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This article presents numerical studies on the deformation of particles during dynamic compaction of metal powders. The analysis of the process is based on a micromechanics approach using multiple particle configurations. The material considered is elastoviscoplastic with interparticle friction. Two-dimensional studies on particles in close packed arrangement were carried out using plane strain conditions for deformation and thermal response. The finite element method using an explicit dynamic analysis procedure was used for the simulations. The influence of speed of compaction, strain hardening, strain rate dependency, interparticle friction and size of the powder particles on the final shape and temperature variations within the particles were analyzed. The studies offer useful information on the shape and temperature variations within the particles. The results provide a better understanding of the dynamic compaction process at the micromechanics level.

We propose an optical image security scheme based on polarized light encoding and the photon counting technique. An input image is encoded using the concept of polarized light, which is parameterized using Stokes–Mueller formalism. The encoded image is further encrypted by applying the photon counting imaging technique to obtain a photon limited image. For decryption, the photon limited decrypted image is obtained by using a polarized light decoding scheme with the help of appropriate keys. The decrypted image has sparse representation, which contains sufficient information for verification. This photon counted decrypted image can be verified using correlation filters. The proposed encryption technique offers benefits over the double random phase encoding in that it does not require active elements such as a lens and provides flexibility in the design of encryption keys. The proposed encryption scheme has also been used for hologram watermarking. The computer simulation results for secure image verification and the hologram watermarking scheme have been presented.

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used explosively powered projectiles to compact diVerent powdered materials. 4 -6 Petro Forge machines and similar This paper investigates the use of a simple drop weight equipments were also used for dynamic compaction process. 7 ,8 instrumented impact loading facility to produce metal Explosive isodynamic compaction also called direct powder compacts with better qualities than attained explosive compaction, is another type of dynamic comby the conventional means. Experiments were perpaction process. The powder to be treated is kept inside a formed on Fe powder, Fe-C-Cu-Mn powder mix, and container surrounded by an appropriate amount of explosive, Cu-Zn powder mix at diVerent height to diameter which on detonation implodes the container thereby comratios and compacted at diVerent energies. The overall pacting the powders. 9 -1 2 This method is useful only for density, density variation within the compact, dimencompacting the more diYcult to process hard metal powders sional accuracy, and microstructure were compared and cannot be used in a production line. Dynamic comwith quasistatic specimens compacted using convenpaction at high compaction rates cause interparticle welding tional hydraulic press. The results showed that the and hence produces strong compacts. 1 3 -1 5 Extensive work dynamic compaction specimens attained better densiwas carried out to analyse the microstructures and study cation and dimensional accuracy than quasistatic the processes leading to bonding in a range metallic powder compaction specimens.PM/0997 compacts. 1 6 -2 0 It was observed that very high localised and relatively high temperatures are achieved at particle surfaces The authors (rkkumar@iitm.ac.in) are in the and involve diVerent mechanisms during the compaction Manufacturing Engineering Section, Department of process. Mechanical Engineering, Indian Institute of TechRecent developments include dynamic compaction of nology Madras, Chennai 600 036, India. Manuscript titanium alloy powders. 2 1 -2 6 Densi cation behaviour of rapidly

Industries rely mostly on off-shore resources to fulfill the increase in demand for oil and gas. In general, for oil extraction and various other refinery processes, fixed or floating structures are being utilized. Floating Production Storage and Offloading (FPSO) system is one of the floating systems which have advantage of storing the crude oil and, if required, it can be easily moved to other places. Also, in deep Ocean where sub-sea pipeline infrastructures are often not possible and so the FPSOs give alternate option of storing and processing the crude oil. Being moored-systems, FPSOs are very flexible structures having high surge natural period and hence they may undergo larger surge displacement. Excessive displacement may cause damage for the riser system also it may affect the workability under extreme sea condition. Therefore, there is a need for investigating the issues of safety, efficiency and response control of FPSO systems under different sea-state conditions. Ocean wave loads on FPSO causes dynamic interaction between FPSO vessel and liquid in the oil storage containers. The liquid motion in containers disturbs the dynamics of the vessel significantly. Hence, it is essential to study the surge response control of FPSO in detail. An easy way to control the response is to use the existing cargo containers of FPSO as passive damping devices. If the natural frequency of liquid oscillation is tuned to the natural frequency of FPSO, these cargo tanks can act as Multiple Tuned Liquid Dampers (MTLDs). In case of simple linear model, Tuned liquid damper (TLD) can be idealized as a Single Degree of Freedom (SDOF) system, namely Tuned Mass Damper (TMD). The present study attempts to model a TLD using three different TMD systems to account the effects of shallow water sloshing.