Development of a 3D finite element acoustic model to predict the sound reduction index of stud based double-leaf walls

Building standards incorporating quantitative acoustical criteria to ensure adequate sound insulation are now being implemented. Engineers are making great efforts to design acoustically efficient double-wall structures. Accordingly, efficient simulation models to predict the acoustic insulation of double-leaf wall structures are needed. This paper presents the development of a numerical tool that can predict the frequency dependent sound reduction index R of stud based double-leaf walls at one-third-octave band frequency range. A fully vibro-acoustic 3D model consisting of two rooms partitioned using a double-leaf wall, considering the structure and acoustic fluid coupling incorporating the existing fluid and structural solvers are presented. The validity of the finite element (FE) model is assessed by comparison with experimental test results carried out in a certified laboratory. Accurate representation of the structural damping matrix to effectively predict the R values are studied. The possibilities of minimising the simulation time using a frequency dependent mesh model was also investigated. The FEA model presented in this work is capable of predicting the weighted sound reduction index R_w along with A-weighted pink noise C and A-weighted urban noise C_tr within an error of 1 dB. The model developed can also be used to analyse the acoustically induced frequency dependent geometrical behaviour of the double-leaf wall components to optimise them for best acoustic performance. The FE modelling procedure reported in this paper can be extended to other building components undergoing fluid–structure interaction (FSI) to evaluate their acoustic insulation.     

The prediction of the vibration reduction index Kij for brick and concrete rigid junctions

The vibration reduction index, K_ij, is related to the transmission of the vibrational power over a junction between structural elements. Two empirical models are proposed to evaluate K_ij, on the basis of statistical evaluations of numerous in-field tests carried out on rigid junctions between floors made by concrete beams and ribbed slab with brick blocks and brickwork walls, a type of junction that is frequently encountered in Southern European and Mediterranean buildings. These models can be applied in order to calculate the sound insulation properties, such as the normalized impact sound pressure level, , and the apparent sound reduction index, R′, of walls and floors in buildings.The first model allows the single number value of the vibration sound reduction index of a junction to be calculated, on the basis of the real properties of the materials that constitute the junction. A new quantity, the “essential” mass per unit area, was introduced to implement the model.The second model provides an estimation of the K_ij as a function of frequency, subdivided between BB-junction, as ribbed slab with brick blocks floor-brick wall, and CB-junction, i.e. concrete beam-brick wall.     

Sound reduction in samples of environmentally friendly building materials and their compositions

In order to reduce the negative effect on the environment, environmentally friendly materials are being chosen for the construction of buildings more and more frequently. The building materials that are now used more commonly are clay, straw and reeds. The sound insulation properties of these environmentally friendly materials have not yet been examined thoroughly. This paper presents most commonly used sound reduction indexes R_W that have been measured in the semi-anechoic chamber and determined during the simulation. It has been found that adobe, pressed straw and reeds (oriented parallel to the sound transmission) are suitable for low-frequency sound insulation. The material with the best sound reduction index was adobe. The sound reduction index R_W of a 200 mm thick adobe wall reached up to 43 dB.     

Adjustment on subjective annoyance of low frequency noise by adding additional sound

Structure-borne noise originating from a heat pump unit was selected to study the influence on subjective annoyance of low frequency noise (LFN) combined with additional sound. Paired comparison test was used for evaluating the subjective annoyance of LFN combined with different sound pressure levels (SPL) of pink noise, frequency-modulated pure tones (FM pure tones) and natural sounds. The results showed that, with pink noise of 250-1000 Hz combined with the original LFN, the subjective annoyance value (SAV) first dropped then rose with increasing SPL. When SPL of the pink noise was 15-25 dB, SAV was lower than that of the original LFN. With pink noise of frequency 250-20,000 Hz added to LFN, SAV increased linearly with increasing SPL. SAV and the psychoacoustic annoyance value (PAV) obtained by semi-theoretical formulas were well correlated. The determination coefficient (R²) was 0.966 and 0.881, respectively, when the frequency range of the pink noise was 250-1000 and 250-20,000 Hz. When FM pure tones with central frequencies of 500, 2000 and 8000 Hz, or natural sounds (including the sound of singing birds, flowing water, wind or ticking clock) were, respectively, added to the original sound, the SAV increased as the SPL of the added sound increased. However, when a FM pure tone of 15 dB with a central frequency of 2000 Hz and a modulation frequency of 10 Hz was added, the SAV was lower than that of the original LFN. With SPL and central frequency held invariable, the SAV declined primarily when modulation frequency increased. With SPL and modulation frequency held invariable, the SAV became lowest when the central frequency was 2000 Hz. This showed a preferable correlation between SAV and fluctuation extent of FM pure tones.     

