Internal Excitation Source Research Articles

Vibro-Acoustic Analysis of an Underwater Cylindrical Shell with Internal Structures and a Comparison with Experiment

Abstract: In this work, the low-frequency vibration response and full-band acoustic radiation characteristics of an underwater reinforced cylindrical shell with internal structures are studied by combining the FEM with SEA. The stiffened cylindrical shell contains internal structures such as the F-shape plates and the support valve frames. The exciting sources have two different exciting forces corresponding to two experimental conditions. In the low-frequency band, the FEM was employed, and in the medium and high-frequency bands, the SEA was used. A comparison of the numerical results and the experiment shows that they agree well. The FEM and SEA give better results at [1,1k] Hz and [1k,10k] Hz, respectively. Due to mesh quality limitations, the FEM is not favorable for medium and high-frequency calculations. The SEA focuses on the structural mean power flow but cannot obtain position-specific vibrational responses. The results show that the internal excitation source mainly causes the structural vibration and sound radiation and are closely related to the free vibration characteristics of the structure. In addition, with the increase in frequency, the circumferential sound pressure level of the underwater structure has more substantial directivity.

Prodrug-based strategy with a two-in-one liposome for Cerenkov-induced photodynamic therapy and chemotherapy

Cerenkov radiation induced photodynamic therapy (CR-PDT) can tackle the tissue penetration limitation of traditional PDT. However, co-delivery of radionuclides and photosensitizer may cause continuous phototoxicity in normal tissues during the circulation. 5-aminolevulinic acid (ALA) which can intracellularly transform into photosensitive protoporphyrin IX (PpIX) is a cancer-selective photosensitizer with negligible side effect. However, the hydrophilic nature of ALA and the further conversion of PpIX to photoinactive Heme severely hinder the therapeutic benefits of ALA-based PDT. Herein, we developed an 89Zr-labeled, pH responsive ALA and artemisinin (ART) co-loaded liposome (89Zr-ALA-Liposome-ART) for highly selective cancer therapy. 89Zr can serve as the internal excitation source to self-activate PpIX for CR-PDT, and the photoinactive Heme can activate the chemotherapeutic effect of ART. The 89Zr-ALA-Liposome-ART exhibited excellent tumor inhibition capability in subcutaneous 4T1-tumor-bearing Balb/c mice via CR-PDT and chemotherapy. Combined with anti-PD-L1, the 89Zr-ALA-Liposome-ART elicited strong antitumor immunity to against tumor recurrence.

Study on the meshing stiffness of plastic helical gear meshing with metal worm via point-contact

Time-varying meshing stiffness is the main internal excitation source for gear dynamic responses. A calculation method for meshing stiffness of point-contact transmission pairs is proposed to analysis the dynamic responses of the plastic helical gear metal worm drive. Based on the curvilinear motion trajectories and the contact ellipse changes of helical gear worm drive, a method of equivalent area rectangle is introduced to convert the contact ellipse into contact line, and the relationship between the contact line and the worm angle is established. The meshing stiffness of plastic helical gear metal worm drive is calculated and compared with the finite element method (FEM) to verify its accuracy. The results show that the meshing stiffness of plastic helical gear metal worm drive is affected by the meshing impact, and the time-varying meshing stiffness value of double-tooth meshing will be close to or even lower than that of single-tooth meshing. In the plastic helical gear metal worm drive, there is no stable stiffness value whether it is single-tooth meshing or double-tooth meshing. The single-tooth meshing stiffness has an upward trend under the influence of the pressure angle. The calculation results of theoretical model are basically consistent with the FEM results, but the theoretical model cannot fully reflect the stiffness change during meshing impact.

Effect of gear topology discontinuities on the nonlinear dynamic response of a multi-degree-of-freedom gear train

Weight reduction is a recurring concern in the design of modern mechanical systems. This search may lead engineers to resort to using gears with holes in order to meet their requirements. This paper presents a methodology to carry out nonlinear dynamic analyses of a gear transmission with holes in the gear blanks subjected to a multiharmonic internal excitation. This work investigates the influence of these holes on the vibration levels, occurrence of contact loss and possible bifurcations. The numerical model features two flexible shafts coupled by a spur gear pair with holes. The gear model consists in two lumped masses and inertias and includes the gear backlash as well as the internal excitation sources that are the time-varying stiffness and the static transmission error (STE). The resulting mechanical system is solved in the frequency domain by the Harmonic Balance Method (HBM) coupled with an arc-length continuation algorithm and its stability is evaluated with Hill’s method. Results show that adding holes not only impacts the STE but also the mesh stiffness. The interactions of these two quantities has a substantial influence on the bifurcation structure along the main solution branch and leads to a decrease of the span of vibro-impact regions. As the applied static torque is increased, it is found that using holed gear blanks can effectively prevent contact loss and lead to a linear response.

Radioiodinated Persistent Luminescence Nanoplatform for Radiation-Induced Photodynamic Therapy and Radiotherapy.

