Longitudinal Resonance Frequency Research Articles

Prediction and analysis for airflow generated noise inside mufflers based on large eddy simulation and Morhing acoustic analogy

The airflow generated noise inside a simple expansion chamber muffler is predicted by combining large eddy simulation and Morhing acoustic analogy in the present work, and a good agreement is observed between the prediction and measurement. Research indicates that wall pressure fluctuations are dominated by hydrodynamic pressure fluctuations at the distance of first three pipe diameters in the outlet pipe, and wall pressure fluctuations at the distance of six pipe diameters downstream are dominated by sound pressure fluctuations. The airflow generated noise is mainly attributed to the vortex generated by structural change in the muffler, and one observes strong influences at the longitudinal resonance frequency and antiresonance frequency of the expansion chamber. In addition, the effects of expansion chamber lengths, extensions of inlet/outlet, filleted structure, conical tube, and perforated tube on airflow generated noise are studied. Predicted results show that the filleted structure, conical tube, and perforated tube structure may reduce the airflow generated noise effectively.

A design methodology of miniature photoacoustic cell based on beam energy distribution and acoustic resonator coupling

In photoacoustic spectroscopy, the photoacoustic cell plays the role of amplifying the photoacoustic signal, and the optimization of its parameters affects the sensitivity and dimensions of the whole system. However, none of the current optimization studies of photoacoustic cells have considered in depth the influence of beam waist radius, which limits the reduction of the size of photoacoustic cells. In this paper, based on the theory of photoacoustic spectroscopy, considering the inhomogeneity of the spatial distribution of the Gaussian beam energy and neglecting the loss of the beam in the acoustic resonator, a theoretical model of the effect of the beam waist radius on the cell constant of the first-order longitudinal resonant frequency is established. Six photoacoustic cells with different resonator radii were designed and measured for acetylene at five different beam waist radii. The relationship among beam waist radius, radius of acoustic resonator and cell constants shows that choosing a radius of resonator that matches the waist radius results in a more sensitive and smaller photoacoustic cell. The study provides a reference for the design of miniaturized photoacoustic cells with high sensitivity, thus promising to further improve the miniaturization of photoacoustic spectroscopy systems for more application scenarios.

Static elastic modulus prediction at early ages using a modified resonant test for concrete cylinders using mems microphones

Concrete Young’s modulus is seldom verified on-site due to the time-consuming and costly nature of current testing standards. This article proposes a new, quick and affordable testing methodology to estimate the ultimate static elastic modulus of normal strength concrete cylinders on-site at early ages using a smartphone. Impact-resonance tests were performed on several concrete cylinders from different mixtures at different ages, using an accelerometer and a smartphone microphone to measure the cylinders' flexural and longitudinal resonant frequencies. Measurements from both sensors were compared to show the validity of estimating the dynamic elastic modulus using acoustic signals from the cylinders recorded with a smartphone's built-in microphone. The cylinders' static and dynamic elastic moduli were determined, and the change in elastic modulus over time as the cylinders aged was also examined. This study shows the advantages of microphones over accelerometers, being less susceptible to measurement errors and proposes a filter algorithm to extract the resonant frequencies from environmental noise. A forecasting methodology to estimate static elastic modulus based on early dynamic impact-resonant tests can help engineers make early decisions on their supplied concrete on-site.

Theoretical study on resonance frequencies of vibration modes of Janus-Helmholtz transducer

