Jaw Functional Orthopedics and Cranoficial Growth
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Experiment and analysis of active vibration isolation system based on rigid pedestal using SDOF actuator
No full textThis paper is about the active-passive isolation system based on single degree of freedom electromagnetic actuator and focuses on different control effect of different measure points. In view of this problem, the authors analyze the vibration characteristics of the active and passive vibration isolation systems of electromagnetic airbags under single and multi-vibration isolators. Then they decompose the rigid pedestal vibration into two orthogonal components, the vertical translation and the fix axis rotation. After that compare simulation and experiment results in terms of the control effect when the single active-passive isolator location varies. Finally, the authors draw a conclusion about the reason why the rigid pedestal vibration can be globally controlled by arranging more than 3 active-passive isolations and design a multiple isolator system experiment to verify
Contribution of magnetic resonance imaging in the biomechanical interpretation of the temporomandibular joint. Clinical case report
Get PDFX-rays and tomography, in their different modalities, are used as auxiliary diagnostic elements in temporomandibular joint (TMJ) dysfunction, both in static and dynamic situations; however, because they only allow the observation of bone structures, magnetic resonance imaging (MRI) is the ideal method to analyze, among other structures, the articular disc. Among the internal disorders of the TMJ are the abnormal postural relationships between the disc, mandibular head, fossa and articular tubercle, which can even lead to a musculoskeletal condition causing noise, pain and functional limitation. The clinical evaluation of temporomandibular dysfunctions is complex, especially in asymptomatic patients; the Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD), place these entities within the AXIS I protocol, considering that the image is not strictly necessary. However, analyzing the disc situation statically and dynamically, with its surroundings, allows considering the loads that generate dysfunction, leading to the correct diagnosis, and selection of the best treatment. A clinical case is presented, an asymptomatic patient, without functional limitation, who reported a history of occasional mouth opening locking upon awakening. MRI was indicated, finding an abnormal position of the disc, in a static and dynamic situation; finding anterior displacement of the disc in the right and left TMJ in closed mouth position, dynamically anterior displacement without recapture in the right TMJ and with recapture in the left TMJ; Treatment was performed with Jaw Functional Orthopedics (JFO), obtaining changes in the dynamic disc-mandibular head relationship, anterior displacement with recapture of the right TMJ and total recapture of the left TMJ
Relationship between mandibular position and support planting in 7-year-old children: pilot study
Get PDFIntroduction: Postural stability can be maintained in balance by muscle tone [1]. Change in the mandibular position or posture, may have influence in the postural reflex, defined as an involuntary defense movement [2] to correct deviations and keep the body in balance. If the postural change is constant, the muscles will move the mandible to a more comfortable position, with consequent postural change2 and plantar support. The aim of the study was to compare the plantar support in centralized and in lateralization mandibular position in seven years’ children. Main text: This study was approved by research ethics committee (No. 4.346.542). A pilot study was carried out with seven-year-old children of both sexes. Photogrammetry was performed with spherical markers in the region of the right tragus and chin symphysis (Fig. 1) concomitantly with baropodometry following (Fig. 2, 3) the protocol established by Bittar et al. [4]. Analysis of mandibular displacement and plantar support were performed with centralized mandibular position (maximum intercuspation) and with lateral displacement to the right and left. Statistical analysis compared the differences in mandibular displacement to the right and left sides using Student’s t test. Differences in plantar support variables with centralized mandibular position and in right and left lateralization position were established by the Anova one way test and the Bonferroni pos test. Significant statistical difference was reached by 5 %. Results: Twelve seven-year-old children were included, 20.8 (3.25) Kg and 1.18 (0.06) meters. The sample present greater lateral displacement of the mandible to the lefts compared to right side. Mandibular lateralization was confirmed with statistical difference compared to mandibular position centralized. No difference in all plantar support variables was observed between the three positions: centralized and left and right lateralization. Conclusions: No differences were observed for plantar support compared position in mandibular lateralization and centralized position. Mandibular lateralization displacements did not change plantar support
Repetitive impacts recovering using variational mode extraction with constructed reference enhanced by improved blind deconvolution
