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In this paper, the boundary discretization method is used to improve the traditional subdomain model. The improved model can be used to calculate the magnetic field distribution in the region containing non-orthogonal boundary, avoiding the influence of the simplified stator slot or permanent magnet shape on the results in calculating the motor magnetic field using the traditional subdomain model. In addition, the improved subdomain model can also be used to calculate the air-gap flux density when the rotor is eccentric, instead of segmenting the air-gap to an equivalent state without eccentricity. The calculation object of this paper is a surface-mount permanent magnet motor with a rectangular stator slot. The air-gap flux density under no-load and load conditions is calculated, respectively. Since the improved subdomain model does not need to simplify the stator slot shape, the magnetic potential in the stator slot is also calculated. Finally, the air-gap flux density under rotor eccentricity is calculated, and the influence of the calculating parameters on the results of the improved subdomain model is discussed. All the calculated results are compared with those obtained by the finite element method, which verifies the accuracy of the improved calculation model. [ABSTRACT FROM AUTHOR]

The textures on the bushing surface have important effects on the performance of journal bearing. In this study, the effects of double parabolic profiles with groove textures on the hydrodynamic lubrication performance of journal bearing under steady operating conditions are investigated theoretically. The journal misalignment, asperity contact and thermal effects are considered, while the profile modifications due to running-in are neglected. The Winkler/Column model is used to calculate the elastic deformation of bushing surface and the adiabatic flow hypothesis is adopted to obtain the effective temperature of lubricating oil. The numerical solution is established by using finite difference and overrelaxation iterative methods, and the rupture zone of oil film is determined by Reynolds boundary conditions. The numerical results reveal that the double parabolic profiles with groove textures with proper location and geometric sizes can increase load carrying capacity and reduce friction loss under steady operating conditions, which effectively overcome the drawbacks of double parabolic profiles. This novel bushing profile may help to reduce the bushing edge wear and enhance the lubrication performance of journal bearing. [ABSTRACT FROM AUTHOR]

A piston slap is one of the main vibration sources of the reciprocating machinery. Much work has been done in this field, most of which was based on a constant rotating speed. However, in practice, the speed of a crankshaft may always fluctuate due to the uneven load or excitation. The inertia forces of moving components are much different at the fluctuating rotating speed comparing with that at a constant speed. In this paper, the piston slap and the induced vibration are analyzed based on the instantaneous angular speed measured on a single-cylinder reciprocating compressor. Firstly, the dynamics of a crank-connecting rod mechanism is analyzed based on the measured instantaneous angular speed which contains the torsional vibration of the air compressor. The time histories of piston slap impact forces considering and without considering torsional vibration are compared. Then, in order to correlate the piston slap impact with the slap-induced vibration, the corresponding transfer functions between the middle stroke of the outer surface of the cylinder liner and the excitation points are measured. And the excitation force on the main bearing is also taken into account to bring the simulation closer to the experimental results. The effects of a torsional vibration on the vibration of the cylinder liner are analyzed, and the simulation results show that the torsional vibration is a factor that must be taken into account in the vibration analysis of the single-cylinder reciprocating compressor. [ABSTRACT FROM AUTHOR]

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]

Torsional vibration of shafts is a very important problem in engineering, in particular in ship engines and aeroengines. Due to their high levels of integration and complexity, it is hard to get their accurate structural data or accurate modal data. This lack of data is unhelpful to vibration control in the form of structural modifications. Besides, many parts in shaft systems are not allowed to be modified such as rotary inertia of a pump or an engine, which is designed for achieving certain functions. This paper presents a strategy for torsional vibration control of shaft systems in the form of structural modifications based on receptances, which does not need analytical or modal models of the systems under investigation. It only needs the torsional receptances of the system, which can be obtained by testing simple auxiliary structure attached to relevant locations of the shaft system and using the finite element model (FEM) of the simple structure. An optimization problem is constructed to determine the required structural modifications, based on the actual requirements of modal frequencies and mode shapes. A numerical experiment is set up and the influence of several system parameters is analysed. Several scenarios of constraints in practice are considered. The numerical simulation results demonstrate the effectiveness of this method and its feasibility in solving torsional vibration problems in practice. [ABSTRACT FROM AUTHOR]

