Bir insansız hava aracına ait kompozit kanadın tasarımı ve yapısal optimizasyonu
Design and structural optimisation of an UAV composite wing
Yazar: MUHAMMED ATIF YILMAZ
Danışman: DR. ÖĞR. ÜYESİ ALAEDDİN BURAK İREZ
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Savunma Teknolojileri Ana Bilim Dalı / Savunma Teknolojileri Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: Makine Mühendisliği = Mechanical Engineering ; Savunma ve Savunma Teknolojileri = Defense and Defense Technologies ; Uçak Mühendisliği = Aeronautical Engineering

Özet:
Hava araçları, kısa mesafelerden uzun mesafelere kadar farklı uçuş gereksinimlerini
karşılamak üzere kullanılmaktadır. Bu çeşitlilik, havacılık endüstrisinin sürekli olarak
gelişmesine ve hava araçlarının çeşitli alanlarda etkili bir şekilde kullanılmasına
olanak tanımaktadır. Teknolojik ilerlemeler, hava araçlarının yakıt verimliliği,
güvenlik ve çevresel etkiler gibi alanlarda sürekli olarak geliştirilmesine olanak tanır.
Elektronik sistemlerin ve uçuş kontrol teknolojilerinin ilerlemesi, hava araçlarının
daha güvenli ve etkili bir şekilde uçmasına yardımcı olur.
İnsansız Hava Araçları da (İHA'ları da) bu çeşitlilik içinde önemli bir yer tutmaktadır.
İHA'lar, uzaktan kumanda veya önceden belirlenmiş programlar doğrultusunda
otonom olarak uçabilen araçlardır. Bu araçlar, askeri operasyonlardan güvenlik
gözetimine, tarımsal faaliyetlerden bilimsel araştırmalara kadar geniş bir yelpazede
görevleri yerine getirmektedirler. İHA'ların tasarımında öne çıkan faktörlerden biri,
hafif ve dayanıklı malzemelerin kullanımıdır. Bu bağlamda, genellikle karbon fiber,
cam fiber ve epoksi reçine gibi bileşenlerden oluşan kompozit yapısal hafif
malzemeler tercih edilmektedir. Hafif malzemelerin kullanımı, İHA'ların daha az
enerji harcayarak uzun uçuş süreleri elde etmelerine yardımcı olur. Bu özellikler,
İHA'ların uzun süreli ve maliyetinin düşük olması gereken görevlerde diğer hava
araçlarına göre avantajlı olmalarını sağlar.
Bu çalışma kapsamında bir insansız hava aracına ait kompozit kanadın uçuşa elverişli
olacak şekilde tasarımı yapılmıştır ve bu tasarımın yapısal optimizasyonu
gerçekleştirilmiştir. Uçuşa elverişli olabilmesi için öncelikle İHA görev profiline
uygun olacak iki boyutlu bir kanat profili seçilmiştir. Bu kanat profilinin ilgili kaldırma
kuvvetini karşılayabilecek şekilde 8 metre uzunluk, 1.2 metre kök genişliği olan üç
boyutlu kanat tasarlanmıştır. Tasarlanan bu üç boyutlu kanadın Ansys Fluent yazılımı
yardımı ile akışkanlar mekaniği analizi yapılmıştır. Bu nümerik çalışma sonucunda
oluşan basınç dağılımı kanat kabuğu uzunluk yönünde 10 eşit parçaya bölünerek
yüzeylerin belirlenen noktalarda oluşturduğu yük ve momentler elde edilmiştir. Bu
yükler yapısal olarak iki kiriş ve iki kabuktan oluşan kanat geometrisine Abaqus
yazılımında yayılı yük ve moment olarak tanımlanmıştır. Kanat yapısı kiriş uçlarından
6 serbestlik derecesinde tutularak sınır koşulu analiz modeline tanımlanmıştır. 40
bölgeye bölünmüş kanat geometrisine tek yönlü fiber takviyeli polimer matrisli
kompozit malzeme ile serim yapılmış ve analiz Hashin hasar kriterine bağlı olarak
çözdürülmüştür. Hasar kriterleri sınır değerinde altında kalmış ve dayanımı
sağlamıştır.
