Numerical Investigations on Non-Rectangular Anchor Groups under Shear Loads Applied Perpendicular or Parallel to an Edge

Anchorages of non-rectangular configuration, though not covered by current design codes, are often used in practice due to functional or architectural needs. Frequently, such anchor groups are placed close to a concrete edge and are subjected to shear loads. The design of such anchorages requires engineering judgement and no clear rules are given in the codes and standards. In this work, numerical investigations using a nonlinear 3D FE analysis code are carried out on anchor groups with triangular and hexagonal anchor patterns to understand their behavior under shear loads. A microplane model with relaxed kinematic constraint is utilized as the constitutive law for concrete. Two different orientations are considered for both triangular and hexagonal anchor groups while no hole clearance is considered in the analysis. Two loading scenarios are investigated: (i) shear loading applied perpendicular and towards the edge; and (ii) shear loading applied parallel to the edge. The results of the analyses are evaluated in terms of the load-displacement behavior and failure modes. A comparison is made between the results of the numerical simulations and the analytical calculations according to the current approaches. It is found that, similar to the rectangular anchorages, and also for such non-rectangular anchorages without hole clearance, it may be reasonable to calculate the concrete edge breakout capacity by assuming a failure crack from the back anchor row. Furthermore, the failure load of the investigated groups loaded in shear parallel to the edge may be considered as twice the failure load of the corresponding groups loaded in shear perpendicular to the edge.

Conceptual Design Of A Modular Morphing Wing

In this dissertation a new modular design method for morphing wings is presented. First, a design method was created, applying modularity and recon gurability to a morphing wing system. With modularity being a requirement for the morphing wing system, a discretization method is developed to determine the discrete number of modules required to perform a desired morphing maneuver. Then, a specialized, modular, recon gurable variable geometry truss mechanism is proposed to facilitate morphing. The specialized modular wing truss is a recon gurable, limited mobility parallel mechanism, adapted to t within the volume of a wing. The mobility of the wing truss module is analyzed via a branch-based mobility and connectivity analysis that imposes kinematic requirements on the truss mechanism. The mobility and connectivity requirements are used to perform an enumeration analysis to isolate candidate module con gurations for morphing. Then, a parametric kinematic constraint system is developed and applied to the wing module and the kinematic performance of the module is evaluated. The kinematics are applied to a mechanical prototype of the wing module for validation purposes. Finally, the kinematics are used to evaluate the motion response of a wing skin system to lay the foundation for detailed design.

Conceptual Design Of A Modular Morphing Wing

In this dissertation a new modular design method for morphing wings is presented. First, a design method was created, applying modularity and recon gurability to a morphing wing system. With modularity being a requirement for the morphing wing system, a discretization method is developed to determine the discrete number of modules required to perform a desired morphing maneuver. Then, a specialized, modular, recon gurable variable geometry truss mechanism is proposed to facilitate morphing. The specialized modular wing truss is a recon gurable, limited mobility parallel mechanism, adapted to t within the volume of a wing. The mobility of the wing truss module is analyzed via a branch-based mobility and connectivity analysis that imposes kinematic requirements on the truss mechanism. The mobility and connectivity requirements are used to perform an enumeration analysis to isolate candidate module con gurations for morphing. Then, a parametric kinematic constraint system is developed and applied to the wing module and the kinematic performance of the module is evaluated. The kinematics are applied to a mechanical prototype of the wing module for validation purposes. Finally, the kinematics are used to evaluate the motion response of a wing skin system to lay the foundation for detailed design.

A Feedrate Planning Method for the NURBS Curve in CNC Machining Based on the Critical Constraint Curve

The curvature of the NURBS curve varies along its trajectory, therefore, the commonly used feedrate-planning method, which based on the acceleration/deceleration (Acc/Dec) model, is difficult to be directly applied in CNC machining of a NURBS curve. To address this problem, a feedrate-planning method based on the critical constraint curve of the feedrate (CCC) is proposed. Firstly, the problems of existing feedrate-planning methods and their causes are analyzed. Secondly, by considering both the curvature constraint and the kinematic constraint during the Acc/Dec process, the concept of CCC which represents the relationship between the critical feedrate-constraint value and the arc length is proposed. Then the CCC of a NURBS curve is constructed, and it has a concise expression conforming to the Acc/Dec model. Finally, a feedrate-planning method of a NURBS curve based on CCC and the Acc/Dec model is established. In the simulation, a comparison between the proposed method and the conventional feedrate-planning method is performed, and the results show that, the proposed method can reduce the Acc/Dec time by over 40%, while little computational burden being added. The machining experimental results validate the real-time performance and stability of the proposed method, and also the machining quality is verified. The proposed method offers an effective feedrate-planning strategy for a NURBS curve in CNC machining.

