Design and Preparation of Bone Tissue Engineering Scaffolds with Porous Controllable Structure

A novel method of designing and preparing bone tissue engineering scaffolds with controllable porous structure of both macro channels and micro pores was proposed. The CAD software UG NX3.0 was used to design the macro channels＇ shape, size and distribution. By integrating rapid prototyping and traditional porogen technique, the macro channels and micro pores were formed respectively. The size, shape and quantity of micro pores were controlled by porogen particulates. The sintered β-TCP porous scaffolds possessed connective macro channels of approximately 500 μm and micro pores of 200-400 μm. The porosity and connectivity of micro pores became higher with the increase of porogen ratio, while the mechanical properties weakened. The average porosity and compressive strength offl-TCP scaffolds prepared with porogen ratio of 60wt% were 78.12% and 0.2983 MPa, respectively. The cells＇ adhesion ratio of scaffolds was 67.43%. The ALP activity, OCN content and cells micro morphology indicated that cells grew and proliferated well on the scaffolds.

Modeling and simulation of CMS04 maglev train with active controller

The application of new-designed levitation controller requires extensive validation prior to enter into commercial service. However, huge mounts of approximations and assumptions lead the theoretical analysis away from the engineering practice. The experimental methods are time-consuming and financial expensive, even unrealizable due to the lack of suitable sensors. Numerical simulations can bridge the gap between the theoretical analysis and experimental techniques. A complete overall dynamic model of maglev levitation system is derived in this work, which includes the simple-supported bridges, the calculation of electromagnetic force with more details, the stress of levitation modules and the cabin. Based on the aforementioned model, it shows that the inherent nonlinearity, inner coupling, misalignments between the sensors and actuators, and self-excited vibration are the main issues that should be considered during the design process of controller. Then, the backstepping controller based on the mathematical model of the module with reasonable simplifications is proposed, and the stability proofs are listed. To show the advantage of controller, two numerical simulation experiments are carried out. Finally, the results illustrating closed-loop performance are provided.

Modeling and Analysis of Mechanical Quality Factor of the Resonator for Cylinder Vibratory Gyroscope

Mechanical Quality factor（Q factor） of the resonator is an important parameter for the cylinder vibratory gyroscope（CVG）. Traditional analytical methods mainly focus on a partial energy loss during the vibration process of the CVG resonator, thus are not accurate for the mechanical Q factor prediction. Therefore an integrated model including air damping loss, surface defect loss, support loss, thermoelastic damping loss and internal friction loss is proposed to obtain the mechanical Q factor of the CVG resonator. Based on structural dynamics and energy dissipation analysis, the contribution of each energy loss to the total mechanical Q factor is quantificationally analyzed. For the resonator with radius ranging from 10 mm to 20 mm, its mechanical Q factor is mainly related to the support loss, thermoelastic damping loss and internal friction loss, which are fundamentally determined by the geometric sizes and material properties of the resonator. In addition, resonators made of alloy 3J53 （Ni42CrTiA1）, with different sizes, were experimentally fabricated to test the mechanical Q factor. The theoretical model is well verified by the experimental data, thus provides an effective theoretical method to design and predict the mechanical Q factor of the CVG resonator.

Compliant landing of a trotting quadruped robot based on hybrid motion/force robust control

A compliant landing strategy for a trotting quadruped robot on unknown rough terrains based on contact force control is presented. Firstly, in order to lower the disturbance caused by the landing impact force, a landing phase is added between the swing phase and the stance phase, where the desired contact force is set as a small positive constant. Secondly, the joint torque optimization of the stance legs is formulated as a quadratic programming(QP) problem subject to equality and inequality/bound constraints. And a primal-dual dynamical system solver based on linear variational inequalities(LVI) is applied to solve this QP problem. Furthermore, based on the optimization results, a hybrid motion/force robust controller is designed to realize the tracking of the contact force, while the constraints of the stance feet landing angles are fulfilled simultaneously. Finally, the experiments are performed to validate the proposed methods.