Janus-Helmholtz transducer has the characteristics of high-power and broadband transmission due to the coupling between the longitudinal resonance of the driver and the liquid cavity resonance of Helmholtz resonator. Traditional view holds that the low frequency resonance peak in the transmitting voltage response curve in water is fluid cavity mode of Helmholtz resonator while the high frequency resonance is the longitudinal mode of Janus transducer. However, in the past few decades, a large number of experimental studies have found that this conclusion is questionable. This work is to distinguish the two resonances in the response curve and the two vibration modes of Janus-Helmholtz transducer. Based on the Janus-Helmholtz transducer prototype reported in the literature, the resonance frequencies of the vibration modes of Janus-Helmholtz transducer are studied theoretically. The structure dimensions and material parameters of the prototype are listed in detail. The test results and simulation results of conductivity are also presented. The longitudinal resonance of the driver is determined by using the equivalent circuit method and finite element analysis. Radiation masses of both Janus transducer and typical longitudinal vibration transducer are also calculated to analyze the phenomenon of the sharp decrease of longitudinal resonance frequency in water. Acoustic modal analysis by using ANSYS software is performed to investigate the resonance frequency of complex Helmholtz resonator in Janus-Helmholtz transducer. Correction length on the vent introduced by external fluid sound radiation is used to obtain the accurate Helmholtz resonance frequency. The sound pressure distribution of Helmholtz resonator obtained through finite element method is investigated, and the correct equivalent formula for solving the Helmholtz resonance frequency is obtained. The results reveal that the first resonance in the response curve is driver resonance while the second one is Helmholtz resonance, which is contrary to the traditional view. The considerable reduction of driver resonance frequency in water is mainly due to the large radiation mass on the four large radiation surfaces of the Janus transducer, which also causes the sharp response of driver resonance. In Janus-Helmholtz transducer, there are two Helmholtz resonators with the same size, instead of only one resonator in the traditional view. The two resonance frequencies solved by the method proposed in this work are in good agreement with the test and simulation results. These conclusions play an important role in correctly understanding the structure and characteristics of Janus-Helmholtz transducer at source, as well as provide technical support for structural optimization and innovation, thus improving the acoustic emission properties of the transducer.

Design of a bulk-lead zirconate titanate ultrasonic transducer array addressing specific excitation modes

Conventional ultrasonic transducer arrays generally use simultaneous or delayed excitation methods to generate various types of wave fronts in ultrasonic testing. Such array excitation modes are relatively simple and unable to maximize the functions of the array elements or element apertures. Accordingly, this study developed a novel excitation ultrasonic transducer array with flexible excitation aperture. A minimum row-column-addressing planar array structure for ultrasonic transducers based on bulk lead zirconate titanate (PZT) was designed for industrial ultrasonic testing. In addition, a transducer structure design scheme and truth table for array addressing with excitation logic were provided. By performing an acoustic field simulation, this study analyzed the relationship between the longitudinal amplitude and resonant frequency of the array elements and the impedance distribution. The transducer was fabricated and packaged using a circuit board and bulk PZT array elements. Testing revealed that the resonant frequency of the array was 1.07 MHz, the effective electromechanical coupling coefficient was 0.40, and the fractional bandwidth of the pulse echo response and spectrum was 38.46%. Using an aluminum block, performance in single-element, row-, column-, and full-array excitation was tested, and echo curves were obtained for multiple apertures. Using a single-circuit module, the transducer realized flexible gating and excitation of the array elements. The research provided a new method for industrial ultrasonic transducer array design.

A sandwich resonant bar method with transfer matrices for measuring the elastic parameters of rock at low frequency

Abstract Rocks and other geological materials have appreciable dispersion in their elastic properties. Rock elastic parameters within the same frequency range as the logging frequency band (1–20 kHz) should be determined to facilitate reservoir prediction and interpretation of logging data. This study suggests a technique for determining the elastic characteristics of rock cores at low frequencies using a sandwich resonant bar by integrating transfer matrices into the one-dimensional transmission model. The frequency response expression of the sandwich resonant bar is derived analytically and then the response is simulated accurately based on this expression. Numerical results show that the first two-order longitudinal resonance frequencies are approximately linearly related to the inverse of the sample's Young's modulus and the density, respectively. In addition, an inversion algorithm based on Gauss–Newton iteration, which converges faster and more efficiently, is proposed in this paper. The residuals between the model's first two resonant frequencies and the simulated results are used as the error function, and the elasticity parameters that minimize the error function are the best estimate for creating the model. This research is valuable for measuring rock elastic parameters accurately in the kilohertz range, which is of practical significance in dispersion-related studies relating to rock cores.