Get PDFThe impulse and modulation characteristic of rolling bearing’ faulty signal is often very weak when early fault arises in rolling bearing or gears, and the main reasons are due to the signal attenuation caused by too long signal acquisition path and the interference of other multi-source vibration. In order to extract the weak feature accurately, a method named as variational mode extraction (VME) based on constructed reference enhanced by improved minimum entropy de-convolution (IMED) is proposed, which combines both the advantages of IMED in solving the influence of the long signal acquisition path and VME based on constructed reference in extracting the impulse and modulation characteristic of vibration signal. Firstly, IMED is used as signal preprocessing method to analyze the vibration signal of rotating machinery to eliminate the influence of long signal acquisition path and enhance the repetitive impulse characteristics. Then, reference signal is constructed according to the prior knowledge of the rotating machinery and input it with the output signal of IMED into the VME model together, and the output result of VME not only could further enhance the impulse characteristic of vibration signal, but also obtain the modulation characteristic simultaneously. Finally, envelope spectral or enhanced envelope spectral is performed on the output signal of VME and satisfactory fault features are extracted. In order to solve the shortcomings of traditional MED, an IMED based on D-norm is proposed which has higher computational efficiency and could extract multi-harmonic impulse features. In addition, VME based on constructed reference is proposed to improve the accuracy of VME in extracting the target signal. Feasibility and superiority of the proposed method are verified by one experimental case and one engineering case
Study on vibration characteristics of ship mining system under composite load
Get PDFThe load that borne by ship mining system is very complex. The vibration of lifting pipe can be significantly affected by ocean current and wind load, which has a key impact on material lifting, ore bin storage and ship towing. Considering the composite load condition, the vibration control equation of mining ship is established based on the transverse swing mechanism of ship hull, and the variation law of transverse disturbance is obtained. The dynamic equation is constructed according to the bearing characteristics of the lifting system and the D’Alembert principle. The Wilson method is used to analyze and obtain the transverse vibration spectrum response of the lifting pipe under different wind loads, hull disturbance velocity and water depth. Based on the analogy method and hammering method, the vibration feedback test-bed of the lifting system is built, and the time-domain and frequency-domain vibration characteristics of the lifting pipe model under different water depths are obtained. The results show that in shallow water, the disturbance of mining ship and the composite load of ocean current are the key factors affecting the vibration amplitude of lifting pipe respectively. With the increase of water depth, the characteristic frequency and amplitude of the system decrease, and the amplitude gradually presents a discontinuous phenomenon
Multi-axis vibration test technology of satellite based on vector-fixture’s design and applications
Get PDFAiming at the problems that the three-direction uniaxial sequential vibration test cannot effectively simulate the real launch environment of the satellite, and the high cost of the multi-axis shaker and the limitation of engineering application, the multi-axis vibration test scheme based on vector-fixture is proposed. Taking the vibration magnitude of uniaxial vibration test on the satellite mounting surface as equivalent reference, the appropriate vector direction is determined to carry out vector-fixture design. By analyzing the multi-axial vibration test data of the real structure of a satellite, it can be seen that: The “satellite-fixture” mounting surface can reach the set vibration magnitude at low frequencies, and undertest occurs at high frequency due to structural resonance and other factors; By optimizing the control strategy, the degree of over-test and under-test in the three directions can be balanced. According to the mission characteristics and development cycle of micro-nano satellites, this paper provides an efficient vibration test scheme
Modelling and experimental investigation of the vibratory conveyor operating conditions
