Search results

The purpose of this paper is to present a novel high-precision relative navigation method for tight formation-keeping based on thrust on-line identification.

Considering that thrust acceleration cannot be measured directly, an on-line identification method of thrust acceleration is explored via the estimated acceleration of major space perturbation and the inter-satellite relative states obtained from space-borne acceleration sensors; then, an effective identification model is designed to reconstruct thrust acceleration. Based on the identified thrust acceleration, relative orbit dynamics for tight formation-keeping is established. Further, using global positioning system (GPS) measurement information, a modified extended Kalman filter (EKF) is suggested to obtain the inter-satellite relative position and relative velocity.

Compared with the normal EKF and the adaptive robust EKF, the proposed modified EKF has better estimation accuracy in radial and along-track directions because of accurate compensation of thrust acceleration. Meanwhile, high-precision relative navigation results depend on high-precision acceleration sensors. Finally, simulation studies on a chief-deputy formation flying control system are performed to verify the effectiveness and superiority of the proposed relative navigation algorithm.

This paper provides a reference in solving the problem of high-precision relative navigation in tight formation-keeping application.

This paper proposes a novel on-line identification method for thrust acceleration and shows that thrust identification-based modified EKF is more efficient in relative navigation for tight formation-keeping.

Structural stress and strain in the key components of aircraft structure is important for structural health monitoring and strength assessment. However, the measure of dynamic strain is often difficult to implement because of the complex test equipment and inconvenient measure points, especially in flight test. This study aims to propose an algorithm of dynamic strain estimation using the acceleration response in time domain to simplify the measure of dynamic strain.

The relationship between the strain and acceleration response is established through the sinusoidal response or modal analysis, which is insensitive to the excitation position and form. A band-pass filter is used to obtain the modal acceleration response, and a filter frequency band selection method is proposed. Then, the dynamic strain at the concerned points can be estimated based on the modal superposition principle.

Simulation and experiment are implemented to validate the applicability and effectiveness of the strain estimation method. The estimated strain results agree well with numerical simulation as well as the experimental results. The simplicity and accuracy of the strain estimation method show practicability for dynamic strength and fatigue analysis in engineering applications.

An algorithm of dynamic strain estimation using the acceleration response in time domain is developed. A band-pass filter is used to obtain the modal acceleration response, and a filter frequency band selection method is proposed. The dynamic strain at the concerned points can be estimated based on the modal superposition principle.

The aim of this paper is to explore the hypothesis that a contractor is entitled to payment for “constructive” acceleration implemented to avoid liquidated damages when denied a warranted time extension request by the employer or certifier under an English law construction contract. This claim is recognised in the US legal system, but not elsewhere.

This paper adopts a “black letter” approach to reviewing the claim of constructive acceleration within the context of English and Commonwealth case law, from the perspective of a claimant contractor.

The research presented in this paper concludes that whilst claims for constructive acceleration are unlikely to succeed in an English court on the basis of US law, a claim might be supportable on more orthodox common law grounds. These include implied instructions under the contract, breach of the contract based on the employer or certifier’s failure to operate the contract, mitigation of damages, unjust enrichment and tortious intimidation.

The focus of this paper is placed on English, Unites States, Canadian and Australasian case law.

The range of potential legal grounds for constructive acceleration examined in this paper provides a toolkit for practitioners preparing to make or defend constructive acceleration claims. This paper also bring more clarity to a potential legal problem faced by practitioners in circumstances of significant tension and limited time.

This paper provides a useful information source for practitioners faced with the prospect of advancing or defending constructive acceleration claims, and it provides a foundation for future related studies examining a wider scope of jurisdictions.

The purpose of this paper is to propose holistic approach to human resources in the situation of organizational acceleration. Authors are postulating that the holistic approach to HR helps in maintaining sustainable individual resources of employees in the situation of continuous organizational changes and time pressure that further can prevent from the individual resources exhaustion.

This conceptual paper builds on the problem of occupational stress that is connected with organizational acceleration. Authors define stress as the individually perceived inability to match expectations caused by the deficiency of individual resources. They conceptualize the individual resources of employees basing on the concepts of human capital and the individual energy at work and propose a framework of individual resources of employees that enables holistic view of an individual in an organization.

In the situation of organizational acceleration HRM function plays important role in sustaining individual resources of employees in order to minimize threat of occupational stress and further burnout. HR practices should apply multidimensionality of individual resources and threat it holistically aiming at sustaining all four potentials – spiritual, intellectual, emotional and physical.

Authors indicate that managers need to understand how to deal with the acceleration in order to overcome the negative consequences for individuals. There is still need for identifying HR practices that are the key success factors in the situation of organizational acceleration.

Authors take up the current problem of organizational acceleration from the individual perspective. They propose a concept of individual resources of employees and connected to it holistic approach to HR in the times of great time pressure, work overload, occupational stress and burnout threat.

The purpose of this study is to solve convective diffusion equation analytically by considering appropriate boundary conditions and using the Taylor-Aris method to determine the solute concentration, the effective and relative axial diffusivities.