The influence of thermal-hygrometric properties of air on the tune of pipe-organs

Pipes of pipe-organ dynamically change their tune during the year due to environmental conditions, sometimes consistently, making these instruments hard to be played. Because thermal-hygrometric properties of air change through the seasons, this study investigates the influence of air temperature and relative humidity on pipes' tune by monitoring a real pipe organ during a year. Normalized frequency was introduced to analyze and compare notes and logs of different extents with each other, and a variation within 7% was reported. Absolute Humidity parameter was introduced to gather temperature and relative humidity under a single parameter, allowing the evaluation of the contribution of the relative humidity to the frequency changes. Fitting models and their equations were extracted, and normalized residuals were estimated. The same analyses were performed on a small pipe organ at a laboratory scale to confirm the reliability of those models. A comparison between standard equations for calculating the resonance frequency of pipes and the introduced models is also discussed. Finally, the slight influence of humidity on the sounding frequency was confirmed. K/coefficients were introduced to align the results of the longitudinal resonance frequency equation for cylindrical cavities from literature with the resulting model by comparing the temperature influence.

Low-frequency Resonant Photoacoustic Gas Sensor by Employing Hollow Core Fiber-Based O-Shaped Multipass Cells.

A low-frequency flexible resonant photoacoustic (PA) gas sensor using an O-shaped multipass cell is demonstrated. The PA sensor employed a flexible gradually tapered leaky hollow core fiber (LHCF). The LHCF was bent to be an end-to-end structure to make full use of the incident light. Additionally, the two ends of the LHCF were put inside a single buffer chamber, yielding an equivalent H-type acoustic resonator. The geometric size was reduced thanks to the bending structure. The geometric length of the LHCF was 500 mm. A micro-electro-mechanical-systems electrical microphone was installed at the center of the resonant tube to detect the PA signal. The proposed PA gas sensor exhibited a first-order longitudinal resonance frequency of 408 Hz. Trace acetylene (C2H2) was used as the target gas. The minimum detectable limit was calculated to be 25.8 parts-per-billion (ppb) with an average time of 400 s, which was 1.93 times higher than that of a single-pass PA gas sensor. The normalized noise-equivalent absorption coefficient and the PA cell constant were calculated to be 9.6 × 10-9 W·cm-1·Hz-1/2 and 8295 Pa/W·cm-1, respectively. The PA gas sensor owns a low resonance frequency and can be used for detection of most of the polar gaseous molecules, especially suitable for gas molecules with a long V-T relation time, such as carbon monoxide and carbon dioxide.

Simultaneous crack and temperature sensing with passive patch antenna

This article presents a novel passive patch antenna sensor for simultaneous crack and temperature sensing, and the antenna sensor has the ability of temperature self-compensation. The passive patch antenna sensor consists of an underlying patch and an overlapping sub-patch. The off-center feeding activates resonant modes in both transverse and longitudinal directions. The resonant frequency shift in transverse direction is used for environmental temperature sensing, while the structural crack width can be sensed by the longitudinal resonant frequency shift after temperature compensation. Furthermore, the unstressed design of the antenna can also eliminate the issue of incomplete strain transfer ratios. In this article, the relationships between the antenna resonant frequencies, the environmental temperature, and the structural crack width were studied. Simulations were conducted to determine the optimal off-center fed distance of the patch antenna sensor. Furthermore, a series of experimental tests were also conducted, where the passive patch antenna was fabricated and installed on the concrete components as well as an actual building. Continuous monitoring was performed for several days to test the temperature sensing ability of the passive patch antenna, and the sensed crack width after temperature compensation was compared with the actual results. The results of these experiments demonstrate the feasibility of using the passive patch antenna for simultaneous temperature and crack sensing.

Assessment of an Optimal Design Method for a High-Energy Ultrasonic Igniter Based on Multi-Objective Robustness Optimization

