Mechanical Engineering Journal Vol. 4(2017) No. 4

In the MFBD (Multi-Flexible-Body Dynamics) (RecurDyn, 2017), the contact analysis is very important. To develop the general purpose contact algorithm for rigid and flexible bodies, the Generalized Geometry Contact algorithm, which is called ‘Geo Contact', has been developed by Choi's (Choi et al., 2013), (Choi and Choi, 2012), (Choi, 2009) for the contact problems between the rigid and flexible bodies with the general shaped geometries. In the previous researches, the nodal approach for flexible body was considered. But, the flexible body is classified as two types. The one is a nodal flexible body based on the Finite Element Method and the other is a modal reduction flexible body. The modal reduction flexible body is widely used in the MFBD system for the efficient analysis for small deformation problems. In order to get a flexible body of modal reduction, the CMS (Component Mode Synthesis) analysis of Craig-Bampton's (Craig and Bampton, 1965) is widely used. Therefore, in this study, we will expand the existing contact algorithm to the modal reduction flexible body. The node of the modal reduction flexible body can be deformed like as the nodal flexible body. Therefore, the contact algorithm is similar to the nodal flexible body. We made two interface functions in pre and post processing in the previous Generalized Geometry Contact (Geo Contact) algorithm in order to support the contact for the modal reduction flexible body. Consequentially, this method can be applied for various contact cases with three types of bodies. There are total six cases using three types of bodies such as (1) rigid-rigid body, (2) rigid-nodal flexible body, (3) rigid-modal reduction flexible body, (4) nodal flexible-modal reduction flexible body, (5) nodal flexible-nodal flexible body, and (6) modal reduction flexible-modal reduction flexible body. We will show that whole contact cases work well with Generalized Geometry Contact algorithm with some examples.

To reduce the collision shock and risk of injury to an infant in an in-car crib (or a child safety bed) during a vehicle crash, it is necessary to limit the force acting on the crib below a certain allowable value. To realize this objective, we propose a semi-active in-car crib system with the joint application of regular and inverted pendulum mechanisms. The crib is supported by an arm similar to a pendulum, and the pendulum system itself is supported by an arm similar to an inverted pendulum. In addition, the arm acting as a regular pendulum is joined with the arm acting as an inverted pendulum through a linking mechanism, and the friction torque of the joint connecting the base and the latter arm is controlled using a brake mechanism, which enables the proposed in-car crib to gradually increase the deceleration of the crib and maintain it at around the target value. This system not only reduces the impulsive force but also transfers the force to the infant’s back using a spin control system, i.e., the impulse force is made to act perpendicularly on the crib. The spin control system was developed in our previous work. The present work focuses on the acceleration control system. A semi-active control law with acceleration feedback is introduced using a dynamic equation for the jerking of the crib. In addition, the effectiveness of the system is demonstrated using numerical software for a multibody dynamics simulation, and some of results are reported.

This paper proposes a novel control technique for a new panel quasi-static deployment and retraction method using electromagnetic force. This panel system is modeled as a multibody dynamic system which will be used for numerical simulations. Although the electromagnetic deployment has various beneficial points, it still has a major technical issue that vibration on panels continues for a certain time, and hence its motion does not converge quickly. To eliminate or damp these vibrations, we propose both feed-forward and feedback control methods using magnetism generated by electronic current. These methods can successfully reduce convergence time of deployment motion by at most 60 percents. Additionally, to realize feedback control, it is required to estimate the state variables of panels, that is, the angle between the panels. For that purpose, we introduce a new approach to determine these angles by sensing electromagnetic field generated by the deployment system with a magnetometer. This new method accomplishes the determination of the angles between the panels to an accuracy of at worst four degrees and one degree on average.

