Maintenance, Reliability and Condition Monitoring
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An on-line monitoring method for the flow excitation in francis hydraulic turbine based on dynamics
Get PDFDuring the operation of hydraulic turbine, the vibration often exceeds the standard due to flow excitation, which affects the safe and stable operation of the hydraulic turbine. In this paper, an on-line monitoring method for the flow excitation in Francis hydraulic turbine is proposed based on the dynamic characteristics of Francis hydraulic turbine. Firstly, based on the flow excitation characteristics in Francis hydraulic turbine and the dynamic equation of main shaft system, the internal relationships between the dynamic response of turbine bearing and the flow excitation in the Francis hydraulic turbine are clarified. Secondly, according to these relationships, a method based on wavelet transform (WT), particle swarm optimization (PSO), and variational mode decomposition (VMD) is proposed for extracting the flow excitation features in Francis hydraulic turbine. Then, by this method, the flow excitation features are acquired. Based on the obtained flow excitation features, the flow excitation can be monitored on-line. Finally, the proposed on-line monitoring method for the flow excitation in Francis hydraulic turbine is verified by experiments. Based on the results, the flow excitation components in the signal extracted by this method are about 35 % more than those extracted by the previous methods. The results show that the on-line monitoring method proposed in this paper is convenient and effective
Nonlinear dynamic behavior analysis of bridge pier impacted by a moving barge
Get PDFThe 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
Skull base flexion and its influence on chewing
Get PDFSkull base asymmetries can occur in the intrauterine period, manifesting from birth as craniofacial asymmetries and should be investigated both in the maxilla and mandible and in the craniofacial region, as they are related to the base of the skull. The objective of this study was to explain that treatment using Craniofacial Biodynamics (CFBD) enables symmetrical craniofacial growth, being recommended from three to six years of age, when the processes of skull base remodeling cease. This study was based on exploratory bibliographic research, aiming at a better understanding of the concepts presented in this therapeutic approach, to verify the influence that such concepts exert on treatment through CFBD. It was evidenced in this research that these asymmetries may be corrected, or even minimized through the CFBD, which relates the ontogenetic development of the skull base with orofacial development
Treatment of vertical problems with jaw functional orthopedics based on scientific evidence. Part 2: deep bite
Get PDFThe vertical problems of the stomatognathic system that alter the overbite, either by increasing in the deep bite (DB) or decreasing in the anterior open bite (AOB), are among the great challenges of the dentofacial corrections in the treatment and the retention and stability protocols. In this paper the state of art of DB treatment with Jaw Functional Orthopedics (JFO) will be discussed. JFO has a unique diagnostic tool for changes in vertical growth of the face, the Articular Compass, developed by Simões. Individuals with hypodivergence and DB are, usually, difficult to treat and more difficult to stabilize the obtained results. Since 1950-decade Planas advocate that the Equiplan – a metal accessory used in functional orthopedic appliances (FOA) is efficient in deep bite treatment by levelling the occlusal plane. Promising results are found with a P = 0,00, but in aweak evidence study design based on the scientific evidence pyramid. Much of the discussion of incisor intrusion or molar extrusion to treat DB seems to be solved with the use of Equiplan, but it still has no scientific evidence, only clinical evidence. In conclusion Randomized Clinical Trials are needed to investigate the efficiency and Modus Operandi of JFO to treat DB
Treatment of vertical problems with jaw functional orthopedics based on scientific evidence. Part 1: anterior open bite
Get PDFThe vertical problems of the stomatognathic system that alter the overbite, either by increasing in the deep bite (DB) or decreasing in the anterior open bite (AOB), are among the great challenges of the dentofacial corrections in the treatment and the retention and stability protocols. It is always good to report that a correct diagnosis is fundamental in the choice of treatment protocol and that skeletal involvement, be it hyper divergence in case of open bite or hypo divergence in case of deep bite, aggravates the problem and as a rule tends to increase treatment and containment time. In this paper the state of art of AOB treatment with Jaw Functional Orthopedics (JFO) will be discussed. It should be emphasized that JFO has a unique diagnostic tool for changes in vertical growth of the face, the Articular Compass, developed by Simões. Studies show that the use of treatment protocols developed by Simões, the SNs (SN2, SN3, SN6) act in the increase of overbite efficiently (P= 0.003) in cases of open bite. This is weak evidence, due to the design of the study, but with promising results, so Randomized Clinical Trials are needed to investigate if these results are replicable