The current deterministic optimization design method ignores uncertainties in the material properties and potential machining error which could lead to unreliable or unstable designs. To improve the design efficiency and anti-jamming ability of a high-energy ultrasonic igniter, a Six Sigma multi-objective robustness optimization design method based on the response surface model and the design of the experiment has been proposed. In this paper, the initial structural dimensions of a high-energy ultrasonic igniter have been obtained by employing one-dimensional longitudinal vibration theory. The finite element simulation method of COMSOL Multiphysics software has been verified by the finite element simulation results of ANSYS Workbench software. The optimal igniter design has been achieved by using the proposed method, which is based on the finite element method, the Optimal Latin Hypercube Design method, Grey Relational Analysis, the response surface model, the non-dominated sorting genetic algorithm, and the mean value method. Considering the influence of manufacturing errors on the igniter’s performance, the Six Sigma method was used to optimize the robustness of the igniter. The Eigenfrequency analysis and the vibration velocity ratio calculation were conducted to verify the design’s effectiveness. The results reveal that the longitudinal resonant frequency of the deterministic optimization scheme and the robustness optimization scheme are closer to the design’s target frequency. The relative error is less than 0.1%. Compared with the deterministic optimization scheme, the vibration velocity ratio of the robustness optimization scheme is 2.8, which is about 15.7% higher than that of the deterministic optimization scheme, and the quality level of the design targets is raised to above Six Sigma. The proposed method can provide an efficient and accurate optimal design for developing a new special piezoelectric transducer.

A compact gas monitoring system for methane based on photoacoustic spectroscopy

A compact system for methane monitoring based on Photoacoustic Spectroscopy has been designed. In this paper, we theoretically derived the photoacoustic pressure and the first-order longitudinal resonant frequency of different photoacoustic cells. Based on theoretical analysis, we improved the acoustic signal amplification capability of the photoacoustic (PA) cell by optimizing the radius and length of the resonator and buffer through the simulation. A compact optimized H-type PA cell was designed, whose total volume was 60*30*30 mm3. The performance of this system was evaluated through Methane detection. Experimental results show good linearity, and the linear fitting R square is 0.9993. The minimum detectable limit of CH4 is calculated to be 4 ppm with an integration time of 10 s.

Modulus of rupture prediction in Pinus sylvestris with multivariate models constructed with resonance, ultrasound, and wood heterogeneity variables

Multivariate models with multiple linear regression (MLR), artificial neural network (ANN), and k-nearest neighbors (KNN) were developed to predict the modulus of rupture of Pinus sylvestris structural timber. The aim of this study was to develop and compare these models obtained from resonance and ultrasound tests, static modulus of elasticity tests, and different measured wood feature. Resonance tests were performed in the three vibration modes (edgewise, flatwise, and longitudinal) to obtain the fundamental resonant frequencies. To compare the goodness-of-fit of the different models, the 10-fold cross-validation method was used, which proved to be an adequate strategy to avoid overfitting. The variable with the best predictive capacity of the modulus of rupture was knottiness. The error was notably lower in the multivariate than the univariate models. The ANN and KNN algorithms showed no improvement over the MLR. The most suitable MLR for prediction of the modulus of rupture was the model with four variables: knottiness, edgewise dynamic modulus of elasticity, velocity of ultrasounds, and longitudinal resonant frequency.

Large-dimension piezoelectric ceramic composite transducer with point-defect, square-lattice phononic crystal

<p indent=0mm>To improve the longitudinal working efficiency of large-dimension sandwich piezoelectric ceramic composite transducers (PccTs), reduce the strong coupling between longitudinal and transverse vibrations, and improve the longitudinal displacement distribution uniformity of the front radiation end of the transducer, three rows and three columns of two-dimensional (2D) air cylindrical holes arranged in a square lattice parallel to the axial direction of the transducer were fabricated on the front cover plate of a large-dimension sandwich PccT. By changing the radius of the air cylindrical hole in the center of the 3×3 supercell, a point defect is introduced to construct 2D square lattice near-periodic phononic crystals based on the abnormal radius point defect. This design can use the incomplete bandgap of the crystal in the radial direction to suppress the transverse vibration of the large-dimension PccT and can use the Anderson localization characteristics of the point defect to adjust the intensity and phase of the local sound field to further improve the uniformity of the displacement distribution of the radiation surface of the front cover plate. In addition, the influence of the structural parameters of the air cylindrical hole with the point defect on the longitudinal resonance frequency and the longitudinal vibration displacement distribution is analyzed. The simulation results show that the large-dimension PccT based on point defect, phononic crystals can suppress the axial stray modal of the transducer, significantly optimize the longitudinal relative displacement distribution of the radiation surface, and improve the performance of large-dimension PccTs.