Justification of standardized level differences in rating of airborne sound insulation between dwellings

It has long been recognized that single-number quantities R′_w, D_nT,w or D_n,w result in different conclusions in objective rating of airborne sound insulation between dwellings. The difference between the values of these single-number quantities (SNQ), however, does not prove which of them describes the sound transmission between rooms most correctly. The main object of this article was to study which SNQ correspond best with transmitted living sound levels in buildings when reverberation time, volume of receiving room and sound insulation are taken into account. Data of 100 field measurements of airborne sound insulation were collected as well as 207 reverberation times of furnished rooms. The transmitted sound levels of living sounds were evaluated on the basis of known living sound spectra and measured level differences D. The results show that the SNQs standardized to reference reverberation time of 0.5 s lead in all cases to best correlation between the SNQs and the sound levels of transmitted living sounds. It was also checked whether the rating by D_nT,w would lead to higher transmitted sound levels of living sounds in larger rooms, but this was not detected. The use of D_nT,w makes rooms of different volumes equal in regard to required sound insulation between them. It is thus justified to replace R′_w with D_nT,w as the SNQ for rating the airborne sound insulation. Widening the frequency range down to 50 Hz or up to 5000 Hz did not give noteworthy improvement in the correlation.     

CO2 sensing properties of semiconducting copper oxide and spinel ferrite nanocomposite thin film

A new active layer for CO₂ sensing based on semiconducting CuO-Cu_xFe_3−xO₄ (with 0 ≤ x ≤ 1) nanocomposite was prepared by radiofrequency sputtering from a delafossite CuFeO₂ target using a specific in situ reduction method followed by post annealing treatment in air. The tenorite-spinel ferrite nanocomposite layer was deposited on a simplified test device and the response in a carbon dioxide atmosphere was measured by varying the concentration up to 5000 ppm, at different working temperatures (130-475 °C) and frequencies (0.5-250 kHz). The results showed a high response of 50% (Rair/RCO₂=1.9) at 250 °C and 700 Hz for a CO₂ concentration of 5000 ppm.     

Sound insulation property of Al–Si closed-cell aluminum foam sandwich panels

Al–Si closed-cell aluminum foam sandwich panels (1240 mm × 1100 mm) of different thicknesses and different densities were prepared by molten body transitional foaming process in Northeastern University. The experiments were carried out to investigate the sound insulation property of Al–Si closed-cell aluminum foam sandwich panels of different thicknesses and different densities under different frequencies (100–4000 Hz). Results show that sound reduction index (R) is small under low frequencies, large under high frequencies; thickness affects the sound insulation property of material obviously: when the thicknesses of Al–Si closed-cell aluminum foam sandwich panels are 12, 22, and 32 mm, the corresponding weighted sound reduction indices (R_W) are 26.3, 32.2, and 34.6 dB, respectively, the rising trend tempered; the increase of density of Al–Si closed-cell aluminum foam can also increase the sound insulation property: when the densities of aluminum foam are 0.31, 0.51, and 0.67 g/cm³, the corresponding weighted sound reduction indices (R_W) are 28.9, 34.3, and 34.6 dB, the increasing value mitigating.     

Airborne sound insulation and graphical indices

The use of graphical indices is interpreted as an approximate approach to the estimation of sound insulation performance of building elements. Differences of weighted sound pressure levels are considered as quantitative measures for subjective sound insulation. The indices considered are formed by shifting a reference curve until the highest position is found at which certain specifications, or rules, are met. General expressions are mathematically derived for the maximum differences between graphical indices and sound insulation in two cases: a maximum allowable sum rule for unfavourable deviations, and a combination for restriction of the maximum single deviation. The results indicate that the maximum deviation rule limits the variation between sound insulation and indices in a very efficient way. This comparison leads to I_a being preferred to R_w, which are special cases of the study.     

