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| 2. |
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| 3. |
- Feng, Leping
(författare)
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A modified honeycomb panel to increase sound transmission loss
- 2003
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Ingår i: Proceedings of the Tenth International Congress on Sound and Vibration. ; , s. 4549-4554
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Konferensbidrag (refereegranskat)abstract
- Honeycomb panels are widely used in aviation industry because of the properties of lightweight and high bending stiffness. However, the sound transmission loss of the panel is often low since the coincident frequency of the panel usually lies below 2 kHz. Previous results show that a single-faced honeycomb panel may acoustically perform much better, especially when it is combined with absorptive materials. This idea is further developed to overcome drawbacks. An improved concept of honeycomb panel is presented, which keeps the basic properties of a honeycomb panel, while the coincident phenomenon in audible frequency is avoided. The theoretical consideration behind this design is discussed. The idea is then tested experimentally. The weighted apparent sound reduction index of the modified honeycomb panel is 4 dB higher than an ordinary honeycomb panel with similar surface density.
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| 11. |
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| 12. |
- Feng, Leping, et al.
(författare)
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Engineering methods to predict noise levels at reference points with known source properties
- 2015
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Ingår i: Applied Acoustics. - : Elsevier BV. - 0003-682X .- 1872-910X. ; 96, s. 68-74
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Tidskriftsartikel (refereegranskat)abstract
- Two engineering methods are proposed to predict the sound pressure levels at a given point when the sound power level of a noise source is known and the transfer function between the source and the reference point can be obtained. The first method is applicable when the source is surrounded by many reflectors, or inside a box-like structure. A single monopole with average transfer function is suggested for this situation. For a source with a strong directivity placed in an essentially free space, the "box-source" method is recommended to take into account of the source directivity. The total sound power is in this case divided into five independent noise sources which are obtained via ordinary sound power measurement methods. Experimental verifications are made for several cases in laboratory. Satisfactory results are obtained for both methods.
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| 13. |
- Feng, Leping
(författare)
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Enhancement of low frequency sound absorption by placing thin plates on surface or between layers of porous materials
- 2019
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Ingår i: Journal of the Acoustical Society of America. - : ACOUSTICAL SOC AMER AMER INST PHYSICS. - 0001-4966 .- 1520-8524. ; 146:2, s. EL141-EL144
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Tidskriftsartikel (refereegranskat)abstract
- Rigid thin plates can be used, either on the surface or between layers of materials, to improve the sound absorption properties of porous materials at low frequencies, especially for materials with low sound absorption. Measurement results obtained from a 100mm impedance tube, for different combinations of porous materials and thin plates, are supplied. Possible physical explanations are discussed. The size of the plate, together with the original properties of the porous material, determines the useful frequency region of the method. The technique of surface-placed thin plates can be directly applied to existing structures without making any changes of the original system, and the results are comparable to those with more complicated modifications.
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| 14. |
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| 15. |
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| 16. |
- Feng, Leping, et al.
(författare)
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Influence of structural damping on radiation efficiency of a mechanically or acoustically excited panel
- 2006
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Konferensbidrag (refereegranskat)abstract
- Previous investigations have shown that damping is a good way to reduce structural vibration, but less effective for sound problems, since the radiation efficiency might be increased dramatically. This problem is further investigated in this paper. Results show that when a constrained damping layer is applied and when mechanical excitation is used, the radiation efficiency is increased by about 9-12 dB. This is mainly due to the near-field radiation around the excitation point, which is more important for a heavily damped structure than for a structure with little damping. The radiation efficiency of an acoustically excited panel, which is directly related to sound transmission, is also increased by about 6-9 dB when damping is added. Instead of radiation from near-field, forced transmission is now the main reason. Although resonant modes, which are the main contributors for vibration, are reduced greatly by added damping, the responses far away from the resonant frequency are little influenced, which are the main contributors for sound radiation and transmission.