Vibro-acoustic characteristics of a coupled pump-jet – Shafting system – SUBOFF model under distributed unsteady hydrodynamics by a pump-jet

This study presents the unsteady hydrodynamics of the excitations from a pump-jet running in the wake of a SUBOFF model and the vibro-acoustic characteristics of a coupled pump-jet – shafting system – SUBOFF model under unsteady excitations. The excitations of the pump-jet are obtained by CFD and the vibro-acoustic responses are predicted by coupled FEM/BEM. A mapping method based on radial basis function is established between CFD and structural mesh to apply the distributed pulsation forces on the wet surface of the pump-jet. The effect of the method used to apply the excitation forces on vibro-acoustic responses is investigated by applying distributed or equivalent pulsation forces at different areas of the pump-jet. Modal shapes, transmitted forces, sound radiation power, radiation directivity pattern and panel contributions are reported to illustrate the characteristics of the vibro-acoustic responses and the influence of the method used to apply the excitation forces on the responses. It is seen that the shaft frequency and the longitudinal mode resonant frequency of the shafting system are the typical characteristic frequencies with large magnitude in vibro-acoustic responses of the coupled system. Compared with applying concentrated forces applied at hub or 0.7 R, the responses produced by applying distributed forces on the whole pump-jet present modes and excitation characteristics with more reasonable magnitudes, illustrating the importance of applying distribute forces instead of concentrated forces. Besides, the contribution of the distributed forces on rotor is dominant since the responses of applying distributed forces on the pump-jet and applying distributed forces on rotor are similar.

A Dual-Gas Sensor Using Photoacoustic Spectroscopy Based on a Single Acoustic Resonator

A dual-gas photoacoustic spectroscopy (PAS) sensor based on wavelength modulation spectroscopy (WMS) was developed and experimentally demonstrated. Distributed feedback (DFB) laser diodes, emitting at 1512 and 1653 nm, were utilized as the excitation sources for the simultaneous measurement of NH3 and CH4, respectively. The PAS signal was excited by modulating the DFB laser at the first longitudinal resonant frequency of a cylindrical acoustic resonator. Absorption lines for NH3 and CH4 were simultaneously recorded during one frequency scan of the DFB lasers without using any optical switch. The interference of NH3 and CH4 on each other was investigated for accurate detection. The limits of detection (LoDs) of the PAS sensor for NH3 and CH4 for an integration time of 100 s were determined to be 0.1 and 0.3 ppm, respectively. The present PAS sensor provides a new scheme for multi-gas analysis with the advantages of cost-effectiveness, a simple structure and multi-wavelength operation.

Long- and short-ranged chiral interactions in DNA-assembled plasmonic chains

Circular dichroism (CD) has long been used to trace chiral molecular states and changes of protein configurations. In recent years, chiral plasmonic nanostructures have shown potential for applications ranging from pathogen sensing to novel optical materials. The plasmonic coupling of the individual elements of such metallic structures is a crucial prerequisite to obtain sizeable CD signals. We here identify and implement various coupling entities—chiral and achiral—to demonstrate chiral transfer over distances close to 100 nm. The coupling is realized by an achiral nanosphere situated between a pair of gold nanorods that are arranged far apart but in a chiral fashion using DNA origami. The transmitter particle causes a strong enhancement of the CD response, the emergence of an additional chiral feature at the resonance frequency of the nanosphere, and a redshift of the longitudinal plasmonic resonance frequency of the nanorods. Matching numerical simulations elucidate the intricate chiral optical fields in complex architectures.

