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The purpose of this paper is to analyze the time-dependent reliability of harmonic drive.

The transient finite element analysis (FEA) of harmonic drive is established to calculate the stress under different loads. Combined with the residual strength model and random variables, the time-dependent reliability model of harmonic drive is deduced by the stochastic perturbation method and Edgeworth series. Based on accelerated life tests, the degradation parameters are estimated by maximizing likelihood function. Under variable load, the key stress from transient FEA is transformed into probability density function by kernel density estimation, and the residual strength model is modified by adding adjustment factors to deal with strength degradation under different loads.

The critical position of stress concentration from transient FEA is consistent with the fatigue fracture position at the accelerated life test sample. Compared with the time-dependent reliability method with equivalent circular-shell static stress or empirical degradation parameters, the proposed method has the smallest prediction error of failure life. Under variable load, the state function should be expanded to second-order series for avoiding error items relevant to variance. The failure life expectation under random variable load is smaller than that under constant load.

The time-dependent reliability method of harmonic drive is firstly proposed under constant and variable load. The transient FEA of harmonic drive is established to calculate the stress for strength analysis. The accelerated life test of harmonic drive is conducted for degradation parameters estimation. The adjustment factor is added to the residual strength model for strength degradation under different loads.

Induction machines for traction applications are operated at working points of high ferromagnetic saturation. Depending on the working point, a broad spectrum of harmonic frequencies appears in the magnetic flux density of induction machines. Detailed loss analysis therefore requires local and temporal highly resolved nonlinear field computation. This loss analysis can be performed in the post processing of nonlinear transient finite element simulations of the magnetic circuit. However, it takes a large number of transient simulation time steps to build up the rotor flux of the machine.

In this paper, hybrid simulation approaches that couple static FEA, transient FEA and analytic formulations to significantly decrease the number of simulation time steps to calculate the magnetic field in steady state are discussed, analyzed and compared.

The proposed hybrid simulation approaches drastically decrease the simulation time by shortening the transient build-up of the rotor flux. Depending on the maximum error of the rotor flux linkage amplitude compared to the steady state value, a reduction of simulation time steps in the range of 55.5 to 98 per cent is found.

The presented hybrid simulation approaches allow efficient performing of the transient FE magnetic field simulations of induction machines operated as traction drives.

The purpose of the paper is to investigate the performance of induction machines with fractional‐slot concentrated‐windings.

This paper examines induction machine performance with fractional‐slot concentrated windings using the standard distributed lap windings as reference. Four designs are compared and various performance tradeoffs highlighted. The first machine has integral‐slot distributed 2 slots/pole/phase lap winding and it serves as the reference winding. The second machine has a double‐layer 1/2 slot/pole/phase winding, a workhorse for brushless DC machines. The third machine has double‐layer 2/5 slot/pole/phase winding. Lastly, the fourth machine has single‐layer 2/5 slot/pole/phase windings. The comparison includes torque‐speed curves (including the effects of major space harmonic components), rotor bar losses, and ripple torque levels.

Based on the analysis results presented here, the traditional distributed lap winding is proven to be superior to FSCW in terms of torque production and rotor bar losses for induction machine applications. The 1/2 spp shows some promising results in terms of torque production, in addition to significant reduction and simplification of end turns with lower number of coils albeit with more turns/coil (12 slots vs 48 slots). The penalty is the additional rotor bar losses due to the 2nd and 4th harmonic mmf components. The 2/5 spp is not promising for torque production and should be avoided. The transient simulation results that simultaneously take into account the effects of all space harmonics and magnetic saturation showed comparable trends compared to the harmonic analysis results. It has also been shown that FSCW tend to have higher torque ripple compared to distributed windings.

To the best of the authors' knowledge, this paper for the first time attempts to quantitatively address the tradeoffs involved in using FSCW in induction machines.

The purpose of this paper is to study the effect of curvature on the magnetic field distribution and no-load rotor eddy current losses in electric machines, particularly in high-speed permanent magnet (PM) machines.