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| 17. |
- Feng, Leping
(författare)
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Influence of structural damping on sound radiation from a point-excited beam
- 2007
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Ingår i: Turkish Acoustical Society - 36th International Congress and Exhibition on Noise Control Engineering, INTER-NOISE 2007 ISTANBUL. - 9781605603858 ; , s. 967-975
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Konferensbidrag (refereegranskat)abstract
- The track is the main noise source of a railway when the frequency is below about 1250 Hz. Quite a few efforts have been made to increase the attenuation of the railway track in order to reduce the radiated sound. The attempt of this paper is to investigate the influence of the structural damping on the sound pressure level at the area close to the excitation point instead of the total radiated sound power. For this purpose, the simplest model, i.e. an infinite beam, is adapted. Both near field solution and the propagating wave are included. Results show that when the sound pressure levels at a certain areas close to the excitation is concerned only, the influence of the structural damping is somewhat lower than what expected on the total sound power, partly due to the contribution of the near field solution and partly due to the wave propagation. If the area concerned is small, this influence is also dependent on frequency, because of the length of the bending wave. It is difficult to estimate the influence of the structural damping on wayside noise from laboratory tests with a short track and a point excitation.
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| 18. |
- Feng, Leping
(författare)
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Modified impedance tube measurements and energy dissipation inside absorptive materials
- 2013
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Ingår i: Applied Acoustics. - : Elsevier BV. - 0003-682X .- 1872-910X. ; 71:12, s. 1480-1485
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Tidskriftsartikel (refereegranskat)abstract
- Impedance tube is an important tool to measure acoustic properties of a material, for which two methods have been standardized. The methods for a "modified" impedance tube have been developed recently to measure material properties in the condition of an anechoic termination. Instead of commonly used two-load or two-source methods, a method with direct and inverted configuration in cooperation with the single-microphone method is suggested in this paper. With the help of transfer matrix method, combined effect of several materials placed in series can be predicted from individual properties. A simple recurrence formula is obtained to relate the acoustic properties of a multilayer structure with the reflection and transmission coefficients of each layer. Very good agreements are obtained between the prediction and the direct measurements. Energy dissipations inside porous materials for different situations are studied and compared.
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| 19. |
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| 20. |
- Feng, Leping, et al.
(författare)
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On application of radiation loss factor in the prediction of sound transmission loss of a honeycomb panel
- 2012
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Ingår i: International Journal of Acoustics and Vibration. - 1027-5851 .- 2415-1408. ; 17:1, s. 47-51
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Tidskriftsartikel (refereegranskat)abstract
- The application of the radiation loss factor in the prediction of sound transmission loss of a lightweight, orthotropic sandwich panel is investigated in this paper. Comparisons with measurements show that predictions often underestimate the sound transmission loss of the panel around the corresponding critical frequency when the measured loss factor, which in principle includes the radiation loss factor, is used. This is due to the measurement methods used for the loss factor and the band average. It is thus recommended to use the loss factor measured at low frequencies plus the theoretical radiation loss factor in order to improve the prediction of the sound transmission loss of a honeycomb panel around the critical frequency.
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| 21. |
- Feng, Leping, et al.
(författare)
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On application of radiation loss factor in the prediction of sound transmission loss of a honeycomb panel
- 2010
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Ingår i: 17th International Congress on Sound and Vibration 2010, ICSV 2010. - 9781617822551 ; , s. 1862-1869
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Konferensbidrag (refereegranskat)abstract
- The application of the radiation loss factor in the prediction of sound transmission loss of a lightweight, orthotropic sandwich panel is investigated in this paper. Comparisons between measurements and predicted results show that predictions often underestimate the sound transmission loss of the panel around the corresponding critical frequency when a measured loss factor, which in principle includes the radiation loss factor, is used. This is due to the methods used for the loss factor measurements and due to the fact that the band average loss factor is applied in the calculation. It is recommended to use the material loss factor measured at low frequencies plus the narrow band, theoretical radiation loss factor in order to improve the prediction of the sound transmission loss of a honeycomb panel around the critical frequency.
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| 22. |
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| 23. |
- Feng, Leping, et al.