Large magnetic entropy change and refrigerant capacity in rare-earth intermetallic RCuAl (R=Ho and Er) compounds

The magnetic properties and the magnetocaloric effects of RCuAl (R=Ho and Er) compounds have been investigated. Both HoCuAl and ErCuAl just undergo a second-order ferromagnetic–paramagnetic phase transition at T_C. Large reversible magnetic entropy changes (ΔS_M) are observed around their respective Curie temperatures due to the ferromagnetic–paramagnetic phase transition. For a field change of 0–5 T, the peak values of −ΔS_M of RCuAl (R=Ho and Er) compounds are 23.9 and 22.9 J kg⁻¹ K⁻¹ at T_C, with the values of refrigerant capacity of 393 and 321 J kg⁻¹, respectively. These properties suggest that RCuAl (R=Ho and Er) compounds could be considered as attractive magnetic refrigerants working in low temperature range.     

Effect of Ga addition on optical properties of crystalline Ga20Se80 system

Ga_xSe_100−x (20 ≤ x ≤ 50) in polycrystalline form was prepared by direct fusion of stoichiometric proportions of pure elements. The spectral behavior of transmittance (T) and the reflectance (R) in the wavelength range 400–2500 nm for all films of different thicknesses were measured to obtain different optical parameters (refractive index, n, and absorption index, k). The study of inter-band transitions indicates that the existence of direct forbidden transitions and indirect forbidden transitions with energy gaps decrease with increasing Ga percentage.     

Development of multiple drywall with high sound insulation performance

Experimental studies for the development of multiple drywalls with a high sound insulation performance are performed. Firstly, a means of preventing the sound insulation deterioration due to the coincidence effect at high frequencies is investigated by layering two plasterboards with different physical characteristics. Based on the results, a double drywall with a sound insulation performance of R_w = 61 is developed. Further more, a double drywall of R_w = 64 , a triple drywall of R_w = 86 and a quadruple drywall of R_w = 90 are developed.     

Sound intensity investigation of the acoustics performances of high insulation ventilating windows integrated with rolling shutter boxes

High sound insulation ventilating windows (HSIVW) were recently proposed for noise control in buildings close to motorways or railways, where noise barriers are not effective or too expensive. These windows are characterized by good insulation performances and at the same time allow airflow through the window itself; such a performance matches summer indoor ventilation and refreshment needs.In the last years at the Acoustics Laboratory of the University of Perugia various prototypes were tested and their acoustic and airflow performances were assessed, also verifying the influence of filtering systems in the aerator.In the present paper a lot of experimental data are presented and in particular the results of a recent campaign, aimed at testing windows samples integrated with insulated rolling shutter boxes are presented. Sound reduction index R and single number sound reduction index R_w are evaluated, considering different exercise conditions; acoustic intensity measurements and analysis have also been performed, in order to verify the parts of the window which need to be optimized.     

Ferromagnetic seeding for the magnetic targeting of drugs and radiation in capillary beds

A new implant assisted-magnetic drug targeting approach is introduced and theoretically analyzed to demonstrate its feasibility. This approach uses ferromagnetic particles as seeds for collecting magnetic drug carrier particles at the desired site in the body, such as in a capillary bed near a tumor. Based on the capture cross section (λ_c) approach, a parametric study was carried out using a 2-D mathematical model to reveal the effects of the magnetic field strength (μ₀H₀=0.01–1.0 T), magnetic drug carrier particle radius (R_p=20–500 nm), magnetic drug carrier particle ferromagnetic material content (x_fm,p=20–80 wt%), average blood velocity (u_B=0.05–1.0 cm/s), seed radius (R_s=100–2000 nm), number of seeds (N_s=1–8), seed separation (h=0–8R_s), and magnetic drug carrier particle and seed ferromagnetic material saturation magnetizations (iron, SS 409, magnetite, and SS 304) on the performance of the system. Increasing the magnetic field strength, magnetic drug carrier particle size, seed size, magnetic drug carrier particle ferromagnetic material content, or magnetic drug carrier particle or seed saturation magnetization, all positively and significantly affected λ_c, while increasing the average blood velocity adversely affected it. Increasing the number of seeds or decreasing the seed separation, with both causing less significant increases in λ_c, verified that cooperative magnetic effects exist between the seeds that enhance the performance. Overall, these theoretical results were encouraging as they showed the viability of this minimally invasive, implant assisted-magnetic drug targeting approach for targeting drugs or radiation in capillary beds.     