The magnetic field distribution is obtained using conformal mapping, and the eddy current losses are obtained using a cylindrical multilayer model. The analytical results are validated using a two-dimensional finite element analysis. The analytical method is based on a proportional-logarithmic conformal transformation that maps the cylindrical geometry of a rotating electric machine into a rectangular configuration without modifying the length scale. In addition, the appropriate transformation of PM cylindrical domains into the rectangular domain is deduced. Based on this conformal transformation, a coefficient to quantify the effect of curvature is proposed.

Neglecting the effect of curvature can produce significant errors in the calculation of no-load rotor losses when the ratio between the air-gap length and the rotor diameter is large.

The appropriate transformation of PM cylindrical domains into the rectangular domain is deduced. The proportional-logarithmic transformation proposed provides an insight into the effect of curvature on the magnetic field distribution in the air-gap and no-load rotor losses. Furthermore, the proposed curvature coefficient gives a notion of the effect of curvature for any particular geometry without the necessity of any complicated calculation. The case study shows that neglecting the effect of curvature underestimates the rotor eddy-current losses significantly in machines with large gap-to-rotor diameter ratios.

The purpose of this paper is to an analytical approach-based prediction of the eddy current loss in the PMs of a concentrated winding machine equipped with 12 slots in the stator and ten poles in the rotor.

The investigation of the PM eddy current loss has been carried out using an analytical model and a 2D time-stepped transient finite element analysis (FEA).

It has been found, in the case of the treated machine, that just the subharmonic of rank 1 and the harmonic of rank 7 have significant contributions to the eddy current loss in the PMs.

A shift between the results yielded by the developed analytical model and those computed by FEA has been noticed. This limitation is mainly due to the slotting effect which has been omitted in the analytical model.

Fractional slot PM machines are currently given an increasing attention in automotive applications. The prediction of their iron loss in an attempt to rethink their design represents a crucial efficiency benefit.

The analytical prediction of the eddy current loss in each PM then in all PMs and their validation by FEA represent the major contribution of this work.

The thermal behavior at the interfaces (of the deposited strands) during fused filament fabrication (FFF) technique strongly influences bond formation and it is a time- and temperature-dependent process. The processing parameters affect the thermal behavior at the interfaces and the purpose of the paper is to simulate using temperature-dependent (nonlinear) thermal properties rather than constant properties.

Nonlinear temperature-dependent thermal properties are used to simulate the FFF process in a simulation software. The finite-element model is first established by comparing the simulation results with that of analytical and experimental results of acrylonitrile butadiene styrene and polylactic acid. Strand temperature and time duration to reach critical sintering temperature for the bond formation are estimated for one of the deposition sequences.

Temperatures are estimated at an interface and are then compared with the experimental results, which shows a close match. The results of the average time duration (time to reach the critical sintering temperature) of strands with the defined deposition sequences show that the first interface has the highest average time duration. Varying processing parameters show that higher temperatures of the extruder and envelope along with higher extruder diameter and lower convective heat transfer coefficient will have more time available for bonding between the strands.

A novel numerical model is developed using temperature-dependent (nonlinear) thermal properties to simulate FFF processes. The model estimates the temperature evolution at the strand interfaces. It helps to evaluate the time duration to reach critical sintering temperature (temperature above which the bond formation occurs) as it cools from extrusion temperature.

The purpose of this paper is to compare the study between two topologies of fractional-slot permanent-magnet machines such that: double-layer topology and single-layer one. The comparison considers the assessment of the iron loss in the laminated cores of the magnetic circuit as well as in the permanent magnets (PMs) for constant torque and flux weakening ranges.

The investigation of the hysteresis and eddy-current loss has been carried out using 2D transient FEA models.

It has been found that the stator iron losses are almost the same for both topologies. Whereas, the single-layer topology is penalized by higher iron loss especially the eddy-current ones taking place in the PMs. This is due to their denser harmonic content of the armature air gap MMF spatial repartition.