(författare)
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On model of gearbox noise and dynamic transmission error
- 2005
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Ingår i: Twelfth International Congresson Sound and Vibration. - 9781627481496 ; , s. 3198-3205
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Konferensbidrag (refereegranskat)abstract
- Gearbox is an important noise source in automotive industry. Dynamic Transmission Error(DTE) describes the dynamic behaviour of the complete gear system and is closely related tothe vibrations of, and hence the noise radiated from, a gearbox. The coherence between DTEand noise radiated has been investigated previously and promising results have been obtained.The paper focuses on the models of DTE and the gearbox noise and the relation betweenthem. In order to understand the behaviour of the signals, a simple model is drawn whereDTE is modelled as the excitation source of a gear system. When the speed of rotation is notextremely high, DTE is expected to be independent of the speed of rotation when theobservation points are located on the wheel. On the other hand, the radiated sound isexpected to increase at the rate of 6 dB per double of the rotation speed, although a bigfluctuation is also expected due to the influence of the shifted frequency and hence thedifferent transfer function. Experimental data is analysed. The dynamic transmission errormeasured on a truck gearbox is separated into deterministic parts and a stochastic part. Theapplied torque has little influence on the averaged DTE of the whole gear because of the highstiffness. However, when the averaged DTE of a single tooth is concerned, the influence ofthe applied torque is rather obvious. The predicted trend of the radiated sound pressure isalso seen in the measured data.
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| 24. |
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| 25. |
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| 26. |
- Feng, Leping
(författare)
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Tone-like signal in the wind-induced noise of perforated plates
- 2012
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Ingår i: Acta Acoustica united with Acustica. - 1610-1928 .- 1861-9959. ; 98:1, s. 188-194
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Tidskriftsartikel (refereegranskat)abstract
- In some special situations the wind-induced noise of perforated plates may show strong power enhancement in a certain frequency band and hence exhibits a "tone-like" character. This problem is investigated experimentally in laboratory and some test results are presented in this paper. It is shown that the "tone-like" phenomenon happens only when the incident angle of the wind is relatively large to the perforated panel; say between 60 and 80 degrees. There seems an "optimum" wind speed corresponding to the size of the holes for this phenomenon. The peak frequency of the tone-like signal is mainly determined by the thickness of the plate and the size of the holes and can be roughly estimated from the geometry of the plate and the wind speed. The condition when the tone-like phenomenon may happen seems very much dependent on the perforation pattern along the wind direction. Same perforated plate may produce totally different sound in the same wind condition if the orientation of the plate is changed. Randomized hole size and distribution may help to reduce the tone-like signal and hence the total wind-induced noise. Possible explanations of the phenomenon are discussed.
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| 27. |
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| 29. |
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| 30. |
- Henriksson, Mats, 1976-
(författare)
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On Noise Generation and Dynamic Transmission Error of Gears
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Noise from heavy trucks is an important environmental issue. Several sources contribute to the total noise level of a vehicle, such as the engine, gearbox, tires, etc. The tonal noise from the gearbox can be very disturbing for the driver, even if the noise level from the gearbox is lower than the total noise level. The human ear has a remarkable way of detecting pure tones of which the noise from loaded gears consists of. To be allowed to sell a heavy truck within the European Union, the so called pass-by noise test must be completed successfully. The maximum noise level permitted is 80dB(A) and undercertain conditions, the gearbox can be an important contributor to the total noise level. Gear noise is therefore an important issue for the automotive industry. In this thesis gear noise and dynamic transmission error is investigated. Traditionally, transmission error (TE) is considered to be the main excitation mechanism of gear noise. The definition of TE is ”the difference between the actual position of the output gearand the position it would occupy if the gear drive were perfect”. Measurements of dynamic transmission error (DTE) and noise have been performed on a gearbox. The measurement object was a commercial truck gearbox powered by an electrical motor. The torque used was in the normal operating range of the gearbox and the correlation between gear noise and DTE, when the torque is changed, is investigated. The result differs for different gear pairs and for the first gear stage, located close to the housing, the correlation is high for most speeds. The measured DTE and noise show a poor correlation with calculated transmission error. A minimisation of TE therefore does not necessarily mean a minimisation of gear noise. A transfer function can be employed to calculate the relationship between DTE and noise. The general trend of the gear noise is an increase of 6dB per doubling of the rotational speed together with fluctuations around the mean due to resonances of the system. The magnitude of the transfer function can be estimated using the amplitudesof the gear mesh orders and harmonics. Two gear pairs with similar macro geometry but different profile modifications are investigated. Although the gear pairs have similar transmission error, the noise level display a significantly different trend, further strengt hening the position that transmission error is not the single most important gear noise excitation mechanism. Further analysis concludes that shuttling forces and friction forces can be more important than what is often suggested. A dynamic model including transmission error and shuttling forces is used to investigate the two gear pairs. The bearing forces show that for some frequency regions shuttling forces can be of the same order of magnitude as the forces caused by transmission error. This work highlights the importance of considering other excitations of gear noise besides transmission error when designing quiet gears. The influence of transmission error can not be determined by investigating the gears only. A deeper knowledge of the gear system is needed in order to minimise gear noise for a specific gear design.
