Load step reduction for adjoint sensitivity analysis of finite strain elastoplasticity

In this paper, load step reduction techniques are investigated for adjoint sensitivity analysis of path-dependent nonlinear finite element systems. In particular, the focus is on finite strain elastoplasticity with typical hardening models. The aim is to reduce the computational cost in the adjoint sensitivity implementation. The adjoint sensitivity formulation is derived with the multiplicative decomposition of deformation gradient, which is applicable to finite strain elastoplasticity. Two properties of adjoint variables are investigated and theoretically proved under certain prerequisites. Based on these properties, load step reduction rules in the sensitivity analysis are discussed. The efficiency of the load step reduction and the applicability to isotropic hardening and kinematic hardening models are numerically demonstrated. Examples include a small-scale cantilever beam structure and a large-scale conrod structure under huge plastic deformations.

A Detection Circuit for Improving the Unloading Transient Performance of the COT Controller

Fast load transient response and high light-load efficiency are two key features of the constant on-time (COT) control technique that has been widely used in numerous applications, such as for voltage regulators and point-of-load converters. However, when load step-down occurs during an on-time interval, the COT controller cannot respond until the COT interval expires. This delay causes an additional output voltage overshoot, resulting in unloading transient performance limitation. To eliminate the delay and improve the unloading transient response of the COT controller, a load step-down detection circuit is proposed based on capacitor current COT (CC-COT) control. In the detection circuit, the load step-down is monitored by comparing the measured capacitor current with the preset threshold voltage. Once the load step-down is monitored, the on-time is promptly truncated and the switch is turned off. With the proposed detection circuit, the CC-COT-controlled buck converter can monitor the load step-down without any delay and obtain less output voltage overshoot when the load step-down occurs during the on-time interval. PSIM circuit simulations are employed to demonstrate the feasibility of the detection circuit.

Adaptive On-Time Control Buck Converter with a Novel Virtual Inductor Current Circuit

This study presents a new virtual inductor current circuit to reduce circuit complexity, which is not necessary to sense inductance current directly. The buck converter was designed to produce an output voltage of 1.0–2.5 V for a 3.0–3.6 V input voltage. The load current range was from 100 mA to 500 mA. It was simulated and verified by SIMPLIS and MathCAD. The simulation results of this buck converter show that the voltage error is within 1%, and the recovery time is smaller than 2 ms for step-up and step-down load transients. Additionally, it achieves less than 26 mV overshoot at full-load step transient response. The circuit topology would be able to fabricate using TSMC 0.35 mm 2P4M CMOS technology. The control mechanism, implementation, and design procedure are presented in this paper.

Development of a Morphing Landing Gear Composite Door for High Speed Compound Rotorcraft

In the framework of fast rotorcraft, smoothness and flushness of external aerodynamic surfaces present challenges for high-speed conditions, where aerodynamics is the driver of helicopter performance. For AIRBUS-RACER helicopter the main landing gear trap doors are parts of the lower wing skins (in retracted configuration) affecting helicopter performance by minimizing the drag. Flushness requirements must not be in contrast with the functionally of the Landing gear system that must open and close the doors during the landing gear retraction-extension phases at moderately low velocity. To manage these goals, a novel design logic has been identified to support the trap doors development phase. The identified way to proceed needs of relevant numerical method and tool as well. This method is aimed at identifying the main landing gear composite compartment doors in pre-shaped configuration to match the smoothness and door-stopper engagements over each aerodynamic conditions. The authors propose a detailed non-linear Finite Element method, based on MSC Nastran (MSC Software, Newport Beach, US) SOL-400 solver in which the structure is modelled with deformable contact bodies in a multiple load step sequence, open door condition and pre-shaped, deformed under actuator pre-load, under flight load conditions. The method includes the entire pre-stressed field due to the preload and the actual door stiffness, considering the achieved large displacement to verify the most representative strain field during loads application. The paper defines a robust methodology to predict the deformation and ensure the most appropriate door “pre-bow” and pre-load, in order to achieve the desiderated structural shape that matches aerodynamic requirements. The main result is the identification of a pre-shaped doors configuration for the Airbus RACER Fast Rotorcraft.

Experiments on Fiber Concrete Foundation Slabs in Interaction with the Subsoil

This article focuses on researching the interactions of fiber concrete slabs with subsoil. The experimental series includes four slabs made of fiber concrete with different dosages of fibers, from 0 to 75 kg/m3. The slabs were exposed to a loading test on a specialized loading frame. The laboratory tests for detailed descriptions of the fiber concrete’s mechanical properties were also an integral part of the experiments, including tests of the compressive strength, the modulus of elasticity, and split and bending tensile strength. Each slab’s deformation in a particular load step was evaluated in two-dimensional (2D) sections based on data measured with displacement sensors and in three-dimensional (3D) charts with the use of interpolation.

A Fast-Transient All-Digital LDO with Adaptive Clock Technique

To get a better tradeoff between the transient performance and current efficiency of Digital Low-Dropout (DLDO) regulator, this paper proposes an all-digital Low-Dropout (LDO) regulator with adaptive clock technique. The sample clock is supplied by a proposed digital oscillator (DOSC) whose output frequency can be changed seamlessly. The frequency of sample clock and loop gain boost adaptively when the output voltage undershoot/overshoot is detected. Proposed DLDO integrates a ripple controller to eliminate steady-state supply ripple and reduce steady-state power. The proposed DLDO is simulated at Semiconductor Manufacturing International Corporation (SMIC) 55 nm with 5.03e-4 mm2 active area. The simulation results show that the operating voltage of proposed DLDO can be down to 0.5 V and the peak current efficiency is 99.99%. The measured voltage undershoot is 40 mV and transient response time is 500 ns with load step of 10 to 800 uA.

Mold taper optimization for continuous casting of H-beam blanks

The objective of this study is to optimize the mold taper for continuous casting of H-beam blanks. A thermo-mechanical coupled mathematical model was established to analyze the heat transfer, solidification, and shrinkage of the strand in the mold based on the multiple load step method. Based on the simulation results of the air gap distribution in the mold, the mold taper was optimized at selected points on the surface of H-beam blank mold by minimizing the air gap thickness and the best taper scheme was proposed. The results show that the original mold tapers are relatively larger and the optimum mold tapers are as follows: (1) taper at the flange surface: 0.81%/m; (2) taper at the narrow face: 0.68%/m; (3) taper at the fillet: −1.44%/m. The optimum mold size obtained from taper optimization was used in the actual continuous casting process and based on the results, it can be concluded that the optimum mold taper scheme proposed in this study reduced the formation of surface cracks in H-beam blanks.