Evaluation of rheological models for concrete submitted to alkali-aggregate reaction based on numerical analysis of damping - free expansion

Abstract The Alkali-Aggregate Reaction (AAR) phenomenon in concrete structures is perceived via expansion and cracking, swelling of gel like material, causing damage and disruption in structural elements. Despite extensive standardization, AAR cases are still persistently occurring worldwide. The literature on susceptibility of concrete to AAR reported examples of false negative and positive results. Hence, long-term prediction is a problem still posing great challenge to engineers. The severity of AAR on the structural integrity can be mostly elucidated by the assessment of the historic of elastic properties. There is consensus that AAR causes decrease in the load capacity concrete, reflected by reduction of elasticity modulus due damage progresses. Non-destructive techniques are often used as first approach, as they can provide relatively fast assessment in situ as well as in large structural elements. Its data interpretation carries certain degree of complexity due intrinsic characteristic of many of these methods. This is the case of Ultrasonic Pulse Velocity (UPV), which have been considered to present several limitations for such purpose. This paper deals the potential use of the Longitudinal Resonance Frequency (LRF) method as tool to evaluate the elastic historic of AAR prone elements. The LRF possesses higher energy than UPV. Also, using modulation of frequency in input signal combined the test geometry, the LRF allow application to larger samples as well as to extract complementary information alongside the dynamic elastic modulus. This way, the LRF was applied to study concrete beams tested under controlled conditions for about 1.5 year. The independent variables to the tests are: time, frequency, aggregate type, cement content, alkali content and water to cement ratio. The dependent variables are: damping, loss factor and elasticity modulus. The analysis associate damage with vibration damping, confirming reduction of elasticity through damage with experimental validation and prediction of AAR under rheological model.

Effects of fuel line acoustics on the self-excited combustion instability mode transition with hydrogen-enriched laboratory-scale partially premixed combustor

A finite-element method study was conducted on a laboratory-scale partially premixed combustor, for investigating the characteristics of combustion instability due to fuel composition variations. The authors’ previous studies reported frequency mode shifting in the same combustor with hydrogen enrichment, and the cause of this phenomenon was analyzed only from the viewpoint of the flame shape change and time lag theory. An increase in hydrogen fraction results in an increase in the speed of sound in the fuel feeding line, resulting in an increase in resonant frequencies determined by the fuel line geometry. This analysis shows that the hydrogen enrichment increases the bulk and longitudinal resonant frequencies of the fuel feeding line. When one of these fuel line resonances is coupled with the intrinsic acoustic mode of the combustor, the hydrogen fraction can be one of the key parameters affecting the main characteristics of combustion instability in a partially premixed system.

Resonance Interactions of Symmetric Surface and Bulk Waves in Oversized Sectioned Slow-Wave Structures

The resonance properties of coupled electromagnetic waves at frequencies of 9 and 35 GHz in the sectioned oversized slow-wave structure of a multiwave Cherenkov generator with radial polarization were investigated theoretically. It has been found how the presence of a drift tube in the slow-wave structure and the diaphragm characteristics of the structure affect the longitudinal resonance frequencies of coupled symmetric TM waves, the quality factor of the slow-wave structure, and the distribution of the electromagnetic field. The configurations of electromagnetic fields in slow-wave structures have been studied that could conceivably provide efficient coupling of the field to an electron beam and ensure stable generation of radiation in a multiwave Cherenkov generator.

Comparative Study Involving Effect of Curing Regime on Elastic Modulus of Geopolymer Concrete

Geopolymer Concrete (GPC) as a cement-less construction material has attracted worldwide attention due to its lower carbon footprint. There are numerous studies reported on GPC made using different by-products including fly-ash. However, since the use of bottom-ash is comparatively limited, making potassium-based GPC using this waste can be an alternative to Portland Cement Concrete (PCC). In this study, two methods of accelerated curing were used to determine the influence of elevated temperature on the compressive strength of GPC, composed of 50% bottom-ash and 50% fly-ash. GPC specimens were cured using various temperatures including ambient, 30 °C, 45 °C, 60 °C, and 80 °C for 24 h, all followed by 28 days of ambient curing. The highest compressive strength was obtained with steam curing at a temperature of 80 °C for a duration of 24 h. It is of great significance to evaluate elastic modulus of the concrete mixture so that the short-term rigidity of structures subjected to elongation, bending, or compression can be predicted. In this study, a longitudinal Resonant Frequency Test (RFT) as a non-destructive test (NDT) was used to calculate the elastic modulus of both GPC and a comparative PCC mix. Based on the results, PCC had higher resonant frequency (by about 1000 Hz) compared to GPC. A review of empirical models for predicting GPC’s elastic modulus showed that all of the predicted elastic modulus values were lower than experimental values.