To analyze the torsional vibration of a diesel engine shaft, the torsional stiffness of the flexible coupling is a key kinetic parameter. Since the material properties of the elastic element of the coupling might change after a long-time operation due to the severe working environment or improper use and the variation of such properties will change dynamic feature of the coupling, it will cause a relative large calculation error of torsional vibration to the shaft system. Moreover, the torsional stiffness of the elastic coupling is difficult to be determined, and it is inappropriate to measure this parameter by disassembling the power unit while it is under normal operation. To solve these problems, this paper comes up with a method which combines the torsional vibration test with the calculation of the diesel shafting and uses the inherent characteristics of shaft torsional vibration to identify the dynamic stiffness of the elastic coupling without disassembling the unit. Analysis results show that it is reasonable and feasible to identify the elastic coupling dynamic torsional stiffness with this method and the identified stiffness is accurate. Besides, this method provides a convenient and practical approach to examine the dynamic behavior of the long running elastic coupling. [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]

An improved Fourier expansion-based differential quadrature (DQ) algorithm is proposed to study the free vibration behavior of truncated conical shells with different boundary conditions. The original function is expressed as the Fourier cosine series combined with close-form auxiliary functions. Those auxiliary functions are introduced to ensure and accelerate the convergence of series expansion. The grid points are uniformly distributed along the space. The weighting coefficients in the DQ method are easily obtained by the inverse of the coefficient matrix. The derivatives in both the governing equations and the boundaries are discretized by the DQ method. Natural frequencies and modal shapes can be easily obtained by solving the numerical eigenvalue equations. The accuracy and stability of this proposed method are validated against the results in the literature and a very good agreement is observed. The centrosymmetric properties of these newly proposed weighting coefficients are also validated. Studies on the effects of semivertex angle and the ratio of length to radius are reported. [ABSTRACT FROM AUTHOR]

Understanding the interaction between ring dynamics and gas transport in ring pack systems is crucial and needs to be imperatively studied. The present work features detailed interring gas dynamics of piston ring pack behavior in internal combustion engines. The model is developed for a ring pack with four rings. The dynamics of ring pack are simulated. Due to the fact that small changes in geometry of the grooves and lands would have a significant impact on the interring gas dynamics, the thermal deformation of piston has been considered during the ring pack motion analysis in this study. In order to get the temperature distribution of piston head more quickly and accurately, an efficient method utilizing the concept of inverse heat conduction is presented. Moreover, a sensitive analysis based on the analysis of partial regression coefficients is presented to investigate the effect of groove parameters on blowby. [ABSTRACT FROM AUTHOR]

This paper presents a method for structural modifications for achieving desired eigenstructures based on receptances, by adding multiple mass-spring systems to some locations of the primary system. This method has the benefit that not only neither analytical nor modal models are needed, but also the original mass and stiffness of the primary system are maintained. Moreover, when a complex structure or machine is designed for some special functions so that its inner structure is not allowed to be modified, it is an effective way in practice to achieve desired dynamical performance resulted from adding several external simple substructures. The theory is presented in this paper, which is suitable for linear undamped systems. Numerical experiment is set up, and the results of the modifications are compared with the method proposed by Braun and Ram. Both theoretical derivation and numerical results demonstrate the effectiveness of this method. [ABSTRACT FROM AUTHOR]

In this paper, an analytical technique, the so-called Fourier Spectral method (FSM), is extended to the vibration analysis of a rotating Rayleigh beam considering the gyroscopic effect. The model presented can have arbitrary boundary conditions specified in terms of elastic constraints in the translations and rotations or even in terms of attached lumped masses and inertias. Each displacement function is universally expressed as a linear combination of a standard Fourier cosine series and several supplementary functions introduced to ensure and accelerate the convergence of the series expansion. Lagrange's equation is established for all the unknown Fourier coefficients viewed as a set of independent generalized coordinates. A numerical model is constructed for the rotating beam. First, a numerical example considering simply supported boundary conditions at both ends is calculated and the results are compared with those of a published paper to show the accuracy and convergence of the proposed model. Then, the method is applied to one real work piece structure with elastically supported boundary conditions updated from the modal experiment results including both the frequencies and mode shapes using the method of least squares. Several numerical examples of the updated model are studied to show the effects of some parameters on the dynamic characteristics of the work piece subjected to moving loads at different constant velocities. [ABSTRACT FROM AUTHOR]

