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The coupling problems between shafting torsional vibration and speed control system of diesel engine are very common. Neglecting the coupling problems sometimes lead to serious oscillation and vibration during the operation of engines. For example, during the propulsion shafting operation of a diesel engine, the oscillation of engine speed and the severe vibration of gear box occur which cause the engine is unable to operate. To find the cause of the malfunctions, a simulation model coupling the speed control system with the torsional vibration of deformable shafting is proposed and investigated. In the coupling model, the shafting is simplified to be a deformable one which consists of several inertias and shaft sections and with characteristics of torsional vibration. The results of instantaneous rotation speed from this proposed model agree with the test results very well and are successful in reflecting the real oscillation state of the engine operation. Furthermore, using the proposed model, the speed control parameters can be tuned up to predict the diesel engine a stable and safe running. The results from the tests on the diesel engine with a set of tuned control parameters are consistent with the simulation results very well. [ABSTRACT FROM AUTHOR]

Two main vibration sources in three-screw pumps , the fluid exciting force and the screw contact force, are studied to provide the basis for vibration control in this paper. A fluid exciting force model and a screw contact model are proposed to calculate these forces. An experimental test is carried out to obtain the vibration response of a three-screw pump. A calibrated finite element model of the three-screw pump is used to verify the vibration response under the fluid exciting force and the screw contact force obtained from the proposed models. The results show that the screw contact force is more dominant than the fluid exciting force. [ABSTRACT FROM AUTHOR]

• A comprehensive stiffness model of intermediate bearing is presented. • A reduced model of dual rotor-bearing-casing coupling system is developed. • The effects of typical parameters on the vibration of the system are discussed. • The mechanism of the comprehensive stiffness and system vibration is revealed. This paper focuses on the vibrational properties of a dual rotor-casing coupled system with nonlinear clearance in the intermediate bearing, considering both the oil film stiffness and Hertzian contact stiffness between rolling elements and raceways. A comprehensive stiffness model for the intermediate bearing has been developed based on elastohydrodynamic lubrication (EHL) and Hertz contact theory. Subsequently, a dynamical model of the dual rotor-bearing-casing system is established using the finite element method, thereby verifying the feasibility of simulating the casing with beam elements. The dimensionality of the system equation is reduced using the fixed-interface component mode synthesis (CMS) method, and the resulting reduced-dimensionality equation is solved using the improved Newmark- β method. The effects of casing support, rotational speed, and radial clearance on the vibration characteristics of the system are investigated. Then, the comprehensive stiffness and coupled vibration characteristics of the system are analyzed to elucidate its intrinsic mechanism. Finally, the contact characteristics within the intermediate bearing under dynamic load are also studied. The results indicate that the support stiffness of the casing has a more significant impact on the second resonance caused by both the inner and outer rotors. The system is prone to experiencing varying compliance (VC) resonance at low rotational speeds. The excessive bearing clearance leads to complex vibrational characteristics of the system, making it challenging to predict its motion. The impact of minor changes in stiffness on system vibration is small when the comprehensive stiffness is large. At this time, the limited effect of oil film stiffness allows it to be disregarded in terms of comprehensive stiffness. Furthermore, the speed significantly influences the contact characteristics within the intermediate bearing under the unbalanced force of the rotor and gravity. [ABSTRACT FROM AUTHOR]

In this paper, an indirect method for measuring torsional vibration of shaft structures is established. In conventional torsional vibration measurement, knowledge of two fundamental quantities is needed: a torque applied to the system and the angle of twist thus produced, which are both difficult to measure in experiment. In this indirect method, neither a deliberate torque excitation system nor an angular transducer is needed. Instead, a T-like beam structure is introduced and attached to one end of a shaft structure whereby the torques are produced by ordinary forces and only linear accelerometers at a few locations of the beam structure are used. Through the small finite element model of the T-like beam structure, the torsional receptance linking the torque to the angle of twist of the shafting systems is derived from the measured receptances of linear acceleration to the excitation force. This indirect theoretical-experimental combined method overcomes the difficulties and the associated poor accuracy in measuring receptances of torsional vibration of shaft structures, and hence is very useful. Numerical simulation of a test structure with noisy parameters and noisy simulated receptance data is made to validate the theoretical soundness of the method. Vibration tests are carried out on a laboratory shaft structure to demonstrate its accuracy and ease of use. [ABSTRACT FROM AUTHOR]