The analysis of the iron loss maps in different parts of each machine including stator and rotor laminations as well as the PMs, in one hand, and the investigation of their variation with respect to the speed, in the other hand, represent the major contribution of this work.

A mathematical description of temperature-dependent boundary conditions is crucial in manifold model-based control or prototyping applications, where accurate thermal simulation results are required. Estimation of boundary condition coefficients for complex geometries in complicated or unknown environments is a challenging task and often does not fulfill given accuracy limits without multiple manual adaptions and experiments. This paper aims to describe an efficient method to identify thermal boundary conditions from measurement data using model order reduction.

An optimization problem is formulated to minimize temperature deviation over time between simulation data and available temperature sensors. Convection and radiation effects are expressed as a combined heat flux per surface, resulting in multiple temperature-dependent film coefficient functions. These functions are approximated by a polynomial function or splines, to generate identifiable parameters. A formulated reduced order system description preserves these parameters to perform an identification. Experiments are conducted with a test-bench to verify identification results with radiation, natural and forced convection.

The generated model can approximate a nonlinear transient finite element analysis (FEA) simulation with a maximum deviation of 0.3 K. For the simulation of a 500 min cyclic cooling and heating process, FEA takes a computation time of up to 13 h whereas the reduced model takes only 7-11 s, using time steps of 2 s. These low computation times allow for an identification, which is verified with an error below 3 K. When film coefficient estimation from literature is difficult due to complex geometries or turbulent air flows, identification is a promising approach to still achieve accurate results.

A well parametrized model can be further used for model-based control approaches or in observer structures. To the knowledge of the authors, no other methodology enables model-based identification of thermal parameters by physically preserving them through model order reduction and therefore derive it from a FEA description. This method can be applied to much more complex geometries and has been used in an industrial environment to increase product quality, due to accurate monitoring of cooling processes.

The purpose of this paper is the fast and accurate modelling of surface-mounted Axial-Flux Permanent-Magnet (AFPM) machines equipped with cylindrical magnets using quasi-3D approach. Furthermore, the accuracy of the method is improved by using leakage coefficient, saturation coefficient and an appropriate permeance function.

Quasi-3D approach is used for fast and accurate modelling of AFPM machines. Air-gap flux density distribution, induced back EMF, and produced cogging torque are calculated using the proposed method with reasonable accuracy.

The results obtained by quasi-3D approach compared to Finite-Element-Analyses (FEA) shows how accurate, fast and efficient this method is. It is proved that, this method can be successfully applied to evaluate the performance of the AFPM machines.

Effectiveness and accuracy of quasi-3D approach is assessed on different AFPM machines. Furthermore, to increase the accuracy of computations, the effects of the magnetic potential drop at iron parts of the machine are taken into account by using a saturation coefficient. Besides, the influence of the slot opening on the flux density distribution is taken into account by using an appropriate relative permeance function.

This paper aims to introduce the moment of inertia of the driving and driven end of the clutch into the analysis of the transient temperature field of a friction plate and studied the influencing factors on that, especially to a marine gearbox.

A three-dimensional transient heat transfer analysis model of a wet clutch friction plate used in a marine gearbox is developed, and the transient characteristics of the temperature field during engagement are analyzed with taking account of the influence factors such as the sliding friction coefficient, engaging revolving speed, moment of inertia and applied engagement pressure.

The paper found out that the hot spot appears on the surface of the friction plate, taking account of the effect of radial slots and spiral groove. To avoid damage to the friction plate as a result of overheating, the appropriate sliding friction coefficient, lower engaging revolving speed and reasonable selection of applied engagement pressure curve can ensure a favorable heating situation of the friction plate. The reasonable structural design for the clutch with a bigger moment of inertia of driving end and smaller moment of inertia of driven end can reduce the engaging time effectively and decrease the peak temperature of the friction plate.

This paper fulfils a method to study the transient temperature field of a wet clutch friction plate, especially used in a marine gearbox.