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As sustainability is one of the main pillars in developing future cities, adopting natural ventilation whenever possible is one way to reduce energy consumption, thus indirectly reducing carbon dioxide emissions. Lately, ventilated acoustic metamaterials have started to receive more research attention because of how they can provide both ventilation and noise control. Motivated by this research attention, we present this timely systematic review of emerging ventilated acoustic metamaterials for noise control. By limiting the review to a five-year coverage (2018–2023), three kinds of ventilated acoustic metamaterials were identified—metamufflers, metapanels, and metacages. Based on the studies included in this review, we discuss the present challenges of metacages. More research efforts are still needed to see real-world applications of metacages as a novel ventilated noise control measure in the future.

Ultrasound-assisted processing of particulate phase in a host fluid relies on the induced acoustic force field. Understanding the agglomeration phenomenon in the particulate phase under acoustic forces will provide better insight about the acoustophoresis quality and a way to design a well-controlled process. In this work, a dynamic model consisting of acoustic and hydrodynamic forces is proposed for tracking the motion of micro-spheres under ultrasound fields with planar and non-planar wave fronts. The agglomeration of particles at the nodal plane was simulated taking into account the contact and collisions between spheres. The numerical simulations were conducted for both sound hard and compressible spheres to investigate the behaviors of single and multiple-phase particle populations. For the case of a plane standing-wave, the interaction between solid-bubble allows the solid particles to stay at the velocity node which is their unstable equilibrium location. With a Bessel standing wave as a non-planar pressure field, the agglomeration patterns of particles are generally different from the case of plane standing wave, which implies the significance of the particle tracking simulations for predicting the agglomeration patterns and locations under ultrasound fields with arbitrary wave fronts.

In this paper, we present a smartphone based platform for mapping and analyzing environmental noise. Smartphones are used to record environmental noise (both audio and sound pressure level) as well as locations (latitude, longitude, and accuracy). The recorded data is uploaded to a server and noise map of a region is generated using the location information along with the sound pressure levels (SPL) at those locations. Noise maps can used to discover sources of noise in a region and also to compare SPL between different places. Thus, they can be an important tool to help implement mitigating steps for reducing noise or planning future developments. To illustrate the capabilities of the platform, we present a case study of noise mapping with five educational institutes and five residential neighborhoods in Singapore. We present noise maps for these places and discuss possible sources of noise. We also discuss potential reasons for observed differences in equivalent continuous sound pressure level between different educational institutes, and residential neighborhoods.

With every passing decade, the issue of noise pollution has worsened in urban areas and the usefulness of noise barriers have increased. To improve the effectiveness of noise barriers in limited frequency bandwidth, a few researchers have reported that quadratic residue diffusers as noise barrier top-profiles have shown promising noise attenuation, albeit in their narrow frequency bandwidth. It has been reported for room acoustics that the frequency bandwidth of quadratic residue diffusers may significantly be extended by a nested or fractal design. Therefore, the aim of this work is to investigate the potential of fractal acoustic diffusers for noise barrier application. Upon conducting a numerical analysis of 1-D fractal diffuser as noise barrier top-profile using finite element method, it is observed that fractal diffusers outperformed T-barriers in both the shadow zone and the transition zone. Hence, fractal acoustic diffusers are promising candidates for our application as these have good diffusion properties in the integrated frequency bandwidth. If properly designed, the fractal diffuser top-edge device can be used to enhance noise attenuation over extended frequency bandwidth.

To achieve the accuracy and anti-interference of the motion control of the soft robot more effectively, the motion control strategy of the pneumatic soft bionic robot based on the improved Central Pattern Generator (CPG) is proposed. According to the structure and motion characteristics of the robot, a two-layer neural network topology model for the robot is constructed by coupling 22 Hopfield neuron nonlinear oscillators. Then, based on the Adaptive Neuro-Fuzzy Inference System (ANFIS), the membership functions are offline learned and trained to construct the CPG-ANFIS-PID motion control strategy for the robot. Through simulation research on the impact of CPG-ANFIS-PID input parameters on the swimming performance of the robot, it is verified that the control strategy can quickly respond to input parameter changes between different swimming modes, and stably output smooth and continuous dynamic position signals, which has certain advantages. Then, the motion performance of the robot prototype is analyzed experimentally and compared with the simulation results. The results show that the CPG-ANFIS-PID motion control strategy can output coupled waveform signals stably, and control the executing mechanisms of the pneumatic soft bionic robot to achieve biological rhythms motion propulsion waveforms, confirming that the control strategy has accuracy and anti-interference characteristics, and enable the robot have certain maneuverability, flexibility, and environmental adaptability. The significance of this work lies in establishing a CPG-ANFIS-PID control strategy applicable to pneumatic soft bionic robot and proposing a rhythmic motion control method applicable to pneumatic soft bionic robot.

