This paper describes the design and performance testing of a vibration isolation and suppression system (VISS) which can be used to isolate a precision payload from spacecraft borne disturbances. VISS utilizes six hybrid isolation struts in a hexapod configuration. Central to the concept is a novel hybrid actuation concept which provides both passive isolation and active damping. The passive isolation is provided using a flight proven D-strut design. The passive design is supplemented by a voice coil based active system. The active system is used to enhance the performance of the passive isolation system at lower frequencies, and provide the capability to steer the payload.
The steady two-dimensional free convection flow of a Waiters fluid (model B') in a vertical channel one 'of whose walls is wavy, has been investigated analytically. The governing equations of the fluid and the heat transfer havff;been solved subject to the relevant boundary conditions by assuming that the solution consists of two parts: a mean part and disturbance or perturbed part. To obtain the perturbed part of the solution, the long wave approximation has been used and to solve the mean part, a well-known approximation used by Ostrach has been utilised. The relevant flow and the heat transfer characteristics, namely the skin-friction and the rate ofheat transfer at both the walls have been discussed in detail.petroleum and polymer solutions. The Waiters fluid is one of such fluids. The constitutive equation for Waiters fluid (model B') is:
A low-loss splicing method, based on discharge fusion of optical fibers by a simple apparatus and by applying pressure between fibers before fusion, was developed. Average splice losses of about 0.07 and 0.15 dB for single-mode (SM) fibers having core diameters of 10 and 7 pm, respectively, and 0.02 dB for 50-pm core diameter gradedindex (GI) fibers are obtained. Fusion loss and fusion time are obtained minimum for better end preparation having low initial alignment losses at critical pressure and temperature. Mathematical expressions for the variation of fusion time and splice loss with effect of applied pressure between the fibers, for different practical axis alignment, showing the optimum condition to have minimum splice loss are made. Experimental fusion losses are analyzed in terms of residual misalignment of off axis, angular tilt of the fibers during aligning, and air gaps in the splicing zone. Optimum fusion time is obtained by considering the forces due to applied pressure, thermal expansion, and surface tension in the viscous melted glass of the fiber. Theoretical curves of fusion times and splicing losses versus applied pressure agree with the experimental results. The decrease of fusion time to about 1.3 times and splice loss to about two times were found when applied pressure is varried from low to its critical value of 20-25 g. The splice losses are found at a minimum for the operating temperature range of 1980°C to 2140°C for silica fibers. Experimental results of the histogram of bar chart of splice losses agree with the derived mathematical expressions assuming a statistical distribution function of splice losses.
In this present work, laser welding experiments were carried out on 1 mm thin Ti6Al4V sheets using a low power Nd-YAG laser machine without using any filler wire and without edge preparation of welding specimens. The influence of different major process control parameters such as welding speed and power on the yield parameters like temperature field, weld bead geometry, microstructure, and mechanical properties are critically investigated. Experimental results are compared in detail with the simulated results obtained using a commercial 3D finite element model. In the simulation model, temperature-dependent thermal and mechanical properties of plates were considered. The temperature readings were recorded with the aid of K type thermocouples. Forced convection has been assumed near weld zone region because of the movement of the shielding gas. Appreciable agreement is found between the experimental and the simulated temperature fields in most of the cases with few exceptions. These deviations on few occasions may be due to the presence of uncertainties inherently present in the experimental domain and uncertainties in the subsequent temperature sensing techniques by the thermocouples. In addition, annealing has been done at 950 °C, 980 °C, and 1010 °C for one selected parameter (192 W, 6 mm/s). The tensile strength of the samples annealed at 980 °C has been found to be 1048 MPa and it is 3% to 4% higher than that of the usual welded samples.
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