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| 31. |
- Henriksson, Mats, et al.
(författare)
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On Shuttling Forces and Transmission Error as Gear Noise Excitation
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Ingår i: Journal of mechanical design (1990). - 1050-0472 .- 1528-9001.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This work studies the influence of shuttling forces on gear dynamics. Dependingon the frequency range of interest, shuttling forces can induce bearing forces of thesame order of magnitude as transmission error. A dynamic model including shuttlingforces is presented and the perturbation method in the order domain is used to solvethe equations of motions. The result of the dynamic model is compared with static calculations using a commercial finite element program.
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| 32. |
- Henriksson, Mats, et al.
(författare)
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On Transmission Error, Shuttling Forces and Friction Forces as Gear Noise Excitation
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Ingår i: International Journal of Acoustics and Vibration. - 1027-5851 .- 2415-1408.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Traditionally, transmission error (TE) has been used to asses the noise propertiesof gears. Measurements of gear noise for a complete truck gearbox have been used tocorrelate noise from a gear pair with calculated static transmission error, shuttling forceand friction forces. Two gear pairs with very similar macro geometry but differentmicro geometry was used. The measurement results show that there is a limitationif transmission error is considered as the only excitation mechanism when designingquiet gears. Often TE is multiplied with the gear mesh stiffness in order to calculatean excitation force. For gear not operating above the critical gear mesh resonance,this often overestimates the importance of TE, thus underestimating the importance ofother sources such as shuttling and friction forces.
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| 33. |
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| 34. |
- Kumar, Sathish, et al.
(författare)
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Sound Transmission Through Double Leaf Partitions : A Criterion for Quick Convergence Using Space Harmonic Analysis
- 2016
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Ingår i: Journal of Vibration and Acoustics-Transactions of the ASME. - : American Society of Mechanical Engineers (ASME). - 1048-9002 .- 1528-8927. ; 138:4
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Tidskriftsartikel (refereegranskat)abstract
- Space harmonic expansion has been used successfully to model sound transmission through infinite, periodically rib-stiffened double leaf partitions. Since the solution to this method is obtained in a series form, computational accuracy needs to be balanced with computational cost as calculation time increases with the number of space harmonic terms. The aim of this article is to provide a criterion to decrease the computational time when using space harmonic analysis. The new criterion helps to select the appropriate space harmonics to be included in the solution based on frequency and the angle of incidence of sound waves. The results are verified by comparing with experimental data available in the literature. For the partition investigated, the computational time is reduced by a factor of ten without compromising the accuracy of the result.
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| 35. |
- Li, Qi
(författare)
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Transmission loss of vehicle seals
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sound transmission loss of vehicle seals was studied in this thesis. Reverberation room test and semi-anechoic chamber test were respectively studied. By comparing the sound pressure level, sound intensity level and average sound power level at the receiving side, it proved that a simple sound pressure level test may obtain same measurement accuracy when there is little reflected sound. A semi-anechoic chamber was designed for testing sound transmission losses of the seals on a trial vehicle. By comparing the sound pressure levels between the location of the passenger ear and door area, it proved that most of outside sound energy passed through the door seals into the interior. The sound transmission losses of different sealing conditions were measured which included well sealed and imperfectly sealed conditions; Sound pressure levels at passenger’s ear in three different types of vehicles were also compared, these comparison results indicated this laboratory was capable of distinguishing different sealing conditions. The installation procedure was compared with the one in reverberation room test. Numerical analysis showed that the latter method produced a different compression shape which would definitely influence the sound insulation abilities of the seals. The transmission mechanism of the acoustic waves through a vehicle seal was also discussed. Contact analysis showed high compression ratio leaded to tremendous inner stress intensity. But any further increase of the contact depth would not improve the effect of wind noise prevention. A vehicle seal with a complex shape was replaced by a simple model. The sound transmission theory of multiple partitions on the basis of mass law was applied. Whereas, compared with the experimental result, a different trend in the high frequency range was found. When taking the transmission though the side material and integration of incident angle into account, the result was quite similar to the experimental one. FEM analysis was also performed. The majority of sound power was believed to transmit along the seal wall into the interior instead of passing through the multiple partitions. A distorted circular duct model is believed to be close to the real geometry.