A new idea of resonator blinds was designed and was tested in an office room. The noise level inside the room was measured using sound quality head and torso simulator. The resonator blinds was designed so that it can attenuate noise within human hearing sensitive frequency range. By overall, the resonator blinds was able to attenuate 5.1 dBA of environmental noise when frequencies were ranging from 100 Hz to 4000 Hz.

The knowledge of weather conditions at the stratosphere is important for the planning and execution of highaltitude balloon flights, which require an accurate modeling of weather data over a period of time. Various methods based on statistical analysis, artificial neural networks, and cluster analysis have been employed to model the temporal variation of weather parameters. In the present study, a proper orthogonal decomposition (POD) method has been used to study the spatial as well as temporal variations of wind data in Singapore. The use of POD facilitates a compact representation of the weather dataset and aids in faster computation of wind profiles for use in balloon trajectory simulation. Further, the results reveal the existence of the quasi-biennial oscillation phenomenon, which is characteristic of equatorial easterly–westerly winds. This phenomenon enables the development of a Fourier prediction model, which can be used in real-time balloon trajectory simulations. The Fourier model is observed to be sensitive towind velocity fluctuations, especially in the vicinity of alternating wind directions. However, it provides a reasonable projection of balloon trajectory, which can be used in preliminary planning and testing of high-altitude flights. Thus, a prior knowledge of wind profiles based onPODor a Fourier model aids in balloon station keeping. A simple case of altitude-controlled balloon flight is presented, and the results highlight the advantages of the present method in balloon station keeping.

Under the influence of acoustic radiation force, particles can be trapped and deformed at the pressure node in a microfluidic channel. Based on this principle, the elastic modulus of biological cells can be estimated. In this study, a numerical framework, consisting of a boundary element model for acoustic field and an axisymmetric shell model, is developed to simulate the cell deformation under acoustic radiation force. The boundary element model is used to calculate the radiation traction exerted on the cell surface. The cell membrane deformation due to this traction is simulated by using the axisymmetric shell model. The Young’s moduli of algae and red blood cell membranes are then estimated by comparing the experimental observation with the simulated membrane deformation. It is found that the value of Young’s modulus of the red blood cell membrane is lower than that of algae cell membrane. Furthermore, for both cells, the estimated Young’s moduli are negligible compared to the bulk moduli of the cells reported in the previous studies.

A constitutive model based on isotropic plasticity consideration is presented in this work to model the thermo-mechanical behavior of high-temperature shape memory alloys. In high-temperature shape memory alloys (HTSMAs), both martensitic transformation and rate-dependent plasticity (creep) occur simultaneously at high temperatures. Furthermore, transformation-induced plasticity is another deformation mechanism during martensitic transformation. All these phenomena are considered as dissipative processes to model the mechanical behavior of HTSMAs in this study. The constitutive model was implemented for one-dimensional cases, and the results have been compared with experimental data from thermal cycling test for actuator applications.

The boundary element method (BEM) is known to have the advantage of reducing the dimension of problem by discretizing only the boundary of the domain. But it becomes less attractive for solving Poisson-type equations, due to the need to evaluate the domain integral which is computationally expensive. In this paper, we present the extension of a recently developed fast algorithm for Laplace equation, based on fast Fourier transform on multipoles (FFTM), to solve large scale 3D Poisson-type equations. We combined the Laplace solver with two fast methods for handling the domain integral based on fast Fourier transform (FFT). The first method uses the FFT on multipoles to accelerate the domain integral, while the second method solves the domain integral as a particular solution using FFT. The particular solution method is found to be faster and more accurate, and it is extended to solve non-linear Poisson-type equations. The algorithm is shown to be efficient when it is used in the inner loop of the iterative solver for the non-linear equations.