The purpose of the present study is to propose an analytical model for tires and to examine the mechanism of polygonal wear based on numerical results obtained using this model. Polygonal wear is an abnormal phenomenon that occurs in time-delay systems. A number of studies on polygonal wear of tires have been conducted. However, investigation of the growth process of polygonal wear is not sufficient because the surface shape of the tire changes constantly with wear. Therefore, a numerical simulation model that can examine transient behavior is necessary. In the present paper, we propose a tire model composed of mass points. The wheel is simulated as a rigid body, and the tire tread as a number of masses positioned around the circumference of the wheel. The tire masses are connected to points around the circumference of the wheel by rotational and translational Voigt elements, and the tire masses are connected by rotational and translational Voigt elements. The contact between the tire and the road surface is assumed to be elastic. Numerical simulations are carried out under several conditions using the proposed model. The distributions of the stress and the slip ratio are obtained, and the wear shapes of tires are examined using the proposed model. We show that polygonal wear occurs under certain conditions. Finally, a tire model that expresses these basic characteristics is proposed and its usefulness is demonstrated.

Although more than 55 years have been passed since its first development, it remains unknown whether a posicast-shaped function (PSF) is a unique intermittent input command for a one-time rapid rest-to-rest motion in one natural period. In addition, it has not been determined whether more generalized expressions exist. We recently deduced an intermittent input command of a feedforward formula, called a vibration manipulation function for one natural period (oVMF), to manipulate an undamped 1-DOF linear floating oscillator in an arbitral operational period based on the dynamics of three vibro-impact oscillators under a Grover algorithm in the field of quantum information. As a special case of oVMF, we can define the formula of an input command for a rest-to-rest motion in one natural period, called roVMF. In this study, we proved that any PSF for an undamped 1-DOF oscillator (uPSF) can be expressed as an infinite series of roVMF. Moreover, because uPSF has a stricter symmetrical property than roVMF, we have concluded that the set of uPSF, U_up, is contained in the set of roVMF, U_roV. Hence roVMF is a more general expression than uPSF.

Accurate modeling of a flexible body must take into account motion with large deformation, rotation and time-varying length. Numerical analysis, employing a variable-domain finite element model and the absolute nodal coordinate formulation, has been used to model such motion. Unfortunately, the calculation cost of this approach is very high due to the use of nonlinear finite elements with time-varying length. In order to the reduce calculation cost without sacrificing accuracy, we apply the multiple timescale method to the equation of motion. We define three timescales for the multiple timescale method, and refer to them as Cases 1, 2, and 3. Case 1 is based on longitudinal vibration, Case 2 is based on lateral vibration, and Case 3 is based on motion of the rigid pendulum. We compare these three sets of timescales and evaluate the analysis range for each of the sets. The numerical results show that Case 1 delivers the best accuracy when the velocity of the time-varying length is high, whereas Case 2 delivers the quickest calculation time.

This paper describes optimum values of an electrical circuit for energy harvesting using a beam and piezoelectric elements. Energy harvesting techniques recover energy from the environment. We target the energy harvesting methods that extract energy from mechanical vibration systems in this research. Vibration energy is usually extracted through electrical circuits using electromechanical transducers such as DC motors and piezoelectric elements. In order to extract energy effectively, these electrical circuits and additional vibration systems must be optimally tuned. The optimum values of an electrical circuit and additional vibration system can be derived based on impedance matching when a vibration source includes only a single excitation frequency; however, in certain cases, vibration sources include several excitation frequencies. The optimum values derived based on impedance matching are not optimum when the vibration source includes several excitation frequencies. Therefore, we additionally investigated the case of random excitation as a representative of such cases in this research. The optimum values for the case of random excitation are also effective for the cases of free vibration including impulse excitation. The governing equations were formulated using equivalent mechanical models in this research. The combination of a beam and a piezoelectric element was used as the piezoelectric energy harvester because the thorough formulation of the governing equations for this configuration was not found in the research literature. The optimum values of the electrical circuit and additional vibration system were derived using the governing equations. The effectiveness of the optimum values was verified through numerical calculations.

