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- 저자 : Ichchou (검색결과 5 건)
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Effective vibration control of multimodal structures with low power requirement
Loukil, Thamina,Ichchou, Mohamed,Bareille, Olivier,Haddar, Mohamed Techno-Press 2014 Smart Structures and Systems, An International Jou Vol.13 No.3
In this paper, we investigate the vibration control of multimodal structures and present an efficient control law that requires less energy supply than active strategies. This strategy is called modal global semi-active control and is designed to work as effectively as the active control and consume less power which represents its major limitation. The proposed law is based on an energetic management of the optimal law such that the controller follows this latter only if there is sufficient energy which will be extracted directly from the system vibrations itself. The control algorithm is presented and validated for a cantilever beam structure subjected to external perturbations. Comparisons between the proposed law performances and those obtained by independent modal space control (IMSC) and semi-active control schemes are offered.
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A WFE and hybrid FE/WFE technique for the forced response of stiffened cylinders
Errico, Fabrizio,Ichchou, M.,De Rosa, S.,Bareille, O.,Franco, F. Techno-Press 2018 Advances in aircraft and spacecraft science Vol.5 No.1
The present work shows many aspects concerning the use of a numerical wave-based methodology for the computation of the structural response of periodic structures, focusing on cylinders. Taking into account the periodicity of the system, the Bloch-Floquet theorem can be applied leading to an eigenvalue problem, whose solutions are the waves propagation constants and wavemodes of the periodic structure. Two different approaches are presented, instead, for computing the forced response of stiffened structures. The first one, dealing with a Wave Finite Element (WFE) methodology, proved to drastically reduce the problem size in terms of degrees of freedom, with respect to more mature techniques such as the classic FEM. The other approach presented enables the use of the previous technique even when the whole structure can not be considered as periodic. This is the case when two waveguides are connected through one or more joints and/or different waveguides are connected each other. Any approach presented can deal with deterministic excitations and responses in any point. The results show a good agreement with FEM full models. The drastic reduction of DoF (degrees of freedom) is evident, even more when the number of repetitive substructures is high and the substructures itself is modelled in order to get the lowest number of DoF at the boundaries.
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An investigation on the vibrations of laminated shells under aeroacoustic loads using a WFE approach
Errico, Fabrizio,Franco, F.,Ichchou, M.,De Rosa, S.,Petrone, G. Techno-Press 2019 Advances in aircraft and spacecraft science Vol.6 No.6
The present work investigates the effect on the flow-induced vibrations of the lay-up sequence of composite laminated axisymmetric structures, using an hybrid approach based on a wave finite element and a transfer matrix method. The structural vibrations, under deterministic distributed pressure loads, diffuse acoustic field and turbulent boundary layer excitations, are analysed and compared. A multi-scale approach is used for the dynamic analysis of finite structures, using an elementary periodic subsystem. Different flow regimes and shell curvatures are analysed and the computational efficiency is also discussed.
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Effective vibration control of multimodal structures with low power requirement
Thamina Loukil,Mohamed Ichchou,Olivier Bareille,Mohamed Haddar 국제구조공학회 2014 Smart Structures and Systems, An International Jou Vol.13 No.3
In this paper, we investigate the vibration control of multimodal structures and present anefficient control law that requires less energy supply than active strategies. This strategy is called modal global semi-active control and is designed to work as effectively as the active control and consume less power which represents its major limitation. The proposed law is based on an energetic management of theoptimal law such that the controller follows this latter only if there is sufficient energy which will beextracted directly from the system vibrations itself. The control algorithm is presented and validated for acantilever beam structure subjected to external perturbations. Comparisons between the proposed lawperformances and those obtained by independent modal space control (IMSC) and semi-active controlschemes are offered.
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Bone Loss and Radiographic Damage Profile in Rheumatoid Arthritis Moroccan Patients
Hamida Azzouzi,Linda Ichchou 대한골대사학회 2021 대한골대사학회지 Vol.28 No.2
Background: Rheumatoid arthritis (RA) is a known cause of joint destruction and systemic bone loss. In this study, we aimed to evaluate the bone damage and bone loss profiles of established RA patients. Methods: We designed a cross-sectional study on a cohort of established RA patients. The bone evaluation was performed by obtaining standard X-ray images of hands and feet combined with bone mineral density (BMD) measurements. Radiographic joint damage was calculated by the modified total Sharp / van der Heijde score (mTSS). BMD was obtained by performing dual energy X-ray absorptiometry of the lumbar spine and femoral neck. Data on age, smoking, alcoholism, steroid prescription, body mass index (BMI), disease duration, disease activity, and functional disability were collected. Results: A total of 93 RA patients were recruited. Their mean age was 51.59±12.38 years, with a mean disease duration of 12.07±9.19 years. A total of 36.6% of patients had osteoporosis, and the mean mTSS was 70.33±48.93. Both hip (P=0.0005) and lumbar BMD (P=0.0005) were correlated with mTSS. Backward regression analyses determined that bone damage was associated with high titers of rheumatoid factor, low lumbar BMD, and low BMI. General bone loss was associated with gender, steroid dose, steroid duration, menopause, and BMI. Conclusions: Bone damage was associated with low BMI and axial bone loss in our RA population.
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