Radionuclide with Cerenkov radiation (CR) can serve as an internal excitation source to activate photosensitizers for photodynamic therapy (PDT) in deep tumor. However, the low efficiency of CR limits its therapeutic efficacy. A 131 I labeled zinc tetra(4-carboxyphenoxy) phthalocyaninate (ZnPcC4) conjugated Cr3+ -doped zinc gallate (ZnGa2 O4 :Cr3+ , ZGCs) nanoplatform (131 I-ZGCs-ZnPcC4) is developed for radiotherapy (RT) and radiation-induced PDT. 131 I can not only activate ZGCs for long-lasting luminescence via both Cerenkov luminescence (CL) and ionizing radiation, which further continuously activate photosensitizer ZnPcC4 for PDT, but also can directly kill cancerous cells. This 131 I-ZGCs-ZnPcC4 exhibits excellent tumor inhibition both in vitro and in vivo. Combining self-activated PDT and RT, it is believed that the 131 I-ZGCs-ZnPcC4 can greatly benefit the deep tumor therapy.

Identification of acoustic sources for bent-axis axial piston motor under variable loads

The bent-axis axial piston motor is the key actuator of the construction machinery's torque drive and hydrostatic walking. The vibration of the whole motor is not only stimulated by the internal excitation sources, but also affected by the load fluctuation. At the same time, the continuous fluctuation of the load aggravates the evolution of the internal excitation source. Therefore, how to evaluate the impact of load fluctuation on motor vibration and identify the internal excitation source of motor is particularly important. In this paper, the theoretical and experimental research on acoustic sources identification of the bent-axis axial piston motor is carried out. Firstly, according to the structure principle and kinematics characteristics of the motor, the theoretical excitation sources and transfer paths are obtained, and the vibration transmission model based on the excitation sources located in the spindle is established, which can evaluate the effect of load excitation on the overall vibration of piston motor. Further vibration and noise tests under variable loads are completed in the semi-anechoic chamber. The experimental results validate the theoretical vibration transfer model effectively, and reveal the noise sources inside the tested motor under various loads and the transfer of the main noise sources. The maximum vibration amplitude of the outer surface of the motor is shifted from the shell to the backend cover in the process of increasing revs from 500 rpm to 1200 rpm, and the main acoustic source inside the motor is shifted from the eccentricity and unbalance of the spindle to pressure pulsation and flow distribution impact in the process of increasing pressure from 5 MPa to 15 MPa. The data in this paper can be applied to the structure optimization design with load matching, and further provide reference for the follow-up work of reducing vibration and noise under full working conditions.

Real-Time Crawling Wave Sonoelastography for Human Muscle Characterization: Initial Results

Imaging of musculoskeletal tissue dynamics is currently an exploratory field with the goal of aiding rehabilitation and performance evaluation of pathological or asymptomatic patients. In this pilot study, initial elasticity assessments of the biceps brachii were conducted in a novel crawling wave sonoelastography (CWS) system implemented on a research ultrasound instrument with graphical processing unit capabilities, displaying quantitative elasticity values at 4 frames per second. The CWS system computes the tissue stiffness with the generation of an interference pattern from external vibrators, which can overcome depth limitations of imaging systems with internal excitation sources. Validation on gelatin-based phantoms reported low bias of elasticity values (4.7%) at low excitation frequencies. Preliminary results on in vivo muscle characterization are in accordance with average elasticity values for relaxed and contracted tissues found in the literature, as well as for a range of weight loads.

Three new models for evaluation of standard involute spur gear mesh stiffness

Time-varying mesh stiffness is one of the main internal excitation sources of gear dynamics. Accurate evaluation of gear mesh stiffness is crucial for gear dynamic analysis. This study is devoted to developing new models for spur gear mesh stiffness evaluation. Three models are proposed. The proposed model 1 can give very accurate mesh stiffness result but the gear bore surface must be assumed to be rigid. Enlighted by the proposed model 1, our research discovers that the angular deflection pattern of the gear bore surface of a pair of meshing gears under a constant torque basically follows a cosine curve. Based on this finding, two other models are proposed. The proposed model 2 evaluates gear mesh stiffness by using angular deflections at different circumferential angles of an end surface circle of the gear bore. The proposed model 3 requires using only the angular deflection at an arbitrary circumferential angle of an end surface circle of the gear bore but this model can only be used for a gear with the same tooth profile among all teeth. The proposed models are accurate in gear mesh stiffness evaluation and easy to use. Finite element analysis is used to validate the accuracy of the proposed models.

Nonlinear torsional vibrations of a wind turbine gearbox

This paper studies the torsional vibrations of wind turbine gearbox having two planetary gear stages and one parallel gear stage. The nonlinear dynamic model developed considers the factors such as time-varying mesh stiffness, damping, static transmission error and gear backlash. Both the external excitation due to wind gust and the internal excitation due to static transmission error are included. With the help of time history, FFT spectrum, phase portrait, Poincare map and Lyapunov exponent, the effects of the static transmission error, mean-to-alternating force ratio and time-varying mesh stiffness on the dynamic behaviour of wind turbine gearbox components are investigated by using the numerical integration method. It is found that the external excitation has the most influence on the torsional vibrations of the wind turbine gearbox components. The mesh stiffness, being another significant factor, has more influence than the other internal excitation source, the static transmission error. The static transmission error has the least influence.