Recently, several types of nursing care equipment to aid the lifting and transfer of aged persons have been developed. Especially, rotational boom-type care lifts are used widely because of their simplicity and usefulness. However, such lifts sometimes provide a feeling of uneasiness because during lift-up, the center of the human body moves backward relative to the position of the heel. Hence, in this paper, we first propose a telescopic boom-type care lift to approximate the trajectory of the lift-up motion of a human standing up naturally. By using a multibody dynamics approach, we show that the proposed mechanism can achieve nearly natural standing-up motion and requires a smaller force for lift-up than that required by the conventional-type lift. Next, we develop a prototype telescopic boom-type care lift and verify experimentally that the proposed lift can reduce mental and physical burden compared with the conventional lift. To compare mental burden, we conduct a sensory evaluation by administering a questionnaire. To compare physical burden, we estimate muscle activation based on users' electromyographic signals. These results show the effectiveness of the proposed telescopic boom-type lift. Finally, we consider the optimal design of the proposed care lift structure. We propose an algorithm to seek optimal design parameters that minimize the error between the tip trajectory of the lift and the human chest trajectory measured using a motion capture system.

The rights-of-way of urban railway systems contain many sharp curves. Since sharp curves can contribute to wheel and rail wear, the ability to predict the development of wheel wear is crucial to maintaining safe operation of such systems. Observation of wear development in practical railway systems is inefficient and time consuming. In order to efficiently predict wheel wear, numerical analysis using multi-body dynamics software, such as Simpack, is proposed. Contact pressure, slip ratio, and other necessary parameters are determined from Simpack's vehicle motion analysis. Wear depth is derived to create a worn wheel profile. The current wheel profile is updated using the wear profile, and is then adopted as the new wheel profile in Simpack. The rail vehicle modeled in our numerical analysis is based on a typical Japanese commuter rail vehicle. Wear depth is calculated based on the Archard wear theory. Wear development in the wheel/rail contact area is calculated, and nodes are replaced by calculated wear depth. Validity of the wear coefficient used in the simulation is discussed. The results of the numerical analysis are compared with experimental results to assess the amount of wear from the viewpoint of mechanical and tribological contact problems.

The fatigue life of austenitic stainless steel is significantly reduced in the environment of a pressurized water reactor (PWR). One of the methods for evaluating the environmental effect involves the use of the environmental correction factor (F_en) determined from the fatigue lives of the material in air and the PWR environment. It has been reported that the environmental correction factor increases with decreasing strain rate, eventually saturating at a low strain rate. However, the exact behavior of the parameter remains unclear considering evidences of a relationship between environmentally assisted fatigue and stress corrosion cracking. It is therefore of importance to examine the possibility of continuity between environmentally assisted fatigue and stress corrosion cracking at very low strain rates. In the present study, time domain analyses of short fatigue cracks initiated in 316 stainless steel in air and simulated PWR water were used to ascertain the existence of such continuity by investigating the relationship between the environmentally assisted fatigue and stress corrosion cracking. The acquired environmentally assisted fatigue life data were uniquely interpreted, and superposition of the plots of the stress corrosion cracking data obtained by slow-strain-rate tensile tests over the time domain analyses and environmentally assisted fatigue data suggested continuity among the parameters. This was clearly substantiated by further time domain analyses.

Transformation plasticity significantly affects the stress distribution of a forging after heat-treatment. In this study, the transformation plasticity in a multi-phase transformation was measured experimentally. Two kinds of low-alloy steels were used: ASME SA508 and JIS SCM420. The materials were heat treated under different conditions to vary the phase fraction of ferrite. Then the transformation plastic strains of bainite were experimentally identified from the deviation between the stress-free total strain value and the strain value with an applied stress. After the tests were finished, an orientation microscopy was performed using EBSD. The grain average misorientation (GAM) values of the bainite phase become higher than those of the ferrite phase due to the bainite sub-unit. The volume fractions of ferrite were defined as the area lower than the threshold value of the GAM. The transformation plastic strain during the bainite transformation decreased with increasing volume fraction of ferrite. Although there is a quantitative difference in the transformation plastic strains between SA508 and SCM420, the normalized values give the same tendency in both materials. Furthermore, the calculated transformation plasticity using a multi-phase model shows a good agreement with the measurements. This result suggests that the transformation plasticity behavior of the bainite transformation is the same as between a single transformation (bainite) and a double transformation (bainite and ferrite).

