• Journal of Power Electronics
• /
• v.9 no.4
• /
• pp.654-666
• /
• 2009

Direct torque control (DTC) of induction machines (IM) is a well-known strategy of these drives control which has a fast dynamic and a good tracking response. In this paper a nonlinear DTC of speed sensorless IM drives is presented which is based on input-output feedback linearization control theory. The IM model includes iron losses using a speed dependent shunt resistance which is determined through some effective experiments. A stator flux vector is estimated through a simple integrator based on stator voltage equations in the stationary frame. A novel method is introduced for DC offset compensation which is a major problem of AC machines, especially at low speeds. Rotor speed is also determined using a rotor flux sliding-mode (SM) observer which is capable of rotor flux space vector and rotor speed simultaneous estimation. In addition, stator and rotor resistances are estimated using a simple but effective recursive least squares (RLS) method combined with the so-called SM observer. The proposed control idea is experimentally implemented in real time using a FPGA board synchronized with a personal computer (PC). Simulation and experimental results are presented to show the capability and validity of the proposed control method.

• Advances in nano research
• /
• v.8 no.1
• /
• pp.25-36
• /
• 2020

Rotating systems concern with torsional vibration, and it should be considered in vibration analysis. To do this, the time-dependent torsional vibrations in a single-walled carbon nanotube (SWCNT) under the linear and harmonic external torque, are investigated in this paper. Eringen's nonlocal elasticity theory is considered to demonstrate the nonlocality and constitutive relations. Hamilton's principle is established to derive the governing equation of motion and consequently related boundary conditions. An analytical method, called the Galerkin method, is utilized to discretize the driven differential equations. Linear and harmonic torsional loads, along with determined amplitude, are applied to the SWCNT as the external torques. SWCNT is considered under the clamped-clamped end supports. In free vibration, analysis of small scale effect reveals the capability of natural frequencies in different modes, and this results desirably are in coincidence with another study. The forced torsional vibration in the time domain, especially for carbon nanotubes, has not been done before in the previous works. The previous forced studies were devoted to the transverse vibrations. It should be emphasized that the dynamical analysis of torsion is novel, workable, and at the beginning of the path. The variations of nonlocal parameter, CNT's thickness, and the influence of excitation frequency on time-dependent angular displacement and nondimensional angular displacement are investigated in the context.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.17 no.2
• /
• pp.145-152
• /
• 2018

This study deals with the method of determining the tip-over stability of a truck mounted on a high place operation car that is frequently used to carry out high-altitude work. Multibody Dynamics Program and Zero Moment Point (ZMP) theory are used to include dynamic effects during the car's high place operation. Through a combination of the Multibody Dynamics Program and ZMP, understanding the dynamic effects of the car's operating parts and building a detailed tip-over model of the car permitted a more precise prediction of the car's tipping-over behavior. It is also expected to help reduce the car's development time due to the time-effective simulation and provide safer work levels for the operating guide (in terms of working radius and lifting capability) with the dynamics effects.

• International Journal of Aeronautical and Space Sciences
• /
• v.12 no.4
• /
• pp.346-353
• /
• 2011

In this study, the structural performance tests, i.e., static tests and dynamic tests of the composite wind turbine blade, were carried out by using the embedded fiber Bragg grating (FBG) sensors. The composite wind turbine blade used in the test is the 1/23 scale of the 750 kW composite blade. In static tests, the deflections along the blade were evaluated. Evaluations were carried out with simple beam theory and quadratic fitting method by using the embedded FBG sensors to predict the structural behavior with respect to the load. The deflections were compared to those obtained from the laser displacement sensor and electric strain gauges. They showed good agreement. Modal tests were performed to investigate the dynamic characteristics using the embedded FBG sensors. The natural frequencies obtained from the FBG sensors corresponding to the nine mode shapes of the blade were compared to those from the laser Doppler vibrometer. They were found to be consistent with each other. Therefore, it is concluded that the embedded FBG sensors have a great capability for measuring the structural performances of the composite wind turbine blade when structural performance tests are carried out.

• Smart Structures and Systems
• /
• v.16 no.1
• /
• pp.141-162
• /
• 2015

The magneto-rheological visco-elastomer (MRVE) is used as a smart core to control the stochastic micro-vibration of a sandwich plate with supported mass. The micro-vibration response of the sandwich plate with MRVE core and supported mass under stochastic support motion excitations is studied and compared to evaluate the vibration suppression capability. The effects of the supported mass and localized magnetic field on the stochastic micro-vibration response of the MRVE sandwich plate are taken into account. The dynamic characteristics of the MRVE core in micro-vibration are described by a non-homogeneous complex modulus dependent on vibration frequency and controllable by applied magnetic fields. The partial differential equations for the coupled transverse and longitudinal motions of the MRVE sandwich plate with supported mass are derived from the dynamic equilibrium, constitutive and geometric relations. The simplified ordinary differential equations are obtained for the transverse vibration of the MRVE sandwich plate under localized magnetic fields. A frequency-domain solution method for the stochastic micro-vibration response of sandwich plates with supported mass is developed based on the Galerkin method and random vibration theory. The expressions of frequency-response functions, response power spectral densities and root-mean-square velocity responses of the plate in terms of the one-third octave frequency band are obtained for micro-vibration evaluation. Finally, numerical results are given to illustrate the large response reduction capacity of the MRVE sandwich plate with supported mass under stochastic support motion excitations, and the influences of MRVE parameters, supported mass and localized magnetic field placement on the micro-vibration response.

