Stress shielding-induced bone resorption around cementless acetabular components has been indicated as a potential failure mechanism that may threaten long-term fixation. Using a bone remodelling algorithm in combination with threedimensional finite element models of intact and implanted pelvises and musculoskeletal loading during normal walking, the objectives of the study were to investigate the deviations in load transfer due to implantation and bone adaptation around cementless metallic and ceramic acetabular components. Variations in implant-bone interfacial condition affected strain shielding and bone remodelling; strain shielding was higher for the bonded condition as compared to the debonded condition. For bonded interfacial condition, severe bone resorption, 20%-50% bone density reduction, was observed within the acetabulum. Considering debonded implant-bone interface, bone density increase of 50%-60% was observed around the supero-posterior part of acetabulum, whereas bone density reductions were low (2%-15%) in other locations. The implant-bone interface appeared less likely to fail, post-operatively and after bone remodelling. Moreover, the implant-bone micromotion was found to be low, less than 100 mm. Strain shielding and bone remodelling were almost similar for the metallic and ceramic components. Based on the results of this study, the ceramic acetabular component appeared to be a viable alternative to metal.

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Fixation of uncemented implant is influenced by peri-prosthetic bone ingrowth, which is dependent on the mechanical environment of the implant-bone structure. The objective of the study is to gain an insight into the tissue differentiation around an acetabular component. A mapping framework has been developed to simulate appropriate mechanical environment in the three-dimensional microscale model, implement the mechanoregulatory tissue differentiation algorithm and subsequently assess spatial distribution of bone ingrowth around an acetabular component, quantitatively. The FE model of implanted pelvis subjected to eight static load cases during a normal walking cycle was first solved. Thereafter, a mapping algorithm has been employed to include the variations in implant-bone relative displacement and host bone material properties from the macroscale FE model of implanted pelvis to the microscale FE model of the beaded implant-bone interface. The evolutionary tissue differentiation was observed in each of the 13 microscale models corresponding to 13 acetabular regions. The total implant-bone relative displacements, averaged over each region of the acetabulum, were found to vary between 10 and 60 μm. Both the linear elastic and biphasic poroelastic models predicted similar mechanoregulatory peri-prosthetic tissue differentiation. Considerable variations in bone ingrowth (13-88%), interdigitation depth (0.2-0.82 mm) and average tissue Young's modulus (970-3430 MPa) were predicted around the acetabular cup. A progressive increase in the average Young's modulus, interdigitation depth and decrease in average radial strains of newly formed tissue layer were also observed. This scheme can be extended to investigate tissue differentiation for different surface texture designs on the implants.

Torque ripple modelling and minimization for interior permanent magnet synchronous machines (IPMSMs) requires accurate information of the inductances which vary nonlinearly due to magnetic saturation. However, existing approaches fail to consider the magnetic saturation and thus their performance is limited under different load conditions. Therefore, this paper improves the torque ripple model by considering magnetic saturation, and employs this model for optimal current design to improve the performance of torque ripple minimization for IPMSMs under different load conditions. At first, numerical studies are performed to analyze and understand how magnetic saturation affects the torque ripples in IPMSMs. Then, a novel torque ripple model for IPMSMs is developed, in which the inductance term is replaced by exploring the machine electrical model. This improved torque ripple model is computation-efficient and it can provide fast and accurate torque ripple prediction. Based on this model, a genetic algorithm (GA) based optimal stator current design approach is proposed to minimize the torque ripple in IPMSMs. The proposed GA-based approach can adaptively optimize the stator current under different load conditions, which can guarantee the robust performance of torque ripple minimization under different saturation levels. The proposed approach is validated through experimental test on a laboratory IPMSM drive system. Index Terms--Geneticalgorithm, magnetic saturation, optimal stator current design, torque ripple modeling and minimization I. NOMENCLATURE t total Total torque T 0 Average torque t h Harmonic torque t cog Cogging torque t ecc Torque induced by cross-coupling effect L d , L q dq-axis inductances L dq , L qd dq-axis mutual inductances . Her research areas include modelling, control and testing of permanent magnet machines and switched reluctance machines. Guodong Feng (M'15) received the B.S. and Ph.D degrees in Engineering

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