Numerical investigation of natural convection heat transfer of nanofluids in a Γ shaped cavity

This paper analyzes the heat transfer and fluid flow of natural convection in a Γ shaped enclosure filled with Al₂O₃/Water nanofluid that operates under differentially heated walls. The Navier–Stokes and energy equations are solved numerically. Heat transfer and fluid flow are examined for parameters of non-uniform nanoparticle size, mean nanoparticle diameter, nanoparticle volume fraction, Grashof number and different geometry of enclosure. Finite volume method is used for discretizating positional expressions, and the forth order Rung-Kuta is used for discretizating time expressions. Also an artificial compressibility technique was applied to couple continuity to momentum equations. Results indicate that using nanofluid causes an increase in the heat transfer and the Nusselt number so that for R = 0.001 in Gr = 10³, the Nusselt number 25%, in Gr = 10⁴ 26%, and in Gr = 10⁵ 28% increases. Furthermore; by decreasing the mean diameters of nanoparticles, Nusselt number increases. By increasing R parameter (d_p,min/d_p,max) and nano particle volume fraction, Nusselt number increases.     

On sound transmission into a thin cylindrical shell under “flight conditions”

In the context of the transmission of airborne noise into an aircraft fuselage, a mathematical model for sound transmission into a thin cylindrical shell is used to study sound transmission under “flight conditions”: i.e., under conditions of external air flow past a pressurized cylinder at flight altitude. Numerical results for different incidence angles are presented for a typical narrow-bodied jet in cruising flight at 10 660 m (35 000 ft) with interior pressure at 2440 m (8000 ft). A comparison is made between no-flow sound transmission at standard conditions on the ground to sound transmission under flight conditions. It is shown that at M = 0, the cylinder transmission loss has dips at f_R (cylinder ring frequency) and f_c (critical frequency for a flat panel of same material and thickness as shell). Below f_R cylinder resonances affect TL. Between f_R and f_c, cylinder TL follows a masslaw behavior. Flow provides a modest increase in TL in the mass-law region, and strongly interacts with the cylinder resonances below f_R. For normally-incident waves, TL is unaffected by flow.     

Exchange coupling and remanence enhancement in nanocomposite Nd–Fe–B/FeCo multilayer films

Nd–Fe–B-type hard phase single layer films and nanocomposite Nd₂₈Fe₆₆B₆/Fe₅₀Co₅₀ multilayer films with Mo underlayers and overlayers have been fabricated on Si substrates by rf sputtering. The hysteresis loops of all films indicated simple single loops for fixed Nd–Fe–B layer thickness (10 nm) and different FeCo layer thickness (d_FeCo=1–50 nm). The remanence of these films is found to increase with increasing d_FeCo and the coercivity decrease with increasing d_FeCo. It is shown that high remanence is achieved in the nanocomposite multilayer films consisting of the hard magnetic Nd–Fe–B-type phase and soft magnetic phase FeCo with 20 nm?d_FeCo?3 nm. The sample of maximum energy product is 27 MG Oe for d_FeCo=5 nm at room temperature. The enhancement of the remanence and energy products in nanocomposite multilayer films is attributed to the exchange coupling between the magnetically soft and hard phases.     

