Al - Azhar University of Indonesia
Jakarta, Indonesia
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Sahputra R.,Al - Azhar University of Indonesia | Astharini D.,Al - Azhar University of Indonesia | Faisal,Al - Azhar University of Indonesia
Advanced Science Letters | Year: 2017

LDPC code is a powerful FEC coding scheme with good error performance under very low BER. For implementation in OFDM scheme, particular decoding algorithm is needed. The project is to implement FEC for OFDM and analyze the system performance with LDPC codes along with two decoding algorithm on OFDM over a AWGN channel. Bit flipping (BF) and sum product algorithm (SPA) are compared for their decoding performance. The parameter used for observation are BER over EbN0. The results obtained shows that the LDPC codes on OFDM can reduce error 1.5% in average compared with without LDPC. Also that SPA decoding can perform better than the BF. © 2017 American Scientific Publishers All rights reserved.

Djojodihardjo H.,University Putra Malaysia | Djojodihardjo H.,Al - Azhar University of Indonesia
Recent Patents on Mechanical Engineering | Year: 2011

Continuous research efforts have been devoted to the fundamental understanding of aircraft aerodynamics and the introduction of new concepts and innovations for the improvement of basic and fundamental aircraft aerodynamic performance, and hence economy, which leads to the enhancement of lift and the reduction of drag. It is also well known that the trailing vortices which reflect the lift as well as drag characteristics of the aircraft could be optimized for better aircraft performance characteristics and reduction of environmental impact as well as hazardous interference to other flight vehicles and/or objects. Research in enhanced aerodynamic efficiency has led to geometrical modifications, novel devices and features on the aircraft wings, such as blended-wing-body configuration, airfoil profiles and winglet designs, introduction of and/or invention of sensors for identifying relevant physical phenomena or measuring devices, introduction of novel computational methods to assess the prevailing force system with better accuracy through meticulous modeling, and introduction of control system and procedures for wake vortices alleviation and aerodynamic configuration optimization. Typical winglets configuration can significantly reduce the induced drag (in the order of less than 10%) with a resulting increase in wing lift-drag ratio and near the design lift coefficient. The corresponding improvement in lift-drag ratio is more than twice as great as that achieved with the comparable wing-tip extension. As also observed in many aircrafts produced in the last decades, only winglets have demonstrated sufficient benefits to find application on modern airliners. Further enhanced aircraft aerodynamic performance are suggested by introduction of recent innovative designs and patents of winglets, sharklets, blended winglets, capped winglets, s-shaped winglets and spiroidal winglet. The review identifies stability of various configurations of vortices, vortex decay and means of reducing vortex hazard. Passive wake vortices alleviation systems utilize the natural evolution of the instability modes with the highest growth rates while active systems rely on accelerating selected modes of instability by imposing the vortices individually or as a system. The passive system is essentially a vortex wake, hence an aerodynamic surface design, while an active system is an actuator design effort, respectively. © 2011 Bentham Science Publishers.

Suryana R.,Al - Azhar University of Indonesia
INTELEC, International Telecommunications Energy Conference (Proceedings) | Year: 2011

This paper presents the frequency control strategy of standalone wind turbine with a doubly fed induction generator supported by a supercapacitor as an energy storage. The electrical power frequency will be oscillation when the amount of active power produced by wind turbine is not equal to the amount of active power required by consumer. The wind power generation is varying because wind existence is not constant. The supercapacitor will support system to maintain frequency stability. © 2011 IEEE.

Djojodihardjo H.,University Putra Malaysia | Djojodihardjo H.,Al - Azhar University of Indonesia
Proceedings of the International Astronautical Congress, IAC | Year: 2013

