The Invisible Contribution of ODTÜ in Defence Industry Projects
Direct and indirect contributions of ODTÜ to industry in general, and to the defence industry in particular, can be in several different ways. Amongst these, the one that is least noticed by the industry is the contribution through the graduate theses that are conducted by the students working in those companies and supervised by academics at ODTÜ without the support of the related organizations. Rather than finding solutions to the immediate problems associated with ongoing projects, these studies generally include research that will contribute to the future projects of the industrial enterprises. However, the industry is usually unwilling to invest in such research work unless it is unavoidable. Therefore, it is the university that identifies the research topic in such graduate theses with the foresight that it will contribute to the enterprise in medium term, and only in few cases the research topic is determined jointly with the industrial organization.
In this article, examples are provided from three graduate theses the outcomes of which are utilized in different defence industry projects and were carried out by my former graduate students employed in defence industry. The significance and critical role of these studies for defence industry are also stated. Furthermore, brief information about a recently completed, as well as an ongoing graduate study and their implementation potentials are presented. None of these graduate theses were financially supported by either the related industrial organization or the project they contributed to. Some were conducted independent of the related establishment, since they did not show any interest at that stage. These graduate studies are good examples which, on one side, scientifically contributed to their fields and their results were published in international journals/conference proceedings, and on the other side, were either used or have the potential to be used in important defence industry projects.
In this article, brief information is given about three graduate theses the results of which were used in defence industry projects and two theses that have the potential to be used. Two of the researches in the first group were carried out by graduate students working at TÜBİTAK-SAGE . The first of these theses was initiated by the TÜBİTAK-SAGE as a result of the institute’s willingness to obtain know-how in the related field. The ultimate goal of those two studies was to develop new methods to be used during the official certification process of new external payloads developed by TÜBİTAK-SAGE for the fighter aircrafts used by Turkish Air Forces. Since a new external payload changes the dynamic and aerodynamic characteristics of the carrier aircraft, there occurs a possibility of aeroelastic instability (flutter). For this reason, it is obligatory to determine loading configuration/airspeed/altitude envelopes that will not cause any aeroelastic instabilities. Determination of these envelopes is possible through mathematical solutions and the following flight tests. These mathematical models that serve such a critical objective need to be built with very high accuracy. Since various assumptions and simplifications need to be made during finite element modeling of a relatively large and complex structure such as an aircraft, the initial finite element model most probably will not predict the behavior of a real aircraft with high accuracy. In the first thesis on this topic, the finite element model of a real fighter aircraft is updated (improved) by making use of the ground vibration test (GVT) results of that aircraft. After the model is updated, the average error between finite element model and GVT data in the natural frequencies has decreased from 20% to 3%; and the correlation of the modes of vibration has increased from 70% to 90%. Thus, an aircraft finite element model that is in good correlation with real test data is obtained. This model is used in the analyses for determining whether aeroelastic instability will occur when the external payloads developed are carried by the aircraft. This research study is used by TÜBİTAK-SAGE for the certification process of the 2000 lb class guided ammunition developed for F-4E/2020 Terminator aircraft in Precision Guided Missile System Development Project (HGSS).
Another study conducted for a similar ultimate goal is on the calculation of the dynamic behavior of an aircraft with payload by using the response of the aircraft itself (which is calculated only once from the updated finite element model of the aircraft) and dynamic properties of the payload. In this research, the effects of external loads on the aircraft dynamics are theoretically calculated using both the existing methods and a new method developed in this study. The new method is verified through modal tests performed on a scaled aircraft structure, and then is used for F-4E/2020 aircraft within the scope of HGSS Project at TÜBİTAK-SAGE. A new approach based on experimental methods is also developed by making use of the know-how obtained in this research. Thus, it is made possible to estimate the ground vibration tests results, which are used in the experimental determination of aircraft dynamic behavior for different fuel configurations/consumption rates, loading and boundary conditions, and this is an essential part of ammunition certification process. The results of these studies will also contribute to the research on the design of new external load(s) that will be used on the same platform. Moreover, the approach can also be applied to any other flight platform in a similar way. Consequently, this study will considerably reduce the tests required with actual aircraft, hence the time required for the use of aircraft which is strategically and economically valuable. This study is used at TÜBİTAK-SAGE, in HGSS, SOM and KGK projects that are realized with F-16 aircraft.
