Effects of macroporosity and double porosity on noise control of acoustic cavity

Sujatha, C.,Kore, Shantanu S. Techno-Press 2016 Advances in aircraft and spacecraft science Vol.3 No.3

Macroperforations improve the sound absorption performance of porous materials in acoustic cavities and in waveguides. In an acoustic cavity, enhanced noise reduction is achieved using porous materials having macroperforations. Double porosity materials are obtained by filling these macroperforations with different poroelastic materials having distinct physical properties. The locations of macroperforations in porous layers can be chosen based on cavity mode shapes. In this paper, the effect of variation of macroporosity and double porosity in porous materials on noise reduction in an acoustic cavity is presented. This analysis is done keeping each perforation size constant. Macroporosity of a porous material is the fraction of area covered by macro holes over the entire porous layer. The number of macroperforations decides macroporosity value. The system under investigation is an acoustic cavity having a layer of poroelastic material rigidly attached on one side and excited by an internal point source. The overall sound pressure level (SPL) inside the cavity coupled with porous layer is calculated using mixed displacement-pressure finite element formulation based on Biot-Allard theory. A 32 node, cubic polynomial brick element is used for discretization of both the cavity and the porous layer. The overall SPL in the cavity lined with porous layer is calculated for various macroporosities ranging from 0.05 to 0.4. The results show that variation in macroporosity of the porous layer affects the overall SPL inside the cavity. This variation in macroporosity is based on the cavity mode shapes. The optimum range of macroporosities in poroelastic layer is determined from this analysis. Next, SPL is calculated considering periodic and nodal line based optimum macroporosity. The corresponding results show that locations of macroperforations based on mode shapes of the acoustic cavity yield better noise reduction compared to those based on nodal lines or periodic macroperforations in poroelastic material layer. Finally, the effectiveness of double porosity materials in terms of overall sound pressure level, compared to equivolume double layer poroelastic materials is investigated; for this the double porosity material is obtained by filling the macroperforations based on mode shapes of the acoustic cavity.

Non-uniform Euler-Bernoulli beams under a single moving oscillator: An approximate analytical solution in time domain

Sudheesh Kumar C. P.,Sujatha C.,Shankar Krishnapillai 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.10

Dynamic responses of simply supported non-uniform beams traversed by a moving oscillator are analysed in this paper. An approximate analytical method based on Rayleigh-Ritz (R-R) formulation is developed. The fundamental approximate mode obtained from R-R method is used in the present formulation to determine the responses of the beam and the oscillator. Effects of surface irregularities on the displacement and acceleration responses of the beam and the vehicle are also analysed. The results are compared with those obtained using Finite element method (FEM). A numerical example is provided to illustrate the validity of the present method which shows that the proposed method is simple, computationally more efficient compared to FEM and gives fairly good results. Though the single-mode approach used in the present paper is a classical one and numerous studies on the responses of uniform beams under moving loads have been reported in the past, its application to non-uniform beams (for which there does not exist any closed form expression for mode shapes) under a moving load, especially a moving oscillator, is presented for the first time.

Theoretical simulation on evolution of suspended sodium combustion aerosols characteristics in a closed chamber

Sujatha Pavan Narayanam,Amit Kumar,Usha Pujala,Subramanian V.,Srinivas C.V.,Venkatesan R.,Athmalingam S.,Venkatraman B. 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.6

In the unlikely event of core disruptive accident in sodium cooled fast reactors, the reactor containmentbuilding would be bottled up with sodium and fission product aerosols. The behavior of these aerosols iscrucial to estimate the in-containment source term as a part of nuclear reactor safety analysis. In thiswork, the evolution of sodium aerosol characteristics (mass concentration and size) is simulated usingHAARM-S code. The code is based on the method of moments to solve the integro-differential equation. The code is updated to FORTRAN-77 and run in Microsoft FORTRAN PowerStation 4.0 (on Desktop). Thesodium aerosol characteristics simulated by HAARM-S code are compared with the measured values atAerosol Test Facility. The maximum deviation between measured and simulated mass concentrations is30% at initial period (up to 60 min) and around 50% in the later period. In addition, the influence ofhumidity on aerosol size growth for two different aerosol mass concentrations is studied. The measuredand simulated growth factors of aerosol size (ratio of saturated size to initial size) are found to bematched at reasonable extent. Since sodium is highly reactive with atmospheric constituents, the aerosolgrowth factor depends on the hygroscopic growth, chemical transformation and density variations besides coagulation. Further, there is a scope for the improvement of the code to estimate the aerosoldynamics in confined environment

LATERAL DYNAMICS OF SINGLE UNIT SKID-STEERED TRACKED VEHICLE

B. JANARTHANAN,C. PADMANABHAN,C. SUJATHA 한국자동차공학회 2011 International journal of automotive technology Vol.12 No.6

In the design and development of high-speed tracked vehicles, it is necessary to have an understanding of the interrelationship between the terrain factors and the vehicle characteristics during steering. The handling behavior of skidsteered tracked vehicles is more complex than that of wheeled vehicles because of non-linear characteristics arising from the sliding interface between the track and the ground. In the present work, a five degree-of-freedom (DOF) steering model of a tracked vehicle is developed, and the handling behavior during non-stationary motion is studied when operating at high and low speeds. It is demonstrated that the inclusion of roll and pitch DOF changes the steering response when compared to the response from three DOF models proposed earlier by several researchers. This is due to the strong coupling between the pitch and yaw motions. The effect of the initial forward velocities on the trajectory of the vehicle during non-stationary motion is also studied. It is observed from the results that the stability is influenced by the type of steering input, steering ratio and vehicle forward speed.

Hybrid LSM-based Image Segmentation and Analysis of Morphological Variations of the Brainstem in Alzheimer MR Images

Ramesh M,Sujatha C. M 대한전자공학회 2018 IEIE Transactions on Smart Processing & Computing Vol.7 No.2

The current diagnostic evaluation criteria for Alzheimer’s disease (AD) are restricted to cognitive deficits, and less consideration is given to AD-related noncognitive, behavioral, and psychological symptoms of dementia. Vascular deterioration in AD subjects manifests neuropsychiatric symptoms (NPS). Early anxiety and depression are associated with cognitive decline. The brainstem undergoes deformation during the initiation of AD due to NPS. In this work, structural deformation of the brainstem is analyzed using Lattice Boltzmann criterion-based hybrid level set method (LSM) and fourth-order diffusion filtering. Contour and skeletal-based shape measures are extracted and analyzed using multilayer perceptron (MLP). Results show that the fourth-order diffusion filter provides strong edges, which aids in accurate segmentation. The Lattice Boltzmann criterion-based hybrid LSM is able to delineate the whole brainstem. Hough transform statistics (HTS) obtained from the segmented brainstem describe the geometric properties of the boundary of the brainstem. Eigen space values identify the skeletal variations of the brainstem for normal, Mild Cognitive Impairment (MCI), and AD subjects. Both HTS and eigen space features are found to represent better differentiation between normal, MCI, and AD subjects with a significance of p<0.05. It is observed that Hough transform–based statistical values have the ability to better discriminate the structural deformity of the brainstem with classification accuracies of 73%, 68%, and 71% for normal–MCI, MCI–AD, and normal–AD classifications, respectively, using MLP. Thus, this analysis identifies the presence of structural abnormality in the brainstem during the progression of AD, and therefore, this analysis could aid in early diagnosis of AD.