Influence of the inclination angle on the sound field in an irregular enclosure containing two elastic walls

The sound field model of an irregular enclosure with two elastic walls and an inclined wall is established by the modal theory. The modal parameters of the irregular enclosure are obtained by the envelope rectangular technique. The influence of the inclination wall angle on the sound field in the irregular enclosure is discussed. When the inclination angle is increased from 0° to 45°, the resonance frequencies of the acoustic enclosure are basically reduced in the frequency range of 0∼250 Hz. When the inclination angle is increased from 0° to 45° every 15° interval, the amplitude of a certain acoustic mode itself decreases, while the amplitudes of the acoustic modes coupled to it basically increase. The acoustic potential energy peaks in the enclosure basically shift to the low frequency with the increase of the inclination angle. Furthermore, the change trend of the acoustic potential energy is regular in the low-order modes, but relatively chaotic in the high-order modes. In addition, in order to verify that the accurate description of the primary sound field is the basis of effective noise control, the two-elastic plate model is deliberately treated as one-elastic plate model, and its influence on the performance of active noise control is discussed. Also, if the multi-elastic plate model is regarded as a simplified automobile cab, the research results can be used for the preliminary acoustic design of the cab; that is, the research results can be used for the acoustic design of similar models.

Development of hybrid method for coupled conduction-radiation heat transfer in two-dimensional irregular enclosure considering thermo-radiative effects and varying thermal conductivity

Purpose This study aims to perform a comprehensive investigation to model the thermal characteristics of a coupled conduction-radiation heat transfer in a two-dimensional irregular enclosure including a triangular-shaped heat source. Design/methodology/approach For this purpose, a promising hybrid technique based on the concepts of blocked-off method, FVM and DOM is developed. The enclosure consists of several horizontal, vertical and oblique walls, and thermal conductivity within the enclosure varies directly with temperature and indirectly with position. To simplify the complex geometry, a promising mathematical model is introduced using blocked-off method. Emitting, absorbing and non-isotropic scattering gray are assumed as the main radiative characteristics of the steady medium. Findings DOM and FVM are, respectively, applied for solving radiative transfer equation (RTE) and the energy equation, which includes conduction, radiation and heat source terms. The temperature and heat flux distributions are calculated inside the enclosure. For validation, results are compared with previous data reported in the literature under the same conditions. Results and comparisons show that this approach is highly efficient and reliable for complex geometries with coupled conduction-radiation heat transfer. Finally, the effects of thermo-radiative parameters including surface emissivity, extinction coefficient, scattering albedo, asymmetry factor and conduction-radiation parameter on temperature and heat flux distributions are studied. Originality/value In this paper, a hybrid numerical method is used to analyze coupled conduction-radiation heat transfer in an irregular geometry. Varying thermal conductivity is included in this analysis. By applying the method, results obtained for temperature and heat flux distributions are presented and also validated by the data provided by several previous papers.

The Response of Irregular Enclosure with Different Excitation

This paper presents a theoretical investigation into the response of the coupled system which consists of a regular or irregular enclosure with different excitation, including noise reduction level and panel vibration energy level. The results show that the noise reduction level curves appear changes in medium and high frequency region when the enclosure change from regular rectangular to irregular trapezoidal, but there is small variation in panel vibration energy. Compared with the incident plane wave perpendicular to the flexible wall, more panel modes are excited by the oblique plane wave, and it means that more noise go through the flexible wall into the enclosure.

The Analysis of Structural–Acoustic Coupling of an Irregular Enclosure Under the Excitation of Point Force and PVDF

The physical model of this paper is an irregular enclosure with double flexible plates. The primary source is the vibration of Plate A excited by a point force. The secondary source is the vibration of Plate B excited by a polyvinylidene fluoride (PVDF) actuator. First, the interaction of the PVDF actuator and a thin plate is analyzed and the distribution of strain and stress is gained. Based on the hypothesis of linear distribution of strain on two sections of the plate–film system, a formula is deduced to calculate the rate of the strain distribution. Then an experiment is proposed to test the sound pressure response in an irregular enclosure under the excitation of the PVDF actuator. Second, the theoretical formulas of the mode contributions of the two plates and the cavity are deduced. Then the formulas are converted into compact matrix equations. Thus the expression of sound response of one point in the enclosure is gained under the excitation of both the primary and the secondary sources. Based on these results, the sound pressure square is taken as the control aim function. At last the optimized curves of control voltage and control phase are achieved.

New Analytical Method for Modeling Active Structure Acoustic Control System within an Irregular Enclosure

A new analytical method for the acoustic-structure coupled problem within an irregular enclosure, which has both inner sound sources, and exterior forces exciting it, was developed based on a method called the covering domain method. The method is not only more accurate and faster than numerical methods, such as FEM/BEM, but also can be used to solve acoustic-structure coupled problems within any irregular enclosure in a convenient way, that are impossible for the traditional analytical method. The model for, the active structure acoustic control (ASAC) system of an irregular enclosure based on the method above was founded, and then the optimized actuators outputs were given, which is the key step for ASAC system design. Then the method was applied to a car-like-cavity and it was found that the simulation result is quite good and shows us this new general analytical method for solving active structure acoustic control problems within an irregular enclosure considering acoustic-structure coupling to be quite effective and fit for any irregular enclosure.

Patterns of Natural Convection Around a Square Cylinder Placed Concentrically in a Horizontal Circular Cylinder

The Galerkin finite element method was used to analyze the natural convection heat transfer in an irregular enclosure made by two isothermal concentric horizontal cylinders: the inner square cylinder and the outer circular cylinder. Two different aspect ratios, A/R = 0.2 and 0.4, are considered for two possible symmetric attitudes of the inner square cylinder. For the case of aspect ratio 0.4, experimental verification has also been made by obtaining field temperature measurement and streamline visualization. It is found that there is no boundary layer separation past the sharp edges of the inner cylinder in the range of Rayleigh numbers less than 105, although this phenomenon plays a negative role in the local and overall heat transfer. Above the upper horizontal surface of the inner square cylinder, a well-defined symmetric plume is found despite its low flow speed and temperature gradient. For the geometry of stand-on-edge position of the inner cylinder, vortex cores exist in the enclosure in quadruple for Ra≤5.0×104 and A/R = 0.4, and in double for other cases including A/R = 0.2.