With the remarkable computing capability and the availability of sophisticated, user-friendly computer-aided analysis software, the analyst main challenge is to insure that the analysis includes all the relevant physical phenomena. However, simple fundamental principles are mandatory, in order not to lose insight on the interrelationships between relevant elements, and to device simple methods that are robust, and amenable to modifications to address various problem categories. Space borne structure must fulfill various requirements, such as to resist the loads induced by the launch environment, and meet all the functhnal performances required on orbit such as dimensional stability and structural integrity. Space borne structure must also interface with some other subsystems. Noise and Vibration should also be taken as critical consideration in the design of aerospace vehicles for fatigue of components arising from interior structural and acoustic pressure fluctuations due to external structural or acoustic loading. Lightweight structures for high-technology applications increasingly have to fulfill not only high demands on stiffness and strength but also on high damping and low sound radiatbn due to the rising comfort requirements. Here, composites offer a very high vibro-acoustic lightweight potential. The great number of design variables allows to synergetically fulfill high stiffness and acoustic standards. Hence the objective of the present paper is to describe the application of BE-FE Fluid Structure interaction on a structure subject to acoustic load and to elaborate FE formulation of the computational scheme for unified approach on acoustic-aeroelastic interaction as developed earlier. The modal representation of a mechanical structure can be determined analytically if a lumped mass-spring system is concerned. In the general case of a continuous structure, a numerical approximation by means of a Finite Element Model (FEM) is made, discretizing the structure in a finite number of physical coordinates. The present work then proceeds with the dynamic response analysis of typical and generic space shell structure subject to acoustic loading. The numerical treatment applicability is investigated and validated through application to generic cases. The analysis carried out in the work is intended to serve as a baseline in the analysis of acoustic structure interaction for lightweight composite structures by analyzing the structural-dynamic response and sound radiatbn of composite shells, utilizing the authors developed numerical vibro-acoustic simulation models. The work carried out thus far is focused on the formulation of the basic problem of acoustic excitation and vibratbn of elastic structure in a coupled fluid-elastic-structure interaction. Copyright © 2013 by the International Astronautical Federation.

Djojodihardjo H.,University Putra Malaysia | Djojodihardjo H.,Al - Azhar University of Indonesia
Proceedings of the International Astronautical Congress, IAC | Year: 2013

The development of high-strength, high-modulus fibers, has allowed the development of current projectile's impact et resistant and compliant laminates. At a sufficiently low velocity, below the critical velocity, initial stress in the laminates increase is insufficient to rupture the fibers; thus allowing transverse deflection and fiber extension time to propagate, resulting in the absorption of energy by the laminate Damage mechanisms are dependent on the projectile geometry and velocity, the properties of the matrix and fibers and the fiber-matrix adhesion. It should be noted that for ballistic applications, weak fiber-matrix adhesion is wanted. Related to spacecraft debris hazard, one has to quantify the risk and determining appropriate means to protect the spacecraft. An improved understanding of the debris environment, combined with the growing availability of analytic and experimental tools to quantify the threat to a spacecraft from debris and the development of techniques to protect against debris impacts, now makes it feasible for designers to assess the debris hazard and protect their spacecraft appropriately. With such perspectives, this work looks at a plate structure modeled as Mindlin plate subject to impact loading and carry out analysis and numerical simulation. The first objective of the work is to develop a computational algorithm to analyze flat plate as a generic structure subjected to impact loading for numerical simulation and parametric study. The second objective is to utilize the computational algorithm for direct numerical simulation. Effort is devoted to arrive at optimum configurations. Copyright © 2013 by the International Astronautical Federation.

Djojodihardjo H.,University Putra Malaysia | Djojodihardjo H.,Al - Azhar University of Indonesia
Acta Astronautica | Year: 2015

The application of BE-FE acoustic-structure interaction on a structure subject to acoustic load is elaborated using the boundary element-finite element acoustic structural coupling and the utilization of the computational scheme developed earlier. The plausibility of the numerical treatment is investigated and validated through application to generic cases. The analysis carried out in the work is intended to serve as a baseline in the analysis of acoustic structure interaction for lightweight structures. Results obtained thus far exhibit the robustness of the method developed. © 2014 IAA. Published by Elsevier Ltd. All rights reserved.

Djojodihardjo H.,University Putra Malaysia | Djojodihardjo H.,Al - Azhar University of Indonesia | Harithuddin A.S.M.,University Putra Malaysia
Advances in the Astronautical Sciences | Year: 2010