• Journal of Navigation and Port Research
• /
• v.47 no.4
• /
• pp.256-270
• /
• 2023

In this study, a sliding mode (SM) controller for dynamic positioning (DP) was specifically designed for a turret connection operation of a ship or an offshore structure in which an arbitrary point on the structure could be controlled as the motion center instead of the center of mass. The SM controller allows control of the arbitrary point and provides capability to manage uncertainties in the dynamics of ships and offshore structures, external forces caused by unknown changing marine environments, and transient performance of DP systems. The Jacobian matrix included in kinematic equations of the controlled object was modified to design the SM controller to control based on an arbitrary point of ships or offshore structures. To ensure robustness of the controller, the Lyapunov stability theory was applied in the design of the SM controller. In general, for robustness in DP control, gain scheduling based on a proportional-derivative (PD) control algorithm is employed. However, finding appropriate gains for gain scheduling complicates the application of DP systems. Therefore, in this study, the SM control algorithm was considered to mitigate the complexity of the DP controller for ships and offshore structures. To validate the proposed SM control algorithm, time-domain simulations were conducted and utilized to evaluate the performance of the control algorithm. The effectiveness of the proposed SM controller was assessed by comparing simulation results with results of a conventional PD control algorithm applied in DP control.

• The Journal of Asian Finance, Economics and Business
• /
• v.7 no.7
• /
• pp.1-13
• /
• 2020

This study analyzes the key drivers (commitment, integration of big data, green supply chain management, and green human resource practices) of sustainable capabilities and the influence to which these sustainable capabilities impact the banks' environmental and financial performance. Additionally, this study analyzes the impact of green management practices on the integration of big data technology with operations. The theory of dynamic capability was deployed to propose and empirically test the conceptual model. Data was collected through a self-administrated survey questionnaire from 319 participants employed at 35 banks located in six ASEAN countries. The findings indicate that big data analytics strategies have an impact on internal processes and banks' sustainable and financial performance. This study indicates that banks committed towards proper data monitoring of its clients achieve operational efficiency and sustainability goals. Moreover, our results confirm that banks practising green innovation strategies experience better environmental and economic performance as the employees of these banks have received advance green human resource training. Finally, our study found that internal and external green supply chain management practices have a positive impact on banks' environmental and financial performance, which confirms that ASEAN banks contributing in reduction of environmental impact through its operations will ultimately experience increased financial performance.

• Proceedings of the Korea Contents Association Conference
• /
• 2008.05a
• /
• pp.725-731
• /
• 2008

In this paper, we propose a novel construction scheme for the personalized e-Learning system based on IRT(item response theory), which can be applied to the content including non-hierarchical and horizontal learning objects in its learning nodes. Especially the proposed system performs tests and re-estimates examinee ability during the learning nodes are operating so that the results are directly applied to the next node. This scheme can be called a dynamic relationship between test and learning which is totally different from conventional customization based on learning procedures separated from test steps. Moreover, we should periodically modify the averages of node difficulties, item parameters, and ability parameters of students so that the system have more accurate personalized learning capability. As a result, this scheme maximizes learning efficiency offering the most appropriate learning objects and items to the individual students according to their estimated abilities and the system itself should obtain continuous improvements by modifying the parameters and fulfilling periodical feedbacks.

• Asia-Pacific Journal of Business
• /
• v.14 no.4
• /
• pp.87-113
• /
• 2023

Purpose - Focusing on Haier, a successful corporate venture in China, we analyse the operating mechanism and success factors of corporate venture, and reveal the necessary factors for the successful implementation of corporate venture. Design/methodology/approach - This study is a single case study centred on Haier, a successful corporate venture in China. Findings - The operational process of Haier's corporate venture includes six key aspects: project selection, team building, resource allocation and support, project implementation, risk control measures, performance evaluation and rewards. In terms of success factors, the support of top management with leadership capability of value creation and sharing is very important for the success of corporate venture. Secondly, a multi reward mechanism can be introduced to motivate employees and improve performance. Thirdly, it is important to integrate corporate culture into the operating mechanism of an corporate venture. Fourthly, flexible operations that break down rigid organisational boundaries and transform the organisation into a more open platform for entrepreneurship can increase the likelihood of success. Finally, empowering employees with operational discretion can also have a positive impact on the success of an Corporate Venture. Research implications or Originality - This study contributes to theory and practice by analysing the success conditions of corporate venture, providing new understanding and drawing new perspectives, especially from the experience of Haier. The results suggest strategies and flexibility for successfully pursuing corporate venture, and provide important experience for international companies to help them gain competitive advantage in global competition. It also helps corporate leaders to promote new directions and innovations and improve their strategies to respond to dynamic environments.

• Journal of KIISE:Computer Systems and Theory
• /
• v.31 no.8
• /
• pp.465-472
• /
• 2004

Proxy signatures is a signature scheme that an original signer delegates one's signature capability to a proxy signer, and then the proxy signer creates a signature on behalf of the original signer. Delegation of authority is a common practice in the real world, in particular, it happens naturally in hierarchical groups such as company, bank and army, etc. In this paper, we propose a new dynamic multi-proxy signature scheme allowing repetitive delegations in a hierarchical group. We adopt multi-proxy signatures to enhance the security of proxy signature. In multi-proxy signatures, plural proxy signers can generate a valid proxy signature collectively on behalf of one original signer. In our scheme, the proxy group is not fixed but constructed dynamically according to some situations. Delegations are processed from higher level to lower level in the hierarchy using delegation tickets. When the original signer wants to delegate one's signature authority, the original signer generates a delegation ticket based on secret sharing and Diffie-Hellman problems. The delegation ticket is shared among proxy signers and then all the proxy signers can generate a valid proxy signature collectively by reconstructing the original signer's delegation ticket. If a certain proxy signer can not attend the proxy signature generating protocol, the proxy signer can also delegate repetitively his partial signature authority to the lower level participants, and then the proxies are constructed dynamically.