke for enhancing hall sensor sensitivity in caliper tool for pipeline inspection

PurposeThe purpose of this paper is to describe how to improve magnetic pick up sensor for detection of weak magnetic field. A magnetic marker detection system, built using hall sensors is improved by providing ferrite cores as back yoke to obtain benchmarked performance with reduced number of hall sensors in an equipment for pipeline inspection called caliper tool.Design/methodology/approachThe paper opts for an exploratory study by making various configurations of sensors possible under given constraints, analyzing results of each one of them and correcting the configuration.FindingsInstead of using highly sensitive hall sensors, one can increase the sensitivity of sensor by putting simple ferrite core as back yoke in order to detect weak magnetic field.Originality/valueThis paper fulfils the need of detection of weak magnetic field by changing field direction and maximizing field component in direction of sensitive axis of magnetic sensor.

Prediction of averaged energy for moderately damped systems with strong coupling

In this paper, the prediction of averaged energy of damped structural-acoustic systems is investigated. A simplified energy finite element method, referred to as EFEM 0, is developed based on the energy flow analysis (EFA) equations and implemented using the finite volume method. The resulting formulations can be incorporated into statistical energy analysis (SEA) software and extends SEA application to moderately damped systems with strong coupling. The formulations are verified against analytical solutions for a single beam and coupled beams with both strong and weak coupling. A hybrid technique consisting of the EFEM 0 approximation superimposed on a direct field is used to model moderately damped plates. For lightly damped systems, both methods produce acceptable results. For moderately damped two-dimensional systems, the EFEM 0 method augmented with the direct field component produces significantly improved results.

A HYBRID ENERGY METHOD FOR PREDICTING HIGH FREQUENCY VIBRATIONAL RESPONSE OF POINT-LOADED PLATES

Modelling of the far-field energy distribution and power flow in point-loaded finite plates is considered. First, the two-dimensional conductivity equation governing the energy distribution in a plate is derived from fundamental energy and intensity considerations. The derivation, previously unreported, illustrated the basic assumptions and limitations of the conductivity method. A hybrid model is then developed in which contributions to the direct and reverberant fields are estimated separately. The direct field component is approximated by the far-field response of an infinite plate; the reverberant contribution is governed by a homogenous conductivity equation with a reflected power distribution along the boundary of the plate. The partition of power between the direct and reverberant fields is approximated by assuming a circular plate with an equivalent surface area. The method is found to be effective for predicting the spatial variation in the response when both the direct and reverberant fields participate strongly, a case not well predicted by statistical energy analysis, or by the conductivity method. The method is applied to examples of a centrally loaded square plate, and a rectangular plate with two uncorrelated point loads.

The Precision of Reverberant Sound-Power Measurements

Determination of sound power in a reverberation room is subject to a random error whose size can be estimated and controlled by the knowledgeable laboratory manager. Under ideal measurement conditions the random error can be expressed as a product of three factors: a frequency-averaging factor governed by spectrum shape and room reverberation time, a spatial-averaging factor determined by the number and separation of fixed microphones or the path shape and size for a traversing microphone, and a rotating-diffuser factor depending on the size and shape of the rotating diffuser in relation to room size and reverberation time. Continuing progress in this field is teaching us to incorporate nonideal measurement conditions into our error estimates. In particular, we report progress in understanding the effects on random error due to (1) finite averaging time, (2) presence of a direct field component, and (3) insufficient modal overlap at low frequency.