Kanat yapısı uçuşa el verişli ve dayanımlı olarak tasarlanmış ve yapısal optimizasyon
çalışmasına geçilmiştir. Bu aşamada oluşturulan analiz modeli Python programlama
dilinde hazırlanmış olan kod yardımı ile Abaqus yazılımı bir alt yazılım halinde
çalıştırılarak optimize edilmiştir. Bu optimizasyon çalışmasında kanat yapısal ağırlığı, 45 analiz adımı sonunda %34.7 oranında hafiflemiştir. Yapılmış olan bu analiz
çalışmalarında oluşan en kalın kompozit serimi, plaka halinde el ile serim metodu
kullanılarak üretilmiştir. Üretilen bu plakadan çekme ve basma numuneleri kesilerek
testlere tabii tutulmuştur. Çıkan sonuçlar doğrultusunda çalışmanın deneysel
doğrulanması yapılmıştır.

Abstract:
Aircrafts are utilized to meet diverse flight requirements, ranging from short to long
distances. This diversity enables continuous development in the aviation industry,
allowing effective utilization of aircraft in various fields. This diversity enables
continuous development in the aviation industry, allowing effective utilization of
aircraft in various fields such as passenger transportation, cargo logistics, aerial
firefighting, and military operations. The adaptability of aircraft to multifaceted roles
has spurred innovation in their design and functionality over the years. Ongoing
technological advancements facilitate the continuous improvement of aircraft in areas
such as fuel efficiency, safety, and environmental impact. Advances in electronic
systems and flight control technologies contribute to safer and more efficient aircraft
operations.
Unmanned Aerial Vehicles (UAVs) also play a significant role within this diversity.
UAVs, capable of flying autonomously based on remote control or pre-determined
programs, fulfill a wide range of tasks from military operations to security
surveillance, agricultural monitoring, and scientific research. A key factor in the design
of UAVs is the utilization of lightweight and durable materials. In this context,
composite materials, typically composed of components such as carbon fiber, glass
fiber, and epoxy resin, are preferred as structural lightweight materials. These
materials not only provide high strength-to-weight ratios but also contribute to the
overall durability and efficiency of UAVs. The use of lightweight materials assists
UAVs in achieving longer flight durations with reduced energy consumption, which
is crucial for extending operational ranges and improving cost-effectiveness. These
features provide UAVs with significant advantages, particularly in tasks requiring
prolonged and cost-effective operations compared to other aircraft. By integrating
advanced composite materials, UAVs can maintain high performance and reliability,
making them indispensable tools in various fields.
Prior to the commencement of this design study, an extensive characterization of the
selected carbon fiber reinforced polymer (CFRP) material was meticulously carried
out. This comprehensive characterization process involved a series of essential
mechanical tests, specifically tensile and compressive tests, to accurately determine
the material properties. These tests were designed to evaluate and quantify the CFRP
material's performance under various loading conditions, providing crucial data on its
tensile strength, compressive strength, and elasticity. The detailed results from these
tests offered a thorough understanding of the material's mechanical behavior, ensuring
that its suitability for the intended application was thoroughly assessed and validated.
The strength and elasticity values obtained from this characterization were integral to
informing and guiding the subsequent phases of the design and optimization process.
In the scope of this study, the design of a composite wing for an unmanned aerial
vehicle was conducted to make it flight-worthy, and structural optimization of this
design was performed. To ensure flight-worthiness, a two-dimensional wing profile
suitable for the UAV mission profile was initially selected. The selected wing profile
serves as a critical component in optimizing lift, minimizing drag, and ensuring the
UAV's adherence to the intended mission objectives. The wing geometry was
designed based on literature review, considering requirements for a takeoff speed of
42.5 m/s and a cruising altitude of 2000 feet. This approach involved consulting
existing research and relevant sources in the field to ensure that the specified
parameters align with established principles and standards in aeronautical engineering.
A three-dimensional wing with a length of 8 meters and a root width of 1.2 meters was
then designed to meet the relevant lift force requirements. Fluid mechanics analysis of
this designed three-dimensional wing was conducted using the Ansys Fluent program.