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| 36. |
- Liu, Bilong, 1970-
(författare)
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Acoustical Characteristics of Aircraft Panels
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A deterministic approach based on a modal expansion and modal receptance method has been developed to evaluate the airborne sound insulation of aircraft panels with stringer and ring frame attachments. Furthermore, this method was extended to predict the noise radiation of stiffening panel subjected to TBL excitation. This approach integrates with the fast and accurate methods in evaluating the modal excitation terms and modal radiation efficiency. Based on these advantages, the effects of the curvature, overpressure, stringers, ring frames, hydrodynamic coincidence, composite structures and structural dissipation on the acoustical properties of a typical aircraft panel are able to be investigated efficiently.Theoretic predictions were compared with laboratory measurements conducted on both model structures and aircraft panels. It was found that a small curvature may result in significant deterioration of the sound transmission loss at frequencies of interest. Unlike a flat uniform panel, the theoretical prediction for curved panels from the infinite model can not provide good agreement with the measurement close to and well below the ring frequency. However, in this frequency range, the finite model has been proved to be applicableFor the large curved airplane panels studied here, it was found that the ring frames have little influence on sound transmission loss in the frequency range of interest. However the stringers may have considerable influence on sound transmission loss. The stringer improves this for a curved panel around the ring frequency, but it may result in a potential deterioration of the sound transmission loss above the ring frequency. In this study it is evident that the sound transmission loss of the composite skin attached with composite stringers is lower than that of the metallic panel attached with metallic stringers.At frequencies higher than the corresponding ring frequency of the curved panel, both experiment and theoretical prediction reveal that the overpressure at the concave side tends to reduce the sound transmission loss at the rate of about 0.5dB /10000 Pa. While at lower frequencies, say well below the ring frequency, the overpressure may increase or reduce sound transmission loss of a finite panel, depending on the shift of the resonant frequencies resulting from the overpressure.For TBL excitation, numerical investigation reveals that the panel with the ring frames behaves more like a sub-panel between two frames. Below 500Hz, the ring frames slightly enhance the sound radiation while dramatically increasing it around 1.3kHz. The TBL forcing field excites the same vibration lever for the panel with and without ring frame attachments, but the modes excited for the panel with ring frames radiate more sound. Unlike the ring frames, the stringers increase sound radiation below 1kHz. Above 1kHz, the sub-panels between two bays respond independently and the stringer effects is therefore not obvious.
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| 37. |
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| 38. |
- Liu, Bilong, et al.
(författare)
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Influence of overpressure on sound transmission through curved panels
- 2007
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 302:4-5, s. 760-776
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Tidskriftsartikel (refereegranskat)abstract
- A great deal of recent research related to the aeronautic industry has been devoted to the theoretical study of sound transmission through fuselage structures. However, the literature records few test data with reference to the influence of overpressure on sound transmission. In this article, the airborne sound transmission through curved panels under the condition of overpressure at the concave side has been investigated experimentally and it is shown that experimental results agree well with a theoretical prediction due to an infinite cylindrical shell model at relatively high frequencies. Discrepancies, which occur at lower frequencies, can be explained, inter alia, by the influence of the finite size and attached stiffeners of the panel.At frequencies higher than the corresponding ring frequency for the curved panel, both experimental and theoretical predictions reveal that the overpressure at the concave side tends to reduce the sound transmission loss at the rate of about 0.5dB/10000Pa. While at lower frequencies, say well below the ring frequency, the overpressure may increase or reduce sound transmission loss of a finite panel depending on the shift of resonant frequencies resulting from the overpressure.