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
Successful balance of occlusal plane using functional orthopedics appliance
Get PDFIn this article, the treatment of two clinical cases is presented, in which the two patients showed distocclusion, severe overbite, required correction of the occlusal plane and movements of the mandible. Both were treated with functional orthopedic appliances In the first case. the patient was 4 years and 5 months old, and in second, 10 years 10 months old. Both had a significant pathological occlusal plane with a large difference in the height between the right and left sides. The lateral movements of the mandible showed completely different Functional Masticatory Angle Planes. The protrusion and opening movements of the mandible also showed deviation. The Functional Orthopedic appliance would advance the position of the mandible forward and would produce better responses if it were able to touch the incisors in the specific area. The forward mandibular position would activate the Ihh (Indian Hedgehog) and produce replication of the mesenchymal cells in the condyle and glenoid fossa. Moreover, it could produce an increase of mandibular length, and regulate the factors of mandibular condylar growth. The space produced between the occlusion as a result of the change to the forward mandible position must stimulate tooth eruption to correct the curve of the occlusal plane. Both cases showed balance of the occlusal plane and same functional masticatory angle Planes. Furthermore, the protrusion and opening movement of the mandible were corrected and no longer showed deviations. Note in both cases that the stability of the mandibular advancement occurred due to maintenance of twice as long to achieve incisor contact
Carbon deposition fault diagnosis of small piston engine based on optimized VMD
Get PDFAiming at the small piston engine carbon deposition fault in the process of running, based on the cylinder pressure and cylinder head vibration signal of the engine, a fault diagnosis method combining variational mode decomposition and support vector machine is used to diagnose the engine carbon deposition fault. Firstly, particle swarm optimization algorithm is used to optimize the parameters of the variational mode decomposition. Then, the intrinsic mode function is obtained by processing the pressure signal and cylinder head vibration signal of the engine. Then, the singular spectrum entropy is calculated by singular value decomposition of the intrinsic mode function. Finally, the singular spectrum entropy is input into the support vector machine classifier as the feature data set for training and testing. The results show that this method can identify the carbon deposition fault of the starting motor well, and the accuracy of fault identification and classification of cylinder pressure and cylinder head vibration signal is 98.33 % and 99.17 % respectively, which verifies the effectiveness of this method
Study on bearing mechanical and thermal characteristic evolvement rules affected by higher ambient temperature
Get PDFIn this paper, the bearing mechanical characteristics and thermal characteristics as it is running under constant speed (2400 r/min) and constant temperature (100 ℃) adopting bearing mechanical-thermal coupling model built on the basis of quasi-statics and elastohydrodynamic lubrication theory are discussed. Among which, the contact deformation between ball and inner/outer ring has same evolution law, besides, the same as the amplitude. Whose curve shape changes in the form of “circular-oblique D”, its amplitude rearches minimum value at 10thd3h between the location of 120° and 270°. The curve shapes belonging to contact angular between ball and inner/outer ring are similar to “circular”. There is opposite trend of them within the range of 90-300°. The amplitude of contact angular between ball and outer ring is the minimum at 10thd3h and 11thd1h. At the same time, the amplitude of that between ball and inner ring is the maximum. The evolution rules of contact stiffness between ball and inner/outer ring are generally consistent, which are similar to “crab”. But the amplitude of that between ball and outer ring is dominant. The maximum value of them occurs at 10thd3 and 11thd1h. The evolvement tendency of node temperatures maintains stable. Thereinto, the temperature of inner ring equals to that of contact location between ball and inner ring, which is the maximum value. It is obvious that ME, MD, MS, MCB, MCR and MOil devote themselves to heat production, the contribution rates of ME, MS, MCB and MCR are 100 %, the contribution rate of MD ranges from 52.6 % to 65.2 %. However, the amplitudes of friction moments have the opposite trend compared to “heat contribution factor”. The expansion amount owing to heat production is dominant in displacement variation and the effect of clearance on displacement can be ignored, whose evolution rules are contrary. The evolution rules of oil film thickness and oil film stiffness between ball and inner/outer ring are alike. Among which, the oil film thickness between ball and outer ring is dominant, its maximum value emerges at 10thd3h. The curve shapes of oil film stiffness between ball and outer/inner ring are oblique “D”, their amplitudes reach the maximum at 11thd1h-11thd3h
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