In this paper, collision-free guidance control of multiple small unmanned aerial vehicles (SUAVs) is designed. Collision avoidance of the SUAVs should be considered in the control system design for safe operation. Therefore, a guidance control system using a distributed model predictive control (DMPC) is proposed to realize the collision avoidance. A constraint for the relative position vector between the each UAV is considered in the design for efficient avoidance. Small multi-rotor helicopter is considered as controlled object, and the guidance control system is designed by using the translational model of the helicopter. DMPC is designed with three constraints, an input constraint, a state constraint, and a relative position vector constraint. An input constraint and a state constraint realize collision avoidance in input within the constant limits. If the moving path of the one helicopter is significantly affected by the moving path of other helicopter, the relative position vector constraint makes the helicopters exchange their relative position each other. By using these constraints, smooth collision avoidance is realized. The numerical simulation and flight experiment is conducted to verify the effectiveness of designed control system.

This paper discusses the stability of a tilt-controlling axial gap self-bearing motor with a single stator. The motor consists of a stator and a disc rotor and is capable of controlling motor torque, axial position, and tilt angles. The stator has six coils, which are driven by separate amplifiers. By adding two types of current (a motor current, which has the same poles as the rotor, and a tilt control current, which has plus two or minus two poles of the rotor), four degrees of freedom of the rotor can be actively controlled. In this paper, the motor torque, axial force, tilt torques, and radial forces are theoretically analyzed and their control methods of them are derived. The stability of the rotor is discussed and the influence of the position of the center of gravity is shown. The experimental results confirm the analytical results, and it is shown that the stable levitation and rotation are achieved with 2-pole and 4-pole rotors.

In this study, we propose a novel endoscopic manipulation system that is controlled by a surgeon's eye movements. The optical axis direction of the endoscopic manipulator is altered intuitively based on the surgeon's pupil movements. A graphical user interface was developed by dividing the monitor screen into several areas with shape boundaries, so that the movement direction of the endoscope can be identified by the area gazed at by the operator. We used a probabilistic neural network (PNN) to decide the regional distribution proportion to recognize the direction in which the operator would want the endoscopic manipulator to move. The PNN model was trained by individual calibration data. We hypothesized that PNN model training could be completed immediately after calibration, which also determines the boundary of the regional distribution portion (RDP). We designed an experiment and recorded the path of direction change to verify the PNN's effectiveness in our proposed system. All participants, including four who wore glasses, completed the requested task. Moreover, wearing glasses had no significant effect on the performance of the proposed system. Furthermore, the PNN training duration only took 2% of the entire time of the procedure to handle individual differences. We conclude that our method can handle individual differences in operators' eyes through machine learning of personal calibration data over a short time frame, which will not take significant extra preoperative setup time.

This paper presents a design method of optimal servo systems based on sliding mode for an active pantograph with flexibility subject to the stiffness variation of the catenary. It is pointed out through our analysis that the flexibility makes the control problem much harder, because it increases not only the freedom of motion but also the relative degree between the control input and the contact force to be controlled. However, it is shown by employing the optimal control theory, especially SRL (Symmetric Root Locus), together with sliding mode theory that pole-zero cancellations play an important role in the controller design. Some numerical simulations in a practical situation, where the actuator dynamics and sensor noise are taken into account, show the effectiveness of the proposed design method.

This paper proposed a stochastic multiscale modeling method by parameterization and quantification of the fluctuated meso/micro-structure of plain woven fabric glass fiber reinforced plastics (GFRP) fabricated by hand layup. The experimental results of static tensile tests of 25 specimens made by 5 persons showed large scattering and the macroscopic parameters could not enough explain the variability. Hence, the meso/micro-structure based stochastic multiscale method was presented first, and its geometrical modeling technique was deeply studied in this paper. By the observation of the specimens, fluctuated geometrical features were parameterized. The defined parameters were statistically measured. The generated 2D models could express the realistic meso/micro-structures. It should be noted that the nesting in laminated composites and the distributed fiber volume fraction were included in the proposed modeling method.