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| 39. |
- Liu, Bilong, et al.
(författare)
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Influence of pressurization on sound insulation of curved airplane panels
- 2005
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Ingår i: 12th International Congress on Sound and Vibration 2005. - 9781627481496 ; , s. 4843-4850
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Konferensbidrag (refereegranskat)abstract
- he purpose of this paper is to investigate the pressurization effects on sound transmission through airplane panels. The airborne sound transmission through airplane panels under the condition of overpressure at one side has been investigated by measurement. The test results agree well with the theoretic prediction of infinite cylindrical shell model at high frequencies, but have considerable discrepancies at low frequencies, which, however, are ready to be explained by the influence of finiteness and stiffeners of the panel. When the frequency is higher than the ring frequency of curved panel, both test and theoretic prediction reveal that the overpressure under laboratory conditions tends to reduce the sound transmission loss at the rate of about 0.5dB/10000 Pa. while at low frequencies, say below around the ring frequency, the overpressure may increase the sound transmission loss of ring-stiffened panel, the reason of this behavior is resulted from the shift of the resonant frequencies led by the increased in-plane tension.
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| 40. |
- Liu, B., et al.
(författare)
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Predicted and measured plate velocities induced by turbulent boundary layers
- 2012
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 331:24, s. 5309-5325
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Tidskriftsartikel (refereegranskat)abstract
- A method for the prediction of velocity levels of a fuselage plate excited by turbulent boundary layers is described. The aim is to identify a method for the prediction of the relative changes of the velocity levels caused by variations of plate geometry and flight conditions. The Corcos, Efimtsov and Chase models are used to characterize the dynamic surface pressure cross-spectra. Predicted results using these models are compared with the result of in-flight measurements of plate velocities. It is found that the Corcos model gives the best agreement with the measured results for three different flight conditions. The Efimtsov extension and Chase models tend to underestimate the plate response in the lower frequency range. It is evident that the velocity level of the plate elements of the fuselage very much depends on the speed of the aircraft. An increase of the speed of the aircraft by 10% is likely to increase the plate velocity level by 3 dB and a reduction of the speed by 10% would give a reduction of 3 dB.
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| 41. |
- Liu, B., et al.
(författare)
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Radiation efficiency of acoustic-excited plates with stringer attachments
- 2007
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Ingår i: 14th International Congress on Sound and Vibration 2007, ICSV 2007. - 9781627480000 ; , s. 3782-3789
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Konferensbidrag (refereegranskat)abstract
- The average radiation efficiency of acoustic-excited plate with stringer attachments is investigated by using a modal expansion method. This work is an extension to author's previous publication (JSV 2007), where the predicted and measured sound transmission loss for curved aircraft panels was reported. For the plate and frequency range studied here, numerical results reveal that the radiation efficiency of acoustic-excited plate is very sensitive to the damping of the structure. Increasing the structure loss factor significantly increases radiation efficiency far below the plate critical frequency.
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| 42. |
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| 43. |
- Liu, Bilong, et al.
(författare)
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Sound transmission through curved aircraft panels with stringers and ring frames attachments
- 2007
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 300:3-5, s. 949-973
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Tidskriftsartikel (refereegranskat)abstract
- A numerical approach based on a receptance method has been developed to evaluate the airborne sound insulation of aircraft panels with stringer and ring frame attachments. Theoretical predictions have been compared with laboratory measurements conducted on both model structures and aircraft panels. Certain parameters were varied in this study to gauge stiffener effects on sound transmission through the panel. For large curved aircraft panels studied here, it was found that the ring frames have little influence on sound transmission loss in the frequency range of interest. However, the stringers may have considerable influence on the sound transmission loss. The stringer improves the sound transmission loss for a curved panel in the vicinity of the ring frequency, but may result in a potential deterioration above this frequency. In addition it was found that the sound transmission loss for the composite skin attached with composite stringers was lower than that of the metallic panel attached with metallic stringers. The results suggest that acoustical optimization design for the stringers is necessary to achieve improved airborne sound insulation for aircraft panels
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| 44. |
- Liu, Zibo, 1989-, et al.