Design and Dynamic Analysis of a Four-Degree-of-Freedom Chaotic Vibrating Screen

In order to address the problems of low screening efficiency, easy blocking of screen holes, and short service life of key parts commonly used in vibrating screen equipment, the TRIZ (Theory of the Solution of Inventive Problems) was applied in the present work to design a four-degree-of-freedom (4-DOF; three translational and one rotational movements) chaotic vibrating screen with a chaotic vibration exciter as the main power source and a 3-DOF (three translational movements) parallel kinetic chain as the kinematic constraint mechanism of the outer screen frame. Based on the topological structure theory, a hybrid mechanism with structure [ 4 SOC − C i 1 ∥ R i 2 ∥ R i 3 − + R , i = 1,2,3,4 ] was constructed as the kinematic constraint mechanism of the inner screen box of the chaotic vibrating screen to solve the freedom of motion and POC (position and orientation characteristic) equations of parallel kinematic constraint mechanism of the outer screen frame and hybrid constraint mechanism of the inner screen box. The dynamic simulation of a virtual prototype of the chaotic vibrating screen was carried out in ADAMS software, and MATLAB was used to chaos recognition of the simulation results. It was found that the chaotic exciter moved aperiodically in X-, Y-, and Z-directions when the chaotic exciter motor rotated at uniform speed, and the amplitude, velocity, and acceleration of the outer screen frame of the vibrating screen had characteristics of reciprocating aperiodic and irregular changes. Through the phase trajectories of the eccentric block and inner screen box of the exciter in all directions, it was observed that the motion output of the vibrating screen was a chaotic vibration. Therefore, the present paper can provide an important reference for the design and application of chaotic vibrating screens.

On the Kirchhoff-Love Hypothesis (Revised and Vindicated)

The Kirchhoff-Love hypothesis expresses a kinematic constraint that is assumed to be valid for the deformations of a three-dimensional body when one of its dimensions is much smaller than the other two, as is the case for plates. This hypothesis has a long history checkered with the vicissitudes of life: even its paternity has been questioned, and recent rigorous dimension-reduction tools (based on standard $\varGamma $ Γ -convergence) have proven to be incompatible with it. We find that an appropriately revised version of the Kirchhoff-Love hypothesis is a valuable means to derive a two-dimensional variational model for elastic plates from a three-dimensional nonlinear free-energy functional. The bending energies thus obtained for a number of materials also show to contain measures of stretching of the plate’s mid surface (alongside the expected measures of bending). The incompatibility with standard $\varGamma $ Γ -convergence also appears to be removed in the cases where contact with that method and ours can be made.

A Subject-Specific Analysis of the Kinematic Constraint Imposed by the Relink Trainer

The relink trainer (RLT) is a novel end-effector device designed for gait-retraining poststroke. The user's foot is constrained to a specific kinematic trajectory relative to the trainer, while the hip and knee are unconstrained. As the RLT only fixes the footplate trajectory, the expected constraint on the hip and knee angles will be subject-specific due to individual lower limb geometries. This study had two objectives (1) to calculate the subject-specific theoretical joint angle trajectories, the RLT should constrain the hip and knee angle to using computer simulation, assuming a fixed hip position relative to the RLT, and (2) experimentally determine the actual hip and knee joint angle trajectories of healthy users walking in the RLT, and compare them to the theoretical joint angle trajectories. The root-mean-square (RMS) error between joint trajectories obtained from motion capture and simulation ranged from 4.31 deg to 20.51 deg for the hip and between 4.48 deg and 22.58 deg for the knee, suggestive of moderate to poor accuracy and distinct kinematic adaptation strategies when using the RLT. A linear fit method (LFM) was used to determine the similarity between the obtained and simulated joint angle trajectories. LFM results would suggest that users' hip and knee joint angles follow the simulated joint angle trajectories when walking in the RLT; however, the actual joint angle trajectories are offset from the simulation trajectories. Post hoc analyses suggest hip motion when using the RLT influences the hip and knee angle trajectory differences for participants.