Abstract: This paper concerns the free vibrations of cylindrical shells with elastic boundary conditions. Based on the Flügge classical thin shell theory, the equations of motion for the cylindrical shells are solved by the method of wave propagations. The wave numbers are obtained by directly solving an eighth order equation. The elastic-support boundary conditions can be arbitrarily specified in terms of 8 independent sets of distributed springs. All the classical homogeneous boundary conditions can be considered as the special cases when the stiffness for each set of springs is equal to either infinity or zero. The present solutions are validated by the results previously given by other researchers and/or obtained using finite element models. The effects on the frequency parameters of elastic restraints are investigated for shells of different geometrical characteristics. [Copyright &y& Elsevier]

Zircon LA-ICP-MS U-Pb dating of the Jingju syenogranites in the southwestern part of Zhejiang Province shows that these rocks were crystallized in the Late Triassic at 215±2 Ma, rather than in the Cretaceous as previously proposed. The Jingju syenogranites are characterized by relatively high KO and FeO*, and low MgO. They have high concentrations of large ion lithophile elements (LIL) and LREE, such as K, Th, La, and Ce, but are depleted in high field strength elements (HFSE) such as Nb, Ta, and Ti. Their 10Ga/Al ratios and (Zr+Nb+Ce+Y) contents are also high. These characteristics are similar to those of A-type granites. The syenogranites have high I (0.7179-0.7203), low ɛ( t) (from −14.2 to −13.2), and relatively old T ages, similar to those of the ancient metamorphic basement in the Cathaysia Block. It is suggested that the Jingju syenogranites were formed by partial melting of the Cathaysia basement rocks during tectonic extension. This identification of Indosinian A-type granite in Jingju has significant implications for understanding the early Mesozoic tectonic evolution of South China. [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]

This paper deals with reconstruction of excitation forces and analyses of the root causes of vibro-acoustic responses of an elastic structure by using nearfield acoustical holography and modal expansion theory. Derivations of formulations for reconstructing excitation forces, including distributed, line, and point forces, acting on the back side of a rectangular thin plate simply supported on an infinite, rigid baffle, are presented. The reason for choosing a baffled plate is that analytic solutions to vibro-acoustic responses are readily available, so the accuracy in reconstruction can be examined rigorously. For simplicity, the effect of fluid loading is neglected, and input data are assumed error-free. Numerical examples of reconstructing excitation forces are presented, and results agree very well with benchmark values. The impacts of various parameters, such as the ratio of measurement aperture versus plate size, microphone spacing, standoff distance, the number of natural modes, etc., on reconstruction accuracy are investigated. Needless to say, in practice such idealized scenario is nonexistent and the accuracy in reconstruction of excitation forces are severely compromised by measurement errors and interfering signals. Nevertheless, the concept as presented is sound, except that more effective regularizations must be employed to enhance signal to noise ratio, and reconstruction results. [ABSTRACT FROM AUTHOR]

A coupled cell-based smoothed radial point interpolation method is presented by combining the cell-based smoothed radial point interpolation method (CSRPIM) and the modified Dirichlet to Neumann boundary condition (MDtN-BC) to effectively control the dispersion error in predicting acoustic scattering. In the coupled CSRPIM, the MDtN-BC is used to satisfy the Sommerfeld radiation condition approaching infinity, and a cell-based smoothing operation together with the radial point interpolation method (RPIM) is adopted to soften the acoustic stiffness of the numerical model. The condensed RPIM shape functions are created by using real and virtual nodes, and virtual node selection schemes are studied to appropriately soften the stiffness. A major advantage of the coupled CSRPIM is that it can achieve very close-to-exact stiffness of the original model without introducing extra degrees of freedom. The properties of the proposed method are numerically studied. Simulations indicate that the six-virtual-node selection scheme performs the best. The results reveal that the developed method can significantly reduce the dispersion error and has excellent computational performance. In addition, the developed method shows good potential for practical acoustic-scattering prediction in engineering applications. [Display omitted] • A coupled cell-based smoothed RPIM is developed to control the dispersion error. • The developed method is far superior in accuracy and computational performance than FEM. • This method can expand the frequency range without increasing degrees of freedom. [ABSTRACT FROM AUTHOR]