(författare)
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Broadband locally resonant metamaterial sandwich plate for improved noise insulation in the coincidence region
- 2018
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Ingår i: Composite structures. - : Elsevier. - 0263-8223 .- 1879-1085. ; 200, s. 165-172
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Tidskriftsartikel (refereegranskat)abstract
- A new design for locally resonant metamaterial sandwich plates is proposed in this paper for noise insulation engineering applications. A systematic method to tune the resonance frequency of local resonators is developed in order to overcome the coincidence phenomenon. This method, based on an impedance approach, additionally explains the ability to overcome the antiresonance associated with these local resonators. The influence of the radiated sound from these local resonators is further investigated with finite element (FE) models, particularly in connection with the sound transmission loss (STL) of the resulting metamaterial sandwich plates. The new sandwich design proposed emerges from these analyses, encapsulating the resonators inside the core material. In addition to overcoming the coincidence effect and limiting the noise radiation by the resonators, the proposed design allows to improve the mass ratio of the metamaterial sandwich structure. This, in turn, enables to broaden the working frequency band independently of the material adopted for the resonator. The proposed metamaterial sandwich plate thus combines improved acoustic insulation properties, while maintaining the lightweight nature of the sandwich plate and its good static properties.
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| 45. |
- Liu, Zibo, 1989-, et al.
(författare)
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Design of broadband acoustic metamaterials for low-frequency noise insulation
- 2017
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Ingår i: The Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966. ; , s. 3574-3574
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- An innovative configuration of an acoustic sandwich structure is proposed in this paper, which uses the locally resonant structures to generate stopbands in desired frequency regions and hence to increase the sound transmission loss of the panel. Effects of different types of resonators, including the mounting techniques, are investigated. The methods to broaden the effective stopbands are discussed. The acoustic properties of the sandwich panel with non-flat laminates are also studied. Numerical analyses show that good results can be obtained when combining the laminate modification with the locally resonantstructure, especially when the stopbands are designed to compensate the corresponding coincidence effects of the sandwich panel. The analysis is based on the Finite Element models constructed in COMSOL. Bloch wave vectors are derived at first Brillouin zone by using wave expansion method. Dispersion relation of the structure is discussed. Experimental validation is planned, and the results will be shown in the conference.
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| 46. |
- Liu, Zibo, 1989-
(författare)
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Design of soundproof panels via metamaterial concept
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The goal of the work is to find a way to improve the sound insulation properties of different types of panels in order to meet different requirements. Inspired by the nontrivial behavior of the locally resonant acoustic metamaterials, this concept is introduced into the design of structures in order to explore the potential ways to improve the sound insulation behavior in the relevant specific frequency regions. At relatively low frequency region when the bending wavelength is much longer than the distance between isolated resonators, which is also the interesting frequency range in the most part of the work, it may be assumed that the effects of the resonators are uniformly distributed over the entire surface. An impedance approach is hence proposed to estimate the sound transmission loss of the metamaterial panels in order to get more insights from physics. This is realized, in general, by integrating the equivalent impedance of the resonators together with the corresponding impedance of the host panel. Valuable theories are derived based on that, laying a solid foundation for effective/efficient design of metamaterial panels. This approach also provides a fast and reliable tool for the designs prior to a time-consuming and computationally expensive numerical simulation. Based on that, a new design for locally resonant metamaterial sandwich plates is proposed to improve the sound transmission loss performance in the coincidence frequency region. A systematic method to tune the resonance frequency of local resonators is developed. This approach also supplies a method to remove the possible side-dips associated with the resonance of the resonators. The influence of the sound radiation from the resonators is further investigated with the Finite Element models. It is proposed to embed the resonators inside the core material in order to eliminate the possible influence, and also to make a smooth surface. The metamaterial sandwich panel designed in this way combines improved acoustic insulation properties with the lightweight nature of the sandwich panel. Besides the coincidence frequency region, the ring frequency area of a cylindrical shell is another important frequency region for bad sound transmission loss. The effectiveness of locally resonant metamaterial is also investigated. Similar to the case of the flat panel, both impedance model and Finite Element model are developed