• The control of premixed and late combustion is crucial for marine diesel engine. • An effective procedure is proposed for detecting SOC, SODC and SOLC. • Instantaneous energy concept and peak detection are utilized in this procedure. • This procedure is validated by two different types of marine diesel engines. In order to improve the energy efficiency and suppress the environmental pollutants of marine diesel engines, analysis and control of combustion phases including late combustion phase and premixed combustion phase are considered as an attractive potential strategy. Consequently, it is necessary to accurately identify the combustion parameters that are representative to these combustion phases, such as start of combustion (SOC), start of diffusive combustion (SODC) and start of late combustion (SOLC). The real-time analysis of the combustion phases can be further applied for closed-loop combustion control (CLCC). However, the existing methods can't guarantee the accurate detection of combustion parameters simultaneously even though high computational resources are invested. In this study, the resonance excitation of in-cylinder pressure was found to be capable for identifying all of the three combustion phases parameters. Hence, several effective signal processing techniques were proposed to detect these combustion phases parameters from resonant pressure signal. Without complex mathematic algorithms, the proposed method shows high potential for CLCC since it is relatively easier and faster to achieve than other existing techniques. The accuracy of this method was validated by experimental heat release rate and in-cylinder temperature. Furthermore, based on combustion phase parameters obtained, the estimations of combustion state and energy efficiency were discussed. Finally, this method was also applied for combustion phase detection in another type of marine diesel engine, which verified the robustness of this method. [ABSTRACT FROM AUTHOR]

This paper proposes a unified semi-analytical method for the free in-plane and out-of-plane vibrations of arbitrarily shaped plates with clamped edges. The method is derived using boundary conformal mapping (BCM). The BCM is first proposed here to overcome the mathematical difficulty in describing the clamped boundary conditions of complex or/and irregular shaped plates. Elliptical, rectangular and horseshoe plates with clamped edges are studied to demonstrate the proposed method. After that, another two groups of arbitrarily shaped plates including three polygonal plates and three curve-edged plates are studied. The efficiency of the proposed method is checked through a convergence study. Results from the proposed method agree well with the available results in the literature and with finite element results. All the case studies demonstrate that the proposed method is versatile and gives good accuracy for both the in-plane and out-of-plane vibrations of arbitrarily shaped plates with clamped edges. New results from the proposed method can serve as benchmarks for further study on the vibration of plates, especially of irregular shaped plates. • Free in-plane and out-of-plane vibration solutions for clamped plates are proposed. • Solutions are semi-analytical, generalized and apply to arbitrarily shaped plates. • Boundary conformal mapping (BCM) is introduced to obtain the solutions. • BCM overcomes mathematical difficulty in describing irregular shaped boundary conditions. • BCM method is versatile and has excellent accuracy. [ABSTRACT FROM AUTHOR]

In this paper, an exact analytical solution is proposed to investigate the free in-plane vibration of sector plates. The highly complex and coupled differential equations of in-plane vibration motion are decoupled by invoking Helmholtz decomposition. The method of separation of variables is used to solve the resulting uncoupled Helmholtz equations. Applying the boundary conditions at both radial edges, the compatible eigenvalue problems for sector plates are obtained. Then, applying the boundary conditions at inner and outer circumferential edges, the corresponding characteristic equations can be solved to obtain the natural frequencies and the associated mode shapes. The results from the proposed method agree very well with the results from the available literature and the FEM. Significant influence of the boundary conditions and the geometric parameters on the free in-plane vibration characteristics of sector plates is investigated and addressed. The superficial frequency veering "aberration" between neighboring modes is discussed and found in fact to be an eigenvalue crossing phenomenon. It is proved that for a sector plate, only with simply supported radial edges, there exists an exact analytical solution. The proposed exact analytical solution can provide not only the detailed characteristics of the free in-plane vibration of sector plates but also the benchmark for further study. [ABSTRACT FROM AUTHOR]