In this paper, the wake and potential flow effects of the rotor–stator interaction in a centrifugal pump with guide vanes are investigated from the view of the separation of turbulent and acoustic pressure fluctuations. The highest vibration levels in pumps are, in general, originated in the potential flow and wake effects. However, it is challenging to distinguish their effects on flow evolution. The pellicular mode decomposition method is applied to innovatively separate potential flow and wake disturbances in a centrifugal pump. By pellicular, we mean an infinitely thin layer of air located on the monitoring surface. The pellicular modes are a set of acoustic modes, with which a set of normalized orthogonal basis can be constructed. The impacts of potential flow and wake disturbances are visualized and evaluated quantitatively. The results show that only a very limited region is where the potential flow disturbance works. The higher the harmonics, the smaller the disturbance range. The wake disturbance is responsible for the modal pressure field. Modal pressure fields with low diametrical nodes decay more slowly than those with low harmonics. In addition, special attention is paid to the impact of the geometric asymmetry of the volute on the impeller force. The circular volute with a two-stage pressure drop improves the radial force of the impeller. More deep understandings on the mechanism of the rotor–stator interaction are reached by decoupling the potential flow and wake disturbances. This work serves as a guide for further research in fault diagnosis and vibration control of centrifugal pumps. [ABSTRACT FROM AUTHOR]

Vibration isolation systems are widely employed in automotive, marine, aerospace, and other engineering fields. Accurate input forces are of great significance for mechanical design, vibration prediction, and structure modification and optimization. One-stage vibration isolation system including engine, vibration isolators, and flexible supporting structure is modeled theoretically in this paper. Input excitation acting on the vibration isolation system is reconstructed using dynamic responses measured on engine and supporting structure under in-suit condition. The reconstructed forces reveal that dynamic responses on rigid body are likely to provide more accurate estimation results. Moreover, in order to improve the accuracy of excitation reconstructed by dynamic responses on flexible supporting structure, auto/cross-power spectral density function is utilized to reduce measurement noise. [ABSTRACT FROM AUTHOR]

In this paper, the mechanism of the rotor–stator interaction in a centrifugal pump with guide vanes is studied numerically and theoretically. The dynamic mode decomposition method is employed to decouple and reconstruct the unsteady flow. A diametrical mode theory suitable for centrifugal pumps with guided vanes is proposed to determine the source of harmonics with higher amplitudes quickly. The results show that the dominant frequencies of the pressure pulsation in the volute and guide vanes are the blade passing frequency and its harmonic frequencies, and the corresponding flow structure is stable and has higher modal energy. The rotor–stator interaction effect around the impeller outlet is most pronounced. The potential flow effect works on the impeller and guide vanes but decays rapidly. The pressure pulsation caused by the wake effect propagates downstream and persists for long distances, which is the main reason for forming the modal pressure field in the volute. The modal reconstruction can reproduce the dynamic evolution process of the pressure field at the characteristic frequencies. The propagation characteristics of the modal pressure field in the volute can be accurately predicted by theoretical analysis. This research can provide an essential reference for fault diagnosis and vibration control of the centrifugal pump. [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]

• A model coupling shaft torsional vibration and advanced injection angle is built to predict engine block vibration. • Formulas of block vibration excitation forces are analyzed and derived by taking in to account the coupling model. • An optimization method for block vibration mitigation by adjusting advanced injection angle is proved. Engine body vibration is an important safety concern for diesel engines as it can lead to severe engine damages and even catastrophic failures. Traditional methods for excitation computation assume that the rotational speed and the cylinder pressure remain stable under each working cycle, which makes it impossible to precisely predict vibration peaks at certain frequencies. But in practice, the existence of shafting torsional vibration will lead to the fluctuation of rotational speed and cylinder pressure. To predict engine block vibration more accurately, this paper proposes a novel method considering the instantaneous variations in rotational speed and cylinder pressure. It is implemented by two steps. Firstly, an innovative model considering the coupling effect between shaft torsional vibration and advanced injection angle is proposed, it particularly explains how the cylinder pressure and instantaneous rotational speed vary due to the coupling effects. Secondly, the excitation forces that cause block vibration are analyzed and their computational formulas are improved. This method also considers the offset of excitation loading position caused by torsional vibration. The coupling model is experimentally verified and the excitations are loaded into a finite element model of the diesel engine for vibration response prediction. The results reveal that the coupled model can predict vibration peaks at sideband frequencies and thus makes the frequency spectrum much richer than that of the traditional method. Furthermore, it shows that the acceleration results obtained by the coupled model have better prediction accuracy than those obtained from traditional methods, with the deviation percentage reducing from 6.31% and 8.41% to 0.64% and 0.32% in the X and Z direction. It indicates that the coupled model is more reliable in predicting the vibration response of the engine block. Finally, the effect of advanced injection angle on engine block vibration is investigated and the optimal value of the advanced injection angle is determined to be 29 CA, which makes the engine block vibration reduced by 3.60%, 2.72%, and 3.16% in the X, Y, and Z direction comparing to the original advanced injection angle. Overall, this study presents an improved approach for predicting engine block vibrations and offers valuable insights for the design of shafting structures and fuel injection parameters in marine diesel engines. [ABSTRACT FROM AUTHOR]