Fault feature analysis of planetary gear system with tooth root crack and flexible ring gear rim

Planetary gear transmission has a wide application in different areas due to its advantages such as compactness, large torque-to-weight ratio, reduced noise and vibrations. However, its dynamic responses are much more complex due to the complicated structures and relative motions, which make it difficult in the fault feature extractions at the view point of fault detection. Better understanding on the dynamic features of a planetary gear transmission and the corresponding internal excitation sources will benefit the fault feature extractions. In this paper, an analytical model for mesh stiffness calculation is developed based on the potential energy principle and uniformly curved Timoshenko beam theory, which enables exploring the effects of the tooth root crack fault and the flexible ring gear rim on the dynamic responses. Based on the developed model, the frequency spectrum structures of the planetary gear transmission can be revealed and analyzed theoretically in the presence of tooth crack and flexible ring gear. A case study is performed to demonstrate the effectiveness of the developed model, where the tooth root cracks are seeded in a tooth of the sun, planet, and ring gears. The simulated results indicate that the complicated modulation phenomenon can be observed where the causes of different frequency components can be revealed. This study is expected to be able to give some theoretical guidance on the identification of vibration sources for planetary gear transmissions.

Cerenkov radiation: a multi-functional approach for biological sciences

Cerenkov radiation (CR) has been used in various biological research fields, which has aroused lots of attention in recent years. Combining optical imaging instruments and most of nuclear medicine imaging or radiotherapy probes, the CR was developed as a new imaging modality for biology studies, called Cerenkov luminescence imaging (CLI). On the other hand, it was novelly used as an internal excitation source to activate some fluorophores for energy transfer imaging. However, it also has some shortages such as relatively weak luminescence intensity and low penetration in tissue. Thus some scientific groups demonstrated to optimize the CLI and demonstrated it to three-dimension tomography. In this article, we elaborate on its principle, history, and applications and discuss a number of directions for technical improvements. Then concluded some advantages and shortages of CR and discuss some prospects of it.

Numerical and experimental analysis of a gear system with teeth defects

The modelling of a one-stage spur gear transmission by a two degrees of freedom system produces two modes: rigid body and elastic. The time varying meshing stiffness is the main internal excitation source for the transmission and governs the behaviour of the elastic mode. Deterioration of one or several teeth, which affects the gear mesh stiffness, is considered in this work. The beginning of crack or spalling are modelled respectively by tooth having localised and distributed defect and are taken into account in the model. Simulation results are analysed by cepstrum and spectrum techniques. It is found that cepstrum and spectrum techniques are very efficient for localised and distributed defects, respectively. Series of tests are made in the experimental setup. Spectrum and cepstrum analysis of the recorded responses, with and without defects, are compared with numerical results and confirms their usefulness in gear monitoring .

Internal photoluminescence in ZnSe homoepitaxy and application in blue–green–orange mixed-color light-emitting diodes

We discuss the controllable color-range in ZnSe-based light-emitting diodes (LEDs) realized by ZnSe homoepitaxy and internal photoluminescence. ZnSe-based LED structures were grown by molecular-beam epitaxy (MBE) on mostly conductive ZnSe substrates, which exhibit under short wavelength light excitation at room temperature strong orange emission around 600 nm. This fact is exploited to fabricate integrated mixed-color LED chips, where light from the active layer sandwiched in a p–n-junction acts as internal excitation source. We named this effect recently “Internal Photoluminescence” (Wenisch et al., J. Appl. Phys. 82 (1997) 4690). It leads to electroluminescence spectra with two distinct emission peaks originated from the active layer and from the ZnSe substrate, respectively. In view of color impression, just by varying the Cd x Zn 1− x Se quantum-well composition and the radiant recombination rate in the substrate by it's choice, as much as two thirds of the visible color space is covered. Under conditions, when only the substrate emission is present, Commission Internationale d'Eclairage (CIE) chromaticity coordinates for orange color LEDs of (0.54, 0.45, 0.01) for the red, green and blue color, respectively, were determined. 490-nm quantum-well-emitting LEDs were found to be best suited in reaching the technologically important balanced white emission (“White Point”) and a value of (0.31, 0.39, 0.30) for the color coordinates close to it was experimentally achieved.

Development of total uranium analytical method by L X-ray fluorescence

This paper describes development of an L X-ray fluorescence technique to perform total uranium analysis using an internal excitation source which is added directly to the sample. The method has been demonstrated with synthetic U samples in the limited concentration range 1–15 g/l, and provides the advantage of simplicity, involving no mechanical parts which would normally be found in an external excitation source. Total uranium is determined by counting L X-rays fluoresced by a microCurie level spike of 109Cd added directly to the sample and without shielding the excitation source from the detector. A method for correction of sample self-absorption is included in the analysis.