Parameter identification of inertially stabilized platforms using current command design

Accurate parameter identification is essential when designing controllers for inertially stabilized platforms (ISPs). But traditional identification methods suffer from observation measurement noise and operating restrictions of ISPs. To address this issue, a novel identification method based on current command design and multilevel coordinate search (MCS) algorithm without any higher order measurement differentiations was proposed. The designed current commands were adopted to obtain parameter decoupled models with the platform operating under allowable conditions. MCS algorithm was employed to estimate the parameters based on parameter decoupled models. A comparison experiment between the proposed method and non-linear least square method was carried out and most of the relative errors of identified parameters obtained by the proposed method were below 10%. Simulation and experiment based on identified parameters were conducted. A velocity control structure was also developed with disturbance observer (DOB) for application in disturbance compensation control system of an ISP. Experimental results show that the control scheme based on the identified parameters with DOB has the best disturbance rejection performance. It reduces the peak to peak value (PPV) of velocity error integral to 0.8 mrad which is much smaller than the value (10 mrad) obtained by the single velocity controller without DOB. Compared with the control scheme based on sweep model with DOB compensation, the proposed control scheme improves the PPV of velocity error integral by 1.625 times.

Mathematical modeling and analysis of thermodynamic processes in a twin-rotor piston engine

In order to study the major performance indicators of the twin-rotor piston engine(TRPE), Matlab/simulink was used to simulate the mathematical models of its thermodynamic processes. With consideration of the characteristics of the working processes in the TRPE, corresponding differential equations were established and then simplified by period features of the TRPE. Finally, the major boundary conditions were figured out. The changing trends of mass, pressure and temperature of working fuel in the working chamber during a complete engine cycle were presented. The simulation results are consistent with the trends of an actual working cycle in the TRPE, which indicates that the method of simulation is feasible. As the pressure in the working chamber is calculated, all the performance parameters of the TRPE can be obtained. The major performance indicators, such as the indicated mean effective pressure, power to weight ratio and the volume power, are also acquired. Compared with three different types of conventional engines, the TRPE has a bigger utilization ratio of cylinder volume, a higher power to weight ratio and a more compact structure. This indicates that TRPE is superior to conventional engines.

THEORY AND EXPERIMENTAL INVESTIGAION OF FLEXURAL WAVE PROPAGATION IN THIN RECTANGULAR PLATE WITH PERIODIC STRUCTURE

With the idea of the phononic crystals, a thin rectangular plate with two-dimensional periodic structure is designed. Flexural wave band structures of such a plate with infinite structure are calculated with the plane-wave expansion （PWE） method, and directional band gaps are found in the ΓX direction. The acceleration frequency response in the ΓX direction of such a plate with finite structure is simulated with the finite element method and verified with a vibration experiment. The frequency ranges of sharp drops in the calculated and measured acceleration frequency response curves are in basic agreement with those in the band structures. Thin plate is a widely used component in the engineering structures. The existence of band gaps in such periodic structures gives a new idea in vibration control of thin plates.

3D numerical simulation and structural optimization of the rod baffle heat exchanger

Because of the complexities of fluid dynamics equations and the structure of heat exchangers, few theoretical solutions have been acquired to specify the shell side characteristics of the rod baffle heat exchanger （RBHE）. Based on the platform of PHEONICS version 3.5.1, a three-dimensional numerical method for predicting the turbulent fluid flow behavior in the shell side of the rod baffle heat exchangers is developed in this paper. With this method, modeling of the tube bundle is carried out based on the porous media concept using volumetric porosities and applicable flow resistance correlations. Turbulence effects are modeled using a standard κ-ε model. It is shown that the simulation results and experimental results are in good agreement in the shell side. The maximum absolute deviation value of pressure drops is less than 5%, and that of the heat transfer coefficients is less than 8%. Furthermore, the numerical model is used to optimize the structure of the RBHE and improves its performance.

An Analysis of Structural-Acoustic Coupling Band Gaps in a Fluid-Filled Periodic Pipe

A periodic pipe system composed of steel pipes and rubber hoses with the same inner radius is designed based on the theory of phononic crystals. Using the transfer matrix method, the band structure of the periodic pipe is calculated considering the structural-acoustic coupling. The results show that longitudinal vibration band gaps and acoustic band gaps can coexist in the fluid-filled periodic pipe. The formation of the band gap mechanism is further analyzed. The band gaps are validated by the sound transmission loss and vibration-frequency response functions calculated using the finite element method. The effect of the damp on the band gap is analyzed by calculating the complex band structure. The periodic pipe system can be used not only in the field of vibration reduction but also for noise elimination.