Tropical Earth Resources Satellites and a large host of operational satellites with similar missions and high-definition three-dimensional images has motivated the present study to look into Near-Earth Spacecraft Formation Flying for Earth Pointing Tropical Environmental Monitoring. The potential of spacecraft formation flying as space platform to carry out such mission in the light of small spacecrafts technological progress and availability leads the study to focus into two aspects: the dynamics of relative motion of multiple spacecrafts and the desirable ground tracks beneficial for tropical environmental and resources monitoring missions. For this purpose, relative motion dynamics incorporating Clohessy-Wiltshire Equation for circular orbits as well as Tschauner-Hempel Equation for more general elliptical orbit will be reviewed. A parametric study is carried out to obtain information on various Spacecraft Formation Flying configurations for near earth orbits of interest. Based on the results of the parametric study corresponding ground-tracks are projected to gain better understanding on the overall spacecrafts characteristics for Earth Pointing Tropical Environmental Monitoring mission analysis purposes. It is envisioned that parametric study carried out to obtain relevant orbital characteristics can then be followed by Multi-Disciplinary Optimization for design and application of small satellite missions at a later stage.

Djojodihardjo H.,University Putra Malaysia | Mahmud A.S.,Al - Azhar University of Indonesia
Applied Mechanics and Materials | Year: 2014

A set of Mindlin plates bonded together is subjected to loading by impact, which is considered to represent a generic engineering structure and is analyzed through numerical simulation. The objective is to identify optimum configuration in terms of loading, structural dimensions, material properties and composite layup associated with micrometeorites impacts on spacecraft that will not penetrate into its structure. Following the algorithm developed for the problem, the work comprises an in-depth analysis of a generic flat plate structure subjected to impact and numerical simulation. The analyses are based on dynamic response with emphasis on the elastic region. The direct numerical simulation is carried out in parallel for the analysis, synthesis, parametric study and optimization. As simulation case study, the panel structure response to impact loading by a spherical rigid body at certain velocity perpendicular to the panel plate itself and numerical simulation is carried out as appropriate. Simulation results are validated through comparison with analytical work. The entire scheme carried out in this work is a novel comprehensive approach for the structural design of non-penetrated impact on metallic composites. The results show that the use of composites, in particular the bi-metallic composite, is instrumental in tailoring the plate materials to achieve non-penetrating impact. © (2014) Trans Tech Publications, Switzerland.

Djojodihardjo H.,University Putra Malaysia | Djojodihardjo H.,Al - Azhar University of Indonesia
Proceedings of the International Astronautical Congress, IAC | Year: 2015

Commercial aviation is experiencing the fast growth exceeding automotive travel; the latter is well known for contributing to air pollution. Commercial aviation impacts climate by two main avenues: the emission of greenhouse gases and cloud effects. While the former impact is similar to other activities that contribute to anthropogenic climate change, the latter is unique to aviation. Anthropogenic solutions that can be offered by Aerospace Technology to address anthropogenic environmental changes, known as green technology initiatives, may only provide partial or temporary solutions. In the efforts to intervene such process and thus maintaining the sustainability of the earth's environment, some scientific and technological guidelines to comprehend the natural phenomena and global changes are reviewed and discussed and selected efforts devoted to aircraft technology and aviation, for maintaining the sustainability of the earth's environment are elaborated. Particular considerations are given to fuel burn affecting greenhouse gases and cloud effects due to trailing vortices and hence contrail.

Hoklie,Al - Azhar University of Indonesia | Zuhal L.R.,Al - Azhar University of Indonesia
2010 The 2nd International Conference on Computer and Automation Engineering, ICCAE 2010 | Year: 2010

Portfolio optimization is an important research field in modern finance. The most important characteristic within this optimization problem is the risk and the returns. Modern portfolio theory provides a well-developed paradigm to form a portfolio with the highest expected return for a given level of risk tolerance. Multi objective portfolio optimization problem is the portfolio selection process that result highest expected return and smallest identified risk among the various financial assets. In this paper, we propose to identify expected return (mean profit) and risk using historical data of stock prices. The downside values of the variance of each stock are considered to be the identified risk in first case. The Value at Risk of each stock that we obtained using parametric and historical simulation methodology are considered to be the identified risk in second case. One of method being widely used lately for optimization need is Genetic Algorithm or GA. This method adapted the mechanism of biology mechanism involving natural selection. With many advantages it has, numerical process of a portfolio optimization in both case are attempted to be coupled with Genetic Algorithm. The values of expected return and risk of each stock will be used as inputs into a fitness function in Genetic Algorithm. Performance evaluation is done by examining the parameters of GA, such as population size, stall generation and number of elitism. ©2010 IEEE.

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