The third study has been recently completed by one of my former PhD students who is employed at Aselsan . The models used for calculating dynamic behavior of mechanical structures in vibration analysis are usually based on the assumption of linear behavior. In reality, however, nonlinear properties exist to some degree in most of the mechanical structures. Though dynamic conditions and loading levels justify the assumption of linear behavior in many cases, complex designs such as satellites, stabilized missile systems and radars may require the consideration of nonlinear characteristics for better performance. Within the scope of this PhD thesis, nonlinear identification methods were developed. These methods provide tools in determining the nonlinear behavior of various systems including weapon systems where nonlinearity is usually due to transmission elements (bearings, gears, screw connections, etc.). In order to develop more accurate dynamic models for such systems, the identified parameters are combined with the finite element model of the system. As an example application to a real engineering problem, the method developed is used for a defence industry product designed by Aselsan to obtain a better mathematical model which improves the servo control performance of the product. The problem of not having an acceptable correlation between theoretical and experimental results for this specific defence industry product was brought to our University by Aselsan to be solved within the scope of an industrial project. However, instead of solving a single problem, methods were developed which would not only help to solve the existing problem, but would also provide an excellent tool for future design activities of the company. Furthermore, and more importantly, the company has gained a valuable researcher qualified in this area. Aselsan’s lack of support to the University in this research is a deficiency in the system, and the Researcher Development Program for Industry (SAYP) that has been initiated quite recently is an excellent mechanism to fill in this gap (a brief information about SAYP will be given below). The new methods developed within the scope of this study were published in international journals and presented in an international conference.
As examples of many graduate theses that have the potential, but have not yet been used in defence industry projects, only two research studies are mentioned here. The first one is the thesis completed by a graduate student working at Roketsan. This study is on the active control of the vibrations of a cylindrical shell structure through the use of piezoelectric patches. The most appropriate alignment of piezoelectric patches for the vibration modes that need to be controlled are determined according to the “controllability” criteria and then active vibration control is maintained on the structure. The research includes the verification of the analytical studies through an experimental work on a simple cylindrical shell structure. Although this study has not been used yet in a Roketsan project, it has a potential to be used in future projects, since active vibration control with piezoelectric patches is an important alternative to suppress vibrations of cylindrical shell structures when panel modes dominate and passive vibration control methods may not be so effective in damping vibrations at these modes. The research findings are presented in an international conference paper. This thesis was initiated by Roketsan, however, it has not received any financial support since SAYP which is the most appropriate mechanism to support such research has not been initiated yet at that time.
Lastly, an example is given for the theses that do not receive the attention of the defence industry companies where the graduate students are working at, although the research conducted has a high potential to contribute to the projects of the related companies. In a recent research carried out by one of my PhD students working at Aselsan, a new approach is developed for the extension of model updating methods proposed for linear structures to nonlinear structures. Though most of the structures in real life show nonlinear behavior, depending on several conditions, they are often assumed to be linear. In cases where this assumption is not valid, it is not possible to use linear models and analysis methods that are developed for linear systems. The existing model updating methods are valid for linear structures only. Development of model updating methods for nonlinear structures is among the current research topics in structural dynamics area. In a nonlinear structure, especially in the presence of friction with other types of nonlinearity, it is rather difficult to identify nonlinearity and update the existing finite element model of the system. With the method developed in this thesis, nonlinear parameters in such structures are identified and the linear frequency response functions that will later be employed in the updating of the finite element model are obtained. In tank gun/turret stabilization projects and in flir targeting and imaging systems stabilization projects carried out at Aselsan Microelectronics, Guidance and Electro-Optics Business Sector, such nonlinear behaviors are observed. Determining the nonlinear parameters in these systems and obtaining updated mathematical models will definitely improve the stabilization performance.
SANTEZ, a program, initiated in 2006, provides a mechanism that allows a graduate study to be supported by industry and the Ministry of Science, Industry and Technology. Only the graduate theses which aim to develop new technology-based products and processes in line with the needs of the industry are eligible for this program. However, many graduate studies in which it is not aimed to develop a product and/or process and therefore cannot benefit from this mechanism, may still contribute to the industry considerably. A very few such examples, even considering my own graduate students employed in defence industry, are given in this article. Similar graduate studies in various fields of defence industry are conducted in several departments in our University. Fortunately, the initiation of the Researcher Development Program for Defense Industry (SAYP), quite recently, with the support of Undersecretariat for Defense Industry, made it possible for an industrial company to support a graduate study with the aim of having a highly qualified researcher specialized in a field required by the company itself. SAYP does not target a specific product but aims to train the employees of defence industry companies who are carrying out PhD studies at ODTÜ, according to the long-term R&D needs of these companies. The program does not only provide funds for the research, but more importantly, enables the graduate students to spend sufficient time at the University for graduate research, and furthermore provides long term research collaboration opportunity between the University and industry. Even though I believe there is still a way to go, my personal view is that, with the significant contributions of programs like SAYP, SANTEZ and funding schemes of TUBITAK such as 1505, interest and support of the defence industry companies to research conducted through graduate studies is increasing.
Acknowledgement
I would like to thank to my former graduate students, Dr. Murat Aykan, Caner Gencoğlu, Dr. Mustafa Tuğrul Kozak, Dr. Sertaç Köksal and to my graduate student, PhD candidate, Güvenç Canbaloğlu, who carried out the graduate studies mentioned in this article, for their contributions.