Researchers have conducted finite element (FE) analyses with human models to predict injuries due to traffic accidents or falling. In most of their analyses, cortical bone was simply modeled as a general isotropic elastoplastic material. In this study, a constitutive model of cortical bone considering anisotropic inelasticity and damage evolution was developed to predict injuries more accurately. The new model can satisfactorily represent mechanical properties of cortical bone including anisotropy of elastic modulus and yield stress with strain-rate dependency, and asymmetric stress-strain curves in tension and compression. Simultaneously the included damage-evolution equation enables to predict failure stress and strain with rate dependency in bone fracture simulations. The proposed model was verified using experimental data obtained from the literature. We applied the proposed model to a simple cylindrical FE model of the human femur, and performed simulations under loading conditions such as tension, compression, and torsion. The results showed some tendency of characteristic fracture patterns such as transverse fracture in tensile loading, oblique fracture in compression, and spiral fracture in torsion. The proposed constitutive model would have the potential for better injury prediction in the future.

We present a domain decomposition technique combining the finite-element analysis and a multiscale simulation scheme that is termed the seamless-domain method. This technique is applicable to any type of linear problems and has the below different features from conventional substructuring techniques used for finite-element methods such as the super-elements. Adjacent substructures do not need to have the same finite-element mesh or the same node layout at their interface. Therefore, the proposed technique allows us to connect a substructure having a coarse mesh and another substructure having a fine mesh. Additionally, the neighboring substructures are partially overlapped each other around their interfacial region. The overlapped region attempts to generate continuous dependent-variable distribution(s) at the interfacial region. We present four types of numerical experiments related to linear elasticity to investigate practical feasibility of the proposed technique and evaluate an effect of different finite-element meshes in region shared by two substructures on the computational accuracy.

To solve the problem that lacks systematic product spectrum plan and serialization of design methods and theoretical basis in the design process of crawler crane boom, the main boom is as the research object in this paper. Force model is established in luffing plane and rotary plane by the load combination II when the lifting mechanism and the rotating mechanism simultaneously works. On the premise of each demand parameters of prototyping products being known, FEM basic equations are expressed in the form of potential function by introducing displacement potential function based on the local coordinate system. Unit similarity criterion is established in the local coordinate system by non-dimensional treatment for FEM basic equations are expressed in the form of displacement potential function. Nonlinear similarity criterion in the global coordinate system is obtained by using coordinate transformation method. The chord member cross-sectional area of design goals is designed by nonlinear similarity criterion and stability principle. The width and height of the boom is calculated based on rigidity principle. The layout of web member has been discussed. The angle between web member and chord member is designed as well as the length of web member.

The current JSME rules on Fitness-for-Service only applies the Elastic Plastic Fracture Mechanics (EPFM) method, including the two-parameters method for flaw evaluation of cast stainless steel (CASS) pipes, while plastic collapse is expected to occur in the case of low ferrite content or low thermal aging condition. The EPFM method of the JSME rules introduces Z-factor for simplification similar to ASME Sec. XI. The Z-factor equation for CASS pipe was derived with the assumption of a penetrated circumferential flaw, 20% ferrite content, J-R curve of fully aged material, and stress-strain (S-S) curve of unaged material, which are very conservative conditions. In order to revise the current JSME rules for a more practical and accurate flaw evaluation of CASS pipe, this paper introduced to the rules, a limit load method for low ferrite content or low thermal aging condition, and prediction models of S-S and J-R curves for thermal aging. These were verified by fracture tests using flat plate specimens with a surface flaw and detailed FE analyses. Also applicability of a Z-factor equation for an axial flaw was proposed by other authors. This paper is a technical basis for the code revision of the JSME rules.