In this paper, the coupling effect between the crankshaft torsional vibration and the low speed diesel engine block vibration is investigated. Using finite element method (FEM), a model of low speed diesel engine is established to study the vibration response. The mode results of FEM agree very well with the test. The additional torques acting on the low-speed diesel engine caused by torsional vibration are discussed in detail. The vibration response of the low-speed diesel engine considering the effect of torsional vibration is studied using FEM simulation. By analyzing the effect of torsional vibration, the results demonstrate that the crankshaft torsional vibrations have important effects on the engine block vibration. The results from this study can provide useful theoretical guidance to predict vibration of low-speed diesel engine. [ABSTRACT FROM AUTHOR]

• Effects of microstructures on the FCP behavior of 42CrMo steel are investigated. • In the later stage of near-threshold and early stage of Paris-regime, FCP rate depends on the single coarse-microstructure. • Roughness-induced crack closure caused by coarse microstructures retards FCP under low ΔK conditions. • FCP behavior in the later stage of Paris-region depends on the microstructure group effects, or overall strength and fracture toughness of materials. Microstructural differences through the thickness have always been an attention focus for large-scale steel structures, since they could significantly influence fatigue crack propagation (FCP) characteristics. Here, the effects of microstructure in FCP behaviors of 42CrMo steel were analyzed with emphasis on two different tempered sorbite/bainite (TS/B) microstructures: (i) fine TS/B structures (M42); (ii) coarse TS/B structures (M52). The results show that the FCP rate is relatively slower for M52 than for M42 in the regime through the later stage of near-threshold (I-L) to the early stage of Paris-regime (Ⅱ-E) with low ΔK, but is fairly similar for the two cases in the other ΔK regimes. Under relatively low ΔK, the FCP path of M52 is more tortuous with numerous micro-cracks in B and larger-sized crack deflections at the carbides and boundaries compared to M42, especially in the I-L where fatigue micro-cracks can deflect at the single coarse carbide, thereby resulting in roughness-induced crack closure and crack retardation behavior. Theoretical analysis shows that FCP behaviors are closely related to the cyclic plastic region size (Δr p) at the crack-tip. In the early stage of near-threshold region, Δr p is restricted within a grain-size scale for both steels, thus leading to a similar FCP rate. However, from the I-L to the Ⅱ-E, coarse B/ferrite-grains in M52 are always larger than the Δr p of fatigue crack-tip, and thereby lead to numerous micro-cracks formation and crack deflections at the carbides and B boundaries, inducing crack closure. In the later stage of Paris region, B/ferrite-grains in the two cases are much smaller than Δr p , so that FCP behaviors depend on the microstructure group effects, or overall strength and fracture toughness of materials, which cause the close FCP rate. [ABSTRACT FROM AUTHOR]

Urbanization is currently considered one of the most rapid types of global environmental change. Urban habitats are biotically and abiotically different from their rural areas, i.e., the ambient temperature, predator, and food availability. These novel challenges create new selection pressures, which allow one to investigate eco-evolutionary responses to contemporary environmental change. A total of 118 breeding nests were monitored for nest predation in both urban and rural areas from 2018 to 2020. We used environmental factors from urban and rural areas and behavioral data from 439 Chinese Blackbird (Turdus mandarinus) valid incubation days to understand the impact of urbanization on the incubation behavior of blackbirds and its adaptation mechanism to the urban environment. Cities have warmer ambient temperatures and lower predation pressures than rural areas. Urban blackbirds chose the incubation strategy with shorter and more bouts, while rural blackbirds selected the incubation strategy with longer and fewer bouts. The plasticity of incubation behavior of urban blackbirds was higher than that of rural areas, and the range of egg temperature was also higher than that of rural areas. In addition, incubation temperature and the number of bouts per day were the key factors affecting the day survival rate of blackbirds, and the hatching rate of urban blackbirds was higher than that of rural blackbirds. Our results provide evidence for behavioral shifts in blackbirds during adaptation to urbanization and support the central role of behavioral adaptation in the successful colonization of new environments by wildlife. These help us understand the behavioral characteristics required for wildlife to live in cities and the urban adaptors faced environmental pressures. [ABSTRACT FROM AUTHOR]