In the fluid mechanics analysis, the wing geometry was placed within a spherical flow
domain, and far-field boundary conditions were defined. The far-field boundary
conditions are specified to represent the conditions at a sufficient distance from the
wing, allowing for an accurate representation of the aerodynamic interactions. The
pressure distribution obtained from this numerical study was divided into 10 equal
parts along the length of the wing shell, generating loads and moments at the volume
center on the surfaces.
These loads were structurally defined as distributed loads and moments on the wing
geometry consisting of two beams and two shells using the Abaqus program. The wing
structure was constrained at the beam ends with six degrees of freedom, and the
analysis model was defined with boundary conditions. Unidirectional carbon polymer
matrix composite layup was meticulously applied to the wing geometry, meticulously
divided into 40 regions to ensure comprehensive coverage. This detailed partitioning
allowed for a nuanced analysis of the structural response across different segments of
the wing, providing valuable insights into localized behaviors and performance
characteristics. The analysis, conducted utilizing sophisticated computational
techniques, was rigorously solved based on the Hashin damage criteria, a robust
methodology for assessing material failure in composite structures. Throughout the
analysis process, meticulous attention was paid to ensuring the structural integrity of
the wing under various loading conditions. The application of the Hashin damage
criteria served as a critical tool in this regard, providing a quantitative measure of
material damage and allowing for proactive mitigation strategies to be implemented.
Remarkably, the examination of the analysis outcomes revealed that the Hashin
damage criterion values consistently remained below the designated threshold of 0.8,
affirming the structural robustness of the wing design. Upon further scrutiny of the
analysis results, a noteworthy observation emerged: in the context of compressive
loads, the wing structure exhibited a tendency to approach the defined limit more
closely. This nuanced exploration underscores the inherent resilience of the wing,
particularly in withstanding compressive forces, as evidenced by the Hashin damage
criterion values maintaining close proximity to the established threshold. This
resilience is a testament to the effectiveness of the design approach and material
selection, highlighting the successful integration of advanced engineering principles
into the development of the UAV wing structure.
The wing structure was designed to be flight-worthy and durable, leading to the
initiation of structural optimization studies. In this phase, an analysis model created
with the Python programming language was executed as a subroutine under the Abaqus software for optimization. This optimization process has been conducted using
the single objective method. In this method, the objective is to reduce the weight.
While fulfilling this objective, the Hashin damage criterion value has been constrained
to a limit of 0.8, as previously mentioned. Additionally, the lay-up has been ensured
to be symmetric and balanced. During the optimization process, the developed code
scrutinizes the Hashin criterion values in pre-defined regions on the wing. Upon
identifying values significantly exceeding the set threshold during this examination,
the code dynamically introduces additional composite layers in the direction of the
effective load. Conversely, if values considerably below the threshold are encountered,
the code initiates the removal of composite layers aligned with the effective load
direction. This iterative procedure is meticulously designed to guide the Hashin
criterion values towards convergence with the specified threshold. Through this
method, the optimization code actively seeks to enhance the overall structural integrity
of the wing by iteratively adjusting the composition of composite layers based on the
Hashin criterion evaluations. In the optimization study, the structural weight of the
wing reduced by 34.7% after 45 analysis steps.
The thickest composite laminate developed in this analysis comprises 18 plies and
follows a unidirectional fiber orientation. Each ply, consisting of carbon fibers
embedded in a polymer matrix, was meticulously layered during the manual hand lay-
up process to ensure a precise unidirectional arrangement. This specific configuration
enhances the laminate's mechanical properties, particularly its strength along the
chosen fiber direction. Tension and compression specimens were then carefully cut
from this composite plate to represent different orientations and positions within the
laminate structure. These specimens underwent a series of experimental tests,
exposing them to varying mechanical stresses in both tension and compression
scenarios. In tensile tests, lower strength values were observed compared to the
analysis, while in compression tests, higher strength values were observed relative to
the analysis. This discrepancy is thought to be due to the thickness in characterization
tests being significantly lower than the final thickness. As the thickness increased, the
tensile strength of the matrix decreased, while the compressive strength increased.
Discontinuities within the matrix contributed to this effect; in the direction of
compression, they enhanced strength by alleviating discontinuities, whereas in the
direction of tension, they increased stress concentrations, thereby reducing strength.
The comprehensive testing regime aimed to evaluate the laminate's response under
different loading conditions, providing valuable insights into its mechanical behavior.