Activation and self-repairing effectiveness of lubrication with nano-tin as additives

Micron grade Sn powder, VG32 oil and active pharmaceutical were mixed and the Nanometer Sn lubricant additives were prepared. Nanometer additives with different Sn concentrations were used in Steel-brass Tribo-pair for friction and wear test. The activating method to nano-Sn and surface of brass samples was investigated, and the method to form relatively thick friction coating on samples was discussed. Surface elemental distribution, coating thickness and its surface appearance were analyzed with X-ray photoelectron spectrum （XPS）, auger electron spectrum （AES） and scanning electron microscope （SEM） respectively. The result shows that the ultra-thick friction coating （approx 20 μm）, with abundant tin and well combined with substrate, has formed on the brass sample. The friction coating revealed superior performance of friction reducing and antiwear properties. Therefore, the results possess practical significance to self-repair usage on steel-brass tribo-pair in mechanical systems.

Response time of variable transparency glass and its application to welding goggles

The behavior of variable transparency glass is studied, and the response time analyzed and measured aimed at applications to welding goggles. Detection apparatus for goggle testing is involved in the design and development. Charac-teristics of the apparatus are discussed based on experiments. The definition of nominal response time and effective response time are presented based on the analysis and calculation with experimental data.

Self-excited vibration problems of maglev vehicle-bridge interaction system

The self-excited vibration problems of maglev vehicle-bridge interaction system were addressed, which greatly degrades the stability of the levitation control, decreases the ride comfort, and restricts the cost of the whole system. Firstly, the coupled model containing the quintessential parts was built, and the mechanism of self-excited vibration was explained in terms of energy transmission from levitation system to bridge. Then, the influences of the parameters of the widely used integral-type proportion and derivation(PD) controller and the delay of signals on the stability of the interaction system were analyzed. The result shows that the integral-type PD control is a nonoptimal approach to solve the self-excited vibration completely. Furthermore, the differential-type PD controller can guarantee the passivity of levitation system at full band. However, the differentiation of levitation gap should be filtered by a low-pass filter due to noise of gap differentiation. The analysis indicates that a well tuned low-pass filter can still keep the coupled system stable.

Analysis of Incomplete Data of Accelerated Life Testing with Competing Failure Modes

Data obtained from accelerated life testing （ALT） when there are two or more failure modes, which is commonly referred to as competing failure modes, are often incomplete. The incompleteness is mainly due to censoring, as well as masking which might be the case that the failure time is observed, but its corresponding failure mode is not identified. Because the identification of the failure mode may be expensive, or very difficult to investigate due to lack of appropriate diagnostics. A method is proposed for analyzing incomplete data of constant stress ALT with competing failure modes. It is assumed that failure modes have s-independent latent lifetimes and the log lifetime of each failure mode can be written as a linear function of stress. The parameters of the model are estimated by using the expectation maximum （EM） algorithm with incomplete data. Simulation studies are performed to check＇model validity and investigate the properties of estimates. For further validation, the method is also illustrated by an example, which shows the process of analyze incomplete data from ALT of some insulation system. Because of considering the incompleteness of data in modeling and making use of the EM algorithm in estimating, the method becomes more flexible in ALT analysis.

Disturbance decoupled fault diagnosis for sensor fault of maglev suspension system

A disturbance decoupled fault diagnosis strategy is proposed.This disturbance decoupled fault diagnosis is both robust to disturbances and sensitive to sensor faults of magnetic levitation control system.First,a robust controller based on a novel disturbance observer is devised to improve the disturbance attenuation ability,which greatly enhances the robustness of the system.Second,a fault reconstruction technique with adaptive method is presented,along with a strict verification for guaranteeing the robustness of fault.This fault reconstruction technique provides an accurate sensor fault reconstruction.From the results of simulation and experiments conducted on the CMS-04 maglev train,the integrated strategy is robust to model uncertainties of the system and the fault reconstruction algorithm is able to reconstruct the dynamic uncertain faults.