>An analysis has been conducted on how body acceleration affects the dispersion of a solute in blood flow, which is known as a Bingham fluid, within an artery. To solve the system of differential equations analytically while validating the target boundary conditions, the blood velocity is obtained.

The blood velocity is impacted by the presence of body acceleration, as well as the yield stress associated with Casson fluid and as such, the process of dispersing the solute is distracted. It graphically illustrates how the blood velocity and the process of solute dispersion are affected by various factors, including the amplitude and lead angle of body acceleration, the yield stress, the gradient of pressure and the Peclet number.

It is witnessed that the blood velocity, the solute concentration and also the effective and relative axial diffusivities experience a drop when either of the amplitude, lead angle or the yield stress rises.

This study was designed to detect the failures in Iranian accelerators. This paper attempts to identify these effects from the perspective of accelerator managers and founders of startups. The main goals of this article are as follows: (1) What are the failures of Iran's acceleration programs from the perspective of accelerator managers? (2) What are the failures of Iran's acceleration programs from the perspective of startup teams? (3) What are some of failures of the acceleration programs that both groups agree on?

It has been attempted to conduct semi-structured interviews with managers of corporate accelerators on the one hand and startups accelerated in these accelerators on the other. The interviewees were selected using snowball method and consisted of 9 accelerator managers out of 7 accelerators and 15 startups based on 5 accelerators. The analysis of the information extracted from the interviews and coding of the failure identified in the accelerators was performed using the thematic analysis method. In order to assess the validity of this study, an entrepreneurial doctoral student was asked to codify the interviews individually to compare the extracted codes.

Finally, 34 problems have been identified that are divided into four main themes related to mentorship, acceleration program, acceleration structure and infrastructure and internal startup team problems. Overall, the greatest agreement among the failures identified as wrong orientation by untrained mentors, the lack of complementary in ability and skills of team members, the lack of knowledge of mentors, the lack of acceleration managers in entrepreneurship and the lack of a proper leader in startup teams.

This study aimed to investigate the failures of corporate accelerators in Iran as a developing country, which is the first survey in Iran. We have many researches about the pathology and identify failures of accelerators, but in corporate accelerators, little research has been done. The authors have a classification of failures in corporate accelerators by using thematic analysis. In this study, accelerators' managers and founders of startups were interviewed and 34 failures were identified.

The purpose of the paper is to study the stability control of permanent magnet (PM) and electromagnetic hybrid Halbach array electrodynamic suspension (EDS) system because of the poor suspension stability caused by the well-known under-damped nature of PM EDS system. The adjustment control is realized by PM and electromagnetic hybrid Halbach array, which is composed by winding active normal conductor coils on PM surface.

The three-dimensional (3-D) electromagnetic force analytical expression of PM and electromagnetic hybrid Halbach array EDS system for a nonmagnetic conductive plate is derived. And the accuracy of the derived equations is verified by a 3-D finite-element model (FEM). Basing on the 3-D levitation force expression, an acceleration feedback suspension controller is designed to suppress the vibration of PM EDS system, and the suspension stability of the system under the track and load disturbance was simulated and analyzed.

The 3-D electromagnetic force comparison of analytical model and FEM are in good agreement, which verifies the correctness of the analytical expression. The simulation results show that the acceleration feedback suspension controller can make the system have good suspension stability under the external disturbance. So it proved that the PM and electromagnetic hybrid Halbach array EDS system can overcome the poor suspension stability caused by the under-damped nature of PM EDS system through the designed acceleration feedback suspension controller.

This paper designed an acceleration feedback suspension controller to suppress the vibration of PM and electromagnetic hybrid Halbach array EDS system under external disturbance, basing on the derived levitation force analytical expression. And the simulation results show that the acceleration feedback suspension controller can make the system have good suspension stability under the external disturbance.

The purpose of this study is to investigate the behavior of ultra-thin film formation at the start-up of motion for different acceleration rates and final entrainment speed, including the effect of intermolecular forces; solvation and Van der Waals’ in addition to hydrodynamic action for the elastohydrodynamic lubrication of point contact problems.

The equation of motion of the ball is considered to account for the applied force on the ball during the start-up of motion. The Newton–Raphson with Gauss–Seidel iterative method is used to solve the Reynolds, film thickness and load balance equations simultaneously. In addition to hydrodynamic effects, solvation and Van der Waals’ forces are taken into account in the calculation of bearing capacity.

The simulation results showed that the effects of acceleration rate are important for ultra-thin film formation at the start-up of motion. Increasing the rate of acceleration results in a higher value of central film thickness during the start-up of motion than the corresponding steady-state film thickness value reached at the final entrainment speed. The effects of intermolecular forces are important to prevent metal-to-metal contact during the inactive period of motion, where a constant value of film thickness is achieved regardless of the value of the acceleration rate or final entrainment speed.

The behavior of ultra-thin film formation at start-up of motion, including the effect of intermolecular forces; solvation and Van-der-Waals’ along with hydrodynamic action, are evaluated after different acceleration rates and final entrainment speeds.