Get PDFThe paper’s objective is to study the dynamic parameters and operating conditions of the vibratory conveyor, which is based on the double-mass oscillatory system and equipped with the pull-type (single-cycle) electromagnetic exciter. The scientific novelty consists in substantiating the conveying capacity of various standard sizes of bolts at different operating conditions defined by the input parameters, particularly supplied voltage. In order to describe the conveying tray vibrations, the simplified mathematical model of the conveyor’s double-mass oscillatory system is developed using the Euler-Lagrange equations and is numerically solved in the Mathematica software with the help of the Runge-Kutta methods. The experimental investigations are carried out at the Vibroengineering Laboratory of Lviv Polytechnic National University and are focused on testing the conveying speed of various bolts at different motion conditions: detachable (bouncing, hopping, jumping over the conveying surface) and non-detachable (sliding along the conveying surface). The obtained results show the basic kinematic parameters of the conveying tray motion at different voltages supplied to the actuating electromagnet and the dependencies of the conveying speeds of various bolts at different motion conditions mentioned above. The paper may be useful for designers and researchers while improving and implementing similar vibratory equipment in various industries
Construction method of strengthening shear walls using prestressed steel bars for a high-rise building
No full text2. In the shear wall reinforcement of a high-rise residence in Changzhou, China, the prestressed steel bar reinforcement method is innovatively used. This paper focuses on the reinforcement principle and construction method of the prestressed steel bar method for strengthening the shear wall. During the construction, combined with the engineering quality problems, the prestressed steel bar method is used to strengthen the shear wall. This method avoids the reduction of the use area caused by the increasing section reinforcement method and the stress lag caused by the replacement method, does not change the structural stiffness and the shape of structural members, and shortens the construction period. After monitoring by the monitoring unit, the reinforcement method has good effect. This study also passed the acceptance of the science and technology plan project of the Ministry of construction, and formed a complete set of construction method of prestressed steel bar strengthening shear wall. The effective implementation of this method can provide technical reference for the reinforcement construction of similar projects
Nonlinear dynamic behavior analysis of bridge pier impacted by a moving barge
No full textThe contradiction between ships and bridges is becoming increasingly prominent, and ship-bridge collision accidents occur frequently. However, the existing researches focus on the impact force, the bridge will be simplified to a single pier, but the single pier collision model cannot accurately reflect the dynamic behaviors and damage evolution process of collision. In order to solve this problem, a refined barge-whole bridge collision finite element model is established. This model can be used to analyze the dynamic characteristics of barge and whole bridge collision. According to finite element results, the impact force can be divided into four phases: (1) Linear elastic phase, (2) Buckling unstable phase, (3) Plastic deformation phase and (4) Unloading phase. The impact velocity and barge mass change the initial kinetic energy of the barge, which is positively correlated with the peak impact force and the duration of the impact force. Compared with the barge-single pier collision model, the barge-whole bridge collision model is more systematic and comprehensive in reflecting the dynamic behavior of collision. In this paper, the research of barge-bridge collision provides a scientific basic theoretical basis for the design of anti-collision facilities, the proposal of post-collision damage assessment techniques and the development of bridge post-collision warning system
Analysis of vibration characteristics of rotating parallel flexible manipulator considering joint elastic constraints
Get PDFThe bolt joint is the key component connecting the rigid moving base body and the flexible manipulator. The dynamic characteristics of the flexible manipulator under the elastic constraint of the joint are analyzed, and the action mechanism of the elastic constraint of the bolt joint on the frequency and vibration mode is revealed. Considering the effects of line constraint and torsion constraint, the elastic constraint model of the joint is established. Based on the principle of virtual work, the boundary constraints of the joint end and the free end are established, and the analytical equation of frequency and the expression of vibration mode function are derived. The first three frequencies and vibration mode characteristics of the flexible manipulator under elastic constraints are analyzed numerically. The sensitivity method is used to analyze the effect of linear constraints and torsional constraints on the frequency, and the elastic constraint region is established to characterize the functional relationship between the binding stiffness and the natural frequency. It is found that under elastic constraints, the influence of torsional stiffness of bolt joint is mainly concentrated in the low-order modal frequency, while the linear stiffness has a great influence on each order modal frequency of the manipulator; With the decrease of elastic constraint stiffness, its influence on modal shapes gradually increases, especially on high-order modal shapes. The research results prove the internal mechanism of the influence of elastic constraints on vibration characteristics, which provide a theoretical basis for improving the dynamic characteristics of flexible manipulator