Adaptive backstepping control for levitation system with load uncertainties and external disturbances

To explore the precise dynamic response of the levitation system with active controller, a maglev guide way-electromagnet-air spring-cabin coupled model is derived firstly. Based on the mathematical model, it shows that the inherent nonlinearity, inner coupling, misalignments between the sensors and actuators, load uncertainties and external disturbances are the main issues that should be solved in engineering. Under the assumptions that the loads and external disturbance are measurable, the backstepping module controller developed in this work can tackle the above problems effectively. In reality, the load is uncertain due to the additions of luggage and passengers, which will degrade the dynamic performance. A load estimation algorithm is introduced to track the actual load asymptotically and eliminate its influence by tuning the parameters of controller online. Furthermore,considering the external disturbances generated by crosswind, pulling motor and air springs, the extended state observer is employed to estimate and suppress the external disturbance. Finally, results of numerical simulations illustrating closed-loop performance are provided.

Design of Nonlinear Decoupling Controller for Double-electromagnet Suspension System

Aiming at the coupling characteristic between the two groups of electromagnets embedded in the module of the maglev train, a nonlinear decoupling controller is designed. The module is modeled as a double-electromagnet system, and based on some reasonable assumptions its nonlinear mathematical model, a MIMO coupling system, is derived. To realize the linearization and decoupling from the input to the output, the model is linearized exactly by means of feedback linearization, and an equivalent linear decoupling model is obtained. Based on the linear model, a nonlinear suspension controller is designed using state feedback. Simulations and experiments show that the controller can effectually solve the coupling problem in double-electromagnet suspension system.

Combustion simulation and key parameter optimization for opposite axial piston engine in small-scale

As potential alternative power sources used in portable electric generators, opposite axial piston engines in small-scale were investigated to show their advantages in power density. A novel cylinder charge system was introduced, based on which a quasi-dimension model and a CFD(computational fluid dynamics) model were established. Comparison of those two models was carried out to validate the quasi-dimension model. Furthermore, optimal diameter of charge cylinder and speed were determined after evaluating the quasi-dimension model based on different parameters. High agreement between the quasi-dimension model and the CFD model validates the quasi-dimension model. Further studies show that the power of engine increases with the diameter of charge cylinder. However, a too big charge cylinder lowers the fuel efficiency instead. Taking economic influence into consideration the charge cylinder should be 1.4 times power cylinder, which could ensure the power density, volumetric efficiency and fuel economic at the same time. Axial piston engine running at 1.0×104 r/min could achieve a better overall performance. The maximal power of engine with optimal parameters is 0.82 k W, which fits the power need of the portable electric generators completely.

Analysis on structural characteristics of rotors in twin-rotor cylinder-embedded piston engine

Twin-rotor cylinder-embedded piston engine is proposed for dealing with the sealing problems of rotors in twin-rotor piston engine where the existent mature sealing technologies for traditional reciprocating engine can be applied.The quantity and forms of its sealing surfaces are reduced and simplified,and what's more,the advantages of twin-rotor piston engine are inherited,such as high power density and no valve mechanism.Given the motion law of two rotors,its kinematic model is established,and the general expression for some parameters related to engine performance,such as the trajectory,displacement,velocity and acceleration of the piston and centroid trajectory,angular displacement,velocity and acceleration of the rod are presented.By selecting different variation patterns of relative angle of two rotors,the relevant variables are compared.It can be concluded that by designing the relative angle function of two rotors,the volume variation of working chamber can be changed.However,a comprehensive consideration for friction and vibration is necessary because velocity and acceleration are quite different in the different functions,the swing magnitude of rod is proportional to link ratio λ,and the position of rod swing center is controlled by eccentricity e.In order to reduce the lateral force,a smaller value of λ should be selected in the case of the structure,and the value of e should be near 0.95.There is no relationship between the piston stroke and the variation process of relative angle of two rotors,the former is only proportional to the amplitude of relative angle of two rotors.

Saturation influence of control voltage on maglev stationary self-excited vibration

This work addresses the saturation influence of control voltage on the occurring of self-excited vibration of maglev vehicle-bridge interaction system, which greatly degrades the stability of the levitation control, decreases the ride comfort, and restricts the cost of the whole system. Firstly, the interaction model of vehicle-bridge system is developed. Based on the interaction model, the relationship between the control voltage and vibration frequency is solved. Then, the variation of the effective direct component and fundamental harmonic are discussed. Furthermore, from the perspective of energy transmission between the levitation system and bridge, the principle underlying the self-excited vibration is explored, and the influence on the stability is discussed. Finally, in terms of the variation of the characteristic roots, the influence is analyzed further and some conclusions are obtained. This study provides a theoretical guidance for mastering the self-excited vibration problems.