MAGNETOENCEPHALOGRAPHIC RESPONSES CORRESPONDING TO INDIVIDUAL SUBJECTIVE PREFERENCE OF SOUND FIELDS

To investigate human cortical responses that correspond to subjective preference of sound fields, an attempt is made here to analyze the autocorrelation function (ACF) of magnetoencephalography (MEG) under the condition of varying delay time of single reflections. According to previous studies, it is assumed that a similar repetitive feature of the MEG alpha-waves range (8-13 Hz) is related to subjective preference in terms of the effective duration of the ACF. The source signal was the word “piano” which had a 0·35 s duration. The delay time, Δt₁, was varied at five levels (0, 5, 20, 60, and 100 ms). The scale values of the subjective preference of each subject were obtained by the paired-comparison tests. To compare the results of the MEG measurements with the scale values of the subjective preference, combinations of a reference stimulus (Δt₁=0 ms) and test stimuli (Δt₁=0, 5, 20, 60, and 100 ms) were presented alternately 50 times, and the MEGs were analyzed. It is found that subjective preference for each individual and the effective duration of the ACF of the MEG alpha waves are linearly related.     

Determination of the electron–phonon coupling parameters from the thermal shifts of R-lines for Cr-doped garnets

The thermal shifts of R₁ and R₂ lines of Cr³⁺-doped garnets Y₃Ga₅O₁₂ (YGG), Y₃Sc₂Al₃O₁₂ (YSAG) and Gd₃Sc₂Al₃O₁₂ (GSAG) are studied by considering both the static contribution (which is frequently neglected in the previous papers) due to lattice thermal expansion and the vibrational contribution due to electron–phonon interaction. In the studies, the static contribution is calculated with the thermal expansion coefficient of the corresponding cluster in the host garnet crystals. The results indicate that the static contributions in sign are opposite to and in magnitude are about 10% of the corresponding vibrational contributions. The true electron–phonon coupling parameters α′ obtaining by taking both contributions into account increase more than 10% in comparison with the corresponding apparent electron–phonon coupling parameters α determined by considering only the vibrational contribution in the previous paper. So, to obtain the complete understanding of thermal shift of a spectral line and the true rather than apparent electron–phonon coupling parameters, one should take account of both the static and vibrational contributions.     

Evaluation of a multiple spin- and gradient-echo (SAGE) EPI acquisition with SENSE acceleration: Applications for perfusion imaging in and outside the brain

Perfusion-based changes in MR signal intensity can occur in response to the introduction of exogenous contrast agents and endogenous tissue properties (e.g. blood oxygenation). MR measurements aimed at capturing these changes often implement single-shot echo planar imaging (ssEPI). In recent years ssEPI readouts have been combined with parallel imaging (PI) to allow fast dynamic multi-slice imaging as well as the incorporation of multiple echoes. A multiple spin- and gradient-echo (SAGE) EPI acquisition has recently been developed to allow measurement of transverse relaxation rate (R₂ and R₂^?) changes in dynamic susceptibility contrast (DSC)-MRI experiments in the brain. With SAGE EPI, the use of PI can influence image quality, temporal resolution, and achievable echo times. The effect of PI on dynamic SAGE measurements, however, has not been evaluated. In this work, a SAGE EPI acquisition utilizing SENSE PI and partial Fourier (PF) acceleration was developed and evaluated. Voxel-wise measures of R₂ and R₂^? in healthy brain were compared using SAGE EPI and conventional non-EPI multiple echo acquisitions with varying SENSE and PF acceleration. A conservative SENSE factor of 2 with PF factor of 0.73 was found to provide accurate measures of R₂ and R₂^? in white (WM) (r_R2 = [0.55–0.79], r_R2? = [0.47–0.71]) and gray (GM) matter (r_R2 = [0.26–0.59], r_R2? = [0.39–0.74]) across subjects. The combined use of SENSE and PF allowed the first dynamic SAGE EPI measurements in muscle, with a SENSE factor of 3 and PF factor of 0.6 providing reliable relaxation rate estimates when compared to multi-echo methods. Application of the optimized SAGE protocol in DSC-MRI of high-grade glioma patients provided T₁ leakage-corrected estimates of CBV and CBF as well as mean vessel diameter (mVD) and simultaneous measures of DCE-MRI parameters K^trans and v_e. Likewise, application of SAGE in a muscle reperfusion model allowed dynamic measures of R₂′, a parameter that has been shown to correlate with muscle oxy-hemoglobin saturation.