for the problem of the sound transmission loss properties. The influence of the resonators is presented, and compared with the case of the flat panel. Unlike the case of the metamaterial flat panel, two side-dips around the sharp improvement cannot be avoided when applying the resonators near the ring frequency of the curved panel. The reason for that is explored by using the impedance approach. It is noticed that, while the impedance of a flat panel near the critical frequency is shifted from a masstype impedance to stiffness-type impedance, the impedance of a cylindrical shell is shifted from a stiffness-type (tension-type) impedance to mass-type iv impedance. For a traditional mass-spring type resonator, however, the equivalent impedance is always shifted from a mass-type impedance to stiffness-type impedance when the frequency crosses the resonance frequency. Therefore, when the traditional resonators are applied near the ring frequency, there are always frequencies at which the impedances cancel each other, resulting in the worsened sound transmission loss. In order to have better improvement of the sound transmission loss in this frequency region, new types of resonators have to be developed. A locally resonant metamaterial curved double wall is proposed and studied, with the aim of addressing the mass-spring-mass resonance and ring frequency effects of the wall. The sound transmission loss properties of a curved double wall are first investigated by introducing the concept of ‘apparent impedance’, which expresses the properties of the entire structure in terms of the impedances of the constituting panels and air cavity. The apparent impedance derivation is validated against Finite Element models. The curved double wall is then specifically designed by adjusting the two characteristic frequencies to be close to each other in order to narrow the region associated with a poor transmission loss. This enables, subsequently, to improve the transmission loss in this region by effectively inserting tuned local resonators. The design principles are discussed, and applications for double walls consisting the same curved panels or different curved panels are both included.
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| 48. |
- Liu, Zibo, 1989-, et al.
(författare)
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Investigation of the sound transmission through a locally resonant metamaterial cylindrical shell in the ring frequency region
- 2019
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 125:11
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Tidskriftsartikel (refereegranskat)abstract
- Locally resonant metamaterial flat panels have proved to potentially exhibit extraordinary sound transmission loss properties when the resonance frequency of the resonators is tuned to the coincidence frequency region. Whether this technique is also effective to address the ring frequency effect for curved panels is investigated in this paper. For this purpose, a cylindrical shell, as a representation of curved panels, is studied from a theoretical and numerical point of view, with a specific focus on the transmission loss behaviour around the ring frequency region when the shell is mounted with local resonators. The influence from the resonators is presented and compared with that for a flat panel. An inverse effect of the resonators is observed on the sound transmission loss between the metamaterial cylindrical shell and the metamaterial flat panel when the resonance frequency of the resonators is tuned to be below or above the ring or coincidence frequency, respectively. Rather than the extraordinary improvement observed for the metamaterial flat panel, tuning such conventional resonators to the ring frequency of curved panels generates two side dips despite a sharp improvement at the ring frequency itself. This phenomenon is explained from an effective impedance point of view developed in this paper. The approach proposed and the conclusions provided may subsequently allow for the design of suitable resonators in order to resolve the ring frequency effect for curved panels.
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| 49. |
- Liu, Zibo, 1989-, et al.
(författare)
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Investigation on the acoustic behaviour of a locally resonant metamaterial curved panel
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In order to seek for new ways to improve the sound transmission loss at ring frequency range for curved aeronautical structures, a semi-infinite curved panel, representing aircraft fuselage, is studied in this research. First, a minor modification on Koval's classical theory for cylindrical shells is made to incorporate effective mass theory for acoustic metamaterials. Then, based on the finite element simulations, the possibility of improving the acoustic behaviour of such panels by using locally resonant acoustic metamaterial treatment is investigated. Both the host curved panel, and the host panel periodically mounted with local resonators, denoted as metamaterial curved panel, are compared from the transmission loss point of view. The observations show that the antiresonance dip appears first rather than the resonance peak in the sound transmission loss for the tested metamaterial curved panel, which may be explained by the effective impedance of the panel. The influences of the panel curvature on the dynamic behaviour of the local resonators are further discussed in comparison to the same resonantsystem acting on the flat panel. Both the finite element simulations and the theoretical estimations show the same trend, thus confirms the proposed explanation.
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| 50. |
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