• The eccentric impeller deteriorates the hydraulic performance of the pump. • The clocking position cannot be negligible for hydrodynamic characteristics. • The eccentric impeller affects the flow-induced force at shaft frequency. • The pulsation amplitude is proportional to the eccentricity ratio to some extent. • The shaft orbit of the impeller is closely related to the flow-induced force. In this paper, the effect of impeller eccentricity caused by parallel misalignment of the coupling is considered, and the impact of the impeller eccentricity on the hydrodynamic characteristics of a centrifugal pump is numerically investigated. The finite volume method is adopted to simulate the dynamic process. The results show that the eccentric impeller will deteriorate the hydraulic performance of the pump, nonetheless the influence is limited. However, it significantly affects the amplitude of the flow-induced force at shaft frequency, and the amplitude is proportional to the eccentricity ratio to some extent. The influence of impeller eccentricity on pressure pulsation can be evaluated by the shaft orbit. The crest factor of the impeller trajectory is positively correlated with the pressure pulsation intensity. The minimum value of the impeller trajectory has a negative relationship with the average radial force of the impeller. The clocking position of the eccentric impeller primarily affects the phase relationship between the shaft frequency and the blade passing frequency. A function is proposed to characterize the fluctuating pressure distribution with a spatially periodic pattern around the volute under eccentric conditions. This research can provide an essential reference for fault diagnosis and vibration control of the centrifugal pump. [ABSTRACT FROM AUTHOR]

In this paper, polyacrylic acid (PAA) was used as a growth modifier to control micron-sized barium sulfate particles via a simple precipitation reaction between sodium sulfate and barium chloride at ambient temperature. The barium sulfate particles were exhibited various morphologies, such as monodisperse spheres, ellipsoids, rose-like aggregates, etc. To better understand the formation mechanisms of the various morphologies of these particles, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA) were employed. It was found that the PAA concentration, pH, and Ba 2+ and SO 4 2− ions concentrations were the most important parameters controlling the morphology of the BaSO 4 particles. These parameters affected the BaSO 4 morphology by influencing the interactions between the PAA carboxyl groups and inorganic ions and the conformation change of the PAA molecular chains. Moreover, this work attempts to provide a preliminary understanding of the formation of the spherical BaSO 4 particles with the randomly coiled conformation of the polymer. [ABSTRACT FROM AUTHOR]

Abstract: A mixed-lubrication model has been developed to study tribological characteristics of a marine stern tube bearing. The finite difference method is employed to obtain numerical solutions of the Reynolds equation using combined Newton–Raphson and iterative relaxation methods. The differential equation of deflection curve of the propeller shaft is used to describe the bending deformation of propeller shaft. The displacement superposition method is used to solve the differential equation of deflection. The influences of cavitation and different boundary conditions, the Reynolds boundary condition and Jacobsson–Floberg and Olsson (JFO) boundary condition, as well as the bending deformation of shaft, on the Stribeck Curves are discussed in this paper. [Copyright &y& Elsevier]

• 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]

• A fracture failure of a marine diesel engine timing gear is investigated in detail. • Both experimental and numerical investigations are performed. • Influence of associated structures is considered while analyzing the fracture. • Two models, one is with inclusion and the other is non-inclusion, are constructed. • Results indicate the fracture is a fatigue fracture and is caused by the inclusion. In this paper, a fracture failure of a marine diesel engine timing gear in a chemical tanker was investigated in detail using both experimental analysis and numerical analysis. The experimental analysis includes macroscopical inspection, Scanning Electron Microscope analysis, Energy Dispersive Spectroscopy analysis, metallographic investigation and mechanical property investigation. The numerical analysis includes torsional vibration analysis and finite element method (FEM) simulations. In the torsional vibration analysis, the coupling influence of the associated structures on the timing gear system was taken into account, not only analyzing the fault gear itself. In the FEM simulations, two models, one is with inclusion and the other is non-inclusion, were constructed. Both investigations indicate that the fracture is a fatigue fracture and the initial cracks are caused by the inclusion. Further investigation should pay attention to finding a way to overcome the problem of fatigue fracture. [ABSTRACT FROM AUTHOR]