RESPONS GETARAN TORSIONAL POROS MODEL TURBIN ARUS LAUT SUMBU VERTIKAL AKIBAT EKSITASI MOMEN PUNTIR

Abstract

Abstrak Penelitian ini mengkaji respons getaran torsional model turbin arus laut sumbu vertikal terhadap pola eksitasi momen puntir yang acak akibat variasi kecepatan arus laut. Model turbin terdiri atas 3 buah blade alumunium jenis NACA 0018 yang masing-masing terhubung pada poros, dengan dimensi chord 10 cm, chamber 1,8 cm dan span 100 cm. Variasi kecepatan arus laut yang digunakan adalah 0,5 m/s, 1,0 m/s, 1,5 m/s, 2,0 m/s, 2,5 m/s dan 3,5 m/s. Model mempunyai 2 derajat kebebasan yang digambarkan dengan 2 persamaan diferensial orde-2. Penyelesaian eigenvalue menghasilkan nilai frekuensi natural model, yaitu 201,38 rad/s dan 457,91 rad/s. Deret Fourier digunakan untuk mendefinisikan persamaan momen puntir eksitasi, sedangkan penyelesaian persamaan getaran menggunakan transformasi Laplace. Hasil analisis menyatakan bahwa tidak terjadi resonansi karena nilai frekuensi natural model tidak sama dengan nilai frekuensi eksitasinya. Model mengalami puntiran statis dahulu sebelum bergetar. Respons yang terjadi diawali dengan respons transien, kemudian respon tunak (steady). Semakin besar eksitasi momen puntir menyebabkan semakin besarnya simpangan sudut dan amplitudonya. Abstract Shaft Torsional Vibration Response of Vertical Axis Ocean Current Turbine Model Due to Torque Excitation. The current research aimed to study the torsional vibration response of Vertical Axis Ocean Current Turbine due to randomly torque excitation pattern, owing to the variety of ocean current velocity. The turbine model is composed of 3 aluminum blades of NACA 0018 connected to steel shaft. Turbine dimensions are 10 cm of chord, 1.8 cm of chamber and 100 cm of span. The variation of ocean current velocity is 0.5 m/s, 1.0 m/s, 1.5 m/s, 2.0 m/s, 2.5 m/s and 3.0 m/s. The Model has 2 degree of freedom which is described into two 2 nd order differential equations. The eigenvalue solution yields the model's natural frequencies; 201,38 rad/s and 457.91 rad/s. Fourier series is used to define the equation of torsional excitation, whilst the vibration equation is solved using Laplace Transform. According to analysis, there is no resonance occur. That because of the system's natural frequencies is diverse to the magnitude of excitation frequencies. Model will be statically twisted first before vibrated. The response will be transient first then constantly steady. Furthermore, the bigger torque excitation will cause the bigger angular displacement as well the amplitude.